Background information on the Rochester Flood Control Project

As part of the League of Minnesota Cities Annual Conference in Rochester we had arranged a bike ride to tour the Rochester Flood Control Project.  As it turned out we got lightning, so some of us will take an unofficial ride another time.  Assistant City Administrator Gary Neumann prepared some of the following information and I thought I would share.

  • Overall the project was designed to handle a flood greater than the July 1978 flood, estimated at 175 year flood.  That flood caused $60 million in damage and killed 5 people.  Prior to 1978 the project was already designed for a bill in Congress at a lower 100 year flood level. In 1981/1982 it was redesigned by the Corps based on the experience of the 1978 flood.  The final design was for the 1978 flood plus 2 additional feet of freeboard, overall over a 200 year flood capacity.
  • Cascade Creek was an exception.  Based on neighborhood concerns that segment was valued-engineered and determined that a lower level of protection (100 year flood plus 2 feet of freeboard) would protect all structures and could be accomplished while retaining some natural areas on Cascade Creek.  This was primarily done to address neighborhood concerns and aesthetics.  I would note, though, that in 2007 Cascade Creek was bankful and close to impacting homes.  That was due to a rainfall event of 7 to 10 inches across the watershed (6 inches in 24 hours is a 100 year event).
  • The Channelization component, constructed by the Corps of Engineers,  starts at the Trader Joe’s drop structure.  That structure was designed so that it did cause any increase in flooding for the areas upstream. It passes the same amount of water that it always passed in a 100 year event.  At this drop structure additional flood flow capacity is started by lowering the former channel by 6 to 7 feet and widening the channel.  It is much wider, 120 to 200 feet. The combination of widening and deepening creates the flood capacity.
  • At the farthest downstream end of the project it was designed to not have any negative impact of flooding areas downstream.
  • There are also 7 flood protection reservoirs constructed by the Natural Conservation Resource Service (NRCS) that store large amounts of flood water on various major creeks: Bear, Willow, Silver and Cascade.  These cumulatively reduce flood flows by 16% overall.  On Bear Creek they reduce flood flows by 35%.
  • The City partnered with the Corps to take the projects’ initial design, which was stark and essentially a plumbing project, to make it into a plum for the City.  The City retained its own landscape engineering firm to provide recommendations to augment the Corps experts, and appointed a Riverfront Committee to recommend various aesthetic and usage improvements.  That effort resulted in the bike paths, underpasses, landscaping in the corridor and various other aesthetic approaches to change the original design, which was a rip rap channel with a strip of blacktop at the top, into the system you see today.   The Committee toured other flood control projects in other communities for some ideas and, basically, attempted to improve upon the elements in those projects.  The view of the Committee, which included the three Councilmembers on the Flood Control Committee of the Council, was that this was an improvement project that could be in existence for 100 years, so we needed to do a job that the community be proud of from a long-term perspective.
  • Some of the design  changes that actually affected the channel design itself included:  sod over rip-rap (first use by the Corps  in Minnesota in several areas: across from the MCC, by the RPU powerplant, and Soldiers Field Golf Course.  Most people do not realize that rip rap is buried under the sod for several hundred feet on both sides of holes number 9 and 18, just look for the sloped areas on those holes), interlocking concrete block with space for grass (first use by the Corps in Minn. across from MCC, Cascade Creek, Bear Creek) architecturally treated concrete (downtown area).
  • Cascade Lake mining has been determined to increase the flood protection for downstream areas by about 10%
  • The overall cost of the projects (Corps and NRCS) was $118 million.  The City share was about $35 million.   The City was responsible to secure all the lands, easements and rights of way for both projects.  That involved roughly 400 property acquisitions, most in part only.
  • The City was the partner with the Corps on the channelization project, and the City, County, and Olmsted Soil and Water Conservation District partnered with the NRCS on the 7 reservoir project.

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