ABSTRACT
Natural or engineered reservoirs are very common structures in hydraulic engineering. They are used as storage reservoirs for flood management or as settling reservoirs for trapping sediments and/or pollutants. For both configurations, controlling sediment transport within these structures is vital to achieve a cost-effective and sustainable management of such structures.
Standard design approaches merely based on the reservoir volume have shown their limitations in terms of sediment management (Dufresne et al. 2012 and Peltier et al. 2013). In addition to the volume, the flow patterns must be taken into account for optimally designing the reservoir (Peltier et al. 2014a, 2014b) and therefore correctly assessing the patterns of sediment deposits (Fig. 1). Indeed, complex flow fields develop in shallow reservoirs, such as large scale turbulent gyres and meandering jets, even for in simple geometry (Peltier et al. 2014b). The flow structures are characterised by their streamwise and spanwise lengths, and by their frequencies. Their respective domains of existence are governed by different flow instabilities, and for rectangular reservoir, they are characterised by (Fig. 2):
the shape factor SF = L/(b 0.4ΔB 0.6), which is a non-dimensional parameter accounting for the length, L, the width of the inlet, b, and the sudden expansion width, ΔB, of the reservoir;
the flow characteristics (Froude and friction numbers defined at the inlet).
Simulated initial flow field and sediments deposits after 2000 seconds for two types of flow patterns: (a) meandering jet, (b) straight jet (<xref ref-type="bibr" rid="ref181_2">Peltier et al. 2013</xref>). https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315623207/4fbc492d-6678-4a12-aaf6-5c2b8ea38e5f/content/fig181_1.tif"/> Flow patterns: domains of existence. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315623207/4fbc492d-6678-4a12-aaf6-5c2b8ea38e5f/content/fig181_2.tif"/>In the present study, we present new experimental data, which clarify the influence on the flow field of ΔB for fixed or for varying SF. New data confirm the contours of the domains of existence (Figure 2). Correlations between the friction number and the newly observed flow patterns highlight that for the considered experimental conditions, the shallowness of the flow influences more the flow structures than the shape factor. In turn, this substantial influence of the friction number on the flow field also affects the resulting sediments deposits.
