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A linked water supply/water quality model of the New York City reservoir system was used toevaluate the feasibility of modifying reservoir operations to reliably control turbidity in NYC's CatskillSystem. In particular, the model was used to evaluate operating rules to meet turbidity and temperaturetargets in diversions from Schoharie Reservoir to Esopus Creek, a Class A trout stream that conveysSchoharie water downstream to Ashokan Reservoir. Schoharie Reservoir supplies up to 615 mgd ofwater to the NYC system, and is a critical source of supply for the City. Additionally, Schohariediversions are required to maintain minimum flows in Esopus Creek and are critical to the health of thetrout fishery. However, discharges of occasionally turbid Schoharie water subsequent to storm eventsmay compromise the overall quality of NYC's unfiltered drinking water supply and may have apotential negative impact on aquatic habitat and recreation in Esopus Creek.The water supply model, OASIS (HydroLogics, Inc., Columbia, MD), simulates the routing of waterthrough the entire NYC reservoir system (including the Catskill, Delaware, and Croton systems and theentire Delaware River basin). The model accounts for environmental constraints and physicallimitations as well as operating rules for water supply reliability. A linear programming moduleoptimizes flow routing operations under user-defined targets and constraints. OASIS is linked to a two-dimensionalhydrodynamic water quality model for Schoharie Reservoir, CE-QUAL-W2 (UpstateFreshwater Institute, Syracuse, New York), which predicts daily turbidity and temperature profiles in thereservoir. Various operating rules, making use of the turbidity and temperature profiles, storage, timeof year, and inflow forecasts, are programmed into OASIS which then models the effects on watersupply reliability. Such operating rules include reducing discharges from Schoharie during elevatedturbidity conditions, reducing drawdown, and reducing withdrawals during early summer to preservethe cold water bank for release to Esopus Creek in late summer. This paper provides a review of thelinked model and demonstrates how it can be used to develop reservoir operating rules that balancewater supply reliability, drinking water quality, and environmental release objectives. Includes abstract only.

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Edition: Vol. - No. Published: 06/01/2006 Number of Pages: 1File Size: 1 file , 210 KB