ENVIRONMENTAL IMPACTS AND DRAINAGE WATER DISPOSAL CASE STUDY OF PAKISTAN

摘要

Pakistan possesses one of the largest contiguous irrigation systems in the world commandingrnabout 16.7 Mha area. Intensive irrigation over a century has developed water logging and salinityrnproblems in a major part of the command area. Unlike the contiguous irrigation network,rnPakistan's drainage network is not interconnected. A number of Salinity Control andrnReclamation Projects (SCARPS) have been constructed since 1960, which cover an area of 7.9rnMha. The existing drainage facilities comprise about 14,000 km of surface drains, 13,000 freshrnground water tube wells, 4,000 saline ground water tube wells and 12,500 km of sub-surface piperndrains. Drainage water disposal modes include reuse within the Indus Basin Irrigation System,rndisposal into Hamal Lake, Manchhar Lake & evaporation ponds and outfall into the Arabian Sea.rnAlthough SCARPs, based on vertical drainage, did provide immediate relief, reuse ofrngroundwater resulted in transportation of salts to the soil profile. In case of saline tube wells, thernsalts are being transported to lower riparian which are being ultimately added to soil profile asrnwell as to groundwater. Disposal into evaporation ponds and lakes has also created severernenvironmental problems. Presently, only Left Bank Outfall Drain is available to transportrnsurplus salts out of the Indus Basin. The overall salt balance is therefore negative, thus posing arnserious threat to the sustainability of agriculture in Pakistan. For long term sustainability, saltrnbalance of surface water, unsaturated root zone and saturated groundwater zone has to bernmaintained. The future strategy is therefore based on integration of drainage needs with waterrnresource management, sub-surface pipe drainage and safe disposal of brackish drainage effluentrninto sea. The Government of Pakistan is already taking steps in this direction throughrnimplementation of the National Drainage Program.rnIn the southern province of Sindh, where groundwater is saline, a major on-going undertaking isrnlining of distributaries. Lining is also a major component in new irrigation projects like GreaterrnThal, Raini and Kachhi Canal systems, alongwith an ambitious program of water course lining,rnwhich is being implemented over the entire country. A project for high efficiency irrigationrnsystem i.e., Drip Irrigation & Sprinkler irrigation system is planned to be launched very shortly.rnFor improving disposal of brackish drainage effluent from the left bank of Indus River into thernsea, remodeling of the existing drain network is to commence shortly. On the Right Bank ofrnIndus another drainage system out falling into the Sea is under construction. Further measuresrnfor overcoming the salinity and water logging problems are also being planned.