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National Program for Inspection of Non-Federal Dams. Nash Pond Dam (CT 00060), Southwestern Coastal Basin, Westport Connecticut. Phase I Inspection Report.

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The dam at Nash Pond is constructed of stone masonry, is approximately 105 feet long, 25 feet high and has a top width of 5 to 7 feet. There have been no significant modifications to the dam since the dam was completed in 1879. The impounded water is primarily used for recreation. The present owner of the dam could not be determined during this report and it is recommended that the State of Connecticut ascertain the ownership of the dam. Based on the visual inspection and past operational performance, the dam is judged to be in FAIR condition. Slight seepage from the masonry joints was noted on the downstream face and some of the joints need repointing. The valve controlling discharge to the 30 inch pipe outlet self-opened in the Summer of 1978 and was subsequently reclosed. A low-level blowoff is believed to exist through the base of the dam. This dam is classified as SMALL in size and a HIGH hazard potential structure in accordance with recommended guidelines established by the Corps of Engineers. The impoundment storage at the top of the dam is 114 ac.-ft. and the maximum height of the dam is 25 feet. Failure of the dam would result in the loss of more than a few lives and excessive economic loss to the downstream urbanized area, two commercial buildings, 2 - 3 residential homes, and an apartment building. The test flood for this dam is 12 the Probable Maximum Flood PMF. The test flood has an inflow equal to 2650 cfs and an outflow discharge equal to 2570 cfs with a stillwater elevation of 64.0 which will overtop the dam by 3.8 feet in a stillwater condition. The maximum outflow capacity of the spillway under stillway conditions is 250 cfs which is 10 percent of the test flood.

Subject Categories:

  • Hydrology, Limnology and Potamology
  • Civil Engineering

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