Some initial thoughts from the Environment Agency. They are aware that the threat of water being dumped further downstream is an issue for us. I will keep abreast of this issue.
We are working with our partners, who include Oxfordshire County Council, Oxford City Council and the Vale of White Horse District Council, to develop a scheme to reduce flood risk in Oxford. One of the options is to improve capacity in the western floodplain of the city with a £120 million flood relief channel.
We have not designed a scheme yet and have not decided what the size and location of the channel will be. However if approved by Defra and HM Treasury, and subject to funding availability, a channel is likely to be formed from a combination of widened existing channels and new sections of channel.
A new channel and/or altered existing channels would work with the natural processes of the local watercourses and the floodplain to help manage the movement of water through Oxford. During a flood this would reduce the risk of water entering homes, businesses and disrupting transport links.
The channel will reduce flood risk but it cannot remove it completely. In extreme weather the western floodplain would still be utilised as the channel would fill up and be overtopped, with flood water spilling into the surrounding floodplain.
What happens during a flood?
After rainfall, flow in rivers increases and water levels rise. After prolonged heavy rainfall the capacity of the local rivers may be exceeded and water will naturally spill out onto the floodplain. The floodplain acts as a temporary additional flow route and storage area taking excess water that will flow downstream and rejoin the river channel when levels fall.
In Oxford flood water and river levels rise slowly in response to rainfall and flooding continues for many days. The size and nature of the Thames catchment upstream of Oxford means that the city is mainly at risk of flooding during periods of excessive rainfall, combined with saturated or frozen ground conditions, which results in more severe flooding.
Consideration of downstream areas
We work to reduce flood risk overall, not to transfer it from one community to another. As part of our detailed design of the Oxford Flood Alleviation Scheme (FAS) we will use our latest river modelling to assess any changes in flow that the scheme may bring. Before the final scheme is approved we will share this information with communities in Oxford and in downstream areas.
We will include a detailed Flood Risk Assessment with any planning application we submit for the scheme. This assessment will contain information on any potential changes to downstream flood risk. It will also include details of any mitigation measures we will take, if required, to protect properties in the unlikely event that their flood risk is changed.
Alongside the Oxford FAS we are also developing business cases to provide flood alleviation schemes for other communities at risk of flooding from the River Thames, as part of our six year plan of works.
Together with our partners we take the management of flood risk very seriously.