Assessing Reliability of Reservoir Firm Yield

Yujuin Yang, Ruben Solis, and John Zhu
Texas Water Development Board, Austin, Texas 78711

In Texas, both issuance of a new perpetual water right and state surface water planning are based upon reservoirs’ firm yields, defined as the maximal annual diversion available in all years including the drought of record year. In practice, the firm yield is computed by the Water Availability Model (WAM), a monthly water budget model, using 50+ years of recorded hydrology (precipitation, evaporation, naturalized inflow) in the past, usually from the 1930s to the 1990s, as model input. An important limitation behind this method is that the hydrology is applied exactly as if occurred historically. In this paper, the effect of this restriction is examined. With randomly re-arranged time series of the hydrologic inputs, firm yields of reservoirs are re-computed by WAM and the antecedence probability of current firm yield is estimated. The result helps assess the reliability or the “firmness” of the firm yield.

AAPG Search and Discovery Article #90158©2012 GCAGS and GC-SEPM 6nd Annual Convention, Austin, Texas, 21-24 October 2012