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:
- The work exposes the gravel to erosion.
- It may also change the depth of the ditch to an undesirable degree.
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 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.
- Always clean ditches while moving uphill
- Place erosion protection or seeding at the end of each day and before any rain
- Have erosion-control material ready before starting (in case of rain)
- When in doubt, GET HELP. Your local Soil & Water Conservation District is a good resource, or contact us for advice.