Hydro-Logic Services

FRA: Residential case study


Courtesy of Hydro-Logic Services

Blandford Consulting
Godreaman, Wales

Hydro-Logic was appointed in 2008 to undertake a Flood Consequence Assessment for a proposed residential development near Aberaman, on a site close to the River Aman that had previously been subject to dumping of soil and possibly waste from coal mining in the area.

The services undertaken by Hydro-Logic included hydrological and hydraulic modelling, using HEC-RAS and preparation of an FCA. The report was initially rejected by the Environment Agency, who pointed out that one of the donor sites used in the determination of design flow has an unusually shaped catchment. Hydro-Logic agreed with that assessment and found another donor, increasing the estimates of design flow. Water level at the site is strongly controlled by a stone footbridge and in order to improve modelling of the structure, Halcrow's ISIS model was used, allowing the bridge to be represented more accurately as an orifice. Separated from the river by a well-developed levee feature, the site was modelled as a tributary, with a nominal 'sweetening flow'.

By fully representing the ground and river features in this way, Hydro-Logic were able to obtain much more accurate estimates of design levels for the 100 and 1000 year floods, showing how residential development could be made safe without impacting on neighbouring sites. The Environment Agency agreed with these assessments and withdrew their objections to the development, conditional upon adoption of the measures suggested in the FCA report.

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