Sedimentation of reservoirs in India

Sedimentation of reservoirs in India B. Bowonder, K. V. Ramana and T. Hanumantha Rao

The sedimentation of Indian reservoirs has become a serious problem due to the synergistic action of population growth, intensity of agricultural operations, poor soil conservation and deforestation. This article examines the reasons for and responses to, sedimentation in three Indian reservoirs Nizamsagar, Tungabhadra and Sriramsagar. The land management practices adopted in each case are analysed with reference to current and future needs. The article highlights particularly the need to monitor methodically the land use changes in the catchments of reservoirs.

Keywords: sedimentation; land management; reservoirs Dr B. Bowonder and Dr K. V. Ramana are with the Centre for Energy, Environment and Technology, Administrative Staff College of India, Bella Vista, Hyderabad-500 049, India. Dr T. Hanumantha Rao is Director, Andhra Pradesh Engineering Research Laboratories, Rajendranagar, Hyderabad-500 030, India. The authors thank the Department of the Environment of the Government of India for financial support for their research. They are particularly grateful to Dr T. N. Khoshoo (Secretary, Department of the Environment, Government of India) and Mr &I. Narasimham (Principal, Administrative Staff College of India) for their support. ‘A. K. Biswas, ‘Environmental implications of water development for developing countries’, Water and Supply Management, Vol 2, pp 283-297. 2t-f. Fukuda, lrrigatio~ in the World, University of Tokyo Press, Tokyo, 1976. 3Dead storage, as opposed to live storage means the provision made in the reservoir for siltation at the time of construction. Live storage is the provision for actual water storage. 4R. Chettri and 8. Bowonder, ‘Siltation in Nizamsagar reservoir: environmental mancontinued on p 749

148

The sedimentation of reservoirs is a major consequence of poor land use management.’ As water passes through land, any changes in land use or improper land use wili intensify the sedimentation process, which is essentially a function of intensity of human activities, soil and agroclimatic characteristics. India is the second largest country in the world with large areas under irrigation.2 Sedimentation not only affects the capacity of reservoirs to store water but also their ability to control floods. The three projects compared in this article are different in terms of catchment characteristics and soil conservation measures undertaken (Table 1).

Nizamsagar

Project

Nizamsagar is one of the most heavily sifted reservoirs in India. The Nizamsagar dam was constructed across the Manjira River in 1931. The project was envisaged in 1923 as an irrigation project to irrigate an area of 110 000 ha. The Manjira River rises in the Bhir District (Maharashtra State) with tributaries from Osmanabad (Maharashtra State) and Bidar (Karnataka State). It runs through Medak before reaching Nizamabad in Andhra Pradesh. This project has shown high se~iiment~~tion rates and very high losses in storage capacity. in 1930, Nizamsagar had a total storage capacity of 841 million m3 (of this 116 million m’ was for dead storage).’ The storage capacity survey (based on contours of periphery) carried out in 1065 showed the total storage to have fallen to 322 million rn’. Andhra Pradesh Engineering Research Laboratories conducted a hydrographic survey in 1967 (to substantiate the results of the 1965 survey) using echo sounding and confirmed that the live storage has come down to 309 million m3 from 841 million m3. The dead storage came down to 3 million m3 from 116 million m3. In the original project report the rate of sedimentation was assumed to be 0.29 ha per 100 km’ of the catchment whereas the actual rate of sedimentation was as high as 6.77 ha per 100 km’.’ The rate of sedimentation and provision for dead storage were both underestimated. Even then, no corrective action was initiated. By 1965 about 61% of the storage capacity of the reservoir was lost.’ Land use The

total

in the

c~l~c~~rn~t~~

catchment

covers

an

0264-%377/%5/02148-07$03.00

area

of 21 694 km’

0 1985 Butterworth

with

50%

in

& Co (Publishers)

Ltd

Table 1. Characteristics

of three project areas. Nizamsagar

Catchment

Project

Tungabhadra

Percentage of forest area in the catchment

Project

Project 91 750 6

11

6

Percentage of area sown more than once

Sriramsagar

28 179

21 694

area (km*)

2

41

50

Soil type of the catchment

Red clay, medium and deep black and lateric soils

Deep black, mixed red and black, red loam and laterite soils

Deep black, medium black with patches of red clay and coarse shallow

Agrocl~matic conditions

Dry, semi-arid

Wet, semi-arid

Dry semi-arid

Population density per km’ (1981)

174

156

187

Livestock density per km2

101

90

95

Capacity (million m3) original present

841.18 336.49

3751.17 3332.75

6.24

5.67

Sedimentation ham/l00 km*

rate

6064F 338.04a _

aAt crest level + 332 478 m.

co~~~ffff~

ffom p 148

agement issues’, Applied Geography,

Vol

Maharashtra, 17% in Karnataka and 33% in Andhra Pradesh. The catchment of the reservoir is fragmented into three states (Figure 1). The part of the catchment, in Maharashtra State consists mostly of flat cultivated black cotton soil. The Nizamsagar catchment contains barely 4% of forest cover. The area in agricultural use is about 66% and it is cultivated once a year for one season only. Black cotton soil with no green cover and seasonal agriculture is especially susceptible to erosion. Table 2 gives changes in land use in the catchment of Nizamsagar. The population density has increased from 116 to 174 per km* during 1961 and 1981 (Table 3). This along with intensive agricultural operations and cattle grazing in soils susceptible to erosion causes severe sedimentation. The areas sown only once remain fallow tracts as a result of continuous heavy grazing. Catchment

of

Sriramsogor

project

Catchment

of

Nizamsagor

project

Cotchment of Tungabhadra

Figure 1. Soil types of three catchment areas.

LAND USE POLICY April 1985

749

Sedimentation

of

reserv0ir.s in India

Table 2. Land use changes in the catchments Total geographical area Nizamsagar Project 196142 1966-67 1972-73 197G77

(ha). Barren and unculti vated land

Net area sown

275 592 (6)a 281 795 (6) 304 121 (6)

182 852 (4) 208 144 (4) 186 795 (4)

3 036 010 (63) 2 895 195 (60) 2 626 054 (55)

1 475 225 (31)

4822816

298

187460(4)

3 187 298(66)

1 974 803 (41)

6 624 102 6 625 100 6 625 100

656113(10)

340 003 (5)

3 848 477(58)

648 811 (10)

317 573 (5)

3 702 892(56)

735 902 (11)

267816(4)

3 717 510 (56)

163386(2)

728 869(6)

440 004 (4)

4838601 4844900 4823

239

Forest

118(6)

Area sown more than once 150 537 (3) 162 131 (3)

Tungabhadra Project 196142

196-7 196%70 Sriramsagar Project 1961-62 1966-67 1972-73 197&77

12221

004

105 291 (2) 94 774 (1)

568 848 (5)

6984

924 (57)

12223900

1009

571 (8)

599308(5)

7998

892(65)

11 909

1029

121 (8)

586395

7363

354(62)

4 892 625 (41)

8665

598(72)

6 039 203 (50)

139

11 998 718

1020118(8)

(5)

586 660(5)

467147(4)

“Figures in parentheses indicate percentage of the total area

Soil conservution Another cause of heavy sedimentation is the cultivation of sloping land along the fringes of water courses and reservoirs, without the implementation of soil conservation measures. The extent of soil conservation efforts has been very small. Though 316 000 ha of the catchment have been identified as needing priority attention only 18440ha have been treated. Climatic conditions further aggravate the problem. The Nizamsagar catchment area suffers semi-arid agroclimatic conditions with a rainfall season of less than four months, when 76GX90 mm of rain can be expected. Violent floods are not uncommon.

Tungabbadra

Project

The Tungabhadra Project was commissioned in 1953. The gross capacity of the reservoir was originally 3751 million m’. The soils are mostly red loamy, mixed red and black soils with patches of laterite and black soils (Figure 1). Land use and sedimentahwt This catchment has the largest amount of forest cover of all the areas. Livestock and population density is the lowest. The area sown more than once is also very small, and hence intensity of agricultural operations is less. These factors, along with the initiation of systematic soil conservation measures have eased the problem of sedimentation. The storage capacity of the Tungabhadra reservoir came down to 3246 million m3 by 1963 from the original value of 3751 million m3. The rate of sedimentation in 1963 was 17.9 ha per 100 km’, whereas the originally estimated sedimentation rate was 4.82 ha per 100 km’. Table 3. Population and livestock in the catchments.

1961 Nizamsagar Project Tungabhadra Project Sriramsagar Project

5 391 668 (116)a

Population 1971

1956 4 437 251 (97) 5241 140 (78) 10 456 580 (85)

6 675 475

(140) 8 316 277

8 184 235 (174) 10547 899

(100) 12841 134

(125) 16 301 956

(156) 19 898 290

(136)

(187)

(105)

6 788 079

Livestock 1981

1972 4 916 143 (101) 5 938 631 (90) 11 442 998 (95)

=Figures in parantheses indicate density per km*.

150

LAND USE POLICY

April

1985

Sedimm~ution of reservoirs in India

Soil conservation In lY63, soil conservation activities were initiated through a centrally sponsored soil conservation scheme. In 1972 the storage capacity was again estimated and it was found that the rate of sedimentation had come down. The 1978 study found the capacity to be 3332 million m’, implying a total capacity loss of 11% since 1953. The 1972 survey was only approximate. The increase in storage capacity between 1963 and 1972 was probably due to the consolidation of silt which results in reduction of silt volume.’ The 1978 survey showed the rate of sedimentation to have considerably reduced. The government of Karntaka has been undertaking soil conservation activities since 1944 and they were intensified in the 1960s.’ Soil conservation measures taken up are mainly bunding, gully plugging, afforestation, land levelling and terracing. From 1962 onwards the scheme was made more rigorous with financial allocation from central government. The Tungabhadra Project authorities have committed more financial resources for soil conservation than the other authorities although the area needing soil conservation is about the same size as that of Nizamsagar. Soil conservation measures were implemented in 146 000 ha out of the 422 000 ha needing priority treatment. One of the major reasons for the intensified soil conservation activities has been that the entire watershed was in the state of Karnataka, cutting out the inevitable inter-state wrangling. The major reasons for the relative success of soil conservation in arresting sedimentation in Tungabhadra are:

l 0 0 0

Identification of the area needing soil conservation on a priority basis. Regular monitoring of areas needing soil conservation. Participation of the farmers in the soil conservation programme. Continuous review and monitoring of the soil conservation measures and sedimentation rates.

Sriramsagar

6J. Raja Rao, ‘Sedimentation studies of Tungabhadra reservoir made in 1963, 1972 and 1978’, Seminar Proceedings; Watershed Management m, Tungabhadra River Valley - An-Appraisal, Tungabhadra Board, Tungabhardra Dam, India, 1982, pp 75-l 18. ‘Ibid.

LAND USE POLICY April 1985

Project

Sriramsagar has a gross capacity of 3172 million m3. When the dam was built, a provision of 849 million m3, was made for dead storage. Up until 1983-84, the capacity had not reached full reservoir level. The present capacity of the reservoir is 606 million m3 at crest level (+ 332.500 m). The catchment of Sriramsagar spreads over 91750 km*. The reservoir is in Andhra Pradesh and the catchment is spread over seven districts of Maharashtra, one district of Karnataka State and two districts of Andhra Pradesh State. The project authorities estimated the capacity in 1972 to have fallen to 389 million m3 from the original value of 606 million m’. In May 1979 this was only 380 million m’. The first two surveys were cross sectional surveys. The third and fourth surveys (in May and December 1981) were conducted by Andhra Pradesh Engineering Research Laboratories using hydrographic methods - the estimates were 329 million m3 and 338 million m3 respectively. The percentage loss in capacity up to December 1981 was 44% of the initial value. Land use patterns The sedimentation

of Sriramsagar

has been

intensified

because

of the 151

of a large number of factors - soil nature, population growth and intensity of agricultural operations. The soil of Sriramsagar catchment is mainly medium to deep black soil and it is susceptible to severe sheet, rill, and gully erosion.x It has been shown that, in the untreated watersheds in black soil areas, the soil loss is 12 to 43 tonnes per hectare per year, and only 4 to 10 tonnes per hectare in the case of red soil. When there is no vegetation, the black soil loses 44 tonnes per hectare per year, whereas when ploughed and harrowed it loses about 82 tonnes per hectare. Black soil loss will be as low as 1 tonne per hectare when there is proper vegetative cover.” The problem of erosion is worsened in Sriramsagar by the lack of sufficient forest cover. The catchment mainly consists of arable and waste land. Both of these in areas of black soil encourage the generation of sediments. In real terms, net area sown in the catchment of Sriramsagar increased from 6.98 million hectares (mha) to 8.66 mha between 1961 and 1977. Without a comprehensive programme of soil conservation. intensive cultivation will increase sedimentation. interplay

Semi-aridity

and sedimentation

The catchment of Sriramsagar is mainly in the dry semi-arid agroclimatic region. Variability in rainfall, intensive rainfall during short periods, and semi-aridity work to degrade land resources at a much faster rate than usual. In semi-arid agroclimatic areas where biomass productivity is low and rainfall variability is high, the washing away of the topsoil is intensified by population growth (which has doubled between 1961 and 1981), intensive agricultural operations and cattle grazing without adequate pasture development. “’ Soil conservation efforts in Sriramsagar have been very meagre. Of the total catchment area, 3.77 mha were identified in 1970 as urgently needing soil conservation. Even 10 years after starting the project, only 6600 ha of the 3.77 mha were treated.

Reasons for sedimentation Compartmentalized

‘M. S. Ram Mohan Rao and S. Chitteranjan, ‘Role of soil and water conservation in the prevention of reservoir sedimentation’, Seminar Proceedings: Watershed Management in Tungabhadra River Valley An Appraisal, Tungabhadra Board, Tun;;&Qadra Dam, 1982, pp 157-l 93. “‘J. .& Singh and M. C. Joshi, ‘Ecology of the semi-arid regions in India with emphasis on land use’, in B. H. Walker, ed, Management of Semi-Arid Ecosystems, Elsevier, Amsterdam, 1979, pp 243-273. “B. B. Vohra, ‘A policy for land and water’, Sardar Pate1 Memorial Lecture, Department of Environment, Government of India, New Delhi, 1980.

152

land use policy

India lacks a central agency responsible for the formulation, coordination, implementation, and monitoring of land use policies. Although a Land Use Resources Commission was established in 1983, the state governments controlling land use policies have not initiated action to constitute a unified agency for coordinating land use management. There has also been poor coordination among central government departments responsible for land use management. such as Agriculture, Irrigation, Forestry, Revenue and Animal Husbandry.” There is no agency at the district level with responsibility for coordinating land use and water management. Land use regulations The absence of land use regulations has meant haphazard change. Consolidation of holdings and land development have not been taken up on the basis of microwatersheds as planning units. Drainage and soil conservation programmes have been taken up after land development on the basis of individual land holdings and not on the basis of mini waterbasins. There has been little finance for, and communication between various agencies responsible for land and water management.

LAND USE POLICY April 1985

Sedimentation

of reservoirs in India

Poor monitoring systems Monitoring of sedimentation and initiation of corrective measures must be institutionalized. In areas prone to high rates of erosion, the monitoring system should check sedimentation rates at frequent intervals. Lack of awareness One of the basic reasons for improper land use in the catchments has been the lack of awareness of soil erosion and the value of soil conservation measures. In the case of Nizamsagar, soil conservation measures require an average of Rs 350 per hectare (for contour bunding, gully plugging, graded bunding. bench terracing and land shaping) depending on the topography and geophysical characteristics of the catchment.‘j The priority treatment of the 316 000 ha of the Nizamsagar catchment would have cost only Rs 110 million. The total corrective cost (in terms of another project to contain silt and increasing the height of the Nizamsagar dam) is now probably about Rs 630 million. Poor political commitment has been a major consequence of this lack of awareness. In many cases, land maintenance and water management activities, initiation, implementation and evaluation of soil conservation programmes have had little support from higher authorities.” Emphasis on short-term gains In a majority of individual and governmental decision-making systems, short-term gains are overemphasized. Often, in irrigation projects, the benefit cost ratio is magnified to obtain approval of the decision makers (mainly by underestimating the siltation rate, and consequently provision for dead storage). Again. soil conservation and land development are considered to lack economic returns. There is a danger that unless the difficulties of reversing the land degradation process are made clear to technical and policy decision makers, poor land management practices will continue with disastrous results. Land development and soil conservation generally get the lowest priority in applications for credit. A part of the initial capital expenditure in irrigation projects must be earmarked for soil conservation, consolidation of holdings and “National Commisslon on Agriculture, Resource Development, (NCA keport Vol 5) Ministry of Agriculture, Government of India, New Delhi, 1976. 13K. Jagannatha Rao, ‘Soil conservation in Tungabhadra river valley’, Seminar Proceedings: Watershed Management in Tungabhadra River Valley - An Appraisal, Tungabhadra Board, Tunghabhadra Dam, India, 1982, pp 491-507; Department of Agriculture, Performance Budget Report, Government of Maharashtra, Pune, India, 1983. 14Vohra, op tit, Ref 11; A. M. van Oosten, ‘Rural organization and land-water balance’, in, P. Laconte and Y. Y. Haimes, eds, Water Resources, Nijhoff, The Hague, the Netherlands, 1982. “B. Bowonder, ‘Environmental risk assessment issues in the Third World’, Technological Forecasting and Social Change, Vol 19. 1981, pp 9%127. “Vohra, op tit, Ref Il.

LAND USE POLICY

April 1985

land

development.

Poor coordinatio~l of activities The Nizamsagar and Sriramsagar catchments are spread over different states. This fragmentation has resulted in poor coordination of land-related activities between the states. Though the National Commission on Agriculture recommended in lY76 that each watershed should be managed by an independent agency cutting across the political and institutional boundaries, no action has yet been initiated.” Since land development is conducted without proper concern for water-use efficiency and management practices, agriculture in marginal areas will suffer serious land degradation. Construction of water courses, field drains and the shaping of land for irrigation should be conducted on the basis of natural drainage units, not on the basis of individual holdings.‘” Although the National Commission on Agriculture had recommended that consolidation of holdings should be made obligatory to force the taking up of land development work before starting irrigation. the recommendation has not been implemented.

153

“Bowonder, op tit, Ref 15.

Unless the essential process of ~~~ri~ultur~l extension covers soil management practices as well, it may not have effect at the farm Icvel. The average holding size is about two hectares - 23 million farmers have less than 0.5 ha. This makes it difficult for agricultural extension workers to approach and educate individual farmers. especially with a slow communications system.” It is essential that land management education is institutionalized so that it occurs in schools as well as farms. The Indian Soil Survey Organization consists of less than 1000 personnel despite the magnitude of area to be covered under soil survey and conservation programmes. This is an unfortunate hut typical indication of the low priority soil conservation in particular, and land rn~ln~~~ernent in general has been given in India. A rn~cl~~nisrn should he evolved for institution~lizill~ public p~~rticip~~ti~~n. Education can precede the formation of these structures.

L B. Bowonder

154

K.V. Ramana

_. Hanumantha Rao

LAND USE POLICY April 1985