Simulation of operations and water quality performance of reservoir multilevel intake configurations

A predictive framework is developed and applied to evaluate benefits of multilevel intake configurations in managing temperature (T-w) and turbidity (C-T,C-W) in water withdrawn from a water supply reservoir, Schoharie Reservoir, New York, that presently, has a single level intake. High values of T-w occur in late summer for the reservoir in major drawdown years, and high C-T,C-W levels occur irregularly following runoff events. The framework, composed of a tested two-dimensional water quality model for temperature and turbidity linked to a heuristic optimization algorithm, supports automated selection of intake levels to meet user-specified operational goals. Multilevel intake configurations are demonstrated to avoid exceedences of a State discharge standard (21.1 degrees C) for T-W for the conditions of a critical historic year, through a strategy of withdrawal of warmer upper layers through early summer and subsequent blending with cooler lower layers as necessary, at both the existing intake site and a deeper down-reservoir location. The adequacy of the existing intake site is challenged for this critical year if a conservative lower Tw standard is set to accommodate the effects of model uncertainty. Amelioration of high C-T,C-W values is demonstrated for multilevel intake configurations. The operation of a multilevel intake facility in the reservoir would result in a shallower epilimnion and metalimnion in many years, and summer surface temperatures would be lower in major drawdown years. The modeling approaches used in this analysis are generally applicable to support evaluations of multilevel intake configurations for other water supply lakes and reservoirs.