Risk assessment of Vaniyar earth dam overtopping using system dynamics and effect of overtopping flood on the downstream lands of the dam.

Abstract

Objective: Dams play a key role in controlling floods and minimizing associated losses. They reduce downstream losses by lowering the flood peak and enable a safer flood stream. Despite the significant advantages of dams, dam failure may cause dramatic casualties and financial losses. Overtopping is a major dam failure that can be induced by one or more geophysical events, e.g., floods, landslides, earthquakes, and intense winds. Overtopping is particularly crucial for earth and aggregate dams as they are more likely to be destroyed due to the flow over the crest. Therefore, the overtopping risk evaluation of dams is important, and it is necessary to bring a trade-off between the reservoir level and overtopping risk. Methods: The risk management of earth dams is complex since multiple factors are involved. System dynamics (SD) can be used to evaluate the effects of a set of complex, interrelated factors on the overtopping risk of dams under several scenarios. Floods and winds are the main causes of overtopping, with each being dependent on a number of variables. This paper used an SD model to evaluate the independent and combined effects of uncertainties with floods and winds of different return periods on the overtopping risk of the Vanyar Dam, Iran. This would help implement efficient measures to minimize the overtopping risk and maximize safety. To measure the effects of overtopping floods on the downstream of the dam, a hydraulic model was developed in HEC-RAS. The geometric parameters/data of the river and the non-steady stream data along with the initial and boundary conditions were introduced as inputs to the hydraulic model. The most critical scenario to identify the overtopping flood zone corresponded to the probable maximum flood (PMF), under which a broad area of the downstream lands would be flooded. Results: This study analyzed the overtopping risk of the Vanyar Dam, Iran, for different flood and wind return periods by modeling the dam reservoir through system dynamics (SD) under initial reservoir level and dam height uncertainties using the Monte Carlo method. The effects of floods and the combined effects of floods and winds on the overtopping risk were evaluated. The results demonstrated that the probable maximum flood (PMF) with a wind return period of 100 years under reservoir level and dam height uncertainties maximized the overtopping risk to 0.122931. The overtopping risk converged in 200,000 iterations. The analysis of the overtopping flood downstream of the dam showed that many villages and facilities would be completely flooded, and it is necessary to implement management measures, such as controlling the reservoir level, to minimize the overtopping risk.

Keywords

• overtopping risk
• system dynamics
• monte-carlo simulation
• flood