Numerical Modeling of Lateral Erosion During Reservoir Drawdown (Tessa Artruc, MS 2020)
Lowering the water level of reservoirs for flushing sediment, flushing fish, and dam removal exposes accumulated sediment to erosion and downstream transport. Typically, models of the reservoir’s geomorphic response have been limited to 1D incisional erosion without the incorporation of widening. It is hypothesized that the drawdown scenario plays an important role in the processes leading to, and relative importance of, lateral erosion (Figure 1).
Figure 1. Lateral erosion during the rapid drawdown at Condit Dam on the White Salmon (Source: https://www.youtube.com/watch?v=4LxMHmw3Z-U)
The coupling of field observations and the development of a bank stability model, which includes retrogressive lateral erosion (Figure 2), will be used to conduct numerical experiments of the rate and mechanism of lateral erosion with varying drawdown scenarios. Four well-monitored case studies will provide input data for robust verification of the model. These include the physical characteristics of the reservoir banks and the change in water level over time from the Elwha Dam (WA), Bloede Dam (MD), and Marmot and Fall Creek Dams (OR). The incorporation of retrogressive bank erosion in this model will address sequential slumping in the bank, with the addition of failed material to the bank toe. By changing the drawdown rate in each case (e.g. rapid, staged, slow, etc.), the impact on the rate and mechanism of lateral erosion in a reservoir can be determined.
Figure 2. Retrogressive lateral erosion (source: Haug et al. 1977)
Degree and mechanisms of reservoir drawdown impacts on dissolved oxygen (Liangang Chen, visiting scholar from the Nanjing Hydraulic Research Institute)
Update coming soon…