Regulation of Flow Downstream of Weirs

In 1991, the Tennessee Valley Authority (TVA) began implementation of a Lake Improvement Plan to provide increased minimum flow and dissolved oxygen in releases from several dams and reservoirs in the Tennessee Valley System. Reregulation weirs, constructed in the first few miles downstream of dams, are one means adopted by TVA to sustain continuous improved minimum flow and wetted area for aquatic life downstream of hydroprojects during off‐generation periods. A series of low‐level pipes through the weirs, where some are fitted with regulating float‐actuated valves, maintain essentially constant releases over a fullrange of weir pool elevations. Previous designs of such float‐control mechanisms were based on empirical measurements from physical modeling. The present paper provides a functional description of 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.