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Natural Flood Storage and Extreme Flood
Events Final Report
11 RECOMMENDATIONS
The following recommendations are made as a result of
this study.
1. It is difficult to provide a generalised assessment
of whether floodplain storage can provide a flood
management solution in any particular catchment without
going into the level of detail needed for a feasibility or
design study. This is because the net effect of managed
storage requires modelling of storage units, including
inlet and outlet controls.
2. However, a broad-scale, generic assessment of the
potential to use the natural floodplain can be made based
on simple routing models and a 2-D flood extent modelling
tool that makes use of DEM data. Further development of
this modelling work is needed with a wider range of flood
scenarios, floodplain roughness, floodplain definition and
channel representation.
3. It is recommended that this broad-scale generic
assessment of the natural floodplain is piloted on a small
catchment in Scotland (<150km
2) for which a new flood alleviation scheme is
being planned.
4. Evidence from flood alleviation schemes in England
and Wales incorporating some element of natural floodplain
storage suggests that early consultation and engagement
with the farming communities affected and other
stakeholders is essential if a proposed scheme is to be
successful. An appropriate level of compensation to farmers
and landowners in Scotland to permit their land to be
flooded is needed if the scheme is to remain sustainable. A
revised payment mechanism within the current Rural
Stewardship Scheme would seem to be the most logical way in
which to manage this. In addition, large coherent areas of
the floodplain would need to be brought into any new
managed 'natural' flood attenuation scheme simultaneously
if it is to be successful.
5. The MDSF-based analysis of the economic impact of
flooding on agricultural land covers should be revised to
specifically incorporate and implement current Scottish
agricultural and rural conditions.
6. The optimum solution would be a whole catchment
'scheme' that aims to reduce flood flows by a combination
of:
Reducing and delaying runoff production (a hydrological
issue) though upland management, if possible
Attenuation of out of bank flows, through a combination
of changes to floodplain management and potentially
innovative use of natural floodplains for lower return
period floods (with a biodiversity benefit)
Improved protection measures in urban or other sensitive
areas
7. Investigations are required to identify what scale
and combination of
catchment land management changes (e.g. upland
grips, modification to hydrological connectivity) coupled
to
floodplain management (improved 'natural'
attenuation or larger engineered schemes) would be required
to alter sub-catchment hydrographs sufficiently to reduce
peak flows and offset the peak hydrograph at the downstream
risk location. This requires the further development of
linked hydrological and floodplain modelling and analysis
tools. In the meantime, the simpler, generic screening
methods proposed here may be used to help decide whether to
take investigations forward in any given catchment.
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