Technical Manual: Conduits through Embankment Dams (FEMA 484)

Table 11.2.—Potential problems and immediate response or emergency repair actionsProblem orconditions Cause Response or emergency repair actionsInternal erosion Water has created an open • Begin monitoring the outflow quantity andand backward pathway, channel or pipe establishing whether water is getting muddier, staying theerosion piping through the embankment dam. same, or clearing up.through the The seepage water is eroding • If the quantity of flow is increasing, the reservoirembankment and carrying embankment should be lowered until the flow stabilizes or stops.dam, foundation materials. Large amounts of • Search for a possible opening on the upstream side ofor abutments water have accumulated on the the embankment dam and plug, if possible, as noted in thedownstream slope. Water and sinkhole section above.embankment materials are• Place a protective filter of sand and gravel over theexiting at one point. Surface exit point(s) to prevent further migration of fineagitation may be causing the embankment materials.muddy water. A break in the • Continue operating the reservoir at a reducedconduit could be allowing water reservoir level until repairs can be made.to discharge out of the conduit, • Engage a qualified professional engineer to inspectin the case of a pressurized the conditions and recommend further corrective actions toconduit beneath thebe taken.embankment dam. A flow pathhas developed along the outsideof the conduit.Seepage water Break in the conduit allowing • Thoroughly investigate the area by probing and/orexiting from a water to discharge out of the shoveling to see if the cause can be determined. Cautionpoint adjacent conduit, in the case of a should be used when shoveling in the embankment whereto the conduit pressurized conduit beneath the seepage is occurring, so as to not aggravate the situation.embankment dam. A flow path As a precaution, a supply of sand and gravel may be neededhas developed along the outside to prevent un controlled seepage.of the conduit or a saturated • Determine if the leakage is carrying soil particles orarea on the embankment above sediments.the conduit has developed. • Construct a measuring device and channel theseepage to the measuring device, to monitor anddetermine the quantity of flow.• Stake out the saturated area and monitor for growthor shrinkage.• Continue frequent monitoring of the seepage areafor signs of slides, cracking or increase or changes in theseepage condition.• If the seepage flow increases or is carryingembankment materials, the reservoir should be lowereduntil the leakage stops or is stabilized.• Engage a qualified professional engineer to inspectthe conditions and recommend further corrective actions tobe taken.Large increase A shortened seepage path or • Accurately measure outflow quantity and determinein flow or increased storage levels amount of increase over previous flow rates.sediment in• Collect jar samples of the seepage to compare theseepageturbidity of the water with time.• If either quantity or turbidity has increased by 25%, aqualified professional engineer should be engaged toinspect the conditions and recommend further correctiveactions to be taken.Sinkholes Backward erosion piping of • Inspect other parts of the dam for seepage or moreembankment materials or sinkholes.foundation causes a sinkhole. A • Identify actual cause of the sinkhole(s).sinkhole can develop when a• Check seepage and leakage outflows for dirty/muddysubterranean erosion feature water.269