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TRANSCRIPT
oak Rldgc Nauonal Laboratory OAK RIDGE NATIONAL LABORATORY
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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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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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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
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Knoxvi l l e , Tennessee