Consequences of an Altered Thermal Regime to Warmwater Fishes below R. L. Harris Dam, Tallapoosa River, Alabama, USA

Adaptive management below R.L. Harris Dam, a hydropeaking facility on the Tallapoosa River, Alabama has been ongoing since spring 2005.  Discharge has been experimentally manipulated at the dam to benefit multiple competing objectives of stakeholders (e.g., fish recruitment, power production).  Because water discharged through the turbines is drawn from depth, river temperature during power production is depressed.  To quantify effects of discharge on temperature regimes, discharge data (2005-2013) were obtained from a USGS gage below the dam and hourly temperature data were collected at the same site.  Similar data were collected at two unregulated tributaries.  Water temperatures in the tailwater were cooler versus temperatures at unregulated sites, especially in summer.  Variation in temperature regime was high and related to power generation: 10°C decreases within hours were common.  Subsequent re-warming of the river to pre-discharge maximum temperatures was prolonged (≈10 days).  We evaluated thermal requirements for spawning for a suite of fishes and determined that thermal conditions were often not provided for some fishes, including important sport fish such as Channel Catfish Ictalurus punctatus and Tallapoosa Bass Micropterus tallapoosae.  These analyses will be used to further refine flow regimes below Harris Dam consistent with stakeholder objectives in the adaptive management program.