Short-Term Reservoir Storage Frequency Relationships

Abstract

The water rights analysis package (WRAP) is a generalized river/reservoir system simulation model that is routinely applied in Texas in regional and statewide planning studies and administration of the water right permit system. The WRAP modeling system was recently expanded by adding short-term storage frequency and supply reliability analysis capabilities. Individual reservoirs and multiple-reservoir systems can be analyzed considering numerous water users and complex water management practices. The new modeling features are based on dividing the hydrologic period-of-analysis into many short-simulation sequences with each starting with the same storage conditions. Two alternative frequency/reliability analysis methodologies, called the equal-weight and probability-array options, are compared in this paper with a case-study application. The probability array option is designed to improve the accuracy of storage frequency estimates by modeling hydrologic persistence as reflected in the preceding reservoir storage contents on the basis of a regression of natural streamflow versus preceding storage from a long-term simulation.