National Program for Inspection of Non-Federal Dams. Bashan Lake Dam (CT 00354), Lower Connecticut River Basin, East Haddam, Connecticut. Phase I Inspection Report

摘要

The dam is a gravity stone wall-earth fill structure founded on rock with a near vertical partially arched granite block retaining wall on the downstream face, and a concrete retaining wall on the upstream face. The dam rises approximately 23 feet above the bed of the Moodus River and has a maximum top width of 35 feet and a length of 169 feet. The spillway is a 29 foot long, broad crested weir of trapezoidal cross-section with an inclined sand and gravel upstream approach and a natural rock exposure as a downstream discharge channel. The low level outlet, a stone culvert approximately 2.1 by 2.5 feet in size discharges at approximate elevation 364.7 to a naturally eroded rock channel. The size, type and invert elevation of the upstream inlet was not ascertained. The gate is operable, but not only with difficulty. Based upon the visual inspections at the site, the dam appears to be in fair condition. No instability of the dam was observed, however conditions were identified which could have a direct bearing on the future stability of the dam. One such condition was in the area of the spillway where significant flow was coming from between and below the granite blocks directly under the spillway crest. The other major concern is the insufficient capacity of the spillway itself. There are other areas requiring monitoring and minor maintenance, as well. The Test Flood will be equivalent to one-half the Probable Maximum Flood (PMF). Peak inflow to the lake is 2200 cfs; peak outflow (Test Flood) is 700 cfs with the dam overtopped 1.0 feet. Based upon our hydraulics computations, the spillway capacity is 165 cubic feet per second (cfs), which is equivalent to 24% of the Test Flood.