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• Comparison of the basic characteristics

of the 'before change' flood hydrographs

with the 'after change' flood hydrographs

showed evidence of lowering and

flattening of the hydrograph shape and a

delay in the timing of the flood peak.

• No property flooding was experienced in

the vulnerable villages during the very wet

winter 2013/14 in Somerset when local

residents reported that they had expected

some flooding to take place.

• The combined effect of the five offline

storage ponds (storing an additional

18,000m3 of floodwater) reduced the flood

peak flow in the River Aller by 10% during

the most severe flood event measured in

winter 2013/14 (which had an estimated

return period of in excess of 1 in 50 years).

• On-going, regular and sensitive

engagement with catchment stakeholders

and the local communities, through a

trusted catchment advocate (National

Trust Project Manager), and provision of

appropriate monetary and non-monetary

incentives for change, has greatly helped

the continuing success of the project.

• Sufficient time and resources are needed

to explore and discuss WwNP aspirations

with catchment stakeholders, as well as

to engage with all the relevant regulatory

authorities with respect to consents and

approving the implementation of

WwNP measures.

the provision of multiple benefits to the

environment and society, including:

improvements to biodiversity, landscape

quality, carbon stewardship, water quality,

and amenity and recreation.

A summary report on the findings of the

Holnicote Project covering the period 2009-

2015 can be found on the National Trust

web site.

We are undertaking further modelling work

to explore NFM options on the Aller channel

and its floodplain upstream of the existing

cascade of offline storage areas.

Click here to

email Steve Rose

Natural Flood

Management Lead


The development, upgrade and

maintenance of this demonstration and

research platform, with the invaluable

support of the National Trust, is helping

to influence, shape and encourage the

wider uptake of the WwNP approach both

regionally and nationally in the UK.

A number of the spatial data analysis

tools and hydrological/hydraulic modelling

techniques which were developed and/or

applied by JBA across the study catchments,

have been successfully transferred to

several other WwNP initiatives in the UK.

The Holnicote project continues to provide

evidence on the impact of WwNP on

downstream flood risk, together with

Modelled flood depths on Aller floodplain - pre and post-WwNP

bund construction during December 2013 severe event. | 01274 714 269 | @JBAConsulting | JBA Consulting


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