Waterlogging and Salinisation
Summary: An analysis of available information suggests that about 55% of the SSP command area may be affected by waterlogging and salinisation due to surface irrigation, an environmental problem of staggering magnitude. Studies are not complete and hence no detailed action plan exists. Current proposals are based on a complex technological system which has not been tried out elsewhere on even a much smaller scale, and one which could easily be defeated by social and managerial difficulties.
Waterlogging and salinisation of the proposed command area represent potentially the largest environmental threat arising from the SSP. In arid and semi-arid areas drainage is usually geared to low rainfall conditions and is usually incapable of handling the much larger water amounts brought by surface irrigation. This, along with seepage from canals, overuse of water by farmers, and other factors depending on the geomorphology of soil and subsoil layers, lead to increasing water accumulation below the surface. Secondly, subsoil water and soils in and regions tend to be saline due to inadequate flushing by rainwater. Irrigation water, being saltier than rainwater, adds more salt to the system, leading to increased likelihood of salinisation.
Waterlogging and salinisation are global problems of staggering magnitude: according to the United Nations Environment Programme (UNEP), between 30 to 80% of the world's irrigated land is suffering from these and the related problem of alkalinisation (the large range of estimates is due to differences in definitions being used by various experts, and the lack of comprehensive information from many countries). In India, it is estimated that at least one-fourth of irrigated land is facing these problems ( DOE 1985).
Pakistan has an arid zone similar to much of the command area of SSP. By the mid-1970s, waterlogging and salinisation were estimated to affect 11 million of the 15 million hectares of irrigated land in Pakistan, leading to "a pronounced reduction in the main crop yield" ( Elgabaly 1980) : more recent estimates are not available with us. A similar region is the command area of the Indira Gandhi Nahar Pariyojana in Rajasthan where large parts of the irrigated and adjoining areas are already facing waterlogging and salinisation, just a few years after commencing irrigation.