Oxford Flood Alleviation Scheme “fundamentally flawed” experts say
"Packed meeting reflects groundswell of concern about climate change, the Oxford Flood Alleviation scheme and effects on biodiversity."
The West Oxford Community centre was filled to capacity last Friday night to hear a range of independent experts comment on the proposed Oxford Flood Alleviation Scheme, which will shortly be submitted for planning application by the Environment Agency. The meeting was organised by the newly formed Oxford Flood and Environment group who are responding to a groundswell of concern about the scheme and people came from all over the Thames catchment to attend.
A packed meeting heard the scheme has serious weaknesses in the opinion of international floods specialist David Ramsbottom, who lives in Oxford.
“I think there is a fundamental flaw in the scheme. The basic concept of a flood relief channel is to allow a large amount of flood water to flow through a flood risk area as efficiently as possible, thereby reducing flood levels. The proposed Oxford flood relief channel is designed in such a way that the flow capacity is actually quite small. The corresponding reduction in flood levels is also small and the overall flood benefit is limited. According to the Flood Risk Assessment for the scheme, a medium flood will reduce water levels by 30 centimetres or less, about one foot. For a large flood the reduction in level would be less than 20 centimetres, about 8 inches.”
He said that the proposed channel, which includes lowering a large area of the floodplain is an inefficient way of moving flood water because the shallow depths mean the speed of water would be low and therefore the flood flow capacity would be small. He said that the Jubilee River flood relief channel at Maidenhead carries about 40% of the total flood flow, whereas the Oxford channel would only carry about 15%.
He also said that flood defences are needed because the channel only lowers water levels by a small amount and flooding would still occur. These include raised banks and walls at several locations. These flood defences may have a problem because water could go underneath them in the floodplain gravels and cause flooding. He acknowledged that some attention had been paid to this but questioned if it was enough.
International economic analyst, Caroline Midgely also cast doubt on the cost benefit analysis of the 13 key elements of the scheme. “Just three elements; resolving the pinch point at North Abingdon Road with a bridge and culvert system, the Botley Tumbling Bay works to Bulstake stream and the widening of the Willow Walk bridge, produce 40% of the scheme’s benefit for a cost of just £20 million.”
She said that the 8 most cost-effective elements deliver 86% of the benefits for 60% of the cost. However, the remaining most controversial parts of the scheme only deliver 24% of the benefit for 40% of the cost. The worst aspect was a poor return on the channel from Botley Road to Willow Walk and the lowered flood plain from South Hinksey.
“The key message is that the channel is the most controversial element of the scheme as it causes by far the greatest environmental damage and is the basis of all the planning application objections and nearly 200 compulsory purchases. But the channel generates just under 5% of the benefits - for 26% of the cost at £32 million.”
She said the EA should take another look at the scheme. “Is the channel worth it?” she asked. “An economic assessment suggests that it isn’t.”
Impact on Ecology
"Potential biodiversity collapse" says plant ecologist Dr Tim King
The audience also watched a video outlining the potential biodiversity collapse of the wildlife corridor of the 133 acres of green belt based on the analysis of Dr King of Wolfson College who has studied the ecology of Hinksey Meadows for several decades. Under threat is the 7 hectares of Hinksey Meadow’ rare MG4a grassland of which only 192 hectares remain in the UK. With only 3% of our meadows left since World War 2 Hinksey Meadow was described as a “jewel in the crown” of rare meadow flood plain grassland. Two hectares will be permanently lost to make way for the new stream and the rest will be threatened by changes in the hydrology as a result of the channel. This could affect the biodiverse plant community and the critically endangered wild fritillaries and creeping marsh wort.
The EA has admitted that translocation is unlikely to work and they will plant a new meadow. But ecologists say it won’t have the same ecological value as a 1000-year-old meadow. Dr King also cast doubt on the EA’s claims that full biodiversity would return to these habitats in 10-25 years. Whereas published evidence suggested 60-100 years. There is also the potential loss of carbon sequestration as grassland is second only to peat for storing carbon.
"Massive potential loss of ecosystem services with carbon costs potentially 'off the scale'.” Dr Therivel
Riki Therivel, sustainability consultant and visiting professor at Oxford Brookes University, backed up these fears of biodiversity loss and forecast massive potential loss of ecosystem services with carbon costs potentially “off the scale.” Dr Therivel said that by her calculations, just the costs of loss of amenity during construction will completely outweigh any net environmental benefit from the scheme, suggesting the figures have been “massaged” by the EA.
“A flood alleviation scheme is definitely needed. But the proposed OFAS scheme will have ecosystem services costs which have not been fully considered by the EA. Other schemes not considered by the EA may deliver the same benefits with fewer costs. For example, smaller, incremental actions that can be monitored and managed.”
"Channel the weakest component of the scheme."Environmental Campaigner Dr Rod Chalk
"Could cause Oxford's biggest environmental catastrophe ever."
Environmental campaigner Dr Rod Chalk from Hinksey and Osney Environment Group (HOEG) claimed the channel was the least effective component of the scheme and would only protect around 150 houses in a 100-year flood event. He said the major flaws in the scheme were that it was a passive, gravity driven system which couldn’t be controlled.
He said that HOEG had identified 3 different options offering the equivalent or even better flood protection options without the prohibitive environmental cost.
He presented the design of a pump pipeline scheme designed by engineer Jonathan Madden who joined the meeting from the Middle East. He described this as an active, enclosed power-driven system that was fully controllable.
“We absolutely want a scheme and don’t want a public enquiry if it can be avoided. But on economic, environmental and hydrological grounds this scheme is flawed. The trees felled, spoil extracted and 30,000 lorry movements over three years will transform an ancient flood plain meadow into an open cast gravel mine. The loss of mixed mature woodland, healthy streams and crack willow will combine to devastate our biodiversity. The purported nature reserve could be the largest environmental catastrophe in Oxford’s history and this wildlife corridor lost forever.”
Oxford Faces Dramatic Increase in Flood Events Due to Climate Change
"City needs to become more flood resilient," Dr Louise Slater
Hydrologist and associate Professor Louise Slater from the School of Geography, University of Oxford gave an overview of the changes in flood risk affecting Oxford. She confirmed flood risk has been increasing and the city needed to become more flood resilient. To illustrate the magnitude of change, she ran a statistical analysis that showed a flood from the 1960s that would have occurred every 100 years, could under today’s conditions happen with much greater frequency. She said there were different ways of calculating these statistics,
“But it tells us that we should expect these very large floods of 1 in 100 years to occur with greater frequency now than they did in the 1960s. A one in a 100-year flood is not a static concept, it is a dynamic concept.”
She said that the likelihood of extreme floods would change over time with factors like urbanisation, deforestation and changes in water management and climate variability.
The way to address flooding is usually with a multi-level approach. You do need hard engineering solutions like flood defences. But you also need softer methods like natural flood management and green infrastructure. This is all part of a combined package and should set the scene for all discussions about flood management.”
Regenerative Farming Could Hold Key to Flood Mitigation
Experimental Projects across the Thames Catchment hold promise
David Ramsbottom said that the jury was currently out on exactly what could be achieved by doing work upstream to reduce flood flows and that had got to be part of the debate. The Environment Agency has started a project looking into the feasibility of measures across the Thames catchment to mitigate the expected increases in flood flows caused by climate change.
He said that on a brighter note that regenerative farming practices held out great hope because increasing ground cover and restoring the topsoil could reduce run off significantly. “There are farmers in the Thames catchment looking at different ways of managing the land including different ploughing practices, having much more ground cover, herbal leys and various other regenerative farming practices. As farming covers very large land areas this could significantly reduce run off. From all I’ve seen this offers the greatest hope simply because we need to go in this more sustainable direction.”