oak Rldgc Nauonal Laboratory OAK RIDGE NATIONAL LABORATORY

UNION CARBIDE CORPORATION for the

U.S. ATOMIC ENERGY COMMISSION

operated by .

4

c

i ORNL- TM- 2343 7 0 7 6 3 0

PREXJMINARY ESTIMATIDN OF EROSION AND RADIOCESIUM REDISPRIBUTION

I N A FESCUE MEADOW

R o g e r C. Dahlman and S. I. A u e r b a c h

BOX No.

FULDER

t;

f 024544

Publicly Releasable

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4-00036 Human Subjects P r o j e c t

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or h is employmnt w i th such contractor. L -l

c -,

ORNL-TM-2 343

C o n t r a c t No. W-7405-eng-26

HEALTH PHYSICS D I V I S I O N

RADIATION EC0IX)GY SECTION

PREUMINARY ESTIMATION OF EROSION AND RADIOCESJXM REDISTRIBUTION

I N A FESCUE MEADOW

R o g e r C. D a h l r n a n and S. I. A u e r b a c h

NOVEMBER 1968

OAK RIDGE NATIONAL LABORATORY

Oak R i d g e , Tennessee

operated by

UNION CARBIDE CORPORATION

for the

U. S. ATOMIC ENERGY COMMISSION

iii

comms Page

A b s t r a c t . . . . . . . . . . . . . . . . . . . . . . , . . . . . . 1

In t roduc t ion . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Measurement of Runoff . . . . . . . . . . . . . . . . . . . . . . 3

Es t imated Radiocesium i n Runoff . . . . . . . . . . , . . . . . . 5

Comparison wi th Other Resul t s . . . . . . . . . . . . . . . . . . 7

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

..

1 0 2 4 5 9 1

PREUMINARY ESTIMATION OF EROSION AND RADIOCESIUM RFDISTRIBUTION

I N A FESCUE MEADOW*

Roger C . Dahlman and S. I. Auerbach

ABSTRACT

The p o t e n t i a l r a d i o a c t i v i t y r e d i s t r i b u t i o n was evaluated f o r

observed and hypo the t i ca l condi t ions of p r e c i p i t a t i o n p r i o r t o

a p p l i c a t i o n of a f a l l o u t simulant t o fescue vegeta t ion . Estimates

from t h i s a n a l y s i s a r e compared with those of t h e rad ionucl ide move-

ment experiment from Area 0807 and a l s o compared wi th p red ic t ions of

e ros ion using t h e Wischmeier and Smith s o i l - l o s s equat ion. Based on

observed e ros ion loss as a func t ion of d i f f e r e n t p r e c i p i t a t i o n events,

approximately .06$ of t h e 137Cs contaminant w i l l move from each

contaminated area annually, and t h e input t o t h e n a t u r a l drainage

2 system w i l l be less than 2 m C i from 4-100 m p l o t s . Th i s es t imate

i s o n e - f o r t i e t h of o t h e r independent p red ic t ions and measurements

because t h e dense fescue vegeta t ion and sod of t h e s imulant-plots

g r e a t l y reduce e ros ion and mineral element loss i n runoff .

*This work i s p a r t o f a cooperat ive p r o j e c t j o i n t l y supported by t h e Off ice of C i v i l Defense, Department of Defense, and t h e U. S. Atomic Energy Commission.

I 0 2 4 5 9 8

3

MEASUREMENT

Runoff c o l l e c t i n g and measuring

OF RUNOFF

devices have been i n s t a l l e d on

2 of 4 p l o t s which w i l l be contaminated with f a l l o u t s imulant .

s p l i t t e r appra tus (F ig . 1) d iv ides the s t ream of water i n t o equal

volumes, and the q u a n t i t y which d ra ins i n t o t h e polyethylene c o l l e c t o r s

i s used t o c a l c u l a t e t o t a l runoff . Subsamples of s o l i d s and s o l u t i o n

w i l l be taken from the c o l l e c t o r s f o r assay of r a d i o a c t i v i t y . This

procedure w i l l monitor m a t e r i a l s c a r r i e d from the p l o t s i n runoff

and w i l l eva lua te lTICs t r a n s f e r t o t h e n a t u r a l drainage system

ou t s ide the experimental a r ea . Before the runoff e x i t s from the

p l o t i t passes through a bas in i n which sand-size p a r t i c l e s s e t t l e ;

therefore , the simulant-sand w i l l not erode from the area .

This

Surface water runoff from p l o t 2 has been observed s ince

October 1967 and from p l o t 7 s i n c e February 1968.

s h i p between p r e c i p i t a t i o n and runoff i s presented i n Table 1, and

the r e s u l t s show t h a t runoff was a l s o r e l a t e d t o s o i l moisture r e -

charge and r a i n f a l l i n t e n s i t y .

r e spec t ive ly , caused d i s s i m i l a r runoff , ye t t he r e s u l t s can be ex-

p la ined on the b a s i s of s o i l water recharge and r a i n f a l l i n t e n s i t y .

By December 21, 3.6 inches of r a i n f a l l had s a t u r a t e d the s o i l dur ing

the preceding 10 days; then, an in t ense r a i n of s h o r t du ra t ion

(0.6 inches) produced 192 l i t e r s of runoff .

r a i n of 3.9 inches caused n e g l i g i b l e runoff because r a i n f a l l dur ing

t h e preceding 10 days had not s a t u r a t e d the s o i l .

much of t he 3.9 inch r a i n f a l l i n f i l t r a t e d the soil.

s o i l system had the capac i ty t o absorb approximately 4 inches of

The r e l a t i o n -

Two r a i n f a l l events, 4 and 5 inches

On January 12, a s teady

I n t h i s case,

I n gene ra l the

. . , , _ . . . _ _ . . . " , "

c

5

accentua ted i n win ter when the water t a b l e i s 1 5 t o 30 inches from the

su r face and i s less s e r i o u s i n summer when i t i s over 50 inches deep.

A f a c t o r l i m i t i n g runoff would be vege ta t ive cover.

s tand of dense g r a s s should enhance t h e absorp t ion of water, thus

reducing runof f . Because the observat ions (Table 1) were made during

the win te r period, a t which time t h e r e i s minimal vege ta t ive cover,

In t h i s case the

low evapo t ransp i r a t ion r a t e s , s a t u r a t e d s o i l and high water tab le ,

the magnitude of runoff from p r e c i p i t a t i o n events during the grow-

ing season probably would not exceed t h a t a l ready measured.

Eroded s o l i d s were almost absent from the runoff water. Apparently

t h e dense cover of g r a s s and l i t t e r f i l t e r e d and removed most of the

s o i l from su r face runoff .

of minera l sediments were adsorbed on the i n s i d e of the polyethylene

Small q u a n t i t i e s (< 1 g/5 l i t e r s runoff )

c o l l e c t o r s . But more than 25 l i t e r s of runoff were necessary t o

d e p o s i t a c o l l e c t a b l e q u a n t i t y of s o l i d ma te r i a l . Obviously, e ros ion

of su r face s o i l should not be a s e r i o u s problem i n t h i s experiment,

a l though w e p l an t o examine the minera l s o l i d s f o r sorbed radiocesium.

ESTIMATED RADIOCESIUM I N RUNOFF

Transfer of radiocesium from the f a l l o u t s imulant t o d i f f e r e n t

components of the system w i l l involve many complex r eac t ions , some

of which would be d i s s o l u t i o n i n water, s o r p t i o n on s o i l , a s s imi l a -

t i o n by p lan ts , and t r a n s p o r t throughout t he p r o f i l e v i a p l an t r o o t s .

The important mechanisms a f f e c t i n g t.he i n i t i a l r e d i s t r i b u t i o n of lyCs

w i l l be s o r p t i o n on s o i l and movement of d i sso lved and s o l i d m a t e r i a l s

i n water . From l a b o r a t o r y tes ts it was determined t h a t t he s imulant

w i l l r e l e a s e 10% of the fixed l r / C s fol lowing con tac t w i th water f o r

7

i

Based on the observed average r a t e of s o i l e ros ion (1 g/5 l i t e r s ) ,

the quan t i ty contained i n 400 l i t e r s of runoff would be 80 g.

q u a n t i t y represented 6.65 x 10

This

$, of the su r face cent imeter of s o i l -3

6 (1.2 x 10 g) i n contac t w i t h the s imulant . The est imated rad io-

cesium t h a t could be removed i n the s o l i d phase i s ca l cu la t ed as 0.04

mCi/plot. Although the g r e a t e s t quan t i ty of r a d i o a c t i v i t y i s c a r r i e d

by s o l i d mater ia l s , the t o t a l loss i n t h i s phase w i l l be n e g l i g i b l e

(0.92 mCi/year from a l l p l o t s ) because the vege ta t ive cover e f f e c t i v e l y

prevents s o i l e ros ion .

The polyethylene c o l l e c t o r s r e t a i n most of the eroded s o i l , and

i n f u t u r e measurements t h i s m a t e r i a l w i l l be removed for rad ioassay

or d i sposa l .

t r a n s f e r r e d d i r e c t l y t o t h e e x t e r i o r drainage system.

are summarized the r a d i o a c t i v i t y movement from p l o t s with c o l l e c t o r s

(480 PCi/year) and without c o l l e c t o r s (1,200 )zCi/year) . the l o s s from p l o t s having no c o l l e c t o r s would be g r e a t e r by a f a c t o r

of 3, t h e r e i s no cause f o r alarm because the p red ic t ed l o s s e s v i a

runoff would c o n s t i t u t e only 0.21% of the 8 c u r i e s of contaminant

i n the 4 p l o t s .

mCi/year) w i l l be r e l eased t o the outs ide dra inage system, and con-

s i d e r i n g the h igh s o r p t i v e capac i ty of l o c a l s o i l f o r cesium, the

contaminant probably w i l l be r e t a ined i n the drainage d i t c h and w i l l

not be c a r r i e d t o the Clinch River.

Thus, contaminated s o i l from only 2 p l o t s w i l l be

I n Table 2

Although

Thus, only a minor quan t i ty of radiocesium (1.7

COMPARISON WITH OTHER RFSULTS

Erosion and runoff va ry g r e a t l y f o r d i f f e r e n t c u l t i v a t i o n p rac t i ces ,

and t h e magnitude of s o i l loss i s a func t ion of many v a r i a b l e s . Because

9

Appl ica t ion of the s o i l - l o s s equat ion was intended f o r c u l t i v a t e d

crops, and i t possesses l i m i t e d u t i l i t y f o r eva lua t ing e ros ion i n

systems of dense cover and i n t a c t sod.

p e r f e c t l y r e a l i s t i c because n e g l i g i b l e e ros ion occurs i n noncul t iva ted

systems such as pas tu re and meadow. Despi te t h i s l i m i t a t i o n i n a p p l i -

c a b i l i t y we w i l l a t tempt t o p red ic t t h e annual e ros ion loss from a

dense s tand of fescue vege ta t ion using appropr ia te terms i n the

s o i l - l o s s equat ion.

t o e s t a b l i s h some understanding of t h e i r meaning and l i m i t a t i o n s .

Also s e l e c t i o n of va lues f o r some terms i s debatab le ; therefore ,

j u s t i f i c a t i o n f o r our choice of va lues i s presented i n the fol lowing

d iscuss ion .

The au thor s ' i n t e n t was

The terms of t h i s equat ion a r e d iscussed b r i e f l y

1 The r a i n f a l l f a c t o r ( R ) , g iven by Wischmeier and Smith , t h e i r

F ig . 1 was based on s o i l loss from c u l t i v a t e d f i e l d s as a func t ion

of E1 ra ins torm c h a r a c t e r i s t i c s . But t he e f f e c t i v e n e s s of the r a i n -

f a l l ' s e ros ive f o r c e would be reduced considerably for a s o i l i n con-

t a c t w i t h an in t ens ive r o o t system and heav i ly covered with f o l i a g e

and l i t t e r . The r o o t - s o i l mat r ix under e s t ab l i shed g r a s s vege ta t ion

p resen t s a completely d i f f e r e n t environment compared wi th fa l low

s o i l . Roots would r e t a i n s o i l t h a t would be dis lodged and eroded

i n the c u l t i v a t e d condi t ion . Because R va lues f o r t he s t a b i l i z e d

s o i l environment should be l e s s than t h a t f o r fa l low s o i l , we propose

t h a t an R of 200 [ repor ted f o r t h i s a r ea by Wischmeier and Smith ]

would r ep resen t a maximum r a t h e r than average r a i n f a l l e ros ive force .

1

The e r o d i b i l i t y f a c t o r (K) i s a f f e c t e d by phys ica l c h a r a c t e r i s t i c s

of the s o i l . Generally, e r o d i b i l i t y i s d i r e c t l y r e l a t e d t o f ineness

-.

11

. The r e s u l t s from 2 l o c a l experiments permit a comparison of pre-

d i c t e d and observed s o i l loss . The terms used i n t h e Wischmeier and

Smith equat ion were based on t h e phys ica l and b i o l o g i c a l cha rac t e r -

i s t i c s of small- and s imulant -p lo ts (Table 3 ) and ca l cu la t ed l o s s e s

were compared a g a i n s t measured e ros ion .

pre l iminary runoff d a t a were c o l l e c t e d f o r six months dur ing which

time the ra te of s o i l loss was approximately 1 g/5 l i t e r s which con-

s t i t u t e s 0.5 g/m and e x t r a p o l a t e s t o 1 g/m /year .

condi t ions of severe runoff, the annual s o i l loss i s p red ic t ed on

t h e b a s i s of 20 r a i n f a l l events each producing 400 l i t e r s of runof f ;

then, we would expect 16 g/m /year [(400 l i t e r s / e v e n t ) (20 even t s ) /

( 5 l i t e r s / g ) (100 m2)].

pred ic t ed va lue (12 g/m ) is more than 1OX g r e a t e r than the observed

t o date, (1 g/m ), bu t under very severe condi t ions the expected 2 (16 g/m ) would be s l i g h t l y g r e a t e r than t h a t pred ic ted from the

model. Agreement between observed and p red ic t ed e ros ion l o s s i s

reasonably gocd cons ider ing t h a t t he s o i l - l o s s model was der ived f o r

c u l t i v a t e d systems. Also, w e must remember t h a t topographic f e a t u r e s

of the s imulant -p lo ts approach the lower l i m i t s for which the model

i s app l i cab le .

Considering the s imulant-plots ,

2 2 For a n t i c i p a t e d

2

Using t h e Wischmeier and Smith model t he 2

2

273 Continuous observa t ion of e ros ion from t a l l meadow smal l -p lo ts

over a two-year per iod provide a d d i t i o n a l r e s u l t s f o r c o r r e l a t i n g

p red ic t ed and observed s o i l l o s s .

loss from the vege ta ted system was 72 g/m

l o s s e s of 42 g/m . 13 g/m , an apprec iab le reduct ion i n e ros ion .

Af t e r one year, the observed s o i l

2 compared wi th pred ic ted

2 For the next year the observed loss was only 2

Averaging both years

1 0 2 4 b 0 3

l e v e l f o r storm e r o s i t i v i t y of t h i s magnitude

Differences i n e r o d i b i l i t y (K) a r e a t t r i b u t e d

i n e a s t e r n Tennessee.

t o v a r i a t i o n i n s o i l

c h a r a c t e r i s t i c s ; Captina--low i n f i l t r a t i o n and f i n e t e x t u r e ; Lindside--

h igh i n f i l t r a t i o n , coarse t e x t u r e .

was recommended by the Soil-Loss P red ic t ion Conference held i n Knoxville,

Tennessee, 1959.

The 0.4 va lue of K f o r Captina

The SL term f o r the s imulant-plot eva lua t ion was taken from

Wischmeier and Smith's s lope e f f e c t c h a r t . Average g rad ien t and s lope

l eng th f o r smal l -p lo ts were determined from r e p l i c a t e d measurements

of m i c r o r e l i e f

s lope length .

a l though they were determined d i f f e r e n t l y . Se l ec t ion of the s imulant-

p l o t C va lue i s descr ibed above ( p . 10) Tamura and Rogowski3 calcu-

l a t e d C from the s o i l - l o s s equat ion assuming t h a t o the r terms a l ready

had been evaluated.

3 and the c a l c u l a t i o n s were 8% ;t 1 f o r 7.5 f t . 2 0.7

The cover f a c t o r s ( C ) were s i m i l a r f o r bo th eva lua t ions ;

A comparison of p red ic t ed and observed r e s u l t s se rves t o t e s t

the model and the choice of terms used i n an eva lua t ion . Long-term

eva lua t ion i s d e s i r a b l e because of v a r i a b i l i t y i n e ros ion responses

a s soc ia t ed with i n d i v i d u a l r a i n f a l l events . Despite the l imi t ed

du ra t ion of observa t ion the re was some agreement between predic ted

and observed e ros ion from both s imulant and smal l p l o t s . For

s i rnulant-plots c o r r e l a t i o n appeared b e t t e r when p red ic t ed e ros ion

was compared with t h e maximum expected assuming extreme condi t ions

of r a i n f a l l e r o s i v i t y . For normal condi t ions , however, the Wischmeier

and Smith model overes t imates e ros ion from a heav i ly vege ta ted sod

( 2 g r e a t e r f o r second year r e s u l t s from smal l -p lo ts 1OX g r e a t e r

1 5

RFFERFNCES CITED

1. Wischmeier, Walter H,, and Dwlght D. Smith. 1965. Predic t ing

r a in fa l l - e ros ion lo s ses frum cropland e a s t of the Rocky Mountains:

Guide f o r s e l e c t i o n of p rac t i ces f o r s o i l and water conservation.

Agricul ture Handbook No. 282, ARS/USDA, Washington, D . C., 47 pp.

2. Rogawski, A . So, and Tsuneo Tamura. 1965. Movement of l y C s b y

runoff, e ros ion and i n f i l t r a t i o n on the a l l u v i a l Captina s i l t

loam. Health Physics - 11: 1333-1340.

3. Tamura, Tsuneo, and A . S. Rogowski. 1967. Movement of l T C s by

runoff, e ros ion and i n f i l t r a t i o n from a s o i l under d i f f e r e n t

cover condi t ions. Unpublished. Presented a t Symposium on

Pos ta t tack Recovery, November 6-19, 1967, For t Monroe, Vi rg in ia .

1 0 2 4 6 0 5

k cd a, h .d V =I.

\

0

0 t

0 cu

k 0

+,a I U oa,

.d 0 S V 52

E: 0 C 5 k bo C .d V I a 0 k a k 0

4 8 A

P

(d 0

0 cu %

I024bOb

LIST OF FIGUFES

Figure 1. View of Splitter Apparatus Used to Measure Runoff from 2 100 m experimental plot.

Figure 2. Predicted Movement of Radiocesium from One Runoff Plot

Shortly After Application of Fallout Simulant.

in Compartments Represent mCi of Ir/Cs/Plot and Other

Numbers

Values Indicate Fractional Transfer Between Compartments.

1 0 2 4 b 0 1 -.

21

ORNL-DWG 68-67!9

3c -cssoil -,ooo

**FRACTIONAL TRANSFER BECAUSE SEDIMENTS WILL BE COLLECTED FOR RADIOASSAY. Kd-Cs SO,'n

Predicted Movement o f Radiocesium from One Runoff Plot Shortly After Application o f Fallout Simulant. Numbers in Compartments Represent mci of 137Cs/Plot and Other Values Indicate Fractional Transfer Between Compartments.

F i g . 1

23

i 1-2. 3-4.

5 .

6-9. 10. 11.

12-111. 112.

114 113 a

115. 116. 117. 118. 119. EO.

321-220. 221. 222. 223. 224. 225. 226.

ORNL-TM-2343

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S. V. Kaye J. T. Kitchings I11 J. L. Liverman T. F. bmenicK H. G. MacPherson C. R. Malone W . C. McClain R. H. Monheimer K. Z. Morgan D. J. Nelson J. S. Olson R. V. O ' N e i l l L. N. Pe t e r s D. E. Reichle A. F. Shinn J. D. S tory E. G . Struxness C. E. Styron, Jr. Tsuneo Tamura F. G. Taylor W . A . Thomas A. M. Weinberg J. P. Witherspoon

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254.

255.

256-260 e

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D. c. 20310

D. c. 20310 261-265. David Benson, Off i c e of C i v i l Defense, The Pentagon, WdShingtOn,

266. C. S. Shoup, Biology Branch, Oak Ridge Operations, USAEC, Oak

267. Carl B e l l , U. T.-AEC Agr i cu l tu ra l Research Laboratory, Oak Ridge,

268. John Cantlon, Department of Botany, Michigan S t a t e University,

269. E. E. C . Clebsch, Department of Botany, Universi ty of Tennessee,

Ridge, Tennessee

Tenne s see

East Lansing, Michigan

Knoxvi l l e , Tennessee