National Program For Inspection Of Non Federal Dams Padanaram Reservoir Dam Ct 00067 Housatonic River Basin Danbury Connecticut Phase I Inspection Report

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.

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.

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.

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.

Margerie Lake Reservoir Dam is an earthfill embankment about 735 ft. long with a maximum height of about 28.5 ft. and a crest width of 10 ft. It is located at the south end of the reservoir. The dike at the north end is also an earthfill embankment, about 1,104 ft. long with a maximum height of about 16 ft. The spillway is located at the right abutment of the main dam, all or mostly in ledge rock, and a 1.2 ft. high concrete control sill with its crest 6.5 ft. below the crest of the dam, near the low point of the valley. The outlet is a 30 in. dia. pipe through the dam and continued in buried trench to the filter plant about 600 ft. south of the dam. No bypass or blowoff from this outlet has been provided. The dam appears to be in good condition. The spillway is adequate to pass the full PMF test flood without overtopping the dam. The north dike also appears to be in good condition. Seepage at the downstream toe of the dam was noted. A toe drain at the north dike appears to be functioning as intended. The outlet control valves may not be serviceable.

The project consists of two earthfill embankments, a spillway with two masonry weirs, and a masonry gatehouse. The upper embankment forms the reservoir dam, and the lower embankment which is 140 + or - feet downstream, forms a filter basin between the two dams. Based upon the visual inspection at the site and past performance of the dam, the dam is judged to be in fair condition. No evidence of instability of the embankments or appurtenant structures was observed. There are some areas requiring attention, maintenance and monitoring, such as seepage on the downstream slope and toe of the filter basin dam, substantial erosion on the downstream slope of the filter basin dam near the outlet pipes and excessive seepage from the gatehouse drain pipe. Deterioration of the spillway training wall and lower spillway weir, and obstructions in the spillway channel were noted. The upper spillway capacity is 29 cubic feet per second (cfs) and the lower spillway capacity is 66 cfs, which is equivalent to 3% and 6% of the routed test blood outflow, respectively.

The dam is a concrete gravity structure with concrete buttresses adjacent to the downstream face of the dam spaced at approximately 18 feet on center. An earthen embankment slopes down from the exposed concrete section at a maximum inclination of 2 horizontal to 1 vertical on the downstream side of the dam. The structure is approximately 1080 feet long and has a maximum height of approximately 48 feet above the old streambed. Outlets consist of a 30 inch cast iron low level line at elevation 172, a 30 inch cast iron transmission main and an 8 inch cast iron service main. The spillway is a 137 foot wide nappe-shaped concrete weir with concrete sidewalls. The area downstream of the dam consists of residential and industrial developments, Connecticut Route 8, and further downstream, urban areas of Stratford. Based upon visual inspections at the site and past performance history, the dam appears to be in good condition. No evidence of structural instability was observed in the concrete section, buttresses or the earthen embankment. However, there are some areas which require attention. Based upon our hydraulic computations, the spillway capacity is 4300 cubic feet per second, which is in excess of 100 percent of the Test Flood. Peak inflow to the reservoir is 2600 cubic feet per second; peak outflow (Test Flood) is 1400 cubic feet per second with the dam maintaining a minimum freeboard of 1.8 feet. It is recommended that the left wingwall adjacent to the spillway be monitored to ascertain whether movement which has occurred to date is continuing.

The dam is a 210 feet long concrete gravity structure with a central concrete round crested ogee weir 40 feet in length, 3.0 feet below top of dam. The dam has a maximum height of 41' feet and a crest width of 6.0 feet. The gate house is adjacent to the left side of the spillway. The regulating outlets include a 16 inch direct supply main and a 20 inch low level intake, which outlets at the toe of the spillway. Based upon the visual inspection and past performance of the dam, the condition of the dam is generally good. The dam appears stable with no signs of movement or settlement. Visual inspection did not disclose an unstable condition due to seepage through the foundation or instability of the dam foundation or abutments. Based upon our hydraulic computations, the spillway capacity is 810 cubic feet per second, which is equivalent to approximately 13 percent of the Test Flood. Peak inflow to the reservoir is 6,600 cubic feet per second; peak outflow (Test Flood) is 6,400 cubic feet per second with the dam being overtopped by 3.6 feet. The spillway is not adequate and will pass only 810 cfs at elevation 290 (top of dam). The average downstream flood stage along Fourmile Brook to its confluence with the Housatonic River will be 10 feet for an outflow of 13,300 cubic feet per second. The major impact of such a flood stage would be to wash out the bridge at Route 34 and another masonry arch located 100 feet upstream of Route 34. Before being washed out, back up would undoubtedly occur effecting a day nursery and at least one dwelling. Thus damage to life and property can occur in the vicinity of Route 34, on the east Bank of the Housatonic River, one mile below the dam.

The dam of the Middle Reservoir is a concrete and masonry structure. It is approximately 300 feet long, 27 feet high and has an average top width of 8 feet. Based on visual inspection and past operational performance, the dam is judged to be in FAIR condition. Seepage and vegetation was noted on the downstream face and the crest is chipped and spalled due to an unfinished rehabilitation project. The test flood for this dam is 1/2 the Probable Maximum Flood (PMF). The test flood has an inflow equal to 770 cfs and an outflow discharge equal to 765 cfs with a stillwater elevation of 269.4 which will overtop the dam by 1.0 feet. These values represent no flood storage in the upstream Beaver Lake. If use is made of the storage capacity of Beaver Lake, the flood inflow to the Middle Reservoir can be greatly reduced. The dam was not overtopped in the 1955 flood because Beaver Lake was low. The maximum outflow capacity of the spillways under a stillwater condition is 132 cfs, which is 17 percent of the test flood.