By David Markham
In preparation for much-needed water quality and habitat improvements, JCPRD began drawing down water levels in Heritage Park on June 5 and reached the target level of 3.5 feet below the normal pool elevation earlier this week.
The lake project involves dredging sediments and native earthen materials from within the lake, as well as from about 1,500 feet of stream at the lake’s north end. The improvements also include removal of Black Bob Island, addition of deep water fish refuge areas near the north shoreline and along a new earthen embankment for increased habitat and recreation, and construction of a 10-acre sediment forebay and wetland area in the upper third of the lake to improve water quality within the lake.
These improvements are expected to increase the storage volume of the 41-acre lake, which has seen sedimentation reduce its capacity by 50% since its original construction in 1980. Heritage Park Lake is the largest body of water in the Blue River Watershed, and also serves as the principal source of irrigation water to Heritage Park Golf Course, Heritage Football Complex, Heritage Soccer, and Heritage Softball.
“Heritage Lake will be restored to its original volume and will once again be a functioning recreational water body for fishing and watercraft,” said Project Manager Jim Wilson. “The irrigation benefits provided by the lake allow JCPRD to provide many sports recreation programs and services to the citizens of Johnson County without purchasing large volumes of domestic water for turf irrigation.”
Goals for the project include: restoring depth to the main portion of lake, improving habitat for fish and wildlife, restoring the original storage volume to the lake, and creating a wetland forebay, which will temporarily retain runoff, allow sediments to filter out, and improve the quality of the water/runoff. The forebay is meant to protect the lake from silting in again in the future.
While the project began in early June with the lake drawdown, earthwork and dredging will commence and operate through the remaining spring, summer, and fall and will shut down in late fall of 2023. The same process will occur over the spring and summer of 2024, with substantial project completion anticipated in the fourth quarter of 2024.
“The lake was initially lowered 3.5 feet to expose the upper end of the lake for construction and excavation of the wetland forebay,” Wilson said. “The project includes a temporary cofferdam to isolate at least 17 acre-feet of water adjacent to the spillway during the project to maintain a minimum irrigation capacity while dredging the center portion of the lake. After the center of the lake is dredged, the minimum irrigation pool will be maintained in the center of the lake while the lower part of the lake is dredged.”
The majority of silt removal will occur in the upper (north) half of the lake.
“The lake will be dredged back to the original depth when the lake was constructed,” Wilson said. “The lower part of the lake will be dredged an average of 4 feet with 12 feet of material removed in the area of the island. The upper part of the lake will have an average of 10 feet of material dredged. Dredged materials will be disposed of on-site within 3,500 feet of the lake in five disposal areas and will be shaped back into the natural landscape.”
Wilson explained that the removal of Black Bob Island is part of increasing lake volume.
“Black Bob Island is being removed to increase the overall storage capacity of the lake and its removal offsets the volume of material added to the lake to create the forebay berm and forebay embankment,” he said. “During the project, the temporary cofferdam will utilize part of the island soil and its causeway to reduce the length of temporary cofferdam required for the project. The remainder of the island, causeway, and temporary cofferdam will be removed at the end of the project.”
This project will affect activities in park areas around the lake, and the surrounding trails are scheduled to close beginning June 20.
“The trails around the lake will be closed to public access for the duration of the project,” Wilson said. “The low water levels will expose mud and other conditions that are not suitable for public access to the water. The Black Bob Trail entrance at the northeast corner of the park is also be closed as that trail crosses through two dredge disposal areas.”
