Predicting Thermal Impact of Future Dams for Ecosystem-Safe Operations

Abstract:

The developing world is planning for extensive hydroelectric development in the near future in pursuit of satisfying growing energy demands with cleaner sources. However, dam development has severe consequences on the ecosystem which deserve major attention to minimize the damage caused. This study focuses on one key influence of dam operations of thermal destabilization or, change in downstream river temperature from the upstream, or pre-dam era temperatures. Our objective is to predict how much thermal modification will be caused by future dams by learning from the historical behaviour of existing dams.

We begin by establishing a relationship between the thermal modification of downstream rivers with structural characteristics of dam and ambient meteorological conditions. Using the existing database of river temperature from USGS monitoring gages, 107 dams across CONUS were selected to study this relationship using a machine learning-based model. The model was fed with inputs of dam height, reservoir area, storage capacity, and bathymetry, terrain elevation, climate class and seasonal air temperature, to predict four classes of moderate to severe cooling and warming. The model was validated on 27 existing dams in the data-scarce regions of Southeast Asia. Remote sensing-based temperature change was obtained for validation from thermal infrared band of Landsat ETM+. The model was on average 95% accurate over the validation set in predicting the sign of thermal change (warming versus cooling). The severity of change was predicted with an average accuracy of 75%. The trained model was then used to predict thermal modification of planned dams in the Mekong River Basin. Results suggest that the planned dams with large reservoirs are likely to cool downstream severely during the warm season. In contrast, those with weaker stratification (smaller storage) will show moderate warming. During the winter season, most dams will tend to moderately warm the downstream waters.

This work presents an efficient and cost-effective approach to qualitatively predict thermal impact of future dams. More importantly, such a tool can help the dam planners and water managers to prioritize ecosystem-sensitive dam development, design ecosystem friendly dam operation protocols, and pre-plan for post-dam impacts on our environment.