Failure of dams arranged in series or in complex

peer reviewedaudience: researcher, professional, studentA practical methodology has been developed for predicting flows generated by dam failures or malfunctions in a complex or a series of dams. A twofold approach is followed. First, the waves induced in the downstream reservoirs are computed, as well as hydrodynamic impacts induced on downstream dams and dikes are estimated. Second, the flood wave propagation and the inundation process are simulated in the downstream valley, accounting for possible dam collapse or breaching in cascade. Two complementary flow models are combined: a two-dimensional fully dynamic model and a simplified lumped model. At each stage, the methodology provides guidelines to select the most appropriate model for efficiently computing the induced flows. Both models handle parametric modeling of gradual dam breaching. The procedure also incorporates prediction of breach formation time and final width, as well as sensitivity analysis to compensate for the high uncertainties remaining in the estimation of breach parameters. The applicability of the modeling procedure is demonstrated for a case study involving a 70m-high gravity concrete dam located upstream of four other dams

Dam rehabilitation study with process oriented numerical flow models

peer reviewedIn the global framework of climate change, hydraulic structures rehabilitation is an up-to-date subject requiring appropriate design and impact studies. In this scope, upgrading the release facilities of dams is an important point when both up and downstream consequences, often irreversible, of badly controlled rising of water in the reservoir, become awarded. Suitable numerical models, coupled with contemporary computational possibilities, allow engineers to forecast the complex situations induced on real structures by extreme events with increasing representativeness and accuracy. In this field, WOLF software, a process oriented free surface flows computation package completely set up by the HACH, has proved its efficiency and reliability for years by numerous theoretical, experimental as well as on real structures applications. In this paper, the rehabilitation study of the Nisramont dam (Belgium) is presented. Due to its temporary primary tasks, the stilling basin downstream of the crest spillway has been designed for a short time use. It’s the same with the 3 bottom outlets, which were never equipped with valves and are thus unusable for the reservoir management. In order to secure the structure and to make it comply with its definitive working objectives, while taking into account climate change observations, the HACH has been entrusted with evaluating up to date critical flood discharges and with designing a system in accord with these new values for the rehabilitation of the bottom outlets and the evacuation of the floods. Several construction options have been compared and optimized by means of the hydrodynamic software WOLF

Comparative analysis of the predictive capacity of breaching models for an overtopped rockfill dam

peer reviewedaudience: researcherThe paper covers a brief description and a comprehensive comparative analysis of several state-of-the-art dam breaching models. The study is specifically focused on the applicability and on the predictive capacity of the models for the gradual breaching of an overtopped rockfill dam. A wide range of modelling techniques is reviewed, from process-oriented numerical simulations to empirical models. Comparisons are performed regarding various aspects, such as the applicability of the model without prior calibration or the possibility of coupling the breaching model with a quasi-3D flow solver such as WOLF. Finally, a sensitivity analysis of the downstream hydrograph to various parameters is conducted and the conclusions drawn are illustrated in the case of a large-scale real application in Belgium

Depth-integrated flow modelling taking into account bottom curvature

Successfully modelling flows over a spillway and on strongly vertically curved bottoms is a challenge for any depth-integrated model. This type of computation requires the use of axes properly inclined along the mean flow direction in the vertical plane and a modelling of curvature effects. The proposed generalized model per-forms such computations by means of suitable curvilinear coordinates in the vertical plane, leading to a fully integrated approach. This means that the flows in the upstream reservoir, on the spillway, in the stilling basin and in the downstream river reach are all handled in a single simulation. The velocity profile is generalized in comparison with the uniform one usually assumed in the classical shallow water equations. The pressure dis-tribution is modified as a function of the bottom curvature and is thus not purely hydrostatic. Representative test cases, as well as the application of the extended model to the design of a large hydraulic structure in Bel-gium, lead to satisfactory validation results.Peer reviewe

Large scale 2D numerical modelling of reservoirs sedimentation and flushing operations

peer reviewedaudience: researcherThe quasi-3D flow solver WOLF has been developed at the University of Liege for almost a decade. It has been used to carry out the simulation of silting processes in large reservoirs and to predict the efficiency of flushing operations. Besides briefly depicting the mathematical and numerical model, the present paper demonstrates its applicability on the case of a large hydropower project in India. The silting process of the reservoir has been simulated by means of the quasi-3D flow model with a quasi-steady approach. For simulating flushing events, both the topography changes and their interactions with the flow have been carefully handled in a strongly coupled approach. This narrow coupling has required the development of a suitable upwind numerical scheme. Results are presented with 2D- and 3D-views, completed by cross-sections and curves of the variation of key variables. The numerous observations based on those results lead to a global assessment of the silting mechanism and of the flushing efficiency

Global design of hydraulic structures optimised with physically based flow solvers on multiblock structured grids

peer reviewedThis paper presents the numerical studies lead by the Laboratory of Applied Hydrodynamics and Hydraulic Constructions of the University of Liège (HACH) for the rehabilitation of the 21-meter high Nisramont dam in Belgium. After determination of the up-to-date 1000-year return flood using the hydrological runoff model WOLFHYDRO on the global 74,000 ha watershed real topography coupled with statistical analyzes, and after validation on the existing situation and for extreme observed events, the 2D finite volume multiblock flow solver WOLF2D has been applied to the design of the new stilling basin and to the bottom outlet rehabilitation impact study. The multiblock solver possibilities allow mesh refinement close to interesting areas, such as dam spillway and stilling pool, without leading to prohibitive CPU times, while suitable shallow water equations formulation allows the computation of the flows on the strongly vertically curved bottom of the spillway. In the described simulation, 270,000 structured finite volumes, from .25 to 1 meters long, are used to simulate as a whole the flows in the upstream reservoir, dam, spillway, stilling basin and downstream river, this on a real topography

Modelling suspended load transport with linear concentration profiles

peer reviewedIn numerical simulations, it is always necessary to find an optimum between the simplicity of the model and a good representation of real phenomena. In the field of hydraulic flows simulations, the models using depth-averaged and moment equations are an interesting compromise between full 3D and simple depth-averaged models. This paper presents the use of a moment equation for suspended load transport. A simple but representative model for the sediment concentration profiles is developed. This original bi-linear concentration profile is compared to the traditional Rouse-profiles and shows a good correspondence despite its great simplicity. Advective and diffusive sediment fluxes are developed analytically and lead to a concise formulation, which is an asset for practical use. A differential equation for the sediment concentration moment is also fully developed, and a special attention is cast to the source term. The finite volume scheme has been chosen to implement the model, because it is particularly well suited for highly advective transport equations, it is conservative and it makes the choice of the upwinding easier. 1D simulations show the capacity of the model to reproduce laboratory experiments described in the literature

Modelling suspended load with moment equations and linear concentration profiles

peer reviewedaudience: researcherIn numerical simulations, it is always necessary to find an optimum between the simplicity of the model and a good representation of real phenomena. In the field of hydraulic flows simulations, the models using depth-averaged and moment equations are an interesting compromise between full 3D and simple depth-averaged models. This paper presents the use of a moment equation for suspended load transport. A simple but representative model for the sediment concentration profiles is developed. This original bi-linear concentration profile is compared to the traditional Rouse-profiles and shows a good correspondence despite its great simplicity. Advective and diffusive sediment fluxes are developed analytically and lead to a concise formulation, which is an asset for practical use. A differential equation for the sediment concentration moment is also fully developed, and a special attention is cast to the source term. The finite volume scheme has been chosen to implement the model, because it is particularly well suited for highly advective transport equations, it is conservative and it makes the choice of the upwinding easier. 1D simulations show the capacity of the model to reproduce laboratory experiments described in the literature

Relative impacts of climate and landuse changes on future flood damage along River Meuse in Wallonia

Climate change is expected to increase flood hazard across most of Europe, both in terms of peak discharge intensity and frequency. Consequently, managing flood risk will remain an issue of primary importance for decades to come. Flood risk depends on territories’ flood hazard and vulnerability. Beside climate change, land use evolution is thus a key influencing factor on flood risk. The aim of this research is to quantify the relative influence of climate and land use changes on flood damage evolution during the 21st century. The study focuses on River Meuse in Wallonia for a 100-year flood. A scenario-based approach was used to model land use evolution. Nine urbanization scenarios for 2100 were developed: three of them assume a “current tend” land use evolution, characterized by urban sprawl, while six others assume a sustainable spatial planning, leading to an increase in density of residential areas as well as an increase in urban functions diversity. A study commissioned by the EU has estimated a 30 % increase in the 100-year discharge for River Meuse by the year 2100. Inundation modeling was conducted for the present day 100-year flood (HQ100) and for a discharge HQ100 + 30%, using the model Wolf 2D and a 5m grid resolution Digital Elevation Model (Ernst et al. 2009). Based on five different damage curves related to land use categories, the relative damage was deduced from the computed inundation maps. Finally, specific prices were associated to each land use category and allowed assessing absolute damages, which were subsequently aggregated to obtain a damage value for each of the 19 municipalities crossed by River Meuse. Results show that flood damage is estimated to increase by 540 to 630 % between 2009 and 2100, reaching 2.1 to 2.4 billion Euros in 2100. These increases mainly involve municipalities downstream of a point where the floodplain width becomes significantly larger. The city of Liège, which is protected against a 100-year flood in the present situation, would undergo about 450 million Euros damage for a 100-year flood in the 2100, i.e. in-between 21% and 25 % of the whole damage increase. The influence of climate is three to eight times higher than the effect of land use change according to the land use evolution scenarios considered. Nevertheless, these two factors have a comparable influence on seven municipalities. Consequently, although a careful spatial planning would not considerably reduce the overall flood damage at the level of theWalloon part of the Meuse Valley, more sustainable spatial planning could efficiently reduce future flood damage at the level of several most critical municipalities. Reference Ernst, J, Dewals, B, Detrembleur, S, Archambeau, P, Erpicum, S, & Pirotton, M. (2010). Micro-scale flood risk analysis based on detailed 2D hydraulic modelling and high resolution geographic data. Natural Hazards, 55(2), 181-209

Integration of Accurate 2D Inundation Modelling, Vector Land Use Database and Economic Evaluation

Within the global framework of the climate change, according to most Regional Climate Mod-els the maximum peak discharges in river will increase in importance and frequency. Therefore the people will have to face worst inundation conditions. In order to protect themselves from the increasing flood risk, the communities have to draw up suitable flood protection measures. The selection and the evaluation among the different possible flood mitigation measures requires developing decision-support system (DSS). This sys-tem has to take into consideration parameters such as hydraulic, economic, social or environmental. This pa-per focuses on the integration between two components of the DSS, namely the evaluation of the economic impacts of floods and the hydrodynamic modelling. The hydraulic simulations are conducted by means of WOLF 2D flow modelling system and provide as an output high resolution flood maps detailing the distribu-tion of water depth and flow velocity in the floodplains. The integration is ensured by the use of very accurate geographic databases and an automated procedure which makes the most of geomatic methods. The paper de-tails the application of the integrated assessment procedure for a case study along the river Ourthe located in the Meuse basin (Belgium). Moreover, possibilities of validation of the economic damage evaluation proce-dure are investigated by comparing computation results with real damage data recorded by the Belgian Disas-ter Fund after several major flood events (2003, 2002, 1995, and 1993)