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Upper Damon Reservoir Dam Reconstruction

 

Upper Damon Reservoir is a privately owned, 55-acre impoundment with a drainage area of approximately 10.8 square miles. The dam is classified as a High Hazard structure, which was originally constructed over 100 years ago. The preexisting dam consisted of a mortared stone masonry spillway approximately 135 ft long and 15 ft high. The primary concern with the preexisting dam was the structural stability of the stone spillway and the inadequate freeboard of and uncontrolled seepage through the earth embankment. D&K designed the replacement structure using Roller Compacted Concrete (RCC) for its strength, safety, and durability. The design made use of on-site material to manufacture/produce the RCC at the project site over a 24-hour-a-day/7-day-a-week operation with local contractors. RCC is low maintenance, with an expected service life of 75 years or more. The project was the first use of RCC for an active spillway in the State of New Hampshire, and received an Engineering Excellence Award in the Water Resources category from the American Council of Engineering Companies (ACEC-NH). Services include:

Engineering safety inspection
Preparation of EAP
Identification of deficiencies
Hydrologic/hydraulic analysis
Structural assessment
Geotechnical assessment
Breach analysis
Evaluation of repair alternatives
Cost analysis
Preparation of an engineering report
Permitting
Final Plans and Specifications
Construction phase services

Union Village Dam Removal

 

DuBois & King provided planning, design, and construction observation services for dam removal and restoration of a section of the Branch River. The Union Village Dam was a 15-ft-high, 103-ft-long high hazard dam that impounded approximately two acres. NHDES identified the 1861 concrete and masonry dam as deficient in a number of areas, and removal of the dam was the preferred option by the owners. Removal eliminated a hazardous dam that posed a public safety risk and a hydraulic and aquatic organism passage (AOP) barrier from the Branch River. Restoring the river to a more natural state is anticipated to establish an expanded habitat for certain aquatic species. Professional services included:

Site inspection and evaluation
Wetland delineation
Site survey
Plans and specifications
Construction cost estimates
Public outreach program
Utility coordination
Emergency Action Plan (EAP)
Permitting
Coordination with NHDES, NH F&G, and local entities
Construction observation
Grant funding assistance

Maxwell Pond Dam Removal

 

DuBois & King planned and designed the removal of the Maxwell Pond Dam, which necessitated the restoration of Black Brook through the 5.4-acre Maxwell Pond. The pond, once used for purposes such as ice harvesting and recreation, was impounded by a 1900-era dam located immediately upstream of Front Street in Manchester. Development in the watershed resulted in declining pond quality, ecological value, and aesthetics. A storm event caused significant flood damage at and around the dam and prompted the decision to remove the dam and restore the affected area of Black Brook to minimize the potential for future flooding and to reduce future maintenance requirements. Services included:

Site inspection and evaluation
Data collection and review
Preliminary and final designs
Plans and specifications
Hydrologic and hydraulic evaluation
Wetland delineation
Utility coordination
Construction cost estimates
Sediment Analysis Plan
Permitting
Quality Assurance Project Plan
Construction and post dam removal monitoring

Lefferts Pond Dam Reconstruction

 

The Lefferts Pond Dam Rehabilitation project involved the renovation of a 130-year-old earthen, concrete spillway dam owned by the USDA Forest Service. The dam is located at a popular recreational destination. The goal was to rehabilitate the East and West Dams to meet modern dam safety standards and maintain the historic look of the structures. The constructed project consists of a low-maintenance earthen and concrete dam, concrete spillway, pedestrian bridge, and rehabilitated step-pool structure.

Unexpected deterioration of existing structural components was encountered during construction. A solution was designed while construction was under way, keeping the project on budget. Regulatory bodies required construction activities to take place without lowering the level of the 75-acre pond. The contractor constructed a temporary bladder dam of maximum size (11 ft high) to safely retain water.

The design for replacing the stone walls, which made up the downstream abutments, involved building a new concrete wall behind the original abutments and using anchors to mechanically connect cobblestone facing to the new concrete walls. To maintain the historic character of the dam and contain costs, existing cobblestones were reused on the facing of the piers and pedestrian bridge.

Great Hosmer Dam Rehabilitation

 

The Vermont Department of Environmental Conservation selected DuBois & King to investigate and evaluate alternatives and prepare design plans and specifications for repairs to the Great Hosmer Dam. The structure is a 6-ft-high, 23-ft-long masonry dam with a concrete cap, a central stoplog spillway, and a stone discharge channel downstream. The dam impounds the top 6 ft of Great Hosmer Lake, which has a surface area of 155 acres. Built in 1875, the Great Hosmer Dam was in poor condition, with concrete sections deteriorating, an inoperable stoplog/slide gate, scour at the left abutment, sinkholes, and a collapsing stone outlet channel. The dam is on a landlocked parcel of State land, so access to the site must be carefully coordinated with neighboring land owners. Services included:

Review of soil borings
Hydrologic and hydraulic analyses
Structural analysis
Rehabilitation alternatives
Final design, construction documents, and technical specifications
Construction costs estimates

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