An underflow dam unit provides a barricade to pollutants suspended in runoff water which otherwise finds a way through streets and streams. They use leaning culverts to allow water which is moving downstream to run off while keeping the spill well contained. The dam unit includes a dam sandwiched between limiting side walls above the dam. The baffle’s lower limit extends below the height of the dam forming a waterway between the baffle and the dam. Floating pollutants become ensnared against the baffle while hydraulic pressure allows subsurface stream water to flow the barrier channel and over the dam.

Overflow dams carry water discharge over their crests and are made of materials not easily eroded by the discharges, therefore, allowing water to flow over from its top and afterward down to its front face. The dam sometimes acts as an overflow spillway. They consist of a mass so heavy that the reservoir's water cannot push the dam downstream (thicker at the base than the top). Horizontal pressure on the dam is exerted as the water becomes deeper. Overflow spillways are constructed where there is intense pressure as compared to underflow spillways which cannot withstand massive pressure on the dam tipping it over.

REFERENCES

Conrad J. D. (1997) Geomorphic Effects of Overflow Dams. Brookfield, VT: Ashgate

Kyle E. J. (1999) The Free Flow and Submergence Of Underflow Dams. U.S. Geological Survey