National Program For Inspection Of Non Federal Dams Sewalls Falls Dam Nh 00091 Merrimack River Basin Concord New Hampshire Phase I Inspection Report

The dam is a run of the river type dam. It is 633 ft. long with a maximum height of 35.9 ft. The visual inspection of the dam revealed that the dam is in generally fair condition. Noted were some minor cracking and spalling of concrete on the abutments and the poor condition of the gates and mechanical operators. It is intermediate in size with a significant hazard potential. Keywords include: DAMS, INSPECTION, DAM SAFETY, Merrimack River Basin, Concord, New Hampshire, and Merrimack River.

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.

St. Pauls School Dam is a concrete overflow section approximately 15 ft. high from the bottom of the upstream channel to the top of the training walls and approximately 100 ft. long between the training walls. The upstream face of the concrete section is vertical and measures approximately 9 ft. from its crest to a concrete apron on the channel bottom. The dam is in fair condition at the present ime, with a few major concerns which must be corrected. The size is intermediate with a significant hazard potential. The dam could be damaged by the discharge over the abutments. It is not anticipated that lives would be lost. Keywords include: Visual inspection, Dam safety, Merrimack River Basin, Concord New Hampshire, and Turkey River.

The earth embankment and concrete gravity dam is considered to be in good condition. It is believed to be safe under normal operating conditions. Based on size and hazard classifications in accordance with Corps guidelines, the test flood is the Probable Maximum Flood. In addition to the long term recommendations, there are several remedial measures which should be implemented immediately. (Author).

The Souhegan River Watershed Dam No. 26 is located on Blood Brook, a tributary of the Souhegan River, approximately 2 miles upstream of West Wilton, New Hampshire. The dam is an earth embankment 692 feet long and 79 feet high with a drop inlet service spillway structure and a 30 inch outlet conduit. An emergency spillway 320 feet wide is cut into the left abutment.

Concord Water Works Dam is an earthen embankment approximately 9 feet high from crest of dam to toe of slope and 265 feet long. The upstream face of the embankment is protected by a 1.0 foot thick concrete wall, a concrete slab and granite block riprap which extends to the bottom of the reservoir. There is no emergency spillway. The dam is in fair condition with a few major concerns which must be corrected. The dam is intermediate in size with a significant hazard potential. The test flood ranges from 1/2 the PMF to full PMF. There are various remedial measures which should be implemented by the owner. Keywords include: Inspection, Dam safety, Merrimack River Basin, Concord, New Hampshire, and Rattlesnake Brook.

The concrete dam is about 180 ft. long and is constructed on a circular arc. It is small in size with a low hazard potential classification. The dam is in fair condition. At the present time, there is no way to draw down the level of the reservoir. A program of annual technical inspections of the dam should be undertaken.

The dam is a gravity structure constructed of split masonry. It is about 80 ft. long and 17 ft. high. The dam is small in size with a significant hazard potential. The dam is in poor condition at the present time. There are remedial measures and studies which should be implemented by the owner as soon as possible. (Author).