Friday, September 1, 2000

September BMP Q&A

By: Jake Donellan, BMP Forester (Ret.), Texas Forest Service 

Q: I have a question about wing ditches. My guys put them in whenever they think one is needed. I was wondering do you have any specific guidelines as to how many and how often they need to install them?

A: Wing Ditches are water turnouts that divert water away from the road and/or a side ditch. The purpose of a wing ditch is to collect and direct water from road surface runoff into an undisturbed area. It is necessary that the wing ditch allow the water to slow down and to channel the water away from the road and roadside ditches. There are some guidelines to use on when to install wing ditches and how often. Experience, which should never be downplayed, also plays a large role in knowing when and where to put the wing ditches along your roads.

You probably want to use wing ditches anywhere where there is an accumulation of water or a section of road or trail. The water should be diverted so as to decrease the volume and velocity of the water especially on slopes. You also should use wing ditches where there is a buildup of drainage water in roadside ditches. This buildup can eat away at roadbeds and scour out the roadside ditch itself. The recommended guidelines for wing ditches are on pages37 and 38 in the Texas Forestry Best Management Practices Manuel sometimes called, “the Bluebook.”

The spacing of your wing ditches depends on slope and soil conditions. On 2%-5% slopes the spacing should be no greater than 200 feet apart. On slopes 5%-10%, the distance between wing ditches should be no greater than 100 feet apart. Slopes greater than 10% should have wing ditches no more than 75 feet apart. Your experience should tell you that you might need more wing ditches if you are working on highly erodible soils. One other thing to keep in mind is that wing ditches should not feed directly into streams, gullies, or adjacent drains or ditches.

Wing ditches should be installed so that they leave the road ditch line at about a 30 to 45 degree angle to the roadbed and be designed to follow the natural shape (contour) of the land. The runoff water can be spread out, filtered by brush, or retained in the wing ditch. Wing ditches are very effective tools to help maintain roads and trails. Wing ditches can be even more effective when used in conjunction with other road BMPs like water bars, rolling dips and crowning the road. I hope that answered your question. Does anybody else have any other suggestions or methods that they use?

If you are in the area stop by see me. If you have a BMP question you would like answered, please contact me.

* This article was published in the September 2000 issue of the Texas Logger

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