Road Runoff Control

1. THE PROBLEM

Throughout the Appalachian Mountains there are many miles of streamside gravel and unsurfaced roads. The runoff from these roads flows into the adjacent streams, dumping sediment into the channel with each rainstorm. Once sediment is in the stream aquatic habitat is degraded, productivity is reduced, and the water unfit for many uses.

These roads are some of the oldest and most used roads in our forest land. The cost of closing and relocating, reconstructing or paving these roads is far beyond the funds available. In many cases the roads cannot legally be closed.

2. A BETTER ALTERNATIVE

Road Runoff Control (RRC) is a simple and effective set of measures that protect the adjacent streams while keeping the road open. These measures are similar to those used to control runoff and sediment at construction sites.

The principle is simple: control road runoff so it does not go directly into stream channels. Runoff must be forced into areas where it will either infiltrate or at least deposit its sediment load.

3. DESIGN

The design and field application of RRC should be kept simple. The three basic criteria for RRC are:

• Simple and low-tech, so only minimal training is needed for designers and implementers;
• Simple yet effective design, planning is done mostly in the field;
• Low cost construction, using locally available equipment and minimal new materials.

	A. DITCH OUTLETS are just that, new outlets in existing ditches to disperse runoff more frequently. This reduces the runoff volume at any one outlet and makes it easier to infiltrate the runoff in a smaller area, like between the road and the adjacent stream. B. HUMPS are built up sections of road surface that create short lengths of reverse grade. This forces runoff that is flowing down the road off to the side.
	C. SEDIMENT TRAPS are holes dug into the ground to catch and hold sediment in the road runoff. Traps are used where concentrated runoff can not be infiltrated. For example, at ditch outlets near streams or in ditches that can not be outletted before reaching a channel. D. RELIEF CULVERTS are new pipes installed to pass ditch water from one side of the road to the other at places where the ditch water can be infiltrated or its sediment trapped.
	E. OUTSLOPES are sections of road surfaces that slope to the outer road edge so runoff drains from the road surface. Outsloping serves to frequently remove water from the road in small amounts rather than allow it to gather and run the length of the road surface. F. BERMS are low mounds or banks at the edge of the road to keep runoff on the road until the flow reaches a filter area or sediment trap site.
	G. OPENINGS are outlets cut into existing berms along the road edge that hold the runoff on the road. Openings let the runoff flow from the road into infiltration areas

5. APPLICATION

Once a section of road is selected for RRC, an overview is made to get an idea of potential sites to divert runoff and measures needed.

Starting at the lower end, walk the road identifying and marking the site for each practice. Detailed field notes should record which practice is needed and its size. This is important so the person actually doing the work will get the desired results.

When your field design is completed, you should be able to see how the entire project fits together. You should see how each practice relates to the practice above and the one below. RRC features are small and should be frequent along the road.

6. GETTING READY TO WORK

Once the field design is done, you can estimate the costs of: gravel, seed, fertilizer, and mulch, and the number of hours for hand labor and each type of equipment (backhoe, motor-grader, bulldozer).

7. DO IT IN THE DRY, DO IT IN ONE DAY

Because this work occurs in places that already put sediment into streams, it is important to schedule your work when the chance of rain is low. Each practice should be finished the same day it's started so there is low risk of construction sediment getting into the stream.

Field adjustments in size, exact site, etc. are expected once the construction starts because the project was field designed. For example you may not be able to make a sediment trap as large as planned or it may have to be moved slightly, which means adjacent practices may need adjusting to compensate.

8. IT DOES WORK

These practices have been applied to a number of streamside gravel roads in the National Forests in North Carolina. Sedimentation of adjacent streams appears to have been reduced by 75% or more. This is allowing the streams to clean previously deposited sediment out their channels.

9. MORE INFORMATION

For more detailed information on this Road Runoff Control method, please contact:

Richard G. Burns
Forest Hydrologist
USDA Forest Service - NFsNC
P.O. Box 2750
Asheville, NC 28802-2750

031996/2030

Persons of any race, color, national origin, sex, age, religion, or with any disability are welcome to use and enjoy all facilities, programs, and services of the USDA. Discrimination of any form is strictly against agency policy, and should be reported to the Secretary of Agriculture, Washington, DC 20250.

© Blue Ridge Bicycle Club Inc. 2004