Drop structure

Drop structures can be classified into three different basic types: vertical hard basin, grouted sloping boulder, and baffle chute.

The purpose of the vertical hard basin drop is to force the water into a hydraulic jump (a small standing wave).

Sediment is often deposited in the basin, requiring frequent removal, and erosion is often exacerbated downstream of the base of the structure.

One of the most efficient yet simple ways to dissipate this energy is to install a stilling basin at the discharge point to calm the flow.

These structures are built by creating a slope of riprap, which consists of large boulders or less commonly, blocks of concrete.

It typically consists of a concrete chute lined with "baffle" teeth to slow the water as it passes over the structure.

Surface turbulence, eddies, and bubbles are generated by drop structures that provide hiding and cover for fish and other aquatic organisms.

The spillway of Leasburg Diversion Dam, part of the Rio Grande Project , is an example of a vertical hard basin, the most basic form of a drop structure, designed to dissipate energy.
This grouted sloping boulder drop on Trabuco Creek in California is almost entirely covered by floodwater.
The canal spillway of Laguna Diversion Dam , shown here, uses a baffle chute drop structure to pass water to a lower elevation.