Flooding study results revealed

The Mankato office of Houston Engineering recently completed a comprehensive hydrology study regarding flooding problems in and around New Richland; the company’s conclusions were presented during the New Richland City Council meeting on Oct. 28. 

 

The city is planning a future public hearing to receive input from citizens regarding the best path forward. 

 

Over the past 20 years, New Richland has experienced numerous high water flooding incidents. 

 

“The purpose of our study is to quantify that flood risk–how high, how often,” Houston Engineering’s Joe Lewis said. “The study looks at different projects or alternatives to reduce that flood risk throughout the city.

 

“There isn’t an expectation that [this problem] will go away on its own,” Lewis added. 

 

Lewis began his presentation discussing how water moves through the current system. 

 

During a normal rain event, water moves through ditches at about 400 to 600 cubic feet per second (CFS). During a “100-year flooding event,” that amount is tripled to as much as 1,300 CFS, or about 10,000 gallons per minute. 

 

“Once excess water comes out of the channel, you start having impacts,” Lewis expanded. “Our purpose is to identify the next steps for the city to look at to create a permanent solution.” 

 

The current water drainage systems–channels, ditches, and their ability to deliver outflow into natural streams–have been in place a long time, and were installed with the intent to serve agricultural needs. Their purpose was for drainage, Lewis said, not for the sake of preventing flooding.

 

“The source of flooding is from runoff conveyed to the city by County Ditch 47 (CD 47) and Joint County Ditch 6 (JCD 6), public drainage systems from the upstream watershed,” the hydrology study reports. 

 

The criteria used for flood mitigation by this study sets the objective of eliminating or minimizing flood damages during rain events which drop up to 7.66 inches during a 24-hour period, the standard for a “100-year” flood. 

 

Council members noted, during the presentation, that at least one rainfall event this summer delivered 11 inches during a 24-hour period. 

 

Houston Engineering provided four plans with alternatives to help address the flooding problem: increasing culvert capacity, widening ditch channels, redirecting water, and constructing structural protections such as levees or floodwalls. Elements of the techniques can be intermingled. 

 

Houston Engineering provided what they called a “soft recommendation,” an option likely to provide the best “value.”

 

This option, referred to as the “northern diversion,” routes flood water from about 70 percent of the local watershed around the city. Doing so, the company reported, would require the installation of new culverts and the purchase of 25 acres of land needed for the route. Council members observed Houston Engineering’s estimated purchase price of $6,200 an acre for the needed land was much too low. 

 

Waseca County Land and Water Resources Director Chris Howard was present during the meeting and contributed numerous observations. He also indicated the County of Waseca will work on CD 47 in conjunction with the City of New Richland. 

 

“An important thing for you as a council [to know] out of this, no one measure will solve the problem on its own,” Howard directed. “We will have to wade through what we take a la cart to achieve a value and the desired outcome.” 

 

City Administrator Anthony Martens said the next step for the city is a grant application necessary for the planning to continue. 

 

“The County has pledged some money to help with this project,” Martens stated. “I think the council's next step should be some sort of public sharing session with a more detailed presentation for the community.”

 

Houston Engineering is expected to be present at that future meeting. 

 

With anticipation of a larger meeting on this topic, the council approved up to $1,000 for technology necessary to hold and record meetings in the large room of city hall. 

 

The regular meeting concluded at 7:55 p.m. Council members will meet again at 6:30 p.m. on Tuesday, Nov. 12.