- 15th June 2018
- Posted by: Sophie Bunker
- Category: Projects
The sailing club on Kingsmill reservoir have problems with boats running aground or masts getting stuck in the mud when they capsize. The problem is gradual sedimentation with plumes of sediment during flood events being flushed into the reservoir from upstream and settling out.
Ashfield District Council developed a concept to restrict future sedimentation to the upstream part of the reservoir where it will not impact the water sports activities and can more easily be managed. This involves construction of submerged islands in the upstream part of the reservoir, with the material sourced by local dredging to form deeper pools.
The Council commissioned us to investigate the efficacy of this design and to cost up the construction in order to support their application for Heritage Lottery Funding. A particular challenge is that there is very little knowledge of the actual sediment supply rates for different flow conditions.
- Geomorphological investigation
- Sediment sampling and analysis
- Discussions with contractors along with 1D, 2D and 3D modelling.
The 1D HEC-RAS model of the upstream catchment was used to develop boundary conditions and calibrate sediment loadings for the more complex models of the reservoir. The 2D model (also HEC-RAS) was used to check there were no impacts on flood risk, but to investigate the sedimentation efficiency of the proposals, 3D Computational Fluid Dynamics (CFD) modelling was used.
CFD software (openFOAM) was configured to include suspended sediment transport modelling and was set up to cover the upper Comart of the reservoir using both the existing and proposed bathymetry. These models were run with a fixed sediment loading, but an increasing flow rate. The results for the existing situation showed how, as flow rates increase, the sediment plume is carried far into the reservoir.
Model results also confirmed the efficacy of the proposed solution, whereby the islands break up the plume and sedimentation is encouraged in the deeper, dredged areas. Further information on velocities and shear stresses were used by our construction engineers for decision making and costing of protection required for the island perimeters.
The CFD modelling demonstrated the sedimentation efficacy of the proposals. Visual outputs of flow and sedimentation patterns are easily understandable by non-modellers and were of great value to the client in supporting their funding application.
The design will allow sediment input to the reservoir to be more easily managed at the upper end of the reservoir, meaning that the sailing boats can move more freely over the rest of the water and will not risk being stuck upside down after a capsize!
Want to know more?
Find out more about HEC-RAS v5.0.4 at the HEC-RAS 2D Modelling Workshop in London on 25-27 June. Following the success of the 2016 and 2017 workshops, we are once again hosting the lead developers of the Hydrologic Engineering Center (HEC) who will discuss the newly released HEC-RAS v5.0.4.