D&K designed the temporary breach of a failed spillway on an 800-foot-long earthen dam. D&K’s water resources staff completed the breach design and provided permitting assistance. D&K assisted the owner in choosing repair/reconstruction alternatives to restore the water body to its originally designed condition. The owner elected to pursue a permanent breach of the dam.
Pomainville Dam Removal
D&K provided evaluation, survey, and preparation of permit applications for an earthen dam. Vermont Agency of Natural Resources (VANR) personnel determined that the dam’s original 30-inch diameter metal spillway riser had been replaced with a 24-inch plastic pipe and the emergency spillway had been filled to the crest elevation of the dam. Presented three potential remedy options to bring the dam back into compliance with VANR dam safety regulations. The determination was made to remove the dam. D&K was responsible to provide hydrologic analysis of the watershed using HydroCAD, and prepare conceptual and final designs for removal of the dam and restoration of the stream. D&K completed the dam safety permit and coordinated with Vermont State wetlands and dam safety officials. D&K provided construction observation services.
Geer Dam Removal
DuBois & King designed a partial removal of the Geer Dam, a former hydroelectric, run-of-the-river dam on the Ompompanoosuc River. The combination concrete gravity and buttress dam was constructed by a private individual in the early 1980s (designed by DuBois & King). The dam has been identified as an obstruction to aquatic organism passage (AOP) and a source of local fluvial geomorphic instabilities evidenced by downstream channel incision and bank instability.
Removing a portion of the dam restored AOP and improved geomorphology. The D&K team performed a structural evaluation, developed a hydraulic model, and determined geomorphic compatibility to identify the effects of partial removal of the dam on the stream and the remaining section of the dam. Services also included a topographic survey of the dam and river reaches up- and downstream, wetland delineation, AOP evaluation, preliminary through final design, and construction observation.
Norwich Reservoir Dam Removal
The Norwich Reservoir Dam was a run-of-the-river, cyclopean gravity dam located on the Charles Brown Brook. The dam formerly impounded a reservoir, but had has no function and caused significant negative impacts to the brook and to downstream reaches. DuBois & King developed removal design to meet the objectives of restoring AOP and the natural functions of Charles Brown Brook through the reach occupied by the obsolescent dam and infilled impoundment.
The reach of the brook above the dam silted in and became a wetland, such that no aquatic organism passage was possible. As a part of the removal design, the project team chose to remove the high-nutrient silt in the impoundment. Services included topographic survey, wetland delineation, hydrologic and hydraulic modeling, geomorphic assessment, regulatory coordination (with the Army Corps of Engineers, State Dam Safety Program, and State Wetlands Program), and community outreach.
Wason Pond Dam Reconstruction
The Town of Chester acquired Wason Pond to preserve the area for public recreational use. DuBois & King conducted an engineering evaluation to assess the condition of the dam and identify short-term repairs and long-term improvements. The primary concerns with the dam was inadequate hydraulic capacity, structural stability, and seepage. This effort led to a full rehabilitation of the dam.
The dam is an earthen embankment with a concrete overflow spillway located near the left abutment. The dam is approximately 165 ft long and 15.5 ft high. Dry laid-up stonewalls form the downstream face of the spillway and adjacent walls. The spillway consisted of a concrete slab set on top of laid-up stones and had a clear width of approximately 18 ft at the upstream crest. Removable flashboards were located along the upstream edge of the spillway crest. The drainage area into the pond is approximately 1,633 acres (2.55 square miles).
The required capacity of the spillway was greater than what the site would accommodate. Due to the confines of the site, the spillway was designed as a two-cycle labyrinth weir to achieve the hydraulic capacity. The rehabilitation included concrete training walls, a seepage cut-off wall, and installation of a mineral toe drain filter for seepage control.
To meet schedule objectives, the project was developed to utilize winter construction. The dam accommodated a new pedestrian crossing, linking hiking trails and improving recreational opportunities of the area. D&K’s services included:
Coordination with NHDES Dam Bureau
Engineering safety inspection
Identification of deficiencies
Structural assessment and design
Hydrologic and hydraulic analysis and design
Geotechnical assessment and design
Evaluation of repair alternatives
Cost analysis
Preparation of an engineering report
Bid phase services
Construction engineering and oversight