- LocationWindsor, Vermont
- OwnerTown of Windsor
- EngineerGeoDesign Inc.
- 45’ deep sediment dredging
- Sediment treatment and dewatering for environmentally sound offsite disposal
- 50’ Deep design/build cofferdam
- Underwater investigation and construction
- Removal and installation of new Low Level Outlet Gate
Meeting the challenge of a difficult job.
The Windsor Upper Dam is a 179 year old masonry gravity dam on the National Historic Register. The dam has been modified many times and has experienced various failures over the years. The low level drain for the dam had been inoperable for years and needed replacement to lower water levels at the dam. The upstream side of the dam was submerged in more than 10 vertical feet of silt that obscured the gate and the lower portion of the dam. Once the silt was removed by dredging, it was discovered that the configuration of the dam at the gate location was significantly different than shown on the plans. A sloped half pipe with tangent cofferdam was designed for embedment in tremie seal and attachment to the dam face. The design was developed to minimize lateral loads into the dam as required by specification.
An Award Winning Project
Our work on this project resulted in Kingsbury Companies receiving the AVG Vermont Best Builders Award in 2013 for the “SPECIALTY CONSTRUCTION” category.
Innovation in construction techniques, materials or scheduling.
The 40’ cofferdam was custom fabricated to account for irregularities of the dam face based on dive reports made in near zero visibility water. Load spreading flanges were attached at the dam interface to reduce point loads on the dam and a rubber bulb seal was attached to facilitate final dewatering. Hooked #10 reinforcing bars were epoxied into the existing rock bottom and were tied to reinforcing mats embedded in the tremie seal to counteract buoyancy. The cofferdam was constructed offsite in three separate pieces to facilitate transport and installation. Gasketed, flanged connections were utilized at the joints for a watertight connection.
Projects contribution to the community.
During Hurricane Irene, the historic dam was overtopped with record breaking flood waters. Preceding the flood, the Town of Windsor had no way to mitigate the potential damage from the flood by lowering the pond elevation before local rivers began overtopping their banks. The new gate now gives the town control of the pond levels for maintenance, repair and flood control.
Sensitivity to the environmental surroundings.
Pond levels during construction were required to remain between specified pond levels to preserve upstream fisheries so a substantial portion of the work occurred in the water. A complete silt curtain was employed and maintained to allow control of downstream turbidity. Tremie concrete pours required isolation from the water flowing downstream. Turbidity in the water was monitored regularly throughout the project.
Outstanding safety record.
For the duration of the diving portions of the project, the dive team consistently met requirements for redundancy, supervision, communication and reporting. While working in the dewatered cofferdam, confined space requirements were strict, regimented and thorough. Contact was regularly maintained with Hartford Fire and Rescue as Windsor Fire does not have confined space rescue capability. Over the span of the 13 month project, there were zero accidents or injuries.