A retrospective analysis of observed US reservoir operations: What actually happens during a drought?

Jen Steyaert1, Laura Condon1, Sean Turner2, and Nathalie Voisin2,3
1Department of Hydrology and Atmospheric Sciences, University of Arizona
2Pacific Northwest National Laboratory
3Department of Civil and Environmental Engineering, University of Washington

In the contiguous United States (CONUS), there are over 52,000 reservoirs ranging from 0.5 to 243 meters high. Collectively they hold 600,000 MCM of water. These structures have dramatically impacted the hydrology of every major watershed in the country. While many studies have explored reservoir operations, existing large-scale analyses rely on derived or optimized reservoir operations as opposed to direct observations. This is primarily due to lack of accessible reservoir operations data. To remedy these concerns, our research has two main focuses: (1) assemble a national dataset of historical reservoir operations and (2) utilize this dataset to evaluate how reservoirs have actually operated during droughts. Historical reservoir inflow, outflow and storage values for approximately 600 reservoirs across CONUS were assembled. These reservoirs cover 55% of the total storage in large reservoirs. The observations from this dataset were then used to evaluate historical reservoir response to drought. Meteorological drought periods were quantified using Standardized Precipitation Indices (SPI), Standardized Precipitation Evapotranspiration Indices (SPEI), and Hydrological drought was quantified via Standardized Streamflow Indices (SSI). All values (SPI and SPEI) were aggregated and calculated (SSI) for USGS four digit Hydrological Units (HUC4s). Next we evaluate observed operations during dry periods to explore how operations change in response to climatic conditions. This analysis provides direct insights into the impacts of drought on both reservoir storage, as well as historical reservoir management and can help illustrate potential bias in existing reservoir simulation approaches which lack direct observations.

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