This document describes the use of a new rule function in RiverWare that allocates water in the accounting network to water rights (accounts) according to priorities given by the priority date on the accounts. Earlier dates have higher priority than later dates; that is, those with an earlier priority dates have first right to the use the available water over those with later priority dates. This function, along with the methods on accounts and objects, and new linking configurations, support modeling water allocation under the doctrine of Prior Appropriation.

Previously, users have implemented a water rights allocation algorithm using logic created in rules. Although this problem can be solved with rules, the solution is sufficiently complex that the resulting ruleset is large, difficult to maintain, and the resulting model runs are inherently slow for a moderately sized basin. To address these modeling issues, CADSWES has developed a rule function that calls a solver and returns the correct allocations.

First, we present the assumptions/requirements considered in the design and a general description of the solver. Next we describe how to set up a model and rules to use the solver. Finally, the detailed solution algorithm and additional modeling recommendations are presented.