R.O. Evans, K.L. Bass, M.R. Burchell, R.D. Hinson, R. Johnson, and M. Doxey

Key words: BMPs-constructed wetlands-drainage-hydrology-water quality

Management alternatives to enhancewater quality and ecological function ofchannelized streams and drainage canals

Abstract: Drainage practices in humid regions historically focllSed on straightening anddeepening natural channels to increase their hydraulic capacity and minimize upstream flood­ing. In most cases, traditional channel improvements disassociated the channel from the natu­ral floodplain, especially for smaller storms, degrading water quality and ecological functionsassociated with the riparian floodplain. Pilot studies were implemented to denlOnstrate andevaluate alternative channel management strategies and design geometries to identifY alterna­tives that might enhance water quality functions while maintaining the necessary drainagefunction. Channel alternatives included: establishment of in-stream and riparian wetlands,lowering of the floodplain to reconnect the channel with the floodplain, redesign of chan­nels using natural channel design principles, and establislU11ent of conservation easementsto encourage establishment of perennial riparian buffer vegetation. This paper summarizesseven projects that were in1plemented between 1995 and 2006 to provide better manage­ment of drainage water in order to enhance water quality and other ecological functions inlarge drainage canals. Hydrology and water quality were monitored fi:om two to four yearsat five sites. In addition, plant conu11unities and macro-invertebrates were nlOnitored at threesites. Nitrogen concentrations and transport were reduced by 20% to 70% with in-stream andconstructed storm water wetlands. Reconnecting the channel with the floodplain damvenedthe hydrograph peak and reduced the "out-of-floodplain" risks outside the project area. Thealternative practices were more expensive and resulted in two to three tin1es more land areabeing taken out of production compared to conventional drainage practices. However, thebenefits were improved water quality, lower peak outflow stage, and enhanced habitat forwildlife. Practices described here are beginning to demonstrate that there are multipurpose,environmentally friendly alternatives to traditional practices of routinely cleaning and mow­ing trapezoidal ditch channels for the sole purpose of satisfYing drainage requirements.

Robert O. Evans is a professor, Kris L. Bass isan extension associate, and Mike R. Burchell isan extension assistant professor in the Depart­ment of Biological and Agricultural Engineering,North Carolina State University. R. Dwane Hin­son is a district conservationist for the USDANatural Resources Conservation Service (NRCS).Rodney Johnson is a retired Albemarle resourceconservation and development coordinatorfor the USDA NRCS. Mike Doxey is a districttechnician for the Currituck Soil and WaterConservation District.

to the drainage formula Q = 0.013CiVj5/",where Q = discharge (m3 S-1 [ft3 S-I]),

M = watershed area (km2 [mi2]), and C = a

regional coefficient determined through localexperience (USDA Soil Conservation Service1971; Schwab et at 1993). Coefficients typi­cally range from 10 to 45 depending on landlISe, crop, rainfall, topography, and desiredlevel of flood protectionValues for row cropsalong the Atlantic and Gulf Coast typicallyrange from 30 to 45. These result in bankfullflow frequencies of 2 to 5 year recurrenceintervals (Schwab et al. 1993), which areapproaching an order of magnitude less thanthe natural frequencies reported by Sweetand Geratz (2003).

Few unchannelized streams remain in thelower and middle coastal plain regions of theAtlantic and Gulf States. This has becomewidely apparent to stream restoration con­sultants who have experienced difficultylocating reference reaches in coastal plainareas for establishment of natural channeldesign criteria. In most cases, traditionalchannel improvements have straightened anddeepened natural channels to increase theirhydraulic capacity. This altered the hydrau­lic connection between the channel and thenatural floodplain thereby degrading riparianzone water quality and ecological functions.Woody riparian vegetation along the sidesof the streams have been removed and ditchbanks routinely mowed to provide access forperiodic clean-out and removal of silt (Lilly1981). In many channelized streams, moststorm flows are confined predominately tothe channel. The riparian floodplain thatonce routinely remained soaked or inundatedduring the winter and spring for months at atime only flood during large storms (stormsgreater than 2 to 3 year recurrence interval)following channelization. In addition to thedecline in the frequency of out-of-bank flow,water table levels both within the riparian

1992; Lowrance et al. 1984). This rIparIanzone function is one of the primary justifica­tions for the USDA Conservation ReserveEnhancement Program initiative to restoreriparian buffers (Cowan 2007; Mayer et al.2005; USDA Farm Service Agency 2007).

Drainage has been an important compo­nent of land management in humid regionsof the US for the past 200 years (Beauchamp1987; Fausey et al. 1987; Lilly 1981).Natural processes affecting the connectiv­ity of a stream channel and its floodplain areseverely altered by past drainage practices.Over the past century, drainage improve­ments in most humid regions were sized toconvey flows within the channel according

Natural channels typically experiencebankfull flows at a recurrence interval of1 to 1.5 years (Rosgen 1996). In flat areaswith wide river valleys representative oflowercoastal plain landscapes, bankfull flows mayoccur more frequently-on the order ofsev­eral times per year (Sweet and Geratz 2003).When a channel overflows its bank, a portionof the flow is stored in the riparian flood­plain thus dampening the peak of the hydro­graph. Flows stored in or passing throughthe riparian floodplain typically undergobiochemical processes that improve the qual­ity of the water prior to it being returned tothe stream (Dukes and Evans 2003; Dukes etal. 2002, 2003; Gilliam et al. 1997; Lowrance

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Table 1Summary of data collection, project durations, and citations to original references.

Project Data collected Reference{s) Duration

lull Creek, Currituck County

Liza's Bottom, Edenton, Chowan County

Newland Ditch, Pasquotank County

Guinea Mill, Currituck County

Edenton Airport, Chowan County

Chowan Golf Course, Chowan County

Core Creek, Craven County

Continuous stream stage

Outflow (stage wi weir eq.r

Monthly grab WQ

Plant surveys

Continuous stream stage

Outflow (stage wi weir eq.)

Automatic WQ samplers

No data collected

No data collected

Continuous stream stage

Outflow (stage wi weir eq.)

Riparian zone WL

Automatic WQ samplers

Benthic macro-invertebrates

Continuous stream stage

Outflow (stage wi weir eq.)

Groundwater WL

Automatic WQ samplers

Benthic macro-invertebrates

Continuous stream stage

Outflow (stage wi weir eq.)

Groundwater WL

Automatic WQ samplers

Benthic macro-invertebrates

Channel cross sections

Evans and Smith 2000

Bass 2000

Bass and Evans 2000

Smith and Evans 2004

Graduate study in progress

Graduate study in progress

Smeltz 2004

Smettz et al. 2004

Lindow et al. 2007

Graduate study in progress

1995 to 1999

1997 to 2000

1998 to 2003

1999 to 2003

2000 to 2006

2003 to present

1999 to present

'Flow computed from stage data and appropriate weir formula.

Notes: WQ ~ water quality samples for chemical analysis. WL ~ water level measurement.

zone and considerable distance (50 to 100 m(150 to 300 ft)) upslope perpendicular to theriparian zone have been lowered (Gilliam andSkaggs 1981; Skaggs et al. 1994). In bypass­ing the floodplain, there is less opportunityfor potential pollutants in the drainage waterto be filtered and assimilated. Restoration ofriparian zones has become a major initiativequalifYing for costs share assistance throughnumerous federal and state incentive pro­grams. WIllie water quality and habitatrestoration have become priorities for thegeneral public, wetness is still a concern tomany landowners. However, intensive drain­age systems sometimes remove more waterthan necessary to satisfY agricultural require­ments, especially on sandy soils during drierperiods, which may lead to the problem of"over drainage" (Doty et al. 1982).

Early Attempts to Address AgriculturalDrainage Water QualityControlled drainage has been implemented ineastern orth Carolina to address the issueof over drainage and agricultural drainage

water quality. Controlled drainage involvesthe use ofadjustable, flow-retarding structuresplaced in drainage outlets to allow the waterlevel in the outlets to be artificially set. Manytypes of structures can be used depending onthe layout of the drainage system (Evans andSkaggs 1985; Evans et al. 1992; Evans 2003).When properly managed, controlled drainagehas been documented to reduce the transportof nitrogen in agricultural drainage watersby as much as 40% (Evans et al. 1995; Fauseyet al 2004). In 1985, controlled drainage wasadopted as a best management practice byNorth Carolina and as such qualified for costshare assistance to landowners under the NorthCarolina Agricultural Cost-Share Programadministered by the North Carolina Divisionof Soil and Water Conservation (Evans andSkaggs 2004). Since 1985, approximately 3500water control structures have been imple­mented on about 120,000 ha (300,000 ac)across eastern North Carolina. The practiceofcontrolled drainage is now being promotedby the Agricultural Drainage ManagementSystems Task Force-a multi state, multi

agency work group-as a practical means toreduce the transport ofnitrogen originating inthe upper Mississippi Valley ii-om getting intowaterways and contributing further to thehypoxic zone in the Gulf of Mexico (ADMS2003).

The rate of implementation of controlleddrainage peaked in North Carolina at about10,000 ha yc l (25,000 ac yr- I

) in 1991 (Evansand Skaggs 2004). Resurgence in public con­cern and interest in water quality arose in theearly 1990s following several major fish killsin the lower Neuse River and Albem.arle/Pamlico Sound Estuary. Controlled drainagewas one of several practices reconU11endedfor agricultural lands to address this problem;however, significant increase in controlleddrainage implementation did not occur. As aresult, the authors initiated a variety of dem­onstration practices to be used in addition to,or in conjunction with, controlled drainageto further reduce the transport of nutrients,especially nitrogen, in agricultural drainage.Seven demonstration projects are discussedin this paper.

I JULY IAUGUST 2007 VOLUME 62, NUMBER 4 ~

Figure 1In-stream wetland reach ofTull Creek project.

-e

Figure 2Schematic of water management treatments and sample locations, lull Creek project.

e Stage recorder and water sample locations

) Water control structure locations

bankfull Q was within an acceptable range.No increase in the water smface profile wasconsidered acceptable within urban water­sheds while about a 50 mm (2 in) rise in thewater surface profile was considered accept­able for agricultural watersheds. Practicalapplications of this design rationale are dis­cussed for several of the following projects.

Tull Creek ProjectThe first drainage alternative project wasinitiated in the Tull Creek watershed inCurrituck County, North Carolina, in 1995.The project involved a 1.6 km (1 mi) reachof the main canal system draining approxi­mately 80 ha (200 ac)of cropland. Onereach of the canal (530 m [1,750 ft]) wasmanaged in the traditional "free" drainage

r---

-Controlled

Conventional Controlled drainage widrainage drainage wetland plantssection section section

e • e. eJ1'1 1500ft -I

Earthen plug

1

what it was prior to the project. HEC-RAS,Hydrologic Engineering Center's RiverAnalysis System (USACE 2002), was used toevaluate the impact of the channel alterna­tives and!or design parameters on the watersmface profile before and after the implemen­tation of each project. The hydraulic designprocedure involved evaluating the existingcondition for each channel using HEC-RASand determining bankfull Q.The HEC-RASanalysis was then repeated incorporating thechannel alternative (weir, in-stream wet­land, floodplain, etc.) and the water smfaceprofile re-com.puted and compared to thepre-project condition. Appropriate channeldimension, for example cross sectional area,was adjusted (sized) in HEC-RAS until thenew water sur£1Ce profile for the pre-project

Drainage Canal Alternatives EvaluatedPilot studies were begun in 1995 to demon­strate and evaluate alternative managementstrategies and channel design geometries thatmight enhance water quality and ecologicalfunctions while maintaining the necessarydrainage function of channelized streams.Channel alternatives included the following:

• Establishment of in-stream. wetlands.• Restoration of riparian wetlands and

buffers.• Re-design of channels using natural

channel design principles to reconnect thechannel with the existing natural floodplain(priority I restoration).A priority I restorationtypically retains the original floodplain eleva­tion and moves the channel laterally withinthe existing floodplain and raises the channelbed elevation to accomplish reconnectionwith the existing floodplain. The new chan­nel bottom is established at approximatelythe pre-drainage!channelization elevation.This results in a more natural channel-flood­plain system, but upslope (perpendicular tochannel) and upstream lands may becomesusceptible to pre-drained flooding orwetness conditions.

• Lowering of the floodplain to reconnectthe floodplain to the existing channel (pri­ority II restoration). A priority II restorationestablishes both the channel and floodplainat a new "lower" elevation than occurrednaturally. This is a more"engineered" system,is more costly to construct, but maintains thepost-drainage capacity of the system and pro­tection of both upslope and upstream. lands.

• Establishment ofconservation easementsto eliminate traditional ditch bank mow­ing and facilitate establishment of perennialriparian vegetation.

It is beyond the scope of this paper toprovide detailed descriptions of each proj­ect including methodology used to monitorand evaluate each practice's effectiveness toaddress water quality and ecological goals.Instead, only general observations thataddress project characteristics and perfor­mance are presented herein. The reader isdirected to original publications for detailedproject descriptions, explanation ofmonitor­ing methodology, and scientific analysis andresults (table 1).

Maintenance of pre-project high flowdrainage capacities were a design require­ment on all projects. That is, the capacity ofeach channel (Q) under high flow condi­tions (bankfull) could not be reduced below

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Table 2Outflow and water quality characteristics. Tull Creek project. January 19.1996. to September 29. 1999 (after Evans and Smith 2000)

Treatment

Controlled drainage w/plants

Controlled drainage

Conventional drainage

Outflow NOiN

2.3a

1.6ab

O.8b

Mean concentrations (mg L-')

NH.-N TN TP OP

O.6a 4.la O.09b O.04b

O.8a 4.4a O.13b O.04b

O.5a 2.6b O.3la O.26a

Outflow (mm yr-') and mean mass transport (kg ha-' yr-')

Sediment

5.lb

8.8ab

l2.3a

Controlled drainage w/plants 330ab 7.4a 1.9a l3.6a O.29b

Controlled drainage 229b 3.6b 1.8a 9.9a O.29b

Conventional drainage 500a 3.9b 2.3a l3.0a 1.56a

Note: Values followed by the same lower case letter vertically (within groups) are not significantly different at the 5% level.

O.13b

O.09b

1.30a

l5b

l8b

55a

mode, a second reach was managed in the"controlled" drainage mode, and the thirdreach was planted with a variety of wetlandplants (figure 1) to provide a combination in­stream wetland/controlled drainage system.Approximately 4,500 plants were planted inthe wetland section. Based on visual observa­tions made during September 1996 and plantsurveys conducted at the end of the secondgrowing season, over 90% of all species,except cattail, survived. Annual re-growth ofwetland vegetation was excellent through­out the evaluation period (1996 to 1999).The outlet of each reach was instrumentedto continuously measure outflow (figure 2).Grab samples were collected monthly toevaluate treatment effects on water quality.In general, nitrogen (N) concentrations werehigher while phosphorus (P) concentra­tions were lower with drainage control bothwith and without the addition of wetlandplants (table 2). Total flow, P, and sedimenttransport were significantly lower with bothcontrolled drainage treatments.

The addition of plants did not appear toprovide an additional water quality benefitother than an improvement in water clar­ity over drainage control alone. Habitat

. benefits may have been enhanced by theplants, but habitat benefits were not evalu­ated. This initial project demonstrated thatit was possible to maintain wetland plants indrainage ditches without frequent mowingor adversely impacting the drainage perfor­mance of the ditch.

Liza's Bottom ProjectThe Edenton urban project, initiated in1997, involved construction to lower theold floodplain along approximately 400 m(1,320 ft) of stream known as Liza's Bottomand create approximately 1 ha (2.5 ac) ofin-stream wetlands. The stream carnesdrainage waters from agricultural lands and

runoff from commercial and urban sourcessuch as a solid waste transfer site and aformer farm supply facility. The channel wasinitially channelized prior to 1900 and wasroutinely cleaned out thereafter such thatthe riparian floodplain was rarely functional.A 1 ha (2.5 ac) wetland was constructedin April to May in 1997. The wetland wasbuilt by excavating the existing hydraulicallydisconnected floodplain down to the streambase-flow level and raising the streambottom (figure 3). The soils found in thefloodplain and used for the wetland sub­strate were variable, with some reduced andhigh in organic matter and others clayey incontent. Islands were built in the interior tominimize transportation of cut/fill mate­rial and create a more sinuous flow path. Alow head, wooden bulkhead was installedat the outlet to maintain water depths of0.1 m to 0.5 m (6 to 18 in). The wetlandbottom was graded for a mixture of shallowand deeper pool areas. Native plants wereused in the wetland and transplanted on a1 m x 1 m (3 ft x 3 ft) spacing. The wetlandintercepts drainage waters fi'om approxi­mately 240 ha (600 ac) of surroundingwatershed. One hundred and sixty hectares(400 ac) are attributed to agricultural andnatural forested area, 60 ha (150 ac) to urbanarea, and 20 ha (50 ac) to intensive conlliler­cial areas. The resulting watershed/wetlandarea ratio is 100:1, which is less than half theminimum size typically reconllilended in theliterature (Scheuler 1992).

The wetland was instrumented tocontinuously measure inflow and outflow(figure 4). Flow measurements were made atthe two main inlet streams (E2 and E3) andat the wetland outlet (E1) using continuouswater level recorders. Stage measurementswere combined with weirs and calibrateddischarge curves to generate a continuousmass flow record at E1 and E3. However, no

weir was installed at the agricultural inlet,E2. Instead, a stage-discharge curve wasdeveloped at E2 by computing flow usingManning's formula from continuously mea­sured stage and flow velocity at the nearbyculvert (Bass 2000). As a check, drainageoutflow from the agricultural watershed wasalso simulated using DRAINMOD (Skaggs1978) and compared to the wetland inflowestimate at E2. Good agreement (estimatedversus simulated water balance closed within5%) was observed between the estimatedand simulated inflow to the wetland atE2 so it was concluded that the overall flowsobserved were reasonable for use with con­centration data to predict nutrient masstransport (Bass 2000). Background grabsamples were acquired bi-weekly upstreamand downstream of the planned wetlandreach from January 1996 until constructionbegan in May 1997. For a six month periodfollowing construction of the wetland, flowproportional water samples were collected atthe wetland inlets and outlet using automaticsamplers. Twice daily time based samplingoccurred thereafter.

During base flow conditions, attenuationwithin the Liza Bottom constructed wet­land was approximately seven days with nosignificant attenuation during large stormflows. Prior to 'wetland construction, therewere no changes in ammonium (NH

4-N)

concentrations between up and downstreammonitoring locations while nitrate-nitrogen(N0

3-N) showed a 40% decrease indicat­

ing some nitrate was likely being removedalong the stream by denitrification. itrogenconcentrations were consistently lowerand P concentrations consistently higher atthe wetland outlet compared to the inlet(table 3).Yearly and seasonal means indicatedthat significant improvements in N0

3-N and

NH.-N concentrations can be achieved withrelatively small wetlands. Initially, total- and

I JULY IAUGUST 2007 VOLUME 62, NUMBER 4 ~

Figure 3Liza's Bottom in-stream wetland, Edenton, construction completed May 1997.

Figure ItSchematic of monitoring locations at Liza's Bottom in-stream wetland, Edenton.

Wetland outlet

E1•

A

Solid wastetransfer station

E31150 ac:urban

Side ditch

400 ac agricultural500 ac commercial

ortho- P concentrations were unchangedby the wetland. However, by the end of yeart\;yO, P concentrations began to increase.The P increase at the wetland outlet mayhave resulted from reduction of iron-Pcomplexes as the aerable soils used for sub­strate became reduced, solublizing the iron(Vepraskas and Faulkner 2001). However,redox measuren"lents were not made, so

[ ~'-~JO-U-R-N-A-L-O-F-5-0-1L-A-N-D-W-A-T-ER-C-0-N-5-E-R-VA-T-IO-N~-

Pre-constructionA

Post-construction

there is no conclusive explanation for theP increase. Over the four-year monitor­ing period which ended December 2000,N0

3-N concentrations were reduced by 60%,

NH"- by 30%, and TK by 9.5% resultingin a flow-weighted total nitrogen reductionof 20% (table 4). During the last two yearsof monitoring, there was a net increase in Pdischarge fi-om the wetland of 55%.

Implementation of Water ManagementService Districts: Case Study ExamplesThe Newland Ditch watershed project(7,000 ha [17,000 ac]) and Guinea Millwatershed project (2,000 ha [5,000 ac])were initiated in 1998 and 1999, respec­tively, to address drainage and waterquality issues arising from rapid urbaniza­tion ofpredominately rural counties. Resultsof the Liza Bottom project previously pre­sented showed potential for using in-streamwetlands to reduce the transport of nitro­gen. The Newland Ditch and Guinea Millprojects represent the implementation of thispractice on a large watershed basis. Neitherof these watershed projects were instru­mented to collect quantitative water qualitydata. However, they are important to the dis­cussion in this paper in that they representdeviation fi-om traditional "drainage only"land management practices to multi-purposeprojects that address regional water man­agement and water quality issues. They alsodemonstrate willingness of local landownersto adopt new water management alternativesfor goals other than just drainage.

A significant component of the NewlandDitch and Guinea Mill projects was forma­tion of tax-supported Water ManagementService Districts, the first in North Carolina.Historically, federal legislation such as theDrainage Districts Acts of 1885 and 1903established authority for states and countygovernments to organize drainage districtsfor the purpose of draining agricultural landsand to reclaim swamps and other wet lands(Beauchamp 1987). While drainage districtlaw has been effective for providing author­ity to drain lands, it can be prohibitive forimplementation of practices within drainagedistrict's jurisdiction for purposes other thandrainage improvement. For example, underdrainage district law, penalties can be assessedfor activities such as addition of weirs orstructures to control flow for the purposeof improving drainage water quality. Thisconstraint has prevented the installation ofwater control structures in North Carolinawithin drainage district right-of-waysfor the purpose of providing controlleddrainage (based on authors' frequentexperiences).

Under North Carolina Statute, a servicedistrict operates similarly to a drainage districtin terms of establishment, taxation and gov­ernance. The advantage of a service district isthe ability to incorporate multiple objectives

Table 3Constituent concentrations at Liza's Bottom in-stream wetland inlets and outlets (after Bass and Evans 2000).

Mean concentrations (mg L-1)

Nutrient Inlet

1997

Outlet Inlet

1998

Outlet Inlet

1999

Outlet Inlet

Overall

Outlet

N03-N 0.6a 0.5a 0.7a 0.2b 0.6a 0.2b

NH.-N OAa OAa 0.6a OAb 0.5a OAb

TKN 1.3a 1.2a 2.0a 1.9a 2Aa 2.1a

TP 0.31a 0.36a 0.32b 0.56a OA7b 0.64a

OP 0.20a 0.28a 0.24b OAla 0.34b OA5a

Note: Values followed by the same lower case letter (horizontally within years) are not significantly different at the 5% level.

Source: After Bass (2000).

0.6a

0.6a

2.1a

0.37b

0.27b

0.2b

OAb

1.9b

0.57a

OA2a

Table IfOverall nutrient reductions on concentration and mass basis, Liza's Bottom wetland, Edenton.

in the charter whereas a drainage district byNorth Carolina Statute has one objective,that being drainage or flood protection. Inthe case of a Service District, it becom.es theresponsibility of the leadership to determineon a case by case basis what activities achievethe overall goals of the District. For example,a service district can have an objective ofproviding flood protection but at the sametime allowing installation of a water controlstructure to enhance water quality. If it isdeemed that water quality is more imp01'-

tant to the District than drainage, drainagecan be compromised for the benefit of waterquality. This has major implementations formulti-use projects in watersheds traditionallygoverned by drainage districts.

Guinea Mill Project. The Guinea Millwatershed resulted in 289 parcel owners, theInajority in eight major subdivisions, exe­cuting taxation easements to maintain theproject. Permanent conservation easementsinvolving 20 ha (50 ac) along both sides ofthe canal were purchased and are managed by

Concentration basis

Mass basis

N03 N

60%

55%

30%

16%

TKN

9.5%

6%

TN

20%

18%

TP

-55%

-50%

OP

-55%

-50%

the county utilizing an advisory board com­prised of five landowners in the watershed.The advisory board is charged with the dutyof investigating, studying and making recom­mendations to the Board of Conmussionerspertaining to the construction, enlargement,improvement, maintenance, operation andregulation of the service district. A countyordinance was established requiring all newsubdivisions and any landowners encroach­ing on the easement and canal to submit aplan for that encroachment (i.e., culvert,drainage swale, etc) to the service districtprior to installation.

Fourteen kilometers (9 nu) of riparianbuffers were established along the GuineaMill canal. Where f.1rnung used to occurnext to the stream bank, buffers are estab­lished with vegetation maintained 0.3 to1 m (1 to 3 ft) high. In-stream constructed

Figure 5Lower section of Guinea Mill after installation of riparian buffer andinstream wetland.

Note: Path was moved away from canal bank.

Figure 6Rock weir raises upstream water level at base flow enhancinghydrologic function of upstream swamp, Guinea Mill project.

Note: Upstream water level is raised about 1 m.

JULY IAUGUST 2007 VOLUME 62, NUMBER 4

Figure 7Section of Shepard Ditch during dry period after establishment ofwetland plants on constructed ledge (right bank), NewlandDitch project.

Figure 8Vegetative buffers were established along ditch banks and thechannel was widened to maintain capacity at the rock structures,Newland Ditch project.

In additionManagement

Figure 9View of lower floodplain after third growing season, Edenton Airport project.

wetlands (figure 5) were installed on3.4 ha (8 ac) within the Guinea Mill canal.In the wetland section, the canal was wid­ened from 10 to 20 m (30 to 70 ft). Thewidened channel section increased the crosssectional area of the channel to offset theincreased flow resistance resulting from thewetland plants. Two in-stream wetland cellswere constructed, one approximately 2 km(1.3 nil) and the second about 1 km (0.6 milin length.

A rock weir water control structure wasinstalled to enhance hydrologic function atlow flows in the main channel.The rock weir(1 m high by 1.2 m top width by 21 m length[3 ft high by 4 ft top width by 70 ft length])was located just downstream ofa 15 ha (40 ac)hardwood swamp (figure 6). The hydrologyof the swamp had been significantly altered(water table lowered) by channelization ofGuinea Mill canal. The rock weir raised thebase flow elevation by approximately 1 m(3 ft), restoring some hydrologic function tothe riparian swamp in terms of raised watertable level and more frequent overflow intothe swamp. In addition, a scour pool formeddownstream of the rock weir which has thepotential to enhance aquatic habitat. As inprevious examples, the channel was widenedin the vicinity of the rock weir to offset thereduction in flow depth resulting from theweir. Annual inspections of all conservationeasements are made by the Advisory Boardand the Currituck SWCD Board withtheir respective reports submitted to theCounty commissioners.

Newland Ditch Project.to establishment of a Water

Service District, this project involved exca­vation of the two nuin channels (158 Canaland Sheppard Ditch) to stabilize streambanks. The ditch bottoms were excavated tocreate a ledge for establishment of just over1 ha (2.5 ac) of in-stream constructed wet­lands (figure 7). Five associated rock weirwater control structures (figure 8) wereinstalled to enhance base flow hydrology andecological function. At each rock weir, thechannel was widened to maintain the sainecross sectional area as existed prior to theproject so that the channel capacity will not

be reduced at high flows. Vegetative bufferswere established along 4.2 km (2.6 nil) of the158 Canal and 3.6 knl (2.3 mil on SheppardDitch. Annual inspections are nude by theadvisory board and the Pasquotank SWCDBoard with their respective reports submit­ted to the county cOlnnussioners.

Edenton Airport ProjectThe Edenton Airport and Industrial Parkrestoration and enhancement project inChowan County was initiated in 2000. Aspart of the construction and developn"lent

JOURNAL OF SOIL AND WATER CONSERVATION~IL-- ___=_~

Figure 10Constructed stream and floodplain of small headwater stream, upper reach of Edenton Airport project.

Figure 11Constructed storm water wetland in series in drainage system, midreach of Edenton Airport project.

of the Edenton Army Base in the 1930s,the lower stream reach of the watershedwas channelized with the spoil deposited inthe adjacent floodplain and a short circuitcutoff constructed that shortened the flowpath of drainage water to the AlbemarleSound by more than one km (0.6 nul. Thisproject involved three hydrologic enhance­ments. The first involved restoration ofstream and riparian floodplain functions inthe lower stream segment. Spoil piles wereremoved to restore hydrologic functionsin terms of more frequent diffuse overlandflow and raised water table elevations withinthe floodplain. Re-growth maples werereplaced with cypress and mixed bottom­land hardwood species. At several locations,the straightened, channelized stream wasre-routed back through existing floodplain(figure 9) at its original elevation (priorityI restoration). Priority I restoration involvesraising the streambed elevation to re-connectthe stream to the existing floodplain.

The second hydrologic enhancementinvolved construction of a 300 m (1,000 ft)reach of stream and riparian floodplain(priority II). Priority II restoration involveslowering the floodplain (stream valley) eleva­tion to an appropriate elevation based on theexisting stream bed elevation. Final designconsisted of a 250 m (800 ft) stream/wet­land valley with floodplain width varyingfrom 7 to 10 m (20 to 30 ft).The stream wasdesigned to meander within the wetlandvalley (figure 10). The resulting sinuosity is1.25 (stream length divided by valley length).The stream/wetland system was designedto be from 0.5 to 1.5 m (1.5 to 5 ft) beloworiginal grade. Lastly a series of two storm­water wetlands were constructed between theconstructed and restored stream reaches(figure 11). A schematic of the flow pathand monitoring locations for this project areshown in figure 12.

Water quality monitoring showed meanpollutant concentrations for all samplinglocations (table 5) were lower than typicalagricultural watersheds (Evans et al. 1995;Skaggs et al. 1994). The relatively unde­veloped status of the watershed was mostlikely a causative factor for the low con­centrations. All constituent concentrationsdecreased through the constructed stream/floodplain reach of the system (uppermostcomponent of the project). Nitrate-N wasreduced through the constructed stormwaterwetland (midreach) but other constituents

were unaffected or increased. All N speciesdecreased through the further most down­stream component of the project (restoredfloodplain swamp) but both P and sedimentconcentrations increased. The increase insediment concentration in the stormwa­ter and restored swamp wetlands was likelythe result of muskrat (Ondatra zibethicus) and

nutria (lVJ.yocaster coypus) disturbance of thebottom sediments. Both species were com­mon in areas of standing water. Disturbanceof the sediments might also account forthe increase in total phosphorus. Wetlandprocesses were likely the primarily causeof nitrate reduction throughout the system.Nitrate reduction on a concentration basis

I JULY IAUGUST z007 VOLUME 6z, NUMBER 4 GiJ

Figure 12Schematic of Edenton Airport project showing surface water sampling locations.

Industrial parkwas relatively high, likely due to the relativelylow inflow concentrations.

Outlet to Albermarie Sound

Location TKN NH4N N0

3N TN TP Sediment

Golf Course ProjectAn innovative approach was initiated in 2003to manage poor drainage and storm water atthe Chowan Golf Course. Existing drain­age ditches were redesigned utilizing natu­ral channel design concepts (Rosgen 1995)along with HEC-RAS hydrologic analysisand were then interconnected to a networkof twelve constructed storm water wetlands(figures 13 and 14) ranging in size from 0.1to 2 ha (0.25 to 5 ac). On this project, theratio of watershed area to wetland area is10: 1. All storm water conveyance channelsand wetlands are protected by a permanentconservation easement under the control ofthe county commissioners.

The golf course wetland system wasdesigned to store and treat the first 50 nU11(2 in) of runoff which is recycled back ontothe course through irrigation resulting in anearly "closed" system except for very largeevents. Evaluation of the hydrologic andwater quality pet{ormance of this system isin progress. Inflow samples to each wetlandare collected for chemical determinationusing passive composite samplers installedin fain¥ay catch basins. Water level stage ismeasured in each wetland using continuouswater level data loggers. Outflow rate fromeach wetland is controlled by a small, V­notch, orifice type weir such that dischargeis relatively constant.

Storm water retention durations in thewetlands have ranged fron1 3 to 30 daysdepending on storm size and the watershedto wetland area ratio. After three growingseasons, there has been no visible adverseeffect on wetland plants from large fluc­tuations (30 to 50 cm) in water levelswithin the wetlands resulting from thelarge range in stormwater retention time.Nitrogen concentrations spiked brieflyfollowing heavy fertilization applied toestablish the fairways in 2003 which werebeing established at the same time the wet­lands were establishing (data not shown). Asa result, the inunature wetlands did not havethe capacity to assimilate the initial pulse ofN in the runoff. After the initial growingseason (establishment phase), concentrationsof the various species of Nand P have beenreduced by the six wetland cells from 16%to 56% on average (table 6). There is con­siderable variation from wetland to wetland.

Restored swamp floodplain

Outflow sampler

Constructedfloodplain valley

Outflow sampler

I '-..IL--,?" Restored swamp channel

/ Inflow sampler

Constructedheadwater natural

channel design

"' Undergrounddrainage conduit

Stormwater wetland 1Conventional

ditch

Upperproject reach

Inflow sampler

Middleprojectreach

Lowerproject reach

0.5 ha mid-reach constructed wetland

Inflow (mg L-ll 1.51 0.39 0.07 1.58 0.24 33

Outflow (mg L-ll 1.66 0.39 0.02 1.67 0.24 48

Reduction -10% 0% 71% -6% 0% -45%

Downstream 600 m restored floodplain swamp

Table 5Mean inflow and outflow concentrations in three wetland components of the Edenton Airportproject, October 1999 to January 2004 (after Evans and Smith 2004).

Upstream 300 m reach of constructed stream and associated constructed floodplain

Inflow (mg L-ll 2.87 0.37 0.08 2.94 0.40 229

Outflow (mg L-ll 1.48 0.18 0.02 1.50 0.24 42

Reduction 48% 51% 75% 49% 40% 82%

Inflow (mg L-ll 3.88 3.58 0.45 4.03 0.30 39

Outflow (mg L-ll 3.49 2.53 0.03 3.51 0.56 101

Reduction 10% 29% 93% 13% -87% -160%

Note: Reduction (%l = (inflow concentration - outflow concentration)/inflow concentration x 100.

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Figure 13Constructed stream channel with riparian floodplain immediatelyafter construction, Chowan Golf Course project.

Figure 11tConstructed stream and wetland six months after planting, ChowanGolf Course project.

Table 6Summary of mean inflow and outflow concentrations in six stormwater wetland cells on theChowan Golf Course project. Values are for calendar years 2005 and 2006.

Location TKN NH4N N0

3N/N02N TP OP

Wetland cell number 1

Inflow concentration (mg L") 3.10 0.19 0.05 1.67 1.17

Outflow concentration (mg L") 2.50 0.17 0.09 1.23 1.03

Reduction 19% 11% -80% 26% 12%

Wetland cell number 3

Inflow concentration (mg L") 3.42 0.21 0.05 1.77 1.23

Outflow concentration (mg L") 1.33 0.03 0.00 0.53 0.19

Reduction 61% 86% 100% 70% 85%

Wetland cell number 6

Inflow concentration (mg L") 2.19 0.08 0.03 2.42 1.81

Outflow concentration (mg L") 1.20 0.09 0.00 0.77 0.48

Reduction 45% -13% 100% 68% 73%

Wetland cell number 9

Inflow concentration (mg L") 3.60 0.17 0.06 1.82 1.29

Outflow concentration (mg L") 2.26 0.11 0.02 0.83 0.48

Reduction 37% 35% 67% 54% 63%

Wetland cell number 18

Inflow concentration (mg L") 3.60 0.20 0.18 2.12 1.83

Outflow concentration (mg L") 2.58 0.27 0.18 1.13 0.87

Reduction 28% -35% 0% 47% 52%

Wetland cell number 19

Inflow concentration (mg L") 2.91 0.12 0.05 1.73 1.19

Outflow concentration (mg L") 2.62 0.14 0.02 1.01 0.70

Reduction 10% -17% 60% 42% 41%

Mean six wetland cells

Inflow concentration (mg L") 3.14 0.16 0.07 1.92 1.42

Outflow concentration (mg L") 2.08 0.14 0.05 0.92 0.63

Reduction 34% 16% 26% 52% 56%

Note: Reduction (%) = (inflow concentration - outflow concentration)/inflow concentration x 100.

This is due in part to differences in water­shed to wetland area ratio, which has not yetbeen accounted for in table 6. Wetlands 18and 19 also have more open water which hasattracted geese, which could be an additionalsource of N which is not accounted for inthe inflow measuren'lents.

Core Creek ProjectThe Core Creek project consisted of relo­cation of an unnamed channelized streamwithin the Core Creek watershed that hadbeen significantly impacted by cattle access(figure 15). The degraded stream was a G5class (Rosgen classification system) channel­ized stream with severe bank erosion anddegraded water quality. Prior to construc­tion, background monitoring showed therewas no significant difference in upstream anddownstream N concentrations (upstreamand downstream of the planned constructionreach) (table 7). Phosphorus concentrationsand fecal coliform levels downstream weresignificantly higher than upstream. Macro­invertebrate sampling indicated that thequality of the stream was severely stressed(Smeltz 2004).

A new channel was designed using a com­bination of analog, empirical, and analyticaldesign techniques (USACE 1995; Shieldset al. 2003). The relocated E5 channel wasconstructed using priority II methodologyin March of 2005. The constructed streamconsisted of a uniform dimensional sec­tion, meandering pattern, and 0.1% slope(figure 16).A 30 to 40 m (100 to 130 ft) wide

I JULY IAUGUST 2007 VOLUME 62, NUMBER 4 ~

Figure 15Cattle in Core Creek tributary stream prior to restoration.

Table 7Nutrient and suspended sedimentconcentrations in stream flow prior tocattle exclusions, Core Creek project.

Downstreamof pasture

Upstreamof pastureNutrient

Summary and ConclusionsPilot studies were demonstrated and evalu­ated to investigate alternative channel designgeometries and management strategies toencourage water quality and ecologicalfunctions while maintaining the neces­sary drainage function. Channel alterna­tives included establishment of in-streamwetlands, lowering of the floodplain toreconnect the channel with the floodplain,redesign of channels using natural channeldesign principles to reconnect the channelwith the natural floodplain, and· establish­ment of conservation easements to eliminatetraditional ditch bank mowing to encourageestablishment of perennial riparian vegeta­tion. Results to date indicate that alternativesexist that can be used to address drainage,water quality and ecological functions moreeffectively than have been achieved in thepast with conventional trapezoidal drain­age canals. Of course, all of the alternativesevaluated are more costly than conventionaldrainage canals required to achieve just the

Total N (mg L-l) 2.45 2.45

N03-N (mg L-l) 0.33 0.32

NH.-N (mg L-1) 0.33 0.65

Total P (mg L-l) 0.38 0.50

Ortho-P (mg L-l) 0.11 0.25

TSS (mg L-l) 96.9 46.3

Note: Data from Smeltz (2004).

designed to meet expected channel hydrau­lics and regional geomorphology (Lindow etal. 2007). Bank mass wasting and slumpingoccurred during and inunediately followingconstruction. This was due to soil instabil­ity caused by a pressurized sand layer at theconstructed streambed elevation. This areastabilized as soon as bank vegetation becameestablished. Water quality monitoring andevaluation S111ce construction IS ongo­ing. Initial macro-invertebrate monitoringindicates improvement in aquatic habitatcompared to the original channel.The streamand associated floodplain appear to be stableand have the capacity to transmit greaterflood volumes than the original trapezoidalchannel without a floodplain (Lindow et al.2007).

(figure 17). Log vanes were used to holdgrade and root wads to armor banks. Flowhydraulics and design structures controlledrime/pool formation (figure 18).

Since construction, periodic cross sectionmeasurements indicate the re-located streamdimension, pattern, and profile were well

stream valley was constrllcted by stockpiling150 nun (6 in) of topsoil then removing 0.5to 0.6 m (1.5 to 2 ft) of subsoil. The top­soil was then redistributed across the valleyfollowed by construction of a 3.5 m (topwidth) by 0.5 m (depth) (14 ft by 1.5 ft)E5 channel with an average sinuosity of 1.3

Figure 16Schematic of Core Creek natural channel design.

318 JOURNAL OF SOIL AND WATER CONSERVATION

Figure 17Core Creek relocated stream just after construction.

Figure 18Core Creek relocated stream one year after construction.

drainage function. A conventional trapezoi­dal channel of comparable flow capacity(2 to 2.5 m 2 cross sectional area by 1.5 mdeep [80 ft2 by 5 ftJ) would costs about $35/linear meter ($1 a/linear ft) based on an earth­moving rate of $4/m3 ($3/yd3

). The projectcosts in these studies ranged from a low ofabout $7/linear m ($2/linear ft) for wetland

planting in the existing canal (Tull Creekproject), $130 to 200/linear m ($40 to 60/linear ft) of channel for weirs, channel exca­vation, and planting of in-stream wetlands(Edenton, Guinea Mill, and Newland Ditchin-stream. projects), to over $450/linear m($140/linear ft) of channel where flood­plain construction was also required (Core

Creek project). Increased costs were associ­ated with the initial costs of additional earthwork required to either widen channels orcreate artificial floodplains and the largerland areas being taken out of production.These projects accon'lplish the first step inthe evaluation process which is to demon­strate technical feasibility. The added costs arenot justified by increased drainage benefits tothe landowner.Therefore, it becomes incum­bent on society to put a value on the waterquality and ecological functions achieved todetermine if public funds should be used tohelp landowners offset the costs of achievingthe additional water quality and ecologicalfunctions.

AcknowledgementsThe projects discussed herein were supported by a com­

bination of grams from the North Carolina Clean Water

Management Trust Fund, North Carolina Department of

Environment and Natural Resources 319(h) Program, North

Carolina Agricultural Cost Share Program, North Carolina

Conservation Reserve and Enhancement Program, and

USDA farm bill along with local government and landownerin-kind contributions.

Portions of this work were presented and printed in the

Proceedings of the Alnerican Society of Agricultural

and Biological Engineers Specialty Conference "Self­

Sustaining Solutions for Streams, Wetlands, and Watersheds,"

Sr. Paul, Minnesota, 2004, and in the Proceedings of rhe

19th International Congress on Irrigation and Drainage,

"Improving Water and Land Management for Increasing

Efficiency in Irrigated Agriculture," Beijing, China, 2005.

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