Flood Studies and Hydraulic Capacity Assessments
UK Reservoir owners are required by legislation to follow the instructions of their appointed Inspecting Engineer. Often, especially at older dams or those with unconventional spillways, a recommendation can be made to undertake a flood assessment in line with the latest Floods and Reservoir Safety guidelines. These currently (as of 4th Edition) require the use of the Flood Estimation Handbook (FEH) and Revitalised Flood Hydrograph (ReFH version 2) methods to determine inflow hydrology. The inspecting engineer may also request a hydraulic capacity assessment of the spillway, which might be possible using hydraulics first principals, but could necessitate use of a computational fluid dynamics model. The reservoir flood attenuation is also assessed using LIDAR or other high resolution DTMs in GIS packages. Finally, these inputs are put together into routing software such as Flood Modeller, and the results can be used to demonstrate the performance of the spillway. |
Dam Break Assessments
Another requirement under UK legislation is the ability to provide an off site plan at reasonably short notice. Whilst the Environment Agency does produce some mapping for reservoirs, it is often advised by the Inspecting Engineer that a more accurate set of maps would be desirable. The Reservoir Flood Mapping (RFM) specification was produced in 2016 although this makes a large number of assumptions that effectively invalidate its use in particularly urbanised (and therefore high consequence) catchments. Rhys Coombs is a published author in this field of work, and has developed cutting edge models to account for urban hydraulics interactions. CCH can also provide RARS Tier 3 compliant consequence assessments, something that cannot be done using the RFM specification. |
Portfolio Risk Assessments
Owners of large portfolios of reservoirs (for example UK Water PLCs, large industrial owners, etc) can benefit from a portfolio risk assessment undertaken with Tier 1, Tier 2 and Tier 3 levels of detail as documented in the Risk Assessment for Reservoir Safety Management (RARS) guidance documentation. Rhys Coombs has previously worked alongside the author of the guide to develop bespoke applications of the method for owner's portfolios. This can help capital expenditure prioritisation which is crucial in determining how an allocated budget can be best spent to minimise the overall risk. Several large portfolio owners in the UK have these assessments and it helps them secure funding for improvement works. |
Hydraulics Analysis
We can use a number of difference techniques to assess the hydraulics of your structures. We can look at steady and unsteady systems in 1D, 2D or 3D depending on the requirements of the assessment. For complex problems we can observe the problem in 3 dimensions using Computational Fluid Dynamics, including both free surface models for assets like spillways and surcharged systems like pipe manifolds. We can also do residence time modelling for service reservoirs and tanks. Where behaviours are found to be unacceptable we can assist with mitigation designs. |
Overtopping Assessments for Embankments
At some reservoir assets flooding will likely result in overtopping. This likely will not meet the requirements of the Inspecting Engineer if left unmodified. We can help determine whether a simple overtoppable section of embankment or flow training bund might resolve the reservoir safety issues. We can work with your QCE to ensure that you address your Measure in the Interest of Safety (MIOS) items from your most recent statutory inspection. |
Surface Water Flooding
We don't only do dam break assessments. We can model the inundation resulting from natural flooding related processes. Our understanding of UK Flood Hydrology (and the associated standard industry tools) is key in delivering these types of study, making use of up to date methodologies such as ReFH2 and the FEH13 DDF curves. |
Catchment Yield Modelling
We can help water infrastructure owners understand the flow statistics for their catchments, and help them understand the reliable yield of their systems. We can also help determine flow statistics at effluent sites, ensuring that you have the understanding to ensure your effluent processes meet the requirements of the Water Framework Directive. |
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