Spillway
Spillway
X-23 PRIME
<catset>Category="Dams"</catset>[image] A <b>Spillway</b> is a structure used to provide for the controlled release of flood flows from a <a href="Dam">Dam</a> or <a href="Levee">Levee</a> into a downstream area, typically being the river that has been dammed. Floods are released by spillways so that the water does not overtop and damage, or even destroy, the dam by overflowing the structure. Except during flood periods, water does not normally flow over a spillway. In contrast, an "intake" is a structure used to release water on a regular basis for water supply, hydropower production, etc.<p>A spillway is located at the top of the reservoir pool. Dams may also have bottom outlets with valves or gates which may be operated to release flood flow, and a few dams rely entirely on bottom outlets and lack an overflow spillway.<p>There are two types of spillways: uncontrolled and controlled. [image]<p>Uncontrolled spillways do not have gates; when the water rises above the lip or "crest" of the spillway it begins to be released from the reservoir. The rate of discharge is controlled only by the depth of water within the reservoir. All of the storage volume in the reservoir above the spillway crest can be used only for the temporary storage of floodwater, and cannot be used as water supply storage because it is normally empty.<p>A controlled spillway has mechanical structures or "gates" to regulate the rate of flow. This design allows nearly the full height of the dam to be used for water storage year-around, and flood waters can be released as required by opening one or more gates. [image] [image] Some spillways are designed like an inverted bell-mouth so that water can enter all around the perimeter (also termed a "morning-glory" design). In areas where the surface of the reservoir may freeze, bell-mouth spillways are normally fitted with some arrangements for breaking the ice to prevent the spillway from becoming ice-bound.