ROLE OF THE FIRM IN THE PROJECT

Transcription

1 PROJECT DESCRIPTION Lake Loramie Dam is a Class I dam located in Lake Loramie State Park in Minster, Ohio. Lake Loramie originally served as the high feeder water supply for the Miami-Erie Canal that began operation after the original dam was constructed in The canals were eventually abandoned and Lake Loramie began to serve as a recreational lake. A new spillway was constructed in 1908 and featured a concrete straight drop buttressed spillway that was 220 feet long and 15 feet high. The spillway was flanked on either side with a variable height earthen embankment that totals approximately 6,575 feet. A 2013 report indicated that the spillway, pedestrian bridge, lake drain, and portions of the abutments exhibited significant deterioration that would be difficult and costly to repair. Due to the extensive deterioration of the existing concrete spillway and lake drain, the Ohio Department of Natural Resources (ODNR) proposed to implement interim risk reduction measures to rehabilitate the existing spillway and address lake drain deficiencies. The improvements to the Lake Loramie dam included: embankment construction (including cutoffs, drains, and filters) construction of labyrinth spillway, stilling basin, bank floodwall, and control tower lake drain upgrades (including stop logs, sluice gate, and low flow valve) demolition of existing spillway instrumentation for monitoring pedestrian bridge over the new spillway site upgrades to the immediate dam area The Lake Loramie dam improvements project was undertaken as part of a statewide initiative by ODNR to evaluate and rehabilitate state-owned dams to ensure the safety of Ohio s lakes and surrounding communities. Normal pool was maintained throughout construction to limit the impact to the park, homeowners, and businesses surrounding the lake. Multiple meetings were held with the public to ensure the community was informed about the rehabilitation project and to address public concerns. Ultimately the project resulted in a new labyrinth spillway and a new earthen embankment to tie the existing embankment to the new spillway. A new lake drain system was incorporated into the spillway to aid in planned and emergency drawdown situations. The top of the old spillway was removed to approximately 5 feet below normal pool and the remainder abandoned in place allowing for additional lake area to be created. ROLE OF THE FIRM IN THE PROJECT Michael Baker provided engineering services for the rehabilitation of Lake Loramie Dam. Michael Baker s services included dam assessment, subsurface investigation, environmental assessment and delineation, cultural resource investigation, hydrologic and hydraulic analysis, geotechnical analysis, structural analysis, permitting, mussel relocation, final design, construction bid documents, and construction management and inspection services.

2 Construction documents included plans and specifications for the bidding of the project. Michael Baker also provided construction management and oversight to ensure that the construction was conducted in accordance with the drawings and specifications. This involved site inspections, progress meetings, and daily inspections. ROLE OF OTHER CONSULTANTS During the design and construction of the new spillway and embankment, Michael Baker teamed with Resource International Inc. to provide the topographic and bathymetric surveys and CTL Engineering Inc. to provide the subsurface investigation and construction materials testing. ENTRANT S CONTRIBUTION TO THE PROJECT Uniqueness and/or innovative application of new or existing techniques Due to the property constraints of the adjacent property owners and the owners request to maintain normal pool levels in the lake throughout construction, lowering the lake and replacing the existing structure in-kind was not an option. To meet the project goals, Michael Baker ultimately designed a labyrinth spillway with a smaller footprint than the existing structure, adjacent to the existing structure. The labyrinth was also designed to mimic the flow characteristics of the former spillway up to the 100-year flood event. This ensured there would be no adverse impacts to property owners upstream or downstream of the dam during flood events. In addition to matching the flows of the previous spillway, Michael Baker designed the new spillway to match the exact normal pool elevation of the existing lake. This was a challenging engineering task as bedrock in the area was over 100 feet deep and the loads from the new spillway and earthen embankment were predicted to cause settlement. To incorporate the predicted settlement, Michael Baker required the contractor to construct the labyrinth weir walls to approximately 2/3 of their height (by adding a control joint), preload the structure with adjacent soil, and monitor the settlement over an extended period of time. After most of the settlement had occurred (confirmed by regularly scheduled surveys and piezometer readings), the contractor was permitted to install the final top portion of the labyrinth weir walls. Future value to the engineering profession and perception by the public The spillway design, called a labyrinth, consists of a zigzag-shaped concrete structure designed to convey large flows of water at low heads by increasing the effective length of the weir, or dam, crest with respect to the channel width. The Lake Loramie project includes a new 113-foot-wide labyrinth spillway that was constructed to the northwest adjacent to the existing structure. A new lake drain system was incorporated into the spillway to control the lake level and allow for lake drawdown during maintenance or emergency situations. Incorporating the lake drain between the spillway walls eliminates the need for a drain pipe through the earthen embankment, a location known to be susceptible to seepage.

3 A new earthen embankment was constructed to tie the existing embankment to the new spillway. The earthen embankment was designed with modern day drainage layers, filter systems, cutoffs, and instrumentation. The ability to provide a design that minimizes the upstream and downstream impacts both during construction and after construction made the project a success in the eyes of the public. Three public meetings were held to present the design and address questions. Additionally, 3D renderings were used to help the public in visualizing the final arrangement of the dam. The spillway structure has since become an attraction for guests visiting the park given the labyrinthtype spillway is one of the first of its kind in an Ohio state park. Overall, the project has brought a positive spotlight to ODNR s dam safety initiative. Social, economic, and sustainable development considerations As previously discussed, normal pool was maintained throughout construction to limit the impact to the park, homeowners, and businesses surrounding the lake. A main source of revenue for the park comes from the campgrounds that surround the lake and from boating and fishing. The ability to construct the new spillway while not draining the lake, closing campgrounds, or closing road access allowed for the revenue to be maintained and preserved the key resource for the surrounding community. During construction, the local economy saw a noticeable increase due to the use of local suppliers, restaurants, and living quarters by the contractor. The contractor also hired several local personnel and used local subcontractors. The project site upheld erosion and sediment controls as required by both local and federal standards. Work within the lake was minimal and all project discharges and wastes were properly managed. The design was focused around limiting the impacts to the environment and community as much as possible. Impacts to two 0.42 acres of category two wetlands were unavoidable and ultimately mitigated by preserving and protecting 3.77 acres of category three wetlands and approximately 72 acres of upland forest buffers on a nearby property. This preservation was protected via an environmental covenant. Along with providing new stream channel in the design, additional stream credits were purchased from the Nature Conservancy to offset the impacts caused by the new dam embankment. The project site had native mussels existing within the project area. Prior to any work, a mussel survey was conducted, and the mussels were safely relocated to an area downstream of the work. Additionally, the Indiana Bat was protected by limiting the tree cutting only between October 1 and March 31. A full cultural resources assessment was conducted given the age of the structure and its history as the higher feeder for the canal system. The assessment led to the inclusion of historic interpretive signage, and per the request of the State Historic Preservation Office (SHPO), a context study investigating the relatively undocumented period between the end of the canal era and the 20th century development of the state park facility. The context study will be used as a guide by SHPO to help evaluate historic properties for state park dam rehabilitation projects.

4 Complexity Michael Baker took into consideration several special constraints when designing the rehabilitations to Lake Loramie Dam. Construction of the spillway and new embankment required normal pool to be maintained throughout the project. As such, the project was phased, and the structural elements were designed to account for fluctuations in pool elevations during construction. Temporary water control measures were provided during construction to control flood events up to and including the 100-year design event. The replacement structure was built adjacent to the existing structure, thereby requiring normal and flood flows to pass around the work area without impacting construction. The amount of space available was highly constrained due to the adjacent property owners, open lake, and access points. To help alleviate some of the constraint issues, ODNR negotiated land acquisition and easements to allow room for the new structure. A bank floodwall was designed instead of embankment placement to limit the amount of land acquisition. Additionally, environmental delineations discovered unavoidable impacts to wetlands and a mussel relocation effort was required to facilitate a protected mussel species discovered on the project site. Subsurface conditions were also a challenge for this site. The dam was underlain by highly variable glacial till and glacial outwash. To prevent undesirable seepage, the design included a variety of cutoffs and drains both within the embankment and under the spillway. To ensure the top of the spillway weirs were at the exact normal pool elevation after settlement of the subsoils, the contractor was required to install a planned control joint and pour the final top portion of the weirs after settlement diminished. Successful fulfillment of client/owner needs The primary goal of the project was to provide interim risk reduction measures to the dam while minimizing the impacts to the surrounding community. To achieve this goal, Michael Baker was engaged with the major stakeholders throughout final design. Multiple progress meetings were held with the owner, regulators, and park personnel to ensure all parties had a complete buy-in on the design. A total of three public presentations were also performed to keep local community members informed. During these meetings, 3D renderings and models were used as a tool to help educate the attendees. Michael Baker took into consideration all comments and suggestions and incorporated them into the final design. The design addressed all the issues and requirements from the owner and stakeholders, including maintaining the lake pool throughout construction, providing a design that would mimic the existing spillway flow characteristics, and providing a design that can be constructed within the limited space available and within the aggressive time schedule of 14 months.

5 Project budgeted cost: $6 million Total project actual cost: $5.4 million; remaining budget was used for other park and dam improvements. Entrant s portion of the budgeted cost: $1.2 million Entrant s portion of the actual cost: $1.2 million Scheduled date of completion: May 10, 2018 (Construction) Actual date of completion: May 10, 2018 (Construction on time) SUMMARY A recreational lake in Lake Loramie State Park in Minster, Ohio, Lake Loramie underwent a significant dam rehabilitation in The project was undertaken as part of a statewide initiative by the ODNR to repair and rehabilitate state-owned dams to ensure the safety of Ohio s lakes and surrounding communities. Michael Baker was tasked to design a replacement spillway structure and mimic the hydraulic capacity of the existing structure to avoid flooding upstream and downstream of the dam. Several design challenges to the project were encountered due to the existing site constraints and conditions at the existing dam. Limited construction access, challenging subsurface conditions, environmental and property constraints, and the request to maintain normal pool throughout the projects were amongst the challenges. From the early stages of the final design through the completion of construction, the project team worked collectively to address all the project challenges. To achieve this, the project team provided a sound, cost effective design that limited impacts to both the environment and local community. This was accomplished by providing a unique labyrinth spillway design which required less of a footprint than traditional spillways; incorporating cutoffs, filters, and drains; complex control of water phasing plans; providing solutions to settlement concerns within the design; addressing environmental concerns with state and federal agencies; and constructing temporary cofferdams to allow for construction to be performed while maintaining normal pool. The extensive planning and partnering of the engineer, owner, and contractor resulted in a project completed on time and on budget. The Lake Loramie labyrinth weir is one of the first of its kind to be built and activated in an Ohio state park and is currently a focal point for visitors of the park.