The following images are from the Petitcodiac River in the Bay of Fundy where they have extensive experience of dams and barrages. It shows graphically the alarming rate at which mud is deposited when the flow is slowed by and obstruction - in this case a causeway with a sluice gate. They experienced deposition rates of 1m per year!

The Petitcodiac River in 1954

The Petitcodiac River in 1996

Stage by Stage

So how long would it take for the Severn to silt up if we made the mistake of building either of the proposed barrages. The smaller ’shoots’ barrage proposal would suffer more rapidly from this fate as the silt load is even higher in this part of the river.

The full report Environmental Impact assessment can be found on the
Petitcodiac Riverkeeper’s website.

The good news is that lessons have been learned. Due to the extent of the unforeseen silting problems and subsequent pressure of flooding, the causeway in now being removed and replaced with a bridge. It is hoped this will restore the river to a healthy and navigable state.