Some critics of the Oxford Flood Alleviation Scheme have talked about the need for a ‘catchment-wide’ approach as an alternative. There are certainly benefits to thinking about the whole upper Thames catchment, but could such an approach deliver results within a meaningful timescale?
One issue OFA looked at early on, once the Flood Alleviation project was underway, was the potential for natural flood management techniques to contribute to reducing flood risk in Oxford. In August 2015 we organized a seminar and heard from a range of experts on this subject.
The overall conclusion was that natural flood-management techniques can bring benefits in smaller catchments, especially in lower-order flooding events. Isolated projects in the upper Thames would, however, have no measurable impact on Oxford with its large catchment (about 2,500 km2 upstream).
A complete re-landscaping of the Thames catchment might, if it could be achieved, reduce flood peaks by 10–15% – so helping with the flood risk but not solving it fully. Achieving the transformations in land-use necessary to deliver this benefit would require radical new legislation and/or a new culture of approaches to land management, taking ‘around 40 years’ to implement.
We found that storage could potentially play some role, but the volume of water involved in a major flood cannot be contained upstream of Oxford. The Environment Agency has always been clear about this. An effective upstream storage area would need to store approximately 50 million m3 of water. This is equivalent to an area the size of Oxford under 1 metre of water. There’s not enough capacity in the floodplain to store that amount of water.
The Environment Agency is exploring options for some future element of storage to mitigate against worsening climate change. Storage is not a viable alternative to the flood scheme but could be a useful backup in the future, as could major changes to land use upstream.
As well as these two options we also spent a lot of time looking at property-level resilience measures. Several steering group members made significant alterations to their homes to reduce the impact of floodwater in their property and speed up recovery after a flood. A number of us were allocated flood gates, air brick covers, and small submersible pumps by the City Council, funded by the EA. The pumps proved vital in Jan 2014 in keeping water out of vulnerable houses on Osney Island (see picture below).
There are things we can do at household level but these are only effective up to a certain scale of flooding. They are not a substitute for the flood scheme. Even with the scheme in place some properties still face risk and will need to deploy property-level defences.
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