Dam and Hydroelectric Engineering

This project entailed removal of the Great Moose Lake Dam in Hartland, Maine, and design and construction of a replacement structure. The April 1987 flood caused significant damage to portions of the right gate structure and the ogee spillway. A 60-foot-long section of the ogee spillway approximately 4-feet thick and up to 3-feet high failed and was washed away. The right gate structure lost a section of concrete measuring approximately 1.5 x 7.5 x 5 feet.

In 1987, the Army Corps of Engineers evaluated several repair and replacement options. They concluded that, given the instability of the then-existing spillway and left gate structure, construction of a new dam was the most prudent alternative. With this alternative, the existing dam could be used as the upstream coffer dam during construction activities.

After being retained to design the replacement dam, Acheron performed a hydrologic study and a geotechnical investigation. The information obtained through these activities was used in the design of a new dam. All phases of the design were reviewed by FEMA’s engineering consultant. During design, Acheron also met with representatives of the Department of Inland Fisheries and Wildlife (DIFW) to develop a method for downstream passage of alewives. Acheron obtained all required State and Federal permits for dam construction.

Acheron was instrumental in obtaining 100-percent funding for the new dam from FEMA and MEMA. The dam includes a 29-foot-high gate structure housing three 9 ½ x 12-foot cast-iron sluice gates, a 100-foot ogee spillway, and a left abutment that contains a minimum-flow pipe and fish passageway. An on-site project representative provided construction monitoring.

In 1991, this dam was dedicated as Morgan Dam, in honor of the efforts of Ms. Peggy Morgan, Hartland’s Town Manager.

Each year since 1986, Hydro Projects North (HPN) has retained Acheron to visually inspect the Whitin Reservoir and Manchaug Reservoir Dams. These dams are located in East Douglas and Sutton, Massachusetts, respectively. The inspection program is conducted for the following purposes:

1. to visually assess the physical condition of the dams and their appurtenances,

2. to visually determine whether significant changes have occurred in the dam's physical condition during the previous year,

3. to review dam operating records and measurements compiled by HPN during the previous year,

4. to evaluate dam-maintenance activities performed by HPN during the previous year,

5. to report to HPN any recommendations developed as a result of the tasks described above.

In 1990, the Gilboa Pond Dam, located in East Douglas, Massachusetts, was added to the program at HPN’s request.

Since the inception of this program, many improvements have been made to the physical condition and operations of these dams. Additionally, Acheron assists HPN personnel in day-to-day dam operations by evaluating stream flows and weather forecasts and assessing their potential impacts on water-level goals and stream-flow requirements. Based upon this information, Acheron provides recommendations on whether to change gate openings and/or install/remove flashboards.

In June 1998, western Massachusetts was inundated with a significant rainfall event that raised reservoir levels throughout the region, including the Whitin Reservoir in Douglas, Massachusetts. A dam owned by Hydro Projects North (HPN) maintains the Whitin Reservoir. During the June 1998 event, water levels in the reservoir began to rise. Water could not be safely released from the reservoirs dam due to the malfunction of a stoplog gate and the hydraulic limitations culverts positioned in a causeway within the reservoir. As a result, water in the upper reaches of the reservoir rose to a level that ultimately began to backflow out of the reservoir through a naturally occurring swale. The backflow of water began to erode the surrounding area and, due to the topography of the area, threatened to drain the entire reservoir.

HPN contacted Acheron to address this potential disaster. An Acheron engineer immediately traveled to the site and worked with the local authorities to assess the situation and develop a plan of attack to stave off the disaster.

To stop the backflow of water from the reservoir, Acheron’s engineer field-engineered an earthen levee to fill the low spots in the swale through which water was back-flowing. The levee design included placement of low permeability soil and riprap. The constructed levee was able to stem the flow of water.

Once the immediate danger of a significant flood was averted, Acheron then worked with HPN to develop a design for a more permanent earthen dam for this low area, and an adjacent area that was only slightly higher, but still a possible area for future backflow problems. Acheron developed a detailed design for the necessary structure and worked closely with HPN officials to obtain the necessary State and local permits necessary to construct the final earthen dam.

With the permits secured, HPN undertook construction of the final structure in the fall of 1998.

In response to comments from the Massachusetts Office of Dam Safety, in 1990, HPN requested Acheron to assist in preparing an Emergency Action Plan (EAP) for the Whitin Reservoir and Manchaug Reservoir Dams. As a result, Acheron prepared inundation mapping for the river basins downstream of the dams. Each map included an aerial photograph and a copy of the U.S.G.S. map for the study area. Two lines on each map depict the approximate 100-year flood plain and the outer limit of the inundation zone expected to be caused by a combination of dam failure and the flood during the spillway design flood. These maps were also accompanied by written descriptions of the procedures used in their preparation, as well as recommendations for routine inspection and maintenance programs for the dams in the event of an emergency.

Acheron was retained in August 1994 to design and monitor the construction of a replacement dam of the West Branch of Davis Stream in the Town of Jefferson, Maine. The previous dam was a timber-crib structure which experienced significant leakage because it overlaid the Presumpscot Soil Formation. The Soil Conservation Service evaluated the Dam and deemed it a Class C Hazard because a number of structures existed in its flood plain and the stream flowed under two (2) State highways. Furthermore, a flood in April 1993 did extensive damage to the dam, rendering it almost useless. The project fell under the jurisdiction of both FEMA and Maine Emergency Management Agency (MEMA).

A number of issues needed to be addressed in this project. First, the Town wanted to maintain the historical aesthetics of the original timber-crib dam and of an historic mill building adjacent to the dam. Second, a bridge for Route 126 crosses Davis Stream immediately downstream of the dam; a wingwall of this dam was constricting the water flowing under it. Third, the soil conductivity of the alluvial plains under the dam site allowed for seepage. And fourth, the adjacent mill building was rotting because of the water flowing under it.

To address these issues, Acheron had to complete several tasks in cooperation with other parties. First, Acheron decided that the dam would not be strong enough if it were replaced with another timber-crib structure. However, to address the desires of the Town, Acheron designed a concrete structure for the stream's flow and a timber-crib facade to be added to the concrete so that the dam resembled the earlier dam. Second, the wingwall of the bridge was replaced under the supervision of the MDOT. To address the seepage, cut-off walls and timber piles were driven into the clay around the dam. A wall was added to the dam to protect the mill building from water and to retain the historical aesthetics of the building. Finally, the Town objected to using pressure-treated lumber on the timber-crib facade because it typically has a greenish tint. Consequently, Acheron located and incorporated into the dam's design a pressure-stained and pressure-treated style of lumber from a firm in New York. Construction of the dam began in the fall of 1994 and was substantially completed by January 1995.

In 1994, the Town of Mercer and the Maine Department of Inland Fisheries and Wildlife (DIFW) retained Acheron to remediate several failures in the Mercer Bog Dam. The dam was a granite and concrete structure over which Mercer’s Main Street passes. The dam also divides the Mercer Bog, which is owned by the DIFW, and Bog Stream. Therefore, both the Town and DIFW own the dam. An outlet control box is located approximately midway along the length of the dam and controls the outlet flow into Bog Stream. During the April 1993 flood, water leaked through the upstream granite retaining wall and caused failures in several areas of the downstream granite retaining wall. The damage was augmented by penstocks, or pipes once used by downstream industries to draw water from the dam. The penstocks allowed water to build up behind the downstream retaining wall.

Acheron was retained by the Town and DIFW to repair the upstream retaining wall and concrete outlet box and to construct new downstream retaining walls. As a first step, we located the penstocks that had allowed seepage behind the downstream wall. After they were located, their intakes were plugged and their outlets were extended into catch drains to collect seepage from them. These catch drains emptied into two catch basins built immediately upstream of the upstream retaining wall. The catch basins and the granite upstream wall were covered by gravel and a new concrete retaining wall. A concrete downstream retaining wall was also built over the existing downstream wall. A granite façade was designed to match the original aesthetics of the dam, but was deemed beyond the scope of this project.

Throughout this project, Acheron worked with both the Town and the DIFW to ensure that the project would be completed to the satisfaction of both clients. Construction of the dam began in September 1994 and was substantially completed by December 1994. The finished dam is approximately 130-feet long including the outlet box, 29-feet high and 50-feet wide. Engineering costs for this project were $74,000. Construction costs were $281,000. Acheron assisted in securing 75-percent Federal funding and 15-percent State funding.

This project involved design and construction of a replacement for flood-damaged portions of the Sebasticook Lake Dam in Newport, Maine. The April 1987 flood caused almost total failure of this dam several days after floodwater peaked at 2.1 feet above the level of the eastern spillway. In addition to the washout of the westerly section of the dam, the west side of the timber-crib structure suffered significant damage and bowed downstream approximately 12 to 14 inches due to the increased loadings during the flood. The dam also tilted downstream, allowing a considerable amount of leakage and flow under the dam.

Acheron was retained by the Town to assess the damages and recommend suitable measures for dam repair/replacement. A geotechnical investigation and hydrologic study were performed. Because the concrete was relatively new and was not affected by the flood, Acheron recommended that only the damaged timber-crib section be replaced. Subsequently, we designed and monitored the construction of an approximately 100-foot-long ogee spillway. All required state and federal permitting for this project was obtained by Acheron. Acheron also assisted in obtaining 90 percent State and Federal funding for this project.

This project involved the evaluation and final design of the Milliken Mills Dam in Old Orchard Beach, Maine. Over the two (2)-day period of October 20, and 21, 1996, southern and coastal Maine experienced a major storm event causing record levels of rainfall throughout the region. The intensity and duration of the storm produced heavy runoff and flooding that devastated the Milliken Mills Dam at the Portland Avenue crossing of Mill Brook. Prior to the October storm, the Milliken Mills Dam was an integral component of the Milliken Mills Bridge spanning Mill Brook. The flood flows generated by the storm runoff caused complete failure of the dam and bridge embankment.

Acheron was retained by the Town of Old Orchard Beach in May 1997 to design a replacement of the Milliken Mills Dam. Specifically, the replacement dam was to be constructed as an integral component of a new bridge structure. The design of the integrated bridge and dam structure took into account the Town's desire that the new dam restore the normal pond elevation in the impoundment to the elevations that existed prior to the old dam's failure, and that the structure demand minimal operational and maintenance attention. To meet these goals and the structural needs of the dam, the Town elected to construct a new cast-in-place concrete gravity structure with an ogee spillway.

The bridge structure was constructed of precast CON/SPAN bridge units set on top of cast-in-place concrete stub abutments. The bridge units have a clear span opening of 32.0 feet. This clear span was dictated by the hydraulic requirement to pass the desired design flow of 1,110 cfs and maintain a bridge deck elevation of approximately 41.0 feet. To facilitate flow to and away from the bridge structure, cast-in-place concrete wingwalls were constructed upstream of the bridge and precast wingwalls placed downstream of the bridge.

The Town removed the existing upstream bridge abutments and regraded the surrounding area to promote flow to the bridge structure. These existing bridge abutments were abandoned in 1951 and remained only to serve as a utility right-of-way for a water main that was suspended between the abutments. During construction, the water main was rerouted through the dam structure facilitating removal and regrading of the bridge abutments. The final design was reviewed by FEMA's engineering consultant and Maine Emergency Management Agency (MEMA) personnel. Acheron also retained all required State and Federal permits required for construction of the replacement structure. Construction of the dam and bridge structures began in the fall of 1997 and was completed in the spring of 1998.

In cooperation with Robinson Manufacturing Company, the Thompson Lake Environmental Association, the DEP and the DIFW, Acheron completed an Operations Plan for Thompson Lake Dam. The basis of this plan is a rule curve defining the desired maximum and minimum water levels for Thompson Lake throughout the year. Acheron developed this curve through computer modeling of the Thompson Lake watershed.

The overall goal of the plan was to successfully address the concerns of all parties involved. The rule curve makes provisions for togue spawning, loon nesting, and recreation in Thompson Lake while also satisfying Robinson’s State requirement to maintain a minimum 25-cubic foot/second (cfs) flow in Thompson Lake Outlet Stream. Acheron believes that the success of this project demonstrates the excellent results that can be achieved in a spirit of cooperation.

Scope of Services: Design of cutoff wall and Steeppass Fishway

During the winter of 1997-98, the Stetson Pond Dam was subjected to significant erosion damage that compromised the dam’s integrity. The damage allowed water from the pond to seep around the dam, increasing the level of erosion. The Town of Stetson contacted Acheron to assist them in repairing the dam. As a short term solution, Acheron recommended a sand-bagging program to stem the seepage around the dam and the placement of low permeability soil adjacent to the dam and a protective layer of riprap. This program was implemented and stabilized the dam.

A long-term solution for the dam’s problems needed to be defined. The Town hired Acheron to develop recommendations to permanently repair the dam. Acheron conducted a site investigation including soil probings and recommended the installation of a concrete cutoff wall adjacent to the dam and the placement of grout under the existing dam to prevent any further seepage either under or around the dam.

The limiting factor for the Town was project financing. The Town could not afford to repair the dam without some economic assistance. The Town again sought Acheron’s assistance and advice. Acheron worked with the Town to identify available funding sources for dam repairs and was able to develop a plan for the Town to receive project funding from both the Maine Department of Marine Resources and the National Resources Conservation System totaling over 80 percent of the estimated project cost of $60,000.

The key to obtaining this funding was the inclusion of a steeppass fishway as part of the dam repairs to restore the natural migration pattern for alewives. The Department of Marine Resources indicated that it was planning to install fishways at a number of dams on the waterways that are downstream of Stetson Pond. The pond is the head of the waterway and represents the ultimate goal of migrating fish. Acheron worked closely with the Department to then gain the involvement of NRCS, which participates in projects aimed at restoring or maintaining fish migration patterns.

Once the project funding was secured, Acheron developed a final design for the concrete cutoff wall and the integral steeppass fishway. Detailed design drawings and contract documents were developed and project permits were obtained. The project was completed in the fall of 1999.