ABSTRACT
Major floods are generated by atmospheric concentrations of water and energy from areas vastly greater than those of watersheds. Although field techniques for rehabilitation of upper watersheds are known, successful restoration of a damaged watershed only reinstates the former natural measure of flood control. As development in lowland areas proceeds, the growth in investments vulnerable to damage by floods increases the insurance value of upstream protective structures. In tropical conditions, the strong seasonal contrasts increase the importance of upstream storage for flood control. The grandest natural theater in which all the problems are being played out is the Himalayan range. Steep, high mountain watersheds supply the crowded alluvial floodplains of the Indus and the Ganges river systems. The floodplains thus evolved as natural storage areas for floodflow and reception areas for sediments. Flood damage will be effectively reduced only if people recognize that the watershed functions naturally as a single system.
