National Program For Inspection Of Non Federal Dams Parks Pond Dam Ct 00071 Housatonic River Basin Danbury Connecticut Phase I Inspection Report

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.

Mercers Pond Dam is an earth embankment approximately 400 feet long and 17 feet high. Granite blocks line the downstream face (250 feet). A 39-foot long spillway is located at the western end of the dam. There is a 24-inch discharge pipe with a slide gate on the upstream face of the dam. The gate is not operable. The drainage basin is 4.5 square miles on which 3.3 square miles is controlled by another dam upstream. There is approximately 61 acre-feet of storage available. 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 fair condition with several areas that require attention. These areas include seepage along the toe of the dam, the poor condition of the stone face and the nonoperating status of the discharge pipe. The dam is classified as small and has a high hazard potential in accordance with guidelines established by the Corps of Engineers. The test flood for these conditions is the Probable Maximum Flood (PMF). The test flood inflow is 6,150 cfs and the routed test flood outflow is 5,885 cfs. The test flood will overtop the dam by 2.75 feet.

The West Lake Reservoir Dam is an earth embankment that is approximately 450 feet long and 31.7 feet high. The embankment has 1.5:1 side slopes and has a puddled clay and gravel core. The spillway is located through the northern abutment of the dam and consists of a 120-foot long concrete weir. There are upper and lower gate houses for the control of 30-inch water main and a 24-inch blowoff that passes through the base of the dam. The valves for the operation of the water main and the blowoff are in the lower gate house and are inoperable. The drainage area is 3.3 square miles and the reservoir has 3,430 acre-feet of available storage. The assessment of dam is based on the visual inspection, past operational performance and hydraulic/hydrologic computations. The dam is judged to be in fair condition with several areas that require attention. These areas include seepage through the dam and along the toe, steepness of the embankment, vegetation on the embankments, along the toe of the dam and in the spillway channel and the nonoperating status of the blowoff. The dam is classified as intermediate and has a high 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 6,520 cfs and the routed test flood outflow is 3,890 cfs. The test flood outflow will overtop the dam by 1.0 feet.

The maximum height of the dam is 27 feet at the left edge of the spillway. The reservoir storage at the top of dam is 11 acre-feet. There are both upstream and downstream spillway training walls composed of mortared and hand placed cobbles respectively. The visual inspection of Risdon Pond Dam indicated that the dam is in fair condition. The inspection revealed that the unprotected upstream face has been slightly eroded by wave action. The downstream face of the dam has a number of blocks which have been displaced, cracked or have unmortared joints, Grass, moss and small trees are growing out of some of the joints. There are several areas of seepage along the downstream wall both sides of the spillway. There is a 3-foot deep depression on the left downstream wall of the dam. Also, there are five large tree stumps along the crest of the dam and a footpath traverses the crest. The spillway will discharge 220 cfs, or 16% of the test flood with the pool level at the top of the dam. The test flood flow of 1420 cfs will overtop the dam by 2.0 feet.

The Padanaram Reservoir Dam is an earth embankment with a stone masonry faced downstream slope that is approximately 325 feet long and 26.3 feet high. The downstream stone face is on a 1:12 slope and the upstream earth embankment is on a 2.25:1 slope. The spillway is located at the southern abutment of the dam and is 24-foot long channel. There is a lower gate house in the center of the dam for the control of a discharge pipe that passes through the base of the dam. The size of the discharge pipe is unknown and the valve for its operation is inoperable. The drainage area is 3.7 square miles and the reservoir has 52 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 fair condition with several areas that require attention. These areas include seepage through the dam and along the toe, vegetation on the stone face and along the toe of the dam and the nonoperating status of the blowoff. The dam is classified as small and has a high 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 3,608 cfs and the routed test flood outflow is 3,460 cfs. The test flood outflow will overtop the dam by 2.3 feet.

Wilton Pond Dam is a stone masonry structure 42 feet long with a maximum height of 16 feet. A centrally located depressed spillway section has been grouted and passes water over the dam. There is no outlet works associated with the dam. Wilton Pond is used as fire pond by the Town of Plymouth and functions as a passive recreational area. The lake has a maximum storage volume of 63 acre-feet. The dam is judged to be in generally poor condition. Seepage is evident around the right end of the dam exiting through gaps in the stone masonry and the right abutment area. Erosion is taking place on the left abutment and extensive grass cover was noted at the right side of the dam. The recently reconstructed spillway section is in good condition. The capacity of the spillway is inadeqaute to pass the 100 year storm test flood outflow (631 CFS) without overtopping the dam. the test flood would overtop the dam by about 0.7 feet. The spillway is adequate to pass 42 percent of the test flood outflow without overtopping the dam.

South Pond Dam is an earthen embankment dam with a vertical stone masonry wall downstream face. The embankment is approximately 300 feet long and has a maximum height of 19 feet. The dam has two spillways. The visual inspection of South Pond Dam indicated that the dam is in fair condition. The inspection revealed that lack of adequate riprap of the upstream face has caused erosion at the splash zone of the embankment. Tree stumps exist in the downstream slope of the embankment along the right training wall and buttress wall of the center spillway. Bulges up to 3 feet offset were located in 3 areas of the vertical stone wall on the downstream face of the dam. Water with staining was observed along the downstream toe along the right side of the embankment. Erosion was found adjacent to the emergency spillway on the left abutment. Brush, trees and debris are located in the downstream channel of the left spillway. Animal burrows were found in the embankment. The spillway will pass 590 cfs or 16% of the test flood with the pool level at the top of the dam. The test flood flow of 3900 cfs will overtop the dam by 2.1 feet.

East Lake Reservoir Dam is an earthfill embankment about 550 ft. long with a maximum height of about 36 ft. The original dam has been raised and widened to accommodate a local road. The spillway is located at a natural saddle and draw about 300 ft. to the left of the left abutment of the dam. A 15 ft. span bridge constricts the spillway outlet channel. The main outlet is a 16 in. dia. pipe through the dam with a blowoff valve below the toe. A 12 in. dia. pipe connects the outlet pipe to Margerie Lake Reservoir. A second pipe outlet, 12. in. dia., is located near the left abutment. Marshy areas below the dam indicate probable leakage from the reservoir in the vicinities of the two outlet pipes. The serviceability of the outlet control and blowoff valves is doubtful. Both sides of the roadway across the dam are unstable and sloughing down. The dam is judged to be in fair condition. The spillway capacity is inadequate to pass the full PMF test flood outflow of 6,050 cfs; it would pass 50% of the test flood. The test flood would overtop the dam by about 1.7 ft. and the spillway discharge would be 1,750 cfs.