Understanding Satellite-based Monthly-to-Seasonal Reservoir Outflow Estimation as a function of Hydrologic Controls

Abstract:

Growing population and increased demand for water in developing nations is causing an increase in dam construction in these regions. Entities and stakeholders downstream of dams experience drastically altered river flows. When rivers cross international boundaries, these downstream stakeholders often have little knowledge of upstream reservoir operation practices. Satellite remote sensing in the form of radar altimetry and multi-sensor precipitation products can be used as a way to provide downstream stakeholders with the upstream information needed to make important water management decisions. This study uses a mass balance between three hydraulic controls, precipitation induced inflow, evaporation, and reservoir storage change, to estimate reservoir outflow at a monthly time scale. Two reservoirs were examined in differing regions of the world, the Hungry Horse Reservoir in a mountainous region in northwest U.S. and the Kaptai Reservoir in a low-lying, forested region of Bangladesh. It was found that this mass balance method estimated the outflow of Kaptai Reservoir with reasonable skill when compared with observed flows. The estimation of outflow from Hungry Horse Reservoir was similarly skillful for outflows in winter and fall months, but summer and spring outflow estimates had high errors due to snowmelt effects. Furthermore, it was found that the important hydrologic controls for reservoir outflow estimation at the monthly time scale differs between the two reservoirs, with precipitation induced inflow being the most important control for the Kaptai Reservoir and storage change being the most important for Hungry Horse Reservoir. In both cases, a standard energy balance approach of evaporation estimation appeared to have little effect on the accuracy of outflow estimation.