Regulation of Flow Downstream of Weirs

Reregulation weirs are one means adopted by the Tennessee Valley Authority (TVA) to provide continuous improved minimum flow and wetted area for aquatic life downstream if hydroprojects during off-generation periods. A series of low-level pipes through the weirs, where some are fitted with regulating float-actuate valves, maintain essentially constant releases over a full range of weir pool elevations. Previous designs of such float-controlled mechanisms were based on physical modeling. This paper describes such a flow-regulating system and presents a quick and reliable analytical technique to determine float movement and pipe discharge rate at different headwater conditions. Data obtained from a full-scale model of the TVA South Holston labyrinth weir pipe and valve assembly were used to develop this analysis. Results of the analytical model were found to compare well with experimental data.