Wetted works - bottom protection and filter-bed

It was not possible for the sill-blocks to be simply placed direct onto the river- bed: rapid accelerations in current would otherwise create major turbulence beneath and in the vicinity of the blocks upon closure of the barrier. Furthermore the sill could be seriously destabilised if water were unable to pass beneath the sill blocks. For this reason the blocks rest on a porous filter-bed, in turn resting on substantial bottom-protection.

Filter-bed