The Severn poses a degree of risk in some reaches which is higher than that encountered elsewhere. This is partly due to the geology of the land through which it flows, but also with headwaters in the Welsh mountains, the high variability of flow makes river conditions less predictable. The depth of the river bed varies considerably – even in a short distance of a few miles, the bed can change from shingle rapids to a deep hole of forty feet in some cases.
Whirlpools can be seen on bends in relatively quiet conditions. Several accidents have resulted in loss of life in deep areas, for example near Blackstone Rock, between Bewdley and Stourport. Also, in flood conditions, where the banks are not over-topped, the velocity of the water, even at the bank-side, can exceed five miles per hour – making rescue of anyone falling in a dangerous option.
Whilst it is sensible to recommend education and awareness – there are a couple of aspects of weirs which suggests small advantages. A weir causes a rise in level, and (under the same conditions of flow) causes a reduction in velocity of the water (due to the increase in cross sectional area). Minimal, of course, but a decrease in velocity would theoretically increase the safety of anyone falling in. Also, in some areas by wharfs, the river bed is now rocky and exposed during times of low flow – seen increasingly as water shortages extend (e.g. at Bewdley). Anyone falling off the wharf onto rocks would likely be injured – but falling into water if a weir is built to maintain normal levels, would stand more chance of swimming or being pulled out, albeit wet.