A Simple Analytical Method to Assess Multiple-Priority Water Rights in Carryover Systems

Simple analytical storage–reliability–yield relationships have traditionally only considered a single reliability for a single yield, yet many reservoirs supply water of different priorities. Simulation models may be used to handle such multiple-priority water rights but these models are complex and usually system specific. Here we propose a simple analytical method based on Gould-Dincer to estimate yields in dual and triple priority allocation systems from a carryover storage. This allows rapid assessment of changes in water resource availability for different water priorities, potentially over large spatial scales. We use a dam simulation model to assess this method at 15 sites across six continents and find that the “dual-priority” and “triple-priority” G-D methods can reproduce the results of the dam simulation model. Thus, the method could be generalized for multiple priority allocation systems use. We demonstrate the potential utility of the “dual-priority” G-D method through an evaluation of the optimum yield between high and low-priority water rights (HPWR and LPWR) from hypothetical (but realistic) carryover systems. It confirms the possibility that “dual-priority” water allocation may be beneficial overall compared to a single-priority water right. By balancing the yield of HPWR and LPWR, the optimum marginal value of available water (i.e., sum of high- and low-priority water) can be achieved. Overall, the method provides a simple way for rapid assessment across multiple sites allowing insights into optimal allocation practices and the interacting driving factors that affect them at a regional-to-global scale.