What is it about?

Sediment deposition in dam-bound reservoirs has become a considerable and widely occurring problem, posing a serious challenge to the design of and completion of dams. The problem is particularly critical for smaller reservoirs lacking a bottom outlet system, as these frequently become completely silted-up. Foods, which involve the mixing of a massive saturated sediment layer with free surface water, occur predominantly during dam-break events that are coupled with silted-up reservoirs. Considering the complex phenomena generated by such events, the behavior of three phases must be considered: air, clear water (no sediment), and subtended by a saturated sediment level. A break in a silted-up dam results in the movement of dense sediment deposited in the reservoir and may lead to irreparable destruction and casualties. Infrastructure and agricultural areas located along the dam, downstream of the dam, or in the lower reaches of adjacent river basins may be buried under a large quantity of mud and debris flow. For instance, in January 2019, Brazil's Brumadinho dam-break released roughly 12 million cubic meters of iron, tailings and mudflows which destroyed houses, farms, inns, mine offices, and roads downstream from the dam. In the Brumadinho township, many agricultural areas were affected or totally destroyed, and at least 270 people died. Our study is novel in that it involved both experimental analysis and numerical verification of multi-laver shock wave characteristics, (e.g., water level, sediment depth, and wave celerity) in a situation where semi-circular obstacles were present. The overall methodology of this study contains six distinct stages that will be discussed in detail in the research paper. Various upstream sediment depths, which occupied 10%-80% of the reservoir's total depth, combined with the m downstream presence or absence of semi-circular obstacles of various cross-sections at a specified distance from a dam section, created 24 different scenarios. The experimental results were filmed using high-speed professional cameras. Experimental data, including water levels and sediment depths along the experimental flume, have been provided and can be used for validation in other studies. The numerical portion of the current research verified the 24 dam-break experimental scenarios via OpenFOAM soltware using two distinct methods: VOF (volume of fluid) and Eulerian. Laboratory records were rigorously compared with the predictions of both numerical methods.

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Why is it important?

Interactions between reservoir water and the large volume of sediment stored in dam reservoirs strongly affect sediment layer motion and flood propagation. In addition, structures and installations located in flood-prone areas downstream from a dam may act as obstacles to a flood propagation following a dam-break, with potentially harmful consequences in terms of the collapse of remaining structures. The presence of such obstacles in the flood plain adjoining the river may also influence flood characteristics, such as wave velocity and depths downstream from obstacles. Consequently, the accurate prediction of silted-up dam-break flow behavior over natural terrain and bumpy downstream reaches is vital to prevent and mitigate catastrophic flood disasters.

Perspectives

To the best of the authors’ knowledge, there are limited numerical or experimental studies concerning dam-break multiphase shock flood waves from a reservoir with a high degree of silting. Nevertheless, there is a great distinction between the usual sediment depth in a typical reservoir or river bed and the high sediment level in a silted-up reservoir, which has rarely been addressed. Since typical forms of obstacles in nature are semi-circular (e.g., humps and hill-like barriers), rounded obstacles with different crosssections were examined in the study to better reflect natural terrain. To the best of the authors’ knowledge, such obstacles have rarely been presented in experiments compared to the more commonly studied triangular and trapezoidal obstacles. A rigorous literature review revealed the limited number of studies on the behavior of floodwaters when they meet a semi-circular obstacle in situations where the failed dam had a silted-up reservoir.

Foad Vosoughi
Shiraz University

Read the Original

This page is a summary of: Downstream semi-circular obstacles' influence on floods arising from the failure of dams with different levels of reservoir silting, Physics of Fluids, January 2022, American Institute of Physics, DOI: 10.1063/5.0079791.
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