Yorkshire Philosophical Society

Event Information

Managing flood risk on the Ouse – a case of looking beyond the walls

Jeff Pacey – The Environment Agency

Lucy Hickson – Flood risk management

Report
by Alan Owen

19 April Managing flood risk on the Ouse – a case of looking beyond the walls, by Jeff Pacey, River Basin Planning Manager (Humber and Northumbria)

Following the floods of June 2007, Mr. Pacey and a colleague decided to search for an alternative solution to flood prevention using costly flood barriers by investigating why such large quantities of water were reaching the flood prone areas. By examining the annual flood height records over 150 years it was clear that maximum flood levels were increasing at an average of 8 mm./ year. The possibility of this being due to canalisation of the river by flood barriers was dismissed as the trend was apparent well before such schemes began. The search was therefore concentrated on the upper reaches of the tributaries, and in particular on Stean Moor.

It was discovered that a post WW2 scheme to rear more sheep had encouraged the draining of the waterlogged moorland by paying for drainage ditches (“grips”) to be dug on per foot basis. Examination of aerial photographs showed that overall about 4800 kilometres of grips had been made in the catchment area! Furthermore, the run-off rate for the water draining from the moors with the grips in place was over 100 times greater than the natural seepage rate of the moorland bog. The high run-off rates caused higher erosion which added to the silting of waterways downstream, and also significantly widened the original narrow drainage grips. The rate of drainage of these catchment areas is now being slowed down by blocking up all the grips at regular intervals to restore the land to natural bog again. Some areas of exposed peat were also being regrassed as this slows run-off by a factor of 10.

Other initiatives involve encouraging landowners to plant trees in high run-off areas though this is not very popular with landowners. The management of crop types and tracks which act as rapid watercourses in storms are also under investigation. A further factor to consider is the water from the moors as high carbon levels react adversely with water chlorination schemes. The use of intermediate dams and other capital flood management works are very effective but also very expensive, costing typically around £15 – 18 million per scheme. Such schemes do however give confidence to people living in flood prone areas.