Sediment dynamics in a semiarid catchment with cascade dam failures

Abstract

The research estimates the risks of cascade dam failures in a network of fifteen reservoirs in the Nogueira River Basin and their effects on sediment mobilization from the dam embankments. The runoff simulation was performed using the HEC-HMS model for the IDF curve of the Pentecoste meteorological station and different return periods. The hydraulic modeling of the cascade dam failure was performed using HEC-RAS. The results indicate that high flows with return periods exceeding 100 years can result in cascade dam failures. In the most extreme flood event, with a return period of 10,000 years, thirteen dams would fail, mobilizing substantial amounts of water and sediments. The results also highlight the ability of larger reservoirs to attenuate flood waves resulting from the failure of smaller dams located downstream. Nevertheless, they are still subject to failure during more extreme events (1,000 and 10,000 years). Regarding sediment dynamics, the results show significant sediment mobilization from the dam embankments during cascade dam failures. In the simulation for the 10,000-year return period, sediment erosion from dam embankments is observed to be thirteen times greater than that produced in the river basin, with negative impacts downstream. The effects of cascade dam failures on sediment dynamics are also analyzed in terms of average sediment concentrations at the reservoir inlet and outlet. The results indicate abrupt changes in the values of this variable due to the large amount of sediments eroded from the dam embankments and transported downstream in the reservoir network.

Keywords: breach formation, cascading dam failure, flood events.