A joined up approach: surface water management – flood storage to supply
Motion Director Richard Bettridge calls for a creative, joined-up approach to flood resilience.
Despite reports to the contrary, the property development industry has acted responsibly, taking flood risk into account when developing land in or near floodplains; planning guidance ensures that great care is taken over the management of flood risk and surface water run-off. Yet there is often a disconnect in England between the treatment of discharge rates for development and the need to relate discharge control to reflect catchment characteristics. Put simply, a ‘one-size-fits-all’ approach needs to change, so that discharge control and storage provision can be optimised across the whole catchment to minimise flooding. This may mean that full attenuation is required at the upper part but is reduced moving down the catchment. Attenuating the discharge into large water bodies, such as the sea, may not be necessary at all.
This kind of joined-up approach, with agencies such as water companies playing a pivotal role, would significantly alleviate the pressure on vulnerable settlements. The problem of flooding is complex, but there is much that can be done to mitigate risk on a catchment-wide basis, by adjusting the storage/discharge regime, depending on the location within a catchment.
I have long been an advocate of appropriate and individual treatment of the different levels within a catchment area. One trick that seems to have been missed is the need to harness the potential of flood storage and link it with water supply management. By combining flood storage with the impounding of water for supply purposes, we could help avoid water rationing in drought conditions, as impounded run-off would be stored for future water supply. The challenge lies in balancing our need for water with flood storage to permit reduced discharge rates downstream.
Use of SuDS
The adoption of sustainable urban drainage systems (SuDS) is but one part of our armoury against flooding. SuDS land take is greater than with piped systems and the challenge of maintaining natural elements, such as swales and ponds, is often prohibitively expensive. At a local level, we should espouse the principle of SuDS, but it may not be appropriate for large-scale management of flooding, which requires strategic defences and storage capacity for attenuation schemes. The reluctance of sewerage undertakers to maintain SuDS schemes, or to accept responsibility, makes it a solution which is vulnerable in the longer term.
I would welcome a debate amongst policy makers, water companies and engineers on the merits of appropriate, retention-based, catchment-wide approaches. Engineers, working with property developers, have successfully taken on and overcome challenges of similar proportions in the past. The political, commercial and infrastructure environment, to ensure discharge is controlled and appropriately channelled, also needs underpinning by systems design and engineering know-how capable of supporting the wider objectives.
Benefits of adopting retention-based, catchment-wide approaches, and integrating flood storage with water supply:
- Alleviation of downstream flooding
- Better management of fluctuations in water demand
- Lower investment required in engineered flood defences
- More profitable use of adjacent land
Motion’s infrastructure design team has many years of experience providing pragmatic advice to help a wide range of clients manage the complex interrelation of property development, drainage and flood risk. Call 01483 531300 to speak to an expert.
This article first appeared in the Winter 2019 issue of Insight.