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Testing of Several Runoff Models on an Urban Watershed October 1978 Approved for Public Release. Distribution Unlimited. TP-59

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4. TITLE AND SUBTITLE Testing of Several Runoff Models on an Urban Watershed

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6. AUTHOR(S) Jess Abbott

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14. ABSTRACT Six models, plus two variants of one and a variant of another, were tested with the objective of making a preliminary evaluation of their relative capabilities, accuracies, and ease of application. For four of the models, plus two variant of one of them, the primary performance criterion was the degree to which simulated values matched observed daily and monthly runoff volumes for the 5.5 square mile Castro Valley Watershed near Oakland, California. In addition, tests were performed for several individual runoff events for all six models. The results showed that each model could be calibrated on a single set of data and verified with acceptable accuracy on a different data set. The ease of application was decidedly different for all models, due to the differing level of detail in input data required. Going from the simplest to mode difficult to apply, the continuous models rank as follows: STORM, HEC-1C, SSARR, and HSP. Similar ranking of the single-event models is HEC-1, SWMM and MITCAT. Also, a recent capability added to the STORM model (i.e., SCS procedures for computing runoff and routing) produced more accurate results than the coefficient method of computing quantity of runoff incorporated in the original version of STORM. These limited tests were not intended to serve as a basis for comparison of the accuracy of the various models. However, they did show that the more complex models did not produce better results than the simple models for the Castro Valley Watershed data. 15. SUBJECT TERMS urban runoff, model studies, California, watersheds (basins), computer models, storm runoff, routing, hydrographs, discharge (water), storm water, management, calibrations, surface runoff, hydrologic aspects, hydrology, unit hydrographs, monthly, analytical techniques, Castro Valley Watershed (CA), urban watersheds 16. SECURITY CLASSIFICATION OF: 19a. NAME OF RESPONSIBLE PERSON a. REPORT U

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Testing of Several Runoff Models on an Urban Watershed

October 1978 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-59

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.

IvIr, J e s s Abbott was k i l l e d on S e p t e d e r 8, 1978, whi le d r i v i n g t o work. He was born on A p r i l 3, 1943, i n Helena, &ntana, and s h o r t l y t h e r e a f t e r h i s family moved t o Boise, Idaho, where he subsequent ly graduated from Meridian High School, He received B.S. and M,S, degrees i n c i v i l engineer ing a t the k i v e r s i t y of Idaho a t Wscow, and was recognized a s an Outstanding C i v i l Engineering Student. i n h i s graduate s t u d i e s ,

A f t e r h i s u n i ~ r e r s i t y work, W , Abbott undertook h i s m i l i t a r y s e r v i c e a s an o f f i c e r i n t h e U,S, h b l i c Heal th Serv ice , Me began h i s hydrau l i c engineering c a r e e r with the U,S, Army Corps of Engineers after f u l f i l l i n g h i s d u t i e s wi th &he Publ ic Heal th Serv ice , He worked f i r s t f o r t h e Walla Walla D i s t r i c t and from t h e r e went t o $he North P a c i f i c Div is ion i n Port land, Oregon, Prom t h e r e i n 1973 he joined the s t a f f of t h e Hydrologic Engineering Genter ,

A t t h e Hydrologic E n c h e e r i n g Center , M r . Abbot& was a Researdh Hydraulic Engineer, i n charge s f t h e Center ' s urban hydrology program, He was ins t rumenta l i n f u r t h e r i n g t h e development and a p p l i c a t i o n of t h e STOW computer program, and coordinated t h e usage o f t h a t program wi th in t h e Corps of Engineers and t h e Environmental P r o t e c t i o n Agency and by many p r i v a t e engineering f i rms se rv ing l o c a l governments, He was an outs tanding c o n t r i b u t o r t o t he publ ic s e r v i c e s o f the ASCE Urban Water Resources Research Council through i. t s Program,

Outside t h e o f f i c e , M r , Abbot& took every oppor tuni ty t o pursue h i s love of t he outdoors , He was an av id p i l o t and was j u s t completing h i s instrument r a t i n g , A t t h e o f f i c e and ou t s ide , h i s enthusi.asm, good humor and i n t e g r i t y were legend, His t r a g i c and untimely dea th has deprived h i s profess ion of a very promising ca ree r , He enriched the l i v e s of a l l who met him and he w i l l be s o r e l y missed by h i s many f r i e n d s , The J e s s e W, Abbott &morial Fund has been e s t a b l i s h e d a t t h e Univers i ty of Idaho, Ho~cow, Idaho 83843,

Background

The following Technical b3emorandum is Addendm 5 of a 1977 ASCE Program repor t on "Urban Runoff Control ~ l a n n i n ~ " . ( ' ) Addendum I, "&tropoli tan Inventories," and Addendum 2 "The Design Storm Concept," were appended t o the l a t t e r report . Addendum 3 ( ~ ) and Addendum 4(3) were the f i r s t of several addi t ional , individual Addenda t o be released over the period 1977-1979.

The pr incipal intended audience of the ASCE Program's June, 1977, repor t was the agencies and t h e i r agents t ha t a r e pa r t i c ipa t ing in the preparation of areawide plans f o r water pol.lution abatement management pursuant t o Section 208 of the Federal Water Pol lu t ion Control Act Amendments of 1972 ( P e l , . 92-500), While the presentat ion which follows i s a l so di rected t o areawide agencies and t h e i r agents, it i s expected t h a t i t w i l l be of i n t e r e s t and use t o many others , pa r t i cu l a r l y l oca l governments.

The ASCE Council on Urban Water Resources Research i n i t i a t e d and developed i t s ASCE Program of the same name, The bas ic purposes of the Council and i t s Program a r e t o help advance the s ta te-of- the-ar t by ident i fy ing and promt ing needed research and by f a c i l i t a t i n g the t r an s f e r of %he findings from research t o us e r s .

Abstracts of the twenty-eight repor ts and t e c h i e a l memoranda of Program f o r the 1967-1974 period a r e included i n a read i ly ava i l ab le paper. 8 f The two repor ts and the s i x technical mermranda of the regular s e r i e s completed s ince a r e iden t i f i ed i n a recent publication.(5) Also included i n the l a t t e r i s a l i s t i n g of a l l but one of the twelve nat ional repor ts i n the specia l technical memorandum s e r i e s f o r the Internat ional Nydrolo i c a l Brograme; and the l a s t nat ional repor t (6) and an in ternat ional summaryk7 ) have been released since.

A Steer ing Commi.ttee designated by the ASCE Council gives general d i rec t ion t o the Program: S. W. Jens (Chairman); W, C. Ackermann; J, C. Geyer; C. F. Izzard; D. E, Jones, Jr,; and L. S, Tucker, Me B , &$herson i s Program Director (23 Watson S t r ee t , Wrblehead, Mass, 01945). Administrative support is provided by ASCE Headquarters in New York City,

The m d e l Tests

The Hydrologic Engineering Center of the Corps of Engineers has provided, in cooperation with others , two previous ASCE Program Technical Memoranda, a documentation of the planning model §TO&$) and a s e t of l ec tu res on urban stormwater management,(9) One of the functions of the Center i s t o provide bas ic technical information in support of urban projects of the Corps of Engineers, such a s f o r the many Urban Studies t h a t have been undertaken. Thus, f o r example, the l a t e s t versions of STORM have been developed a t the NEC, where the computer program i s cont inual ly upgraded and made ava i lab le t o Corps of Engineers' o f f i ces and other public agencies including l oca l governments,

In t h e U,S, national f epor t on urban h ~ , ~ d r o I s c a l modeling and c a t c h e n t research f o r the I n t e r n a t i o n a l Hydrological Programe, we r e f e r r e d t o two s t u d i e s i n progress a t t h e MEC, one on the use of STOBI appl ied t o four C a l i f o r n i a urban catckrnents ( q u a n t i t y and q u a l i t y ) and t h e o t h e r on the use of s eve ra l models ( q u a n t i t y on ly ) on a s i n g l e catclment , The r e p o r t which fol lows i s f o r &he second s tudy , We expect t o i s sue the o t h e r r e p o r t subsequent ly,

STOml apparent ly enjoys the most exrens ive use n a t i o n a l l y of t he va r ious models used i n planning appl icaz ions , p a r t i c u l a r l y for t o t a l j u r i s d i c t i o n s o r e n t i r e metropol i tan areas, T% w a s Eke primary t o o l w e d f o r t he most r ecen t n a t i o n a l assessment of urban runoff pollution,QB's'2) and we know o r have heard of a number of i n s t ances where i t has been o r i s being employed i n connection wi th areawide planning under Sec t ion 208 of PL 92-500 and i n severa l urban s t u d i e s of t h e Corps of Engineers, The on12 d e c a i l e d v a l i d a t i o n of S T O M t h a t has been widely disseminated has been i n the r epor t no$sed e a r l i e r c 8 ) and i n t h e u s e r s ' guide, (13) S d s e q u e n t v a l ida&ions have been mostly i n f e r e n t i a l o r incompletely repor ted , The purposes of t he fol lowing r e p o r t were: t o compare %he performance of t he newer ve r s ions s f STOm with the o r i g i n a l version, aad f o r t he longer record of f i e l d d a t a t h a t has s i n c e accumla tedg t o t e s t t he r e l i a b i l i t y of' SmM, a r e l a t i v e l y s i m p l i s t i c model, against another simple mode8 and more complica%ed and comprehensive models; and t o t e s t ~ h e s e l a e i v e ease and c o s t of using a wide range of models t o expand t h e r epe rzo i r e of &he Corps oE Engineers at l a r g e ,

The t e s r res:ri ts reporeeea enhance the credibility of t h e use of STOm, once c a l i b r a t e d a g a i n s t fieEd data, However, one eatchrnent does no t c o n s t i t u t e a very good sample s f urban An~erxcs r , Fur ther , t h i s s tudy was n o t a con te s t , p i t t i n g one m d e l a g a i n s t zhe o t h e r , Fhe i n t e n t i o n was t o make a reasonable e f f o r t i n t h e c a l i b r a t i o n of each model, g iv ing squable a c t e n t i o n t o each, bu t n o t t o engage i n e l a b o r a t e f i n e tun ing such as t o maximize the agreement between obsemed and ca l cu la t ed runof f , There2ore, the r e p o r t should be read 1% terms of t h e r e l a t i v e pepfomance of s i m p l e versus rare canspPieated models and t h e r e s u l t s f o r t h e wide v a r i e t y of models used should not b e judged a s being t y p i c a l of any of them, To r e i t e r a t e , t h i s was an exploraeory o r probing s tudy, However, d e s p i t e t h e f a c t t h a t water q u a l i t y was not included, it appears t o be t h e most ex tens ive in s t ance of t h e use or" a v a r i e t y o f models an a UeSe urban catc7a4r'98ents

Las t ly , readers a r e advised t h a t t h e MEC has r e c e n t l y issued gu ide l ines f o r the c a l i b r a e o n a ~ d appl icakiora ox ST OM;^'^^ and has descr ibed the capabfl i t l e s o f STOBH and two ozhe-c coroinpuber packages in a symposium paper. Q 1s >

The ASCE Urban 'Y$;a$en Resources Resaarrh Count fi. i s indebted t o I&, Abbot& and The Hydrologic Engineering Center for t h e i r generaus con t r ibu t ion of t h i s r e p o r t a s a pub l i c s e n r i c e ,

References

McPherson, M. B., "Urban Runoff Control Planning," ASCE, New York, N.Y., 118 pp., June, 1977. (Avai lable a s PB 271 548, a t $ 5 3 0 per copy, from the Nat iona l Techni.ca1. 1,nformation Serv ice , 5285 Por t Royal &ad, S p r i n g f i e l d , Vi.rgini.a 22161).

I t Espey, W. H., Jr., D. 6. Altman and C. B, Graves, Jr., Nomographs f o r Ten-Minute Unit Hydrographs f o r Small Urban Watersheds," ASCE UWRR Program Technical Memorandum No. 32, ASCE, New York, N.Y,, 22 pp., December, 1977. (NTIS: PB 282 158).

Mbrsalek, J ir i , "Research on t h e Design Storm Concept," ASCE UWRR Program Technical Memorandum No. 33, ASCE, New York, N.Y., 37 pp., September, 1978.

McPherson, M. B e , and 6. F. Mangan, Jr., "ASCE Urban Water Resources Research Program," J.Hyd.Div., ASCE Proc., Vol. 101, No. HY7, pp. 847-855, J u l y , 1975.

McPherson, M. B., and G. F. Mangan, Jr., Closure t o Discussion of "ASCE Urban Water Resources Research Program," J.Hyd.Div., ASCE Proc., Vol. 103, No. HY6, pp. 661-663, m y , 1977,

Ramaseshan, S,, and P. B. S. Sarma, "Urban Hydrological Modeling and Catchment Research i n 1,ndia , 'QSCE UWRR Program Techni.ca1 Memorandum No. IHP-12, ASCE, New York, N,Y., 21 pp,, May, 197'7. (NTIS: PB 271 300).

McPherson, M, B., and F. 6, Zuidema, "Urban Hydrological Modeling and Catchment Research: I n t e r n a t i o n a l Summary,'' ASCE UWRR Program Technical Memorandum No. IHP-13, ASCE, New York, N.Y., 48 pp., November, 1977. (NTIS: PB 280 754).

Water Resources Engineers, The Hydrologic Engineering Center/Corps of Engineers and the DPW/City and County of San Francisco, "A Model f o r Evaluat ing Runoff- Qua1 i t y i n Metropol i t a n Mbster Planning, " ASCE UWRR Program Technical Memorandum No, 23, ASCE, New York, N,Y., 73 pp,, A p r i l , 1974. (NTIS: PB 234 212; o r from HEC),

Water Resources Engineers and The Hydrologic Engineering CenterlCorps of Engineers, "Management of Urban Storm Runoff , " ASCE UWRR Program Technical Memorandum No. 24, ASCE, New York, N.Y., 92 pp., May, 1974. (NTIS: PB 234 316; o r from HEC).

McPherson, M. B., "Urban Hydrological Modeling and Catchment Research i n t h e U.S.A.," ASCE UWRR Program Technical Memorandum No. IHP-1, ASCE, New York, N.Y., 49 pp., November, 1975. (NTIS: PB 260 685).

American Pub1 i c Works Assoc ia t ion and Un ive r s i t y of F lo r ida , Nationwide Evaluat ion of Combined Sewer Overflows and Urban Stormwater Discharges, Volume I: Executive Summary, Environmental P r o t e c t i o n Technology S e r i e s EPA-600/2-77-064a, Municipal Environmental Research Laboratory, U.S. EPA, C inc inna t i , Ohio 45268, 95 pp., September, 1977. (NTIS: PB 273 133).

12. Heaney, 3 , P,, e t ale, Nationwide Gva1uatiox1 of Combined Sewer Overflows and 3

Environmental Protection Technology Series EPA-600/2-77-064, hicipal Environmental Research Laboratory, Cincinnati, Ohio 45268, 364 pp., March, 1977. (NTTS: PI% 266 0 0 5 ) ,

1 3 , Hydrologic Engineering Center, Corps of Engineers, "Storage, Treatnent, G-verfEow, Runoff kdeE (STOW), 93sersg &nual,'~omputer Program 923-S8-L7520, 609 2nd S&reet, Davis, California 95616, 270 pp, , August, 1977,

54. Hydrologic Engineering Center, Corps af Engineers, "GuidePines for Calibration and Application of STOW," Training Document No, 8, 609 2nd Street, Davis, California 95616, 48 p p , , December, 3.977,

15, Hayes, Richard J , , '%EG Gompeeter Programs for Urban WaEer Wandl ing: HEC-1, HEC-2, and S T O ~ Y , " pp, 369-373 in "Proceedings, International Symposium on Urban Hydrology, Hydraulics and Sediment @ontrol," Repport Urn BULT4, University of Kentucky, Lexington, December, 1977,

( * Reference 10, above, has been publ i shed by Unesco as one of the first five of twelve national reports : U~esco, Vo lame l , Technical Papers in Hydrology 15, Imprimevie Beugnet, Paris, 185 p p , , 2 9 7 9 ) -

Page

SECTIOU 1 . INTRODUCTION AND SUMMARY . . . . . . . . . . . . . . . . . . . . 1 In t roduc t ion . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 . . . . . . . . . . . . . . . . Table 1 Model C a p a b i l i t i e s 3 Resul t s and Conclusions . . . . . . . . . . . . . . . . . . . . . 2

. . . . . . . . . . . . . . . SECTION 2 DESCRIPTIONS OF WATERSHED AND mDELS 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . Watershed 5 . . . . . . . . . . . . . . Figure 1 Gastro Valley Watershed 6 Continuous &de l s . . . . . . . . . . . . . . . . . . . . . . . . 5 . . . . . . . . . . . . . . . . . . . . . . . Single-Event Models 8

. . . . . . . . . . . . . SECTION 3 . S I U T I O N RESULTS. GONTWUOUS mDELS 11 . . . . . . . . . . . . . . . . . . . . . . . . . . . . Procedure II Resul t s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Table 2 . Resul t s f o r Continuous Pbdels f o r t h e C a l i b r a t i o n Period. Cas t ro Valley Monthly Volumes ( ~ n c h e s ) . . . . . . . . . . . . 12

Table 3 . Resul t s f o r Continuous Models f o r t h e C a l i b r a t i o n Period. Cas t ro Valley Daily Runoff Volumes ( Inches) . . . . . . . . . . 13

Table 4 . Resul t s f o r Continuous Pbdels f o r t h e V e r i f i c a t i o n Period. Gastro Valley b n t h l y Volumes ( Inches) . . . . . . . . . . . . 16

Table 5 . Resul t s f o r Continuous E/bdels f o r t h e V e r i f i c a t i o n Period. Cas t ro Valley Dai ly Runoff Volumes ( Inches) . . . . . . . . . . 17

I n t e r p r e t a t i o n of Resul t s . . . . . . . . . . . . . . . . . . . . 11 Table 6 . S t a t i s t i c a l Analysis of Resul t s

f o r t h e Continuous b d e l s . . . . . . . . . . . . 19

SECTION 4 . SIMULATION RESULTS. SINGLE-EVmT WDEES . . . . . . . . . . . . 2 1 Procedure e e 21 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Resul t s 21

Figure 2 . Continuous b d e l s - C a l i b r a t i o n (1/16/73) . . . . . 22 Figure 3 . Sing le Event &de l s -Ca l ib ra t ion (1/16/73) . . . . 23 Figure 4 . Continuous k d e l s - C a l i b r a t i o n (1117-18/73) . . . 24 Figure 5 . Sing le Event &de l s -Ca l ib ra t ion (1/17-18/73) . . 25 Figure 6 . Continuous b d e l s - C a l i b r a t i o n (2/6/73) . . . . . 26 . . . . Figure 7 . Sing le Event Models-Calibration (2/6/73) 27 F igure 8 . Continuous Plbdels-Verification (1/4/74) . . . . . 28 Figure 9 . Sing le Event Pbdels -Ver i f ica t ion (1/4/74) . . . . 29 Figure 10 . Continuous l"lodels-Verification (1/5/74) . . . . . 30 Figure 11 . Sing le Event &de l s -Ver i f i ca t ion (1/5/74) . ' . . . 31 Figure 12 . Continuous &$@Is-Ver i f ica t ion (1/16/74) . . . . 32 Figure 13 . S i n g l e Event Ibde l s -Ver i f i ca t ion (1/16/74) 33 . . . . . Figure 14 . Continuous %de l s -Ver i f i ca t ion (4/1/74) 34 Figure 15 . Sing le Event k d e l s - V e r i f i c a t i o n (4/1/74) . . . . 35

Model Parameters . . . . . . . . . . . . . . . . . . . . . . . . . 36 Table 7 . STORM Model Parameters f o r

SCS Method, Cas t ro Valley . . . . . . . . . . . . 37 Table 8 . HEC-1 Optimized Parameters f o r t h e . . . . . . . . C a l i b r a t i o n Period, Gastro Valley 38 Table 9 . SWMEl and MITWT Parameters, Cas t ro Valley . . . . 38

I n t e r p r e t a t i o n of Resul t s . . . . . . . . . . . . . . . . . . . . 36 (cont inued )

TABLE OF 60NTmTS (Continued)

Page

. . . . . . . . . . . . . . . . . . . SECTION 5 SIMULATION RESULTS. CE;NEUL 39 Table 10 . Rela t ive A c c u r a c y of Individual

Event Runoff Hydrographs . . . . . . . . . . . . 40 . . . * . . . . . . . . Table 11 Computer Time Requiremeazs 41

SECTION 6 -AGIOVOWLEDGWTS . . . . . . . . . . . . . . . . . . . . . . . . 42

. . . . . S E C T I O N 7 . . U F E W C E S o . . e a . . e e . e e * + a . e . s e e . 43

SECTION I

INTRODUCTION AND SUMMARY

In t roduc t ion

For s e v e r a l decades t h e Rat iona l Formula had been t h e almost exc lus ive method used f o r planning and des igning urban s t o r m a t e r f a c i l i t i e s , With t h e advent of high-speed d i g i t a l computers more comprehensive and more conceptua l ly r e a l i s t i c techniques have been developed f o r t he s tudy and design of urban water resource systems. In p a r t i c u l a r , t h e r e i s now a mul t i tude of urban runoff mathematical models, b u t t hese d i f f e r widely i n t h e i r intended a p p l i c a t i o n , scope, r e l i a b i l i t y , d a t a requirements and output ; y e t o f t e n have c e r t a i n c a p a b i l i t i e s o r f e a t u r e s i n common, To compiicate mat te rs , a l l such models a r e cont inuously subjec ted t o modif i , ca t ion and f u r t h e r v e r i f i c a t i o n .

Unceasing e f f o r t s t o develop model ref inements and the l a r g e number and kind of models have hindered development of acceptab le c r i t e r i a f o r sys temat ic eva lua t ion of model performance. However, s e v e r a l a t tempts have been made t o c a t e g o r i z e and compare t h e i r c a p a b i l i t i e s , Examples a r e an assessment of mathematical models f o r storm and combined sewer management,(l) a review of models and methods a p p l i c a b l e t o Corps of Engineers ' Urban S tud ie s , ( 2 ) and a comparison of t h e performance of f i v e watershed models. ( 3 )

S i x models, p lus two v a r i a n t s of one and a v a r i a n t o f another , were t e s t e d i n t h e s tudy repor ted here , w i t h t h e o b j e c t i v e of making a pre l iminary eva lua t ion o f t h e i r r e l a t i v e c a p a b i l i t i e s , accu rac i e s and ease of a p p l i c a t i o n , A d e t a i l e d comparison of t h e many c a p a b i l i t i e s and f e a t u r e s of t h e s e models was beyond the scope of t h e study. For fou r of t h e models, p lus two v a r i a n t s of one of them, the primary performance c r i t e r i o n was t h e degree t o which s imulated va lues matched observed d a i l y and monthly runoff volumes f o r t h e 5-5-square mi le Cas t ro Valley Watershed near Oakland, Ca l i fo rn i a . I n a d d i t i o n , t e s t s were performed f o r s e v e r a l i nd iv idua l runoff events fo r a l l s i x models,

Procedure

Urban runoff models a r e o f t e n c l a s s i f i e d i n terms of t h e i r a p p l i c a t i o n o r t he type of procedures used i n computations wi th them, P r i n c i p a l usage ca t egor i e s a r e planning, design and ope ra t ions . In o rde r t o categori .ze t he models used i n t h i s s tudy , four computat iona l a t t r i b u t e s a r e d i s t i ngu i shed :

Single-event s imula t ion models, which genera te a runoff hydrograph from a d i s c r e t e storm event , u s u a l l y over a d u r a t i o n of a few hours o r days, S o i l moisture processes r e f l e c t t h e accumulated we t t i ng from p r e c i p i t a t i o n b u t n o t t h e dry-weather per iods between s torms,

Continuous s imula t ion models, which genera te a runoff hydrograph from a continuous s e r i e s of s torm events . The period of record f o r which continuous runoff hydrographs may be ca'culated v a r i e s from a few months t o many years . A continuous h i s t o r y of p r e c i p i t a t i o n d a t a i s normally the primary type of input , and so i l -mo i s tu re condi t ions a r e c o n t i n u a l l y s imulated by t h e model a s a func t ion of p r e c i p i t a t i o n , l eng th of an tecedent d r y per iods , evapoteanspi ra t ion , e t c .

Hydraulic rou t ing techni.ques, which approximate i n vary ing degrees t h e b a s i c equat ions desc r ib ing unsteady flow i n open channels o r on land su r f aces ,

Hydrologic computation techni.ques, whi.ch employ empi.rical re l .a t i .onships t o e s t ima te i n d i r e c t l y t h e e f f e c t s of phys ica l processes ,

Four continuous s imula t ion m d e l s were t e s t e d : S torage Treatment Overflow Iiunof f Model ( S W M ) ; ( 4 ) Hydrocom Simulat ion Program (HSP) ; ( 5 ) Streamf low Synthes is and Reservoir Regulation (SSARR) ; P 6 and Continuous Flood Hydrographs (HEC-1~) . ( 7 ) Comparisons f o r s e v e r a l s ing le-s torm events were made us ing STOW, BSP, SSAm, Storm Water Management Model ( swMM), (~ ) Flood tlgrdrograph Package ( H E C - ~ ) ( ~ ) and Massachusetts I n s t i t u t e of Technology Catchment Model (MTTCAT), ( 9 I n Tab1 e P a r e l i s t e d t h e s a l i e n t f e a t u r e s of each model, A d e s c r i p t i o n of each model is presented i n Sec t ion 2,

The Cas t ro Valley Watershed (5,5-square mi l e s ) n e a r Oakland, C a l i f o r n i a , was chosen t o a s s e s s t he p e r f o r m c e of t h e models because of a v a i l a b i l i t y of p e r t i n e n t da t a , The bas in c o n s i s t s of approximately 80% s ingle- fami ly r e s i d e n t i a l a r e a s and schools , 5% is strip-commercial development and the remaining 15% i s undeveloped, The d a t a base cons i s t ed s f 42 months of continuous r a i n f a l l and runoff da t a . Data c o l l e c t i o n was funded by t h e S a n Francisco D i s t r i c t o f t h e Corps of Engineers a s p a r t o f a s tudy t o provide d a t a t o a s s e s s t h e quan t i t y and q u a l i t y of storm runoff e n t e r i n g t h e San Francisco Bay, The U,S, Geological Survey a t Menlo Park, C a l i f o r n i a , conducted t h e f i e l d d a t a c o l l e c t i o n i n cooperat ion wi th The Hydrologic Engineering Center , The MEC publ ished t h e annual d a t a r e p o r t s . ( I0 )

While the per fomance c r i t e r i o n f o r t h e f o u r continuous s imula t ion models was t h e degree of c o r r e l a t i o n between observed and s imulated d a i l y and monthly runoff volumes, s ing le-event t e s t s were r e s t r i c t e d t o seven ind iv idua l runoff events from t h e 42-month record ,

A s p l i t - r e c o r d t e s t was used t o e v a l u a t e each of t h e fou r continuous s imula t ion rmdels, Each mode% was caPibra$ed wi th t h e first two- f i f t h s of t h e 42 -mnth record and t h e r e s u l t a n t s e t o f c o e f f i c i e n t s were used i n s imula t ing t h e runoff f o r t h e remaining t h r e e - f i f t h s of t h e record , The s ingle-event models were c a l i b r a t e d w i t h t h r e e ind iv idua l events from t h e f i r s t p a r t s f t h e record and appl ied t o f o u r events from t h e second p a r t , The same seven s i n g l e events from t h e STOW s imula t ions were ex t r ac t ed f o r comparison, w i t h no a%%empt t o r e c a l i b r a t e t h a t model f o r i nd iv idua l events , SSAM and HSP were a l s o n o t r e c a l i b r a t e d f o r t h e ind iv idua l even t s ; however, because of a v a i l a b l e channel rou t ing op t ions they were r e run f o r t h e ind iv idua l events u s ing s h o r t e r t ime-s teps ,

Resul t s and Conclusions

The r e s u l t s showed t h a t each m d e l could be c a l i b r a t e d on a s i n g l e s e t of d a t a and v e r i f i e d wi th accep tab le accuracy on a d i f f e r e n t d a t a s e t , The ease o f a p p l i c a t i o n was decidedly d i f f e r e n t f o r a l l models, due t o t h e d i f f e r i n g leve l of d e t a i l i n input d a t a requi red , Going from the s imples t t o t h e most d i f f i c u l t t o apply, t he continuous models rank a s folfows: STO,W, HEC-16, SSAM, and HSP, S imi l a r ranking o f t h e single-event models I s : HEC-1, SWMM and mTWT, Also, a r e c e n t c a p a b i l i t y added t o the S%lg)M model ( i , e , , SCS procedures f o r computing runoff and rou t ing ) produced more a c c u r a t e r e s u l t s than t h e c o e f f i c i e n t method of computing q u a n t i t y of runoff incorpora ted i n t h e o r i g i n a l ve r s ion of STORM,

TABLE 1

MODEL CAPABILITIES

function of

Infiltration

These l imi t ed t e s t s were no t intended t o s e rve a s a b a s i s f o r comparison of t h e accuracy of t h e va r ious models. However, they d i d show t h a t t h e more complex models d id n o t produce b e t t e r r e s u l t s than the simple models f o r t he Cas t ro Valley Watershed d a t a ,

General concl.usions regard ing t h e app l i cab i . l i t y and accuracy of t h e seve ra l models cannot be made on t h e b a s i s s f t h i s s tudy, and t h a t was n o t t h e i n t e n t , However, some genera l impressions surfaced a s a r e s u l t of a t tempts t o apply each model t o the same d a t a s e t .

The continuous models were c a l i b r a t e d on d a i l y and monthly volumes f o r t h e f i r s t 17 m n t h s of t h e record, Therefore, t hese models may n o t adequately r ep re sen t che peak flows f o r t h e s i n g l e events , e s p e c i a l l y f o r such a small d ra inage a rea , Their response could have been improved by r e c a l i b r a t i n g them a g a i n s t d i s c r e t e events .

The models which u t i l i z e hydrologic computation techniques (SMRM, H Z - I , and SSARR) produced r e s u l t s f o r t h e Cas t ro Valley Watershed t h a t were of an equal a c c e p t a b i l i t y t o those which use hydraul ic techniques (SWMM, HITCAT, and HSP), A poss ib l e explanat ion i s t h a t , a t l e a s t f o r t h e d a t a s e t used i n t h i s s tudy, t he lumped-parameter hydrologic models requi red l e s s judgment i n a s s ign ing magnitudes t o t he var ious model parameters, Because t h e d a t a a v a i l a b l e were l imi t ed , t h e e x e r c i s e of having t o e s t ima te t he magnitudes of a l a r g e r number of parameters f o r t h e more complex models may have introduced e r r o r s . Therefore, while t h e models which use hydraul ic techniques may produce more accu ra t e r e s u l t s where adequate d a t a a r e a v a i l a b l e , t he r e s u l t s of t h i s s tudy suggest t h a t t he s impler models can d e f i n i t e l y be used e f f e c t i v e l y i n planning o r sc reening type a p p l i c a t i o n s ,

The r e l a t i o n s h i p between t h e time s t e p used i n t h e aodels and t h e b a s i n time of concent ra t ion may have introduced e r r o r s , Each continuous model was operated on a 1-hour time s t e p , which i s approxi .mte ly equal t o t h e time of concent ra t ion f o r t he Castro Valley Watershed, One would normally r e s t r i c t t h e t ime s t e p t o something l e s s than the time of concent ra t ion of t h e bas in i n o r d e r t o d e f i n e hydrographs adequately,

A disadvantage of STOPaPS and BEG-LC i s t h a t n e i t h e r s imula te base fl.ow, Therefore, t h e base flow had t o be est imated and added t o t he app ropr i a t e va lues f o r use i n comparison wi th observed d a t a , SSARR and HSP r e s u l t s inc lude base flow, making d i r e c t comparison wi$h observed flow d a t a wre s t r a i g h t f o r n a r d ,

SECTION 2

DESCRIPTIONS OF WATEaHED AND mDELS

Watershed

The Castro Valley Watershed was chosen f o r t h i s s imula t ion s tudy p r imar i ly because of a v a i l a b i l i t y of p r e c i p i t a t i o n and runoff da ta . A t t h e present time t h e r e a r e fou r record ing r a i n gages i n t h e bas in and one record ing flow gage a t t h e o u t l e t of t h e bas in , The flow gage, operated by t h e U,S, Geological Survey, and one r a i n gage, operated by t h e Cas t ro Valley F i r e Department, were placed i n ope ra t ion i n November, 1971, Three o t h e r record ing r a i n gages, two funded by The Hydrologic Engineering Center and one by the Alameda County Flood Control and Water Conservation D i s t r i c t , were put i n ope ra t ion i n t h e f a l l of 1975. The purpose of t h e s e a d d i t i o n a l r a i n gages was t o provide d a t a on the s p a t i a l v a r i a t i o n of r a i n f a l l ac ros s t h e bas in and thus t o al low b e t t e r computation of bas in average p r e c i p i t a t i o n . However, two success ive and unusual ly d ry years have precluded c o l l e c t i o n of a s i g n i f i c a n t amount of da ta . Runoff q u a l i t y f o r s e v e r a l s e l e c t e d storms each y e a r was.%ollected dur ing t h e 71-72, 72-73, and 74-75 water years . The storm runoff q u a l i t y -measurements and t h e flow gage were funded by t h e San Francisco D i s t r i c t , Corps of Ehgineers, and t h e equipment was opera ted by t h e Men10 Park o f f i c e of t h e U,S, Geological Survey wi th guidance from The Hydrologic Engineering cen te r . ( l o )

F igure 1 i.s a topographic map of t h e Cas t ro Val ley Watershed. The dra inage a r e a above the flow gage i s 5.5-square miles , The bas in i s p r i m a r i . 1 ~ r e s i d e n t i a l (80%) wi th a small amount of strip-commercial development (5%), and t h e remainder i s i n t h e undeveloped, h i l l y , brush-covered headwaters of Cas t ro Valley Creek, The c e n t r a l por t ion of t h e v a l l e y is r e l a t i v e l y f l a t whi le t h e perimeter of t h e b a s i n i s q u i t e s t e e p and h i . l l y , The minimum e ' leva t ion i n t h e b a s h i s 100-fee t MSL while t h e maxi.mum i.s l l . l .0 - fee t MSL.

The c l ima te of t h e a r e a is cha rac t e r i zed by w a r m , dry, summer-fall seasons and r e l a t i v e l y humid wi.nter seasons, The average annual prec i ,p i . t a t ion i s approxi.mately 23-inches, almost a l l o f which occurs dur ing t h e period of November through March, Temperatures below f r e e z i n g a r e extremely r a r e .

Because l i t t l e change i,n land use occurred over t h e 42-month period f o r which d a t a were used, t h e runoff record was considered t o be s t a t i s t i . c a l l y homogeneous,

Continuous Models

STORM

The Storage, Treatment, Overflow, Runoff b d e l is a continuous s imula t ion model designed t o be used pr imar i ly i n planning s t u d i e s f o r eva lua t ing s t o r a g e and t rea tment capac i ty requi red t o reduce p o l l u t i o n from stormwater runoff o r combined sewer system overf lows,(4) Pol lutograph ( v a r i a t i o n s i n po1,lutant mass-emission r a t e s wi th time) loadings can a l s o be computed f o r u se i n a r ece iv ing water assessment model. STORM uses a one-hour computation i n t e r v a l .

Because STOm was intended f o r use i n met ropol i tan planning o r t o t a l j u r i s d i c t i o n master planning f o r sc reening a l t e r n a t i v e s , some of i t s a n a l y t i c a l techniques a r e n e c e s s a r i l y s imp l i f i ed . For example, t h e two procedures used t o compute the quan t i t y of runoff i n STORM a r e t h e c o e f f i c i e n t method and t h e S o i l

SCALE 1 24000 , ,,,, HAYWARD, GAL - --p - - - . -. NE 4 HAYWARD 15 OUADRA

4000 5000 6000 '000 FiET -~--AyL:-: 2!g-L -= E=e-F7z ~ -~:-.=: ::---7yy:: N3737.5-W12200/

I 5 0 l KILOMETFR i-L -1'- ~ ~ - ill~-AL I= >--:< =:.-*-- -= -==--=~ ~-3 1959

CONTOUR INTERVAL 20 FEET DOTTEO L iNFS REPFESEN- 5 FOOT CONTOURS

DATUM I S MEAN SEA LEVEL

Conservation Serv ice (SCS) method, I n t he c o e f f i c i e n t method, a s i n g l e runoff c o e f f i c i e n t weighted according t o Jand-use is appl ied t o each hour of r a i n f a l l i n excess of depress ion s to rage t o compute runoff , Therefore, t h e runoff c o e f f i c i e n t i s a func t ion of on ly t h e r e l a t i v e amowts of pervious and impervious a reas i n t h e watershed, Antecedent condi t ions and r a i n f a l l i n t e n s i t y a r e n o t taken i n t o account.

The SCS runoff -cuwe-number technique is considered t o be more conceptua l ly c o r r e c t than t h e c o e f f i c i e n t method, The SCS curve c o n s i s t s of a non l inea r r e l a t i o n s h i p between accumulated r a i n f a l l and a c c u m l a t e d runoff , (11) The procedure, a s developed by the SCS, was intended t o b e used on s i n g l e events , Three an tecedent moisture condi t ions were a v a i l a b l e t o a d j u s t t h e curve number f o r p r i o r p rec ip i t a t i . on , Because STORM i s fundamentally a continuous model, HEC developed a procedure t h a t computes t h e curve number f o r each event based on t h e number of d ry hours s i n c e t h e previous runoff event and t h e in t e reven t evapo t r ansp i r a t ion and percola t ion . A t h i r d method used i s a combination, w i t h t h e coe f f i c i . en t method appl ied t o impemious a reas and t h e SCS method appl ied t o pervious a r e a s of t he watershed,

STORM possesses many o t h e r c a p a b i 1 i t i . e ~ which were n o t used i n t h i s s tudy , These include q u a l i t y of storm runoff a s def ined by s i x parameters, snow accumulati,on and melt , land-surface e ros ion , quan t i t y and q u a l i t y of dry-weather flow, and a n a l y s i s of s to rage volumes and t reatment r a t e s ,

HEC - l G

HEC-%E i s an adapta t ion of The Hydrolsgic Engineering Center" computer program, Flood Hydrograph Package (HEC-l) , ( 7 ) I t performs a s imp1 e continuous syn thes i s of bas in m i s t u r e , Basin moisture i s expressed a s a func t ion of p r e c i p i t a t i o n , l o s ses , and an evapot ranspi ra t ion recovery f a c t o r , Basin moisture, i n t u rn , c o n t r o l s t h e l o s s r a t e func t ion , whfch governs how much of t h e p r e c i p i t a t i o n i s d iv ided between l o s s e s and runoff excess , Runoff excess is transformed by a u n i t hydrograph i n t o sub-basin outflows, Outflows may then be c o d i n e d and routed t o o b t a i n a continuous watershed response, Various computation time i.nerements may be used, depending on watershed s i z e and p r e c i p i t a t i o n d a t a a v a i l a b l e , Output inc ludes event hydrographs a s wed1 a s d a i l y , m n t h l y , and annual runoff summaries.

The Streamflow S p t h e s i s and R e s e w s i r Regulation (SSAU) Nodel is a continuous s imula t ion m d e l designed t o be used f o r ope ra t ion of a r i v e r bas in system, I t s development began i n 1956 as an ope ra t iona l t o o l f o r t h e Columbia River system.(6) However, i n r ecen t years it has been used succes s fu l ly i n many loca t ions i n t h e U,S, and abroad, I t s func t iona l use i s f o r l a r g e non-urban watersheds, bu t i n t h i s s tudy it was succes s fu l ly appl ied t o a smkl urbanized watershed,

The model c o n s i s t s of watershed, r i v e r system, and r e s e r v o i r r egu la t ion m d u l e s f o r comprehensive ana lyses and day-to-day operat ional . use, Obviously, t h e r i v e r system and r e s e r v o i r r egu la t ion modules were no t used i n t h i s s tudy,

I n t h e SSAm m d e l , runoff i n any given t i m e per iod i s a func t ion of an empi r i ca l ly der ived r e l a t i o n s h i p between mnof f and t h e s o i l moisture index (SMC), The §MI i s then increased by t h e m i s t u r e input no t con t r ibu t ing t o runoff and reduced by an ad jus t ed evapot ranspi ra t ion index, Computations a r e made f o r each incremental t ime period, The SMC i s a r e l a t i v e s o i l wetness used t o determine

runof f , %en t h e s o i l m i s t u r e is deple ted (by evapo t r ansp i r a t ion ) t o a va lue approximately equiva len t t o the pe rmnen t wilting poin t , the va lue of t h e S'Kf is considered t o be zero, m e n r a i n and/or s n o m e l t recharges s o i l m i s t u p e , t h e va lue of t h e SMI increases u n t i l it reaches a maximm va lue considered $0 r ep resen t i t s f i e l d capac i ty . The cornpuked runoff , which i s a percentage of t o t a l m i s t u s e input , based on the SXI , i s divided i n t o surface, subsurface, and baseflow components; and each of khcse c s ~ p o n e n t s a r e routed separately through bas in s to rage and combined t o develop bas in outflow,

The Hydrocomp S i m l a t i a n Program ( E P ) i s an improved ve r s ion of t h e S t m f o r d Watershed m d e 1 and is one of t h e most comprehensive continuous m d e l s a v a i l a b l e f o r a n a l y s l s of runof f quantlcy, The program i s organized i n t o subprograms f o r : (1) data management; 6,121 rmdeling the r a i n f a l l - r u n o f f process on t h e land su r f ace ; and ( 3 ) r o u t i n g Hand s u r f a c e runoff through a %%ream network of open channels and closed condui t s t o produce continuous hydrographs a t a s e r i e s of l o c a t i o n s wi th in $he watershed,

The "Landsgs subprogram i s the prirac i p a l component i n t h e d e t e m i n a t i o n of t h e t o t a l s t ream f low timing and runoffs iBLa4ad~'' i s intended t o r ep re sen t t h e hydrologic cyc l e f o r a u n i t area u s l n g obse~-ved p r e c i p i t a t i o n t o s imula te e i t h e r r a i n o r snowfall, and accoun$s for Lntercept ion s to rage , i n f i l t r a t i o n (based upon t h e equat ion f o r i n f i l t r a z i o n developed by R i g l i p s ) t o t h~o s o i l m i s t u r e s to rages , rou t ing of s u r f a c e maof f over an overland flow p la in from pervious su r f aces , impervious runoff , i n t e r f low runo f f , axid groundwater runoff , E s t i m t e d continuous p o t e n t i a l evapotrazspiratiox~ is ddezerrnl.ned from observed evaporat ion and used i n the mdeE t o estimate the actual evaporation from each skorage, Watersheds wi th d i f f e r e n t land-use c h a r a c t e r i s t i c s can be represented by a s e r i e s of subwatersheds wi th s p e c i f i c parameters assign& ra them f o r unique hydrologfc c h a r a c t e r i s t i c s , The channel network is represented by a s e r i e s of channel l engths where each l e n g t h has a t r i b u t a r y area, The d e s c r i p t i o n of the channel network is entered a s t h e phys ica l c h a r a c t e r i s t i c s of &he individual c h a n ~ e l length , The upstream and domskream e l eva t ions , bottom and t o p width, charmel depth, overbank f lood p l a i n s lope , and b n n i n g g s n fo r Lhe channel and sve-rlamk flood plain are s p e c i f i e d f o r each open channel reach, Closed cond.iri%: channel lengths are represented by i n v e r t s lope , diameter , and 3hnning" aa, A good physical representatton of t h e channel network i s necessary f o r evaluat ing the impac t o f proposed changes ts t h e channel system,

The HSP rouzing a X g o r i t h is based upan %he k i n e w g i c wave approach, Other c a p a b i l i t i e s of RSP !r.clude the simulatjon of strean water q u a l i t y and r e s e r v o i r rou t ing ,

The Flood H ~ d r o g r a p k Pscksge (HE@-1 9 is suitable far most r a i n f a l l - runof f computations f o r a ccmplex, m111 ti-bas in, mulzi-charnel river bas in , ( 7 ) P r e c i p i t a t i o n must be input a s a s i n g l e hypothetical. o r r ~ c o r d e d evenz because t h e r e a r e no computatians for loss - ra te recTverIJ during periods dl thout p r e c i p i t a t i o n , a s opposed t o WEG-16, described earii.ar, REG-$ has a user-spezjfied -,omputation i n t e r v a l ,

Five major types of f lood hydrograph ana lyses can be performed us ing HEC-1:

R a i n f a l l - r m o f f rou t ing t o s imula te t h e hydrologic response of a watershed,

Stream system computations f o r a watershed us ing p r e c i p i t a t i o n depth-area r e l a t i o n s h i p s .

Optimizat ion of u n i t hydrograph and l o s s r a t e parameters.

Optimizat ion of r o u t i n g parameters,

S imulat ion of mul t ip le -bas in development plans us ing mul t ip l e f loods and economic a n a l y s i s of fl.ood damages.

The model may be used t o opt imize l o s s r a t e and rou t ing parameters t o achieve a b e s t - f i t r econs t i t u t i . on of an observed hydrograph us ing known p r e c i p i t a t i o n . This opti.on was used i n t h e c a l i b r a t i o n phase of t h i s s tudy t o develop a s e t of parameters f o r s e v e r a l observed events .

Severa l techniques a r e provided t o process and d i s t r i b u t e p r e c i p i t a t i o n d a t a , compute p ~ e c i p i t a t i o n ~ s r snow accumulation, compute p r e c i p i t a t i o n o r snow- melt excesses , d e f i n e sub-basin outf lows by us ing u n i t hydrographs, and t o r o u t e hydrographs using hydrologic methods, D i f f e r e n t techniques f o r each process may be combined i n t h e same p r o j e c t i f appropr ia te . Graphical d i s p l a y of p r e c i p i t a t i o n excess and runoff hydrographs can be provided.

The Ejnvlronmeneal P ro t ec t ion Agencyfs S t o m Water Management &del (SWMM) was designed s p e c i f i c a l l y f o r a n a l y s i s of urban s t o m water runoff and i s one of t h e most comprehensive of such t o o l s a v a i l a b l e , (8) Storm runoff and s a n i t a r y sewage flows from seve ra l subcatchments can be computed us ing d a t a from s e v e r a l p r e c i p i t a t i o n s t a t i o n s . Flow and q u a l i t y a r e routed i n a converging o r " t ree- l ike" network of p ipes o r open channels , Bjiversion f e a t u r e s can be nodeled and e i t h e r on - l ine o r o f f - l i n e s to rage can be s imulated, Of f - l i ne t rea tment can b e modeled. The program a l s o conta ins a module t o a s s e s s t h e impact of p o l l u t a n t loadings on a r ece iv ing water body.

The only po r t ion used i n t h i s s tudy was t h e runoff module. Techniques used i n t h i s module a r e hydrau l i c i n na tu re , i , e . , e x p l i c i t c a l c u l a t i o n s a r e made of t h e depth of water In overland flow and i n channels, This technique r equ i r e s d e t a i l e d subcatchment d a t a , inc luding subcatchment c h a r a c t e r i s t i c s and channel geometry. R a i n f a l l excess i s computed us lng Horton 5 i n f i l t r a t i o n equat ion, a simple time-decay of i n f i l t r a t i o n r a t e , R a i n f a l l i n t e n s i t y is n o t considered. The m d e l has t he c a p a b i l i t y of us ing da&a from a d i f f e r e n t raingage ( a s i n g l e hyetograph) f o r each subeatchment, The kinematic wave method is used f o r overland flow and channel flow rou t ing i n t h e ve r s ion of SWW employed i n t h i s study.

The m s s a c h u s e t t s I n s t i t u t e of Tee'ranology Catchment m d e l (MITGAT)(~) is a comprehensive mathematical model used f o r t h e s tudy of stormwater runoff , It has many s i m i l a r i t i e s t o t h e S M m d e l except t h a t MITGAT has no runoff q u a l i t y computation capab i , l i t y and does n o t possess computational elements f o r t rea tment and r ece iv ing waters ,

Runoff volume is calculated by one of four infiltration equations: Horton's method, Holtan's method, SCS method and the coefficient method. A oatchment is discretized into a series of overland flow planes, stream segments and pipe segments. Runoff excesses are routed over the watershed surface and in conveyance elements by the kinematic wave method. The model also possesses a reservoir routing module,

SECTION 3

Procedure

A spl i t - record t e s t was devised t o d e m n s t r a t e the appl ica t ion of each continuous si.mulation m d e l . The avai lable r m o f f record was divided in to two subsets , The f i r s t subset consisted of the records f o r the 1 9 m n t h s beginning i n November 1991 and continuing through b r c h 9973. The second subset consisted of the records f o r the 25 m n t h s beginning in Apri l 1973 and ending i n Apr i l 1975. For severa l of the m n t k s i n each subset the re was no measurable p rec ip i t a t ion ( four months i n the f i r s t subset a d 22 i n t h e second subset). S T O m and HE@-16 did not generate any simulated r m o f f f o r these m n t h s because they do not simulate base flow,

The f i r s t d a t a subset was used a s the c a l i b r a t i o n period, Appropriate coef f i c ien t s regula t ing t h e r m o f f quant i ty i n each model were adjusted so t h a t computed t o t a l period runoff volumes, fltonthly volumes and d a i l y volumes most near ly matched obsemed values f o r the data subset, Each model was considered ca l ib ra ted when fu r the r adjustment of c e r t a i n coef f i c ien t s did not produce s i g n i f i c a n t l y c lose r agreement, One c a m o t guarantee t h a t the f i n a l sets of parameters a r e unique s ince the re a r e more parameters requir ing adjustment i n each m d e l than $he n u h e r t h a t are measurable o r can be e a s i l y defined,

The following rout ing metbds were used in the continuous m d e l applicati.ons, with a one-hour time s t e p employed i n each instance:

Land Surface: uni.1: u n i t k inem t i e m l t i p l e hydrograph hydrograph wave rese rvo i r

C hanne 1. s : none none kinernat i c mul t i p l e wave r e s e m o i r

Results

Table 2 presents the computed and observed r w o f f volumes f o r the c a l i b r a t i o n period, Table 3 presents the cornput s emed runof l volumes f o r the ca l fb ra t ion period,

Conclusions with respect t o the accuracies of each m d e l f o r the Gastro Valley appl ica t ion should be made on the bas is of agreement between computed and observed r e s u l t s from the second da ta subset o r v e r i f i c a t i o n period, A l l r e s u l t s f o r the v e r i f i c a t i o n period were obtained by using the coef f i c ien t s developed during the c a l i b r a t i o n phase f o r each model, Table 4 presents the computed and observed runoff vo f o r the v e r i f i ca t ion period. Table 5 presents the camp observed rurnoff volumes f o r the v e r i f i ca t ion period,

A s t a t i s t i c a l analys is was perfomed using the %IEC W l t i p l e Linear Regression prograrn(l2) &a order t o quantify the degree of agreement between computed and observed r e s u l t s , '%he r e s u l t s of that: analys is a r e presented i n Table 6 , page l9+

(Continued on Page 20)

TABLE 2

RESULTS FOR CONTINUOUS lrlDDELS FOR THE WEIBaATION PERIOD,

GASTRO VALLEY BDNTHLY VOLUMES (INCHES)

1.60 1.68 1.56 1.87

1 , O l 1.28 2.73

2.30 2.16 2.80 2.65 2.62

.a8 1.16

5.00 5.36 5.59 6.00

2.95 3.03 3.82 3.24 4.21

1,58 1 ,46 2.33 1.70 2.28

SUM 18.28 2.83 12.16 17.25 16.83 20,70 19.54 21,22

1 ,33 1.29 1.59 1.50 1.63

*: Baseflow e s t i m a t i o n s have been added t o v a l u e s f o r STOM and HEC-lC, (Baseflow is inc luded i n v a l u e s computed by WSP and SSARR).

*: LEQ-1 = Loss Equat ion No, 1 ( C o e f f i c i e n t Method) LEQ-2 = Loss Equat ion No. 2 (SCS &thod) LEQ-3 = Loss Equat ion No, 3 (Combination o f both methods)

TABLE 3

RESULTS FOR CONTINUOUS MODELS FOR THB CALIBRATION PERIOD,

CASTRO VAUEY D ~ I L Y RUNOFF VOLUMES ( INCHES)

- - - - -

DATE OBSERVED STORM

RUNOFF LEQ- 1 LEQ - 2 LEQ-3 ; HEC-1C HS P SSARR

0 , 000 .008 -008 0.000 .lo6 .I39 .038 .054 .I14 . I 2 7 .I44 .I74 .030 .020 .068 0.000 .068 ,125 .213 .I24 .053 .027 .380 ,415 .440 .446 ,068 .011 -152 -049 -023 ,006 -053 .011 .061 .033 . 1 2 1 .076 ,091 .030 .213 -112 .061 .030 .273 ,180 .030 0.000 .030 .024 .09 1 .052 .030 .012 .046 .070 .030 .030 .053 .062 .061 .074 .068 .082 .334 .645 .038 0 . 000 .O08 0.000 .I21 .088 ,091 .034 .I37 ,087 .07 6 .OX2 .008 0,000

0,000 0.000 .I14 .I57 .I14 -149 .008 0.000

0.000 0,000 .I14 .096 .008 0.000

( C o n t i n u e d )

T U L E 3 (Continued)

RIESaTS FOR CONTmUOUS WDEES FOR THE CALIBRATION PERIOD,

CASTEU) VALLEY BA ILY RWOFF VOLUMES ( PNCBES )

DATE OBSERVZD STGM RUNOFF LEQ - 9 LEQ-2 LEQ-3 NEC - 1C HS P

.008 .806 ,258 .300 .I21 .067 .008 0.000 .I67 .I74 .288 .005 .615 .982 .281 .038 .I14 0.000 -030 0,000 .I67 .059 .228 -142 .I37 .046 -015 0,000 0,000 0,000 .053 .034 ,121 .1 22 .I29 .I42 .220 .084 -023 0,000 .046 .012 -038 .012 .387 .310 .653 .561 .091 0.000 .49 3 .418 .425 .345 -030 0.000 .008 0,000 0.000 0,000 .956 ,9 14 -49.7 .424

1.154 1.140 .061 0.000 -008 0,000 .I67 .045 .I29 -030 .266 .I05 . 137 .048 -030 -018 -812 -620 . 137 0.000 -023 0.000 .250 .222 .296 -050 -213 .082 .243 .I81

(Continued )

TABLE 3 ( C o n t i n u e d )

RESULTS FOR CONTINUOUS M3DELS FOR THE CALIBRATION PERIOD,

CASTRO VALLEY DAILY RUNOFF VOLUMES (IYCHES)

TABLE 4

RESULTS FOR CONTINUOUS MODELS FOR THE VERIFICATION PERIOD,

CASTRo VALLEY MONTHLY VOLUMES ( INCHES)

Jc: Baseflow es t imat ions have been added t o va lues f o r STORM and HEC-1C, (Baseflow i s included i n va lues computed by HSP and SSARR).

J c : LEQ-1 = Loss Equation No. 1 ( C o e f f i c i e n t Method) LEQ-2 = Loss Equation No. 2 (SCS Method) LEQ-3 = Loss Equation No, 3 (Combination of bo th methods)

RESULTS FOR CONTMUOUS MIDELS FOR THE VERIFICATION PERIOD,

CASTRO VALLEY DAILY RUNOFF VOLUMES (INCHES)

DATE OBSERVED STORM

RUNOFF LEQ-1 LEQ-2 LEQ - 3 HEC - LC HS P S SARR I .I37 .012 .008 .I74

0.000 0.000 .030 0,000 .053 ,104 .342 1.071 .410 .289 .038 0.000 .008 0,000 .053 -029 .266 .155 .478 .498 .402 .430 -083 .007 .516 .369 .380 -302 ,7 13 1.1.13 .653 .304 .I97 .080 .213 .075 .220 . lo7 . 7 2 1 .566 .243 .I41 .182 -025 -091 .026 .091 .022 -395 .216 .213 .032 .046 0.000 .lo6 .029 .11.4 .047 .I29 .034 .091 -039 .053 .037 .288 .I49

0.000 -082 .243 .320 .304 .065 .205 .I26 .I97 .092 .175 .I15 . 220 -251 .334 .I53 .I21 .044

1,442 1,760 .I67 0,000 .266 .I17 106 -096

(Continued )

TABLE 5 ( C o n t i n u e d )

H S U E T S FOR CONTINUOUS M36)ELS FOR THE VERIFICATIOH PERIOD,

CASTRO VALLEY DAILY R m O F F VOLUMES (INCHES)

BATE OBSERVED STORM RUNOFF LEQ-1 LEQ - 2 LEQ-3 HEC-16: HS P S S A M

TABLE 6

S t a n d a r d E r r o r ( i n . )

S t a n d a r d E r r o r ( i n , )

S t a n d a r d E r r o r ( in . )

S t a n d a r d E r r o r (in.)

STATISTICAL ANALYSIS O F RESULTS FOR THE CONTINUOUS W D E L S

S T O M LEQ-3

HEC - 1C

PlDNTHLY CALIBRATION PERIOD

.9 4 .97 .9 7

m M T U Y V E R I F I U T I O N PERIOD

.95 094 .9%

DAILY WLIBRfaTION PERIOD

.79 .85 .79

DAILY VERIF I U T I O N PERIOD

.89 .88 .75

NSP - S SARR

The r e s u l t s presented i n Table 6 show t h a t t h e SCS Runoff-Curve-Number Technique i n STORM (combined wi th t h e HEC-developed s imple mo i s ture-accounting procedure) produced b e t t e r r e s u l t s than t h e c o e f f i c i e n t method, One would expect t h i s t o be t h e c a s e s i n c e t h e HEC-developed method a t tempts t o account f o r an tecedent condi t ions (a l though crudely) and the SCS method a t tempts t o account f o r t h e n o n l i n e a r i t y between r a i n f a l l and runoff dur ing a r a i n f a l l sequence. The c o e f f i c i e n t method uses a land-use weighted runoff c o e f f i c i e n t computed from runoff c o e f f i c i e n t s f o r t h e pervious and impervious p o r t ions of t h e watershed. The b a s i s of weight ing i s t he r e l a t i v e per cent o f imperviousness of each land use , The composite runoff c o e f f i c i e n t i s held cons tan t throughout an e n t i r e s imula t ion r ega rd l e s s of r a i n f a l l amounts o r antecedent condi t ions .

The degree of complexity of d a t a prepara t ion and rainfal .1-runoff c a l c u l a t i o n s had l e s s e f f e c t on r e s u l t s than expected. While r a i n f a l l - r u n o f f procedures i n HSP and SSARR a r e q u i t e involved, they d id no t produce b e t t e r r e s u l t s than STORM o r HEC-1C when comparing d a i l y and monthly vol.umes. It should be pointed ou t t h a t SSARR w a s developed t o model r a t h e r l a r g e nonurban bas ins i n t h e Columbia Ri.ver System, whi le STORM and HEC-1.C were developed t o be used a s genera l ized planning t o o l s f o r sma l l e r urban o r urbaniz ing bas ins . Despi te t h i s d i f f e r e n c e i n o r i g i n a l purpose, SSARR was succes s fu l ly adapted t o an urban watershed.

SECTION 4

S IFNUTION RESULTS, S INGLE-EVENT ElODEkS

Procedure

Comparisons of r e s u l t s from STOW, HSB, SSARR, HEC-I, SWMM and MITCAT were made f o r s e v e r a l i nd iv idua l runoff events , Three events were taken from t h e c a l i b r a t i o n period and four from t h e v e r i f i c a t i o n period, For t h e continuous s imula t ion model STOIITr, t he corresponding s ingle-event hydrographs were simply e x t r a c t e d from t h e r e s u l t s previously obtained dur ing t h e c a l i b r a t i o n and v e r i f i c a t i o n o f m n t h l y and d a i l y runoff volumes ( i , e , , no s p e c i a l a t tempt w a s made t o r e c a l i b r a t e f o r t h e s i n g l e events) . For t h e continuous s imula t ion models SSARR and HSB, no s p e c i a l a t tempt was made t o r e c a l i b r a t e them f o r s i n g l e events ; however, because of a v a i l a b l e channel rou t ing opt ions they were re run f o r t h e ind iv idua l events us ing s h o r t e r time s t e p s (6-min, f o r SSARR and 15-mine f o r HSP),

The fol lowing rou t ing methods were used i n t h e s ingle-event model appl i . ca t i,ons :

HEC- I P

SWWd - MSTWT

Land Surface: u n i t kinematic kinematic hydrograph wave wave

Channels : none kinematic kinematic wave wave

Resul t s

The observed versus the computed r e s u l t s f o r t h e t h r e e events i n t he c a l i b r a t i o n period a r e shown i n f i g u r e s 2 through 3 , and Figures 8 through 15 show t h e r e s u l t s f o r t h e four events i n t h e v e r i f i c a t i o n period:

G a l i b r a t ion 16 Jan 73

Continuous Models: S ing le Went kbdels :

17-18 Jan 73 @ontinuous Pbde1.s : Sing le Wen t Ikde l s :

6 Feb 73 Continuous k d e l s : S ingEe Event Models :

V e r i f i c a t i o n 3-4 Jan 74

Gont inuous k d e l s : Sing le Event Mbdels :

5 Jan 74 Gontinuous f i d e l s : S ing le Event b d e l s :

16-17 Jan 74 Continuous Models: S ing le Event Models:

1 Apr 7 4 Continuous Models : S i n g l e Event I k d e l s :

Pigure 2, page 22 Fi.gure 3 , page 23

Figure 4, page 2 4 Figure 5, page 25

Figure 6, page 26 Pigure 7, page 27

Fi.gure 8, page 28 Figure 9 , page 29

Figure 10, page 30 Figure 11, page 31

Figure 12, page 32 Figure 13, page 33

Figure 14, page 34 Pigure 15, page 35

(Continued on Page 36)

CO

NTI

NU

OU

S

MO

DE

LS -

CA

LIB

RA

TIO

N

s43 '39aw~3sla FIGURE 3

FIGURE 4

S43 ' ~ ~ U V H ~ S I Q FIGURE 5

FIGURE 6

FIGURE 7

FIGURE 8

FIGURE 9

s43 '39tlv~3sla FIGURE 10

s4-3 ' 3 9 ~ t l ~ 3 ~ l a FIGURE 12

FIGURE 13

FIGURE 14

FIGURE 15

Model Parameters

Several parameters required fo r the SCS method i n S'EORMwere obtained from References 13 and 14, A summary of the important STOW loss parameters i s given i n Table 7, page 37.

The parameters fo r the single-event version of HEC-1 (Flood Hydrograph Package) were developed on a number of individual events in the ca l ib ra t ion period. I n i t i a l estimates of the un i t hydrograph charac te r i s t i cs required fo r HE@-1 fo r @as t ro Valley were developed using a U,S, Geological Survey procedure,(15) Seven storms were selected from the ca l ib ra t ion period to serve as the basis fo r development of average un i t graph, loss r a t e , and antecedent moisture parameters. The HEC-1 model has the capabi l i ty of optimizing the magnitudes of these parameters fo r individual events on the basis of accurate reproduction of the observed individual events, The optimized parameters a r e shown in Table 8, page 38. Mean values of the parameters were then used for each of four individual events i n the ve r i f i c a t i on period. The r e su l t s using HE@-1 a r e presented i n Figures 3, 5, 7 , 9 , 11, 13 and 15.

Recal.1 t h a t the SWMM and MI.TWT m d e l s were a lso applied to a t o t a l of seven individual events. Table 9 , page 38, presents the adopted va1.ues fo r the several parameters used to ca l ib ra te these two models, These adopted val,ues, developed from three events in the ca l ib ra t ion period, were used t o recons t i tu te four events i n the ve r i f i c a t i on period. The r e su l t s a r e shown in Figures 3, 5 , 7 , 9 , 11, 13 and 15,

Based on the r e su l t s from reconst i tu t ing four hydrographs i n the ve r i f i c a t i on period, none of the models tes ted exhibited a d i s t i n c t advantage in accuracy, Each model produced acceptable r e su l t s , in view of the limited e f f o r t of each appl ica t ion,

TABLE 8

HEC - 1 OPTIMIZED PARAMETERS FOR THE CALIBWTION PERIOD, CASTELO V A U E Y

DATE - TC - 2 2 D e c 7 1 1,06

27 Dec 7 1 . 94

11 Qc t 7 2 .22

9 Jan 73 .37

16 Jan 73 -35

1 7 Jan 73 $17

6 Feb 73 .4'7

PRECP

.42

.19

1.4.5

.67

1,35

.70

1.39

XCESS

.1.6

.03

0 45

.45

.98

.48

.67

TABLE 9

SWM AND MITCAT PARAMETERS, CASTRO VALLEY

SWMM Parameters

Impervious area res is tance fac tor = 0.013

Pervious area res i s tance fac tor = 0.250

Depression storage on impervious areas = 0.04 inches

Depression storage on pervious areas = 0.06 inches

Maximum i n f i l t r a t i o n r a t e = 0.3 incheslhr,

Minimum i n f i l t r a t i o n r a t e = 0.1 incheslhr.

Decay r a t e f o r i n f i l t r a t i o n = 0.00115

MITCAT Parameters

SCS Curve Number fo r impervious areas = 98

SCS Curve Number f o r pervious areas = 89

I n i t i a l surface detention = 0-02 inches

SECTION 5

S IMULATION RESULTS, GENERAL

The ease of data preparation and application was judged to be the most significant basis for differentiation among the models tested, STORM required the least amount of data preparation, while SWMM and MITCAT required the most. HEC-1 required moderate data preparation. The amount of data required is directly related to the type of computations performed by the model. STORM and HEC-1 use lumped-parameter hydrologic methods. These include generalized loss-rate functions based on land use, accumulated loss or some other nongeometric attributes of the watershed or of rainfall-runoff characteristics. These two hydrologic methods usually require a minimum amount of data. By contrast, SWMM, HSP and MITCAT use a hydraulic method to compute the routing of flow over watershed surfaces and in conveyance elements (pipes and channels), namely, the kinematic wave method of routing flows, Considerable effort was required to subdivide the watershed and to determine subcatchment detailed characteristics such as areas, surface slopes, surface roughness, pipe and channel geometry and roughness, and the connectivity of the conveyance elements. Table 10 presents a summary of the relative accuracies of all six models for both the calibration and verification periods. Table 11 summarizes computer processing-time requirements for the continuous models and provides typical requirements for the single-event models. CPU requirements in Table 11 are all for a GDC 7600 computer, except for the HSP which was run on an IBM 370.

1

Yo.?, 99o.0,

I m o m m d s ~ m4-\o I PICOmpI m e , mi-irla

m m * 1

m m m I

m m m 4 - 4 - 4 - 4 - I b b b b

3 G d d k c d a c d a

TABLE I1

COmUTER %Im REQUIEeEMENTS

CONTINUOUS mDELS,* PERIOD OF S I~PATION NOVEMBER 1971 THROUGH APRIL 1975

STOREa SmRM STORM HEC-1C HSP - SSARR

P

@W Seconds 1.1 4 ,1. 3 -9 9 - 1 29.4 1 1 , O Time Step, Minutes 60 60 6 0 6 0 60 60 Number of

Subcatchments 1 1 1 1. 2 2 Number of

Routing Reaches 0 0 0 0 0 I

( 2 : HSP was run on an I B M 3701168, A l l o t h e r s were run on a GBG 7600, which is approximately twice as f a s t ) ,

S INGLE-EVENT rnDELS, ** PER SINGLE EVm%

Average Execution Time, CPU Seconds 0,129 3.1.3

Time Step, Minutes 15 10 Number of Time Steps

Simulated 150 9 0 Average Execution Time

Per T ime Step, CPU Seconds 0.00086 0,035

Number o f Subcatchments 1 3 2 Number of Routing Reaches 0 38

(**: MITCAT has a g r e a t e r amount of ~npu t /Ou tpu t processi,ng than WE-1. and SWMM),

The cooperat ion and a s s i s t a n c e o f s e v e r a l persons a t The Hydrologic Engineering Center is g r a t e f u l l y achowledged by the w r i t e r , Thei r con&ribut ions have significantly assisted in the completion of this study, Kenneth Brooks accomplished t h e c a l i b r a t i o n o f the SSkM rmdel, A r t Pitbst a s s i s t e d i n the c a l i b r a t i o n of H Z - I 6 and mTMT, A l l appl icatduns using STOW, BEG-1, HEC-1C, SSARE, SWm and mTWT were accomplished by Paul Ely, David Williams, John Koltz and a;he w r i t e r ,

Constructive com'ients on t h i s r e p o r t were provided by B i l l Elchert, Dale Burne t t , J o b Pe te r s , Arlen Feldman and Darryl Davis.

Brook &aeger of Hydrocowp Inkerna t iona l , Inc, , Palo Al to , Cal i f ~ m i a , accamplished t h e a p p l i c a t i o n of HSP,

This r e p o r t was prepared a t The Hydrologic Engineering Center by J e s s Abbott under tee d i r e c t i o n o f Tony Thon~as and Arlen Feldman,

B r a n d s t e t t e r , A., assessment of Mthemat ica l k d e l s f o r Storm and Combined Sewer bnagement , B a t t e l l e P a c i f i c Northwest Labora tor ies , Richland, Washington, August 1976,

Brown, J, W,, e t al,, Padels and Mxtkods Applicable t o Corps of Engineers Urban S tud ie s , U,S, Army Engineer Waterways Experiment S t a t i o n , Vicksburg, Mis s i s s ipp i , August 1974,

Eumb, A, M,, Comparison of t h e Georgia Tech, Kansas, Kentucky, S tanford and TVA Watershed k d e l s i n Georgia, Georgia I n s t i t u t e of Technology, A t l an t a , Georgia, January 1976,

S torage Treatment Overflow Runoff Model, 'Users PSanual, T ie Hydrologi.c Engineering Center , Davis, Cal.iforni.a, August 1977

Slydrocomp S imulati .o~s Programing, Operat ions %nual, Second Edi t ion , Palo Al to , Ca l i fo rn i a , July 1969, wi th r e v i s i o n s of November 1970 and February 1972.

Streamflow Synthes is and Reservoir Regulation, Users Manual, U,S, Army Engineer Div is ion , North Pac i f ic., Por t land , Oregon, Septenber 1972 wi th r e v i s i o n s of December 197 2 ,

HEC-1 Flood Hydrograph Package, Users Mnua l , The Hydrologic Engineering Center, Davis, C a l i f ~ m i a , January 1973,

Storm Water mnagement b d e l , Users Manual, Version 91, U,S, Environmental P ro t ec t ion Technology S e r i e s EPA-670/2-75-017, Wrch 1975,

MITGAT Catckment Simulat ion &de%, Descri .ption and U s e r g s Mnua l , Version 6, Draf t , September 1975, Resource Analysis Ine,, Cambridge, Massachusetts,

The Hydrologic Engineering Center, PY 71-75 Reports on t h e Q u a l i t y of Urban Storm Runoff Enter ing $he San Francisco Bay, Davis, Cal i forn i .a ,

%ckus, V, , e t a l e , U,S, S o i l Consemat ion Serv ice , Nati.onal. Engineering Handbook, Sec t ion 4 , Hydrology, 1964, w i & & r e v i s i o n s of 1969,

%I t i p l e Linear Regression, Users k n u a l , The Hydro'logic Engineering Center , Davis, Cal i , forn ia , January 1975,

Urban Hydrology f o r Small Watersheds, Technical Release No, 55, U,S, S o i l Consenvation Serv ice , January 1975,

S o i l Survey Alameda Area, C a l i f o r n i a , U,S, S o i l Conservation Serv ice and C a l i f o r n i a Agr i cu l tu ra l Experiment S t a t i o n , S e r i e s 1961, No, 41, Wrch 1966.

Suggested C r i t e r i a f o r Hydrologic Design of Storm Drainage i n t h e San Francisco Bay Region C a l i f o r n i a , U,S, Geckogical Survey, Menlo Park, C a l i f o r n i a , 1971.

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