Large reservoirs provide multiple benefits for water supply, downstream flood reduction, and environmental objectives.  Weather and climate forecasts play a critical role in helping reservoir operators balance multiple, often competing objectives. Accordingly, this session will highlight successful examples of collaborative development and application of forecasts to support reservoir management.

The practice of using forecast informed flood management to mitigate downstream flooding is well established and reservoir operators fully consider that information while managing releases through the dam. However, extreme events challenge both forecaster and operators to quickly determine how to manage designated flood storage and prevent failure of the dam, which include: early releases, increasing spillway releases, and storing water.  Incorrect forecasts can magnify the impacts to any one requirement. Interdisciplinary cooperation is necessary to understand the accuracy of the forecasts and improve lead time to optimize operational flood management releases and preventing dam failure. For water supply management, utilization of codified forecast informed flood management for reservoir operation and recent advancements in weather forecasts such as those underlying the National Weather Service’s Hydrologic Ensemble Forecasting System (HEFS) afford operators improved capability to develop probabilistic projections to support proactive and dynamic operational decisions, such as how much water to release or divert over the next several days.

As an example, New York City’s Operations Support Tool (OST) is a system simulation platform that integrates a water supply operations model, mechanistic reservoir water quality models, statistical and climatological hydrologic forecasts, and various near-real-time data sources. In addition to routine forecast-driven operating plans, near-term simulations are used to evaluate operational strategies to deal with infrastructure outages, downstream flood mitigation, and weather-driven episodes of degraded water quality. OST simulations are currently being used to support development of an operations plan for an extended shutdown of the City’s critical Delaware Aqueduct, which supplies roughly 60% of the City’s water, based on operational triggers that rely on HEFS forecasts. Critical in development and application of the OST has been collaboration among water supply managers and operators, water resources engineers, hydrologists, and meteorologists in developing a common understanding on end user needs and forecast capabilities.