Rule-based storage accounting for multipurpose reservoir systems

The needs for conservation, efficient management, and accounting of water uses intensify as demands increase relative to supplies. Storage accounting, properly performed, can provide a framework to meet these needs and to efficiently and equitably allocate the benefits, costs, and risks of water resource systems. Rule-based storage accounting is one approach that allows actual water uses and reservoir operations to be tracked against prior existing systemwide rules. This approach is especially well suited to sustainable and adaptive management policies that accommodate: (1) updated allocations of storage in multipurpose reservoirs to most beneficial uses; and (2) targeted credits and penalties for water use and reservoir operations to incentivize conservation, prevent cross-subsidization among included purposes, and check unsustainable demands on the system. The writers review and contrast rule-based with traditional storage accounting methods, and provide an example application of the former to a reservoir system operated to meet multiple consumptive and nonconsumptive uses in conjunction with complex instream flow regimes. Rule-based accounting does not facilitate initial or reallocations of water and storage but, by holding both reservoir operators and water users accountable for compliance with established allocations, discloses their efficiency, fairness and sustainability, and consequently serves to guide future adaptive management strategies.