Geomorphic Approach to Infrastructure Design at Road-Watercourse Intersections

floodplain area in relation to culverts and stream channel

Minnesota’s roads intersect our natural flowing rivers at approximately 65,000 locations around the state. There are numerous more intersections at intermittent channels. Roads that encroach onto the watercourse will impact the watercourse's natural processes and ecological functions. Applying this geomorphic approach when designing the infrastructure will encourage the design to work with the natural system and allow for stable watercourses long-term. This approach can be applied anywhere a channel exists on the landscape.

The infrastructure we place onto our watercourses will always impact natural process and function. Site design guidance and tools are available for infrastructure designers to design a low impact infrastructure project.

This approach:

  • describes how to define basic "stable" channel and floodplain metrics
  • provides standard reporting form for defined channel and floodplain metrics
  • guides designers of watercourse infrastructure on applying channel and floodplain metrics into site design

A key to this approach is to design for both channel and floodplain independently through the Define, Design and Refine method of placement and sizing of infrastructure outlined within. When properly applied, the approach will establish a low impact design, allowing for a naturally maintaining channel and floodplain to form over time. This can minimize the impact to natural watercourses and infrastructure.

This approach allows designers to quickly establish critical local land form metrics for both channel and floodplain, then apply those metrics to design a low impact infrastructure project on our watercourses.


Design of Channel Opening

A stable channel will effectively manage its water and sediment loads with minimal change to its form. Past design processes have focused on water; often placing over-widened on-channel openings with no floodplain consideration. The design process of concentrating all flows to the channel has many detrimental impacts to the stability of the natural watercoursesystem.

Two common impacts are:

  • disrupting natural sediment transport
  • disconnection with associated floodplain

When designing for channel openings, the design should begin by applying the proper channel width. Then, as proficiency is gained, additional channel metrics can be applied into the channel design opening.


Design of Floodplain (Culverts)

Throughout Minnesota, the link between channels and floodplains have been commonly overlooked by infrastructure designers. Floodplain culverts should be designed to convey flood flows. This requires the designers to accommodate for flows outside the natural channel boundary by defining, then designing for a natural floodplain.

Floodplain culverts are set outside and above the main channel flowline, across the entire floodplain, at the defined floodplain elevation and slope. Through proper application of this approach, floodplain connectivity can be achieved or re-established through time through this adaptive design approach.



A set of procedures are available to document site land form metrics to be used in site design. An interactive spreadsheet form will help document basic land form metrics that designers can apply into site design.

If used in your site design, return a copy of the information to Kevin Zytkovicz, River Specialist, or Salam Murtada, Floodplain Hydrologist. This information will be used to improve this geomorphic approach.

Minnesota Permit and Reporting System (MPARS)

Resources for applicants processing culvert permits through MPARS.