Raid Weir
An attack weir is a weir that is characterized by a solid weir body and its simple construction. Most of the area exposed to the flow is vertical in the upstream water, to which the overflow crown, the weir ridge and the stilling basin are connected .
Reinforced concrete is the most common building material .
The horizontal weir crown can be round, elliptical or shaped according to the specifications of the WES ( US Army Corps of Engineers : Waterway Experiment Station). The aim of the rounding is to avoid negative pressure on the bluff body and thus cavitation and its damage to the structure.
On the top of the weir there is a flow change from streams to shooting , which is reversed in the stilling basin .
The raid is often regulated by combining it with a segment gate that can be lowered onto the weir crown.
The holdover weir is an insurmountable obstacle for all aquatic life forms. For this reason, bypass channels or fish ladders are attached to many holdover weirs, and in some places the weir is replaced by a rough ramp .