Rehabilitation planning for small tanks in cascades : a methodology based on rapid assessment

That is, the impacts of system improvements on water users in other areas of the basin must be assessed to avoid creating or aggravating discord and ensure that investments provided the expected benefits. However, in many places hydrologic data for basins does not exist. This report describes a methodology for planning the rehabilitation of small tank (reservoir) systems in the dry zone of Sri Lanka, where the hydrologic database is deficient. The method uses data from topographic maps, rapid assessments, and farmers to assess the hydrology of tank cascades (subbasins). Data are gathered from farmers at participatory sessions that provide a basis for planning the improvement of irrigation systems. The key value defined is the outflow from the cascade under present conditions. The value determines the types of irrigation system improvements that can be permitted within the subbasin, as well as a means for avoiding conflicts over water within the basin area. By involving farmers in the assessment and planning, the method lays a foundation for farmer cooperation in carrying out the rehabilitation. The method also requires the use of nonhydrologic criteria for selecting irrigation systems and evaluating rehabilitation plans. The methodology was field-tested in Sri Lanka"s dry zone in 50 tank cascades that cover an area of 25,000 hectares and have 700 minor and medium-sized tanks. This method can be applied in similar situations in India and elsewhere. With slight modifications, it can also be used for evaluating water resources development projects in many river basins dominated by small-scale irrigation systems. (Author abstract)