Annual Meeting 2017

A Guide to Why Ditches Matter  

By Jesse Schomberg

Program Leader and Coastal Communities Extension Educator for the University of Minnesota Sea Grant Program

Even in sparsely developed watersheds, the length of ditches can be about the same as the length of all the existing stream channels.

When issues of stormwater and water quality arise, impervious surfaces often receive the blame. The mind’s eye sees vast expanses of parking lots and rooftops, or urban freeways with eight lanes of traffic, and fingers are pointed without a second thought. While these features can certainly funnel large volumes of runoff to nearby lakes and streams, stormwater issues extend beyond city limits. Rural watersheds also have issues with too much water rushing off after storms.

The water can lead to washed-out roads and damaged bridges and culverts, and the streams and lakes where this rushing stormwater ends up bear the brunt of this excessive erosion.

While these rural areas lack the storm sewers that move water so efficiently in urban areas, roadside ditches take over the same function. These ditches are ubiquitous and have the potential to drastically alter the way water flows through rural watersheds. Even in sparsely developed watersheds, the length of ditches can be about the same as the length of all the existing stream channels (Fig. 1). This means that the ditches have essentially doubled the network of water conveyance structures in rural areas.

Figure 1. Miles of stream channel vs. miles of ditches in three watersheds along the north shore of Lake Superior in Northern Minnesota. The calculations assume that all roads have ditches down both sides.

Well-designed ditches have some distinct advantages over storm sewers: vegetation in ditches slows and filters the water, it provides for some infiltration to reduce the runoff volume, and it takes up nutrients. Ditches also help protect the roadbed from saturation, which can lead to issues with frost heaves and potholes. But ditches, like other infrastructure, require regular maintenance and, given their ubiquitous nature, that maintenance can be a real chore and cost for the cities, counties, and townships that are responsible for them.

In 2007-2008, the University of Minnesota Duluth’s Natural Resources Research Institute (NRRI) conducted a study to evaluate the contribution of ditches to stormwater issues in northeast Minnesota. The study found that many ditch problems are caused by poor, improper, or a complete lack of maintenance. One of the primary recommendations by local and regional road experts was to develop guidance for maintaining rural roadside ditches.

 

Figure 2: A severe headcut in a rural ditch outside Duluth, Minn.

 

Problems such as headcuts (Fig. 2) or incisions can quickly result in literally tons of sediment being eroded from ditch bottoms and carried downstream, where it can cause headaches such as filled-in ditches, blocked culverts, or water quality problems in streams or lakes.

When a headcut or incision is caught early, they can be managed before significant problems occur. Unfortunately, these early stages are often missed. Once the problem has developed and can’t be ignored, inadequate repairs, such as filling eroded areas with more soil, typically don’t address the cause, and the problems are likely to return.

To respond to these needs, NRRI and Minnesota Sea Grant worked with county, state, and city engineers, road experts, and consultants to develop a Field Guide for Maintaining Rural Roadside Ditches (Fig. 3). 

One of the major objectives of the guide is to help city, county, and township field staff identify ditch problems and know when they encounter a routine problem that they can fix, and when a problem needs professional analysis, engineering, or permits.

The guide provides advice for conducting routine maintenance practices to minimize erosion and ensure that the ditch will function as designed, and provides a background on why some problems - such as enlarging a culvert or fixing a headcut - are more complicated than they seem. Regulations affecting ditches are also discussed, with guidance on permits that are likely to be needed.

Also included is a series of customizable checklists to help ensure everything gets remembered. The guide was designed to be useful for road supervisors in training their crews, for maintenance crews to bring with them into the field for reference, and for township officials responsible for the difficult task of supervising road work with very limited budgets and, often, limited expertise.

Visit the website for a free PDF, or to order hardcopies, printed on durable paper designed for rough use, spiral-bound, and with a built-in slope estimation tool for use on ditch side-slopes.

The website also includes additional resources, including customizable checklists and links to in-depth information on a variety of topics such as beaver management, culverts, erosion control, and more.

For further information, email jschombe@d.umn.edu.

Figure 3. The Field Guide for Maintaining Rural Roadside Ditches is available as a free PDF or durable printed version.

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