Sir - You correctly highlight the difficulties posed by flash flooding (Leader, March 21). However, your suggestion that they would be solved if waterways were kept clear is too simplistic. Keeping watercourses clear is vital but does not solve the problem.

Cumnor parish has a severe problem of routine flash flooding in its Dean Court Ward.

The situation has always existed in the Eynsham Road area: it is the bottom of a valley formed by the Wytham and Cumnor hills.

Historically, rainwater ran off the hills collecting in water meadows where once watercress was grown. Part of the area was boggy for most of the year.

Enter mankind. The building of the A420 rechannelled some of the water flows. Despite heroic efforts by the county's engineers, not all drains cope as well as they should. The area is under severe developmental pressure.

Each development increases the rate of run-off and reduces the area available for water absorption.

There is a variety of sustainable drainage schemes (SUDS) that could be employed. Correctly engineered, they can reduce the rate of run-off from sites.

However, even when SUDS are used, no thought appears to be given to the way in which they will be maintained.

For example, the maximum flow rate through a porous surface can fall to ten per cent of its design value if the surface is not correctly maintained.

Maintenance is possible but expensive. The victim of poor maintenance is seldom the owner of the porous surface so the pressure to skimp is great.

Even if the use of SUDs becomes widespread, there is a major backlog to be overcome. Before further piecemeal developments are sanctioned, the effect on the local environment should be evaluated and the necessary infrastructure elements put in place.

P Hawtin (Dr), Chairman, Cumnor Parish Council, V Cheel (Dr), Councillor