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How a Dam Works

Dry Dams
All of the dams are gateless with large concrete structures at their base with openings, or conduits, through which the river flows. During times of normal flow, the river passes through the dam unimpeded — there are no permanent pools of water behind the dams, which is why they are called "dry dams." The conduits in each dam are sized to allow the amount of water to flow through the dam that the river channels in the protected cities below can safely handle within their banks. Any excess flow backs up behind the dams in the retarding basins upstream of the dam.


Cross Section of Huffman Dam
Hydraulic Jump and Stilling Basin
The dam conduits feed water down a series of stepped concrete stairs that dissipate the kinetic energy of water flowing at a high velocity during floods. The stairs and stilling pool beneath cause the water to turn back upon itself and create a standing wave, which reduces the speed and force of the water using internal friction.

Retarding Basin
The land upstream of a dam and below the elevation of the spillway that is reserved for temporary storage of floodwaters is called the retarding basin. MCD has flood easements on 35,650 acres of land upstream of the five dams in the retarding basins. Because the land is reserved for storage of floodwater, MCD has regulations controlling development. The land in the retarding basins is predominantly used for agriculture and parkland.