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Pipestone County Judicial Ditch 1 has remained within its banks this spring, but that’s not always the case. A recent study looked into
several options to prevent flooding in the area around the ditch.
Photo by Kyle Kuphal
Representatives of the city of Pipestone, Pipestone County and Pipestone National Monument, and others, heard a presentation about flood mitigation options for Pipestone County Judicial Ditch 1 during a special Pipestone City Council meeting on May 5.
The mitigation options were part of a floodplain improvement study conducted by Bolton & Menk. The study cost approximately $89,000 and was paid for by a grant from the Minnesota Pollution Control Agency (MPCA). According to the executive summary of a 154-page report based on the study, the goal of the study was “to identify opportunities to protect the city facilities, homes and businesses, and residents in the community from recurring flooding concerns” along the Judicial Ditch 1.
Five potential alternatives were studied and their potential outcomes were assessed.
Alternative A included raising the grade at the intersection of North Hiawatha Avenue and 111th Street/Ninth Street NE, and replacing and increasing the length of the bridge on 111th Street/Ninth Street NE. Potential outcomes of that option included a reduction of flooding of along those two roadways, a minor reduction of flooding between that area and Eighth Avenue NE, and minimal benefits to residences. The preliminary cost estimate for that alternative was $3,419,000.
Alternative B included increasing the length of the state Highway 23 bridge. Brady Nahkala, a water resources engineer with Bolton & Menk, referred to that alternative as a “significantly futuristic” option due to the fact that the bridge deck was replaced last year. The potential benefits of that option were expected to be localized to the area around the bridge with a minimal impact on structures and properties in the area. Nahkala said the company also looked at possible modifications to the railroad bridge nearby and it was thought that any benefits of that would be very localized. The preliminary cost estimate of Alternative B was $1,416,000.
Alternative C included replacing and lengthening the North Hiawatha bridge over the ditch. Potential outcomes included a moderate reduction of flooding, but minimal benefits to the roadway. The benefits would terminate at 111th Street and were not expected to provide significant benefits to properties upstream. Nahkala recommended that if that option were pursued, the potential effects on Pipestone National Monument be considered. The estimated cost was $1,148,000.
The red line on this map is Pipestone County Judicial Ditch 1. A recent study found that the most effective way to address flooding of the ditch during heavy rains could be floodwater detention areas upstream. Source: Bolton & Menk
Alternative D included a levee to protect residential areas, realignment of the ditch and controlled over-topping of 111th Street. Potential outcomes included the removal of more than 20 parcels from the floodplain, increased flooding north of 111th Street and a high cost, which was estimated to be $3,600,000.
“This is probably the most disturbance out of any of the options that we evaluated and would require the most community buy in, I would say, as well, but largely the most surefire way to protect those, short of a full buyout, that we had evaluated,” Nahkala said.
Alternative E included distributed floodwater detention areas upstream and was determined to be the most universally beneficial option.
“This would include installing berms with outlet control structures or digging out sections of storage with outlet control structures, either within city limits, but more likely outside of city limits, to temporarily detain water during these large flood events and release it slowly to the ditch system, which ultimately would result in peak flow reduction and decrease high water high levels through the city,” Nahkala said.
Typically, he said, such projects are done in collaboration with landowners willing to install such projects. City Engineer Travis Winter, a principal engineer with Bolton & Menk, said Alternative E could be implemented over time as properties are put up for sale. They said it would likely involve coordination with the county and other agencies to secure funding for projects.
Such projects are considered a good standard practice, according to the report, and would involve significant community engagement. A challenge would be that it would be difficult to scale. A peak flow reduction of 10 percent, for example, would require storage volume of 1,500 acre-feet of water. The cost of Alternative E was not evaluated.
Winter said there was no “silver bullet” to address the flooding issues and that the floodplain improvement study could help secure funding to implement flood mitigation projects in the future.
Pipestone County Administrator Steve Ewing thanked the city of Pipestone and Bolton & Menk for taking on the study and providing the report. He said the information that could be helpful in the future and that he’d like to keep the conversation going.
Additional conversations and identifying and pursuing funding opportunities were among the next steps cited in the information presented by Bolton & Menk.