Downstream Flooding Concerns

Below are a series of memos addressing concerns expressed in the community about the Rochester Flood Control Project and potential impacts downstream with the recent flooding. If you have any further questions, comments, or concerns please contact Michael.

From Gary Neuman:

Mayor and Council

Some Olmsted County officials are receiving expressed concerns from some people who, mistakenly, believe that the Rochester flood control project has had the impact of increasing flooding problems at Lake Zumbro and elsewhere downstream.  That has been a persistent question and erroneous belief over the years.  The Corps has addressed this on several occasions.  As the attached information from the Corps of Engineers below indicates, the design of the Rochester flood control project incorporated many measures, including the construction of 7 reservoirs that hold back flood waters and release that volume of water slowly over 10 days.  Anyone who has visited these reservoirs during the recent flood event could testify that there is a larger volume of water stored in these sites.  These reservoirs actually reduce the downstream impacts at Lake Zumbro and beyond. Downstream impacts were an item that was studied and positively addressed in the design of the Rochester flood control project.  Our project causes a positive impact to reduce flooding downstream, though that benefit is small due to the large size of the overall drainage area in comparison to the smaller size of the Rochester watershed.  Bottomline is that it is some help to those downstream, it does not harm downstream properties.

And also from Gary…..

The Rochester Flood Control Project REDUCES downstream discharges. See the message below from the Corps of Engineers.  That has been my understanding since the beginning of the project.  The design memorandum for the construction of the Corps project notes that:  The SCS reservoirs reduce the design discharge by 16 percent on the Zumbro River at the downstream end of the project.

From Russell Snyder, US Army Corp of Engineers

We have been asked about impacts that the Rochester project has on downstream communities a number of times since the project was completed. I anticipate this will come up again after the flooding last week. Inserted below are some notes I have from fielding such a question after flooding in 2001. I am pretty sure my primary information source on this was Scott Jutila. I think we provided this to the City of Rochester to respond to inquiries placed to them:
“Flows at the 37th Street gauge just downstream of Rochester, Minnesota peaked at 5400 cfs on April 12.  The six NRCS reservoirs upstream of Rochester were only discharging 380 cfs on April 12 [2001] and where not “full”.

Past responses to downstream communities regarding the impacts of the Rochester project indicate that downstream flooding is not impacted and actually benefit from the NRCS reservoir storage.  The Zumbro River basin above Zumbro Falls is approximately 1150 square miles while the basin above Rochester is approximately 300 square miles. Some points made in previous correspondence related to downstream effects:

“…the project will reduce peak flows through and immediately downstream of the City of Rochester for flood events up to the standard project flood of 80,000 cfs.  The combined effect of the Corp’s channel modification and the NRCS reservoirs will result in both a discharge reduction and a time delay of peak flows as they exit Rochester”

“The project is designed to move water through the City (Rochester) without causing damage, which is achieved by lowering and enlarging the river channel together with storage in upstream reservoirs.  The water is not accelerated, and due to the NRCS reservoirs the peak flows are actually reduced.  The positive downstream impacts the flood control project are less noticeable as one moves further downstream of Rochester.”

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