National Program Of Inspection Of Non Federal Dams

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.

This dam generally consists of a 190 foot masonry spillway, an earthfill embankment and 2 outlet pipes. The dam was designed in 1955 by Stone and Webster Engineering Corporation to replace an earlier dam, which was damaged by the flood of that year. Construction which utilized portions of the original structure was completed in 1957. The visual inspection showed the dam to be in good condition. However, water passing over the spillway limited the inspection of the spillway. The spillway is capable of passing 96% of the test flood outflow. The top of the embankment, elevation 175, would be overtopped by about 1 foot. However, failure under this condition would only cause insignificant damage as the downstream flooding would have already occurred. The dam is generally in good condition. However, it is recommended that the owner repair the drawdown outlet, and operate it at least once yearly to insure continued adequacy. After this outlet is repaired, or during a period of low flow, the owner should engage a qualified engineer to inspect the spillway without water flowing over it. Also the erosion of a retaining wall downstream of the spillway on the right abutment side should be repaired.

The dam at the American Can Company building in Greenwich, Connecticut, consists of the north wall of a parking garage which retains earth and the adjacent created pond (North Lake) to a depth of five levels below grade. The height of this wall is 53 feet. There are no visible signs of physical distress and for reasons of fire protection, the water level is monitored very closely. Based on the visual inspection and a review of the technical data available, this dam is judged to be in good condition. This dam is classified as intermediate in size and a high hazard structure in accordance with the recommended guidelines established by the Corps of Engineers. The test flood for this dam is equal to the Probable Maximum Flood (PMF) and has an overflow discharge equal to 83 cfs. The maximum outflow capacity of the overflow weir under a stillwater condition; at the top of the weir opening is equal to 500 cfs, which represents more than 100 percent of the test flood. Rebuilding the headwall at the 48 inch outfall pipe is recommended within a 2 year period so that sedimentation buildup at this location can be monitored and clogging prevented.

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.

The dam is a 188 ft. long, 16 ft. high earth embankment dam. The condition is fair. The visual inspection did not disclose any immediate safety problems. The dam's spillway will not pass the test flood, therefore it is recommended that the owner engage a qualified engineer to evaluate further the potential for overtopping the inadequacy of the spillway. (Author).

The dam is basically comprised of 2 stone masonry vertical faced spillways. The main spillway has a length of 69 ft. and a structural height of 32 ft. The secondary spillway has a length of 30 ft. and a height of about 9 ft. The visual inspection did not disclose any findings that indicate an immediate unsafe condition. The size classification is small with a hazard potential of significant. Due to the lack of drawdown capabilities, the dam is considered in fair condition. (Author).

The dam is generally comprised of a 401-foot long, 10 to 28 foot high main spillway, a head gate building, an overflow canal spillway and a canal leading to two 8 foot diameter penstocks used in electrical power generation. There are two inoperable gates located in the main dam. The dam is normally operated with two feet of flashboards above the spillway crest. The visual inspection did not disclose any findings that indicate an immediate unsafe condition. The 1 /2 PMF test flood used will produce an inflow/outflow of 70,830 cfs. The dam is a run-of-the-river type and the spillway crest would be overtopped by about 14 feet. The spillway has a capacity of 29,500 cfs (42 percent of 1/2 PMF outlfow) at elevation 166.6, top of non-overflow section. The non-overflow section is overtopped by about six feet. This flow would not overtop the upstream training walls which are at elevation 174.0. The overall condition of the dam is considered fair due to the lack of adequate draw down capacity. Remedial measures consist of removing vegetation from the downstream face of the dam, further observation of seepage at the right abutment, repair the wooden crest cover, and develop a formal warning system to warn downstream areas in case of an emergency.

Upper Reservoir Dam is a earthen structure with an overall length of 1340 ft. The dam has a height of 30 ft. as measured from the streambed to the crest of the dam. The top width is 9 ft. The upstream face is on a 2.25 horizontal to 1 vertical slope and the downstream slope is 2 horizontal to 1 vertical. The spillway consists of a 25 ft. long crest, concrete weir with training walls, which outlets to a 10 ft. wide stone wall channel. The dam is considered to be in good condition. It is small in size with a significant hazard potential. Keywords include: Visual inspection, Dam safety.

The North Dam is a 318 ft. long earth dam with a maximum height of 34.7 ft. Generally, the dam is in fair condition. There are deficiencies which must be corrected. The South Dam is a 551 ft. long earth dam. The dam is also in fair condition. Both dikes are in fair condition. They also have deficiencies which must be corrected. (Author).