US Army Corps of Engineers Hydrologic Engineering Center

Spatial Data Analysis of Nonstructural Measures August 1976 Approved for Public Release. Distribution Unlimited. TP-46

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4. TITLE AND SUBTITLE Spatial Data Analysis of Nonstructural Measures

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6. AUTHOR(S) Robert P. Webb, Michael W. Burnham

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7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) US Army Corps of Engineers Institute for Water Resources Hydrologic Engineering Center (HEC) 609 Second Street Davis, CA 95616-4687

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12. DISTRIBUTION / AVAILABILITY STATEMENT Approved for public release; distribution is unlimited. 13. SUPPLEMENTARY NOTES Presented at an ASCE conference, "River 76", Fort Collins, Colorado, July 1976. 14. ABSTRACT Consistent and expedient evaluations of nonstructural flood loss reduction measures for existing and alternative future land use patterns can be performed using spatial analysis concepts. The techniques developed center about the processing of spatial geographic data into a grid cell data bank and the subsequent accessing and manipulation of pertinent data variables by a computer program. The results are an automatically constructed elevation-damage function at damage reach index locations for selected land use patterns. The modification of the damage function resulting from specific nonstructural alternatives may be performed by inputting into the computer programs a target protection level or a specified stage of protection for selected land use categories. These functions may be analyzed conventionally by damage frequency integration methods or used as input into more complex system models. 15. SUBJECT TERMS spatial analysis methods, nonstructural flood loss reduction measures, geographic data variables, damage reaches, reference floods, composite damage reaches, flood proofing, permanent evacuation, flood warning, regulatory policies 16. SECURITY CLASSIFICATION OF: 19a. NAME OF RESPONSIBLE PERSON a. REPORT U

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Spatial Data Analysis for Nonstructural Measures

August 1976 US Army Corps of Engineers Institute for Water Resources Hydrologic Engineering Center 609 Second Street Davis, CA 95616 (530) 756-1104 (530) 756-8250 FAX www.hec.usace.army.mil TP-46

Papers in this series have resulted from technical activities of the Hydrologic Engineering Center. Versions of some of these have been published in technical journals or in conference proceedings. The purpose of this series is to make the information available for use in the Center's training program and for distribution with the Corps of Engineers. The findings in this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents. The contents of this report are not to be used for advertising, publication, or promotional purposes. Citation of trade names does not constitute an official endorsement or approval of the use of such commercial products.

SPATIAL DATA ANALYSIS OF NONSTRUCTURAL MEASURES

R. P. ebb,' and M. W. urnh ham,' A.M., ASCE

ABSTRACT

Consistent and expedient evaluations of nonstructural flood loss reduction measures for existing and alternative future land use patterns can be performed using spatial analysis concepts. The techniques developed center about the processing of spatial geographic data into a grid cell data bank and the sub- sequent accessing and manipulation of pertinent data variables by a computer program. The results are an automatical ly constructed el evation-damage function at damage reach index locations for selected land use patterns. The modification of the damage function resulting from specific nonstructural a1 ternatives may be performed by inputting into the computer program a target protection level or a specified stage of protection for selected land use categories. These functions may be analyzed conventional ly by damage frequency integration methods or used as input into more complex system models.

INTRODUCTION

Water resource planners are charged in the plan formulation process to evaluate a broad range of alternative flood loss management measures that will provide flood damage reduction for existing and alternative future land use conditions. The plan formulation process is comprised of developing a1 ternative means for accomplishing performance targets and selecting from those alternatives the ones which are the most attractive. One criteria of an attractive alternative is the minimization of environmental impact which has resulted in an increased emphasis in the evaluation of nonstructural a1 ternatives. Even with this increased emphasis on 1 ess construction intensive measures which are less disruptive to the environment, there con- tinues to be a need for the systematic assessment of the economic value of the proposed alternatives. It is desirable that alternatives be compared quickly, with the comparisons based on a consistent methodology,

Spatial analysis methods can provide the mechanism for expedient and consistent economic evaluation of alternative flood loss management measures. The methods used include the evaluation of geographic information which has been digitized and stored in computer files in digital form. Each geographic data variable is encoded separately and a registered grid cell representation of each data variable is stored in a sequential grid cell record on a computer file which then represents the data bank.

'planning Analysis Branch, Corps of Engineers Hydrol ogic Engineering Center, Davis ,Ca,

Technology has been developed and applied by Corps of Engineers, Hydrologic Engineering Center, which accesses geographic information stored i n a g r i d ce l l data bank for an integrated evaluation of flood hazard potential , flood damage and environmental e f fec ts of 1 ) existing land use condition, 2 ) a1 ternat ive future land use conditions and 3) specific land devel opment proposals . A powerful analytical capabi 1 i t y i n the spat ial flood damage analysis is the a b i l i t y t o evaluate the nonstructural a1 ternatives of 1 ) flood plain management pol i c i e s , 2 ) flood proofing al ternat ives which may include rais ing s tructures , ring levees or the addition of flood proofing materials t o s t ructures , 3) permanent evacuation of structures i n the flood plain 4 ) temporary s tructural protection and content removal i n response t o flood warning disseminations, and 5) combinations of the above. These a1 ternatives may be evaluated i n terms of providing a ta rge t protection level (such as protection from the 100-year frequency flood) or a s providing uniform land use category protection (for instance flood proofing industrial structures four f e e t above ground elevation).

The eographic data variables tha t a re used t o perform the analysis are: 1 7 topographic elevation, 2) reference flood elevations, 3) damage reach delineations, 4 ) existing land use c lass i f ica t ion , and 5) a1 t e r - native future land use patterns. The output for each spat ial flood damage analysis is an aggregated elevation-damage function fo r each land use category a t each damage reach index location. These functions may subsequently be analyzed conventional ly by damage frequency integration methods o r used as i n p u t in to more complex system formulation models.

The objective of the nonstructural evaluation procedures developed and presented herein is the systematic and consistent development and modifi- cation of elevation-damaqe relationships corresponding t o specif ic non- s t ructural flood loss reduction measures. The procedures described i ncl ude the automatic generation of the damage functions fo r selected land use patterns by processing selected spat ial gridded data variables, and the modification of these damage functions fo r specified nonstructural a l ternat ives based on uniform structural protection c r i t e r i a o r a prescribed level of protection. These concepts were appl ied for the Trail Creek watershed located near Athens i n northeast Georgia.

DAMAGE FUNCTION DEVELOPMENT

General Approach.--Methods of computing the flood damage potential of a stream reach requires the development of elevation-damage functions a t selected damage reach index locations throughout the system. The elevation- damage functions a re then integrated w i t h hydrologic flow-frequency and flow-elevation data t o compute the expected value of annual damages. Damage reaches a re defined t o a1 1 ow capturing economic and hydrologic variation tha t occur i n the reach, E l evati on-damage re1 ations h i p s a re developed fo r individual s tructures and the associated value of the contents. The s tructure functions a r e aggregated t o an index location and adjusted t o account for the slope of water surface profi les t h r ~ ~ g h o ~ t the damage reach,

The technique developed fo r automat ica l ly generating elevation-damage funct ions adapts t h i s t r a d i t i o n a l method t o the g r i d c e l l data bank concept. The methodology consists of const ruct ing a unique e l evation-damage r e l a t i o n s h i p f o r each g r i d c e l l w i t h i n the f lood p l a i n (based on topagraphic ground e le - vat ion, land use, and composite damage func t ion assigned t o the g r i d c e l l ) and aggregating a11 the g r i d c e l l s assigned t o a p a r t i c u l a r damage reach t o the appropr iate index locat ion, using a reference f l ood as the mechanism f o r ad jus t ing fo r a s lop ing water surface p r o f i l e .

Damage Reaches. --Damage reach boundaries are selected based on the t r a d i t i o n a l procedure t h a t inc ludes determining reaches w i t h cons is tent p a r a l l e l water surface p r o f i l e s f o r a range o f discharges wh i le maintain ing the economic d e t a i l desired f o r analysis. The boundaries extend t o a reason- ab le l a t e r a l d istance from the stream t o the f looded area o f the l a rges t f l o o d event determined necessary f o r economic-damage evaluations, p lus an a r b i t r a r y v e r t i c a l d istance (say 5 f ee t ) . Fig. 1 Damage Reach Del ineat ion i l l u s t r a t e s a t y p i c a l damage reach de l ineat ion. The damage reaches a re encoded and pro- cessed i n t o the g r i d c e l l data bank w i t h each c e l l w i t h i n a reach assigned the reach i d e n t i f i c a t i o n value. The damage reach i d e n t i f i c a t i o n i s used t o aggregate g r i d c e l l s t o the appropr iate damage reach index locat ion.

Reference Flood. --Since f l ood p r o f i 1 es r e s u l t i n d i f f e r e n t water surface e levat ions throughout a damage reach, a reference f l ood i s requ i red t o proper ly ad jus t the e levat ion f o r aggregation purposes o f each c e l l w i t h i n the reach w i t h respect t o the index locat ion. Each c e l l i s assigned a reference f l ood water surface e leva t ion which i s used w i t h the reference f l ood e levat ion a t the index l oca t i on t o ad jus t the composite damage funct ion fo r proper aggregation o f damages a t the index locat ion.

The reference f l ood should be an event w i t h i n the range which i s c r i t i c a l f o r f l ood damage computation, a mid-range f l ood (say 25 t o 50 year) i s a b e t t e r choice than a r a r e f l ood such as a 500-year exceedance i n t e r v a l event. If the f l ow p r o f i l e s are cons is ten t l y p a r a l l e l throughout the po ten t i a l damage range, the se lec t ion o f the reference f l ood i s less c r i t i c a l . The reference f l ood elevat ions should be determined from de ta i 1 ed water surface prof i 1 e analysis. If water surface p r o f i l e s are no t ava i lab le , the slope of the f l ood p r o f i l e through a damage reach may be assumed t o correspond t o the slope o f the thalweg o f the main stream o r the slope o f the adjacent f lood p l a i n i t s e l f . F ig. 2 Reference Flood Concepts i l l u s t r a t e s the adjustments performed using the reference f l ood .

Composite Damage Functions.--The general ob jec t i ve o f the a n a l y t i c a l methods developed are t o provide a cons is tent and expedient methodolosv .,- o f evaluat ing a range o f nonst ructura l a l t e rna t i ves f o r e x i s t i n g and selected a l t e r n a t i v e f u t u r e land use pat terns. The concept o f using gen- e ra l i zed composite stage-damage re1 a t ions hips f o r the 1 and use category assigned t o each g r i d c e l l was selected as the mechanism t o perform the analys is r a the r than the conventional i nd i v i dua l s t r uc tu re approach. The use o f these general i zed funct ions provides the capabi 1 i ty of expedient ly eva luat ing a l t e r n a t i v e land use 'pat terns t h a t a re cons is tent w i t h the e x i s t i n g (base) cond i t i on land use pat tern .

WATER SURFACE PROFILES

I -- - - -- - / + - _ _ _ C - L - - - A - _ - . -

rc c-

c-

..,p e-\r /

- f l

Channel Inver t Elevat ion

DAMAGE REACH DELINEATION

Hydrologic Hydro1 ogic Hydro1 ogic R o u t i n g Routing Routing

Reach Reach Reach

Damage Reach Boundary --- Damage Reach Index ~ ~ c a t i o n @

FIG. 1 . --Damage Reach Del i nea ti on

WATER SURFACE PROF I LES 7-

REFERENCE FLOOD BOUNDARIES

Reference Flood Elevations \

# Structure Locations

Index locat ion = 614.5 @ Index Location

---- Boundary o f Reference Flood

Damage Functions a t A must be adjusted by adding 4.5 feet (614.5-610.0) before aggregating t o the i ndex 1 ocation.

Damage Functions a t B must be adjusted by subtracting 2.5 fee t (614.5-617.0) before aggregating t o the index location.

FIG. 2. --Reference Flood Concepts

A composite damage function i s defined as a stage-damage function fo r a u n i t area for each land use category tha t has significant damage potential . These functions may be developed for each land use category by averaging the structural and related content values obtained from samp7ing a range of s t ructure values and types within each land use category by use of f i e l d surveys, review of tax records and interviews conducted w i t h regional and local agencies. The composite damage function may include d i rec t and i n - d i rec t damages tha t a re associated w i t h each particular land use category. Table l Composa"te Damage Function for Low Density Residential Land Use Category i l l ustrates an example of a composi t e stage-damage function of a land use category. These functions can be developed For other land use categories such as pasture and developed open space although the corres- ponding damages would probably be small compared t o those occurring in the structural 1y developed areas.

Aggregate Damage Function. --The flood damage associated with each grid ce l l i s determined by matching the land use for each grid ce l l w i t h the appropriate composi<e damage function ( i n effect placement of the function on the elevation assigned t o the cel l ) . The individual ce l l el evation-damage functions a re then aggregated t o the index location by use of the mechanism of the reference flood. A schematic s f t h i s procedure is shown i n Fig. 3 Damage Function Development. The computer program tha t performs the aggre- gation may also be used in the development of the composite damage functions. To ctcvelop the composite stage-damage function for a specif ic land use category, the fol lowing types of information are used.

e stage vs % damage for s t ructure o stage vs % damage for contents

a value of s t ructure

values of contents (option, % of s t ructure value) o indirect damage (dol lar amount o r % structure and contents)

development density (number of s t ructure per grid c e l l ) s vacancy allowance (amount of land c lass i f ied i n the part icular

category tha t is developed)

The data i s prepared by land use category and the program accesses the g r i d data f i l e and computes elevation-damage relat ions for a1 1 pertinent land use categories and damage reaches. Table 2 Aw-eqate Damage Functions contains an example elevation-damage tabulation for selected land use categories of a typical damage reach index location.

Once the damage function is developed for the land use pattern of in teres t (base condition) the function can be adjusted t o r e f l e c t each specified nonstructural measure (with condition) and corresponding per- formance c r i t e r i a tha t a re o f in teres t i n plan formulation. The cap- a b i l i t y t o automatically adjust these functions i s provided by the computer program tha t 5s used t o develop the aggregated damage functions.

TABLE 7

COMPOSITE DAMAGE FUNCTION FOR LOW DENSITY RESIDENTIAL

LAND USE CATEGORY (1 )

*****k*******k****A**********&*k***k*~**************

* D E P T H * PER C c n T * P E R C ~ Y T .r. Atrl'lUrjT OF* D A ~ I A C ; ~ , * * flF * D A L r A G k * Q A M A G E k PEH G R I D Ck1.C * * W A T L R * S T H ! I L T C J Q L : ~ CUhlTEf.rTS rIlv ~".tu5Awn Dll l .LAkY* * * * * * t * k * * * * R * * * * * * * * * k k * * * * * k k k * * * * * * * * e * * * * * * & * * * * * * * * * * * * * * %4

* 1 2 0 0 0 * l r O O * 0.00 * r 12 JI k * * * It

* e i D a O * 1 , 0 f l * O , O O * @ 12 * * * * * * * O s O O * 1 0 o O D * ~ , O U * 1 0 2 4 * * * * * * * l,no * 13 .00 * 3 ~ ~ 0 0 * 3, O R * * * * * * * 2,oo * Z O , O O * 54,00 * 4.90 $I * * 6 * * * 3 . 0 0 * 27,00 * 65,00 * b e d 7 * * * * * * * Y e 0 0 * 3 0 e O o * 73,OO * 9 95 & * * * * * * 5 ,QO * 3 3 . 0 0 R 77,QQ * 7948 * * * * * * * 6,QQ * 3S.00 * 60,08 * 7 r 8 5 rt R k * * * * 7 , O O * 35,OO * 01,OQ * @ , O 1 $I * Jr * * * * ' 9 0 0 0 * 4O,QO * 81.00 * 8.45 Jr * I * tr *

m O a O O * 4ieO0 * B I 0 0 0 * 8.57 k * * * * * * I O O O O * 41.00 * el,no * t l rs7 * * * * * X

* l l r O O * 45,86 * 8 1 s 0 0 * Y e O ! * Ir * * * * * i t ? a O Q * 4S,00 * B f , O O * YeOi * * * * * * ****************************************************

DENSITY nF THE LANU USE UklXTS PER G R I D CkLL 8 l e O O

BASE VALUE OF THE S T R U C ~ U R E s 185~0,00

B A S E VALUE PF THE CUNTENTS z 8E?SOoO0

DATA REQUlRED

Typical Grid Ceii

index Location for

Grid representation o f 1 and use (exhaustive f a r study area) . 1

I

/ 321.6/ Grid representat ion of topo- I I graphy (elevations).

/ 325.0/ Grid representation of reference I flood (water surface elevation i I

a t reference flood) for each grid I c e l l . 1 / 12A / Grid representation of Damage

I , Reach Boundary.

/ Composite s tage-damage functions for each s igni f icant land use.

INDEX LOCATION DAMAGE FUNCTION CONSTRUCTION

STEP 1 , Develop Elevation -damage Function at Each Cell

a. Determine land use from grid f i l e b . Retrieve appropriate composite stage damage function c . Determine grid elevation of ce l l from grid f i l e d. Tabulate elevation-damage for ce l l from above

STEP 2, Aggregate Cells to Index Location

a. Determine ce l l damage reach assignment b . Determine index location reference flood elevation (XI) c . Determine cel l reference flood elevation (X2) d. A d j u s t ce l l elevation-damage function by (X2-XI) e. Aggregate ce l l adjusted elevation-damage function a t index s ta t ion f . Repeat for a1 1 grid cells

FIG. 3.--Damage Function Development (1).

TABLE 2

AGGREGATE DAMAGE FUNCTIONS (1) (1 000 ' s o f Do1 1 ars)

1 Land Use Categories Are:

El ev . 640.0 645.0 650.0 651.0 652.0 653.0 654.0 655.0 656.0 657.0 658.0 659.0 660.0 661.0 662.0 663.0 664.0 665.0

1 = Natural vegetat ion 7 = I n d u s t r i a l 6 = Ag r i cu l t u ra l 9 = Pasture

Exist . Land Use 1

1 6 7 9 Tota l I 0.0 0.0 0.0 0.0 0.0 0.5 0.1 0.0 0.0 0.6 1.2 0.4 0.0 0.0 1.6 1.4 0.4 0.0 0.1 1.9 1.5 0.4 0.0 0.1 1 - 9 1.6 0.4 0.0 0.1 2.1 1.9 0.4 0.0 0.1 2.4 2.4 0.4 0.0 0.1 2.9 2.8 0.4 1.2 0.2 4.6 3.1 0.4 1.2 0.2 4.9 3.2 0.4 20.4 0.2 24.2 3.4 0.4 86.1 0.2 90.1 3.7 0.4 175.9 0.3 i m . 3 4.0 0.4 267.5 0.3 272.2 4.2 0.4 325.1 0.4 330.1 4.4 0.4 372.2 0.4 377.4 4.5 0.5 410.6 0.4 416.0 4.6 0.5 442.8 0,5 448.3

EVALUATION OF NONSTRUCTURAL MEASURES

General Approach.--The evaluat ion of the f lood damage po ten t i a l of a stream reach f o r e x i s t i n g (o r base) condi t ions and w i t h the assumed imple- mentation of' proposed f lood loss reduct ion measures i s an i n t e g r a l p a r t o f the p lan formulat ion process. The general procedure used t o perform these analyses i s the computation o f "expected" annual damages o f the system f o r the w i t h and wi thout cond i t i on o f each a1 t e rna t i ve t o ob ta in the average annual benef i ts associated w i t h each plan. The bene f i t s are the "expected" annual damage for the base (wi thout ) cond i t i on 1 ess the "expected" annual damage associated w i t h the a l t e r n a t i v e (wi th) condi t ion. The hydrologic information of f low r a t i n g curves (discharge vs. e levat ion) and flow-fre- quency re la t ionsh ips a re combined w i t h the elevation-damage funct ion t o y i e l d a damage-frequency curve f o r the cond i t i on analyzed. The damage- frequency func t ion i s then in tegrated t o compute the "expected" annual damage of the cond i t i on o r a1 t e rna t i ve evaluated.

The imp1 enicntation of nonstructural flood 1 oss reduction measures typically modify the elevation-damage function of the damage reach and have 1 i t t l e effect on the hydrologic response of the system ( 2 ) . The computer program used t o construct elevation-damage functions a t damage reach index locations for existing o r alternative future land use patterns i s also used in developing these functions for modified conditions. The types of nonstructural a1 ternatives for which elevation-damage functions may be constructed by the automatic spatial analysis method are: 1 ) flood proofing specified land use categories a desired number of feet above or below the ground floor level, 2 ) flood proofing specified land use cate- gories w i t h i n a damage reach $0 a unlfsrm flood pro tee t ion l eve l , 3) temporary protection of structures and evacuation of contents for damage reaches i n response t o a flood warning dissemination, 4) permanent relo- cation of structures from flood prone areas, and 5) regulatory policies restricting development i n the flood plain. Each of these nonstructural a1 ternatives are evaluated by modifying either the appropriate 1 and use category composite stage .. damage function and/or the el evatt on-damage function of the grid cells which are t o be aggregated to a specified damage index 1 ocation,

Flood Proofing Land Uses t o a Specified Stage.--The flood proofing of selected land use categories t o a specified stage results in a11 grid cells of the land use category being protected t o a designated non-damage stage. The assessment of the potential flood damage reduction resulting from uniform flood proofing of specified land use categories i s accomplished either by directly modifying the inputted composite stage-damage function or by automatically truncating the composite stage-damage function a t the appropriate stage. Fig. 4 Flood Proofing Land Uses t o a Specified Stage schematically i l lustrates and describes the method used to perform the analysis. The evaluation of existing and alternative future land use patterns for the without condition requires t h a t the nonmodified composite damage function be used t o construct the el evation-damage relationship for each cell. When the with condition i s analyzed, a11 of the grid cells of land uses categories that are to be flood proofed use the modified composite damage function to construct the elevation-damage function. To i l lustrate the evaluation of flood proofing only future development, the grid cell in Fig. 4 t h a t i s classified as land use 6 i s converted t o land use 1. In the aggregation process, the base condition composite damage function would be used for the four original grid cells and the modified composite damage function would be used for the converted grid cell . I t i s possible in a single computer run to uniformly flood proof as many land use categories as desired and each land use category may have i t s own unique flood proofing level.

Flood Proofing t o Set ected Protection Levels, -bFl ood proofing specified land uses t o a selected protection level within a damaqe reach requires the computation of the depth of flooding resulting from the protection level event for each g r i d cell and i f a cell i s flooded, i t i s flood proofed t o that elevation. As an example, flood proofing a damage reach t o a 58-year frequency protection level may require some g r i d cells ~f a

- =.- / @ index

location

6' ' k Damage Reach Boundary

NOTE: Only selected q r i d ce l ls are shown for c lar i ty b u t i n application the grid cel ls are exhausite for the entire damage reach.

COMPOSITE DAMA~~FUIJCTIONS . (Land Use Category

$ Damage

I,' I

$ Damage Base Condition Modified Condition

GENERAL PROCEDURE --

1. The composite damage functions of a l l grid ce l l s assigned land use category 1 are truncated to the specified protection level. The process i s repeated for other flood proofed land use categories usina thei r modified composite damage functions.

2. An elevation-damage curve i s developed for each g r i d cel l (composite damage function plus assigned top0 elevation) i n the damage reach.

3. The elevation-damage curves are adjusted by the reference flood elevation of the g r i d cell and index location and aggregated to the index 1 ocation t o generate the total el evation-damage re1 ationship for the damage reach .

FIG. 4.--Flood Proofing Selected Land Use Categories to a Specified Stage

given land use t o be protected 5.3 feet , while others may only need the basements flood proofed or no protection. The reason for the difference i n flood proofing depths i s because of varying ground topography as i l lus - trated i n Fig. 5, Example Cross Section.

The construction of the elevation-damage functions for th is alternative can be performed only a f te r flow and rating curve data are available for each index location of interest. From the rating curve the elevation of the water surface a t the index location which corresponds to the desired protection level i s determined and inputted into the computer program. The corresponding elevation of the protection event is then computed for each grid cell by use of the reference flood, since the water surface elevation a t the cel l changes consistently w i t h the change i n water surface elevation a t the index location. The designated g r i d ce l ls are corres- pondingly flood proofed to protect against the specified flood event.

0 Denotes Depth of Flood Proofing Required

1 Indicates Low Density Housing Land Use

4 Indicates Water Bodies Land Use

Fig. 5--Example Cross Section (From A t o 8)

These detai 1 ed computations are performed as fol l ows : The reference flood elevation i s substracted from the target protection elevation a t the index location, and then th is difference i s added to the reference flood elevation of the g r i d ce l l . This elevation then represents the computed protection level water surface elevation. The amount of pro- tection required by the cell i s the protection level elevation less the topography elevation. If the g r i d cell requires flood protection, the program truncates the elevation-damage curve a t the protection level elevation. This process i s repeated for each g r i d cell assigned t o the damage reach. F ig . 6 Grid Cell Damage Functions i l lus t ra tes an example of a g r i d cell which has a reference flood elevation of 424.5 feet and a topographic elevation of 420.0 feet. The damage reach index location has a reference flood water surface elevation of 427.0 feet and the target protection level is 425.5 feet. The difference i n water surface elevations a t the index location is a minus 1.5 feet (425.5-427.0). This difference is added t o the reference flood elevation of the grid cel l to compute the corresponding target protection elevation (424.5-1.5 = 423.0 feet) for the cel l . The resulting truncated elevation damage curve i s then aggregated to the index location i n the usual manner. The alternative of the flood proofing land use categories w i t h i n a damage reach t o various frequency flood events may be done for 1 ) existing con- ditions, 2) alternative land use conditions, and 3) alternative future land use conditions with only the future development flood proofed.

Response to Flood Warning Dissemination.--The temporary evacuation of facTl i t i e s w i t h i n a damage reach i s a component of the implementation of a flood warning system i n conjunction w i t h the people reacting t o the flood warning. T h i s type of a1 ternative i s d i f f i cu l t - t o evaluate, not because of theory, b u t because i t requires the estimation of the effect of the flood warning system on the stage-damage functions for each land use category as temporary protection measures are implemented. To evaluate th is a1 ternative, the inputted stage-damage functions are modifled for each damageable land use category that will be affected. This modifi- cation i n the stage-damage functions should include damage reduction to both the contents and the structure.

Since i t i s d i f f i cu l t to accurately estimate these damage reductions, several runs could be made for a range of percent damage reduction to calculate the break p o i n t necessary for th i s alternative to be cost effective, and then evaluate whether or not the level of damage reduction can be reasonably achieved. Because the eval uation of th is a1 ternative flood loss management measure i s done by direct ly modifying the composite stage-damage functions of the affected land use categories prior to the aggregation of the damage potential of a g r i d cel l t o the appropriate index location, flood warning may be evaluated as an alternative by i t s e l f or as an alternative i n combination with any of the other nonstructural a1 ternatives,

Permanent Evacuation of a Flood Plain.--The evaluation of permanent evacuation of the flood plain requires that the spatial location of the f l ood plain be defined and a l l specified land uses be removed from t h a t

$ Damages

A ) Land Use Composite Stage-Damage Function

$ Damages

C ) E l evation-Damage Function with Reference Flood and Target Protection Elevations

418 !-- $ Damages

B ) Elevation-Damage Function of the Grid Cell

$ Damages

D ) Truncated El evati on-Damage Function for the Grid Cell

Fig. 6 . Grid Cell Damage Functions

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Flood Plain Regulation.--Flood plain regulation is the zoning of the flood plain to r e s t r i c t encroachment by major damageable land uses, hope- fu l ly resulting i n minimizing future damages. T h i s usually means tha t i f a damageable land use i s placed within the flood plain, f i l l o r some other means must be used t o ra ise the ground f loor elevation above the flood plain elevation. I t i s , therefore, desirable to evaluate the effect flood plain regulation has on potential flood damage reduction. The effectiveness of flood plain regulation in reducing potential damage i s determined by con- s t ruct ing an aggregate elevation-damage curve for each index location for the future land use pattern, and then reconstructing the aggregate elevation- damage curves again, b u t w i t h the regulatory policy i n e f fec t . 'These aggregate elevation-damage curves are then used as the basis t o make the comparisons.

To subject a land use pattern t o flood plain regulation, the analysis makes use of the reference flood t o determine the flood plain of in teres t . The elevation of the regulatory flood a t the index location is determined similar t o tha t for flood proofing damage reaches to a uniform protection level. If the computed regulatory flood event water surface elevation i s higher than the topography elevation of the grid c e l l , the elevation damage function for the grid cel l i s elevated so tha t the ground f loor i s the same as the event water surface elevation.

The corresponding change i n the elevation damage function i s shown i n F i g . 8 Grid Cell Elevation-Damage Function Adjustment f o r Flood Plain Regulation, based on the grid ce l l example used in Fig. 6. For a regulatory elevation of 423.0 f e e t , the elevation-damage function must be raised 3 f ee t t o r e f l ec t the placement of the ground f loor above the regulated flood plain.

Ref. Flood Elev. Ref. Flood Elev.

- - Flood Plain Elev. Flood Plain and Modified Ground Floor Elev.

- - - Original Ground F1 oor 420 -- 419 -- 41 8

$ Damage $ Damage

A ) Elevation-Damage Function B ) Elevation-Damage Function After Before Flood Plain Regulation Flood Plain Regulation

Fig.. 8. Grid Cell Elevation - Damage Function Adjustment f o r Flood Plain Regul a t i on.

- 7

Even though a g r i d ce l l may have i t s ground f loor moved above a flood plain, i t could incur damages from tha t flood plain event. To accommodate t h i s , the program has the capabili ty to place e i ther the ground f loor ele- vation or the zero-damage elevation above the flood plain elevation. Table 3 Expected Annual Damages shows an example from t h e Trail Creek data i n which a comparison of expected annual damages i s made for a 1990 al ternat ive future land use pattern with 1 ) no flood plain regulation, 2 ) flood plain regulation i n which the new development i s required t o place the ground f loor above the 100-year flood plain, and 3) flood plain regulation i n which the new develop- ment i s required t o place the zero-damage elevation above the 100-year flood plain. Results such as those shown i n the table may be very helpful i n persuading !and use planners to be aware of the consequences of taking an inactive ro le i n the regulation of the flood plain.

Theeva1uat;ionof flood plain regulation i s not res t r ic ted t o the 100-year flood plain, and i t may be an a l te rna t ive evaluated singularly or i n combi- nation w i t h other flood proofing al ternat ives. An example of a combination of these al ternat ives might be t o place the structures above the 75-year flood plain and uniformly flood proof t o the 100-year flood frequency event.

TABLE 3 AVERAGE ANNUAL DAMAGES

(1000's of Dollars)

REACH 2

2.5

350.0

63.8

6.7

EVALUATION CONDITION

Existing Land Use

1990 Land Use Without pol icy

1990 Land Use W i t h policy of Ground Floor

199C Land Use With policy o f Zero Damage

REACH 3

- .

12.0

32.7

23.8

3.0

REACH 1

1.5

1033.3

79.3

9.2

I

SUMMARY

Spatial analys is techniques make i t possible t o rapidly and cons i s ten t ly evaluate 1) t he flood damage potent ia l of ex i s t ing and a l t e r n a t i v e fu tu r e land use condit ions and 2 ) the potent ia l flood damage reduction resu l t ing from various nonstructural measures. The nonstructural measures t h a t may be evaluated individually o r i n combination by this technology a r e shown i n Table 4 Evaluation of Nonstructural Alternatives by Spatial Analysis Methods.

TABLE 4

EVALUATION OF NONSTRUCTURAL ALTERNATIVES BY SPATIAL ANALYSIS METHODS

Land Use Pattern Nuns t ruc tura l A1 t e rna t i ve A1 t e rn . Future A1 te rna t ive Exist ing Future New Dev. Only

Do Nothing (Without Condition)

Uniform Flood Proofing of a Land Use

Uni form Fl ood Protection of a Damage Reach

Temporary Evacuation

*Permanent Evacuation

*Flood Pla in Regulation

X indicates analyt ical capab i l i ty

*Evaluations may be rnade f o r s t r uc tu r e s i n the flood plain and f o r s t r uc tu r e s which have t h e i r zero damage e levat ion i n the flood plain.

The technology described has potential to be helpful in the consistent and rapid evaluation of structural and nonstructural flood damaqe reduction a1 ternatives for 1 ) existing land use pattern 2) a1 ternative future land use patterns and 3) specific development proposals. This technology is in the development stage and will be undergoing further testing. The Corp of Engineers is currently making test applications of this technology in the Savannah, St. Louis, and Ft. Worth Districts, with other districts scheduled to make applications in the next fiscal year.

ACKNOWLEDGEMENTS

The authors would like to acknowledge Mr. Darryl W. Davis, Chief, Planning Analysis Branch, The tIjidroiogic Engineering Center for his guidance in the development of this technology, and more specifically for his part in the initial development of the method of aggregating the elevation-damage function of the grid cells.

REFERENCES

1. "Phase 1 Oconee Basin Pilot Study, Trail Creek Test," Hydrologic Engineering Center Corps of Engineers, September 1975.

2. Johnson, W. K., and Davis, D. W., "Analysis of Structural and Nonstructural Flood Control Measures Using Computer Program HEC-SC," Hydrologic Engineering Center Corps of Engineers, November 1 975.

Technical Paper Series TP-1 Use of Interrelated Records to Simulate Streamflow TP-2 Optimization Techniques for Hydrologic

Engineering TP-3 Methods of Determination of Safe Yield and

Compensation Water from Storage Reservoirs TP-4 Functional Evaluation of a Water Resources System TP-5 Streamflow Synthesis for Ungaged Rivers TP-6 Simulation of Daily Streamflow TP-7 Pilot Study for Storage Requirements for Low Flow

Augmentation TP-8 Worth of Streamflow Data for Project Design - A

Pilot Study TP-9 Economic Evaluation of Reservoir System

Accomplishments TP-10 Hydrologic Simulation in Water-Yield Analysis TP-11 Survey of Programs for Water Surface Profiles TP-12 Hypothetical Flood Computation for a Stream

System TP-13 Maximum Utilization of Scarce Data in Hydrologic

Design TP-14 Techniques for Evaluating Long-Tem Reservoir

Yields TP-15 Hydrostatistics - Principles of Application TP-16 A Hydrologic Water Resource System Modeling

Techniques TP-17 Hydrologic Engineering Techniques for Regional

Water Resources Planning TP-18 Estimating Monthly Streamflows Within a Region TP-19 Suspended Sediment Discharge in Streams TP-20 Computer Determination of Flow Through Bridges TP-21 An Approach to Reservoir Temperature Analysis TP-22 A Finite Difference Methods of Analyzing Liquid

Flow in Variably Saturated Porous Media TP-23 Uses of Simulation in River Basin Planning TP-24 Hydroelectric Power Analysis in Reservoir Systems TP-25 Status of Water Resource System Analysis TP-26 System Relationships for Panama Canal Water

Supply TP-27 System Analysis of the Panama Canal Water

Supply TP-28 Digital Simulation of an Existing Water Resources

System TP-29 Computer Application in Continuing Education TP-30 Drought Severity and Water Supply Dependability TP-31 Development of System Operation Rules for an

Existing System by Simulation TP-32 Alternative Approaches to Water Resources System

Simulation TP-33 System Simulation of Integrated Use of

Hydroelectric and Thermal Power Generation TP-34 Optimizing flood Control Allocation for a

Multipurpose Reservoir TP-35 Computer Models for Rainfall-Runoff and River

Hydraulic Analysis TP-36 Evaluation of Drought Effects at Lake Atitlan TP-37 Downstream Effects of the Levee Overtopping at

Wilkes-Barre, PA, During Tropical Storm Agnes TP-38 Water Quality Evaluation of Aquatic Systems

TP-39 A Method for Analyzing Effects of Dam Failures in Design Studies

TP-40 Storm Drainage and Urban Region Flood Control Planning

TP-41 HEC-5C, A Simulation Model for System Formulation and Evaluation

TP-42 Optimal Sizing of Urban Flood Control Systems TP-43 Hydrologic and Economic Simulation of Flood

Control Aspects of Water Resources Systems TP-44 Sizing Flood Control Reservoir Systems by System

Analysis TP-45 Techniques for Real-Time Operation of Flood

Control Reservoirs in the Merrimack River Basin TP-46 Spatial Data Analysis of Nonstructural Measures TP-47 Comprehensive Flood Plain Studies Using Spatial

Data Management Techniques TP-48 Direct Runoff Hydrograph Parameters Versus

Urbanization TP-49 Experience of HEC in Disseminating Information

on Hydrological Models TP-50 Effects of Dam Removal: An Approach to

Sedimentation TP-51 Design of Flood Control Improvements by Systems

Analysis: A Case Study TP-52 Potential Use of Digital Computer Ground Water

Models TP-53 Development of Generalized Free Surface Flow

Models Using Finite Element Techniques TP-54 Adjustment of Peak Discharge Rates for

Urbanization TP-55 The Development and Servicing of Spatial Data

Management Techniques in the Corps of Engineers TP-56 Experiences of the Hydrologic Engineering Center

in Maintaining Widely Used Hydrologic and Water Resource Computer Models

TP-57 Flood Damage Assessments Using Spatial Data Management Techniques

TP-58 A Model for Evaluating Runoff-Quality in Metropolitan Master Planning

TP-59 Testing of Several Runoff Models on an Urban Watershed

TP-60 Operational Simulation of a Reservoir System with Pumped Storage

TP-61 Technical Factors in Small Hydropower Planning TP-62 Flood Hydrograph and Peak Flow Frequency

Analysis TP-63 HEC Contribution to Reservoir System Operation TP-64 Determining Peak-Discharge Frequencies in an

Urbanizing Watershed: A Case Study TP-65 Feasibility Analysis in Small Hydropower Planning TP-66 Reservoir Storage Determination by Computer

Simulation of Flood Control and Conservation Systems

TP-67 Hydrologic Land Use Classification Using LANDSAT

TP-68 Interactive Nonstructural Flood-Control Planning TP-69 Critical Water Surface by Minimum Specific

Energy Using the Parabolic Method

TP-70 Corps of Engineers Experience with Automatic Calibration of a Precipitation-Runoff Model

TP-71 Determination of Land Use from Satellite Imagery for Input to Hydrologic Models

TP-72 Application of the Finite Element Method to Vertically Stratified Hydrodynamic Flow and Water Quality

TP-73 Flood Mitigation Planning Using HEC-SAM TP-74 Hydrographs by Single Linear Reservoir Model TP-75 HEC Activities in Reservoir Analysis TP-76 Institutional Support of Water Resource Models TP-77 Investigation of Soil Conservation Service Urban

Hydrology Techniques TP-78 Potential for Increasing the Output of Existing

Hydroelectric Plants TP-79 Potential Energy and Capacity Gains from Flood

Control Storage Reallocation at Existing U.S. Hydropower Reservoirs

TP-80 Use of Non-Sequential Techniques in the Analysis of Power Potential at Storage Projects

TP-81 Data Management Systems of Water Resources Planning

TP-82 The New HEC-1 Flood Hydrograph Package TP-83 River and Reservoir Systems Water Quality

Modeling Capability TP-84 Generalized Real-Time Flood Control System

Model TP-85 Operation Policy Analysis: Sam Rayburn

Reservoir TP-86 Training the Practitioner: The Hydrologic

Engineering Center Program TP-87 Documentation Needs for Water Resources Models TP-88 Reservoir System Regulation for Water Quality

Control TP-89 A Software System to Aid in Making Real-Time

Water Control Decisions TP-90 Calibration, Verification and Application of a Two-

Dimensional Flow Model TP-91 HEC Software Development and Support TP-92 Hydrologic Engineering Center Planning Models TP-93 Flood Routing Through a Flat, Complex Flood

Plain Using a One-Dimensional Unsteady Flow Computer Program

TP-94 Dredged-Material Disposal Management Model TP-95 Infiltration and Soil Moisture Redistribution in

HEC-1 TP-96 The Hydrologic Engineering Center Experience in

Nonstructural Planning TP-97 Prediction of the Effects of a Flood Control Project

on a Meandering Stream TP-98 Evolution in Computer Programs Causes Evolution

in Training Needs: The Hydrologic Engineering Center Experience

TP-99 Reservoir System Analysis for Water Quality TP-100 Probable Maximum Flood Estimation - Eastern

United States TP-101 Use of Computer Program HEC-5 for Water Supply

Analysis TP-102 Role of Calibration in the Application of HEC-6 TP-103 Engineering and Economic Considerations in

Formulating TP-104 Modeling Water Resources Systems for Water

Quality

TP-105 Use of a Two-Dimensional Flow Model to Quantify Aquatic Habitat

TP-106 Flood-Runoff Forecasting with HEC-1F TP-107 Dredged-Material Disposal System Capacity

Expansion TP-108 Role of Small Computers in Two-Dimensional

Flow Modeling TP-109 One-Dimensional Model for Mud Flows TP-110 Subdivision Froude Number TP-111 HEC-5Q: System Water Quality Modeling TP-112 New Developments in HEC Programs for Flood

Control TP-113 Modeling and Managing Water Resource Systems

for Water Quality TP-114 Accuracy of Computer Water Surface Profiles -

Executive Summary TP-115 Application of Spatial-Data Management

Techniques in Corps Planning TP-116 The HEC's Activities in Watershed Modeling TP-117 HEC-1 and HEC-2 Applications on the

Microcomputer TP-118 Real-Time Snow Simulation Model for the

Monongahela River Basin TP-119 Multi-Purpose, Multi-Reservoir Simulation on a PC TP-120 Technology Transfer of Corps' Hydrologic Models TP-121 Development, Calibration and Application of

Runoff Forecasting Models for the Allegheny River Basin

TP-122 The Estimation of Rainfall for Flood Forecasting Using Radar and Rain Gage Data

TP-123 Developing and Managing a Comprehensive Reservoir Analysis Model

TP-124 Review of U.S. Army corps of Engineering Involvement With Alluvial Fan Flooding Problems

TP-125 An Integrated Software Package for Flood Damage Analysis

TP-126 The Value and Depreciation of Existing Facilities: The Case of Reservoirs

TP-127 Floodplain-Management Plan Enumeration TP-128 Two-Dimensional Floodplain Modeling TP-129 Status and New Capabilities of Computer Program

HEC-6: "Scour and Deposition in Rivers and Reservoirs"

TP-130 Estimating Sediment Delivery and Yield on Alluvial Fans

TP-131 Hydrologic Aspects of Flood Warning - Preparedness Programs

TP-132 Twenty-five Years of Developing, Distributing, and Supporting Hydrologic Engineering Computer Programs

TP-133 Predicting Deposition Patterns in Small Basins TP-134 Annual Extreme Lake Elevations by Total

Probability Theorem TP-135 A Muskingum-Cunge Channel Flow Routing

Method for Drainage Networks TP-136 Prescriptive Reservoir System Analysis Model -

Missouri River System Application TP-137 A Generalized Simulation Model for Reservoir

System Analysis TP-138 The HEC NexGen Software Development Project TP-139 Issues for Applications Developers TP-140 HEC-2 Water Surface Profiles Program TP-141 HEC Models for Urban Hydrologic Analysis

TP-142 Systems Analysis Applications at the Hydrologic Engineering Center

TP-143 Runoff Prediction Uncertainty for Ungauged Agricultural Watersheds

TP-144 Review of GIS Applications in Hydrologic Modeling

TP-145 Application of Rainfall-Runoff Simulation for Flood Forecasting

TP-146 Application of the HEC Prescriptive Reservoir Model in the Columbia River Systems

TP-147 HEC River Analysis System (HEC-RAS) TP-148 HEC-6: Reservoir Sediment Control Applications TP-149 The Hydrologic Modeling System (HEC-HMS):

Design and Development Issues TP-150 The HEC Hydrologic Modeling System TP-151 Bridge Hydraulic Analysis with HEC-RAS TP-152 Use of Land Surface Erosion Techniques with

Stream Channel Sediment Models

TP-153 Risk-Based Analysis for Corps Flood Project Studies - A Status Report

TP-154 Modeling Water-Resource Systems for Water Quality Management

TP-155 Runoff simulation Using Radar Rainfall Data TP-156 Status of HEC Next Generation Software

Development TP-157 Unsteady Flow Model for Forecasting Missouri and

Mississippi Rivers TP-158 Corps Water Management System (CWMS) TP-159 Some History and Hydrology of the Panama Canal TP-160 Application of Risk-Based Analysis to Planning

Reservoir and Levee Flood Damage Reduction Systems

TP-161 Corps Water Management System - Capabilities and Implementation Status