U.S. Fish & Wildlife Service Low Hazard Dams - Association of State ...

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U.S. Fish & Wildlife Service Low Hazard Dams - Association of State ...

STANDING OPERATING PROCEDURESCommon signs of the presence of beaver include gnawed or cut vegetation around thewaterline; burrows or sunken or collapsed areas in the crest or slopes of the embankment;and obstructions across spillways and inlets that produce unusual changes in the waterlevel of the reservoir.Figure 5-10: Schematic of Animal Burrows In Embankment Illustrating Potentialfor Developing a Piping FailureBarriers such as properly constructed riprap and filter layers offer the most practicalprotection from these animals. When an animal tries to construct a burrow, the sand andgravel of a filter layer will cave in and discourage den building. Filter layers and riprapshould extend at least three feet below the waterline. Heavy wire fencing laid flat againsta slope and extending above and below the waterline can also be effective. Eliminatingor reducing aquatic vegetation along a shoreline will also discourage habitation.Methods of repairing rodent damage depend upon the nature of the damage but, in anycase, extermination of the rodent population, if possible, is the most effective method. Ifthe damage consists mostly of shallow holes scattered across an embankment, repair maybe necessary to maintain the appearance of the dam, to keep runoff waters frominfiltrating the dam, or to discourage rodents from subsequently returning to theembankment. In these cases, tamping of earth into the rodent hole should be sufficientrepair. Soil should be placed as deeply as possible and compacted with a pole or shovelhandle.Large burrows on an embankment should be filled by mud packing. This simple,inexpensive method involves placing one or two lengths of metal stove or vent pipevertically over the entrance of the den with a tight seal between the pipe and den. Amud-pack mixture is then poured into the pipe until the burrow and pipe are filled withthe earth-water mixture. The pipe is removed and more dry earth is tamped into the den.5-17Revision No. 0October 2008

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