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| Titel |
The role of local observations as evidence to inform effective mitigation methods for flood risk management |
| VerfasserIn |
Paul Quinn, Greg O'Donnell, Gareth Owen |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250093685
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| Publikation (Nr.) |
 EGU/EGU2014-8646.pdf |
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| Zusammenfassung |
| This poster presents a case study that highlights two crucial aspects of a catchment-based
flood management project that were used to encourage uptake of an effective flood
management strategy. Specifically, (1) the role of detailed local scale observations and (2) a
modelling method informed by these observations.
Within a 6km2 study catchment, Belford UK, a number of Runoff Attenuation Features
(RAFs) have been constructed (including ponds, wetlands and woody debris structures) to
address flooding issues in the downstream village. The storage capacity of the RAFs is
typically small (200 to 500m3), hence there was skepticism as to whether they would work
during large flood events. Monitoring was performed using a dense network of water level
recorders installed both within the RAFs and within the stream network. Using adjacent
upstream and downstream water levels in the stream network and observations within the
actual ponds, a detailed understanding of the local performance of the RAFs was gained.
However, despite understanding the local impacts of the features, the impact on the
downstream hydrograph at the catchment scale could still not be ascertained with any
certainty.
The local observations revealed that the RAFs typically filled on the rising limb of the
hydrograph; hence there was no available storage at the time of arrival of a large flow peak.
However, it was also clear that an impact on the rising limb of the hydrograph was being
observed. This knowledge of the functioning of individual features was used to create a
catchment model, in which a network of RAFs could then be configured to examine the
aggregated impacts. This Pond Network Model (PNM) was based on the observed local
physical relationships and allowed a user specified sequence of ponds to be configured into a
cascade structure.
It was found that there was a minimum number of RAFs needed before an impact on peak
flow was achieved for a large flood event. The number of RAFs required in the network was
also found to differ between events, due to the timing and shape of the hydrograph. However,
once a threshold was crossed, for each additional RAF added, a clear impact on the peak flow
was observed. Using a selection of observed flood events and design storms; a typical range
of 15 to 35 percent reduction in flow peak was achieved with 35 RAFs. Now that 40 RAFs
have been constructed in Belford, the local Environment Agency is confident that the
scheme is working satisfactory. Crucially, it was the detailed local observations
that informed the design of the PNM and it demonstrated to end users why the
approach was working. The RAF network approach is being taken up elsewhere. |
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