Technical Manual: Conduits through Embankment Dams (FEMA 484)

Conduits through Embankment Damsmaintain a water level below a certain elevation to reduce the risk of internal erosionor backward erosion piping of the embankment dam to an acceptable level of risk.The water level selected is typically lower than the normal water surface. Theestablishment of a reservoir operating restriction should consider not only thereduction of risk, but also potentially significant adverse impacts, such as:• Limiting the operational flexibility of the reservoir.• Reducing or severely curtailing water storage availability for project purposes.• Severely compromising flood control operations.• Endangering reservoir habitat.• Sensitive and significant cultural resource sites may be exposed morefrequently, as the reservoir is lowered, and subject to vandalism.• During droughts, the reservoir could be severely reduced because of a lack ofopportunity to store water as a buffer against drought.A reservoir restriction should remain in place until dam safety modifications havebeen completed or until a review of additional performance data (i.e., seepage [weir]flows, piezometer data, settlement point data, and visual inspections) leads to otherconclusions.288