Modeling and Risk Analysis of Dam-Break Flooding in a Semi‐Arid Montane Watershed.

The risk related to embankment dam breaches needs to be evaluated in order to prepare emergency action plans. The physical and hydrodynamic parameters of the flood wave generated from dam-failure event correspond to various breach parameters such as width, slope and formation time. This study aimed to simulate dam-breach failure scenario of Yabous dam (NE Algeria) and analyze its influence on areas (urban and natural environments) downstream the dam. The simulation was completed using the sensitivity analysis method in order to assess the impact of breach parameters on the dam-break scenario. The propagation of flood wave associated to dam-break was simulated using the one-dimensional HEC-RAS hydraulic model. This study ap-plied a sensitivity analysis of three breach parameters (slope, width, and formation time) in five sites selected downstream the embankment dam. The simulation showed that the maximum flow of the flood wave recorded at the level of the breach was 8768 m3/s, which gradually attenuated along the river course to reach 1579.2m3/s at about 8.5km downstream the dam. This study estab-lished the map of flood-prone areas that illustrated zones threatened with the flooding wave trig-gered by the dam failure due to extreme rainfall events. The sensitivity analysis showed that flood wave flow, height and width revealed positive and similar changes for the increase in adjustments (±25% and ±50%) of breach width and slope in the 5 sites. However, flood wave parameters of breach formation time showed significant trends that changed in the opposite direction compared to breach slope and width.

Sensitivity analysis for dam breach parameters using different approaches for earth-fill dam

The prediction of dams breach geometry crucial in studies of dam breaking. The hydrographs characteristics of flood that resulting from breaking of dam is mainly depend on the geometry of breach and the time formation of breach. Five approaches (Froehlich, Macdonald and Langridge-Monopolis, Von thun & Gillete, USBR and Singh % Snorrason) was used in order to predict dam breach parameters (breach width, breach side slope, breach formation time). The Sensitivity analysis was performed in order to assess the effect of each parameter on the resulting hydrograph of the flood. HEC-RAS model was used to calculate the effect of each parameter on the hydrograph of the flood that resulted. The width of breach (Bavg), side slope (z) and formation time of breach (tf) increased by 25%, 50%, 75% and 100% and decreased by 25%, 50% and 75%, respectively. Flood hydrograph was estimated at the dam site for each case. Sensitivity analysis was performed in order to check the effect of each parameter of breach and time of breaching. Sensitivity analysis was performed with Froehlich method with the mode of overtopping failure and maximum operating level at 107.5 meter above sea level. Result of sensitivity analysis show that peak discharge and time to reach it is adequately sensitive to breach side slope, highly sensitive to the breach formation time and less sensitive to breach width.

Baur dam breach analysis using various manning’s roughness values

This paper describes the importance of flood mapping in terms of saving downstream agricultural area. Flood can cause high impact on the nearby crops productivity which further affects the country’s economy. The Baur dam has a Culturable Command Area of 31453,6572 hectares. It’s key focus is on describing the importance of Manning’s roughness value in dam breach modelling and shows it’s bad impact on downstream areas of dam. In this work hypothetical breach modelling of Baur dam is performed by using Hydrologic Engineer’s Centre- River Analysis System (HEC-RAS). Details about study area, breach parameters, modelling procedure, and outflow flood values are also described in this paper. Flow hydrographs are plotted at different Manning’s roughness value for the two populated downstream areas of dam and it has been observed from results that as roughness value increases flow decreases which justifies Manning’s theory. As a Final result Inundation maps are plotted with the detail of inundated area values for different Manning’s values so that the effect of roughness can be analysed numerically on study area. The Manning’s roughness value of 0.030 causes 37.75km2 inundated area in the downstream of dam.1

Breach parameters for cascade dams’ breaks using physical, empirical and numerical modeling

ABSTRACT The environmental, economic, and social consequences of dam breaks are catastrophic and require their prior knowledge to minimize risks. These consequences are directly related to rupture breach parameters, such as formation time and breach geometry (width, height, and lateral slopes). These parameters must be adequately representative of a real rupture to obtain a rupture hydrograph also representative (temporal evolution, volume, and peak flow). This representation becomes more reliable as the closer to the actual consequences of a rupture it is, thus creating conditions for an adequate emergency action plan. This research evaluates the parameters of breach formation for a possible rupture, specifically for the case of reservoirs in a sequence, also called cascade reservoirs. The adopted methodology uses physical reduced models and numerical modeling to define these parameters, trying to represent two cascade dams, based on a reference case, determining their values in each dam after the simulated rupture events.

Experimental study of embankment breach based on its construction parameters

Laboratory data obtained from the overtopping failure of eight cohesive embankments built with different construction parameters are presented in this paper. Experiments were performed in two phases. Five experiments under phase 1 were carried out in small width flume having dimension viz. 17 m long, 0.6 m wide and 0.6 m high. In phase 2, three experiments were performed on large width flume having dimensions viz. 13 m long, 1.75 m wide and 0.5 m high. The construction parameters which were varied in embankments are compaction effort, compaction moisture content, and the moisture content at the time of failure. Phase 1 investigate the effect of compaction effort and compaction moisture content on breach parameters. As the water content of clay decreases or increases, the soil shrinks or swells which can cause damage ranging from small hairline cracks to severe structural distress. The sudden rise of water level in the reservoir due to heavy rain will cause rushing of water through cracks and if water overtopped the embankment will lead to quick failure. An attempt was made in phase 2 to investigate the effects on breach evolution when the embankments were air dried to reduce its moisture content and to develop cracks. The final breach shape and parameters noted in experiments show remarkable change for each dam failure. In the remainder of this paper, we report results of a set of small and large scale dam-overtopping experiments that were designed to; (1) investigate the effect of changing compaction effort and moisture content of the headcut migration, breach parameters, and flood hydrograph; (2) assess the overtopping behaviour of embankments when they are air dried for a long time.