Flood catastrophe highlights need for new water storage options

Floodwater storage options will become a major priority after the immediate flooding catastrophes have come under control flooding, experts predicted this week.

Multi functional reservoirs operated with capacity to spare to take flood water in emergencies, sustainable drainage regimes for upper river catchments, permeable street surfacings and even large scale flood relief channels in urban areas could all be on the agenda in future following the catastrophic flooding seen across the UK over the last month.

“Right now some spare capacity in the west London reservoirs would help with the Thames Valley flooding,” said chief executive of the Association of Drainage Authorities Jean Venables. “However there is no statutory obligation on water companies to help with flood relief and economically they do not want to run reservoirs at 80 or 90% capacity or have the addition of dirty flood water to treat.

“Multi functional reservoirs – probably a large number of small ones - are one option for the future,” she said. They would need to be operated outside of the current water supply regime but would provide back up in the event of drought or extra capacity as towns and cities grow as well as creating new amenity and habitat.

Venables also said there was a new urgency on Department for Communities and Local Government to put in place requirements for sustainable drainage schemes particularly in upland developments to hold water back and prevent it flooding those living in the valleys.

“We have not been paying enough attention to managing water in the upland areas and the impact on the lower catchment,” she said. “If you live at the bottom of a hill and your neighbours higher up keep pouring water on your head, you are going to get wet.”

Local government and developers will also need to reconsider their approach to hard standing, she said. York stone paving which allows water to permeate is being taken up and replaced with impermeable asphalt as it is cheaper, Venables pointed out. “And look at the new development at Kings Cross station in London – where is the grass there?”

Peter Brett Associates partner and flood risk specialist Ben Mitchell said SuDS had an important role to play in the future but warned that they must not necessarily be adopted as a blanket approach.

“At the downstream end of some medium scale catchments the delayed release of surface water can actually increase peak flows and make flooding worse. Furthermore, after prolonged rainfall, if the ground is saturated then the water has nowhere else go and the implementation of SuDS could result in flooding at source,” he said.

“With the projected climate change impacts, I think we are going to have increased intensity rainfall in the future and our natural drainage in this country has not evolved for that," he added. "We are going to have to look to those countries that are used to dealing with high intensity rainfall for solutions. The US and Japan for example build large overflow drainage channels to contain the water and if we are going to need those we need to start planning now for ‘reserved corridors’ at least in to our urban designs now for future generations."