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development of natural instream debris dams has also

been encouraged in the existing

historic woodland (Horner Wood).

• Soil management practices:

tenant farmers across both

catchments have been advised

on applying in-field soil

management best practices in

managed grassland and arable

fields, including the use of a soil

aerator in fields experiencing

soil compaction.

• Moorland runoff attenuation

features: surface runoff from the

Horner headwaters has also been

slowed and connectivity with

the arterial drainage network

has been reduced through the

construction of 800 shallow

earthen cross bunds along 20km

of footpaths and tracks across

the moorland.

• Woodland creation/restoration:

pockets of woodland have been

created and wet woodland

restored in the middle Aller

catchment to intercept and

slow floodwater, and improve

infiltration of water into the

soil profile.

• Land use change: reverting

arable land to grassland on

moderately sloping ground in

the Aller catchment provides a

more permanent and continuous

vegetative surface that can slow

surface runoff and/or improve

inception and infiltration of

direct rainfall.



From Source to Sea: The Holnicote Project


Defra, National

Trust, Environment

Agency, Penny

Anderson Associates,

Wessex Water,

Exeter University,

National Trust

tenant farmers


West Somerset,



Feasibility Stage,

2009-ongoing | 01274 714 269 | @JBAConsulting | JBA Consulting

The Holnicote Project is one of three multi-objective flood

management demonstration projects commissioned in 2009 as a

direct result of the recommendations from the Pitt Review which

followed the Summer 2007 floods.


These projects were all tasked with providing evidence around

Working with Natural Processes (WwNP). To demonstrate how

slowing and storing flood water in the landscape can contribute to

reducing flood risk to downstream receptors, whilst also providing

a range of other benefits to the environment and society. Two

instrumented catchments on the National Trust Holnicote Estate

- Horner Water (22km2) and the River Aller (18km2), saw a range

of WwNP measures implemented.


• Offline storage ponds

and wetlands: five

shallow earthbunded

flood meadow areas

(with outlet control

pipes) and some

surface water scrapes

have been created

on the middle Aller

floodplain to

increase floodplain

storage capacity.

• Instream structures:

instream woody

debris dams and

accumulations have

been installed to slow

flows in the Horner

headwaters. The


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