Estimating flood flows and hydrographs in small catchments and plots.

The Joint Environment Agency/Defra flood risk R&D programme are working with the Centre for Ecology & Hydrology (CEH) and JBA Consulting to improve flow estimates within small catchments – right down to single plot scale.

We aim to get a better understanding of how large floods may be in a type of catchment which is traditionally associated with high uncertainty. The increased uncertainty is caused by a range of factors, including:

• Local conditions average out in larger catchments – but can often drive local flooding patterns
• There is a distinct lack of gauges within small catchments to use for validation and pooling
• And what about ‘catchments’ with no watercourse (such as single sites?) do the same conceptualised processes apply? How do they scale down?

Despite these uncertainties – the Environment Agency, Lead local flood authorities and forthcoming SABS still need to assess planning applications and drainage proposals; utility operators need to know what to protect and developers need to know how much water to store on site.

The improvements will be delivered through three main activities– collecting new data, analysing the data & to inform new guidance and/or methods, and finally identifying where further research can make a difference.

Our earlier work suggests the FEH statistical method and the Revitalised Flood Hydrograph (ReFH) event-based method both outperform the older methods, some of which are still in use. More details of our Phase 1 findings are available here.

Phase 2 is bringing those conclusions forward, by combining the academic strengths of CEH with JBA’s practical portfolio.

More information about our project – and our plans for phase 2 – is available online here ; You can visit the joint EA/Defra R&D portal here for more information about our other flood risk research projects.

by Mark Whitling
email: mark.whitling@environment-agency.gov.uk

Estimating flood flows and hydrographs in small catchments and plots

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