Understanding the Impacts of Reservoirs in Developing Regions Using Satellite Remote Sensing
[Thesis]
Bonnema, Matthew
Hossain, Faisal
University of Washington
2019
216 p.
Ph.D.
University of Washington
2019
Dams provide immense societal benefits in the form of hydropower generation, flood control, and water supply. However, they also cause significant negative environmental impacts by altering the timing and magnitude of natural streamflow, limiting the transport of sediment, nutrients, and biota upstream and downstream, and altering aspects of water quality such as sediment concentration and water temperature. Dam development in developing regions has been increasing in the last 30 years and will continue to intensify in the coming decades. This is leading to rapid hydrologic transformations of developing river basins, with potentially dire consequences for local populations dependent on the natural river systems for food and livelihood. In-situ hydrologic observations in such regions are limiting, making satellite remote sensing the only viable option for studying the impacts of this rapid dam development. This dissertation aims to advance our ability to study the impacts of reservoirs in data limited regions. First, a method for estimating reservoir outflow using purely remote sensing observations was developed and tested on reservoirs in the United States and Bangladesh. This method was then applied to ungauged reservoirs in the Mekong River Basin and their impact the river system was evaluated in terms of flow alteration and residence time. It was found that smaller reservoirs on upper tributaries exerted a higher degree of flow alteration and residence time on the rivers they impound than larger, more downstream reservoirs. However, the reservoirs on larger rivers exert their impacts on significantly larger volumes of streamflow, so their contribution to the overall flow alteration and residence time of the river system was found to be more significant. Looking towards upcoming satellite missions, the applicability and usefulness of the Surface Water and Ocean Topography (SWOT) Mission for monitoring reservoir outflow and river discharge was tested using by generating synthetic observations based on the expected performance of the SWOT instrument. It was found that SWOT is expected to observe reservoir storage change with higher accuracy than methods from existing sensors in most cases. However, some reservoirs were unable to be accurately observed by simulated SWOT observations, indicating a cooperative multi-sensor approach may be useful. The performance of SWOT observations of river discharge was found to be satisfactory given there are currently no satellite sensors capable of estimating discharge. However, the dramatic differences between wet season and dry season discharge in monsoonal rivers proved difficult and some adjustments to the discharge estimation methods may be needed. Finally, impacts on river temperature downstream of major dam development in the 3S Basin, the largest tributary to the Mekong River, were observed using satellite remote sensing. Dam construction in the basin coincided with significant temperature decreases downstream, providing clear evidence of hydropower induced river cooling. The findings of this dissertation and the remote sensing methods employed here represent valuable steps towards understanding the hydrologic impacts of dams and predicting the impacts of further dam development in developing basins around the world.