Flood Control Operation of Reservoirs

Inasmuch as the tendency of agencies operating multi-purpose reservoirs for flood control is to gain the immediately foreseeable benefits of power production, irrigation, and other conservation services at the expense of dependable flood protection, dependable flood control operation of multi-purpose reservoirs requires the formulation and strict observance of a set of operating rules designed to provide essential flood control while assuring essential conservation accomplishments. In the Central Valley of California, fully satisfactory protection against unpredictable rain floods requires firm flood control space throughout the rainy season, with varying space requirements at the beginning and end of the season. Where conservation functions warrant, however, rain space requirement may be governed in part by ground conditions. Protection against snowmelt floods can usually be provided on a forecast basis, with good utilization of the flood control space for conservation purposes. Ungated spillways usually provide an important moderating effect on excessive floods, whereas gated spillways usually do not and must be operated with great care in accordance with prearranged schedules.