Effect of wave exposure dynamics on gut content mass and growth of young-of-the-year fishes in the littoral zone of lakes

Total length, body mass and gut content mass of young-of-the-year (YOY) perch Perca fluviatilis, dace Leuciscus leuciscus and bleak Alburnus alburnus were recorded over the summer of 2006 at three littoral sites at Upper Lake Constance. In P. fluviatilis and L. leuciscus, gut content mass correlated positively with wave-induced energy flux (EF) of the respective site and sampling day, while no correlation of gut content mass with EF was found in A. alburnus. It was assumed that benthivorous P. fluviatilis and L. leuciscus profited from suspended or uncovered benthic food items generated by wave action at sites and periods with high EF. Alburnus alburnus, in contrast, feeding mainly on zooplankton in upper parts of the water column, could not profit from increased EF. In P. fluviatilis, increased gut content mass during periods of high EF resulted in higher growth rates. For L. leuciscus, no real growth rates in local fish populations could be determined, as individuals were less sedentary, and when increased growth occurred at sites during the periods of high EF, migration of fish levelled out the resulting size differences within few days. The results of this study show that dynamic habitat variables affect site profitability in the littoral zone of lakes, especially in benthivorous fishes. Therefore, dynamic habitat variables should be considered in addition to fixed habitat properties in analyses of habitat choice of fishes in the littoral zone of lakes

Evaluation of the impact forces on buildings due to floods: experimental and numerical modelling.

The number of flood events has risen sharply over the past 30 years. Among the natural disasters that occur all over the world, floods affect the largest number of persons, by far. The episode of dramatic floods in July 2021 that affected a large part of Belgium was yet another warning signal. It is in this context that CSTC (Centre scientifique et technique de la construction - https://www.cstc.be/) in collaboration with the SPW (Service Public de Wallonie) and UCLouvain has launched the FLOOD project to establish standards and guidelines for the construction and especially reconstruction of buildings under flood loads. Flooding causes many hazards to buildings: hydrostatic loading, hydrodynamic loading, soil erosion and scour, impact of debris, etc. This article focuses on the determination of hydrodynamic loads and aims at determining the pressure increase on the walls of a building of variable geometry and in different configurations. Such an evaluation based on the FEMA (Federal Emergency Management Agency, USA) standard will be checked against numerical simulations results of different severe transient flows situations carried out using a finite-volume resolution of the shallow-water equations. The simulations are first validated against experimental work carried out at the Hydraulics laboratory of LEMSC at UCLouvain (Belgium). The existing case of a rectangular building that is subjected to hydrostatic and hydrodynamic loads from the sudden flow of a dam-break is first considered. Then, a new set of experiments consisting in a dam-break flow hitting a simplified city will be considered, with measurements of the forces against the buildings to complement the existing data set of Soares-Frazão and Zech (2007). Once validated, the numerical simulation results for these two cases are used to evaluate the forces against the buildings. These forces are then be compared with the laboratory measurements. From there, a procedure to be applied to more complex cases such as the flooding of a city will be developed. An application to the city of Pepinster in Belgium that was severely hit by the floods with numerous damages to the buildings is finally considered

Erosion modeling over a steep slope: application to a dike overtopping test case

The most violent floods are due to the failure of embankments, such as dams or levees. In case of dike overtopping, the erosion over the steep downstream slope is one of the main processes leading to the breaching. This study analyses the ability of numerical models to simulate this process. Various sediment transport formulations are presented and compared. A special attention is paid to the ways to account for the slope effects in these expressions. These sediment transport equations are included in two different one dimensional numerical models, based on the assumptions of a clear water layer and of a sediment-water mixture layer respectively. These two models are applied on a new dike overtopping experimental test-case, representing a small-scale sand dike with a sand layer downstream of the dike. The numerical results are compared to the experimental measurements, with a special attention paid on the sediment transport formulation, on the steep slope correction factor, and on the choice of the numerical model

One-dimensional finite-volume modeling of the flow and morphological processes during the 1996 Lake Ha!Ha! dyke break event

The major flood following the Lake Ha!Ha! dyke-break in 1996 in Québec (Canada) induced important morphological changes in the valley. For instance, massive erosion was witnessed along with significant valley enlargements. Another interesting observation was the creation of an avulsion, i.e. a new river bed. Due to the very complex and irregular topography of the valley, flow simulations in that area constitute a real challenge for numerical models. Indeed, the river presents very steep slopes at some locations, or very abrupt changes in cross-section shape. The presence of rocky outcrops creates another difficulty because of its impact on the erosion process. The focus of the research is to simulate the Lake Ha!Ha! dyke-break event using a one-dimensional finite-volume scheme solving the Saint-Venant-Exner equations in a decoupled way. First, the analysis is conducted from the pure hydrodynamical point of view allowing the characteristics of the flow to be computed. Then, these characteristics are used to determine the sediment transport and, finally, the morphological changes. Even though the model uses a one-dimensional framework, bank erosion and bank failure processes are also accounted for. Comparisons between the computed final topography and field measurements are provided, along with a discussion about the quality of the results and the key issues for future research