Simulated streamflow data for North Carolina

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UNC

-WRRT

-P1 -1 70

STNULATFP STREAFTFLOW DATA

FOR

N O R 9 3 HAROLTNA

Edward H. W i s e r

Department of R i o l o g i c a l and A g r i c u l t u r a l E n g i n e e r i n g A g r i c u l t u r a l R e s e a r c h F e r v i c e

S c h o o l o f A g r i c u l t u r e and L i f e S c i e n c e s North C a r o l i n a S t a t e U n i v ~ r s i t y

R a l e i g h , North C a r o l i n a 27650

The work upon which t h i s p u b l i c a t i . o n i s based was s u p p o r t e d i n p a r t by f u n d s p r o v i d e d by t h e O f f i c e of Water R e s e a r c h and Technology, U. S.

E e p a r t m e n t o f t h e I n t e r i o r , t h r o u g h t h e Water R e s o u r c e s R e s e a r c h I n s t i t u t e o f The U n i v e r s i t y of P o r t h C a r o l i n a a s a u t h o r i z e d b y t h e W a t e r R e s e a r c h and Development Act o f 1978.

_

P r o j e c t 110. A-Oaz-FC

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DISCLAIMER STATENENT

C o n t e n t s o f t h i s p u b l i c a t i o n do n o t n e c e s s a r i l y r e f l e c t t h e v i e w s and p o l i c i e s o f t h e O f f i c e of Water R e s e a r c h and Technology, U. S. D e p a r t - ment o f t h e I n t e r i o r , n o r d o e s mention o f t r a d e names o r commercinl p r o d u c t s c o n s t i t u t e t h e i r endorsement o r recommendation f o r u s e by t h e

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ACKNOWLEDGMENTS

T h i s r e p o r t i s based on r e s e a r c h s u p p o r t e d p a r t l y by f u n d s p r o v i d e d by t h e O f f i c e o f Water Research and Technology, Department o f t h e

I n t e r i o r , through t h e Water Resources Researeh T n s t i t u t e of The U n i v e r s i t y o f North C a r o l i n a a s a u t h o r i z e d by She Water Research and Development Act o f 1978, Pro,ject Plumber A-093-PC, Agreement No. 14-34-0001-7070; and by t h e A g r i c u l t u r a l Research S e r v i c e , North

C a r o l i n a S t a t e U n i v e r s i t y . The s u p p o r t and a s s i s t a n c e of t h e D i r e c t o r s o f t h e I n s t i t u t e , N e i l Grigg and James S t e w a r t , a n d o f t h e

A d m i n i s t r a t i v e A s s i s t a n t , Linda K i g e r , i s g r a t e f u l l y acknowledged. The s u p p o r t of t h e D i r e c t o r and A s s s r i a t e D l r e c t o r of t h e A g r i c u l t u r a l Research S e r v i c e , Durward Bateman and George K r i z , i s a l s o g r a t e f u l l y acknowledged.

Much o f t h e r e s e a r c h d e a l t w i t h t h e S t r e a m f l o w S y n t h e s i s and

R e s e r v o i r R e g u l a t i o n model developed by t h e Water C o n t r o l Branch o f t h e North P a c i f i c D i v i s i o n ,

U.

S. Army Corps o f E n g i n e e r s , David Rockwood, Chief. The c o o p e r a t i v e s p i r i t shown by Mr. Rockwood, R i l l y J. Thomas, and o t h e r s o f t h a t o f f i c e i s a p p r e c i a t e d .

A p p r e c i a t i o n i s a l s o due t o members o f t h e s t a f f o f t h e O f f i c e o f Water Resource P l a n n i n g o f t h e North C a r o l i n a Department o f N a t u r a l Resources and Community Development. The c o n t i n u e d a d v i c e and

c o o p e r a t i o n o f John Wray, B i l l Bland and Byron Kagol, p a r t i c u l a r l y w i t h r e s p e c t t o t h e Level R Planning Study on t h e Yadkin-Pee Dee R i v e r b a s i n ,

i s g r a t e f u l l y acknowledged.

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ABSTRACT

A s y s t e m h a s been developed f o r s i m u l a t j o n s f s t r e a m f l o w d a t a a t

any p o i n t i n .i region. The s y s t e m i s known ;13 F1CSSAF.R ( ~ o r t h C a r o l i n a

v e r s i o n of t h e Streamflow S y n ~ h e s i s and R e s e r v o i r R e g u l a t i o n model). RTCSSARR i s based on t h e S t r e a m f l ~ w S y n t h e s i s and R e s e r v o t r Regula- t i o n (SSARR) program developed a t t h e North P a c i f i c D i v i s i o n of t h e Corps of E n g i n e e r s i n P o r t l a n d , Oregon. C o n t r o l programming m i n i m i z e s i n p u t r e q u i r e m e n t s t o p e r m i t a p l a n n e r w i t h l i m i t e d h y d r o l o g i c o r com- p u t e r background t o u s e t h e system. The system i s i n t e r f a c e d w i t h t h e d a t a s t o r a g e and r e t r i e v a l system known a s HTSARS t o p r o v i d e c o n v e n i e n t d a t a a c c e s s a s w e l l a s r o u t i n e p r o c e s s i n g o f t h e s i m u l a t e d s t r e a m f l o w d a t a .

S i m u l a t e d s t r e a m f l o w d a t a have been o b t s i n e d f o r most r i v e r b ~ s i n s i n North C a r o l i n a o P a r a m e t e r s r e q u i r e d f o r t h e s i m u l a t i o n have been o b t a i n e d by comparing t h e s i m u l a t e d d a t a w i t h observed d a t a wherever a v a i l a b l e . A f t e r f i t t i n g , t h e s i m u l a t e d d a t a hsve been compared w i t h observed d a t a w i t h r e s p e c t t o s e v e r a l c r i t e r i a , incl-udkng mean f l o w , low f l o w , h i g h f l o w and monthly d i s t r f b u t i o n . The d a t a a r e i n r e a s o n a b l e agreement f o r most s t r e e m gages, i m p l y i n g t h a t t h e s i m u l a t e d d a t a may be used i n l i e u o f o b s e r v a t i o n s wherever t h e l a t t e r a r e n o t a v a i l a b l e .

The s i m u l a t e d s t r e a m f l o w d a t a may be used t o s t u d y a l t e r n ~ t i v e management of t h e w a t e r r e s o a r c e s

~f

a b a s i n . It i s p o s s i b l e t o i n t r o - duce one o r more proposed r e s e r v o i r s i n t o t h e s y s t e m t o d e t e r m i n e t h e e f f e c t of o p e r a t i o n o f t h e r e s e r v o i r s on downstream f l o w s . It i s a l s o p o s s i b l e t o s i m u l a t e t h e e f f e c t oP d i v e r s i o n o f f l o w , w i t h r e t u r n t o a n o t h e r l o c n t i o n . It i s a l s o p o s s f b l e t o modify w a t e r s h e d c h a r a c t e r - i s t i c s and i n t h i s way s t u d y t h e e f f e c t of p o t e n t i a l development on streamflow.

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TARLR

OF CONTENTS

ACKNOWLEDGMENTS. e ~ ~ ~ e e ~ o B B B B B B B B B D D D iii D D o ~

ABSTRACT

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v

TABLE OF CONTENTS

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vii

LIST

OF

FIGURES

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X SWMARY

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xi

1

.

INTRODUCTION

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1

2

.

THE WCSSARR SYSTEM

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2

2.1. SSARR

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2

2.2. KISARS

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7

2.3. CONTROL

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8

2.4. System Outline

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10

2.5. Sub-basin Organization

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12

2.6.

Basin Simulation

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13

2.7. Stored file^...^^..^^^^^^^.^^.^^^^.^^..^^^... 13

3 .

PARAMETER FITTTWG

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15

7.1. Fitting Criteria

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15

3.2. Model Parameters.*

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17

7 1.3. Effect of Parameter Modiffcation on Fitting Criteria

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18

4

.

RESULTS.~..

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23

4.1.

Introduction

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27

4.2. Tar River Basin

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24

4.3. Neuse River Basin

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25

4.4.

Cape Fear River Basin

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26

4.5. Yadkin-Pee Dee River Rasin

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27

4.6. Catawba River Basin

...

29

4.7.

Rroad River Basina

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70

4.8.

New River B ~ s i n . . . o s s e a . . e . . .

30

4.9.

Watauga River Basin*

...a..e...

71

4.10.

French Rroad River Basin

...

31

4.11.

Hiwassee River Basin . . . a e a a e . e s . . . 32

4.12. Little Tennessee River Basin

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32

4.13. Savannah River Basin . . . e . e * . . . e . . . . 73

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Page

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....

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5

APPLICATIONS . . . o . . . . e . . . B e o . . . a e . * . . e e . . * . . . e . 3 6

5.1. The Level R Study on the Yadkin-Pee Dee River Basin

....

₃₆

.

5.2. Total Streamflow . . . o . . e . o . . . * . . .

38 ...

5.3.

Simulation of Unfitted Watersheds ₇₉

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5.4.

Hourly Simulation . . . a . a a e . e . . n e . . . . e . . o . . 40

6 .

REFERENCES

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4.1

.

APPENDIX A TAR RIVER BASINeeo*.e.ee.e.o

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A- 1

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Comparison of Simulated and Observed Data

A-

7

Sub-basin Organization

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A-

5

Simulation Job Control . . . a . . e . . . O e e e . O e O . . . A-

9 .

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APPENDIX R NEUSE RIVER BASIN a a . e . e o a e e . m ...o..e.... 3- 1

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_B-

₃

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B-

7

Simulation Job Control

. . . o e ~ . ~ o ~ . . .

B-11

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APPENDIX C

.

CAPE FEAR RIVER BASINe.e...oe

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a * . . . C- I

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C-

7 ...

C-

9

Simulation Job Control ......e..............e.ee............ C-19

.

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APPENDIX

D

YADKIN PEE DEE RIVER BASIN

n-

1 ...

D-

3

Sub-basin Organization . . . e . . e e . e . . . D-11

Simulation Job Control . . . a e . e ~ ~ . e . e . . . D-29

...

.

APPENDIX E CATAWBA RIVER BASIN

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E-

1

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E-

3 ...

Sub-basin Organization E- 7

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E-11

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APPENDIX F BROAD RIVER BASIN.

...

. . . . m . . . * . . .

F-

1

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Comparison of Simulated and Observed Data F-

3 ...

F- 5

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Simulation Job Control F-

7 .

APPENDIX

G

NEW

/

WATAUGA RIVER BASINS

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G- 1

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Comparison of Simulated and Observed Data G-

7 ...

G-

5 ...

G- 7

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Page

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APPENDIX

H

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FRENCH H3ObD RIVEN RBSTD.a.ee . . ~ e a s e n e e ~ o e e. . e e s s e . e

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C o m p a r i s o ~ l of S i m u l a t e d m c E Observed

Da

t~

S u b - b a s i n O r g a n i z a t i o n . . ~ ~ o e ~ ~ ~ B B ( i ~ ~ ~ ~ e e ~ Y ~ o o ~ ~ D D D ~ o ~ ~ ~ ~ ~ .

S i m u l a t i o n Job ContrboS

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APPENDIX

I

.

HIWASSEE ! ZETTEE

TRNEESSRR

/ BAVATJRAH RIVER BASINS

.

Comparison o f S i m u l a t e d and Observed Data

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S u b - b a s i n O r g a n i z a t i o n

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S i m u l a t i o n J o b C o n t r o l o

...

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APPENDIX J AUXTLTARY P I L E S . . . O . .

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C r e a t i o n s f t h e NCSSARR Main Program

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C o m p i l a t i o n ( ~ ~ ~ i c a l )

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Linkage E d i t i n g

C r e a t i o n of A u x i l i a r y P i l e s . . . e . . . . ~ e e o . . m . a ~ . . .

C r e a t i o n of CRFIEE

-

J o b C o n t r o l

...

C r e a t i o n of CBFTEE

-

C a t a l o g e d P ~ o c e d u r e

C r e a t i o n o f CCFILE

-

Job C o n t r o l . . . m e . . . . e . . .

C r e a t i o n of CCPIEE

-

C a t a l o g e d P r o c e d u r e

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C r e a t i o n o f CFIEE

-

J o b C o n t r o l

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C r e a t i o n of CFILS

-

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C r e a t i o n o f PFIEE

-

J o b C o n t r o l ......te..e.e..........

C r e a t f o n o f PFTEE

-

...

C r e a t i o n of S i m u l a t e d Date F i l e s . . . e . . . s . a . . . .

.

INZT

-

I n i t i a t i o n sf S u b - b a s i n S i m u l a t i o n

...

CONT

-

C o n t i n u a t i o n o f S i m u l a t i o n

CHAR

-

C r e a t i o n of Common C h a r a c t e r i s t i c P i l e

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TSO CEEST f o r C r e a t i o n o f S i m u l a t e d Data F i l e

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Comparison o f S i m u l a t e d Data w i t h Observed Records

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NCSRSAS

-

P r o c e d u r e f o r T e s t i n g o f S i m u l a t e d Data

TSO CEIST f o r T e s t i n g o f S i m u l a t e d Data

...

BASINPPT.CNTE

-

J o b C o n t r o l . . . e . . . e . o

...

TSTCARD

-

P i l e o f Card Images f o r T e s t S p e c i f i c a t i o n

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E x e c u t i o n o f WCSSARR

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RCSSARR

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P r o c e d u r e f o r Fxectxtion o f NCSSARR

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TSO CEIST f o r E x e c u t i o n o f NCSSARR

...

RUN.CNTE

-

J o b C o n t r o l

...

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LEST

OF

FIGURES

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S t r e a m f l o w d a t a have been s i m u l a t e d f o r a number of r i v e r b a s i n s i n North C a r o l i n a . The d a t a were s i m u l a t e d u s i n g t h e NCSSARR s y s t e m ,

f i t t i n g t h e model p a r a m e t e r s f o r gaged w a t e r s h e d s i n t h e b a s i n s .

A number of t e s t c r i t e r i a were used i n f i t t i n g t h e model p a r a - m e t e r s , t o e n s u r e t h a t t h e mean f l o w , low f l o w , h i g h f l o w and monthly d i s t r i b u t i o n of t h e s i m u l a t e d d a t a were i n r e a s o n a b l e agreement w i t h t h e o b s e r v a t i o n s . The v a l u e s o f t h e t e s t c r i t e r i a have been t a b u l a t e d .

The r e s u l t s show t h a t t h e s i m u l a t e d d ~ t a a r e i n r e a s o n a b l e a g r e e - ment w i t h t h e observed d a t a i n all b a s i n s , and c s n be used f o r l o c a t i o n s where observed d a t a a r e n o t a v a i l a b l e . The s i m u l a t e d d a t a a r e most r e l i a b l e i n t h e mountains and i n a r e a s w i t h an a d e q u a t e number of p r e c i - p i t a t i o n gages. They a p p e a r t o be somewhat l e s s r e l i a b l e i n t h e Pied- mont and Coastal. P l a i n . Although t h e e f f e c t of i n a d e q u a t e p r e c i p i - t a t i o n measurements a f f e c t s t h e comparison o f s i m u l a t e d and observed d a t a , i t should have l i t t l e e f f e c t on t h e u t i l i t y of t h e s i m u l a t e d d a t a .

Data a r e s i m u l a t e d on h e a d w a t e r and t r i b u t a r y w a t e r s h e d s a s w e l l a s on main s t r e a m s under n a t u r a l c o n d i t i o n s . Where t h e s t r e a m s a r e u n a f f - e c t e d by r e g u l a t i o n o r d i v e r s i o n , t h e agreement i s v e r y good. Where r e g u l a t i o n i s s i g n i f i c a n t , however, t h e s i m u l a t i o n should be m o d i f i e d a c c o r d i n g l y .

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INTRODUCTION

The i m p o r t a n c e of r e g i o n a l p l a n n i n g i s d e m o n s t r a t e d by t h e l a r g e number o f s t a t e w a t e r p l a n s now under development. Developers of t h e s e p l a n s must know how much w a t e r i s a v a i l a b l e , a s i t v a r i e s through s p a c e and through time.

P r o s p e c t i v e development p r o j e c t s such a s r e s e r v o i r s and d i v e r s i o n s c a u s e changes t o t h e s t r e a m f l o w regime. While t h e g e n e r a l e f f e c t o f s u c h p r o j e c t s i s u n d e r s t o o d , o c c a s i o n a l l y u n f o r e s e e n consequences o c c u r which c a u s e s e r i o u s problems. I n a d d i t i o n , changes i n t h e urban dewe- lopment p a t t e r n s of a r e g i o n change both t h e h y d r o l o g i c c h a r a c t e r i s t i c s and t h e w a t e r r e q u i r e m e n t s of t h e a r e a . E v a l u a t i o n of t h e consequences o f such changes r e q u i r e s d e t a i l e d a n a l y s i s u s i n g t e c h n i q u e s such a s s i m u l a t i o n .

I n a p r e v i o u s s t u d y ( w i s e r , 1976), a s i m u l a t i o n system c a l l e d HCSSARR was developed. T h i s system provided a means f o r o b t a i n i n g a s y n t h e t i c s t r e a m f l o w r e c o r d a t any p o i n t g i v e n o n l y a sub-basin i d e n t i - f i c a t i o n and t h e upstream watershed a r e a . To d e m o n s t r a t e i t s u t i l i t y , a s i m u l a t i o n o f t h e Meuse R i v e r b a s i n was made and r e s u l t s were compared w i t h observed r e c o r d s a t gaged l o c a t i o n s .

T h i s r e p o r t summarizes work done t o extend t h e s i m u l a t i o n t o t h e e n t i r e s t a t e of North C a r o l i n a . Emphasis i s on t h e c r i t e r i a used t o f i t t h e p a r a m e t e r s , t h e t e c h n i q u e s o f f i t t i n g t h e p a r a m e t e r s and a comparison of t h e s i m u l a t e d r e s u l t s w i t h observed r e c o r d s . Only t o t h e e x t e n t r e q u i r e d t o f u l f i l l t h e s e a i m s i s b a s i c m a t e r i a l on t h e system i t s e l f i n c l u d e d , and t h i s i s d r a w n l a r g e l y f r o m t h e r e p o r t o f t h e p r e v i o u s s t u d y , which w i l l be r e f e r r e d t o a s t h e f i r s t r e p o r t .

Some changes have been made t o t h e o r i g i n a l v e r s i o n o f t h e system. These, t o g e t h e r w i t h c o r r e c t i o n s t o t h e f i r s t r e p o r t w i l l be d e s c r i b e d s p e c i f i c a l l y . For c o m p l e t e d e t a i l s on t h e s y s t e m t h e r e a d e r i s

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THE NCSSARR SYSTEM

NCSSARR i s a system t h a t h a s been developed t o s i m u l a t e s t r e a m f l o w a t any p o i n t i n a r i v e r b a s i n . Watershed s i m u l a t i o n and b a s i n o r g a n i z a - t i o n a r e based on t h e S t r e a m f l o w S y n t h e s i s and R e s e r v o i r R e g u l a t i o n (SSARR) program. To t h i s h a s been added f e a t u r e s t o make o u t p u t compat- i b l e w i t h t h e Hydrologic I n f o r m a t i o n S t o r a g e and R e t r i e v a l System

(HISARS), and o r g a n i z a t i o n o f t h e whole t o make i t more c o n v e n i e n t f o r u s e r s .

T h i s c h a p t e r summarizes t h e NCSSARR system. For more d e t a i l , t h e r e a d e r i s r e f e r r e d t o t h e f i r s t r e p o r t ( ~ i s e r , 1976).

2.1

.

SSARR

- -

The S t r e a m f l o w S y n t h e s i s and R e s e r v o i r R e g u l a t i o n program was developed by t h e North P a c i f i c D i v i s i o n o f t h e U. S. Army Corps o f E n g i n e e r s ( ~ o c k w o o d , 1968). The system h a s been used on l a r g e complex r i v e r

b a s i n s i n c l u d i n g t h e Columbia and Aekong Rivers. It i s c u r r e n t l y b e i n g used f o r o p e r a t i o n a l f o r e c a s t i n g i n t h e P a c i f i c Northwest.

The s y s t e m i s much t o o complex t o d e s c r i b e h e r e i n d e t a i l .

E x c e l l e n t d o c u m e n t a t i o n i s a v a i l a b l e i n t h e Program D e s c r i p t i o n and User Manual

--

f o r SSARR, (u. S. Army Engineer D i v i s i o n , North P a c i f i c ,

m27

which may be o b t a i n e d from t h e d i v i s i o n o f f i c e i n P o r t l a n d , Oregon. b

g e n e r a l knowledge of SSARR i s n e c e s s a r y i n o r d e r t o u n d e r s t a n d BCSSARR, s o a b r i e f o u t l i n e o f t h e s y s t e m i s g i v e n here. The above r e f e r e n c e h a s been drawn upon f r e e l y i n t h i s d e s c r i p t i o n .

I n SSARR, r i v e r b a s i n s a r e broken down i n t o f o u r m a j o r t y p e s of components:

a ) Watersheds;

b ) Lakes and r e s e r v o i r s ; c ) Channel r e a c h e s ; d ) Summing p o i n t s .

The a c t u a l s e l e c t i o n of b a s i n s i s t o a c o n s i d e r a b l e e x t e n t

a r b i t r a r y . Each o f t h e b a s i n s i n d i c a t e d could i t s e l f be s u b d i v i d e d i f r e q u i r e d . On t h e o t h e r hand, making t h e b a s i n s much l a r g e r could i n t r o d u c e e x c e s s i v e h e t e r o g e n e i t y i n t o each b a s i n which could n o t be a d e q u a t e l y modelled.

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SSARR p r o c e s s e s t h e p a r t s i n t h r e e s t a g e s :

a! a watershed model f o r s y n t h e s i z i n g o u t f l o w from each w a t e r s h e d ; b) a r i v e r system model f o r a c c u m u l a t i n g and r o u t i n g s t r e a m f l o w through channel and l a k e s t o r 8 g e ;

c) a r e s e r v o i r r e g u l a t i o n model f o s a n a l y s i s of r e s e r v o i r o u t f l o w and c o n t e n t s .

The watershed model i s i l l u s t r a t e d i n F i g u r e 2.1. l l o i s t u r e i n p u t (which may i n c l u d e r a i n f a l l and snowmel-t) i s d i v i d e d i n t o r u n o f f and

a c c u m u l a t i o n t o s o i l m o i s t u r e by STIII:

-

t h e s o i l m o i s t u r e index. The s o i l m o i s t u r e i s d e p l e t e d o n l y by e v a p o t r a n s p i r a t i o n , a l t h o u g h deep s e e p a g e o u t of t h e w a t e r s h e d c m presumably be i n c l u d e d . Runoff i s d i v i d e d i n t o b a s e f l o w and d i r e c * r u n o f f by B I T

-

t h e base f l o w i n f i l t r a t i o n index. D i r e c t r u n o f f i s f u r t h e r d i v i d ~ d i n t o s u r f a c e and s u b s u r f a c e components by S-SS

-

t h e s u r f a c e

-

s u b - s u r f a c e flow s e p a r a t i o n .

S e v e r a l a s p e c t s o f t h e model a r e worth emphasizing:

1 ) R a i n f a l l i n p u t may be m u l t i p l i e d by a f a c t o r t o o b t a i n t h e m o i s t u r e i n p u t , i n c a s e t h e r a i n g a g e i s known t o be n o n - r e p r e s e n t a t i v e o f t h e w a t e r s h e d .

2) M o i s t u r e i n p u t i s d i v i d e d i m m e d i a t e l y i n t o r u n o f f and s o i l

m o i s t u r e accumulation. T h i s means t h a t n e i t h e r s u b s u r f a c e f l o w n o r b a s e f l o w a r e i n t e r p r e t e d a s p a r t o f t h e s o i l m o i s t u r e a t any t i m e , and a r e t h e r e f o r e n o t s u b j e c t t o l o s s by e v a p o r a t i o n o r deep seepage.

3)

The o n l y ways by which w a t e r l e a v e s t h e watershed a r e by e v a p o t r a n s p i r a t i o n and s t r e a m f l o w . E v a p o t r a n s p i r a t i o n may be l i m i t e d e i t h e r by r a i n f a l l o r by low s o i l m o i s t u r e c o n t e n t . I f t h e r e i s

groundwater f l o w i n t o o r o u t o f t h e w a t e r s h e d , t h i s i s lumped w i t h t h e e v a p o t r a n s p i r a t i o n , and t h e q u a n t i t y i s r e f e r r e d t o a s t h e

e v a p o t r a n s p i r a t i o n i n d e x (ETI!

.

4) There i s no l i m i t placed on t h e s o i l . m o i s t u r e index. It c s n however be c o n t r o l l e d by making t h e r u n o f f p e r c e n t a g e s u f f i c i e n t l y h i g h a t a g i v e n v a l u e o f t h e s o i l m o i s t u r e i n d e x .

5)

A unique f e a t u r e of t h e model i s t h e u s e o f t a b u l a r f u n c t i o n s f o r t h e S M T , B I T and S-SS r e l a t i o n s . Values a r e o b t a i n e d by t a b l e lookup and i n t e r p o l a t i o n r a t h e r t h a n by e q u a t i o n .

6 ) The SMI r e l a t i o n r e l a t e s t h e runoff p e r c e n t a g e

(ROP)

t o t h e s o i l m o i s t u r e i n d e x , o p t i o n a l l y a s a f u n c t i o n of t h e r a i n f a l l i n t e n s i t y .

7) The

BIT

r e l a t i o n r e l a t e s t h e b a s e f l o w p e r c e n t a g e (RFP) t o t h e b a s e f l o w i n f i l t r a t i o n i n d e x and an o p t i o n a l b a s e f l o w i n p u t l i m i t .

8 ) The S-SS r e l a t i o n r e l a t e s t h e r a t e o f r u n o f f t o t h e r a t e o f d i r e c t r u n o f f . T h i s i s g e n e r a l l y s e t s o t h a t s u b s u r f a c e r u n o f f i s dominant a t v e r y low d i r e c t r u n o f f r a t e s , b u t a s t h e r a t e o f d i r e c t r u n o f f i n c r e a s e s , t h e s u b - s u r f a c e r u n o f f becomes c o n s t a n t and t h e e x c e s s

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I

A C C U M U L A T I O Y

G V A P O T R A N S P I R 4TTOY

SOIL M O I S T U R E

R U U O F F

0

RASE

FLOW

Cr;

d

- --- STREAMFLOW --

-_-

Figure 2.1. SSARR Watershed Yodel

{u.

S. Army ~ n ~ i n e e r s )

0

zz H € 4

='

C

P:

C3 2 I+

E+

3 C

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(2) A l l t h r e e components o f r u n o f f ( s ~ a r f a c e , s u b s u r f a c e and b a s e flow) a r e r o u t e d s e p a r a t e l y t o t h e s t r e a m . T h i s p e r m i t s r e q u i r e d t i m e s e p a r a t i o n of t h e components t o produce a d e s l r e d hydrograph form. Routing i s c o n t r o l l e d by t h e number o f p h a s e s and t i m e o f s t o r a g e p e r phase

-

b a s i c a l l y t h e same method a s i s used i n t h e r i v e r system model.

10) There i s f a i r l y comprehensive m o d e l l i n g o f snowmelt. S i n c e t h i s i s of minor i m p o r t a n c e i n n o r t h C a r o l i n a , t h e procedure has n o t been e v a l u a t e d a s p a r t of t h i s p r o j e c t .

The r i v e r system model o r g a n i z e s t h e components o f t h e r i v e r b a s i n a s i n F i g u r e 2.2. T h i s r e q u i r e s a c c u m u l a t i o n of f l o w a t t h e summing p o i n t s , r o u t i n g o f f l o w through channel r e a c h e s , l a k e s and r e s e r v o i r s , and c o n t r o l f u n c t i o n s such RS r e s e r v o i r o p e r a t i o n and d i v e r s i o n s .

The r o u t i n g method i s based on t h e c o n t i n u i t y e q u a t i o n and assumes a r e l a t i o n between s t o r a g e ( 3 ) and o u t f l o w ( 0 ) o f t h e form:

S = TsO.

The p r o p o r t i o n a l i t y f a c t o r Ts i s r e f e r r e d t o a s t h e

--

t i m e o f s t o r a g e . For channel r o u t i n g , i t may be assumed t o v a r y w i t h d i s c h a r g e . One method i s t o assume t h e r e l a t i o n

-

(KTS)

Ts -

---

Q"

where KTS i s an e m p i r i c a l l y determined c o n s t a n t ;

Q i s t h e d i s c h a r g e ;

n i s an e m p i r i c a l c o e f f i c i e n t usual3.y between -1 and + l .

A l t e r n a t i v e l y , i t i s p o s s i b l e t o s p e c i f y any complex r e l a t i o n s h i p of Ts t o Q i n t a b u l ~ r form.

During a run, t a b l e s and s t a t i o n c h a r a c t e r i s t i c s a r e s t o r e d i n a

f i l e r e f e r r e d t o a s t h e c h a r a c t e r i s t i c file. T h i s f i l e may be stored permanently, so t h a t r e p e a t e d r u n s u s i n g t h e same s t a t i o n s and t a b l e s do

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2 . 2 . HISARS

The Hydrologic I n f o r m a t i o n P t o r a g e and R e t r i e v a l System (HISARS) was developed a t North C a r o l i n a F t a t e U n i v e r s i t y ( w i s e r , 19751. The system i s d e s i g n e d f o r s t o r a g e , r e t r i e v a l and r o u t i n e p r o c e s s i n g of h y d r o l o g i c d a t a .

Data l i s t i n g and p r o c e s s i n g f u n c t i o n s have been used w i d e l y f o r observed d a t a , and many u s e r s have become f a m i l i a r w i t h i t s use. It seemed r e a s o n a b l e , t h e r e f o r e , t o u s e t h e s e same c a p a b i l i t i e s on t h e s y n t h e t i c d a t a produced by SSARR. F u r t h e r , w i t h s t a t e w i d e r a i n f a l l d a t a f i l e s a l r e a d y a v a i l a b l e from permanent s t o r a g e , t h e s e should be d i r e c t l y a v a i l a b l e t o SSARR.

S t a n d a r d i z e d f i l e f o r m a t s have been developed f o r HISARS. Although d a t a could be c o n v e r t e d from HISARS f o r m a t t o SSARR f o r m a t b e f o r e

p r o c e s s i n g by SSARR, i t i s more e f f i c i e n t t o modify SSARR t o read t h e HISARS f i l e s d i r e c t l y , and t h i s h a s been done f o r t h e v e r s i o n o f SSARR used i n NCSSARR.

HISARS u s e s an e i g h t - d i g i t code t o i d e n t i f y s t r e a m f l o w s t a t i o n s , w h i l e SSARR can a c c e p t up t o nine. T h i s t h e r e f o r e caused no problems. However, HISARS u s e s a s i x - d i g i t code t o i d e n t i f y r a i n f a l l s t a t i o n s , w h i l e SSARR i s l i m i t e d t o f o u r . T h i s was s o l v e d by i n c l u d i n g i n t h e SSARR i n p u t deck ( a s a r a i n f a l l s t ~ t i o n c h a r a c t e r i s t i c ) a number t r a n s l a t i o n t o c o n v e r t t h e i n t e r n a l (SSARR) code t o t h e e x t e r n a l

(HISARS) code.

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2.3. CONTROL

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The f u n c t i o n o f t h e CONTROL program i s t o read u s e r - o r i e n t e d i n p u t , produce t h e r e q u i r e d c o n t r o l s t a t e m e n t s f o r SSARR and/or HISARS, and t o c o n t r o l t h e subsequent p r o c e s s i n g . Although i t i s designed t o p e r m i t t h e c a s u a l u s e r t o u s e t h e s y s t e m w i t h minimal i n p u t r e q u i r e m e n t s , CONTROL a l s o p e r m i t s a s u b s t a n t i a l p a r t o f t h e f u l l SSARR c a p a b i l i t y t o

be u t i l i z e d .

CONTROL r e c o g n i z e s t h e f o l l o w i n g commands:

S T R E A M F L O W / O ~ ~ /0p2 R E S E R V O I R ~ O ~ I /0p2 DIVERSION/OPI /0p2 R E T U R N / O ~ ~ /0p2 T E S T / O ~ I /0p2

PERIOD ml/yyyl TO m2/yyy2 HISARS.

I N a d d i t i o n , SSARR and HISARS c o n t r o l c a r d s a r e a c c e p t e d under c e r t a i n r e s t r i c t i o n s .

The purpose o f t h e f i r s t f o u r commands i s t o s p e c i f y where s y n t h e - t i c strea.mflow r e c o r d s a r e r e q u i r e d and where a r e s e r v o i r , d i v e r s i o n o r r e t u r n p o i n t i s t o be l o c a t e d . I n each c a s e , t h e f i r s t operand s p e c i - f i e s t h e s u b - b a s i n i n which t h e p o i n t i s l o c a t e d , and t h e second

( o p t i o n a l ) operand s p e c i f i e s t h e watershed a r e a above t h e p o i n t .

The TEST command i s used t o compare s i m u l a t e d and observed s t r e ~ m - f l o w r e c o r d s . The s i m u l a t e d record i s f o r t h e p o i n t s p e c i f i e d by t h e f i r s t STREAMFLOW control. card. The f i r s t operand s p e c i f i e s t h e U. S.

-

G e o l o g i c a l Survey s t a t i o n number f o r t h e observed r e c o r d , and t h e second operand s p e c i f i e s t h e watershed a r e a .

The PERIOD command l i m i t s t h e period o f r e c o r d f o r which s i m u l a t i o n i s r e q u i r e d . l f i t i s o m i t t e d , t h e s t a n d a r d p e r i o d used i n c r e a t i n g t h e permanent f i l e i s used.

The HISARS command s p e c i f i e s t h a t HISARS p r o c e s s i n g i s d e s i r e d . I t must be followed by HISARS commands t o s p e c i f y t h e p r o c e s s i n g r e q u i r e d .

SSARR c o n t r o l c a r d s may be i n c l u d e d i n t h e i n p u t deck, and a r e r e q u i r e d i n some c a s e s . R e s e r v o i r , d i v e r s i o n and r e t u r n p o i n t

c h a r a c t e r i s t i c s must be e n t e r e d on SSARR c o n t r o l c a r d s , and should be e n t e r e d i m m e d i a t e l y f o l l o w i n g t h e CONTROL command f o r t h e p o i n t . A

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What CONTROL does a s a consequence o f c e r t a i n commands b e i n g g i v e n depends on t h e p a r t i c u l a r c h a r a c t e r o f t h e commands. There a r e t h r e e major s u b - c l a s s e s i n t h e p r o c e s s i n g :

1 ) No SSARR p r o c e s s i n g i s r e q u i r e d . T h i s w i l l be t r u e i f o n l y STREANFLOW, HISARS and o p t i o n a l PERIOD commands a r e u s e d , and i f on t h e STREAMFLOW commands o n l y t h e f i r s t operand i s s p e c i f i e d . I n t h i s c a s e , t h e r e q u i r e d simul-ated s t r e a m f l o w r e c o r d s a r e a l r e a d y i n t h e permanent f i l e , and no s i m u l a t i o n i s r e q u i r e d . C o n t r o l p a s s e s d i r e c t l y t o HISARS.

2) S t r e a m f l o w s i m u l a t i o n i s r e q u i r e d , b u t no r e s e r v o i r s , d i v e r s i o n s o r r e t u r n p o i n t s a r e s p e c i f i e d . T h i s w i l l be t r u e i f STREAMFLOW

commands a r e used, w i t h b o t h operands s p e c i f i e d on one o r more commands, w i t h o p t i o n a l TEST, PER103 and HISARS commands. I n t h i s c a s e , s i m u l a t e d s t r e a m f l o w r e c o r d s f o r whole s u b - b a s i n s (second operand o m i t t e d ) a r e copied from t h e permanent f i l e . For p a r t i a l s u b - b a s i n s , t h e r e a r e two a l t e r n a t i v e s . I f t h e p a r t i a l sub-bnsin i s i n t e r n a l t o a s u b - b a s i n , o n l y t h e watershed c h a r a c t e r i s t i c and c o r r e s p o n d i n g c o n f i g u r a t i o n c a r d s must be c r e a t e d . I f t h e p a r t i a l s u b - b a s i n i s a l o n g a main c h a n n e l , t h e watershed and channel r e a c h c h a r a c t e r i s t i c s must be c r e a t e d , t h e

upstream p o i n t must be i d e n t i f i e d , and c o n f i g u r a t i o n c a r d s t o r o u t e t h e upstream f l o w t o t h e s p e c i f i e d p o i n t and add i n t h e l o c s l i n f l o w must b e s p e c i f i e d .

3)

F u l l s i m u l a t i o n i s ~ e q u i r e d . T h i s w i l l be t r u e i f r e s e r v o i r s , d i v e r s i o n s o r r e t u r n p o i n t s a r e s p e c i f i e d . The p a r t i c u l a r i n f o r m a t i o n r e q u i r e d depends on t h e s p e c i f i c a t i o n , b u t i n g e n e r a l , w a t e r s h e d ,

channel r e a c h , r e s e r v o i r and d i v e r s i o n c h a r a c t e r i s t i c s w i l l be r e q u i r e d . C o n f i g u r a t i o n c a r d s n e c e s s a r y t o r o u t e f l o w s from r e s e r v o i r s , d i v e r s i o n s and r e t u r n p o i n t s (assumed upstream) t o s t r e a m f l o w p o i n t s (assumed

downstream) a r e r e q u i r e d , and t h e p o s s i b i l i t y of segments i n two r i v e r b a s i n s ( f o r i n t e r - b a s i n t r a n s f e r s ) i n c l u d e d .

CONTROL does n o t p e r m i t two o r more s t r e a m f l o w , r e s e r v o i r ,

d i v e r s i o n o r r e t u r n p o i n t s w i t h i n a s i n g l e sub-basin. I n c a s e s where t h i s i s r e q u i r e d , e i t h e r t h e s u b - b a s i n must be s u b d i v i d e d o r c o m p l e t e SSARR c o n t r o l c a r d s can be g i v e n .

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2.4. System O u t l i n e

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T h i s s e c t i o n i s p r e s e n t e d f o r t h e purpose o f i d e n t i f y i n g t h e r e l a t i o n s h i p s between t h e v a r i o u s p a r t s o f t h e system. The t e x t u a l m a t e r i a l i s a l s o i l l u s t r a t e d i n F i g u r e 2.7.

P r o c e s s i n g s t a r t s w i t h t h e CONTROL program. T h i s program u s e s t h e system i n p u t t o d e t e r m i n e what f u n c t i o n s a r e t o be performed:

a ) i f SSARR p r o c e s s i n g i s r e q u i r e d , a SSARR c o n t r o l d a t a s e t i s c r e a t e d u s i n g t h e s y s t e m i n p u t , a c a r d image d a t a s e t , and i n t e r n a l c o n t r o l i n f o r m a t i o n ;

b) i f HISARS p r o c e s s i n g i s r e q u i r e d , a HISARS c o n t r o l d a t a s e t and a n i n d e x d a t a s e t a r e c r e a t e d u s i n g t h e s y s t e m i n p u t and i n t e r n a l

c o n t r o l i n f o r m a t i o n ;

c ) f o r SSARR p r o c e s s i n g , t h e permanent c h a r a c t e r i s t i c f i l e i s copied t o a t e m p o r a r y d a t a s e t , This i s n e c e s s a r y because SSARR m o d i f i e s t h e c h a r a c t e r i s t i c f i l e d u r i n g p r o c e s s i n g , and such m o d i f i c a t i o n s c a n n o t be p e r m i t t e d t o t h e permanent f i l e .

P r o c e s s i n g may t h e n c o n t i n u e w i t h SSARR, HISARS o r b o t h , o r i t may t e r m i n a t e i m m e d i a t e l y . Both SSARR and HISARS a r e l a r g e programs, and i t

was d e c i d e d n o t t o t r e a t them a s sub-procedures w i t h i n CONTROL. They a r e i n s t e a d t r e a t e d a s s e p a r a t e s t e p s w i t h i n a job. P r o c e s s i n g c o n t r o l

i s e s t a b l i s h e d by s e t t i n g t h e r e t u r n code (RC) w i t h i n CONTROL. The v a l u e o f t h e r e t u r n code i s t h e n used a s a c o n d i t i o n f o r e x e c u t i n g o r b y p a s s i n g l a t e r s t e p s .

I f t h e r e t u r n code i s e i t h e r 0 o r 1 , t h e SSARR s t e p i s executed. SSARR r e c e i v e s a s i n p u t t h e c o n t r o l d a t a s e t (passed from CONTROL), t h e temporary c h a r a c t e r i s t i c f i l e , r a i n f a l l d a t a i f r e q u i r e d f o r b a s i n s i m u l a t i o n , observed s t r e a m f l o w d a t a (used o n l y f o r t h e t e s t o p t i o n ) , and t h e permanent s i m u l a t e d s t r e a m f l o w d a t a s e t . The s i m u l a t e d o u t p u t

i s n o r m a l l y c r e a t e d a s a t e m p o r a r y d a t a s e t , b u t i t may o p t i o n a l l y b e s t o r e d f o r f u r t h e r p r o c e s s i n g .

I f t h e r e t u r n code i s e i t h e r 0 o r 2, t h e HISARS s t e p i s executed. HISARS r e c e i v e s a s i n p u t t h e c o n t r o l d a t a s e t and s t r e a m f l o w index f i l e

(passed from CONTROL). I f t h e r e t u r n code i s 0, t h e d a t a s e t used f o r s t r e a m f l o w d a t a i n p u t i s t h e s i m u l a t e d o u t p u t d a t a s e t (passed from SSARR). I f t h e r e t u r n code i s 2, t h e permanent s i m u l a t e d s t r e a m f l o w d a t a s e t i s used i n s t e a d .

The p r o b l e m s o f m a i n t a i n i n g c o n t r o l between job s t e p s , and of

(23)

e.:

(24)

2.5. Sub-basin O r g a n i z a t i o n

-

I n NCSSARR, a r i v e r b a s i n i s d i v i d e d i n t o a numbsr o f r e l a t i v e l y homogeneous sub-basins. These s u b - b a s i n s n e c e s s a r i l y v a r y c o n s i d e r a b l y i n s i z e , t y p i c a l l y from a few s q u a r e m i l e s t o s e v e ~ a l hundred s q u a r e m i l e s . While t h e r e would be a d v a n t a g e s t o s i m u l a t i o n a c c u r a c y i n u s i n g s m a l l s u b - b a s i n s , t h i s must be balanced with i n c r e a s e d computer c o s t s .

There a r e two b a s i c t y p e s o f s u b - b a s i n s : a ) w a t e r s h e d s o f t r i b u t a r y s t r e a m s which r e a c h a m a j o r s t r e a m a t t h e o u t l e t ; b) l o c a l a r e a s which c o n t r i b u t e more o r l e s s d i r e c t l y t o a major s t r e a m .

L o c a t i o n s w i t h i n t r i b u t a r y s u b - b a s i n s a r e d e f i n e d by t h e w a t e r s h e d a r e a upstream o f t h e p o i n t . For l o c a t i o n s a l o n g t h e main t r i b u t a r y t h i s may be a unique i d e n t i f i c a t i o n . For s m a l l e r a r e a s , t h e r e may be a

number o f l o c a t i o n s having t h e same watershed area. S i n c e t h e s u b - b a s i n

i s assumed t o be homogeneous, r e s u l t a n t s t r e a m f l o w s c o u l d be assumed t o be s i m i l a r f o r a l l such l o c a t i o n s . Where a p a r t i c u l a r watershed i s known t o have c h a r a c t e r i s t i c s f a r d i f f e r e n t from t h e whole s u b - b a s i n , s p e c i a l a c t i o n may be taken.

L o c a t i o n s i n l o c a l a r e a s a r e a l s o d e f i n e d by t h e w a t e r s h e d a r e a . When a s m a l l a r e a i s r e q u i r e d , t h e s i t u a t i o n i s analogous t o t h e

t r i b u t a r y a r e a . P o i n t s a l o n g t h e main s t r e a m i t s e l f a r e a l s o w i t h i n t h e l o c a l a r e a s , b u t t h e i r wa-tershed a r e a s a r e much l a r g e r t h a n t h e a r e a o f t h e c o n t a i n i n g sub-basin and t h e y a r e d e f i n e d u n i q u e l y .

There a r e a d d i t i o n a l p o i n t s a t b o u n d a r i e s of s u b - b a s i n s and connec- t i o n s w i t h t r i b u t a r i e s which i t i s c o n v e n i e n t t o l o c a t e s p e c i f i c a l l y , These p o i n t s a r e r e f e r r e d t o a s summing p o i n t s . No w a t e r s h e d a r e a need be s p e c i f i e d f o r t h e s e l o c a t i o n s .

Any p o i n t can be l o c a t e d by i t s c o n t a i n i n g sub-basin and watershed a r e a , and t h i s i s t h e l o c a t i o n i d e n t i f i c a t i o n system used by NCSSARR. It does d e f i n e p o i n t s u n i q u e l y a l o n g major s t r e a m s a s w e l l a s on

downstream r e a c h e s of t r i b u t a r i e s . The d i s t i n c t i o n between o t h e r p o i n t s i s o f t e n u n i m p o r t a n t , and can be handled a s a s p e c i a l c a s e when

r e q u i r e d . S e v e r a l examples o f s p e c i a l c a s e s a r e g i v e n i n t h e t e s t r e s u l t s

.

The d e s i g n a t i o n system f o r s u b - b a s i n s i s r e l a t i v e l y f r e e . Methods f o r l a y i n g o u t s u b - b a s i n s and naming them a r e d e s c r i b e d i n t h e f i r s t r e p o r t . NCSSARR does however r e q u i r e r i g i d i t y i n i t s o p e r a t i o n s , and a n i n t e r n a l numbering s y s t e m i s a l s o used. For most a c t i v i t i e s t h e u s e r

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2.6. B a s i n S i m u l a t i o n

--

S i m u l a t i o n o f s t r e a m f l o w i n a r i v e r b a s i n w i l l u s u a l l y proceed i n a s e r i e s o f s t e p s . For b a s i n s of any s i z e , t h e s e w i l l u s u a l l y be organ- i z e d a s s e p a r a t e jobs.

1 ) S i m u l a t i o n i s i n i t i a t e d by a job which c r e a t e s t h e SSARR c h a r a c t e r i s t i c f i l e and s i m u l a t e s s t r e a m f l o w from one sub-basin. The job i n p u t must c o n t a i n a l l t a b u l a r (CT) r e l a t i o n s r e q u i r e d by SSARR, t h e s t a t i o n l o c a t i o n (CP) c a r d s used t o i d e n t i f y t h e HISARS i d e n t i f i c a t i o n codes, and t h e s e t s o f s t a t i o n c h a r a c t e r i s t i c (CB) c a r d s t h a t p r o v i d e t h e sub-basin p a r a m e t e r s .

2) The s u b - b a s i n s i m u l a t i o n i s t h e n extended t o t h e r e m a i n d e r o f t h e sub-basins. It h a s been found convenient t o u s e groups o f 8-12 s u b - b a s i n s i n a job, a l t h o u g h t h i s should depend on t h e a c t u a l computer t i m e r e q u i r e d . The s u b - b a s i n s must be o r d e r e d i n i n c r e a s i n g numeric o r d e r ( u s i n g t h e i n t e r n a l c o d e s ) .

3)

S i m u l a t i o n o f t h e r i v e r b a s i n model t h e n p r o c e e d s w i t h t h e summing p o i n t s , r e a c h e s and r e s e r v o i r s . T h i s r e q u i r e s f o r each p o i n t t h e a s s o c i a t e d c h a r a c t e r i s t i c c a r d s , CC c a r d s f o r summing p o i n t s , CR c a r d s t o p r o v i d e r o u t i n g p a r a m e t e r s f o r r e a c h e s , and CL c a r d s t o p r o v i d e s t o r a g e and r o u t i n g p a r a m e t e r s f o r r e s e r v o i r s . C o n f i g u r a t i o n (P) c a r d s a r e a l s o r e q u i r e d t o d e f i n e t h e o r g a n i z a t i o n o f f l o w i n t h e b a s i n . T h i s s i m u l a t i o n must a l s o proceed i n s t r i c t l y i n c r e a s i n g numeric sequence. I n a d d i t i o n , because i t w i l l u s u a l l y be n e c e s s a r y t o b r e a k it up i n t o a s e r i e s of j o b s , b r e a k s must be c a r e f u l l y s e l e c t e d s o t h a t a l l i n p u t s t o e v e r y s t a t i o n a r e c o n t a i n e d w i t h i n o r p r e c e d i n g t h e job.

4)

A s a f i n a l job s t e p , t h e b a s i n c h a r a c t e r i s t i c f i l e must be d e l e t e d . The r e a s o n f o r t h i s i s t h a t SSARR w i l l s i m u l a t e s t r e a m f l o w i n a sub-basin i f i t can f i n d t h e a s s o c i a t e d CB c a r d s . NCSSARR g e n e r a t e s CB c a r d s i f r e q u i r e d f o r sub-basin s i m u l a t i o n , and o t h e r w i s e u s e s t h e s t o r e d d a t a f o r t h e watershed.

Examples o f b a s i n s i m u l a t i o n a r e g i v e n i n t h e a p p e n d i c e s .

2.7. S t o r e d F i l e s

-

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The form used i s d a i l y f i l e s t o t h i s

i n which observed s t r e a m f l o w i s most w i d e l y a v a i l a b l e and a v e r a g e s t r e a m f l o w , s o i t was decided t o l i m i t s t o r e d

form.

It was a l s o decided t o l i m i t t h e p e r i o d of record t o

25

y e a r s . This i s n e c e s s a r i l y a compromise between s i z e o f s t o r a g e r e q u i r e m e n t and h y d r o l o g i c u t i l i t y . Because t h e most r a i n f a l l r e c o r d s were a v a i l a b l e s t a r t i n g i n l a t e

1948,

r e c o r d s were s i m u l a t e d f o r t h e p e r i o d 1449-1973.

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PARAMETER FITTING

A number o f p a r a m e t e r s o r r e l a t i o n s used by t h e SSARR w a t e r s h e d model must b e f i t t e d f o r i n d i v i d u a l b a s i n s . T h i s i m p l i e s t h a t c r i t e r i a a r e a v a i l a b l e by which g o o d n e s s o f f i t c a n b e judged. I n t h i s c h a p t e r , t h e f i t t i n g c r i t e r i a and p a r a m e t e r s a r e d e s c r i b e d , and t h e e f f e c t s o f m o d i f y i n g p a r a m e t e r s on t h e c r i t e r i a a r e d i s c u s s e d .

The g o a l o f t h e f i t t i n g p r o c e s s was t o o b t a i n a g e n e r a l p u r p o s e s i m u l a t i o n . The mean f l o w s h o u l d a l w a y s b e matched. Low f l o w v a l u e s s h o u l d b e i n r e a s o n a b l e a g r e e m e n t . High f l o w v a l u e s a r e assumed o f l e s s i m p o r t a n c e , b u t t h e maximum d a i l y f l o w s h o u l d a g r e e . O t h e r p a t t e r n s t h a t s h o u l d a g r e e a r e t h e m o n t h l y f l o w d i s t r i b u t i o n and t h e f l o w

d u r a t i o n curve. T r y i n g t o f i t a l l t h e s e r e l a t i o n s n e c e s s a r i l y e n t a i 1 . s compromise, and r e s u l t s f o r more s p e c i f i c p u r p o s e s c o u l d b e e x p e c t e d t o b e more s a t i s f a c t o r y .

3.1. F i t t i n g C r i t e r i a

-

C e r t a i n s t a t i s t i c s o f t h e m o n t h l y t o t a l s w e r e o b t a i n e d . The f o l l o w i n g w e r e used i n a c o m p a r a t i v e s t u d y by t h e World M e t e o r o l o g i c a l O r g a n i z a t i o n (1

975):

C o e f f i c i e n t o f v a r i a t i o n o f t h e r e s i d u a l e r r o r s

2 1 2

rc(s-o)

,

' n '

Y =

,

8

R a t i o o f r e l a t i v e e r r o r t o t h e mean

R =

c

t s-0) ₉

nB

R a t i o o f a b s o l u t e e r r o r t o t h e mean

A =

21s-oL

₉

n

i?

where S i s t h e s i m u l a t e d monthly f l o w , 0 i s t h e o b s e r v e d monthly f l o w ,

6

is t h e a v e r a g e o b s e r v e d monthly f l o w , and n i s t h e number o f months.

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The c o r r e l a t i o n c o e f f i c i e n t was a l s o c a l c u l a t e d :

C' 5

c

Cs!

( 0 )

[ ( c s ~ ) ( c 0 2 ? ] ~ 2

S i n c e i t i s r e a s o n a b l e t o a r g u e t h a t a h i g h c o r r e l a t i o n c o e f f i c i e n t about a l i n e o f b e s t f i t does n o t t e l l much about t h e u t i l i t y o f t h e model u n l e s s t h e l i n e p a s s e s through t h e o r i g i n and h a s a s l o p e o f 1

(observed = s i m u l a t e d ) , a second c o r r e l a t i o n c o e f f i c i e n t was used:

T h i s i s t h e c o r r e l a t i o n c o e f f i c i e n t f o r t h e l i n e S=O. I t can n e v e r be g r e a t e r t h a n C', and may be c o n s i d e r a b l y l e s s i f t h e s i m u l a t i o n i s b a d l y biased. I n f a c t , if t h e r e i s a n e g a t i v e c o r r e l a t i o n , t h e term in t h e numerator w i l l be g r e a t e r t h a n t h e term i n t h e denominator and t h e

r e s u l t w i l l be undefined. S e v e r a l examples of t h i s w i l l be found i n t h e r e s u l t s .

HISARS produces an o u t p u t p l o t o f c u m u l a t i v e f r e q u e n c y o f o c c u r r - ence o f d a i l y s t r e a m f l o w , analogous t o a f l o w d u r a t i o n curve. The f o l l o w i n g s t a t i s t i c was used t o measure t h e d i f f e r e n c e between f l o w d u r a t i o n c u r v e s f o r s i m u l a t e d and observed d a t a :

D

= msx IFs-FoI

,

where Fs i s t h e c u m u l a t i v e frequency of s i m u l a t e d d a i l y f l o w s , and

Fo i s t h e c u m u l a t i v e f r e q u e n c y o f observed d a i l y f l o w s ,

T h i s s t a t i s t i c i s analogous t o t h e Kolmogorov-Smirnov t e s t s t a t i s t i c , b u t i t c a n n o t be used f o r t e s t i n g because t h e d a i l y f l o w v ~ l u e s a r e

h i g h l y c o r r e l a t e d .

These 6 s t a t i s t i c s a r e i d e n t i f i e d a s s t a n d a r d s t a t i s t i c s , and have been e v a l u a t e d f o r each of t h e w a t e r s h e d s t e s t e d .

I n a d d i t i o n t o t h e above s t a t i s t i c s , s t a t i s t i c s o f t h e monthly d i s - t r i b u t i o n o f f l o w , and flow e x t r e m e s , were c a l c u l a t e d :

a! The p e r c e n t a g e o f a n n u a l f l o w o c c u r r i n g d u r i n g each month w ~ s o b t a i n e d . The v a l u e s f o r t h e observed d a t a a r e t a b u l a t e d , and t h e

d e v i a t i o n s from t h e s e v a l u e s f o r t h e s i m u l a t e d d a t a a r e t s b u l a t e d ;

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3.2. Model Parameters

--

A

number of parameters are required for each sub-basin. These can be divided conveniently between fixed characteristics, parameters that must be estimated, and parameters that are assumed to be constant.

Values of the following fixed characteristics are required:

a) Drainage area, square miles;

b) Climatological stations used to obtain precipitation data.

Tables or values of the following parameters must be estimated:

a) Soil moisture index

(SMI)

vs runoff percent

(ROP)

table; b) Baseflow infiltration index

(BTI)

vs percent of runoff to

baseflow

(BFP)

table;

c) Evapotranspiration index (ETI) table; d) Weights for each climatological station; e) Base flow time of storage, hours;

f) Subsurface time of storage, hours; g) Surface time of storage, hours;

Tables or values of the following parameters are assumed to be constant:

a) Rase flow infiltration index time of storage

(TSBIT),

hours

-

taken as 100 hours;

b) Precipitation vs evapotranspiration effectiveness coefficient

(KE)

table

-

Table 8400;

c) Maximum baseflow infiltration index (BIZ), inches per day

-

taken as one inch per day;

d) Surface-subsurface total vs surface component

(s-SS)

table

-

Table 8089.

h ) Number of base flow routing phases

-

taken as one; i) Number of subsurface routing phases

-

taken as two;

j) Number of surface routing phases

-

taken as two in the Coastal Plein, four in the Piedmont and mountains.

Certain SSARR parameters have been ignored. In addition to all the snowmelt parameters, the following are not used:

a) Base flow infiltration index time of storage for falling discharge (same value as for rising discharge);

b) Outflow vs surface time of storage table (constant surface time of storage used).

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The t a b l e s f o r t h e e v a p o t r a n s p i r a t i o n i n d e x (FTI) a r e v a l u e s o f ETI f o r each month. I f t h e a s s u m p t i o n i s made t h a t t h e v a l u e o f ETI depends o n l y on e v a p o t r a n s p i r a t i o n (and n o t on deep s e e p a g e ) , i t would be expected t h a t one t a b l e should a p p l y f o r s e v e r a l s u b - b a s i n s i n t h e same g e n e r a l region. T h e r e f o r e , s e v e r a l t a b l e s were p r e p a r e d , one group o f t a b l e s each f o r t h e mountains, Piedmont and C o a s t a l P l a i n , and t a b l e s w i t h i n each g r o u p w i t h d e c r e a s i n g v a l u e s moving from s o u t h t o n o r t h . These v a l u e s r e f l e c t e d t o a s m a l l e x t e n t p r e l i m i n a r y t e s t s o f t h e model, b u t were more g e n e r a l l y o b t a i n e d from e s t i m a t e s o f p o t e n t i a l evapo- t r a n s p i r a t i o n o b t a i n e d from o t h e r s o u r c e s *

T a b l e s o f t h e s o i l m o i s t u r e i n d e x (SPIT) v s r u n o f f p e r c e n t (ROP) and of t h e b a s e f l o w i n f i l t r a t i o n i n d e x (BIT) v s p e r c e n t o f r u n o f f t o

b a s e f l o w

(BFP)

were more troubl.esome. These v a l u e s should be expected t o v a r y from s u b - b a s i n t o s u b - b a s i n , presumably i n a c o n s i s t e n t manner. The p r e l i m i n a r y a p p r o x i m a t i o n used i n t h e f i r s t r e p o r t o f u s i n g one t a b l e f o r a l l C o a s t a l P l a i n s u b - b a s i n s , and a n o t h e r f o r t h e Piedmont and mountains was c l e a r l y u n s a t i s f a c t o r y , and t h e a l t e r n a t i v e o f h a v i n g a s e p a r a t e t a b l e f o r each s u b - b a s i n became unwie1d.y.

It was decided, t h e r e f o r e , t o compromise w i t h t h e SSARR f o r m a t and p u t v a l u e s o f t h e p a r a m e t e r s i n a s i m p l i f i e d t a b u l a r f o r m a t on t h e

c h a r a c t e r i s t i c c a r d s f o r t h e s t a t i o n , D e t a i l s of t h e f o r m a t changes a r e g i v e n i n Appendix K. E s s e n t i a l l y , r u n o f f p e r c e n t v a l u e s a r e t a b u l a t e d f o r s o i l m o i s t u r e i n d e x v a l u e s o f 0, 2 and

7

i n c h e s and f o r r a i n f a l l i n t e n s i t y v a l u e s o f 0, I , and

5

i n c h e s p e r day. The r e l a t i o n s h i p between b a s e f l o w i n f i l t r a t i o n i n d e x and b a s e f l o w p e r c e n t a g e i s assumed t o t a k e a c e r t a i n shape, w i t h a c t u a l v a l u e s d e f i n e d a t b a s e f l o w i n f i l - t r a t i o n i n d e x v a l u e s o f 0 and

999

i n c h e s . Although t h e s e s i m p l i f i c a - t i o n s n e c e s s a r i l y reduce some of t h e f l e x i b i l i t y of SSARR, t h e y were p r o b a b l y r e q u i r e d i n t h e f a c e o f t h e number o f s u b - b a s i n s b e i n g f i t t e d .

Values o f a l l t h e p a r a m e t e r s f o r each sub-basin a r e giveri i n t h e Appendices. Complete t a b l e s which were r e p e a t e d f o r a l l b a s i n s ,

i n c l u d i n g t h e

ETI

t a b l e s and t h e

KE

and S-SS t a b l e s , a r e g i v e n o n l y i n Appendix I). I n f i t t i n g watershed d a t a , i t was sometimes n e c e s s a r y t o make l o c a l m o d i f i c a t i o n s t o t h e p a r a m e t e r s . When t h i s was done, t h e mod-ified p a r a m e t e r s a r e l i s t e d a t t h e end o f t h e t e s t s t a t i s t i c s , and t h e r e a s o n s f o r making t h e m o d i f i c a t i o n s a r e d i s c u s s e d i n t h e c h a p t e r on r e s u l t s .

3.3.

E f f e c t o f P a r a m e t e r N o d i f i c a t i o n on P i t t i n g C r i t e r i a

-

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I n a r e g i o n w i t h homogeneous p r e c i p i t a t i o n , i t would be e x p e c t e d t h a t t h e measurements a t any r a i n g a g e should be r e p r e s e n t a t i v e o f t h e sub-basin and t h e w e i g h t used f o r t h e s t a t i o n should be 1007. I f s e v - e r a l gages e x i s t i n t h e b a s i n , t h e a v e r a g e weight f o r a l l t h e gages should be loo$, even i f t h e i n d j v i d u a l w e i g h t s v a r y w i t h t h e coverage a s s i g n e d t o e a c h gage. On t h e o t h e r hand, i f p r e c i p i t a t i o n is known t o be non-homogeneous a s i n mountainous w a t e r s h e d s , w e i g h t s might be expected t o vary. If f o r example t h e o n l y gage i n a watershed i s i n t h e v a l l e y , and p r e c i p i t a t i o n i n t h e mountains a s known t o be h i g h e r , t h e weight f o r t h e gage should be g r e a t e r t h a n 100?. S i n c e t h e r e i s n o t any v e r y good way t o d e c i d e on t h e weight i n t h i s c a s e , i t seems l o g i c a l t o u s e t h e mean f l o w t o a d j u s t t h e weight. I n t h i s s t u d y , t h i s i s t h e o n l y

c i r c u m s t a n c e i n which t h e weight was used t o a d j u s t t h e mean flow.

The e v a p o t r a n s p i r a t i o n

(ETJ)

v a l u e s w i l l a l s o a f f e c t t h e mean f l o w , s i n c e i n c r e a s e d e v a p o t r a n s p i r a t i o n must be a t t h e expense o f s t r e a m f l o w . The r e l a t i o n between t h e two i s n o t d i r e c t , however, p a r t i c u l a r l y d u r i n g summer months. It w i l l be r e c a l l e d t h a t t h e r u n o f f p e r c e n t a g e d e t e r - mines t h e amount o f r u n o f f , a f f e c t e d o n l y by t h e s o i l m o i s t u r e index. The e v a p o t r a n s p i r a t i o n i n d e x can a f f e c t r u n o f f o n l y by r e d u c i n g t h e s o i l m o i s t u r e index. I f d u r i n g t h e summer t h e s o i l m o i s t u r e index i s a l r e a d y reduced t o z e r o , i n c r e a s e d RTT v a l u e s d u r i n g t h a t p e r i o d w i l l have

l i t t l e i f any e f f e c t on runoff. During t h e l a t e w i n t e r and e a r l y

s p r i n g , t h e s o i l m o i s t u r e index i s s o h i g h t h a t m o d i f i e d E T I v a l u e s w i l l have l i t t l e immediate e f f e c t , b u t t h e e f f e c t may be a p p a r e n t s e v e r a l months l a t e r . S i n c e a l l t h e s e r e l a t i o n s a r e compounded w i t h t h e r u n o f f p e r c e n t a g e r e l a t i o n , i t was decided t o b a s e t h e ETI v a l u e s on a p r i o r i r e l a t i o n s , f o r example t h e v a l u e s o f p o t e n t i a l e v a p o t r a n s p i r a t i o n g i v e n by van Bavel and V e r l i n d e n (1956).

The mean f l o w v a l u e s were t h e r e f o r e c o n t r o l l e d p r i m a r i l y by t h e r e l a t i o n between t h e s o i l m o i s t u r e i n d e x and t h e r u n o f f p e r c e n t . It should be noted t h a t t h i s i s a c t u a l l y a three-way t a b u l a r r e l a t i o n , i n which t h e r a i n f a l l i n t e n s i t y a l s o h a s an e f f e c t on t h e r u n o f f p e r c e n t . However, s i n c e i n t h i s s t u d y o n l y d a i l y v a l u e s o f p r e c i p i t a t i o n and r u n o f f a r e e v a l u a t e d , t h e r a i n f a l l i n t e n s i t y e f f e c t on r u n o f f p e r c e n t a g e i s s e e n o n l y i n a g r o s s way, a n d t h e r e s u l t s cannot be e x t r a p o l a t e d t o s h o r t - p e r i o d r a i n f a l l e v e n t s .

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f i n a l t o t a l may be reduced.

I t may a l s o be noted i n t h i s c o n n e c t i o n t h a t , a l t h o u g h t h e s o i l m o i s t u r e i n d e x would be c o n s i d e r e d t o be t h e independent v a r i a b l e i n t h e r e l a t i o n , i t i s a f f e c t e d by t h e v a l u e s o f t h e r u n o f f percentage. I f t h e v a l u e s o f t h e runoff p e r c e n t a g e a s s o c i a t e d w i t h h i g h s o i l m o i s t u r e i n d e x v a l u e s a r e r e l a t i v e l y low, t h e s o i l m o i s t u r e index v a l u e w i l l c o n t i n u e t o i n c r e a s e t o l a r g e v a l u e s o f 10 i n c h e s o r more, and i t may t a k e most of t h e summer b e f o r e t h i s i s d e p l e t e d by e v a p o t r a n s p i r a t i o n . On t h e o t h e r hand, i f t h e v a l u e s of t h e r u n o f f p e r c e n t a g e a r e v e r y h i g h , a s i n some s t e e p mountain w a t e r s h e d s w i t h v a l u e s of 805 f o r a s o i l m o i s t u r e index o f o n l y two i n c h e s , t h e maximum v a l u e of t h e s o i l m o i s t u r e i n d e x may n e v e r exceed two i n c h e s , a n amount t h a t w i l l be d e p l e t e d i n t h e s p r i n g .

The monthly d i s t r i b u t i o n of f l o w i s c o n t r o l l e d p r i m a r i l y by t h e r u n o f f p e r c e n t a g e r e l a t i o n , b u t i t i s a f f e c t e d a l s o by t h e b a s e f l o w p e r c e n t a g e r e l a t i o n and b a s e f l o w t i m e o f s t o r a g e . A s i n d i c a t e d above, t h e magnitude o f t h e r u n o f f p e r c e n t a g e c o n t r o l s t h e mean f l o w , b u t

v a r y i n g t h e v a l u e s a s t h e y r e l a t e t o t h e s o i l m o i s t u r e i n d e x w i l l modify t h e monthly d i s t r i b u t i o n . I n c r e a s i n g p e r c e n t a g e s f o r a low s o i l mois- t u r e i n d e x w i l l i n c r e a s e summer r u n o f f . I n c r e a s i n g p e r c e n t a g e s f o r a h i g h s o i l m o i s t u r e i n d e x w i l l i n c r e a s e w i n t e r r u n o f f and d e c r e a s e s p r i n g r u n o f f , w h i l e d e c r e a s i n g p e r c e n t a g e s f o r t h e h i g h s o i l m o i s t u r e i n d e x

w i l l d e c r e a s e w i n t e r r u n o f f and i n c r e a s e s p r i n g and summer r u n o f f .

I n c r e a s i n g t h e b a s e f l o w p e r c e n t a g e w i l l reduce f l o w i m m e d i a t e l y f o l l o w - i n g a p r e c i p i t a t i o n e v e n t and s t r e t c h i t o u t o v e r an extended p e r i o d o f time. Most o f t h i s e f f e c t i s t o reduce w i n t e r r u n o f f and i n c r e a s e s p r i n g and summer r u n o f f . The magnitude o f t h e e f f e c t i n t h e s p r i n g , and t h e e x t e n t t o which i t i s c a r r i e d i n t o t h e summer i s c o n t r o l l e d by t h e b a s e f l o w t i m e o f s t o r a g e .

Low f l o w v a l u e s a r e c o n t r o l l e d by t h e b a s e f l o w p e r c e n t a g e and t h e b a s e f l o w t i m e of s t o r a g e . S i n c e s h o r t low f l o w e v e n t s o c c u r p r i m a r i l y i n t h e f a l l , a f t e r any c a r r y o v e r from t h e w i n t e r i s p r o b a b l y gone, t h e y a r e c o n t r o l l e d p r i m a r i l y by t h e b a s e f l o w percentage. Long low f l o w e v e n t s a r e a f f e c t e d by c a r r y o v e r from t h e w i n t e r a s w e l l a s summer e v e n t s , s o t h e y a r e a f f e c t e d by b a s e f l o w p e r c e n t a g e , b a s e f l o w t i m e o f s t o r a g e and runoff percentage. I n g e n e r a l , t h e f i t o f t h e 90 day mean low f l o w w i l l correspond w i t h t h e f i t of t h e monthly d i s t r i b u t i o n d u r i n g t h e summer and f a l l , and t h e f i t o f t h e 90 day mean h i g h f l o w w i l l