Livewire by Bob Crompton - 23/2/2011

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With reference to your recent feature regarding a proposed barrage across the River Wyre at Fleetwood.

Twenty years ago, Lancashire County Council, in conjunction with Norweb and the National Rivers Authority, commissioned a preliminary feasibility study on this exact scheme. The final comprehensive report was published in 1991.

The cost of the scheme at that time was estimated at about £100m.

Current costs of such a scheme today would be mindboggling, and beg the question of cost-effectiveness. The project was dropped by Lancashire County Council and its partners.

There is a major problem with the site because of the heavy sedimentation of the waters in this area.

The sediment distribution, fine particles of sand in suspension, has been studied over many years and detailed reports produced by ABP and others in connection with dredging operations.

It comes from two sources, the sea in Morecambe Bay and from the erosion of the river banks during high river flows.

Users of the river have long described the sedimented waters as grinding paste. It has a serious wearing effect on engines, pumps and revolving machinery.

An estimated annual sediment influx at Fleetwood is 250,000 cubic metres, which equates to the annual amount dredged from the estuary.

Fleetwood marina is regularly dredged to remove sediment accretion. Ever since the harbour was built, it has been a battle with nature to keep it open because it is not a natural harbour.

However, what will happen now dredging has ceased and it is proposed to place a solid barrier across the river?

The sedimentation flows in the estuary and river will be drastically changed. A barrage in operation would at high tide hold the lake behind it for a lengthy period before squeezing the water out through the turbines at a slow rate.

The sedimentation in the river will obviously be seriously affected because still or slow moving water causes the silt to drop.

It is reasonable to conclude the sedimentation post barrage would over time choke up the river and reduce the amount of stored water to turn the turbines.

In 1991, the preliminary model showed potentially 4,000 tonnes of sediment move upstream past Fleetwood on a spring tide, of which there are several each month.

The report acknowledged much more study was needed on this.

Perhaps a more viable scheme would be to build a dam at Fleetwood north of the marina with a sea lock and fish pass and create a freshwater lake half the size of Windermere.