Reservoir Operation with Imperfect Flow Forecasts

Where a large proportion of the runoff originates from snow melt it is usually possible to forecast inflow to a reservoir with reasonable accuracy. However, in the case of reservoirs which are used for both flood control and conservation there is always some conflict between the flood control requirement for reservation of space and the conservation requirement to store as much water as possible, even though good forecasts can minimize the conflict. Okanagan Lake in British Columbia, Canada, is typical of such multi-purpose reservoirs and each year the dilemma arises as to whether space should be reserved to meet flood control needs or filled to guard against possible droughts. The problem of developing optimal operating policies is examined and a method is presented which uses simulation to assemble available information from the flow forecast, past records of the pattern of flow and the present lake level in a form which illustrates the probable consequences of various courses of action during the forthcoming time period. The operator must still make his own decision but can use the explicit information as a basis for judgment.