Hydrogeology in the Service of Man, Mémoires of the 18th Congress of the International Association of Hydrogeologists, Cambridge, 1985.

Transcription

1 Hydrogeology in the Service of Man, Mémoires of the 18th Congress of the International Association of Hydrogeologists, Cambridge, SALINE GROUNDWATER MANAGEMENT IN HARYANA STATE, INDIA 1 2 B.S. Tanwar and G.P. Kruseman Haryana State Minor Irrigation (Tubewells) Corporation Ltd., The Mall, Karnal , India Food and Agricultural Organization of the United Nations, Rome, Italy; present address: TNO-DGV Institute of Applied Geoscience, P.O. Box 285, 2600 AG DELFT, The Netherlands ABSTRACT The state of Haryana ( km 2 ) lies in the northwestern part of India on the watershed between the Ganges and Indus River Basins. Nearly the whole state lies in the Indo-Gangetic plain and is an important food grain producer. About 80% of the state's area is agricultural land ( km 2 ), of which some km 2 can at present barely be irrigated with the available water resources. The northeastern part of the state is extensively underlain by fresh groundwater that is pumped for irrigation, resulting in certain trends of groundwater level decline. The remaining km 2 is underlain by brackish to very saline groundwater and mainly depends on canal water for irrigation. Losses through deep percolation in the conveyance system and in the field, and the absence of pumping of saline groundwater result in a rapid rise of the water table and subsequent waterlogging and soil salinization. At present km 2 are critically affected by saline water table rise: this area may ultimately increase to about km 2. Haryana State Minor Irrigation (Tubewells) Corporation Ltd. (HSMITC) in co-operation with the Food and Agricultural Organization of the United Nations (FAO) is studying ways to remedy this problem. The studies focus on how the water table in the saline groundwater belt can be controlled by draining the uppermost layers which contain better quality, although still brackish, water. The drainage could be effected through shallow skimming wells and horizontal pipe drains. Ideally the drainage water should be re-used to irrigate salt-tolerant crops. When the salinity is too high, the drainage water will have to be diluted with fresh canal water before it is re-used. Furthermore, other methods of using or discharging the excess saline groundwater are being studied. INTRODUCTION Haryana is located in the semi-arid northwestern part of India. It covers an area of about km 2 (Fig. 1). Rising saline groundwater in two thirds of the state creates conditions critical to agriculture because of increasing waterlogging and soil salinization. At present, about 4000 km 2 of agricultural land are criti

2 Fig. 1. Shallow groundwater quality map of Haryana cal, but eventually km 2 may be affected, threatening the livelihood of one million farmers and their families and having a significant influence on the food grain production of Haryana and, in turn, of India as a whole. Haryana State Minor Irrigation (Tubewells) Corporation Ltd., a Haryana state undertaking, was asked to find a solution for this problem. HSMITC received assistance from United Nations Development Programme (UNDP) and the Food and Agricultural Organization of the United Nations (FAO) through project IND/81/010 "Studies for the use of saline water in the command areas of irrigation projects, Haryana". This project ran from September March Some of the results of the

3 project (FAO, 1985) are summarized in this paper. Harayna lies on the Indogangetic plain on the watershed between the Yamuna river, which runs along its eastern border and belongs to the Ganges basin, and the Ghaggar river along its northwestern border which belongs to the Indus basin. In the north it abuts on to the Siwalik hills (elevation 1200 m) and in the south on to the Aravalli-Belhi hills (elevation 300 m). A string of shallow depressions (at an elevation of 200 in) runs from Delhi via Rohtak and Hissar to Sirsa. Average annual rainfall decreases from 1000 mm in the northeast to 200 mm in the southwest. Most (80%) of the annual total falls in heavy monsoon showers between June and October and 15% falls in the winter months from December through March. A large part (17207 km 2 ) of Haryana has no proper surface water drainage. Only the zones adjacent to the Yamuna river (16330 km 2 ) and Ghaggar river (10675 km 2 ) have natural drainage to the rivers. HYDROGEOLOGY The Indo-Gangetic plain is the surface expression of a structural depression. In front of the Siwalik hills this structural depression forms a deep (> 3000 m) trough, but south of the line Narwana FRESH GROUNDWATER FRESH 10 BRACKISH SHALLOW WATER BRACKISH DEEP WATER SALINE 1= mvd 1= mvd EC-Q.1-1,0 msafc EC.O.i-1,6 ms/cm T=S mvd C-0,7-1,6 ras/cw T=1000 m2/d C-Q,6-<..9 ms/cm T=SOO-600 wvd EC ,2 ms/cm 1= mvd EC «0,4-6,1. rasan V 40 km PREDOMINANT LITHOLOGY clay (with sandy intercalations) \/f['-//\ fine sand with clayey intercalations I """j medium and coarse sand with I 1 finer intercalations i i 1 medium and coarse sand with I * I gravel intercalations * + bedrock '- depth of hydrogeological investigations Fig. Schematic cross-section through Haryana

4 - Sonipat the basement occurs at much shallower depth ( m). The depression is filled with alluvial material (Fig. 2). In the depth range that is most interesting from the groundwater point of view, the average grain size of the deposits decreases from north to south. In the north, clayey layers are intercalated in medium sand and gravel deposits, while in the south the clay and silt layers are clearly predominant, although intercalated with fine sand layers. The clay layers often contain, sometimes in large amounts, irregular nodules of calcium carbonate (kankar). Despite its large number of clayey layers the whole of the aquifer system can be considered as a single heterogeneous unconfined aquifer. Sometimes the clayey layers may create semi-confined conditions (leaky aquifers) locally but the clay layers may also be pervious, especially when mixed with kankar. Transmissivity values obtained from well tests range from 170 to 2600 m 2 /day (2x10-3x10 m 2 /s) and the specific yield in the depth range affected by water level fluctuations is 10-15%. On the basis of its hydrochemistry, Haryana can be broadly divided into an area with fresh groundwater in the north and east and an area with saline groundwater, which covers 65% of the state in the south and west. The saline water area is intersected by fresh water "fingers" along the rivers Yamuna and Ghaggar and between Jind and Hissar along the Hansi branch (irrigation canal). The latter is probably located on fossil stream deposits. AGRICULTURAL DEVELOPMENT A century ago the central and western parts of Haryana were still mostly covered by semi-arid woodland and scrub and the groundwater level was reportedly at a depth of m. Canal irrigation was introduced about 100 years ago by diverting water from the river Yamuna. In 1960 the Bhakra system of canals was built. Now, a network of canals more than km in length is spread over the state. The canal water is distributed according to the so called "warabandi system". The principal objective of this distribution system is to provide an equal opportunity to all farmers, whatever the geographic location of their holdings in the command area. They each receive an equitable amount of water in the sowing, growing and maturing periods of the crops, the equity being related only to the size of the holding. The system is thus supply controlled and is not designed to cater for the needs of an individual farmer (demand control). Farmers are obliged to use the water whenever it is made available, because there is no tail drainage and therefore the tail-end farmers might otherwise be flooded. When irrigation and monsoon rainfall coincide, deep percolation increases and there is a corresponding rise in the groundwater table. In the freshwater areas this has been more than counterbalanced by the draft from nearly 3000, deep state-owned tubewells and more then shallow, private tubewells, resulting in a watertable decline. In the southern and western parts of the state there are far fewer tubewells because much of groundwater is of unsuitable quality. Consequently, the water levels in the saline zones show a persistent rise. At present an area of 4000 km 2 is considered "critical"; that is water levels are less than 3 m below surface all year round. Under such conditions the soils

5 easily become salinized, making the land unfit for agriculture in the absence of sufficient irrigation water to leach out the accumulating salt. If nothing is done the "critical area" will continue to expand, resulting in an increasing loss of net production value. AN INTEGRATED APPROACH TO WATER TABLE CONTROL To achieve control of the water table and of salinization, three systems must be integrated: surface water drainage system; irrigation water supply system; groundwater drainage system. The role of the surface water drainage system is: (a) to prevent inundation of soils by monsoon rainfall, which otherwise would result in excessive groundwater recharge, a high drainable surplus and soils unfit for cropping, and (b) to evacuate groundwater drainage water to its place of re-use or final disposal. The irrigation water supply system provides (a) the soil moisture needed by the crops and (b) the leaching water to dissolve the salt left behind by the évapotranspiration of irrigation and capillary water. In turn the downward movement of leaching reduces the upward movement of saline capillary water. The purpose of the groundwater drainage system is (a) to evacuate excess groundwater to prevent water table rise and, consequently, to reduce the capillary transport of salt to the root zone and the surface and (b) to evacuate salt that has been leached from the root zone by the downward percolating excess rainfall and irrigation water. SURFACE WATER DISPOSAL The disposal of the groundwater drainage effluent is one of the major constraints in Haryana. In the part of Haryana that has internal drainage there is no possibility of discharging surface water through any streams. The Yamuna river is a potential receiver of saline drainage effluent but the Ghaggar river is not, because of its very irregular flow regime. However, if it is not to become too saline, the EC value of the Yamuna river water should not exceed ms/cm, because it is used for the Delhi water supply. This restricts the period that it can receive limited amounts of saline water to the period of high flow in July and August. Two other non-beneficial disposal options have been studied: subsurface storage in areas with deep groundwater levels; and storage in evaporation ponds. Both solutions are unattractive. Subsurface storage through artificial recharge is technically difficult to realize, it is very expensive and will only be possible for a limited period. Evaporation ponds require large tracts of land (equal to at least one-tenth of the size of the drained area) to be abandoned. Moreover, the salt deposits are of non-commercial quality if traditional means of extraction are used. The most interesting solution is the re-use of the subsurface water for irrigation, because this helps to alleviate the shortage of irrigation water. This imposes a strict quality constraint on the subsurface drainage effluent. Water with an EC value not exceeding 4-6 ms/cm can be used in undiluted form for irrigation, because the decline in crop

6 yield will be less than 30% which is the limit accepted by the farmer under prevailing agricultural conditions. Water with an EC value between 4-6 and 10 ms/cm can be re-used after mixing with fresh canal water (EC ms/cm). Within the tertiary block the maximum acceptable EC value is 4-6 ms/cm but in the primary and secondary distribution systems it is restricted to ms/cm because the canal water is used to supply domestic water. Mixing effluent with an EC value above 10 ms/cm into the canal water is not recommended because (1) if undiluted water is accidently used for irrigation it will ruin the crop and (2) the mixing ratio will become unfavourable, because the amount of fresh canal water that can receive effluent is limited. The problem of disposal is not only a question of the quantity of the effluent but also of its quality. GROUNDWATER DRAINAGE The limited possibilities for disposing of draining water make it imperative that the salinity of the drainage effluent be reduced as much as possible. The groundwater salinity increases rapidly with depth to unacceptable values. Consequently, vertical drainage using deep tubewells of the type installed in the freshwater zone is not possible. So the only solutions are vertical drainage by shallow skimming wells and horizontal drainage by subsurface gravity flow (pipe drain) systems. Shallow well systems have three advantages: (1) the water table can be controlled at any depth, (2) they are relatively simple to operate, especially if the groundwater quality permits direct use for irrigation and (3) the investment costs are lower than for pipe drain sytems. The drawbacks are that to prevent upconing of the underlying more saline water the wells should not penetrate more than 30-40% of the saturated thickness of the brackish water layer, and thus the brackish water zone (EC less than 4-6 ms/cm) must be at least m thick. Whenever intercalated clay layers restrict the upcoming of the saline water the wells may penetrate more of the brackish water layer. The transmissivity must be in the order of at least 100 m 2 /day (1x10 m 2 /s) to prevent too large drawdown values in the pumped well. The groundwater quality will gradually improve because the recharge water has a better quality than the original ground water that is being pumped out. As the layer affected by the pumping is relatively thick this process is slow. The operation and maintenance costs are higher than for a pipe drain system. The horizontal subsurface gravity flow system (pipe drains) is the other alternative method of groundwater drainage. The advantages of the pipe drain system are twofold: it can be installed in soils with low hydraulic conductivity values (say up to 10 times smaller than those required for skimming wells), and the water layer affected is much thinner than with a shallow well system hence the water quality in the affected zone improves much faster. The system requires hardly any maintenance and operates automatically, although discharge from the collector system into the disposal system may require pumping and thus attendance. The disadvantages are: the high capillary capacity of the soil causes evaporation effects to reach a depth of 3 m below the surface; however, the maximum depth at which the pipe system can be installed is restricted to

7 m if the collector system has a maximum depth of 3.5 m, and therefore the pipe system is not fully effective in controlling soil salinization. The investment costs are approximately twice as high as those of a skimming well system. CONCLUSIONS The hydrogeological situation notably the high salinity content of the groundwater and the constant rise in saline water table, are the main elements in the increasing deterioration of the agricultural resource base of Haryana. The other elements are the lack of possibilities for discharging surface water and the shortage of irrigation water. The permanent solution to this problem has to be found in a programme of a groundwater level control that takes into account the necessity to recycle the subsurface drainage effluent as much as possible. Hence the subsurface drainage system should be a shallow system using skimming wells or horizontal drain pipes. The groundwater drainage system can only be fully effective if the surface water disposal system and the irrigation water supply are improved also. ACKNOWLEDGMENTS The authors, who were at the time National Project Director and Chief Consultant of the project, respectively, would like to thank the Managing Director of Haryana State Minor Irrigation (Tubewells) Corporation Ltd. and the Director General of the Food and Agricultural Organization of the United Nations for their permission to present this paper. It goes without saying that the authors are indebted to the Director Groundwater HSMITC and project staff, including the national and international consultants, for their contributions to the project and hence to this paper. REFERENCE FAO, Studies for the use of saline water in the command areas of irrigation project, Haryana (in press)