Riverbank Slumping Demonstrates Another Reason Not To Allow New Homes Too Close To Rivers

Thanks to the Cass County Soil Convervation District and Riverkeepers for the excellent tour of the many river bank failures on the Sheyenne, Red, and Wild Rice Rivers.

The attendees included Fargo planning commissioners, three of us city commissioners (The media was notified and present) and others that are working on extending our setbacks to prevent any new homes being built too close to rivers and drains.  Besides the vulnerability to flooding, the instability of the soils on riverbanks in our area is even more of a reason to back away from rivers here.

We had a good turnout despite the rain.  Here’s Riverkeepers chief Bob Backman explaining the dynamics that make riverbanks slump with our unique clay soil conditions on the Red, Wild Rice, and Sheyenne Rivers in our Fargo area.

There was a good turnout on a rainy day.

This is NDSU professor of geology Dr. Donald Schwert explaining how the clay soils in Fargo react with the rivers here.  The more weight from buildings and removing vegetation near the riverbank, the more the chance of severe slumping as we saw in many housing sites on the tour.


Expensive buyouts another reason why Fargo shouldn’t allow homes to be built too close to rivers

Posted on June 13, 2011 by Mike Williams

Today’s articles on the high cost of buyouts of vulnerable homes too close to rivers is one of the primary reasons I initiated a Fargo setback of 450′ from rivers or 100′ from the floodway whichever is further to prevent these high costs to taxpayers.

Fargo buyouts cost The Fargo buyout average reflects a large disparity between mid-range homes that have been getting a bit above assessed value (closer to Moorheads 108% above assessed value average) and the the high end homes that have been paid well above assessed value.  I’ve asked city staff to address this disparity as future buyouts are considered and a moratorium on building on river lots now includes a 450′ setback or 100′ (whichever is further away from the river) along the Red and Wild Rice Rivers.  I believe the Sheyenne River also needs to be addressed in the same manner as allowing new homes and building too close to that river even with the West Fargo diversion is not in taxpayers interest either.

Here’s what experts show us about why it’s vital to back away from rivers especially with our soils in our Fargo area:

Back away from rivers with new construction

Posted on May 12, 2011 by Mike Williams
“Soils near the Red River of the North and its tributaries are inherently weak and natural forces are always moving the river channels.  These soils display weak engineering properties and when exposed to the slopes of the riverbanks and valley walls their high plasticity frequently and naturally leads to foundation shifting and pavement failure.”
The paragraph above is some background from the Cass County website on why river setbacks are so important to avoid new homes being built too close to rivers.  http://www.casscountynd.gov/county/depts/planning/Pages/RiverbankSlumping.aspx
The Fargo Commission has a moratorium on new buildings on river front lots since 2009.  At last Monday’s meeting we clarified that moratorium applies to undeveloped plats on the Red and Wild Rice Rivers and all unplatted areas along all the rivers in Fargo.
Here’s the rest of the information on the Cass County website.  Kudos to the Cass County Commission for passing their watercourse setback ordinance in 2006, it’s helped prevent buildings from being built too close to watercourses.
Soils near the Red River of the North and its tributaries are inherently weak and natural forces are always moving the river channels.  These soils display weak engineering properties and when exposed to the slopes of the riverbanks and valley walls their high plasticity frequently and naturally leads to foundation shifting and pavement failure.
Despite the vulnerability, these areas have in recent years undergone extensive urbanization, leading to an artificial acceleration of riverbank slumping and instability.  This natural process is often accelerated by the following homeowner activities:
House Placement
Houses are often built too close to the riverbank where the soils are most susceptible to bank instability.  The weight of the structure places pressure on the riverbank and increases soil hydration because of increased storm water runoff.  When the riverbank begins to actively slump, the placement of the home close to the river often provides homewoners little options except to move the house off the property.
Irrigation systems and septic drain fields add extra weight and excessive water, both reducing the soils structural strength.  The saturating of the soil decreases the strength of these already weak soils and is one of the biggest contributors to increased and accelerated slumping.
Adding additional weight to the riverbank with houses, structures, retaining walls, riprap, soil and fill, and extensive landscaping places greater pressures on the riverbank and can increase and accelerate riverbank slumping.
Replacing deep-rooted, native vegetation with shallow-rooted vegetation, which further weakens the soils.  The shallow roots of turf grass provides little soil strength and the absence of trees diminishes water removal from the soils. 

Because riverbank slumping is a natural process and often inevitable, attempts to stop it have not typically proven successful.  Attempted bank stabilization techniques including lime stabilization and homeowner constructed retaining walls are not always successful.  Many homeowners also confuse riverbank slumping with erosion and place riprap, concret, or other material on the slope in an attempt to stop the erosion; the added weight of these materials on the riverbank often accelerates the slumping.
Even professionally engineered techniques such as riprap or sheet piling for single sites are not always enough and typically require application to large stretches of the riverbank to be successful.  The costly design and construction associated with these techniques is most often cost prohibitive to the average homeowner.
The best solution to this natural process is not building too close to the riverbank in the areas most susceptible to bank instability.  Landowners are also highly encouraged to reduce their activities that accelerate this natural process by liimiting the artificial introduction of water on their property, limiting the amount of weight on the riverbank, and maintaining or planting deep-rooted vegetation.

Time Lapse Animations
Following are four instances of slumping in Cass County.  Click on each photo to view a time lapse animation of each example over the course of a few years.

Slumping Animations
The following animations illustrate the processes that are occurring in the instances described.

~End Cass County Site~
The Fargo Commission is in the process of upgrading our own ordinance right now.  If you have concerns or ideas about river setbacks and permanent flood protection please contact me and the other Fargo commissioners.
Another way to weigh in is at GO2030.net and the Mind Mixer community input tool.   Fargo is undergoing our new comprehensive development plan that’s done once in a generation.  http://www.go2030townhall.com/land-use-and-urban-design click the link to submit your input and comment on other ideas.
We’ll be more successful building a more safe, more vibrant, livable, and efficient community with your help and input!