Ditch Maintenance

Maintenance of ditches needs to be done on a regular basis. Two very different items are the most common maintenance techniques, cleaning and reshaping. Be sure to do the right maintenance. Any ditch work does two undesirable things if not managed and repaired:

Cleaning

Cleaning ditches involves removal of sediment and vegetation from the bottom of the ditch. Very small amounts of material should be removed. Cleaning should be checked by walking the ditch after the cleaning. A small amount of annual and perennial grass seed can be spread ahead of the person checking the work. Their walking will bed the seed into the exposed ground. Cleaning the ditch does not involve changing the width or depth of the ditch. If it is too deep, the ditch may become a hazard to motorists.

Reshaping

Reshaping is often referred to as cleaning, but it is not. Reshaping involves significant changes to the cross-section of a ditch, or the slope (grade line), or both.

Except in rare cases, ditch reshaping should avoid making the cross-section larger. In fact, most ditches have evolved to be deeper than needed. Such ditches can be a safety hazard. For the same cross sectional area, a wide ditch is safer and more erosion resistant than a deep one, and the capacity differences are negligible. In many cases, it may be advisable to fill in a portion of the ditch.

Reshaping should be laid out prior to beginning work, and it should be checked by the foreman with a hand level to make sure the proper slope and cross-section are achieved. Generally the slope of the ditch follows the grade line of the road, but this is not always the best design. Whenever possible, the ditch slope should be at least 0.5 percent and no more than 2 percent. Remember, the purpose of the ditch is to carry water. If it is too flat the water may not be able to flow. If the ditch is too steep, it may erode and wash away.

The grade line of the ditch bottom should be on a straight line between relief culverts (that cross under the road) and driveway pipes. If the ditch slope varies, in places where the slope flattens out the ditch will fill in rapidly with sediment and possibly vegetation. Those locations will become a maintenance problem.

General Tips

ditch slope too flat, will result in sedimentation

ditch too deep, creating a hazard for motorists
Two examples of poor ditching practices.
Upper photo: ditch slope too flat, will result in sedimentation.
Lower photo: ditch too deep, creating a hazard for motorists.

Spring 2010

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This work by the Cornell Local Roads Program (CLRP) is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 Unported License.