Groundwater Management Model of Salinity Control and Reclamation

Abstract

The Indus Basin constitute the heartland of Pakistan. Its plain area supports the greater part of the population, and contains the land and water resources for agriculture on which major part of Pakistan’s economy depends. According to a rough estimate agricultural exports generate over 72% of the country’s total foreign exchange earnings. About 52.7% of work force derives employment from agriculture. Therefore, sustained agricultural growth is vital to the future development of the country. The expenditure under Annua Development Plan on agriculture increased from Rs. 1421 millions in 1977-78 o Rs. 3106 million in 1985-86 and that on water sector from Rs. 1556 to Rs. 5197. The country lies in the sub-tropical region with a semi-arid to arid climate and covers an area of 79.61 million hectares out of which 20.54 million hectares are cultivated 1984-85. The climate allows double cropping with Kharif crop season from April to October and Rabi season comprising the remainder of the year. Principal Kharif crops are cotton, rice, sorghum, millets, and Fodder and Rabi crops are wheat, barley, gram, pulses, oil seeds. Fruit, vegetables, sugarcane are grown throughout a year in both seasons. The rainfall distribution in the country is erratic a really as well as time-wise. It varies from 40 inches/year in the north to five inches in the south. Seasonally, 80% of annual rainfall occurs during the monsoon months from June to September. With such old rainfall distribution, and high evapotranspiration rate, artificial irrigation becomes essential for sustain agricultural growth in the country. The world largest canal irrigation network was, therefore, established during the last century to provide more reliable irrigation supplies and thus enhance crop production. At present canal network consists of 40,000 miles of canals to convey water from different headworks to agricultural fields. The network comprises of main-canals, branch-canals, distributaries, minors and water courses. The average watercourse command area is 310 hectares, which is very large in comparison to other countries. Snow- and glacier melt in the mountains and monsoon rains provide the irrigation water to the Indus, Jhelum, Chenab, Ravi and Sutlej rivers. During the year when the monsoon rainfall is light and irrigation requirements are highest, water supplies are short and attendant crop failures and food shortages require large amount of food rains to supplement domestic supplies. The Indus Plain is formed of alluvium deposited by the Indus and its tributaries to depths upto thousand feet and more, forming an essentially featureless level plain with but very slight slope, averaging about one foot per mile. The entire alluvium is saturated by groundwater to within a few feet f the land surface in the affected areas. The alluvium varies in texture from medium sand to sandy clay, with sandy soils predominating. Investigators have shown presence of an enormous quantity of groundwater reservoir comes from infiltration from rainfall, and river and canal seepage. The recharge provides a perennial source of irrigation supplies by tube wells. In addition, the stored groundwater is available for mining subject to economic limits. However, not all of the available water is suitable for agricultural use. Quality of water problems exists is many areas and detailed investigations are required before complete development of the groundwater resource can be planned and accomplished. Salinity concentrations in terms of total dissolved solids (TDS) vary from 550ppm in the good quality groundwater areas of the Upper Punjab to over 30000 ppm in Sindh. In addition to salinity, the presence of potentially harmful quantities of sodium constitutes a quality problem that also requires careful evaluation.