National Program Of Inspection Of Dams

The activities in this study consists of a compilation of data for an inventory of dams; a survey of each state and federal agency's capabilities, practices and regulations in regard to the design, construction, operation and maintenance of dams; development of guidelines for the safety inspection and evaluation of dams; and recommendations of a comprehensive national program for the inspection and regulation of dams. The inventory included in the report consists of data on 49,329 dams which are 25 feet or more in height or have a maximum impounding capacity of 50 acre-feet or more. Inventory data consists of the name of the dam; the river or stream on which the dam is located; the type of dam; year completed; purpose of the dam; height and maximum storage capacity; and the name, population and distance from the dam to the nearest downstream city, town or village; the downstream hazard potential; owner of the dam; and the Congressional district in which the dam is located. This report presents the first Federal study of the problems of the safety of dams on a nationwide scale. It reveals that approximately 20,000 of the 49,329 dams are so located that failure or misoperation of the discharge facilities could result in loss of human life and appreciable or greater property damage. It was also found that existing dam safety programs in most states and in some Federal agencies are either non-existence or inadequate.

This report is a summary of the results of the National Program of Inspection of Non-Federal Dams, by the U.S. Army Corps of Engineers and completed on 30 September 1981. The recommendations provided in this report for improving the safety of non-Federal dams augment those offered in the report submitted to the Congress in 1976, prior to initiating the inspection of Non-Federal dams, and reflect additional findings resulting from these inspections.

Parks Pond Dam is a cyclopean masonry/earth embankment that is approximately 180 feet long and 12 feet high. The earth embankment is on the downstream side and has a 2:1 slope. The upstream face is cyclopean masonry with a vertical face. The spillway is located on the southern half of the dam and consists of a 30.5 foot long weir. There is a lower gate house for the control of a discharge pipe that passes through the base of the dam. The size of the pipe is unknown. The valve for the operation of the discharge pipe is inoperable. The drainage area is 0.5 square miles and the reservoir has 100 acre-feet of available storage. The assessment of the dam is based on the visual inspection, past operational performance and hydraulic/hydrologic computations. The dam is judged to be in poor condition with several areas that require attention. These areas include seepage through the dam and around the spillway's west training wall, deteriorated concrete of the spillway and upstream face of the dam, vegetation on the embankments and along the toe of the dam and the nonoperating status of the blowoff. The dam is classified as small and has a significant hazard potential in accordance with guidelines established by the Corps of Engineers. The test flood for this dam is 1/2 the Probable Maximum Flood (PMF). The test flood inflow is 625 cfs and the routed test flood outflow is 473 cfs. The test flood outflow will overtop the dam by 0.55 feet.

Kelleys Falls Dam is a run of the river type dam, with an overall length of 503 feet. Visual inspection of the dam indicated that the dam is in poor condition. The inspection revealed a number of leaks through the mass concrete spillway section, considerable loss of concrete from the spillway section, seepage around the concrete wall on the right side of the dam, and general deterioration of concrete on the abutments and hydro-building. Based on the intermediate size of the dam and the significant hazard classification and in accordance with Corps of Engineers guidelines, the test flood is one half the Probable Maximum Flood (PMF) or 55,900 cfs. The one half PMF outflow overtops the dam by 6.8 feet. With the water level at the top of the dam, the spillway will pass 38 percent of the test flood outflow. It is recommended that the owner engage a qualified engineer to make thorough investigation of the condition of the foundation of the spillway section of the dam, investigate the structural stability of the spillway section and ways to increase the spillway capacity. Also, the owner should remove the flashboards on the dam immediately. Additional keywords: Merrimack River Basin, Manchester, and New Hampshire.