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This presentation describes the development of a comprehensive program for controlling turbidity inNew York City's 600 mgd Catskill supply system. Though the watershed is relatively pristine (~75%forested) and generally provides very high quality water, the system faces geological challenges thatare difficult to control with traditional land management BMPs. In particular, stream banks andchannels in the region are often minimally armored and underlain by natural glacial clay deposits.These deposits are mobilized during storm events and contribute to periodically elevated turbiditylevels in Schoharie and Ashokan Reservoirs. Elevated turbidity is of concern with respect to both theoverall quality of NYC's unfiltered drinking water supply, and to aquatic habitat and recreationalissues in receiving waters.In order to protect and improve the quality of its unfiltered drinking water supply, NYC developed aprogram to identify feasible, effective, and cost-effective measures for providing reliable turbiditycontrol in the Catskill System. The alternatives under consideration move beyond traditional watershedBMPs, and include in-reservoir structural measures such as impermeable baffle walls, permeableturbidity curtains, depth-selective withdrawal systems, clarification facilities, adjustable weirs andwaste discharge structures. Operational measures for optimizing management of the multi-reservoirsystem to meet both water supply and water quality objectives are also considered.The performance, cost, and feasibility of each of these alternatives were evaluated for the purpose ofeliminating infeasible or unreliable alternatives. Turbidity control performance was evaluated usingtwo-and three-dimensional reservoir water quality models, bench-testing, and in-reservoir pilot-testing.Further detailed performance evaluation of surviving alternatives is ongoing based on long-termprobabilistic modeling using 2-D and 3-D models of Schoharie, Ashokan, and Kensico Reservoirs.Non-structural alternatives are evaluated using a reservoir systems operation model that relies on linearprogramming to identify optimum diversion strategies and operating rules for turbidity control.This presentation summarizes the development and evaluation of structural and operational alternativesfor improving turbidity control in the Catskill System, and provides an example for utilitiesconsidering active source water quality management measures as an alternative to treatment processmodifications. Includes abstract only.

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Edition: Vol. - No. Published: 06/01/2006 Number of Pages: 1File Size: 1 file , 220 KB