Journal of Hydrology, 98 (1988) 53~5
53
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
[21
TEMPORAL, SPATIAL AND SIZE VARIATION IN THE SEDIMENT
TRANSPORT IN THE KRISHNA RIVER BASIN, INDIA
R. RAMESH* and V. SUBRAMANIAN
School of Environmental Sciences, Jawaharlal Nehru University, New Delhi.110 067 (India)
(Received October 8, 1986; revised and accepted August 6, 1987)
ABSTRACT
Ramesh, R. and Subramanian, V., 1988. Temporal, spatial and size variation in the sediment
transport in the Krishna River basin, India. J. Hydrol., 98: 53~5.
The total sediment transport of the Krishna River to the Bay of Bengal is estimated to be
4.11 x 106 ton yr -1. The sediment load decreases sharply from 67.72 × 106 ton yr -1 from the
upstream region ((Morvakonda) to 4.11 × 106 ton yr -~ at the river mouth (Vijayawada). The
depletion of sediment supply in the river mouth and lack of uniformity in sediment transport within
the basin is mainly due to several human activities such as dams, cropping, etc. This has been
substantiated by the temporal and spatial variation of the suspended sediments based on fourteen
years data (197144). One of the tributaries of the Krishna, the Bhima River is the main sediment
contributor to the Krishna with an average annual sediment transport of 25.91 × 10s ton and
sediment concentration of 2070 mg 1 - 1. The bulk of sediment transport ( > 95%) takes place in the
monsoon period. Erosion rate shows no systematic relationship either spatially or temporarily. The
total sediment erosion of the Krishna is estimated to be 16 t o n k m -2 yr -1. Rates of erosion
calculated for various subbasins indicate that smaller basins erode more rapidly than larger
basins. The particle size distribution of the suspended sediments were correlated with the mean
monthly sediment transportation to evaluate the downstream and temporal variation of grain size
with sediment transport. At the river mouth, it is seen that enormous amounts of fine particles
(1 10 #m) add to the monthly sediment load of the river.
INTRODUCTION
In material transport, the river plays a very important role. More than 90%
of the continental weathering products are transported by rivers to the oceans
(Garrels et al., 1975). Over the past two or three decades growing awareness of
the wide ranging environmental significance of the suspended sediment
transport by rivers has generated a considerable body of information
concerning the magnitude of sediment yields and their control by human
activity, climate and other catchment characteristics (e.g. UNESCO, 1982;
Peart and Walling, 1986). Many relationships between solid and dissolved
* Present address: Department of Geological Sciences, McGill University, 3450 University Street,
Montreal, Que. H3A 2A7 (Canada)
0022-1694/88/$03.50
© 1988 Elsevier Science Publishers B.V.
54
transport rates and environmental factors have been described by several
authors (Leopold et al., 1964; Judson and Ritter, 1964; Gibbs, 1970). It is now
well established from earlier workers (e.g. Meybeck, 1976; Milliman and
Meade, 1983) that improved understanding of continental fluvial processes and
their impact on the oceans requires detailed studies of medium size rivers in
Asia. Erosion and sediment transport of a number of Indian rivers are reported
briefly by several authors (e.g. Subramanian, 1979; Bikshamiah and Subramanian, 1980; Abbas and Subramanian, 1984) based on very limited observations.
There is no systematic long-term monitoring programme and most of these
studies were restricted to short-term studies with a restricted monitoring
programme over a period of one to two years. The sediment and discharge data
vary monthly, seasonally and annually in most of the river basins, and hence
these short-term studies can result in large-scale under- or overestimations of
load. In this paper, an attempt has been made to give a comprehensive picture
of Krishna River sediment transportation and its relation with grain size
distribution based on long-term data. In this study, seasonal observations of
suspended sediment variations for the period 1981-84 were made. In addition,
monthly discharge and sediment data for the period 1971-81 (except 1976-77)
were obtained from the Central Water Commission, Government of India. Both
the sets of data were processed together to evaluate the sediment yield and
erosion characteristics in the Krishna River basin.
F
14-"
F
)
]
Fig. 1. Map of the Krishna River basin with sampling locations. Numbers 1 to 13 correspond to
locations in Table 1, column 2 and 3. For clarity, only some important sampling locations a r e
shown (triangles) for the samples collected between 1981-84.
55
TABLE 1
Hydrological and average sedimentdata for the Krishna River basin (from 197141)
Location
no.
River
1
2
3
4
5
6
7
8
9
10
11
12
13
Krishna
Krishna
Krishna
Nira
Sina
Bhima
Bhima
Tunga
Varadha
Tunga-Bhadra
Krishna
Krishna
Krishna
Site
Karad
Bagalkot
Huvanur
Sarati
Wadakbal
Takali
Yadgir
Shimoga
Morol
Harlahalli
Bawapuram
Morvakonda
Vijayawada
Drainage
area
(km 2)
Annual
runoff
(106 m 3 )
Total
sediment
transport
Annual
monsoon*
( × 10,000 ton)
A n n u a l mean
sediment
concentration
(mgl 1)
Erosion r a t e
(ton km 2 yr
5462
8610
11400
7200
12092
33916
69863
2831
4901
14582
67180
210500
251360
4518
3388
1751
1531
1136
7362
11495
5473
2062
8144
6923
41873
32397
169
281
917
232
648
953
2591
37
72
145
638
6772
411
168
272
876
231
636
950
2578
37
70
138
630
6765
410
372
803
4862
983
5949
1209
2070
63
332
175
945
1572
122
275
327
804
203
525
289
369
130
146
99
94
322
16
1)
* J u n e to November.
KRISHNA RIVER BASIN
The Krishna River catchment lies between 13° N and 19° 30' N; and 73° 23'E
and 80° 30' E. The basin map of the Krishna is shown in Fig. 1. The river rises
in the western Ghats from a slender spring near Mahabaleshwar at an
elevation of 1337 m, about 64 km from the Arabian Sea. Some of the hydrological characteristics are given in Table 1. Drainage area and annual runoff data
for the different locations were obtained from the Central Water Commission
(unpublished report) and from Rao (1975). The Bhima and Tungabhadra are the
major tributaries. Except in the upper reaches, semi-arid conditions prevail in
the basin.
Archaean and younger crystalline rocks occupy nearly 80% of the basin
while the remaining 20% comprises Tertiary Deccan Traps (basaltic) and
recent sediments. The Tungabhadra tributary flows through 70% Archaean
and 30% Precambrian crystalline rock terrain while the Bhima tributary flows
through 80% Deccan Trap terrain.
METHODOLOGY
One-litre water samples were collected in polythene bottles four times (April
1982; February 1984; June 1984; and August 1984) at sixteen stations in the
entire region of Krishna River basin and its major tributaries. Fig. 1 shows the
sampling locations. In addition, five-litre water samples were collected at a few
locations during the month of June and August 1984 to study the grain size
distribution. The size distribution of the suspended sediments was determined
using a model TA 11 Coulter Counter interfaced with an Hewlett-Packard '85
desk-top computer.
56
wet
[]
Dry []
10.000
1000
I00
18
tD
I--
1:1lit:tlII;tiIllil
..i
!I
.,L
:i:l
..4
V~iayowodo
yoperlio
lfl,O O0
1000
100
I(1
0
,
aJ
Yeors
Fig. 2. Seasonal variation of TSM during the year 1971-84.
RESULTS AND DISCUSSION
Temporal and spatial variation of the suspended sediments
Average annual runoff, sediment load, sediment concentration and erosion
rate for selected locations (Fig. 1) on the river have been computed based on ten
years (1971-81) data and the values are listed in Table 1, along with some
hydrological data. Table 1 points out that the tributaries carry relatively less
Total Suspended Sediments (TSM) except the Bhima. The Bhima is the main
sediment contributor to the Krishna River. The Bhima predominantly drains
an area of partially weathered Deccan Trap, a geological setting from which
sediment particles can be easily released by physical weathering. Semi-arid
climate and high runoff also influence the environment of TSM in the Bhima.
The sediment load and TSM varies widely within the basin. For example, a
threefold increase in sediment load and a sixfold increase in TSM for the
Krishna between Bagalkot and Huvanur has been observed (Table 1). This
significant increase in both sediment load and TSM is perhaps due to the
influence of tributaries Ghataprabha and Malaprabha which were not sampled
for the present study. Relatively high TSM values were observed upstream as
compared to downstream in all years. Sediment delivered from the upland areas
is trapped within the basin mainly due to several human activities. For
57
I~?~-?~
Ig?J .?)
I!?).?~
10000
1000
D---41. W t l
Owy
I0{
i
,
J
1971.
"75
,
I
J
I
,
t
1 9 7 5 - ?6
,
I
1977"
I
,
J
I
*
I
leOSo~lJunL'
llo$on
[ Dec
IoNov)
MOy}
to
?B
1000(
~
~
100(
100
L
i
I
,
1
*
I
1978-79
*
[
,
I
1979 - 8 0
l
,
1981 - Bc
Ig80-81
1(:000
1000
1C0
10
,
L
,
I
,
I
,
I
,
L
,
12
i
x IC~G O o w n s t r ~ ' c ) m
E/
;n
,
112
l<m
Fig. 3. Downstream variation of TSM with season during the year 1971-84. D = Dannur;
Y = Yaperli; M = Morvakonda; S = Srisailam; V = Vijayawada.
example, e n g i n e e r i n g s t r u c t u r e s in r i v e r s m a y d i s t u r b the n a t u r a l s e d i m e n t a tion processes. T h e m a x i m u m to m i n i m u m r a n g e of T S M in the K r i s h n a for
i n d i v i d u a l years, not s h o w n in this paper, v a r i e s by a f a c t o r of t h r e e u p s t r e a m
a n d by a f a c t o r of s e v e n d o w n s t r e a m . T h e T u n g a b h a d r a h a s n o t s h o w n m u c h
a n n u a l v a r i a t i o n except in 1971-72, w h e r e a s the B h i m a v a r i e s by a f a c t o r of
four. F r o m T a b l e 1 we c a n also infer t h a t m o r e t h a n 95% of the a n n u a l s e d i m e n t
load o r i g i n a t e s d u r i n g t h e m o n s o o n period ( J u n e - N o v e m b e r ) .
T h e s e a s o n a l v a r i a t i o n of s u s p e n d e d s e d i m e n t s d u r i n g wet s e a s o n ( J u n e N o v e m b e r ) a n d dry s e a s o n ( D e c e m b e r - M a y ) for a 14 yr period (1971-84) for four
i m p o r t a n t l o c a t i o n s in K r i s h n a f r o m u p s t r e a m to d o w n s t r e a m a r e s h o w n graphically in Fig. 2. I r r e s p e c t i v e of the t e m p o r a l and s p a t i a l v a r i a t i o n s , the conc e n t r a t i o n of the s u s p e n d e d s e d i m e n t s seems to be in s a m e p r o p o r t i o n of
a p p r o x i m a t e l y 2:1 w i t h r e s p e c t to the w e t and dry season. P a r t i c u l a r l y at
V i j a y a w a d a , the h i s t o r i c a l s e d i m e n t c o n c e n t r a t i o n a p p e a r s to r e m a i n quite
u n i f o r m f r o m wet to dry season. This c a n be also seen in the line of the best fit
58
I0.000
A - Entire
bos~n
B - Karod
C - Viiayawoda
7
o
oO/
0
~o 1000
X
o
O.
X
0
X
C
C
"~
100
/
I
i
000
I
I0,000
Annual
runoff
I
1.00.000
1 0 6 m 3 y e o r "1
Fig. 4. Variation of annual sediment load with runoff in the Krishna River basin.
of Fig. 4. Subramanian (1978) reported significant seasonal variations in
suspended sediment load on major Indian rivers. He also reported that during
the monsoon all non-Himalayan rivers except the Cauvery carry a sediment
load greater than 1000 ppm. The present study also shows (Fig. 2) that except
at Vijayawada all the suspended sediment contents are greater than 1000 ppm.
There are two major dams in between Srisailam and Vijayawada. The
suspended sediments settle down at the dams, and hence the sediment concentration at Vijayawada is one-tenth of that observed upstream both in wet
and dry seasons.
Figure 3 demonstrates the downstream variation of suspended sediments in
59
wet and dry seasons for the 14 yr period. The suspended sediments for all the
years decrease sharply downstram of the dam region (beyond Srisailam) in both
seasons. A downstream decrease in sediment concentration has been reported
for a number of world rivers (e.g. Gibbs, 1967; Meybeck, 1976; Subramanian,
1979; Bikshamiah and Subramanian, 1980).
Sediment transportation
Figure 4 shows a systematic relationship between runoff and sediment
transport over the 10yr period. At Vijayawada station during low flows a
twofold increase in flow occurs from about 5000-10,000 × 106 m 3 yr - 1; about a
100-fold increase occurs in the sediment transport. Conversely, at high flow in
the 10,000-100,000 × 106m3yr -1 range only a two- to threefold increase in
sediment transport occurs. Figure 4 also shows evidence that the increase in
runoff is not associated with proportionate increase in the sediment load. For
example, the annual sediment transport at the river mouth is small when
100
O00q
I000
K|rld
(~ Morv|konds
o
(~) Yijtyswsd8
qr o
(~ Har|hsili
I 001
©
i
(~
©
|
w
I(
PI-12 12-13 13.14 14-I$ I~-14 11-11 18-19 19-I0
YEARS
80-81
IL+IZ 12-13 13-14 14-P5 15-16 11-18 18-19 19-80
YEARS
80-81
Fig. 5. (a) Annual variation of sediment load; (b) annual variation of erosion rate.
Ysdgir
60
compared to annual runoff (Fig. 4c) which may be due to the influence of dams.
Upstream of the dams, the river carries an enormous sediment load, but below
the dams, the sediment concent r a t i on show only about 13% of those observed
upstream (1572 mg 1-1 at Marvokonda and 122 mg 1-1 at Vijayawada).
Figure 5a shows the annual variation of sediment transport for the Krishna
River and its major tributaries. The individual year data ranges from a
minimum of 0.28 x 106ton for the year 1972-73 to a maximum of
11.75 x 106 ton for the year 1975-76. The mean annual sediment transport of
the Krishna River is estimated to be 4.11 x 106 ton (Table 1). These sediment
transport and erosion rates are based on continuous study for the 10 yr period.
Thus, these rates would not change significantly unless major changes, such as
floods, droughts, or any other significant changes in flow take place. To avoid
the discharge fluctuations from one year to another, the 10yr average
discharge was used in sediment transport calculations. Upstream of dams, the
river carries an enormous sediment load of 68 x 106 ton. Below the dams, i.e.,
at Vijayawada, there is a sudden depletion of 64 x 106 ton of sediment load to
4 x l0 s ton. Most of the sediments settle in this area and the sediment load of
the basin does not reach the river mouth. The Krishna River contributes
relatively less sediment than other Indian and world rivers (Ramesh and
Subramanian, 1986). For example, according to recent estimates the Godavari
River basin (Biksham 1985), which has more or less the same drainage area and
500 -
400
E
,.
300
o
a
20C
100
0
I
l
I
I
I
i
50
100
150
200
250
300
Oromoge
ores (tO)
Km 2)
Fig. 6. Variation of erosion rate with drainage area in various subbasins of the Krishna river
system.
61
water discharge as the Krishna, contributes 170 x l0 s t o n of sediments
annually.
Erosion rates
The rate of erosion, which is the index of intensity of erosion in a river basin,
is expressed in ton km - 2yr -~. Recent estimates (Ramesh, 1985) show that the
total erosion rate of the Krishna River basin is 57 t o n k m 2yr
(41 ton km-2 yr ~chemical + 16 ton km 2 yr ~sediment). The sediment erosion
rate of the Krishna River is much lower as compared to any other Indian
(except the Cauvery) and world rivers (Ramesh and Subramanian, 1986): Indian
average 46.8; world average 150; and Cauvery 0.5 ton km- 2yr- ~. Figure 5b shows
the fluctuations in annual erosion rates. There is no constancy with time,
which is mainly perhaps due to human interference r a t h e r t han natural erosion
process. Based on the data for the river mouth it has been estimated an average
erosion rate of 2 m m l 0 0 y r ] and that in 2.17 × 106yr, the basin would be
reduced to mean sea level.
Relationship between erosion rate and drainage area
Figure 6 demonstrates that drainage area is an important control on
sediment yield. Several of the small upstream subbasins are being eroded more
UPSTREAM
,~-~,
2.0
Jut~
I0~ ~ i
i
August
K (~ L H ~,R
SANGAM
90
16
¢
c
n
~
16
)
I
so
I
I
$
°'f
%-- /'
: ~ so
Y~
-g
~a,o
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E
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I
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9t
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d~-A
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t
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in
I
i
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,
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m~¢ron$
Fig. 7. Grain size vs. mean monthly sediment transportation in upstream reaches of the Krishna
River basin. Total sediment transportation at Kolhar in June is 124.63 x 104 ton; at Sangam in
June 358.47 x 104 ton; and in August 354.30 x 104 ton.
62
intensively than the entire basin and the overall erosion rate for the basin may
be controlled by the erosion rates prevailing in these smaller subbasins. Such
observations agree with those of Gibbs (1967) for the Amazon system, where a
large proportion of the sediment load is derived from a small Andean
subsystem. Figure 6 indicates that erosion rates are higher in small basins.
With such high rates of erosion, the small basins will reach base level very
much earlier than the entire basin and erosion rates computed for large basins
may be meaningless without corresponding values of subregions.
Relationship between grain size and sediment transportation
Five samples collected in June and four samples collected in August 1984 at
the same sampling points of the Central Water Commission were chosen to
correlate grain size with the sediment transportation. Mean monthly sediment
60
M~DS/REAM
$6
Ku nool
o---,-~ S r i s a ; L a m
S2
H
June "O,~
KUrnO01.
St;so;Iota
~)---~
august
'84
/,6C
¢8
~ ~gG
.<
iI
400
4O
0
"4"
36
160
-£ 320
37
._~
2ao
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24
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Ip
E
0
E
"o
IE
t
"~ )60
I
i 170
"s
; /L
b
'i
%.1
,
I
•
l
,
I
I
i
I
tO
I
l
I
6fei~
4c
|
l
100
I;le
i'~'
l -
,
I
•
I0
it*
i
Li
60
I
•
I
,
a ~ .
tO0
m;crens
Fig. 8. Grain size vs. m e a n m o n t h l y sediment transportation in midstream r e a c h e s of the Krishna
River basin. Total sediment transportation at Kurnool (June) is 462.67 × 104 ton, (August)
1549.92 × 104 ton; and at Srisailam (June) 499.91 × 104 ton, (August) 1560.03 × 104 ton.
63
IS
¢:
c
10
°A
a
~"e
.e
4
2
IKI*I,I,
440
DOWNSTREAM
V I JAYAWA DA
40(
_
350
320
c
c
o
280
.E
2z.o
2oo
a
"~
1eC
80
g
IE
1,0
00.1 I
I
I
I
I
I
1
GrOin
I
'
I
10
size
~n
,
I
,
/
I O0
r~;c r o~ ~.
Fig. 9. G r a i n size vs. m e a n m o n t h l y s e d i m e n t t r a n s p o r t a t i o n in d o w n s t r e a m r e a c h e s a n d a t r i b u t a r y
of K r i s h n a . T o t a l s e d i m e n t t r a n s p o r t a t i o n at V i j a y a w a d a ( J u n e ) 0.49 × 104 t o n a n d at B h i m a
(June) 118.73 × 104 ton.
transportation was calculated from the 10 yr data for the months of June and
August and plotted against the grain size at different size intervals. Figures 7,
8 and 9 clearly demonstrate the temporal and spatial variations of grain size
with sediment transportation. At Kolhar (upstream) most of the sediments are
transported in fine grain sizes (i.e., 1-10 #m) in June. A similar peak is obtained
for August, about 150km downstream at Sangam, indicating the temporal
variations in sediment properties. This is simply due to the time required for
64
the transport of sediment from one location to another (Fig. 7). Again at
Sangam, the quantity of sediment transported increases in the coarser
fractions (i.e., 10-100 pm) during June, which may be due to the confluence of
tributaries, namely the Malaprabha and the Ghataprabha, carrying coarser
particles in suspension.
At midstream (both at Kurnool and Srisailam) fine grains are abundant in
June and coarse grains are abundant in August (Fig. 8). Kurnool and Srisailam
are more or less in the same elevation and are made up of similar rock type
(granites and gneisses). Hence, there is not much variation in the grain size
with sediment transportation. However, in August at Srisailam (upstream of
dams) more coarse grain particles are present essentially due to settling down
of finer particles near the dam.
At the river mouth (Vijayawada) fine particles are more dominant in the
sediment transportation. Coarser particles are trapped between Srisailam and
Vijayawada due to dams and only fine particles are transported towards the
river mouth ( Fig. 9). The Bhima carries relatively more coarse grain particles,
which may be due to its high altitude and its geological setting.
CONCLUSION
The sediment supply of the Krishna River, an intensively utilised river basin
in southern India, is mainly due to human activities rather than as the natural
consequence of geological processes. Further engineering structures (for
example, the Upper Krishna Project in Karnataka, now underway) may disturb
the natural geochemical processes in the river basin. The present study
indicates that the Krishna River delivers annually 4.11 × 10s ton of sediment
load to the Bay of Bengal at an erosion rate of 16tonkm -~. It is also evident
from the present study that nearly 95% of the sediment load is derived during
the monsoon period, and that at the river mouth only finer particles were added
to the monthly sediment load of the river owing to human interference.
REFERENCES
Abbas, N. and Subramanian, V., 1984. Erosion and sediment transport in the Ganges river basin
(India). J. Hydrol., 69: 173-182.
Biksham, G., 1985. Geochemistry of Godavari river basin. Ph.D. Thesis, Jawaharlal Nehru
University, New Delhi, 265 pp.
Bikshamiah, G. and Subramanian, V., 1980. Chemical and sediment mass transfer in Godavari river
basin. J. Hydrol., 46: 331-342.
Garrels, R.M., Mackenzie, F.T. and Hunt, C., 1975. Chemical cycles and the global environment:
assessing human influences. Kaufmann, Los Atlas, Calif., 206 pp.
Gibbs, R.J., 1967. Geochemistry of the Amazon river system. Bull. Geol. Soc. Am., 78: 1203-1232.
Gibbs, R.J., 1970. Mechanism controlling world water chemistry. Science, 170: 1088-1090.
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Leopold, J.B., Wolman, M.G. and Miller, J.P., 1964. Fluvial Processes in Geomorphology. Freeman,
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Meybeck, M., 1976. Total dissolved transport by world major rivers. Hydrol. Sci. Bull., 21: 265-289.
65
Milliman, J.D. and Meade, R.H., 1983. World wide delivery of river sediment to the oceans. J.
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Ramesh, R., 1985. Geochemistry of Krishna river basin. Ph.D. Thesis, J a w a h a r l a l Nehru
University, New Delhi, 228 pp.
Ramesh, R. and Subramanian, V., 1986. Mass transport in Krishna river basin, India. Proc. Int.
Assoc. Hydrol. Sci. Denver, 159: 18~197.
Rao, K.L., 1975. India's Water Wealth. Oxford University Press, New Delhi, 255 pp.
Subramanian, V., 1978. Input of Indian rivers into the world ocean. Proc. Ind. Acad. Sci., 87A:
77 88.
Subramanian, V., 1979. Chemical and suspended sediment transport by rivers of India. J. Hydrol.,
44: 34-55.
Subramanian, V., 1982. Erosion and sediment yield in the Krishna river basin, India. IAHS Publ.,
137: 193-198.
UNESCO., 1982 Sedimentation problems in river basins. UNESCO Stud. Rep. Hydrol., no. 35.