National Program For Inspection Of Non Federal Dams Rockwell Pond Dam Ma 00882 Merrimack River Basin Leominster Massachusetts Phase I Inspection Report

Rockwell Pond Dam is a 460-foot lon>, 20-foot high earthfill dam built in the 1800's. The 75.7-foot long, modified sharp-crested spillway has a crest at El 416.4. A concrete bridge spans the spillway channel. The main outlet is a 12-inch diameter pipe controlled by a valve which is submerged in a manhole. The following deficiencies were observed at the site: mssing riprap and localized growth of brush and small trees on the upstream face of the right embankment; localized erosion of upstream and downstream earth slopes; voids exposing soil behind the spillway weir wall; cracked or missing mortar from joints in the spillway training walls; spalled concrete and exposed reinforcing steel on the bridge pier; efflorescence and spalling on the underside of the bridge deck; a submerged inoperable valve on the main outlet; and an inoperable slide gate on the intake of the auxiliary outlet. The test flood would overtop the dam by about 1.6 feet. The spillway can discharge 60 percent of the test flood before the dam is overtopped.

Simonds Pond is approximately 365 feet long and has a hydraulic height of 26 feet. The storage capacity is 86.5 acre-feet. The dam has a concrete cap and stone abutments. The emergency spillway is 48 feet long and occupies the center portion of the dam. As a result of the visual inspection and a review of available data, Simonds Pond Dam is considered to be in poor condition. Major concerns are: significant seepage at the toe of the dam; missing mortar and poor condition of the joints of the spillway; extensive spalling and cracking of the concrete cap on the top of the dam and spillway; deterioration of the spillway apron; extensive spalling of the concrete gatehouse foundation; and inadequate spillway capacity. The test flood inflow was estimated to be 2,500 cfs and resulted in an outflow discharge estimated to be 2,460 cfs, which would overtop the dam by approximately 1.3 feet. The maximum spillway capacity with the water level at the dam crest was estimated to be 700 cfs, which is approximately 28 percent of the test flood discharge.

The dam is a 470 ft. long earthfill dam with a maximum height of 14 ft. There are deficiencies which must be corrected to assure the continued performance of the dam. Generally the dam is in poor condition. It is small in size with a hazard potential of high. (Author).

The impounding structures at Fall Brook Reservoir include a 1392-foot long, 37-foot high main dam with a spillway and outlet, and a 256-foot long, 11-foot high dike. The spillway is located at the south abutment of the dam, and consists of a broad-crested weir 19 feet long with vertical stone masonry training walls that extend the length of the discharge channel. The outlet for the dam consists of a 30-inch diameter cast-iron pipe which discharges at the toe of th dam. The dam is generally in fair condition. The test flood outflow of 2,370 cfs and pool at El 657.6 will overtop the dam by 0.6 feet and the dike by 1.4 feet. The spillway capacity at El 646.2 (the low point on the crest of the dike) is 500 cfs, which is 21 percent of the test flood outflow.

Crocker Pond Dam is a 520-foot long earthfill dam built in 1933 for storage. The facility has a maximum height of 38.5 feet and includes a spillway, flood gate, gate house and outlet structures. The spillway is a concrete ogee weir, 120-feet long (including the closed flood gate). There are five separate outlets for the dam, and 8-foot wide by 12-foot high flood gate, which when closed is part of the spillway; a 42-inch diameter main low level outlet; a 24-inch diameter auxiliary low level outlet; a 3-foot square drain; and a 3-foot square trash chute. The following deficiencies were observed at the site: spalled, cracked and deteriorated concrete on the east and west approach channel sidewalls, the spillway face, the sidewall between the spillway and the flood gate, the east and west sidewalls of the spillway, and the west face of the gate house; burrow holes and foot paths on the downstream face of the dam; missing stones along the downstream bench of the east section of the dam; logs and debris caught on the spillway weir and trees overhanging the west side of the downstream channel. The test flood would overtop the dam by 2.2 feet with no flashboards in place andf 3.8 feet with flashboards in place. Hydraulic analyses indicate that the spillway without flashboards can discharge 10,500 cfs, or 57 percent of the test flood outflow before the dam is overtopped with flashboards, the spillway can discharge 6,300 cfs or 34 percent of the test flood outflow before the dam is overtopped. This assumes that the flood gate remains closed during the test flood.