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.

Modeling of the spatial distribution of the components for the ecosystem of the Novosibirsk reservoir

The object of the study is the ecosystem of the largest in Western Siberia — the Novosibirsk reservoir. The aim of the study is forecast the response of hydrobiocenosis on the implementation of different methods for the aquatic ecosystem restoration. Novelty: structural-dynamics modeling of ecological processes based on the reproduction of biogeochemical cycles of limiting elements in the conditions of spatial heterogeneity for the reservoir is performed. A preliminary conclusion is formulating about the main role of autochthonous processes in the eutrophication of the Novosibirsk reservoir. A comparative assessment of the influence for three variants of washing the reservoir with a flood wave on the annual variability of the phytoplankton content and nitrate concentration in three characteristic parts of the Novosibirsk reservoir was carried out.

Surface Water–Groundwater Interactions and Bank Storage during Flooding: A Review

The interaction between river floods and groundwater not only replenishes groundwater resources, but also contributes to the attenuation of flood waves and is therefore a hydrologic factor in flood risk management. The magnitude of this interaction is expressed as bank storage, that is, the volume of the surface water that is temporarily stored in the riverbanks and slowly released back into the river after the peak of the flood wave. The amount of bank storage depends not only on the hydrograph of the river, but also on the morphology and hydrogeology of the river valley. This article offers a review of the current understanding and description of water exchange between the river and aquifer, with a focus on exchange due to flood events. The main field measurement methods of river-aquifer interactions, made to determine the properties of the aquifer, are summarized. The foundations of mathematical models are also reviewed, centered on how the surface and groundwater flow models are coupled, as well as on dimensional and process-related simplifications.

2D-HEC-RAS Modeling of Flood Wave Propagation in a Semi-Arid Area Due to Dam Overtopping Failure

Dam overtopping failure and the resulting floods are hazardous events that highly impact the inundated areas and are less predictable. The simulation of the dam breach failure and the flood wave propagation is necessary for assessing flood hazards to provide precautions. In the present study, a two-dimensional HEC-RAS model was used to simulate the flood wave resulting from the hypothetical failure of Al-Udhaim Dam on Al-Udhaim River, Iraq, and the propagation of the resulting dam-break wave along 100 km downstream the dam site for the overtopping scenario. The main objective is to analyze the propagation of the flood wave so that the failure risk on dam downstream areas can be assessed and emergency plans may be provided. The methodology consisted of two sub-models: the first is the dam breach failure model for deriving the breach hydrograph, and the second is the hydrodynamic model for propagating the flood wave downstream of the dam. The breach hydrograph is used as an upstream boundary condition to derive the flood impact in the downstream reach of Al- Udhaim River. The flood inundation maps were visualized in RAS-Mapper in terms of water surface elevation, water depth, flow velocity, and flood arrival time. The maximum recorded values were: 105 m (a.m.s.l.), 18 m, 5.5 m/s, and, respectively. The flow velocity decreased from upstream to downstream of the terrain, which means less risk of erosion in the far reaches downstream of the study area. The inundation maps indicated that the water depth and flow velocity were categorized as Catastrophic limits on the terrain's area. The results offer a way to predict flood extent and showed that the impact of a potential dam break at Al-Udhiam Dam will be serious, therefore, suitable management is needed to overcome this risk. Moreover, the maps produced by this study are useful for developing plans for sustainable flood management. Doi: 10.28991/cej-2021-03091739 Full Text: PDF

Flood Management of Diyala River

Diyala Governorate was recently exposed to high flood waves discharged from Hemrin Dam. Since the dam was at its full capacity during the flood period, these waves were discharged to the Diyala River. Because of the reduction in Diyala River capacity to 750m3/s, the cities and villages on both sides of the river banks were inundated. Thus, the study's objective is to design a flood escape out of the Diyala River, to discharge the flood wave through it. The flood escape simulation was done by using HEC- RAS software. Two hundred twenty-three cross sections for the escape and 30 cross-sections of the Diyala River were used as geometric data. Depending on the geological formation that the escape passed through, two roughness coefficients of 0.035 and 0.028 were applied. An outflow downstream Hemrin Dam varies from 1100m3/s to 1800m3/s was applied as boundary condition upstream Diyala River. One dimensional hydraulic model was developed for the escape and the river, the results showed that aside weir could be constructed at the escape entrance with crest level 67m.a.m.s.l. and 800m width, followed by drop structure of four rectangular steps, this case provides safe discharge to Diyala River if flood wave of 1500m3/s released from Hemrin Dam.

Dam Break Wave Propagation on a Non- Erodible Bed – Comparison of Experimental and Numerical Results

Dams are vital for production of electricity, storage of water and irrigation purposes but pose a serious risk to the community, if breached. The downstream flood wave propagation, resulting from failure of a dam can subject the population and infrastructure to considerable damage. No matter how low the chances of failure, the cost of failure makes it a higher risk. Mitigation of such risks requires better understanding of the hazard that a dam may pose in case of failure. This study focuses on the effects of flood wave propagation on a fixed bed on the downstream side resulting from sudden dam break. Two conditions are simulated: 1. when the downstream side is open, 2. when the downstream side is closed. It is observed that the flood wave diminishes in velocity and height with increase in time for both cases. For downstream open condition, the flood wave attains maximum height in 2 to 4 sec and maximum velocity within 2 to 5 sec. For downstream closed condition, the flood wave attains maximum height within 5to 10 sec and maximum velocity within 3 to 5 sec. The results obtained from the two-dimensional shallow water equation based numerical model are in close agreementwith the experimental results.

Simulation of Dam-Break Flood Wave and Inundation Mapping: A Case study of Attabad Lake

The break study of Landslide or embankment dams is more essential due to uncertainty in their composition and lack of knowledge of their response to other natural events because they are natural and not properly designed for any disaster. The paper aims to improve different methods of hydraulic modeling of dam break. In this present study dam break of Attabad lake is simulated using the computational fluid dynamics technique. The numerical model (FLOW-3D) is developed to solve the Reynolds averaged Navier-Stoke equation fully in 3D to predict peak flow depth at different cross-sections, peak velocity, peak discharge, time to peak depth, and time to peak discharge. The standard RNGturbulence model is employed to simulate turbulence and then flood inundation maps and velocity vectors for flow at villages are drawn. The results show that most of the flood wave modeled through the Hunza river channel, is contained by the flood plain of Hunza River but for some of the villages i.e. Miaun and chalat, which are situated inside the flood plain of Hunza River are at higher risk of inundation but the flood arrival time estimated for these villages is 31 and 44 min respectively which is enough time for the evacuation of the population to safer areas while for some villages like Hassan Abad situated adjacent to Ali Abad is at higher risk of inundation while the estimated flood arrival time for the village is 12 min which are not enough for the evacuation of the population hence will need some extra flood protection structures for flood containment. The estimate of the peak velocities implies higher shear stress in the river plain, risk of heavy erosion, damage to agricultural lands, residencies, and morphological changes are projected. The analysis of the dam break i.e. Peak depths, Peak Velocities, flood arrival time, and flood inundation maps should only be used as a guide in future risk analysis and flood management.