FOLLOWING is a suggestion on how to improve the Derwent River flood alleviation plans.

The upstream Derwent River is kept full of water by the weir at Kirkham Priory. There the bypass channel and sluice gate's depth gauges indicate that there is a vertical drop in water level in excess of 2 metres (or about 7 feet).

From the confluence with Thornton Beck to the Kirkham Priory weir the River Derwent is some 20 kilometres long (almost 12.5 miles). This stretch appears to average an estimated 20 metres in width, so its total area would thus be 400,000 square metres (or 1.55 square miles). This is without taking areas upstream from the confluences with the River Rye and Thornton Beck into account.

My proposal is to lower the average levels of the River Derwent upstream from Malton by expanding the width and the depth of the Kirkham Priory weir's bypass. In this way the river would be free to run at a more natural level. This would dramatically reduce the risk of flooding up-stream from Malton.

I calculate that so lowering the Derwent River's level would create up to a 2-metre vertical flood risk safety margin. The between banks water fill capacity would then take about one million cubic metres of river flood water (or 220,000,000 imperial gallons), before the reduced level river when passing Malton and Norton could rise to today's low water level.

In this way potential floodwater would first have to fill a volume equal to that of over 1 inch of rainfall over a 122 square miles upstream watershed area, before additional rain could cause the river to rise further.

Residents in the Derwent River local flood plains would thus have the assurance of the planned river constraining flood defences being complemented by the natural Derwent River channel absorbing a first inch of rainfall on much of the watershed area and perhaps also most of a second continuing inch of rain. Any resulting floodwater's down-river drainage would also be faster than in recent years.

Updated: 09:01 Thursday, July 26, 2001