A successful erosion control plan is crucial to long-term resiliency and water quality. Success of the plan also comes down to good partnerships and, in many cases, a great deal of patience.
Take, for example, a major project conducted in the St. Paul-Minneapolis metropolitan area for Minnesota’s Minnehaha Creek. After several years of work, Stantec and its project partners have developed a master plan for the creek, but it took years of restoration and repair work to get there.
Unprecedented flooding hits Minnesota
The Twin Cities region in Minnesota witnessed unprecedented rainfall and floods in the spring of 2014. That year, washed-out roads, sandbags and bank slumping were common sights following heavy rains and subsequent flooding. Minnehaha Creek is a 23-mile-long tributary that begins at the outlet of Lake Minnetonka (the ninth-largest lake in Minnesota). During the peak of the 2014 flooding, Minnehaha Creek exceeded its 100-year flow by 30%, and Lake Minnetonka set an all-time-high record at 931.11 feet above sea level. At the time, a total of 35 counties in Minnesota declared a state of emergency.
The Minnehaha Creek Watershed District (MCWD) is a regional watershed planning agency that collaborates with public and private partners to protect and improve land and water resources for current and future generations. The MCWD covers approximately 178 square miles from Lake Minnetonka to the Mississippi River, through multiple communities along the way.
Stantec was brought on to be part of the project team through a collaborative effort with MCWD and the Federal Emergency Management Agency (FEMA). Together, the group secured over $500,000 in funding for flood repair. With that funding, MCWD, FEMA, and Stantec also worked with local partners – including the City of Minneapolis and the Minneapolis Park and Recreation Board – to help facilitate repairs after the floods.
The project had two major goals. First, the team needed to repair eroded sections of the creek bank and damaged adjacent infrastructure that resulted from flooding. The second goal was to restore the pre-2014 flood geometry of the Creek.
Minnehaha Creek’s main corridor flows through a highly urban environment. The creek demonstrates typical characteristics of an urban stream, having flashy flows associated with a gridded watershed drainage that were on display with the 2014 floods.
The precipitation that led to the floods was the highest ever recorded in the area, with 11.36 inches falling in the month of June (normal precipitation for June is 4.58 inches). The result of the intensity and volume of precipitation led to significant flooding of Minnehaha Creek. Not only did the high flows create significant erosion issues, but the creek also saw slumping and slope stability issues due to the overall volume of flows. In total, Minnehaha Creek recorded over 40 damaged locations, including 10 bank failures, along with structural damage to boardwalks and pathways.
Smart planning in the aftermath
When the floodwaters receded, staff inspected the entire channel to document erosion issues and provide context on the immediacy of repairs needed. Through these inspections the MCWD was also able to help partner agencies in their response to the floods, allowing for disaster declarations to be a much more collaborative effort. MCWD led a significant endeavor to take a systematic approach in evaluating how restoration of erosion issues could be done with other partner plans and restoration strategies.
MCWD decided to take an integrated approach to restoration, recognizing that the need to repair the creek was always at the forefront. This more deliberate approach looked at the area as a whole and allowed MCWD to prioritize specific areas, identify where risks could be minimized, and determine how to align partner funding streams.
Through the analysis, partners came together to layer the new erosion issues through a lens of their existing capital improvement plans at the time. This included road reconstruction, bridge and trail replacements, and stormwater infrastructure enhancements adjacent to the creek.
Taking a broader look at these various plans facilitated greater alignment and helped limit the number of times that slopes, the creek bed, and stream floodplain would need to be disturbed. This meant that the risk of potential future erosion issues could be limited.
Once priorities were identified, the project team broke them down into two phases:
- Issues that needed to be fixed immediately
- Areas that would benefit from protection through enhanced restoration and design
Breaking the work down into these phases allowed the MCWD to not only maximize public dollars through collaborative funding of the repairs but limited the needs for partner agencies to work in the same area – or worse, duplicate work in subsequent years at the same location.
Phasing the projects led to the identification of eight projects that required immediate repair to prevent Minnehaha Creek from experiencing further bank erosion and potential damage to adjacent trails and infrastructure. These projects were then expedited for restoration design and construction.
The final 21 sites identified for project work had the ability to provide greater benefit to the creek by going through an enhanced design. Planning these projects out into future capital improvement plans could be adjusted and aligned for the repairs to occur – while also allowing lead time for the identification of additional grant funding. If all 21 projects are installed, it is estimated that they will restore over two miles of creek in Minneapolis.
Over the course of seven years, this phased approach has been extremely successful. It allowed partners to collaborate to repair 500 linear feet of stream and banks at a cost of $215,000, which is a significant savings to the partner agencies.
Because of careful, patient planning and a reliable partnership approach, MCWD and partners have now cultivated and strengthened these relationships to develop a master plan for the creek. The Minnehaha Parkway Regional Trail Master Plan addresses resiliency and recreational needs for the 1,000-acre parkway, along with implementing significant water quality improvements, and it is now well-equipped to serve the Twin Cities region for years to come.
Chris Meehan
Chris Meehan is senior principal, water resources engineer for Stantec.
