National Program For Inspection Of Non Federal Dams Stevens Pond Outlet Dam Ma 00232 Merrimack River Basin Lawrence Massachusetts Phase I Inspection Report

The dam appears to be in good condition, The 'V' spillway is 90 ft. long with effective abutments of about 10 ft. on either end. The dam is about 15 ft. high at the abutments. Although the dam is in the small size category the hazard potential is extremely high and thus the situation was analyzed using the full probable maximum flood. A failure of the dam would overflow the left bank immediately below the dam, flood nearby buildings and streets.

Chaffin Pond Dam is actually a section of roadway embankment approximately 135 ft. long, 11 ft. high and with a minimum width of 100 ft. Three submerged culvert outlets pass through the dam between upstream and downstream headwalls, allowing the water level to be the same on both sides of the dam. The control entrance to the assumed 30-in. diameter outlet on the left side has slots for stoplogs; however, none are in place. The control for a 4-ft. box culvert in the center is an open wood gate. The third outlet culvert is also gated but apparently blocked. Water from Chaffin Pond flows to outlet works at a second pond downstream from the dam where water is drawn for hydraulic research purposes. The dam is in poor condition, based on a visual examination of the structure. The headwalls have experienced major structural failures and the potential for a collapse of the upstream headwall with possible obstruction of flow to the outlet does exist. Hydraulic analyses indicate that the test flood would surcharge the pond by 680 acre-ft. and raise the pond level to about 4.2 ft. below the top of the dam. Therefore, no overtopping would be expected.

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.

The 410 ft. by 700 ft., stone lined reservoir which is located near the top of Tower Hill is almost entirely surrounded by an earthfill embankment. The embankment is 1870 ft. long and has a maximum height of 29 ft. There are deficiencies which must be corrected to assure the continued performance of the reservoir and embankment. Generally, both are in good condition.

Lake Wampanoag Dam is approximately 660 feet long including the spillway and has a maximum height of approximately 22 feet. It consists of an earth embankment with riprap at the upstream face and a loamed and seeded crest and downstream face. Based on the size classification (intermediate) and hazard potential classification (high), the spillway test flood is the PMF.

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 consists of an earth dike, about 250 ft. long on the left bank of the river, and a z-shaped stone masonry spillway about 212 ft. long. The dam itself is generally in good condition. There was no evidence of settlement, lateral movement or other signs of structural failure. It is small in size with a high hazard potential.

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.

Pleasant Street Dam consists of an approximately 93 ft. long stone masonry spillway with a brick building at each abutment. The spillway itself is approximately 15 ft. high and probably founded on bedrock. There is a 4 ft. square low-level gated outlet through the spillway structure and stoplogged conduit outlets through the building at the right abutment. The overall condition of Pleasant Street Dam can only be considered fair, primarily because the spillway of the dam was obscured by heavily flowing water and the operation of the low-level outlet was not demonstrated. However, visible portions of the dam are generally in good condition, and the dam is performing adequately. There was no evidence of settlement, lateral movement or other signs of structural failure, or other conditions which would warrant urgent remedial action. With the water level 3.8 ft. above the spillway crest, corresponding to the estimated top of dam level, the spillway capacity is approximately 2,500 cfs, which is 12 percent of the test flood outflow.