tm 5-820-4 drainage for areas other than airfields

ARMY TM 5-820-4AIR FORCE AFM 885, chap 4

TECHNICAL MANUAL

DRAINAGE FOR AREAS OTHER THAN AIRFIELDS

This copy is a reprint which includes current

pages from Chang e 1.

D E P A R T M E N T S O F T H E A R M Y A N D T H E A I R F O R C E‘

OCTOBER 1983

REPRODUCTION AUTHORIZATION/RESTRICTIONS

This manual has been prepared by or for the Government and is publicproperty and not subject to copyright.

Reprints or republications of this manual should include a credit substan-tially as follows: “Joint Departments of the Army and Air Force, USA,Technical Manual TM 5-820-AFM 88-5, Chapter 4, Drainage for AreasOther Than Airfields, date.”

TM 5-820-4AFM 88-5, chap 4

C-1

Change

No. 1

DEPARTMENTS OF THE ARMY,AND THE AIR FORCE

Washington, DC 16 July 1985


TM 5-820-4/AFM 88-5, Chapter 4, 14 October 1983, is changed as follows:1. Remove old pages and insert new pages as indicated below. New or changed material is indicated by a

vertical bar in the margin of the page.

2. File this change sheet in front of the publication for reference purposes.

By Order of the Secretaries of the Army and the Air Force

JOHN A. WICKHAM, JR.General, United States Army

Official: Chief of Staff

DONALD J. DELANDROBrigadier General, United States Army

The Adjutant General

CHARLES A. GABRIELGeneral, United States Air Force

Official: Chief of Staff

JAMES H. DELANEYColonel, United States Air Force

Director of Administration

DISTRIBUTION:To be distributed in accordance with DA Form 12-34B requirements for TM 5-800 Series: Engineering

and Design for Real Property Facilities.

Technical ManualNo. 5-820-4Air Force ManualNo. 88-5, Chapter

● TM 5-820-4/AFM 88-5, Chap. 4

HEADQUARTERSDEPARTMENTS OF THE ARMY

AND THE AIR FORCE4 Washington, D.C. 14 October 1983


CHAPTER 1.

2.

3.

4.

5.

6.

APPENDIX A.B.c.D.E.

Figure 3-13-23-33-43-53-63-74-14-24-34-4B-1B-2B-3B-4

INTRODUCTION Paragraph Page

*This manual supersedes TM 5-820-4/AFM 86-5, Chap 4, 14 August 1964

TM 5-820-4/AFM 88-5, Chap. 4

LIST OF TABLES

Table Page

TM 5–820-4/AFM 88–5, Chap 4

CHAPTER 1

INTRODUCTION

1–1. Purpose and scope. The purpose of thismanual is to discuss normal requirements for de-sign of surface and subsurface drainage systemsfor military construction other than airfields andheliports at Army, Air Force and similar instal-lations. Sound engineering practice should be fol-lowed when unusual or special requirements notcovered by these instructions are encountered.

1–2. General investigations. An on-site inves-tigation of the system site and tributary area isa prerequisite for study of drainage requirements.Information regarding capacity, elevations, andcondition of existing drains will be obtained. To-pography, size and shape of drainage area, andextent and type of development; profiles, crosssections, and roughness data on pertinent exist-ing streams and watercourses; and location of pos-sible ponding areas will be determined. Thoroughknowledge of climatic conditions and precipitationcharacteristics is essential. Adequate informationregarding soil conditions, including types, perme-ability on perviousness, vegetative cover, depthto and movement of subsurface water, and depthof frost will be secured. outfall and downstreamflow conditions, including high-water occurrencesand frequencies, also must be determined. Effectof base drainage construction on local interests’facilities and local requirements that will affectthe design of the drainage works will be evalu-ated. Where diversion of runoff is proposed, par-ticular effort will be made to avoid resultant

downstream conditions leading to unfavorablepublic relations, costly litigations, or damageclaims. Any agreements needed to obtain drain-age easements and/or avoid interference with waterrights will be determined at the time of designand consummated prior to initiation of construc-tion. Possible adverse effects on water quality dueto disposal of drainage in waterways involved inwater-supply systems will be evaluated.

1–3. Environmental considerations.

a. Surface drainage systems have either bene-ficial or adverse environmental impacts affectingwater, land, ecology, and socio-economic consid-erations. Effects on surrounding land and vege-tation may cause changes in various conditions inthe existing environment, such as surface waterquantity and quality, groundwater levels andquality, drainage areas, animal and aquatic life,and land use. Environmental attributes relatedto water could include such items as erosion, floodpotential, flow variations, biochemical oxygen de-mand, content of dissolved solids, nutrients andcoliform organisms. These are among many pos-sible attributes to be considered in evaluating en-vironmental impacts, both beneficial and adverse,including effects on surface water and ground-water.

b. Federal agencies shall initiate measures todirect their policies, plans, and programs so as tomeet national environmental goals and stand-ards.

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TM 5–820-4/FM 88-5, Chap 4

CHAPTER 2

HYDROLOGY

2–1. General. Hydrologic studies include a care-ful appraisal of factors affecting storm runoff toinsure the development of a drainage system orcontrol works capable of providing the requireddegree of protection. The selection of design stormmagnitudes depends not only on the protectionsought but also onthe type of construction con-templated and the consequences of storms ofgreater magnitude than the design storm. Groundconditions affecting runoff must be selected to beconsistent with existing and anticipated arel de-velopment and also with the characteristics andseasonal time of occurrence of the design rainfall.For areas of up to about 1 square mile, where onlypeak discharges are required for design and ex-tensive pondig is not involved, computation ofrunoff will normally be accomplished by the s-called Rational Method. For larger areas, whensuitable unt-hydrograph data are available orwhere detailed consideration of pondng is re-quired, computation should be by uit-hydro-graph and flow-routing procedures.

2–2. Design storm.

a. For such developed portions of military in-stallations as administrative, industrial, andhousing areas, the design storm will normally bebased on rainfall of 10-year frequency. Potentialdamage or operational requirements may war-rant a more severe criterion; in certain storageand recreational areas a lesser criterion may beappropriate. (With concurrence of the using Serv-ice, a lesser criterion may also be employed inregions where storms of an appreciable magni-tude are infrequent and either damages or oper-ational capabilities are such that large expendi-tures for drainage are not justified.)

b. The design of roadway culverts will normallybe based on 10-year rainfall. Examples of condi-tions where greater than 10-year rainfall may beused are areas of steep slope in which overflowswould cause severe erosion damage; high road fillsthat impound large quantities of water; and pri-mary diversion structures, important bridges, andcritical facilities where uninterrupted operationis imperative.

c. Protection of military installations againstfloodflows originating from areas exterior to theinstallation will normally be based on 25-year orgreater rainfall, again depending on operationalrequirements, cost-benefit considerations, andnature and consequences of flood damage result-ing from the failure of protective works. Justifi-cation for the selected design storm will be pre-sented, and, if appropriate, comparative costs anddamages for alternative designs should be in-cluded.

d. Rainfall intensity will be determined from thebest available intensity-duration-frequency data.Basic information of this type will be taken fromsuch publications as (see app A for referenced pub-lications);

Rainfall Frequency Atlas of the United States.Technical Paper No. 40.

Generalized Estimates of Probable MaximumPrecipitation and Rainfall-Frequency Datafor Puerto Rico and Virgin Islands. Tech-nical Paper No. 42.

Rainfall-Frequency Atlas of the Hawaiian Is-lands. Technical Paper No. 43.

Probable Maximum Precipitation and Rain-fall Frequency Data for Alaska. TechnicalPaper No. 47.

TM 5-785/AFM 88-29/NAVFAC P-89.These publications may be supplemented as ap-propriate by more detailed publications of the En-vironmental Data and Information Center and bystudies of local rainfall records. For large areasand in studies involving unit hydrography and flow-routing procedures, appropriate design stormsmust be synthesized from areal and time-distri-bution characteristics of typical regional rainfalls.

e. For some areas, it might reasonably be as-sumed that the ground would be covered with snowwhen the design rainfall occurs. If so, snowmeltwould add to the runoff. Detailed procedures forestimating snowmelt runoff are given in TM 5-852-7/AFM 88-19, Chap 7. It should be noted, how-ever, that the rate of snowmelt under the rangeof hydro-meteorological conditions normally en-countered in military drainage design would sel-

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TM 5–820-4/AFM 88-5, Chap 4

dom exceed 0.2 inches per hour and could be sub-stantially less than that rate.

f. In selecting the design storm and making otherdesign decisions, particular attention must be givento the hazard to life and other disastrous conse-quences resulting from the failure of protectiveworks during a great flood. Potentially hazardoussituations must be brought to the attention of theusing service and others concerned so that ap-propriate steps can be taken.

Table 2–1. Typical Values of Infiltration Rates

Soil group Infiltration,Description symbol inches/hour

Sand and gravel mixture GW, GP 0.8-1.0SW, SP

Silty gravels and silty sands to GM, SM 0.3–0.6inorganic silt, and well-devel- ML, MHoped loams OL

Silty clay sand to sandy clay SC, CL 0.2–0.3Clays, inorganic and organic CH, OH 0.1–0.2Bare rock, not highly fractured -------- 0.0-0.1

U.S. Army Corps of Engineers

2–3. Infiltration and other losses.

a. Principal factors affecting the computation ofrunoff from rainfall for the design of militarydrainage systems comprise initial losses, infiltra-tion, transitory storage, and, in some areas, per-colation into natural streambeds. If necessary dataare available, an excellent indication of the mag-nitudes of these factors can be derived from thor-ough analysis of past storms and recorded flowsby the unit-hydrograph approach. At the onset ofa storm, some rainfall is effectively retained in“wetting down” vegetation and other surfaces, insatisfying soil moisture deficiencies, and in fillingsurface depressions. Retention capacities varyconsiderably according to surface, soil type, cover,and antecedent moisture conditions. For high in-tensity design storms of the convective, thunder-storm type, a maximum initial loss of up to 1 inchmay be assumed for the first hour of storm pre-cipitation, but the usual values are in the rangeof 0.25 to 0.50 inches per hour. If the design rain-fall intensity is expected to occur during a stormof long duration, after substantial amounts of im-mediately prior rain, the retention capacity wouldhave been satisfied by the prior rain and no fur-ther assumption of loss should be made.

b. Infiltration rates depend on type of soils, veg-etal cover, and the use to which the areas aresubjected. Also, the rates decrease as the durationof rainfall increases. Typical values of infiltrationfor generalized soil classifications are shown intable 2-1. The soil group symbols are those givenin MIL-STD-619, Unified Soil Classification Sys-tem for Roads, Airfields, Embankments, andFoundations. These infiltration rates are for un-compacted soils. Studies indicate that compactedsoils decrease infiltration values from 25 to 75 per-cent, the difference depending on the degree ofcompaction and the soil type. Vegetation gener-ally decreases the infiltration capacity of coarsesoils and increases that of clayey soils.

c. Peak rates of runoff are reduced by the effectof transitory storage in watercourses and minor

ponds along the drainage route. The effects arereflected in the C factor of the Rational Formula(given below) or in the shape of the unit hydro-graphy. Flow-routing techniques must be used topredict major storage effects caused by naturaltopography or man-made developments in the area.

d. Streambed percolation losses to direct runoffneed to be considered only for sandy, alluvial wa-tercourses, such as those found in arid and semi-arid regions. Rates of streambed percolation com-monly range from 0.15 to 0.5 cubic feet per secondper acre of wetted area.

2-4. Runoff computations.

a. Design procedures for drainage facilities in-volve computations to convert rainfall intensitiesexpected during the design storm into runoff rateswhich can be used to size the various elements ofthe storm drainage system. There are two basicapproaches: first, direct estimates of the propor-tion of average rainfall intensity that will appearas the peak runoff rate; and, second, hydrographymethods that depict the time-distribution of run-off events after accounting for losses and atten-uation of the flow over the surface to the point ofdesign. The first approach is exemplified by theRational Method which is used in the large ma-jority of engineering offices in the United States.It can be employed successfully and consistentlyby experienced designers for drainage areas up to1 square mile in size. Design and Construction ofSanitary and Stem Sewers, ASCE Manual No.37, and Airport Drainage, FAA AC 150/5320-5B,explain and illustrate use of the method. A mod-ified method is outlined below. The second ap-proach encompasses the analysis of unit-hydro-graph techniques to synthesize complete runoffhydrography.

b. To compute peak runoff the empirical formulaQ=C(1-F)A can be used; the terms are defined

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TM 5–820-4/AFM 88-5, Chap 4

in appendix D. This equation is known as the mod-ified rational method.

(1) C is a coefficient expressing the percentageto which the peak runoff is reduced by losses (otherthan infiltration) and by attenuation owing totransitory storage. Its value depends primarily onsurface slopes and irregularities of the tributaryarea, although accurate values of C cannot readilybe determined. For most developed areas, the ap-parent values range from 0.6 to 1.0. However, val-ues as low as 0.20 for C may be assumed in areaswith low intensity design rainfall and high infil-tration rates on flat terrain. A value of 0.6 maybe assumed for areas left ungraded where mean-dering-flow and appreciable natural-ponding ex-ists, slopes are 1 percent or less, and vegetal coveris relatively dense. A value of 1.0 may be assumedapplicable to paved areas and to smooth areas ofsubstantial slope with virtually no potential forsurface storage and little or no vegetal cover.

(2) The design intensity is selected from theappropriate intensity-duration-frequency rela-tionship for the critical time of concentration andfor the design storm frequency. Time of concen-tration is usually defined as the time required,under design storm conditions, for runoff to travelfrom the most remote point of the drainage areato the point in question. In computing time of con-centration, it should be kept in mind that, evenfor uniformly graded bare or turfed ground, over-land flow in “sheet” form will rarely travel morethan 300 or 400 feet before becoming channelizedand thence move relatively faster; a method whichmay be used for determining travel-time for sheetflow is given in TM 5-820-1/AFM 88-5, Chap 1.Also, for design, the practical minimum time ofconcentration for roofs or paved areas and for rel-atively small unpaved areas upstream of the up-permost inlet of a drainage system is 10 minutes;smaller values are rarely justifiable; values up to20 minutes may be used if resulting runoff ex-cesses will not cause appreciable damage. A min-imum time of 20 minutes is generally applicablefor turfed areas. Further, the configuration of themost remote portion of the drainage area may besuch that the time of concentration would belengthened markedly and thus design intensityand peak runoff would be decreased substantially.

In such cases, the upper portion of the drainageareas should be ignored and the peak flow com-putation should be based only on the more effi-cient, downstream portion.

(3) For all durations, the infiltration rate isassumed to be the constant amount that is estab-lished following a rainfall of 1 hour duration. WhereF varies considerably within a given drainage area,a weighted rate may be used; it must be remem-bered, however, that previous portions may re-quire individual consideration, because a weightedoverall value for F is proper only if rainfall in-tensities are equal to or greater than the highestinfiltration rate within the drainage area.In design of military construction drainage sys-tems, factors such as initial rainfall losses andchannel percolation rarely enter into runoff com-putations involving the Rational Method. Suchlosses are accounted for in the selection of the Ccoefficient.

c. Where basic hydrologic data on concurrentrainfall and runoff are adequate to determine unithydrography for a drainage area, the uncertain-ties inherent in application of the Rational Methodcan largely be eliminated. Apparent l0SS rates de-termined from unit-hydrograph analyses of re-corded floods provide a good basis for estimatingloss rates for storms of design magnitude. Also,flow times and storage effects are accounted forin the shape of the unit-hydrograph. Where basicdata are inadequate for direct determination ofunit-hydrographs, use may be made of empiricalmethods for synthesis. Use of the unit-hydro-graph method is particularly desirable where de-signs are being developed for ponds, detention res-ervoirs, and pump stations; where peak runoff fromlarge tributary areas is involved in design; andwhere large-scale protective works are under con-sideration. Here, the volume and duration of stormrunoff, as opposed to peak flow, may be the prin-cipal design criteria for determining the dimen-sions of hydraulic structures.

d. Procedures for routing storm runoff throughreservoir-type storage and through stream chan-nels can be found in publications listed in appen-dix E and in the available publications on thesesubjects.

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TM 5–820-4/AFM 88-5, Chap 4

CHAPTER 3

HYDRAULICS

3-1. General. Hydraulic design of the requiredelements of a system for drainage or for protectiveworks may be initiated after functional design cri-teria and basic hydrologic data have been deter-mined. The hydraulic design continual y involvestwo prime considerations, namely, the flow quan-tities to which the system will be subjected, andthe potential and kinetic energy and the momen-tum that are present. These considerations re-quire that the hydraulic grade line and, in manycases, the energy grade line for design and per-tinent relative quantities of flow be computed, andthat conditions whereby energy is lost or dissi-pated must be carefully analyzed. The phenom-ena that occur in flow of water at, above, or belowcritical depth and in change from one of these flowclasses to another must be recognized. Water ve-locities must be carefully computed not only inconnection with energy and momentum consid-erations, but also in order to establish the extentto which the drainage lines and water-courses maybe subjected to erosion or deposition of sediment,thus enabling determination of countermeasuresneeded. The computed velocities and possible re-sulting adjustments to the basic design layout oftenaffect certain parts of the hydrology. Manning’sequation is most commonly used to compute themean velocities of essentially horizontal flow thatoccurs in most elements of a system:

n

The terms are defined in appendix D. Values of nfor use in the formula are listed in chapters 2 and9 of TM 5-820-3/AFM 88-5, Chapter 3.

3-2. Channels.

a. open channels on military installations rangein form from graded swales and bladed ditches tolarge channels of rectangular or trapezoidal crosssection. Swales are commonly used for surfacedrainage of graded areas around buildings andwithin housing developments. They are essen-tially triangular in cross section, with some bot-tom rounding and very flat side slopes, and nor-mally no detailed computation of their flow-

carrying capacity is required. Ditches are com-monly used for collection of surface water in out-lying areas and along roadway shoulders. Largeropen channels, which may be either wholly withinthe ground or partly formed by levees, are usedprincipally for perimeter drains, for upstream flowdiversion or for those parts of the drainage systemwithin a built-up area where construction of a cov-ered drain would be unduly costly or otherwiseimpractical. They are also used for rainfall drain-age disposal. Whether a channel will be lined ornot depends on erosion characteristics, possiblegrades, maintenance requirements, availablespace, overall comparative costs, and other fac-tors. The need for providing a safety fence not lessthan 4 feet high along the larger channels (es-pecially those carrying water at high velocity) willbe considered, particularly in the vicinity of hous-ing areas.

b. The discussion that follows will not attemptto cover all items in the design of an open channel;however, it will cite types of structures and designfeatures that require special consideration.

c. Apart from limitations on gradient imposedby available space, existing utilities, and drainageconfluences is the desirability of avoiding flow ator near critical depths. At such depths, smallchanges in cross section, roughness, or sedimenttransport will cause instability, with the flow depthvarying widely above and below critical. To insurereasonable flow stability, the ratio of invert slopeto critical slope should be not less than 1.29 forsupercritical flow and not greater than 0.76 forsubcritical flow. Unlined earth channel gradientsshould be chosen that will product stable subcrit-ical flow at nonerosive velocities. In regions wheremosquito-borne diseases are prevalent, special at-tention must be given in the selection of gradientsfor open channels to minimize formation of breed-ing areas; pertinent information on this subjectis given in TM 5-632/AFM 91–16.

d. Recommended maximum permissible veloci-ties and Froude numbers for nonerosive flow aregiven in chapter 4 of TM 5-820-3/AFM 88-5, Chap-ter 3. Channel velocities and Froude numbers of

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TM 5–820-4/AFM 88–5, Chap 4

flow can be controlled by providing drop struc-tures or other energy dissipators, and to a limitedextent by widening the channel thus decreasingflow depths or by increasing roughness and depth.If nonerosive flows cannot be attained, the chan-nel can be lined with turf, asphaltic or portland-cement concrete, and ungrouted or grouted rub-ble; for small ditches, half sections of pipe can beused, although care must be taken to prevent en-trance and side erosion and undermining and ul-timate displacement of individual sections. Thechoice of material depends on the velocity, depthand turbulence involved; on the quantities, avail-ability, and cost of materials; and on evaluationof their maintenance. In choosing the material,its effect on flow characteristics may be an im-portant factor. Further, if an impervious lining isto be used, the need for subdrainage and end pro-tection must be considered. Where a series of dropstructures is proposed, care must be taken to avoidplacing them too far apart, and to insure that theywill not be undermined by scour at the foot of theoverpour. The design of energy dissipators andmeans for scour protection are discussed subse-quently.

e. Side slopes for unlined earth channels nor-mally will be no steeper than 1 on 3 in order tominimize maintenance and permit machine mow-ing of grass and weeds. Side-slope steepness forpaved channels will depend on the type of mate-rial used, method of placement, available space,accessibility requirements of maintenance equip-ment, and economy. Where portland-cement con-crete is used for lining, space and overall economicconsiderations may dictate use of a rectangularchannel even though wall forms are required.Rectangular channels are particularly desirablefor conveyance of supercritical channel flow. Mostchannels, however, will convey subcritical flow andbe of trapezoidal cross section. For relatively largeearth channels involving levees, side slopes willdepend primarily on stability of materials used.

f. An allowance for freeboard above the com-puted water surface for a channel is provided sothat during a design storm the channel will notoverflow for such reasons as minor variations inthe hydrology or future development, minor su-perelevation of flow at curves, formation of waves,unexpected hydraulic performance, embankmentsettlement, and the like. The allowance normallyranges from 0.5 to 3 feet, depending on the typeof construction, size of channel, consequences ofoverflow, and degree of safety desired. Require-ments are greater for leveed channels than thosewholly within the ground because of the need to

is:

The terms in both equations are defined in ap-pendix D. The rise in water surface at the outsidebank of a curved channel with a trapezoidal sec-tion can be estimated by the use of the precedingformulas.

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TM 5–820-4/AFM 88–5, Chap 4

h. For most open channel confluences, properdesign can be accomplished satisfactorily by com-putations based on the principle of conservationof momentum. If the channel flows are supercrit-ical, excessive waves and turbulence are likely tooccur unless a close balance of forces is achieved.In such confluences, minimum disturbances willresult if the tributary inflow is made to enter themain channel in a direction parallel to the mainflow, and if the design depth and velocity of thetributary inflow are made equal to those in themain channel. Further, even though minimumdisturbances appear likely under such design con-ditions, it must be remembered that natural flood-flows are highly variable, both in magnitude anddistribution. Since this variability leads to unbal-anced forces and accompanying turbulence, a needmay well exist for some additional wall height orfreeboard allowance at and downstream from theconfluence structure.

i. Side inflows to channels generally enter overthe tops of the walls or in covered drains throughthe walls. If the main channel is earth, erosionprotection frequently is required at (and perhapsopposite) the point of entry. If the sides of a chan-nel through an erosible area are made of concreteor other durable materials and inflows are broughtin over them, care must be taken to insure positiveentry. There are two methods of conducting stormwater into a concrete-lined channel. Entry of largeflows over the top is provided by a spillway builtas an integral part of the side slope while smallerflows are admitted to the channel by a conduitthrough the side slope. Gating of conduit is notrequired at this location because any pending isbrief and not damaging. Where covered tributarydrains enter, examination must be made to seewhether the water in the main channel, if full,would cause damaging backflooding of the tribu-tary area, which would be more damaging thantemporary stoppage of the tributary flow. If so,means for precluding backflow must be employed;this can often be accomplished by a flap gate atthe drain outfall, and if positive closure is re-quired, a slide gate can be used. If flow in the mainchannel is supercritical, the design of side inletstructures may require special provisions to min-imize turbulence effects.

3–3. Bridges.a. A bridge is a structure, including supports,

erected over a depression or an obstruction, suchas water, a highway, or a railway, having a trackor passageway for carrying traffic or other mov-ing loads, and having an opening measured along

the center of the roadway of more than 20 feetbetween undercopings of abutments or spring linesof arches, or extreme ends of the openings for mul-tiple boxes; it may include multiple pipes where the clear distance between openings is less thanhalf of the smaller contiguous opening.

b. Sufficient capacity will be provided to passthe runoff from the design storm determined inaccordance with principles given in chapter 2.Normally such capacity is provided entirely in thewaterway beneath the bridge. Sometimes this isnot practical, and it may be expedient to designone or both approach roadways as overflow sec-tions for excess runoff. In such an event, it mustbe remembered that automobile traffic will beimpeded, and will be stopped altogether if theoverflow depth is much more than 6 inches. How-ever, for the bridge proper, a waterway openingsmaller than that required for 10-year storm run-off will be justifiable.

c. In general, the lowest point of the bridge su-perstructure shall clear the design water surfaceby not less than 2 feet for average flow and trashconditions. This may be reduced to as little as 6inches if the flow is quiet, with low velocity andlittle or no trash. More than 2 feet will be requiredif flows are rough or large-size floating trash isanticipated.

d. The bridge waterway will normally be alinedto result in the least obstruction to streamflow,except that for natural streams consideration willbe given to realinement of the channel to avoidcostly skews, To the maximum extent practicable,abutment wings will be alined to improve flowconditions. If a bridge is to span an improved trap-ezoidal channel of considerable width, the needfor overall economy may require consideration ofthe relative structural and hydraulic merits of on-bank abutments with or without piers and warpedchannel walls with vertical abutments.

e. To preclude failure by underscour, abutmentand pier footings will usually be placed either toa depth of not less than 5 feet below the antici-pated depth of scour, or on firm rock if such isencountered at a higher elevation. Large multi-span structures crossing alluvial streams may re-quire extensive pile foundations. To protect thechannel against the increased velocities, turbu-lence, and eddies expected to occur locally, re-vetment of channel sides or bottom consisting ofconcrete, grouted rock, loose riprap, or sacked con-crete will be placed as required. Criteria for se-lection of revetment are given in chapter 5.

f. Where flow velocities are high, bridges should

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TM 5–820-4/AFM 88-5, Chap 4

be of clear span, if at all practicable, in order topreclude serious problems attending debris lodg-ment and to minimize channel construction andmaintenance costs.

g. It is important that storm runoff be controlledover as much of the contributing watershed aspracticable. Diversion channels, terraces, checkdams, and similar conventional soil conservingfeatures will be installed, implemented, or im-proved to reduce velocities and prevent silting ofchannels and other downstream facilities. Whenpracticable, unprotected soil surfaces within thedrainage area will be planted with appropriateerosion-resisting plants. These parts of the drain-age area which are located on private property orotherwise under control of others will be consid-ered fully in the planning stages, and coordinatedefforts will be taken to assure soil stabilizationboth upstream and downstream from the con-struction site.

h. Engineering criteria and design principles re-lated to traffic, size, load capacity, materials, andstructural requirements for highway and railroadbridges are given in TM 5-820-2/AFM 88-5, Chap-ter 2, and in AASHTO Standard Specifications forHighway Bridges, design manuals of the differentrailroad companies, and recommended practicesof AREA Manual for Railway Engineering.

3-4. Curb-and-gutter sections.

a. Precipitation which occurs upon city streetsand adjacent areas must be rapidly and econom-ically removed before it becomes a hazard to traffic.Water falling on the pavement surface itself is re-moved from the surface and concentrated in thegutters by the provision of an adequate crown.The surface channel formed by the curb and gut-ter must be designed to adequately convey therunoff from the pavement and adjacent areas toa suitable collection point. The capacity can becomputed by using the nomograph for flow in atriangular channel, figure 3-2. This figure can alsobe used for a battered curb face section, since thebattering has negligible effect on the cross sec-tional area. Limited data from field tests with clearwater show that a Manning’s n of 0.013 is appli-cable for pavement. The n value should be raisedwhen appreciable quantities of sediment are pres-ent. Figure 3-2 also applies to composite sectionscomprising two or more rates of cross slope.

b. Good roadway drainage practice requires theextensive use of curb-and-gutter sections in com-bination with spillway chutes or inlets and down-spouts for adequate control of surface runoff, par-ticularly in hilly and mountainous terrain where

it is necessary to protect roadway embankmentsagainst formation of rivulets and channels by con-centrated flows. Materials used in such construc-tion include portland-cement concrete, asphalticconcrete, stone rubble, sod checks, and prefabri-cated concrete or metal sections, Typical of thelatter are the entrance tapers and embankmentprotectors made by manufacturers of corrugatedmetal products. Downspouts as small as 8 inchesin diameter may be used, unless a considerabletrash problem exists, in which case a large sizewill be required. When frequent mowing is re-quired, consideration will be given to the use ofburied pipe in lieu of open paved channels or ex-posed pipe. The hydrologic and hydraulic designand the provision of outfall erosion protection willbe accomplished in accordance with principlesoutlined for similar component structures dis-cussed in this manual.

c. Curbs are used to deter vehicles from leavingthe pavement at hazardous points as well as tocontrol drainage. The two general classes of curbsare known as barrier and mountable and each hasnumerous types and detail designs. Barrier curbsare relatively high and steep faced and designedto inhibit and to at least discourage vehicles fromleaving the roadway. They are considered unde-sirable on high speed arterials. Mountable curbsare designed so that vehicles can cross them withvarying degrees of ease.

d. Curbs, gutters, and storm drains will not beprovided for drainage around tank-car or tank-truck unloading areas, tank-truck loading stands,and tanks in bulk-fuel-storage areas. Safety re-quires that fuel spillage must not be collected instorm or sanitary sewers. Safe disposal of fuelspillage of this nature may be facilitated by pro-vision of ponded areas for drainage so that anyfuel spilled can be removed from the water sur-face.

3–5. Culverts.

a. A drainage culvert is defined as any structureunder the roadway with a clear opening of twentyfeet or less measured along the center of the road-way. Culverts are generally of circular, oval, el-liptical, arch, or box cross section and may be ofeither single or multiple construction, the choicedepending on available headroom and economy.Culvert materials for permanent-type installa-tions include plain concrete, reinforced concrete,corrugated metal, asbestos cement, and clay. Con-crete culverts may be either precast or cast inplace, and corrugated metal culverts may haveeither annular or helical corrugations and be con-

3 - 5

TM 5–820-4/AFM 88–5, Chap 4

U. S. Army Corps of Engineers

Figure 3–2. Nomograph for flow in triangular channels.

3–6

TM 5-820-4/AFM 88-5, Chap 4

structed of steel or aluminum. For the metal cul-verts, different kinds of coatings and linings areavailable for improvement of durability and hydrau-lic characteristics. The design of economical culvertsinvolves consideration of many factors relating to re-quirements of hydrology, hydraulics, physical envi-ronment, imposed exterior loads, construction, andmaintenance. With the design discharge and gen-eral layout determined, the design requires detailedconsideration of such hydraulic factors as shape andslope of approach and exit channels, allowable headat entrance (and pending capacity, if appreciable),tailwater levels, hydraulic and energy grade lines,and erosion potential. A selection from possiblealternative designs may depend on practical con-siderations such as minimum acceptable size, avail-able materials, local experience concerning corrosionand erosion, and construction and maintenanceaspects. If two or more alternative designs involvingcompetitive materials of equivalent merit appear tobe about equal in estimated cost, plans will be devel-oped to permit contractor’s options or alternate bids,so that the least construction cost will result.

• b. In most localities, culvert pipe is available insizes to 36 inches diameter for plain concrete, 144inches or larger for reinforced concrete, 120 inchesfor standard and helically corrugated metal (plain,polymer coated, bituminous coated, part paved, andfully paved interior), 36 inches for asbestos cementor clay, and 24 inches for corrugated polyethylenepipe. Concrete elliptical in sizes up to 116 x 180inches, concrete arch in sizes up to 107 x 169 inchesand reinforced concrete box sections in sizes from3 x 2 feet to 12 x 12 feet are available. Structuralplate, corrugated metal pipe can be fabricated withdiameters from 60 to 312 inches or more. Corru-gated metal pipe arches are generally available insizes to 142 by 91 inches, and corrugated, structuralplate pipe arches in spans to 40 feet. Reinforced con-crete vertical oval (elliptical) pipe is available in sizesto 87 by 136 inches, and horizontal oval (elliptical)pipe is available in sizes to 136 by 87 inches. De-signs for extra large sizes or for special shapes orstructural requirements may be submitted by manu-facturers for approval and fabrication. Short culvertsunder sidewalks (not entrances or driveways) may beas small as 8 inches in diameter if placed so as to becomparatively free from accumulation of debris orice. Pipe diameters or pipe-arch rises should be notless than 18 inches. A diameter or pipe-arch of notless than 24 inches should be used in areas wherewind-blown materials such as weeds and sand maytend to block the waterway. Within the above rangesof sizes, structural requirements may limit the maxi-

mum size that can be used for a specific installation.

c. The selection of culvert materials to withstanddeterioration from corrosion or abrasion will bebased on the following considerations:• (1) Rigid culvert is preferable where industrial

wastes, spilled petroleum products, or other sub-stances harmful to bituminous paving and coating incorrugated metal pipe are apt to be present. Con-crete pipe generally should not be used where soil ismore acidic than pH 5.5 or where the fluid carriedhas a pH less than 5.5 or higher than 9.0. Polyethyl-ene pipe is unaffected by acidic or alkaline soil condi-tions. Concrete pipe can be engineered to performvery satisfactorily in the more severe acidic or alka-line environments. Type II or Type V cementsshould be used where soils and/or water have a mod-erate or high sulfate concentration, respectively;criteria are given in Federal Specification SS-C-1960/GEN. High-density concrete pipe is recom-mended when the culvert will be subject to tidaldrainage and salt-water spray. Where highly cor-rosive substances are to be carried, the resistivequalities of vitrified clay pipe or plastic lined con-crete pipe should be considered.• (2) Flexible culvert such as corrugated-steel pipe

will be galvanized and generally will be bituminouscoated for permanent installations. Bituminous coat-ing or polymeric coating is recommended for corru-gated steel pipe subjected to stagnant water; wheredense decaying vegetation is present to form organicacids; where there is continuous wetness or contin-uous flow; and in well-drained, normally dry, alkalisoils. The polymeric coated pipe is not damaged byspilled petroleum products or industrial wastes.Asbestos-fiber treatment with bituminous coated ora polymeric coated pipe is recommended for corru-gated-steel pipe subjected to highly corrosive soils,cinder fills, mine drainage, tidal drainage, salt-waterspray, certain industrial wastes, and other severelycorrosive conditions; or where extra-long life is de-sirable. Cathodic protection is rarely required forcorrugated-steel-pipe installations; in some in-stances, its use may be justified. Corrugated-alu-minum-alloy pipe, fabricated in all of the shapes andsizes of the more familiar corrugated-steel pipe,evidences corrosion resistance in clear granularmaterials even when subjected to sea water. Corru-gated-aluminum pipe will not be installed in soilsthat are highly acid (pH less than 5) or alkaline (pHgreater than 9), or in metallic contact with othermetals or metallic deposits, or where known cor-rosive conditions are present or where bacterial cor-rosion is known to exist. Similarly, this type pipe will

Change 1 3-7

TM 5-820-4/AFM 88-5, Chap 4

not be installed in material classified as OH or OLaccording to the Unified Soil Classification System aspresented in MIL-STD 619. Although bituminouscoatings can be applied to aluminum-alloy pipe, suchcoatings do not afford adequate protection (bitumi-nous adhesion is poor) under the aforementionedcorrosive conditions. Suitable protective coatings foraluminum alloy have been developed, but are noteconomically feasible for culverts or storm drains.For flow carrying debris and abrasives at moderateto high velocity, paved-invert pipe may be appro-priate. When protection from both corrosion andabrasion is required,smooth-interior corrugated-steel pipe may be desirable, since in addition to pro-viding the desired protection, improved hydraulicefficiency of the pipe will usually allow a reduction inpipe size. When considering a coating for use, per-formance data from users in the area can be helpful.Performance history indicates various successes orfailures of coatings and their probable cause and areavailable from local highway departments.

d. The capacity of a culvert is determined by itsability to admit, convey, and discharge water underspecified conditions of potential and kinetic energyupstream and downstream. The hydraulic design ofa culvert for a specified design discharge involvesselection of a type and size, determination of theposition of hydraulic control, and hydraulic computa-tions to determine whether acceptable headwaterdepths and outfall conditions will result. In consider-ing what degree of detailed refinement is appropri-ate in selecting culvert sizes, the relative accuracy ofthe estimated design discharge should be taken intoaccount. Hydraulic computations will be carried outby standard methods based on pressure, energy,momentum, and loss considerations.Appropriateformulas, coefficients, and charts for culvert designare given in appendix B.

e. Rounding or beveling the entrance in any way willincrease the capacity of a culvert for every designcondition. Some degree of entrance improvementshould always be considered for incorporation indesign. A headwall will improve entrance flow overthat of a projecting culvert. They arc particularlydesirable as a cutoff to prevent saturation sloughingand/or erosion of the embankment. Provisions fordrainage should be made over the center of the head-wall to prevent scouring along the sides of the walls.A mitered entrance conforming to the fill slope pro-duces little if any improvement in efficiency over thatof the straight, sharp-edged, projecting inlet, andmay be structurally unsafe due to uplift forces. Bothtypes of inlets tend to inhibit the culvert from flow-ing full when the inlet is submerged. The most effi-

3-8 Change 1

cient entrances incorporate such geometric featuresas elliptical arcs, circular arcs, tapers, and para-bolic drop-down curves. In general elaborate inletdesigns for culverts are justifiable only in unusualcircumstances.

f. Outlets and endwalls must be protected againstundermining, bottom scour, damaging lateral ero-sion and degradation of the downstream channel.The presence of tailwater higher than the culvertcrown will affect the culvert performance and maypossibly require protection of the adjacent embank-ment against wave or eddy scour. Endwalls (outfallheadwalls) and wingwalls should be used wherepractical, and wingwalls should flare one on eightfrom one diameter width to that required for theformation of a hydraulic jump and the establishmentof a Froude number in the exit channel that will in-sure stability. Two general types of channel instabil-ity can develop downstream of a culvert. The con-ditions are known as either gully scour or a localizederosion referred to as a scour hole. Gully scour is tobe expected when the Froude number of flow in thechannel exceeds that required for stability. Erosionof this type maybe of considerable extent dependingupon the location of the stable channel section rela-tive to that of the outlet in both the vertical anddownstream directions.A scour hole can be ex-pected downstream of an outlet even if the down-stream channel is stable. The severity of damage tobe anticipated depends upon the conditions existingor created at the outlet. See chapter 5 for additionalinformation on erosion protection.

g. In the design and construction of any drainagesystem it is necessary to consider the minimum andmaximum earth cover allowable in the undergroundconduits to be placed under both flexible and rigidpavements. Minimum-maximum cover require-ments for asbestos-cement pipe, corrugated-steelpipe, reinforced concrete culverts and storm drains,standard strength clay and non-reinforced concretepipe are given in appendix C. The cover depthsrecommended are valid for average bedding andbackfill conditions. Deviations from these conditionsmay result in significant minimum cover require-ments.

h. Infiltration of fine-grained soils into drainagepipelines through joint openings is one of the ma-jor causes of ineffective drainage facilities. Thisis particularly a problem along pipes on relativelysteep slopes such as those encountered with bro-ken back culverts. Infiltration of backfill andsubgrade material can be controled by watertightflexible joint materials in rigid pipe and with wa-tertight coupling bands in flexible pipe. The re-

sults of laboratory research concerning soil infil-tration through pipe joints and the effectivenessof gasketing tapes for waterproofing joints andseams are available.

3–6. Underground hydraulic design.

a. The storm-drain system will have sufficientcapacity to convey runoff from the design storm(usually a 10-year frequency for permanent in-stallations) within the barrel of the conduit. De-sign runoff will be computed by the methods in-dicated in chapter 2. Concentration times willincrease and average rainfall intensities will de-”crease as the design is carried to successive down-stream points. In general, the incremental con-centration times and the point-by-point totalsshould be estimated to the nearest minute. Thesetotals should be rounded to the nearest 5 minutesin selecting design intensities from the intensity-duration curve. Advantage will be taken of anypermanently available surface ponding areas, andtheir effectiveness determined, in order to holddesign discharges and storm-drain sizes to a min-imum. Experience indicates that it is feasible andpractical in the actual design of storm drains toadopt minimum values of concentration times of10 minutes for paved areas and 20 minutes forturfed areas. Minimum times of concentrationshould be selected by weighting for combined pavedand turfed areas.

b. Storm-drain systems will be so designed thatthe hydraulic gradeline for the computed designdischarge in as near optimum depth as practicableand velocities are not less than 2.5 feet per second(nominal minimum for cleansing) when the drainsare one-third or more full. To minimize the pos-sibility of clogging and to facilitate cleaning, theminimum pipe diameter or box section height willgenerally be not less than 12 inches; use of smallersize must be fully justified. Tentative size selec-tions for capacity flow may be made from the nom-ography for computing required size of circulardrains in appendix B, TM 5-820-l/AFM 88-5,Chapter 1. Problems attending high-velocity flowshould be carefully analyzed, and appropriate pro-visions made to insure a fully functional project.

c. Site topography will dictate the location ofpossible outlets and the general limiting gradesfor the system. Storm drain depths will be held tothe minimum consistent with limitations imposedby cover requirements, proximity of other struc-tures, interference with other utilities, and veloc-ity requirements because deep excavation is ex-pensive. Usually in profile, proceeding downstream,the crowns of conduits whose sizes progressively

TM 5–820-4/AFM 88-5, Chap 4

increase will be matched, the invert grade drop-ping across the junction structure; similarly, thecrowns of incoming laterals will be matched tothat of the main line. If the downstream conduitis smaller as on a steep slope, its invert will bematched to that of the upstream conduit. Someadditional lowering of an outgoing pipe may berequired to compensate for pressure loss within ajunction structure.

d. Manholes or junction boxes usually will beprovided at points of change in conduit grade orsize, at junctions with laterals of branches andwherever entry for maintenance is required. Dis-tance between points of entry will be not morethan approximately 300 feet for conduits with aminimum dimension smaller than 30 inches. If thestorm drain will be carrying water at a velocityof 20 feet per second or greater, with high energyand strong forces present, special attention mustbe given such items as alinement, junctions, an-chorage requirements, joints, and selection of ma-terials.

3–7. Inlets.

a. Storm-drain inlet structures to intercept sur-face flow are of three general types: drop, curb,and combination. Hydraulically, they may func-tion as either weirs or orifices depending mostlyon the inflowing water. The allowable depth fordesign storm conditions and consequently the type,size and spacing of inlets will depend on the to-pography of the surrounding area, its use, andconsequences of excessive depths. Drop inlets,which are provided with a grated entrance open-ing, are in general more efficient than curb inletsand are useful in sumps, roadway sags, swales,and gutters. Such inlets are commonly depressedbelow the adjacent grade for improved intercep-tion or increased capacity. Curb inlets along slop-ing gutters require a depression for adequate in-terception. Combination inlets may be used wheresome additional capacity in a restricted space isdesired. Simple grated inlets are most susceptibleto blocking by trash. Also, in housing areas, theuse of grated drop inlets should be kept to a rea-sonable minimum, preference being given to thecurb type of opening. Where an abnormally highcurb opening is needed, pedestrian safety may re-quire one or more protective bars across the open-ing. Although curb openings are less susceptibleto blocking by trash, they are also less efficientfor interception on hydraulically steep slopes, be-cause of the difficulty of turning the flow into them.Assurance of satisfactory performance by anysystem of inlets requires careful consideration of

3-9

TM 5–820-4/AFM 88–5, Chap 4

the several factors involved. The final selection ofinlet types will be based on overall hydraulic per-formance, safety requirements, and reasonable-ness of cost for construction and maintenance.

b. In placing inlets to give an optimum arrange-ment for flow interception, the following guidesapply:

(1) At street intersections and crosswalks, in-lets are usually placed on the upstream side. Gut-ters to transport flow across streets or roadwayswill not be used.

(2) At intermediate points on grades, thegreatest efficiency and economy commonly resultif either grated or curb inlets are designed to in-tercept only about three-fourths of the flow.

(3) In sag vertical curves, three inlets are oftendesirable, one at the low point and one on eachside of the low point where the gutter grade isabout 0.2 foot above the low point. Such a layouteffectively reduces pond buildup and deposition ofsediment in the low area.

(4) Large quantities of surface runoff flowingtoward main thoroughfares normally should beintercepted before reaching them.

(5) At a bridge with curbed approaches, gutterflow should be intercepted before it reaches thebridge, particularly where freezing weather oc-curs.

(6) Where a road pavement on a continuousgrade is warped in transitions between super-elevated and normal sections, surface water shouldnormally be intercepted upstream of the pointwhere the pavement cross slope begins to change,especially in areas where icing occurs.

(7) On roads where curbs are used, runoff fromcut slopes and from off-site areas should, wher-ever possible, be intercepted by ditches at the topsof slopes or in swales along the shoulders and notbe allowed to flow onto the roadway. This practiceminimizes the amount of water to be interceptedby gutter inlets and helps to prevent mud anddebris from being carried onto the pavement.

c. Inlets placed in sumps have a greater poten-tial capacity than inlets on a slope because of thepossible submergence in the sump. Capacities ofgrated, curb, and combination inlets in sumps willbe computed as outlined below. To allow for block-age by trash, the size of inlet opening selected forconstruction will be increased above the computedsize by 100 percent for grated inlets and 25 to 75percent, depending on trash conditions, for curbinlets and combination inlets.

(1) Grated type (in sump).(a) For depths of water up to 0.4 foot use

the weir formula:

If one side of a rectangular grate is against a curb,this side must be omitted in computing the perim-eter.

(b) For depths of water above 1.4 feet use theorifice formula:

(c) For depths between 0.4 and 1.4 feet, op-eration is indefinite due to vortices and other dis-turbances. Capacity will be somewhere betweenthose given by the preceding formulas.

(d) Problems involving the above criteria maybe solved graphically by use of figure 3-3.

(2) Curb Type (in sump). For a curb inlet in asump, the above listed general concepts for weirand orifice flow apply, the latter being in effectfor depths greater than about 1.4h (where h is theheight of curb opening entrance). Figure 3-4 pre-sents a graphic method for estimating capacity.

(3) Combination Type (in sump). For a com-bination inlet in a sump no specific formulas aregiven. Some increase in capacity over that pro-vided singly by either a grated opening or a curbopening may be expected, and the curb openingwill operate as a relief opening if the grate be-comes clogged by debris. In estimating the capac-ity, the inlet will be treated as a simple gratedinlet, but a safety factor of 25 to 75 percent willbe applied.

(4) Slotted drain type. For a slotted drain inletin a sump, the flow will enter the slot as either allorifice type or all weir type, depending on the depthof water at the edge of the slot. If the depth is lessthan .18 feet, the length of slot required to inter-cept total flow is equal to:

If the depth is greater than .18 feet, the length ofslot required to intercept total flow is equal to:

d = depth of flow-inchesw = width of slot---.l46 feet

d. Each of a series of inlets placed on a slope isusually, for optimum efficiency, designed to in-tercept somewhat less than the design gutter flow,the remainder being passed to downstream inlets.The amount that must be intercepted is governedby whatever width and depth of bypassed flow canbe tolerated from a traffic and safety viewpoint.

3–10

TM 5-820-4/AFM 88-5, Chap 4

PREPARED

❑ UREAU OF PUBLIC ROADS

Figure 3-3. Capacity of grate inlet in sump water pond on grate.

3–11

HE

IGH

T

OF

O

PE

NIN

G

(h)

IN

FE

ET

TM 5–820-4/AFM 88–5, Chap 4

Such toleration levels will nearly always be influ-enced by costs of drainage construction. With theflat street crowns prevalent in modern construc-tion, many gutter flows are relatively wide and inbuilt-up areas some inconveniences are inevita-ble, especially in regions of high rainfall, unlessan elaborate inlet system is provided. Theachievement of a satisfactory system at reason-able cost requires careful consideration of use fac-tors and careful design of the inlets themselves.However, it must also be remembered that a lim-itation on types and sizes for a given project isalso desirable, for standardization will lead to lowerconstruction costs. Design of grated, curb, andcombination inlets on slopes will be based on prin-ciples outlined below.

(1) Grated type (on slope). A grated inlet placedin a sloping gutter will provide optimum inter-ception of flow if the bars are placed parallel tothe direction of flow, if the openings total at least50 percent of the width of the grate (i.e. normalto the direction of flow), and if the unobstructedopening is long enough (parallel to the directionof flow) that the water falling through will clearthe downstream end of the opening. The minimumlength of clear opening required depends on thedepth and velocity of flow in the approach gutterand the thickness of the grate at the end of theslot. This minimum length may be estimated bythe partly empirical formula:

A rectangular grated inlet in a gutter on a con-tinuous grade can be expected to intercept all thewater flowing in that part of the gutter cross sec-tion that is occupied by the grating plus an amountthat will flow in along the exposed sides. However,unless the grate is over 3 feet long or greatly de-pressed (extreme warping of the pavement is sel-dom permissible), any water flowing outside thegrate width can be considered to bypass the inlet.The quantity of flow in the prism intercepted bysuch a grate can be computed by following in-struction 3 in figure 3-2. For a long grate the in-flow along the side can be estimated by consid-ering the edge of the grate as a curb opening whoseeffective length is the total grate length (ignoringcrossbars) reduced by the length of the jet directlyintercepted at the upstream end of the grate. Toattain the optimum capacity of an inlet consistingof two grates separated by a short length of pavedgutter, the grates should be so spaced that thecarryover from the upstream grate will move suf-ficiently toward the curb to be intercepted by thedownstream grate.

(2) Curb type (on slope). In general, a curbinlet placed on a grade is a hydraulically ineffi-cient structure for flow interception. A relativelylong opening is required for complete interceptionbecause the heads are normally low and the di-rection of oncoming flows is not favorable. Thecost of a long curb inlet must be weighed againstthat of a drop type with potentially costly grate.The capacity of a curb inlet intercepting all theflow can be calculated by an empirical equation.The equation is a function of length of clear open-ing of the inlet, depth of depression of flow line atinlet in feet, and the depth of flow in approachgutter in feet. Depression of the inlet flow line isan essential part of good design, for a curb inletwith no depression is very inefficient. The flowintercepted may be markedly increased withoutchanging the opening length if the flow line canbe depressed by one times the depth of flow in theapproach gutter. The use of long curb openingswith intermediate supports should generally beavoided because of the tendency for the supportsto accumulate trash. If supports are essential, theyshould be set back several inches from the gutterline.

(3) Combination type (on slope). The capacityof a combination inlet on a continuous grade isnot much greater than that of the grated portionitself, and should be computed as a separate gratedinlet except in the following situations. If the curbopening is placed upstream from the grate, thecombination inlet can be considered to operate astwo separate inlets and the capacities can be com-puted accordingly. Such an arrangement is some-times desirable, for in addition to the increasedcapacity the curb opening will tend to interceptdebris and thereby reduce clogging of the grate.If the curb opening is placed downstream fromthe grate, effective operation as two separate in-lets requires that the curb opening be sufficientlydownstream to allow flow bypassing the grate tomove into the curb opening. The minimum sepa-ration will vary with both the cross slope and thelongitudinal slope.

e. Structural aspects of inlet construction shouldgenerally be as indicated in figures 3-5, 3-6, and3-7 which show respectively, standard circulargrate inlets, types A and B; typical rectangulargrate combination inlet, type C; and curb inlet,type D. It will be noted that the type D inlet pro-vides for extension of the opening by the additionof a collecting trough whose backwall is cantile-vered to the curb face. Availability of gratings andstandards of municipalities in a given region maylimit the choice of inlet types. Grated inlets sub-ject to heavy wheel loads will require grates of

3-13

TM 5–820-4/AFM 88-5, Chap 4

SECTION-TYPE “A” INLET SECTION ‘TYPE “B” INLET

Figure 3-5. Standard type "A" and type "B" inlets.

3 - 1 4

TM 5–820-4/AFM 88–5, Chap 4

TM 5–820-4/AFM 88–5, Chap 4

3-16


Figure 3–7. Standard type “D” inlet.

precast steel or of built-up, welded steel. Steelgrates will be galvanized or bituminous coated.Unusual inlet conditions will require special de-sign.

3–8. Vehicular safety and hydraulically effi-cient drainage practice.

a. Some drainage structures are potentiallyhazardous and, if located in the path of an errantvehicle, can substantially increase the probabilityof an accident. Inlets should be flush with theground, or should present no obstacle to a vehiclethat is out of control. End structures or culvertsshould be placed outside the designated recoveryarea wherever possible. If grates are necessary to

TM 5–820-4/AFM 88–5, Chap 4

cover culvert inlets, care must be taken to designthe grate so that the inlet will not clog duringperiods of high water. Where curb inlet systemsare used, setbacks should be minimal, and gratesshould be designed for hydraulic efficiency andsafe passage of vehicles. Hazardous channels orenergy dissipating devices should be located out-side the designated recovery area or adequateguard-rail protection should be provided.

b. It is necessary to emphasize that libertiesshould not be taken with the hydraulic design ofdrainage structures to make them safer unless itis clear that their function and efficiency will notbe impaired by the contemplated changes. Evenminor changes at culvert inlets can seriously dis-rupt hydraulic performance.

3–17

TM 5–820-4/AFM 88–5, Chap 4

CHAPTER 4

HYDRAULIC STRUCTURES

4–1. Manholes and junction boxes. Drainagesystems require a variety of appurtenances to as-sure proper operations. Most numerous appurte-nances are manholes and junction boxes. Man-holes and junction boxes are generally constructedof any suitable materials such as brick, concreteblock, reinforced concrete, precast reinforced-con-crete sections, or preformed corrugated metal sec-tions. Manholes are located at intersections,changes in alignment or grade, and at interme-diate joints in the system up to every 500 feet.Junction boxes for large pipes are located as nec-essary to assure proper operation of the drainagesystem. Inside dimensions of manholes will not beless than 2.5 feet. Inside dimensions of junctionboxes will provide for not less than 3 inches ofwall on either side of the outside diameter of thelargest pipes involved. Manhole frames and coverwill be provided as required; rounded manhole andbox covers are preferred to square covers. Slabtop covers will be provided for large manholes andjunction boxes too shallow to permit corbeling ofthe upper part of the structure. A typical largebox drain cover is shown in figure 3-5, TM 5-820-3/AFM 88-5, Chapter 3. Fixed ladders will be pro-vided depending on the depth of the structures.Access to manhole and junction boxes without fixedladders will be by portable ladders. Manhole andjunction box design will insure minimum hy-draulic losses through them. Typical manhole andjunction box construction is shown in figures 4-1through 4-3.

4–2. Detention pond storage. Hydrologic stud-ies of the drainage area will reveal if detentionponds are required. Temporary storage or pend-ing may be required if the outflow from a drainagearea is limited by the capacity of the drainagesystem serving a given area. A full discussion oftemporary storage or ponding design will be foundin appendix B, TM 5-820-l/AFM 88-5, Chapter 1.Pending areas should be designed to avoid crea-tion of a facility that would be unsightly, difficultto maintain, or a menace to health or safety.

4-3. Outlet energy dissipators.

a. Most drainage systems are designed to op-erate under normal free outfall conditions. Tail-water conditions are generally absent. However,it is possible for a discharge resulting from adrainage system to possess kinetic energy in ex-cess of that which normally occurs in waterways.To reduce the kinetic energy, and thereby reducedownstream scour, outfalls may sometimes be re-quired to reduce streambed scour. Scour may oc-cur in the streambed if discharge velocities exceedthe values listed in table 4-1. These values are tobe used only as guides; studies of local materialsmust be made prior to a decision to install energydissipation devices. Protection against scour maybe provided by plain outlets, transitions and still-ing basins. Plain outlets provide no protective worksand depend on natural material to resist erosion.Transitions provide little or no dissipation of en-ergy themselves, but by spreading the effluent jetto approximately the flow cross-section of the nat-ural channel, the energy is greatly reduced priorto releasing the effluent into the outlet channel.Stilling basins dissipate the high kinetic energyof flow by a hydraulic jump or other means. Rip-rap may be required at any of the three types ofoutfalls.

(1) Plain type.(a) If the discharge channel is in rock or a

material highly resistant to erosion, no specialerosion protection is required. However, since flowfrom the culvert will spread with a resultant drop

Table 4-1. Maximum Permissible Mean Velocities toPrevent Scour

MaximumPermissible

Material Mean Velocity

Uniform graded sandand cohesionless silts 1.5 fps

Well-graded sand 2.5 fpsSilty sand 3.0 fpsClay 4.0 fpsGravel 6.0 fps


4–

TM 5–820-4/AFM 88–5, Chap 4

ELEVATION

HALF PLAN - MANHOLE COVER AND FRAME

4-2

TM 5–820-4/AFM 88–5, Chap 4

SECTION “A-A” SECTION “B-B”

4-4

TM 5–820-4/AFM 88–5, Chap 4

in water surface and increase in velocity, this typeof outlet should be used without riprap only if thematerial in the outlet channel can withstand ve-locities about 1.5 times the velocity in the culvert.At such an outlet, side erosion due to eddy actionor turbulence is more likely to prove troublesomethan is bottom scour.

(b) Cantilevered culvert outlets may be usedto discharge a free-falling jet onto the bed of theoutlet channel. A plunge pool will be developed,the depth and size of which will depend on theenergy of the falling jet at the tailwater and theerodibility of the bed material.

(2) Transition type. Endwalls (outfall head-walls) serve the dual purpose of retaining the em-bankment and limiting the outlet transitionboundary. Erosion of embankment toes usuallycan be traced to eddy attack at the ends of suchwalls. A flared transition is very effective, if pro-portioned so that eddies induced by the effluentjet do not continue beyond the end of the wall orovertop a sloped wall. As a guide, it is suggestedthat the product of velocity and flare angle shouldnot exceed 150. That is, if effluent velocity is 5 feetper second each wingwall may flare 30 degrees;but if velocity is 15 feet per second, the flare shouldnot exceed 10 degrees. Unless wingwalls can beanchored on a stable foundation, a paved apronbetween the wingwalls is required. Special caremust be taken in design of the structure to pre-clude undermining. A newly excavated channelmay be expected to degrade, and proper allowancefor this action should be included in establishingthe apron elevation and depth of cutoff wall. Warpedendwalls provide excellent transitions in that theyresult in the release of flow in a trapezoidal sec-tion, which generally approximates the cross sec-tion of the outlet channel. If a warped transitionis placed at the end of a curved section below aculvert, the transition is made at the end of thecurved section to minimize the possibility of ov-ertopping due to superelevation of the water sur-face. A paved apron is required with warped end-walls. Riprap usually is required at the end of atransition-type outlet.

(3) Stilling basins. A detailed discussion ofstilling basins for circular storm drain outlets canbe found in chapter 7, TM 5–820–3.

b. Improved channels, especially the paved ones,commonly carry water at velocities higher thanthose prevailing in the natural channels into whichthey discharge. Often riprap will suffice for dis-sipation of excess energy. A cutoff wall may berequired at the end of a paved channel to precludeundermining. In extreme cases a flared transi-

tion, stilling basin, or impact device may be re-quired.

4–4. Drop structures and check dams. Dropstructures and check dams are designed to checkchannel erosion by controlling the effective gra-dient, and to provide for abrupt changes in chan-nel gradient by means of a vertical drop. Thestructures also provide satisfactory means for dis-charging accumulated surface runoff over fills withheights not exceeding about 5 feet and over em-bankments higher than 5 feet provided the endsill of the drop structure extends beyond the toeof the embankment. The check dam is a modifi-cation of the drop structure used for erosion con-trol in small channels where a less elaboratestructure is permissible. Pertinent design fea-tures are covered in chapter 5, TM 5–820–3/AFM88–5, Chapter 3.

4–5. Miscellaneous structures.

a. A chute is a steep open channel which pro-vides a method of discharging accumulated sur-face runoff over fills and embankments. A typicaldesign is included in chapter 6, TM 5–820–3/AFM88–5, Chapter 3.

b. When a conduit or channel passes through orbeneath a security fence and forms an openinggreater than 96 square inches in area a securitybarrier must be installed. Barriers are usually ofbars, grillwork, or chain-link screens, Parallel barsused to prevent access will be spaced not morethan 6 inches apart, and will be of sufficientstrength to preclude bending by hand after as-sembly.

(1) Where fences enclose maximum securityareas such as exclusion and restricted areas,drainage channels, ditches, and equalizers will,wherever possible, be carried under the fence inone or more pipes having an internal diameter ofnot more than 10 inches. Where the volume of flowis such that the multipipe arrangement is not fea-sible, the conduit or culvert will be protected bya security grill composed of 3/4-inch-diameter rodsor 1/2-inch bars spaced not more than 6 inches oncenter, set and welded in an internal frame. Whererods or bars exceed 18 inches in length, suitablespacer bars will be provided at not more than 18inches on center, welded at all intersections. Se-curity grills will be located inside the protectedarea. Where the grill is on the downstream end ofthe culvert, the grill will be hinged to facilitatecleaning and provided with a latch and padlock,and a debris catcher will be installed in the up-stream end of the conduit or culvert. Elsewherethe grill will be permanently attached to the cul-

4-5

ELEVATION


vert. Security regulations normally require theguard to inspect such grills at least once everyshift. For culverts in rough terrain, steps will beprovided to the grill to facilitate inspection andcleaning.

(2) For culverts and storm drains, barriers atthe intakes would be preferable to barriers at theoutlets because of the relative ease of debris re-moval. However, barriers at the outfalls are usu-ally essential; in these cases consideration shouldbe given to placing debris interceptors at the in-lets. Bars constituting a barrier should be placedin a horizontal position, and the number of ver-tical members should be limited in order to min-imize clogging; the total clear area should be atleast twice the area of the conduit or larger undersevere debris conditions. For large conduits anelaborate cagelike structure may be required.Provisions to facilitate cleaning during or imme-diately after heavy runoff should be made. Figure4–4 shows a typical barrier for the outlet of a pipedrain. It will be noted that a 6-inch underclear-ance is provided to permit passage of normal bed-load material, and that the apron between the

TM 5–820-4/AFM 88–5, Chap 4

conduit outlet and the barrier is placed on a slopeto minimize deposition of sediment on the apronduring ordinary flow. Erosion protection, whererequired, is placed immediately downstream fromthe barrier.

(3) If manholes must be located in the im-mediate vicinity of a security fence their coversmust be so fastened as to prevent unauthorizedopening.

(4) Open channels may present special prob-lems due to the relatively large size of the water-way and the possible requirements for passage oflarge floating debris. For such channels a barriershould be provided that can be unfastened andopened or lifted during periods of heavy runoff orwhen clogged. The barrier is hinged at the top andan empty tank is welded to it at the bottom toserve as a float. Open channels or swales whichdrain relatively small areas and whose flows carryonly minor quantities of debris may be securedmerely by extending the fence down to a concretesill set into the sides and across the bottom of thechannel.

4–7

TM 5-820-4/AFM 88-5, Chap 4

CHAPTER 5

EROSION CONTROL AND RIPRAP PROTECTION

5-1. General .

a. Hydraulic structures discharging into openchannels will be provided with riprap protectionto prevent erosion. Two general types of channelinstability can develop downstream from a culvertand stormdrain outlet. The conditions are knownas either gully scour or a localized erosion referredto as a scour hole. Distinction between the twoconditions of scour and prediction of the type tobe anticipated for a given field situation can bemade by a comparison of the original or existingslope of the channel or drainage basin down-stream of the outlet relative to that required forstability.

b. Gully scour is to be expected when the Froudenumber of flow in the channel exceeds that re-quired for stability. It begins at a point down-stream where the channel is stable and pro-gresses upstream. If sufficient differential inelevation exists between the outlet and the sec-tion of stable channel, the outlet structure will becompletely undermined. Erosion of this type maybe of considerable extent depending upon the lo-cation of the stable channel section relative tothat of the outlet in both the vertical and down-stream directions.

c. A scour hole or localized erosion is to be ex-pected downstream of an outlet even if the down-stream channel is stable. The severity of damageto be anticipated depends upon the conditions ex-isting or created at the outlet. In some instances,the extent of the scour hole may be insufficientto produce either instability of the embankmentor structural damage to the outlet. However, inmany situations flow conditions produce scour ofthe extent that embankment erosion as well asstructural damage of the apron, end wall, and cul-vert are evident.

d. The results of research conducted at US ArmyEngineer Waterways Experiment Station to de-termine the extent of localized scour that may beanticipated downstream of culvert and storm-drainoutlets has also been published. Empirical equa-tions were developed for estimating the extent ofthe anticipated scour hole based on knowledge ofthe design discharge, the culvert diameter, and

the duration and Froude number of the designflow at the culvert outlet. These equations andthose for the maximum depth, width, length andvolume of scour and comparisons of predicted andobserved values are discussed in chapter 10, TM5-820-3/AFM 88-5, Chapter 3. Examples of rec-ommended application to estimate the extent ofscour in a cohesionless soil and several alternateschemes of protection required to prevent localscour downstream of a circular and rectangularoutlet are illustrated in Practical Guidance for De-sign of Lined Channel Expansions at Culvert Out-lets, Technical Report H-74-9.

5-2. Riprap protection,

a. Riprap protection should be provided adja-cent to all hydraulic structures placed in erosivematerials to prevent scour at the ends of the struc-ture, The protection is required on the bed andbanks for a sufficient distance to establish velocitygradients and turbulence levels at the end of theriprap approximating conditions in the naturalchannel. Riprap can also be used for lining thechannel banks to prevent lateral erosion and un-desirable meandering. Consideration should begiven to providing an expansion in either or boththe horizontal and vertical direction immediatelydownstream from hydraulic structures such as dropstructures, energy dissipators, culvert outlets orother devices in which flow can expand and dis-sipate its excess energy in turbulence rather thanin a direct attack on the channel bottom and sides.

b. There are three ways in which riprap hasbeen known to fail: movement of the individualstones by a combination of velocity and turbu-lence; movement of the natural bed materialthrough the riprap resulting in slumping of theblanket; and undercutting and raveling of the rip-rap by scour at the end of the blanket. Therefore,in design, consideration must be given to selectionof an adequate size stone, use of an adequatelygraded riprap or provision of a filter blanket, andproper treatment of the end of the riprap blanket.

5–3. Selection of stone size. There are curvesavailable for the selection of stone size required

5–1

TM 5-820-4/AFM 88–5, Chap 4

for protection as a function of the Froude number.(See TM 5-820-3AFM 88-5, Chapter 3. Two curvesare given, one to be used for riprap subject todirect attack or adjacent to hydraulic structuressuch as side inlets, confluences, and energy dis-sipators, where turbulence levels are high, andthe other for riprap on the banks of a straightchannel where flows are relatively quiet and par-allel to the banks. With the depth of flow and av-erage velocity in the channel known, the Froudenumber can be computed and a stone size deter-mined from the appropriate curve. Curves for de-termining the riprap size required to prevent scourdownstream from culvert outlets with scour holesof various depths are also available. The thicknessof the riprap blanket should be equal to the long-est dimension of the maximum size stone or 1.5times the stone diameter (50 percent size), which-ever is greater. When the use of very large rockis desirable but impractical, substitution of agrouted reach of smaller rock in areas of high ve-locities or turbulence maybe appropriate. Groutedriprap should be followed by an ungrouted reach.

5-4. Riprap gradation. A well-graded mixtureof stone sizes is preferred to a relatively uniformsize of riprap. In certain locations the available

material may dictate the gradation of riprap to beused. In such cases the gradation should resembleas closely as possible the recommended mixture.Consideration should be given to increasing thethickness of the riprap blanket when locality dic-tates the use of gradations with larger percentsof small stone than recommended. If the grada-tion of the available riprap is such that movementof the natural material through the riprap blan-ket would be likely, a filter blanket of sand, crushed,rock, gravel, or synthetic cloth must be placed underthe riprap. The usual blanket thickness is 6 inches,but greater thickness is sometimes necessary.

5-5. Riprap design. An ideal riprap design wouldprovide a gradual reduction in riprap size untilthe downstream end of the blanket blends withthe natural bed material. This is seldom justified.However, unless this is done, turbulence causedby the riprap is likely to develop a scour hole atthe end of the riprap blanket. It is suggested thatthe thickness of the riprap blanket be doubled atthe downstream end to protect against undercut-ting and unraveling. An alternative is to providea constant-thickness rubble blanket of suitablelength dipping below the natural streambed to theestimated depth of bottom scour.

5-2

TM 5–820-4/AFM 88–5, Chap 4

CHAPTER 6

SUBSURFACE DRAINAGE

6-1. General.

a. The water beneath the ground surface is de-fined as subsurface water. The free surface of thiswater, or the surface on which only atmosphericpressure acts, is called the groundwater table.Water is contained above an impervious stratumand hence the infiltration water is prevented fromreaching a groundwater table at a lower eleva-tion. The upper body of water is called perchedgroundwater and its free surface is called a perchedwater table.

b. This water infiltrates into the soil from sur-face sources, such as lakes, rivers and rainfall, andsome portion eventually reaches the groundwatertable. Groundwater tables rise and fall dependingupon the relation between infiltration, absorp-tion, evaporation and groundwater flow. Seasonalfluctuations are normal because of differences inthe amount of precipitation and maybe relativelylarge in some localities. Prolonged drought or wetperiods will cause large fluctuations in thegroundwater level.

6-2. Subsurface drainage requirements. Thedetermination of the subsurface soil properties andwater condition is a prerequisite for the satisfac-tory design of a subsurface drainage system. Fieldexplorations and borings made in connection withthe project design should include the followinginvestigations pertinent to subsurface drainage.A topographic map of the proposed area and thesurrounding vicinity should be prepared indicat-ing all streams, ditches, wells, and natural res-ervoirs. The analysis of aerial photographs of theareas selected for construction may furnish val-uable information on general soil and ground-water conditions. An aerial photograph presentsa graphic record of the extent, boundaries, andsurface features of soil patterns occurring at thesurface of the ground, The presence of vegetation,the slopes of a valley, the colorless monotony ofsand plains, the farming patterns, the drainagepattern, gullies, eroded lands, and evidences of theworks of man are revealed in detail by aerial pho-tographs. The use of aerial photographs may sup-plement both the detail and knowledge gained in

topographic survey and ground explorations. Thesampling and exploratory work can be made morerapid and effective after analysis of aerial pho-tographs has developed the general soil features.The location and depth of permanent and perchedgroundwater tables maybe sufficiently shallow toinfluence the design. The season of the year andrainfall cycle will measurably affect the depth tothe water table. In many locations informationmay be obtained from residents of the surround-ing areas regarding the behavior of wells andsprings and other evidences of subsurface water.The soil properties investigated for other pur-poses in connection with the design will supplyinformation that can be used for the design of thedrainage system. It may be necessary to supple-ment these explorations at locations of subsurfacedrainage structures and in areas where soil in-formation is incomplete for design of the drainagesystem.

6-3. Laboratory tests. The design of subsurfacedrainage structures requires a knowledge of thefollowing soil properties of the principal soils en-countered: strength, compressibility, swell anddispersion characteristics, the in situ and com-pacted unit dry weights, the coefficient of perme-ability, the in situ water content, specific gravity,grain-size distribution, and the effective void ra-tio. These soil properties may be satisfactorily de-termined by experienced soil technicians throughlaboratory tests, The final selected soil propertiesfor design purposes may be expressed as a range,one extreme representing a maximum value andthe other a minimum value. The true value shouldbe between these two extremes, but it may ap-proach or equal one or the other, depending uponthe variation within a soil stratum.

6-4. Flow of water through soils.

a. The flow of water through soils is expressedby Darcy’s empirical law which states that thevelocity of flow is directly proportional to the hy-draulic gradient. This law is expressed in equationform as:

V = k i

6–1

TM 5-8204/AFM 88-5, Chap 4

or

Q = v A = k i A

Variables in the equations are defined in appendixD. According to Darcy’s law the velocity of flowand the quantity of discharge through a porousmedia are directly proportional to the hydraulicgradient. The flow must be in the laminar regimefor this condition to be true.

b. A thorough discussion of the Darcy equationincluding the limitations, typical values of perme-ability, factors affecting the permeability, effectsof pore fluid and temperature, void ratio, averagegrain size, structure and stratification, formationdiscontinuities, entrapped air in water or void, de-gree of saturation, and fine soil fraction can befound in TM 5-820-2/AFM 88-5, Chapter 2.

6-5. Drainage of water from soil. The quantityof water removed by a drain will vary dependingon the type of soil and location of the drain withrespect to the groundwater table. All of the watercontained in a given specimen cannot be removedby gravity flow since water retained as thin filmsadhering to the soil particles and held in the voidsby capillarity will not drain. Consequently, to de-termine the volume of water that can be removedfrom a soil in a given time, the effective porosityas well as the permeability must be known. The

effective porosity is defined as the ratio of thevolume of the voids that can be drained undergravity flow to the total volume of soil. Limitedeffective porosity test data for well-graded base-coarse materials, such as bank-run sands andgravels, indicate a value for effective porosity ofnot more than 0.15. Uniformly graded soils suchas medium coarse sands, may have an effectiveporosity of not more than 0.25.

6-6. Backfill for subsurface drains.

a. Placing backfill in trenches around drain pipesshould serve a dual purpose: it must prevent themovement of particles of the soil being drained,and it must be pervious enough to allow free waterto enter the pipe without clogging it with fine par-ticles of soil. The material selected for backfill iscalled filter material. An empirical criterion forthe design of filter material was proposed by Ter-zaghi and substantiated by tests on protective fil-ters used in the construction of earth dams. Thecriterion for a filter and pipe perforations to keepprotected soil particles from entering the filter orpipe significantly is based on backfill particle sizes.

b. The filter stability criteria for preventingmovement of particles from the protected soil intoor through the filter and the exceptions to thiscriteria are discussed in chapter 5, TM 5-820-2/AFM 88-5, Chapter 2.

6–2

TM 5-820-4/AFM 88-5, Chap. 4

APPENDIX A

REFERENCES

Government Publications

Federal Specifications (Fed. Spec. )

• SS-C-1960/GEN Cement and Pozzolan, General Requirements for

• WW-P-402C Pipe, Corrugated (Aluminum Alloy)& Notice 1 and Am-1

• WW-P-405B Pipe, Corrugated (Iron or Steel, Zinc Coated)& Am-1

Military Standards (Mil. Std.)

• MIL-STD-619B

• MIL-STD-621A& Notices 1 & 2

Departments of the Army, Air Force, and the Navy

TM 5-632/AFM 91-16

TM 5-785/AFM 88-29/NAVFAC P-89

TM 5-820-l/AFM 88-5,Chap. 1

TM 5-820-2/AFM 88-5Chap. 2

TM 5-820-3/AFM 88-5,Chap. 3

TM 5-852-7/AFM 88-19,Chap. 7

Unified Soil Classification System for Roads,Airfields, Embankments and Foundations

Test Method for Pavement Subgrade, Subbase,and Base-Course Materials

Military Entomology Operational Handbook

Engineering Weather Data

Surface Drainage Facilities for Airfieldsand Heliports

Drainage and Erosion Control: SubsurfaceDrainage Facilities for Airfields

Drainage and Erosion-Control Structuresfor Airfields and Heliports

Arctic and Subarctic Construction: SurfaceDrainage Design for Airfields and Heliports toArctic and Subarctic Regions

Change 1 A-1

TM 5-820-4/AFM 88-5, Chap. 4

Engineers Waterways Experiment Station, P.O. Box 631, Vicksburg, Mississippi 39180

• Technical Report H-74-9, Practical Guidance for Design of Lined Channel Expansions at Culvert Outlets

Department of Commerce

National Oceanic and Atmospheric Administration, Environmental Data and Information Center, FederalBldg., Asheville, N.C. 28801

Generalized Estimates of Probable Maximum Precipitation and Rainfall--Frequency Data for Puerto Ricoand Virgin Islands, Technical Paper No. 42, 1961

Probable Maximum Precipitation and Rainfall--Frequency Data for Alaska, Technical Paper No. 47, 1963

Rainfall Frequency Atlas of the Hawaiian Islands, Technical Paper No. 43, 1962

Rainfall Frequency Atlas of the United States, Technical Paper’ No. 40, 1961

Department of Transportation

Federal Aviation Administration, M 494.3, 400 7th Street, S. W., Washington, D.C. 20590

• Airport Drainage, AC 150/5320-5B, July 1970

• Hydraulics of Bridge Waterways, J.N. Bradley, Hydraulic DesignSeries, No. 1, August 1960 (Revised March, 1978)

Non-Government Publications

American Association of State Highway and Transportation Officials (AASHTO), 444 N. Capital, N. W.,Suite 225, Washington, D.C. 20001

• T99-81 The Moisture-Density Relations of Soils Using a 5.5-lb (2.5 kg) Ramer and a 12-in.(305 MM) Drop

• HB-12 Highway Bridges (1977, 12th Ed.; Interim Specifications 1978, 1979, 1980, 1981, 1982, 1983)

American Railway Engineering Association (AREA), 2000 L Street, N. W., Washington, D.C. 20036

• Manual for Railway Engineering (Fixed Properties) (Current to Jul 31, 1982) (Supplement 1982-1983)

• Chapter 15 Steel Structures-1981

American Society of Civil Engineers (ASCE), United Engineering Center, 345 E. 47th Street, New York,N.Y. 10017

• Manuals and Reports on Engineering PracticeNo. 37 Design and Construction of Sanitary and Storm Sewers, 1969 (Reprinted 1974)

A-2 Change 1A-3 Change 1

TM 5-820-4/AFM 88-5, Chap 4

APPENDIX B

HYDRAULIC DESIGN DATA FOR CULVERTS

B-1. General.

a. This appendix presents diagrams, charts,coefficients and related information useful in de-sign of culverts. The information largely has beenobtained from the U.S. Department of Transpor-tation, Federal Highway Administration (for-merly, Bureau of Public Roads), supplemented ormodified as appropriate by information from var-ious other sources and as required for consistencywith design practice of the Corps of Engineers.

b. Laboratory tests and field observations showtwo major types of culvert flow: flow with inletcontrol and flow with outlet control. Under inletcontrol, the cross-sectional area of the culvert bar-rel, the inlet geometry and the amount of head-water or pending at the entrance are of primaryimportance. Outlet control involves the additionalconsideration of the elevation of the tailwater inthe outlet channel and the slope, roughness, andlength of the culvert barrel. The type of flow orthe location of the control is dependent on thequantity of flow, roughness of the culvert barrel,type of inlet, flow pattern in the approach channel,and other factors. In some instances the flow con-trol changes with varying discharges, and occa-sionally the control fluctuates from inlet controlto outlet control and vice versa for the same dis-charge. Thus, the design of culverts should con-sider both types of flow and should be based onthe more adverse flow condition anticipated.

B-2. Inlet control. The discharge capacity of aculvert is controlled at the culvert entrance bythe depth of headwater (HIV) and the entrancegeometry, including the area, slope, and type ofinlet edge. Types of inlet-controlled flow for un-submerged and submerged entrances are shownat A and B in figure B–1. A mitered entrance (figB–lC) produces little if any improvement in effi-ciency over that of the straight, sharp-edged, pro-jecting inlet. Both types of inlets tend to inhibitthe culvert from flowing full when the inlet is sub-merged. With inlet control the roughness and lengthof the culvert barrel and outlet conditions (in-cluding depths of tailwater) are not factors in de-termining culvert capacity. The effect of the bar-

rel slope on inlet-control flow in conventionalculverts is negligible. Nomography for determin-ing culvert capacity for inlet control were devel-oped by the Division of Hydraulic Research, Bu-reau of Public Roads. (See Hydraulics of BridgeWateways.) These nomography (figs B–2 throughB–9) give headwater-discharge relations for mostconventional culverts flowing with inlet control,

B-3. Outlet control.

a. Culverts flowing with outlet control can flowwith the culvert barrel full or partially full for partof the barrel length or for all of it (fig B–10). Ifthe entire barrel is filled (both cross section andlength) with water, the culvert is said to be in fullflow or flowing full (fig B–1OA and B). The othertwo common types of outlet-control flow are shownin figure B–1OC and D. The procedure given inthis appendix for outlet-control flow does not givean exact solution for a free-water-surface condi-tion throughout the barrel length shown in figureB-1OD. An approximate solution is given for thiscase when the headwater, HW, is equal to or greaterthan 0.75D, where D is the height of the culvertbarrel. The head, H, required to pass a given quan-tity of water through a culvert flowing full withcontrol at the outlet is made up of three majorparts. These three parts are usually expressed infeet of water and include a velocity head, an en-trance loss, and a friction loss. The velocity head(the kinetic energy of the water in the culvert

the type or design of the culvert inlet and is ex-pressed as a coefficient& times the velocity head

entrances are given in table B–1. The friction loss,Hf, is the energy required to overcome the rough-ness of the culvert barrel and is usually expressedin terms of Manning’s n and the following expres-sion:

B-1

TM 5-820-4/AFM 88-5, Chap 4

S Q U A R E E N D - S U B M E R G E D


Figure B-1. Inlet control.

B-2

TM 5–820-4/AFM 88-5, Chap 4

w

z

z

Figure B–2. Headwater depth for concrete pipe culverts with inlet control.

B-3

TM 5-820-4/AFM 88–5, Chap 4

Figure B-3. Headwater depth for oval concrete pipe culverts long axis vertical with inlet control.

B-4

TM 5-820-4/AFM 88–5, Chap 4

Figure B-4. Headwater depth for oval concrete pipe culverts long axis horizontal with inlet control.

B-5

TM 5–820-4/AFM 88–5, Chap 4

B–6

TM 5-820-4/AFM 88-5, Chap 4

3 0 0

2 0 0

B-7

5-820-4/AFM 88-5, Chap 4

.6

.5

Figure B-7. Headwater depth for box culverts with inlet control.

B - 8

TM 5-820-4/AFM 88-5, Chap 4

B-9

TM 5-820-4/AFM 88-5, Chap 4

Figure B–9. Headwater depth for circular pipe culverts with beveled ring inlet control.

B-10

TM 5-820-4/AFM 88–5, Chap 4

A

B-11

ITM 5–820-4/AFM 88–5, Chap 4

Type of Structure and Design of Entrance Coefficient Ke

U.S. Army Corps of Engineers,

Variables in the equation are defined in appendixD.

Adding the three terms and simplifying, yields forfull pipe, outlet control flow the following expres-sion:

This equation can be solved readily by the useof the full-flow nomography, figures B–II throughB–17. The equations shown on these nomo-graphy are the same as equation 1 expressed ina different form. Each nomograph is drawn fora single value of n as noted in the respectivefigure. These nomography may be used for other

values of n by modifying the culvert length asdirected in paragraph B–6, which describes useof the outlet-control nomography. The value ofH must be measured from some “control” ele-vation at the outlet which is dependent on therate of discharge or the elevation of the watersurface of the tailwater. For simplicity, a valuehO is used as the distance in feet from the culvertinvert (flow line) at the outlet to the control el-evation. The following equation is used to com-pute headwater in reference to the inlet invert:

HW = hO + H – LSO . . . . . . . . . . . . . . . . . . . . . . (2)

b. Tailwater elevation at or above the top of the _culvert barrel outlet (fig B–1OA). The tailwater

B–12

– 30

– 20

– l o

– 8

– 6

– 5

– 4

Z

B-13

TM 5–8204/AFM 88–5, Chap 4

B–14

TM 5-820-4/AFM 88-5, Chap 4

TM 5-820-4/AFM 88-5, Chap 4

B-18

TM 5-820-4/AFM 88-5, Chap 4

5000

4000

3000

2000

3 0

2 0

10

8

6

5

TM 5-820-4/AFM 88–5, Chap 4

(TW) depth is equal to hO, and the relation ofheadwater to other terms in equation 2 is illus-trated in figure B–18.

c. Tailwater elevation below the top or crown ofthe culvert barrel outlet. Figure B–1OB, C, and Dare three common types of flow for outlet controlwith this low tailwater condition. In these caseshO is found by comparing two values, TW depth

d c+ Din the outlet channel and

2 ’and setting hO

d C + Dequal to the larger value. The fraction

2 is

a simplified mean of computing hO when the tail-water is low and the discharge does not fill theculvert barrel at the outlet. In this fraction, dC

is critical depth as determined from figures B–18 through B–23 and D is the culvert height. Thevalue of DC should never exceed D, making theupper limit of this fraction equal to D. FigureB–19 shows the terms of equation 2 for the casesdiscussed above. Equation 2 gives accurate an-swers if the culvert flows full for a part of thebarrel length as illustrated by figure B–23. Thiscondition of flow will exist if the headwater, asdetermined by equation 2, is equal to or greaterthan the quantity:

If the headwater drops below this point the watersurface will be free throughout the culvert barrelas in figure B–1OD, and equation 2 yields an-swers with some error since the only correctmethod of finding headwater in this case is bya backwater computation starting at the culvert

Fairly regular section:

Some grass and weeds, little or no brush ---------------------------------Dense growth of weeds, depth of flow materially greater than weed

height -------------------------------------------------------------------Some weeds, light brush on banks ----------------------------------------Some weeds, heavy brush on banks ---------------------------------------Some weeds, dense willows on banks -------------------------------------For trees within channel, with branches submerged at high stage, in-

crease all above values by -----------------------------------------------

Irregular sections, with pools, slight channel meander; increase valuesgiven above about ------------------------------------------------------------

Mountain streams, no vegetation in channel, banks usually steep, treesand brush along banks submerged at high stage:

Bottom of gravel, cobbles, and few boulders -----------------------------Bottom of cobbles, with large boulders -----------------------------------

0.030–0.035

0.035-0.050.035–0.050.05–0.070.06–0.08

0.01–0.02

0.01–0.02

0.04–0.050.05–0.07


B-20

TM 5-820-4/AFM 88-5, Chap 4

Figure B-18, Tailgater elevation at or above top of culved.

TM 5-820-4/AFM 88-5, Chap 4


Figure B-19. Tailwater below the top of the culvert.

B-4. Procedure for selection of culvert size.

Select the culvert size by the following steps:Step 1: List given data.

a.

b.c.

d.

e.

f.

Design discharge, Q, in cubic feet per sec-ond.Approximate length of culvert, in feet.Allowable headwater depth, in feet, whichis the vertical distance from the culvertinvert (flow line) at entrance to the water-surface elevation permissible in the ap-proach channel upstream from the cul-vert.Type of culvert, including barrel mate-rial, barrel cross-sectional shape, and en-trance type.Slope of culvert. (If grade is given in per-cent, convert to slope in feet per foot.)

Allowable outlet velocity (if scour is a

TM 5–820-4/AFM 88–5, Chap 4

b. Compute and record headwater for out-let control as instructed below:

(1)

(2)

(3)

c.

d.

Compare the headwater found in Step 3aand Step 3b (inlet control and outlet con-trol). The higher headwater governs andindicates the flow control existing underthe given conditions.Compare the higher headwater abovewith- that allowable at the site. If head-water is greater than allowable, repeatthe procedure using a larger culvert. Ifheadwater is less than allowable, repeatthe procedure to investigate the possi-bility of using a smaller size.

Step 4: Check outlet velocities for size se-lected.

a. If outlet control governs in Step 3c, out-let velocity equals Q/A, where A is thecross-sectional area of flow at the outlet.If dC or TW is less than the height of theculvert barrel, use cross-sectional areacorresponding to dC or TW depth, which-ever gives the greater area of flow.

b. If inlet control governs in Step 3c, outletvelocity can be assumed to equal normalvelocity in open-channel flow as com-puted by Manning’s equation for thebarrel size, roughness, and slope of cul-vert selected.

Step 5: Try a culvert of another type or shapeand determine size and headwater bythe above procedure.

Step 6: Record final selection of culvert withsize, type, outlet velocity, requiredheadwater, and economic justifica-tion.

B–23

TM 5–820-4/AFM 88–5, Chap 4

B–24

Figure B–20. Circular pipe—critical depth.

TM 5–820-4/AFM 88-5, Chap 4

Figure B–21. Oval concrete pipe long axis horizontal critical depth.

B-25

TM 5-820-4/AFM 88-5, Chap 4

Figure B–22. Oval concrete pipe long axis vertical critical depth.

B-26

TM 5-820-4/AFM 88–5, Chap 4

B-28

TM 5-8204/AFM 88-5, Chap 4

Figure B–25. Critical depth rectangular section.

B-29

(1) above to given discharge and read di-ameter, height, or size of culvert required.

c. To detemine discharge.

(1)

(2)

(3)

B–6. Instruction for use of outlet-control nom-ography.

a. Figures B–n through B–17 are nomographyto solve for head when culverts flow full with out-let control. They are also used in approximatingthe head for some partially full flow conditionswith outlet control. These nomography do not givea complete solution for finding headwater. (Seepara B–4.)

B-30

(1) Locate appropriate nomograph for type ofculvert selected.

(2) Begin nomograph solution by locatingstarting point on length scale. To locatethe proper starting point on the lengthscale, follow instructions below:

(a)

(b)

(c)

If the n value of the nomograph corre-sponds to that of the culvert being used,

on the appropriate nomograph locatestarting point on length curve for the

for the culvert selected differs from thatof the nomograph, see (c) below.

intermediate between the scales given,connect the given length on adjacentscales by a straight line and select a pointon this line spaced between the two chart

For a different value of roughness coef-ficient nl than that of the chart n, usethe length scales shown with an ad-justed length Ll, calculated by the for-mula:

(See subpara b below for n values.)(3)

(4)

Using a straight edge, connect point onlength scale to size of culvert barrel andmark the point of crossing on the “turningline.” See instruction c below for size con-siderations for rectangular box culvert.Pivot the straight edge on this point onthe turning line and-connect given dis-charge rate. Read head in feet on the headscale. For values beyond the limit of thechart scales, find H by solving equationgiven in nomograph or by H = KQ2 whereK is found by substituting values of H andQ from chart.

b. Table B–3 is used to find the n value for theculvert selected.

c. To use the box-culvert nomograph (fig B–17)for full flow for other than square boxes:

(1) Compute cross-sectional area of the rec-tangular box.Note: The area scale on the nomograph is calculated

for barrel cross sections with span B twice theheight D; its close correspondence with areaof square boxes assures it may be used for allsections intermediate between square and B= 2D or B = 2/3D. For other box proportionsuse equation shown in nomograph for moreaccurate results.

TM 5-820-4/AFM 88-5, Chap. 4Table B-3. Roughness Coefficients for Various Pipes

n = 0.012 for smooth interior pipes of any size, shape or type*

n Value for Annular Corrugated Metal

Unpaved0.011-0.014

24-30 inches 0.016-0.01836-96 inches 0.019-0.024 0.017-0.021

*Includes asbestos cement, bituminized fiber, cast iron, clay, concrete (precast or cast-in-place) or fully paved (smooth interior) corruga -ted metal pipe.


• NOTE: Limitations helical coefficient - The designer must assure that fully developed spiral flow can occur in his design situa-tion before selecting the lower resistance factor. Fully developed spiral flow, and the corresponding lower resistance factors, can onlyoccur when the conduit flows full. For conduits shorter than 20 diameters long, it is felt that the full development of spiral flow cannotbe assured. Bed load deposition on the culvert invert may hinder the development of spiral flow until sediment is washed out. Whenthese conditions exist, the resistance factors for annular C.M .P. of the same size and corrugation shape should be used.

(2) Connect proper point (see para B-6b ) onlength scale to barrel area and mark pointon turning line.

(3) Pivot the straight edge on this point onthe turning line and connect given dis-charge rate. Read head in feet on the headscale.

B-7. Culvert capacity charts. Figures B-26 throughB-43, prepared by the Bureau of Public Roads,present headwater discharge relations convenientfor use in design of culverts of the most commontypes and sizes.The solid-line curve for each typeand size represents for a given length: slope ratiothe culvert capacity with control at the inlet; thesecurves are based generally on model data. For thoseculvert types for which a dashed-line curve is shownin addition to a solid-line curve, the dashed linerepresents for a given length: slope ratio the dis-charge capacity for free flow and control at the out-let; these curves are based on experimental data andbackwater computations. The length: slope ratio is

case is the value at which the discharge with outlet

control equals the discharge with inlet control. Forculverts with free flow and control at the outlet,

values is permitted in the range of headwater depthsequal to or less than twice the barrel height. Theupper limit of this range of headwater depths isdesignated by a horizontal dotted line on the charts.

do not impose any limitation; merely read the solid-line curves. The symbol AHW means allowableheadwater depth. The charts permit rapid selectionof a culvert size to meet a given headwater limitationfor various entrance conditions and types and shapesof pipe. One can enter with a given discharge andread vertically upward to the pipe size that will carrythe flow to satisfy the headwater limitation of thedesign criteria. The major restriction on the use ofthe charts is that free flow must exist at the outlet.In most culvert installations free flow exists, i.e.,flow passes through critical depth near the culvertoutlet. For submerged flow conditions the solutioncan be obtained by use of the outlet control nomo- graphs.

Change 1 B-31

TM 5-820-4/AFM 88-5, Chap. 4

2

6

B-32

TM 5–820-4/AFM 88–5, Chap 4

Figure B–27. Culvert capacity circulur concrete pipe groove-edged entrance 6O'' to 18O''.

B-33

TM 5–820-4/AFM 88-5, Chap 4

B - 3 4

TM 5-820-4/AFM 88–5, Chap 4

B-35

TM 5–820-4AFM 88-5, Chap 4

8

7

2

8

7

2

o 10 2 0 3 0 4 0 5 0 6 0

BUREAU OF PUBLIC ROADS

B-36

TM 5–820-4/AFM 88–5, Chap 4

B–37

TM 5–820-4/AFM 88–5, Chap 4

B–38

TM 5–820-4/AFM 88–5, Chap 4

B-39

TM 5–820-4/AFM 88–5, Chap 4

TM 5–820-4/AFM 88-5, Chap 4

B–41

TM 5-820-4/AFM 88–5, Chap 4

9

8

7

B-42

TM 5-820-4/AFM 88-5, Chap 4

9

8

B-43

ITM 5-820-4/AFM 88-5, Chap 4

B - 4 4

TM 5–820-4/AFM 88–5, Chap 4

B–45

TM 5–820-4/AFM 88–5, Chap 4

B-46

TM 5-820-4/AFM 88–5, Chap 4

5I I

, / / t ’ I

B-47

TM 5–820-4/AFM 88–5, Chap 4

9

8

3

2

10

9

8

W

4

3

2

B-48

TM 5–820-4/AFM 88-5, Chap 4

B-49

TM 5–820-4/AFM 88-5, Chap 4

APPENDIX C

PIPE STRENGTH, COVER, AND BEDDING

C–1. General. A drainage pipe is defined as astructure (other than a bridge) to convey waterthrough a trench or under a fill or some otherobstruction. Materials for permanent-type instal-lations include non-reinforced concrete, rein-forced concrete, corrugated steel, asbestos-ce-ment, clay, corrugated aluminum alloy, andstructural plate steel pipe.

C-2. Selection of type of pipe.

a. The selection of a suitable construction con-duit will be governed by the availability and suit-ability of pipe materials for local conditions withdue consideration of economic factors. It is desir-able to permit alternates so that bids can be re-ceived with contractor’s options for the differenttypes of pipe suitable for a specific installation.Allowing alternates serves as a means of securingbidding competition. When alternate designs areadvantageous, each system will be economicallydesigned, taking advantage of full capacity, bestslope, least depth, and proper strength and in-stallation provisions for each material involved.Where field conditions dictate the use of one pipematerial in preference to others, the reasons willbe clearly presented in the design analysis.

b. Several factors should be considered in se-lecting the type of pipe to be used in construction.The factors include strength under either maxi-mum or minimum cover being provided, pipe bed-ding and backfill conditions, anticipated loadings,length of pipe sections, ease of installation, re-sistance to corrosive action by liquids carried orsurrounding soil materials, suitability of jointingmethods, provisions for expected deflection with-out adverse effect on the pipe structure or on thejoints or overlying materials, and cost of main-tenance. Although it is possible to obtain an ac-ceptable pipe installation to meet design require-ments by establishing special provisions for severalpossible materials, ordinarily only one or two al-ternates will economically meet the individual re-quirements for a proposed drainage system.

C-3. Selection of n values. A designer is con-tinually confronted with what coefficient of

roughness n to use in a given situation. The ques-tion of whether n should be based on the new andideal condition of a pipe or on anticipated condi-tion at a later date is difficult to answer. Sedi-mentation or paved pipe can affect the coefficientof roughness. Table B–3 gives the n values forsmooth interior pipe of any size, shape or type andfor annular and helical corrugated metal pipe bothunpaved and 25 percent paved. When n values otherthan those listed are selected, such values will beamply justified in the design analysis.

C-4. Restricted use of bituminous-coated pipe.Corrugated-metal pipe with any percentage of bi-tuminous coating will not be installed where sol-vents can be expected to enter the pipe. Polymericcoated corrugated steel pipe is recommended wheresolvents might be expected.

C–5. Minimum cover.

a. In the design and construction of the drain-age system it will be necessary to consider bothminimum and maximum earth cover allowable onthe underground conduits to be placed under bothflexible and rigid pavements. Underground con-duits are subject to two principal types of loads:dead loads (DL) caused by embankment or trenchbackfill plus superimposed stationary surface loads,uniform or concentrated; and live or moving loads(LL), including impact. Live loads assume increas-ing importance with decreasing fill height.

b. AASHTO Standard Specifications for High-way Bridges should be used for all H–20 HighwayLoading Analyses. AREA Manual for RailwayEngineering should be used for all Cooper’s E 80Railway Loadings. Appropriate pipe manufac-turer design manuals should be used for maxi-mum cover analyses.

c. Drainage systems should be designed in orderto provide an ultimate capacity sufficient to servethe planned installation, Addition to, or replace-ment of, drainage lines following initial construc-tion is costly.

d. Investigations of in-place drainage and ero-sion control facilities at 50 military installations

C-1

TM 5–820-4/AFM 88-5, Chap 4

were made during the period 1966 to 1972. Thefacilities observed varied from one to more than30 years of age. The study revealed that buriedconduits and associated storm drainage facilitiesinstalled from the early 1940’s until the mid-1960’sappeared to be in good to excellent structural con-dition. However, many reported failures of buriedconduits occurred during construction. Therefore,it should be noted that minimum conduit coverrequirements are not always adequate duringconstruction. When construction equipment, whichmay be heavier than live loads for which the con-duit has been designed, is operated over or nearan already inplace underground conduit, it is theresponsibility of the contractor to provide any ad-ditional cover during construction to avoid dam-age to the conduit. Major improvements in thedesign and construction of buried conduits in thetwo decades mentioned include, among other items,increased strength of buried pipes and conduits,

increased compaction requirements, and revisedminimum cover tables.

e. The necessary minimum cover in certain in-stances may determine pipe grades. A safe minimum cover design requires consideration of anumber of factors including selection of conduitmaterial, construction conditions and specifica-tions, selection of pavement design, selection ofbackfill material and compaction, and the methodof bedding underground conduits. Emphasis onthese factors must be carried from the design stagethrough the development of final plans and spec-ifications.

f. Tables C-1 through C-6 identify certain sug-gested cover requirements for storm drains andculverts which should be considered as guidelinesonly. Cover requirements have been formulatedfor asbestos-cement pipe, reinforced and non-rein-forced concrete pipe, corrugated-aluminum-alloy

Table C–1. Suggested Maximum Cover Requirements for Asbestos-Cement PipeH–20 Highway Loading

Suggested Maximum Cover Above Top of Pipe, ftDiameter

in. Circular Section

Class

1500 2000 2500 9000 375012 9 13 16 19 2415 10 13 17 19 2418 10 13 17 20 2521 10 13 17 20 2524 10 14 17 20 2527 10 14 17 20 2530 11 14 17 21 2433 11 14 17 21 2636 11 14 17 21 2642 11 14 17 21 26


Notes:1. The suggested values shown are for average conditions and are to be considered as guidelines only for dead load plus

H–20 live load.2. Soil conditions. trench width and bedding conditions vary widelv throughout varying climatic and geographical areas.3. Calculations to determine maximum cover should be made for all individual pipe and culvert installations underlying

4.5.

6.

7.

8.

roads, streets and open storage areas subject to H-20 live loads. Cooper E–80 ; railway loadings should be independentlymade.Cover depths are measured from the bottom of the subbase of pavements, or the top of unsurfaced areas, to top of pipe.Calculations to determine maximum cover for Cooper E–80 railway loadings are measured from the bottom of the tieto the top of the pipe.The number in the class designation for asbestos-cement pipe is the minimum 3-edge test load to produce failure inpounds per linear foot. It is independent of pipe diameter. An equivalent to the D-load can be obtained by dividing thenumber in the class designation by the internal pipe diameter in feet.If pipe produced by a manufacturer exceeds the strength requirements established by indicated standards then coverdepths may be adjusted accordingly.See table C–9 for suggested minimum cover requirements.

—

C-2

TM 5-820-4/AFM 88-5. Chap. 4Table C-2. Suggested Maximum Cover Requirements for Concrete Pipe

Reinforced Concrete

Suggested Maximum Cover Above Top of Pipe, ft.

Circular SectionDiameter

in. I II

12 14 14 1724 13 13 1436 9 12 12


Notes:1.

2<

3!

4.5.

6.

7.

8.

9.

The suggested values shown are for average conditions and are to be considered as guidelines only for dead load plus H-20live load.Soil conditions, trench width and bedding conditions vary widely throughout varying climatic and geographical areas.Calculations to determine maximum cover should be made for all individual pipe and culvert installations underlying roads,streets and open storage areas subject to H-20 live loads. Cooper E-80 railway loadings should be independently made.Cover depths are measured from the bottom of the subbase of pavements, or the top of unsurfaced areas, to top of pipe.Calculations to determine maximum cover for Cooper E-80 railway loadings are measured from the bottom of the tie to thetop of the pipe.“D” loads listed for the various classes of reinforced-concrete pipe are the minimum required 3-edge test loads to produceultimate failure in pounds per linear foot of interval pipe diameter.Each diameter pipe in each class designation of non-reinforced concrete has a different D-load value which increases withwall thickness.If pipe produced by a manufacturer exceeds the strength requirements established by indicated standards, then coverdepths may be adjusted accordingly.See table C-9 for suggested minimum cover requirements.

pipe, corrugated-steel pipe, structural-plate-alu-minum-alloy pipe, and structural-plate-steel pipe.The different sizes and materials of conduit and pipehave been selected to allow the reader an apprecia-tion for the many and varied items which are com-mercially available for construction purposes. Thecover depths listed are suggested only for averagebedding and backfill conditions. Deviations fromaverage conditions may result in significant mini-mum cover requirements and separate cover analy-ses must be made in each instance of a deviationfrom average conditions. Specific bedding, backfilland trench widths may be required in certain loca-

Change 1 C-3

Change 1 C-3

tions; each condition deviating from the averagecondition should be analyzed separately. Wherewarranted by design analysis the suggested maxi-mum cover may be exceeded.

• C-6. Classes of bedding and installation. FiguresC-1 through C-5 indicate the classes of bedding forconduits. Figure C-6 is a schematic representationof the subdivision of classes of conduit installationwhich influences loads on underground conduits.

Change 1 C-3—

TM 5-820-4/AFM 88-5, Chap. 4

Table C-3. Suggested Maximum Cover Requirements for Corrugated-A luminum-A lloy Pipe,Riveted, Helical, or Welded

Fabrication 2 2/3 Inch Spacing, ½ -Inch Deep CorrugationsH-20 Highway Loading

Suggested Maximum Cover Above Top of Pipe, ft

Circular Section Vertically Elongated Section

Thickness, in. Thickness, in.Diameter — —

in. .060 .075 .105 .135 .164 .060 .075 .105 .135 .164

12 50 50 86 90 9315 40 40 69 72 7418 33 33 57 60 6224 25 25 43 45 4630 20 20 34 36 3736 16 16 28 30 3142 16 16 28 30 3148 28 30 3154 28 30 3160 30 3166 3172 31

50 52 5343 45 47


Notes:1. Corrugated-aluminum-alloy pipe will conform to the requirements of Federal Specification W W-P-402.2. The suggested values shown are for average conditions and are to be considered as guidelines only for dead load plus

H-20 live load Cooper E-80 railway loadings should be independently made.3. Soil conditions, trench width and bedding conditions vary widely throughout varying climatic and geographical areas.4. Calculations to determine maximum cover should be made for all individual pipe and culvert installations underlying

roads, streets and open storage areas subject to H-20 live loads.5. Cover depths are measured from the bottom of the subbase of pavements, or the top of unsurfaced areas, to top of pipe.6. Calculations to determine maximum cover for Cooper E-80 railway loadings are measured from the bottom of the tie

to the top of the pipe.7. Vertical elongation will be accomplished by shop fabrication and will generally be 5 % of the pipe diameter.8. See table C-9 for suggested minium cover requirements.

C-4 Change 1

• C-7. Strength of pipe. Pipe shall be consideredof ample strength when it meets the conditionsspecified for the loads indicated in tables C-1through C-8. When railway or vehicular wheel loadsor loads due to heavy construction equipment (liveloads, LL) impose heavier loads, or when the earth(or dead loads, DL) vary materially from those nor-mally encountered, these tables cannot be used forpipe installation design and separate analyses mustbe made. The suggested minimum and maximumcover shown in the tables pertain to pipe installa-tions in which the back fill material is compacted toat least 90 percent of CE55 (MIL-STD-621 ) orAASHTO-T99 density (100 percent for cohesionlesssands and gravels). This does not modify require-ments for any greater degree of compaction speci-fied for other reasons. It is emphasized that properbedding, backfilling, compaction, and prevention ofinfiltration of backfill material into pipe are impor-tant not only to the pipe, but also to protect overlyingand nearby structures. When in doubt about mini-mum and maximum cover for local conditions, a

C-4 Change 1

separate cover analysis must be performed.

C-8 Rigid pipe. Tables C-1 and C-2 indicatemaximum and minimum cover for trench conduitsemploying asbestos-cement pipe and concrete pipe.If positive projecting conduits are employed they arethose which are installed in shallow bedding with apart of the conduit projecting above the surface ofthe natural ground and then covered with an em-bankment. Due allowance will be made in amountsof minimum and maximum cover for positive pro-jecting conduits. Table C-9 suggests guidelines forminimum cover to protect the pipe during con-struction and the minimum finished height of cover.

C-9. Flexible pipe. Suggested maximum coverfor trench and positive projecting conduits are in-dicated in tables C-3 through C-6 for corrugated-aluminum-alloy pipe, corrugated-steel pipe, struc-tural-plate-aluminum-alloy pipe, and structural-plate-steel pipe. Conditions other than those statedin the tables, particularly other loading conditionswill be compensated for as necessary. For

C-4 Change 1

TM 5-820-4/AFM 88–5, Chap 4

Corrugations

DIAMETER,

MAXIMUM

H-20 HIGHWAY LOADING

COVER ABOVE TOP OF PIPE, FEET

92 101

74 80

61 67

53 57

46 50

41 44

37 40

30 33

34 47

30 41

36

- — .U. S. Army Corps of Engneers

Notes :1.2.

3.4.

5.6.

7.

8.

130

104

86

74

65

57

52

43

74

65

57

52 54

49

45

170

136

113

97

85

75

68

56

81 48

71

63

213

170

142

121

106

94

85

71

60

53

266

212

173

139

120

109

101

88

76

66

59

372

298

212

164

137

120

110

98

92

88

82

74

155

133

119

103

95

91

88

86

85

79

99

93

90

87

86

85

84

75

Corrugated steel pipe will conform to the requirements of Federal Specification WW–P–405.The suggested maximum heights of cover shown in the table are calculated on the basis of the current AASHTOStandard Specifications for Highway Bridges and are based on circular pipe.Soil conditions, trench width and bedding conditions vary widely throughout varying climatic and geographical areas.Calculations to determine maximum cover should be made for all individual pipe and culvert installations underlyingroads, streets and open storage areas subject to H–20 live loads. Cooper E–80 railway loadings should be independentlymade.Cover depths are measured from the bottom of the subbase of pavements, or the top of unsurfaced areas, to top of pipe.Calculations to determine maximum cover for Cooper E–80 railway loadings are measured from the bottom of the tieto the top of the pipe.If pipe produced by a manufacturer exceeds the strength requirements established by indicated standards then coverdepths may be adjusted accordingly.See table C–9 for suggested minimum cover requirements.

C-5

TM 5-820-4/AFM 88–5, Chap 4

Table C-5. Suggested Maximum Cover Requirements for Structural-Plate-Aluminum-Alloy Pipe, 9-Inch Spacing, 2 1/2-InchCorrugations

H–20 Highway Loading

Suggested Maximum Cover Above Top of Pipe, ft

Circular Section

Thickness, in.

Diameter,in. 0.10 0.125 0.15 0.175 0.20 0.225 0.250

728496

108120132144156168180

24 3220 2718 2416 2114 1913 1712 16

1413

41353027242220181716

48413632292624222019

55474137333027252322

61524540363330282624

64555044403633302826

U.S. Army Corps of EngineersNotes:

1.2.3.

4.5.

6.

7.

8.

Structural-plate-aluminum-alloy pipe will conform to the requirements of Federal Specification WW–P–402.Soil conditions, trench width and bedding conditions vary widely throughout varying climatic and geographical areas.Calculations to determine maximum cover should be made for all individual pipe and culvert installations underlyingroads, streets and open storage areas subject to H–20 live loads. Cooper E-80 railway loadings should be independentlymade.Cover depths are measured from the bottom of the subbase of pavements, or the top of unsurfaced areas, to top of pipe.Calculations to determine maximum cover for Cooper E–80 railway loadings are measured from the bottom of the tieto the top of the pipe.The number in the class designation for asbestos-cement pipe is the minimum 3-edge test load to produce failure inpounds per linear foot. It is independent of pipe diameter. An equivalent to the D-load can be obtained by dividing thenumber in the class designation by the internal pipe diameter in feet.If pipe produced by a manufacturer exceeds the strength requirements established by indicated standards then coverdepths may be adjusted accordingly.See table C-9 for suggested minimum cover requirements.

C-6

TM 5–820-4/AFM 88–5, Chap 4

Table C–6. Suggested Maximum Cover Requirements for Corrugated Steel Pipe, 125-mmSpan, 25-mm Deep Corrugations

H–20 Highway Loading

Maximum cover above top of pipe, feet

Helical—thickness, inches

Diameter,inches .064 .079 .109 .138 .168

48 54 68 95 122 13254 48 60 84 109 11760 43 54 76 98 10766 39 49 69 89 10172 36 45 63 81 9678 33 41 58 75 9284 31 38 54 70 8590 29 36 50 65 8096 34 47 61 75

102 32 44 57 70108 42 54 66114 40 51 63120 38 49 60

U.S. Army Corps of EngineersNotes:

1. Corrugated steel pipe will conform to the requirements of Federal SpecificationWW-P-405.

2. The suggested maximum heights of cover shown in the table are calculated on thebasis of the current AASHTO Standard Specifications for Highway Bridges and arebased on circular pipe.

3. Soil conditions, trench width and bedding conditions vary widely throughout vary-ing climatic and geographical areas.

4. Calculations to determine maximum cover should be made for all individual pipeand culvert installations underlying roads, streets and open storage areas subjectto H–20 live loads. Cooper E–80 railway loadings should be independently made.

5. Cover depths are measured from the bottom of the subbase of pavements, or thetop of unsurfaced areas, to top of pipe.

6. Calculations to determine maximum cover for Cooper E–80 railway loadings aremeasured from the bottom of the tie to the top of the pipe.

7. If pipe produced by a manufacturer exceeds the strength requirements establishedby indicated standards then cover depths may be adjusted accordingly.

8. See table C–9 for suggested minimum cover requirements.

C–7

TM 5–820-4/AFM 88–5, Chap 4


C-8

TM 5-820-4/AFM 88-5, Chap. 4

C-9

TM 5-820-4/AFM 88-5, Chap. 4

Figure C-3. Embankment Beddings Circular Pipe

C-10 Change 1

TM 5-820-4/AFM 88-5, Chap. 4

Figure C-4. Trench Beddings for Circular PipeC-11 Change 1

TM 5–820-4/AFM 88–5, Chap 4

DIAMETER OF

IMPERMISSIBLE BEDDINGS

ORDINARY BEDDINGS

FIRST-CLASS BEDDING CONCRETE–CRADLE BEDDING

C-12

TM 5-820-4/AFM 88-5, Chap. 4

C-12 Change

TM 5-820-4/AFM 88-5, Chap 4

Table C–7. Suggested Maximum Cover Requirements for Structural Plate Steel Pipe, 6-Inch Span, 2-Inch DeepCorrugations

DIAMETER,FEET

5.05.56.06.57.07.58.08.59.09.5

10.010.511.011.512.012.513.013.514.014.515.015.516.016.517.017.518.018.519.019.520.020.521.021.522.022.523.023.524.024.525.025.5


MAXIMUM COVER ABOVE TOP OF PIPE, FEET

.109

46423835333129272524232221201918171716161515

.138

6862575249454340383634323129282726252423222221202019

THICKNESS , INCHES. 1 6 8 . 1 8 8 . 2 1 8

908175696460565250474542403937363433323130292827262525242323

10393867973686460575451494644434139383635343332313029282727262525

124113103958882777369656259565451494746444241403837363534333231313029282827

.249

14613312211210497918681777369666361585654525048474544434140393837363534343332313130

.280

1601451331231141061009488848076726966646159575553515048474544434241403938373635343433323231


C-13

TM 5–820-4/AFM 88-5, Chap 4

1. Corrugated steel pipe will conform to the requirements of Federal Specification W–P–405.2. The suggested maximum heights of cover shown in the table are calculated on the basis of the current AASHTO

Standard Specifications for Highway Bridges and are based on circular pipe.3. Soil conditions, trench width and bedding conditions vary widely throughout varying climatic and geographical areas. --4. Calculations to determine maximum cover should be made for all individual pipe and culvert installations underlying

roads, streets and open storage areas subject to H–20 live loads. Cooper E–80 railway loadings should be independentlymade.

5. Cover depths are measured from the bottom of the subbase of pavements, or the top of unsurfaced areas, to top of pipe.6. Calculations to determine maximum cover for Cooper E-80 railway loadings are measured from the bottom of the tie

to the top of the pipe.7. If pipe produced by a manufacturer exceeds the strength requirements established by indicated standards then cover

depths may be adjusted accordingly.8. See table C–9 for suggested minimum cover requirements.

Table C–8. Suggested Maximum Cover Requirements for Corrugated Steel Pipe, 3-Inch Span, 1-Inch Corrugations


MAXIMUM COVER ABOVE TOP OF PIPE, FEET

DIAMETER,INCHES

36

42

48

54

60

66

72

78

84

90

96

102

108

114

120

53 66

45 56

39 49

35 44

31 39

28 36

26 33

24 30

22 28

21 26

24

23

98

84

73

65

58

53

49

45

42

39

36

34

32

30

29

117

101

88

78

70

64

58

54

50

47

44

41

39

37

35

130

112

98

87

78

71

65

60

56

52

49

46

43

41

39

101

87

76

67

61

55

50

47

43

40

38

35

142

122

107

95

85

77

71

65

61

57

53

50

47

45

42

178

142

122

110

102

97

92

84

78

73

69

64

61

58

55

201

157

132

117

107

101

96

93

91

89

84

79

75

71

6 7


C-14

TM 5–820-4/AFM 88–5, Chap 4

Notes:1. Corrugated steel pipe will conform to there requirements of Federal Specification WW-P-4O5.2. The suggested maximum heights of cover shown in the table are calculated on the basis of the current AASHTO

Standard Specifications for Highway Bridges and are based on circular pipe.3. Soil conditions, trench width and bedding conditions vary widely throughout varying climatic and geographical areas.4. Calculations to determine maximum cover should be made for all individual pipe and culvert installations underlying

roads, streets and open storage areas subject to H–20 live loads. Cooper E–80 railway loadings should be independentlymade.

5. Cover depths are measured from the bottom of the subbase of pavements, or the top of unsurfaced areas, to top of pipe.6. Calculations to determine maximum cover for Cooper E–80 railway loadings are measured from the bottom of the tie

to the top of the pipe.7. If pipe produced by a manufacturer exceeds the strength requirements established by indicated standards then cover

depths may be adjusted accordingly.8. See table C-9 for suggested minimum cover requirements.

unusual installation conditions, a detailed analy-sis will be made so that ample safeguards for thepipe will be provided with regard to strength andresistance to deflection due to loads. Determina-tions for deflections of flexible pipe should be madeif necessary. For heavy live loads and heavy loadsdue to considerable depth of cover, it is desirablethat a selected material, preferably bank-rungravel or crushed stone where economically avail-able, be used for backfill adjacent to the pipe. TableC-9 suggests guidelines for minimum cover to pro-tect the pipe during construction and the mini-mum finished height of cover.

C-1O. Bedding of pipe (culverts and stormdrains). The contact between a pipe and the foun-dation on which it rests is the pipe bedding. It hasan important influence on the supporting strengthof the pipe. For drainpipes at military installa-tions, the method of bedding shown in figure C-3is generally satisfactory for both trench and pos-itive projecting (embankment) installations. Somedesigns standardize and classify various types ofbedding in regard to the shaping of the founda-

tion, use of granular material, use of concrete, andsimilar special requirements. Although such re-finement is not considered necessary, at least forstandardized cover requirements, select, finegranular material can be used as an aid in shapingthe bedding, particularly where foundation con-ditions are difficult. Also, where economicallyavailable, granular materials can be used to goodadvantage for backfill adjacent to the pipe. Whenculverts or storm drains are to be installed in un-stable or yielding soils, under great heights of fill,or where pipe will be subjected to very heavy liveloads, a method of bedding can be used in whichthe pipe is set in plain or reinforced concrete ofsuitable thickness extending upward on each sideof the pipe. In some instances, the pipe may betotally encased in concrete or concrete may beplaced along the side and over the top of the pipe(top or arch encasement) after proper bedding andpartial backfilling. Pipe manufacturers will behelpful in recommending type and specific re-quirements for encased, partially encased, or spe-cially reinforced pipe in connection with designfor complex conditions.

C - 5

Table C–9. Suggested Guidelines for Minimum Cover

H-20 Highway Loading

Steel

12” to 108”

12” to 36”

Diameter/2 or 3.0’whichever is greater



1.5’Diameter

Diameter/2

60” and over Diameter/2

TM 5-820-4/AFM

Notes:1. All values shown above are for average conditions and are to reconsidered as guidelines only.

88-5, Chap 4

2. Calculations should be made for minimum cover for all individual pipe installations for pipe underlying roads, streetsand open storage areas subject to H–20 1ive loads.

3. Calculations for minimum cover for all individual pipe installations should be separately made for all Cooper E–80railroad live loading.

4. In seasonal frost areas, minimum pipe cover must meet requirements of table 2–3 of TM 5–820-3 for protection ofstorm drains.

5. Pipe placed under rigid pavement will have minimum cover from the bottom of the subbase to top of pipe of l. Oft. forpipe up to 60 inches and greater than l. Oft. for sizes above 60 inches if calculations so indicate.

6. Trench widths depend upon varying conditions of construction but maybe as wide as is consistent with space requiredto install the pipe and as deep as can be managed from practical construction methods.

7. Non-reinforced concrete pipe is available in sizes up to 36 inches.8. See tables C-1 through C–8 for suggested maximum cover requirements.

C–17

TM 5–820-4/AFM 88–5, Chap 4

APPENDIX D

NOTATION

A

AHWBcDddc

F

gHHf

hO

IiK

Ke

kLL1

Ls

Lt

n

QRRC

ssoT

vv

Y

Drainage area, acres, total area of clear opening, or cross-sec-tional area of flow, ft2.

Allowable headwater depth, ft.Width, ft.Coefficient.Height of culvert barrel, ft.Depth or thickness of grate, ft.Critical depth, ft.Infiltration rate, in/hr.Acceleration due to gravity, ft/sec2.Depth of water, ft.Headloss due to friction, ft.Headwater, ft.Distance from culvert invert at the outlet to the control eleva-

tion, ft.Rainfall intensity, in/hr.Hydraulic gradient.Constant.Coefficient.Coefficient of permeability.Length of slot or gross perimeter of grate opening, or length, ft.Adjusted length, ft.Length of spiral, ft. (nonsuperelevated channel).Length of spiral, ft. (superelevated channels).Manning’s roughness coefficient.Discharge or peak rate of runoff, cfs.Hydraulic radius, ft.Radius of curvature center line of channel, ft.Slope of energy gradient, ft/ft.Slope of flow line, ft/ft.Top width at water surface, ft.Tailwater, ft.Mean velocity of flow, ft/sec.Discharge velocity in Darcy’s law, ft/sec.Depth of water, ft.

D-1

TM 5–820-4/AFM 88–5, Chap 4

APPENDIX E

BIBLIOGRAPHY

A Policy on Design of Urban Highways and Arterial Streets, AmericanAssociation of State Highway Officials, 1973.

Baker, R. F., Byrd, L. G., and Mickle, D. E., Handbook of Highway Engi-neering, New York: Van Nostrand-Reinholde, 1974.

Concrete Pipe Design Manual, American Concrete Pipe Association, 1974.Handbook of Drainage and Construction Products, Armco Drainage and

Metal Products, Inc., Ohio, 1967.Handbook of Steel Drainage and Highway Construction Products, Amer-

ican Iron and Steel Institute, New York, 1971.King, H. W., and Brater, E. E., Handbook of Hydraulics, McGraw-Hill Book

Company, Inc., New York, N.Y., 1963.Morris, H. M., and Wiggert, J. M., Applied Hydraulics in Engineering, 2nd

Edition, New York: Ronald Press Company, 1971.Paguette, R. J., Ash ford, N., and Wright, P. H., Transportation Engineering,

New York: Ronald Press Company, 1972.Ritter, L. J., Jr., and Paquette, R. J., Highway Engineering, New York:

Ronald Press Company, 1967.Sewer Manual For Corrugated Steel Pipe, National Corrugated Steel Pipe

Association, Illinois, 1978.Silberman, E., and Dahlin, W. Q., Friction Factors for Helical Corrugated

Aluminum Pipe, Project Report No. 112, University of Minnesota, St.Anthony Falls Hydraulic Laboratory, 1969.

Stevens, M. A., Simmons, D. E., and Watts, F. J., Riprapped Basins forCulvert Outlets, Highway Research Record, No. 373, 1971.

U.S. Department of Agriculture, Friction Factors for Helical CorrugatedPipe, by C. E. Rice, ARS 41–119, 1966.

U.S. Army Engineer Waterways Experiment Station, Erosion and RiprapRequirements at Culvert and Stem-Drain Outlets, by J. P. Bohan,Research Report H–70-2, 1970.

U.S. Army Engineer Waterways Experiment Station, Evaluation of ThreeEnergy Dissipators for Stem-Drain Outlets, by J. L. Grace and G. A.Pickering, Research Report H–71–1, 1971.

U.S. Army Engineer Waterways Experiment Station, Practical Guidancefor Estimating and Controlling Erosion at Culvert Outlets, by B. P.Fletcher and J. L. Grace, Jr., Miscellaneous Paper H–72-5, 1972.

U.S. Department of the Interior, Bureau of Reclamation, Hydraulic Designof Stilling Basin for Pipe or Channel Outlets, by G. L. Beickley, Re-search Report No. 24, 1971.

U.S. Department of Transportation, Federal Highway Administration, Hy-draulic Design of Improved Inlets for Culverts, Hydraulic EngineeringCircular No. 13, August 1972.

E-1

TM 5-820-4/AFM 88-5, Chap 4

Viessman, W., Jr., Knapp, J. W., Lewis, G. L., and Harbaugh, T. E., Intro-duction to Hydrology, 2nd Edition, New York: TEP, 1977.

Yen, B. C., and Ying-Chang Lieu, Hydraulic Resistance in Alluvial Chan-nels, Research Report No. 22, University of Illinois Water ResearchCenter, Urbana, Illinois, 1969.

E-2

TM 5–820-4/AFM 88–5, Chap 4

The proponent agency of this publication is the Office of the Chief of Engineers,United States Army. Users are invited to send comments and suggested im-provements on DA Form 2028 (Recommended Changes to Publications andBlank Forms) direct to HQDA (DAEN-ECE-G), WASH DC 20314.

By Order of the Secretaries of the Army and the Air Force:

JOHN A. WICKHAM, JR.General, United States Amy

Official: Chief of StaffROBERT M. JOYCE

Major General, United States AmyThe Adjutant General

CHARLES A. GABRIEL, General, USAFOfficial: Chief of StaffJAMES H. DELANEY, Colonel, USAF

Director of Administration

Distribution:Army: To be distributed in accordance with DA Form 12–34B, re-

quirements for TM 5–800 Series: Engineering and Design forReal Property Facilities.

Air Force: F

tm 5-820-4 drainage for areas other than airfields

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