Flood Control System
On June 13, 2008, the Cedar River crested to its highest level in Cedar Rapids, Iowa history, 31.12 feet, far exceeding the previous record of 20 feet. The flood waters penetrated 10 square miles or 14 percent of the City. This historic flood impacted 5,390 houses and dislocated more than 18,000 residents. On December 4, 2013, the State of Iowa’s Flood Mitigation Board awarded the City of Cedar Rapids $264 million toward a flood mitigation project to protect both sides of the Cedar River. In September 2014, the Cedar Rapids City Council approved a program management and engineering contract with HR Green to perform design work on the City’s $570 million flood-protection project.
Since securing this assignment, HR Green was actively engaged in developing a series of open house and work session events to solicit public input on setting alignment for the flood control system and associated improvements. HR Green also worked closely with the City’s Flood Control Systems Committee, City staff, outside agencies, as well as organizations involved in the review and permitting process. These efforts culminated in the adoption of the Flood Control System Master Plan which is a document that establishes the alignment, implementation plan, budget, and acquisition/disposition policy.
Since the adoption of the Master Plan, HR Green focused on designing select improvements that were consistent with the implementation strategy, with the first two bid packages prepared in February 2016. The overall implementation of this project is scheduled to occur over the next 20 years.
The 7.5-mile flood-protection system balances the priorities of the community to provide better protection, preserve neighborhoods and assets, and maximize open space. HR Green is responsible for the West Side Flood Mitigation System concept which will extend for an estimated three miles along the Cedar River. The plan includes levees, flood walls, road closure gates, gravity outfalls with gatewells, storm sewer interceptors, and pump stations. Other removable floodwalls were conceived to allow access to the river.
In developing this plan, interior drainage considerations were critical factors in pump station sizing and the ponded area designated limits. The Corps of Engineers performed the initial work completed for the interior drainage review on the West Side. HR Green refined the interior watershed sub-basins from the Corps Study using LiDAR terrain data. The ultimate objective of the interior drainage analysis was to identify locations within the areas protected by the flood control system that could be subject to flooding during a 1-percent annual-chance event to satisfy the interior drainage requirements. However, the modeling results also provided City staff important information about existing storm sewer capacities, overland flow paths, and where conveyance bottlenecks create flooding issues all based on interior rainfall events.
HR Green leads the collaboration and everyday operations of four leading engineering firms, bringing top local talent and national expertise to the project. As the project lead, HR Green is responsible for augmenting current client staff and facilitating coordination with a team comprised of many different local teams and subconsultants. Additionally, this project required active communication and coordination with third-party permitting agencies such as the Iowa Department of Transportation (DOT), USACE, Utility Companies, Iowa Department of Natural Resources (IDNR), and developers.