The logic behind compulsory sustainable urban drainage systems (Suds) is clear: past generations of drainage engineers adopted the approach of trying to dispose of surface drainage as quickly as possible with rapid discharges to receiving river channels which cannot cope with the volumes.
These channels have often been constrained through engineering and building works with resultant loss of the functional river flood plains which could provide natural attenuation storage for floodwaters.
The implementation of wide scale development driven Suds can obviously cumulatively contribute to reducing flood problems, but we are a long way from a long term solution. To tackle future flooding, particularly given increased rainfall predictions, requires more extensive measures to be established across and within river catchments, to provide temporary storage of water and to reduce run-off rates in the first place. There are various approaches that can be adopted to achieve this goal, but all require political will and good coordination between the government, local authorities, statutory organisations, technical specialists and landowners. Such measures may include re-establishment of woodland to reduce catchment run-off rates, or reconnection to areas of fragmented upstream floodplain to provide floodwater attenuation areas to protect downstream urban areas.
This will have economic implications, as many areas where such measures would need to be implemented are currently used for agriculture. Compensatory funding would be necessary to offset these potential losses to farmers. It may even be better in the long-term to develop a policy to purchase these areas of land specifically for flood protection purposes and engage the local communities and wildlife organisations to further develop them as ecological and conservation areas. Landowners could receive long-term compensation payments for assisting in any routine maintenance works under an “Ecosystem Services” funding scheme for this multi-functional green infrastructure.
Maximising the ecological diversity and productivity within these areas would require the hydraulic regime of the reclaimed floodplain to mimic as far as possible the natural processes of seasonal flooding and drying. So reclaiming and reconnecting areas of undeveloped floodplain, combined with other upstream catchment management measures, may not only contribute to reducing the potential for flooding downstream but may also provide significant ecological benefits to the watercourse and its borders and banks. Maximising the ecological quality or potential of the UK rivers is also the key objective of the Water Framework Directive (WFD), the European legislative framework under which the “performance” of UK rivers is monitored and managed. So a large-scale Suds approach may also assist in helping UK rivers meet their principle WFD objectives.
We need a shift in emphasis from building barriers to flood water to creating connected wetlands to act as large scale natural Suds to soak up the excess water and allowing it to drain back to the river it at a slower rate. Yes, there will be substantial legislative, engineering, economic and political hurdles to overcome, but given the climate change predictions and the increasing problems and economic impacts already being caused by excessive rainfall events across the UK, the time for implementing new flood strategy approaches in the UK is surely already upon us.
- Richard Steel is technical director of eco-hydrology for Atmos Consulting