Improving NYC System Operations with Forecasts
- Grantley Pyke - Hazen and Sawyer
- Paul Rush - NYCDEP
New York City’s innovative Operations Support Tool (OST) uses near real-time data, hydrologic forecasting, and predictive modeling to guide reservoir system operations, identify future water stress conditions, and take preventive actions to maintain supply reliability, water quality, and environmental performance. NYCDEP uses OST on a daily basis to assess drought risk for a 19-reservoir system that provides 1 BGD of drinking water to 9 million people. OST allows system operators to look ahead at reservoir storage levels months in advance, assess drought risk, and take proactive measures to mitigate low storage conditions.
OST has been used extensively to help NYCDEP prepare for the extended outage of a major aqueduct that supplies two-thirds of NYC’s water supply. OST analyses have been critical in identifying how long remaining supplies can reliably meet water demand, quantifying supplemental water supply needs, and developing forecast-based triggers for demobilizing repair operations when there is a risk of shortfall.
OST has also been used to develop and implement reservoir stream release policies that depend on forecasted water availability. When hydrologic conditions are favorable, releases are increased to enhance downstream fisheries habitat. When conditions begin trending dry, releases are ramped down to preserve water supply reliability. When there is a risk of flooding, releases are increased to mitigate peak spills.
OST’s ability to simulate turbidity in key reservoirs has become a cornerstone of NYCDEP’s strategy for maintaining a high quality unfiltered supply. NYCDEP uses OST to prepare for major forecasted storm events, and to optimize diversions and releases from multiple reservoirs in order to deliver the highest quality water to consumers.
OST relies on state-of-the-art probabilistic streamflow forecasts from the National Weather Service to quantify the range of reservoir inflows over an operational horizon that extends from the current day out for one year. Multiple potential future inflow sequences are generated through this process in order to capture both the central tendency and the extremes of the forecast. Each forecast is input to a model that simulates the operation of the NYC reservoir system and reservoirs throughout the Delaware River Basin.
Output from the model includes daily reservoir diversions, releases, spills, and storage levels from the current day out for one year. System operators analyze model output in a probabilistic manner to analyze the risk of low storage levels or drought conditions. When stress conditions are detected, operators run simulations that test the efficacy of alternative mitigation measures. Trying out different options ‘on screen’ allows operators to choose the option(s) that best balance among competing objectives. Simulations are conducted on a daily basis to allow for adaptive management of the reservoir system as hydrologic conditions change.
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