Flood Damage Threatens Local Dam & Water Supply Source
Summit Lake spans 250 acres on the west side of Creston, Iowa. It’s partially surrounded by homes and is a popular area for recreation and fishing. The lake features a dam that was originally constructed in 1894 by the CB&Q Railroad to meet its water supply needs. In the 1930s, the dam and spillway were raised for additional water storage capacity. The dam and lake were later remanded to Creston Water Works and supplied drinking water to the city into the mid-1980s.
To repair flood damage to the dam that occurred in summer 2008, improve recreational access the lake, and stabilize the shoreline, Snyder & Associates assisted Creston Water Works by providing a variety of civil engineering and design services.
Dam Repair & Reconstruction to Meet Community Water Supply Needs
Flood damage occurred to the existing earthfill dam and concrete spillway. Snyder & Associates was retained to evaluate the dam spillway and provide an engineering report detailing our findings. The damage was evident and a geotechnical exploration was undertaken to determine how stable the dam was. Our investigation determined that the earthen section of the dam was in stable condition. However, the concrete spillway section was in very poor condition. Not much design information existed, so we utilized our expertise with dam removal and modification projects and inference of the original design to determine hazard risks and formulate a cost-effective repair plan.
We also designed an extensive spillway replacement that enables the owner to maintain the lake in a safe and usable condition for water supply. To make the project possible financially, we assisted Creston Water Works in securing funding from FEMA and the Iowa Department of Economic Development (IDED).
A Dam Breach Analysis report was provided to determine hazard classification and assure downstream safety prior to the Iowa Department of Natural Resources (IDNR) permitting for reconstruction. During design and permitting, the existing structure became less capable of withstanding large flows. Working with the owner, permitting agencies, and stakeholders, we developed a plan to drain the lake and supervised the process to simplify the construction of improvements and increase safety. A new concrete spillway section was designed to safely accommodate the expected flow rates established by the breach analysis. A new energy-dissipating outlet structure, stilling basin, and downstream creek stabilization were constructed as part of the project. The new spillway section was designed to comply with IDNR regulations and the desire to control undesirable fish migration into the lake.
Services provided for dam repair and reconstruction include topographic survey, shoreline restoration, structural evaluation, breach analysis, eathern dam design, concrete spillway design, stream stabilization, construction administration, funding assistance, and permitting assistance.
Improving Recreational Lake Access & Fishing Habitat
Although Summit Lake is publicly owned, access is limited by private property. A publicly owned boat ramp and fishing area were difficult to use and provided limited access, so Creston Water Works applied for IDNR funding assistance to improve fishing access and habitat.
Snyder & Associates led recreational improvement efforts by designing a new fishing jetty. Excess material from the dam reconstruction was used to build the jetty, which has an earthen core protected by riprap overlaying geotextile fabric. The top of the jetty features a surface that’s usable by wheelchairs and provides roll-off protection. In addition, plastic piping and other artificial habitat were installed in the area, making the jetty a hot spot for fishing.
The project required approximately 800 cubic yards of backfill, 700 tons of riprap, and over 750 square yards of geotextile fabric. The project cost was approximately $100,000.
Permitting was included with the dam repair and reconstruction project as well as shoreline improvements project, which occurred simultaneously. Services provided by the Snyder team for this project included jetty design, earthwork design, accessible design, construction administration, funding assistance, and permitting assistance.
Erosion Control & Lake Shoreline Restoration
Summit Lake was experiencing significant shoreline erosion and slope failures. In some locations, the shoreline was over 100 feet beyond the original location, indicating an ongoing erosion problem. In many areas, brush and scrub trees had proliferated, preventing lake access. To preserve and enhance the condition of the lake and its shoreline, stabilization and restoration project were critical.
With expertise in erosion control and streambank stabilization, we assisted Creston Water Works in developing a stabilization plan and design. The project was publicly bid and constructed. Funding provided by the Iowa Watershed Improvement Board (WIRB) was used to fund this extensive shoreline stabilization project.
To provide equipment access to the lake, the water level was lowered by approximately five feet according to a plan that we worked closely with Creston Water Works to develop. Construction was programmed to occur during winter while the lakebed was frozen to allow access for required machinery and trucks.
The project required approximately 7,000 tons of riprap, over 2,000 square yards of geotextile fabric, and extensive brush removal. The project cost was approximately $300,000 for over 18,0000 feet of shoreline stabilization.
Snyder & Associates completed the design and all permitting for the project including U.S. Army Corps of Engineers and IDNR. Permitting included cultural resources, endangered species, and waters of the United States. Working with the owner and permitting agencies, a construction procedure was developed to comply with permit requirements.
Services provided by Snyder & Associates for this shoreline stabilization project included SWPP development, construction administration, funding assistance, and permitting assistance.