Reallocation Of Storage In Federal Reservoirs For Future Water Supply

Interest in converting portions of the large volumes of flood control storage capacity in federal multiple-purpose reservoirs in Texas and elsewhere to water supply and other conservation purposes has been growing for some time. Evaluation of storage reallocations involving tradeoffs between flood control and conservation purposes in multiple-purpose, multiple-reservoir systems represents a new area for applying the Water Rights Analysis Package (WRAP) and Texas Water Availability Modeling (WAM) System. A system of 12 multiple-purpose reservoirs operated by the U.S. Army Corps of Engineers (USACE) and Brazos River Authority (BRA) was adopted as a case study in this research to develop and test expanded WRAP/WAM-based methods for analyzing modifications in reservoir storage allocations and related system operations. The research consisted of the following tasks: The Brazos River Basin WRAP input dataset from the Texas WAM System (Brazos WAM) has a 1940-1997 hydrologic period-of-analysis. The research included developing and applying methods to extend the period-of-analysis to 1900-2007 providing a better representation of river basin hydrology. The methodology developed could potentially be used to update the other river basin datasets in the statewide WAM System. The Brazos WAM has 3,830 control points, 670 reservoirs, and hundreds of water rights. The research included developing and applying methods to create a much easier-to-apply condensed dataset focused on the USACE/BRA reservoir system and associated water rights that have only 48 control points and 14 reservoirs. The WRAP/WAM System was developed based on a monthly computational time step. The research included applying developmental methodologies for converting a monthly model to a daily time step that includes disaggregation of monthly naturalized flows to daily flows, calibration of flow routing coefficients, and incorporation of forecasting in the simulation. The WRAP/WAM System is designed for assessing water supply reliabilities and stream flow and storage frequencies from the perspective of conservative purposes. The research added flood risk indices to the WRAP modeling system in order to address tradeoffs between flood control and conservation purposes. The WRAP/WAM-based simulation study performed with the modified WAM dataset developed in this research demonstrates the improvements in water supply capabilities and tradeoffs with flood control associated with various reservoir storage reallocation strategies and other modifications in reservoir system operations.

In recent years several policy have been conducted by the Institute for Water Resources, Corps of Engineers on reallocation of reservoir storage for municipal and industrial water supply. The investigation is continuation of that effort. Its purpose is to indentify opportunities for reallocation of storage at Corps reservoirs by examining specific studies, projects and Federal-State partnerships where reallocation has been considered. Sixteen study reports were examined and are reported here. In addition, discussions were held with Corps engineers in district and division offices on other projects where reallocation has been or is being considered. Together, the reports and discussions identified eight general opportunities for reallocation. The applicability of these general cases to Corps' reservoirs nationwide will depend upon the conditions at each individual site and must be evaluated on a site by site basis. A Memorandum of Understanding (MOU) between the State of Kansas and the Department of the Army is discussed as an example partnership where innovative opportunities can be developed. (FR).