The effects of Vegetation properties on supercritical Air-Water FLOWs (V-A-W-Flow)

• Applicant: Professor Dr.-Ing. Holger Schüttrumpf
• Subject Area: Geotechnics, Hydraulic Engineering
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 471796635

Flooding, such as the Elbe flood in 2002, can cause high monetary costs and bodily loss or damage, especially if the technical flood protection measures fail and the flooding extends into the hinterland. Flood retention areas help to influence the flood hydrograph and to reduce the peak flow rate. For this, part of the high water flow is redirected via overflow sections into natural or man-made retention areas where it is temporarily stored. Overflow sections are often constructed as concrete structures or as earthen structures protected by grey revetments. With increasing environmental awareness and rising costs for maintenance of aging infrastructure, nature-based solutions such as vegetated (overflow) dikes have received greater emphasis in recent years. Overflow dikes and spillways have to be constructed in such a way that the design overflow rate can be transferred across the structure without inducing damage. The flow parameters, flow aeration, energy dissipation and flow resistance, including friction factors, relevant for the structural design are influenced by the characteristics of the surface. Extensive research has been conducted for typical spillway structures, such as smooth spillways, stepped spillways and rock chutes. Further, the effects of vegetation on flow velocity and flow resistance in nonaerated flows have been investigated in several studies, though primarily for subcritical flows. Yet, the effects of vegetation properties on flow and aeration in supercritical air‐water flows down vegetated chutes such as overflow dikes are barely explored affecting the design process with uncertainties in the design parameters. Therefore, the proposal at hand aims at an improved understanding of flow and aeration processes on vegetated chutes and the quantification of design parameters, such as energy dissipation and flow resistance, as function of vegetation properties under consideration of flow aeration.In order to understand the flow and aeration processes on vegetated chutes and to quantify energy dissipation and flow resistance depending on the vegetation properties of the chute surface, overflow simulations on a chute model are performed. The hydraulic boundary conditions and vegetation properties are systematically varied during these experimental investigations. For this, natural chute covers in the form of rolled turf with different vegetation heights and vegetation densities are tested. Botanical analyses allow for parameterization of the tested vegetation. During the experimental tests, flow and aeration data is measured with double-tip conductivity probes. With the data gathered and under consideration of theoretical considerations, the effects of vegetation properties on flow parameters, flow aeration, energy dissipation and flow resistance in supercritical air‐water flows down vegetated chutes are analyzed and the relation of flow, aeration and vegetation parameters is established.

• DFG Programme: Research Grants