August 1, 2003
A small industry of road and sediment surveyors has arisen in response to awareness of the impacts of roads and sediment on our fisheries. Ranging from rag-tag seasonal field crews to full-service companies employing Ph.D.s, these companies and non-profits are tackling the critical task of repairing, redesigning, or removing roads to deal with the sedimentation that has choked many of our fine salmon and steelhead creeks.
Despite the proliferation of road and sediment experts, many North Coast rural landowners do not have access to their services. This article provides an overview of some of the things they look at when they are out in the field. Landowners can use this information to guide the maintenance of roads in their neighborhoods.
Basically, these groups offer some variation on the same service: they walk your road network, identify sites where improvements could be made, where culverts should be installed/upgraded, and where it might make sense to remove roads no longer in use.
Many surveyors like to do their work in the dry season. They have a trained eye, and can visualize how water is flowing over and off of the road even when it's not raining. However, for the rest of us, it is best to check on roads during the rain. Actually, the heavier the storm, the better. So, go out there, and get wet!
Here are some things to look for:
Road Surface: As you walk the road, watch for areas where water is running length-wise down the road. If there is a "creek" in the middle of your road, you can bet that the water is carrying sediment away with it. You want that road fill to stay on the roadbed for smooth driving. The sooner you catch this problem, the easier it is to solve. If you have this problem, locate spots where water might be coaxed into running off the road, and install a water bar. Install water bars as often as needed to keep water moving off the road. Don't go too far before installing another one - keeping water moving off before it concentrates is critical for maintaining the integrity of a road. Try to avoid sending water over an active landslide site. Those are best left untouched.
Also, note whether the road is outsloped or insloped (see last issue). If your road has a berm (a running pile of material on the outboard edge), you may wish to punch some holes through it to allow water to drain off the road, or better yet, remove the berm altogether. If you road is in-sloped, make sure there is a clear ditch on the inboard edge, and make sure that the water in the ditch is draining off through a ditch relief culvert. Ideally, you will have a series of small ditch relief culverts (the interval depends on volume of runoff and the steepness of the road). Make sure that the ditch relief culverts are not plugged or prone to plugging. If there is wood or brush that could end up in the culvert, remove it.
Culverts: At each culvert, you want to check for five things: Is the culvert big enough to handle storm runoff? Is the culvert placed to allow for fish passage? Is all of the water going through the culvert, rather than under or around it? Is the culvert at risk of plugging with debris? What would happen if the culvert did plug?
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Is all of the water going through the culvert? Go to the culvert outfall. If water is coming out under or outside the culvert, your culvert is at risk of imminent failure. Although some culverts seem to function this way for years, this means that the culvert has holes in it, or it means that only part of the water is going in to the culvert to begin with. With its erosive powers, the water will eventually undermine the culvert and the road fill above it, damaging your road and depositing sediment in to the creek.
The quickest way to lose a road at a stream crossing is if the culvert plugs up with debris. When debris, such as branches, silt, rocks, or garbage clogs the culvert intake, the culvert's ability to transport water is compromised. This can lead to serious trouble during a big storm. Is the culvert plugged? If so, remove the obstruction. Is it at risk of plugging? Remove any debris in intake area - this doesn't mean that you need to clear everything out of the creek bed, just those items that may clog the culvert before your next maintenance visit.
What would happen to the culvert and road if the culvert plugged? This is the critical question. Imagine a plugged culvert. The water backs up behind the culvert, and at some point, starts spilling on to the road. Where does it go once it is on the road? If the road has a dip at or near the stream crossing, you are in good shape. If you can visualize the water heading down the road one direction or another, then you have a potential diversion. Culverts can be diversion-proofed by installing a "critical dip" in the road at crossing. In all cases, you want to ensure that, in the event of plugging, that your water will stay in its drainage, and not travel down the road. If it travels down the road, it is likely to jump off at the next possible spot, probably some random hillside. That hillside isn't armored to deal with large amounts of water like a creek bed is, and large-scale erosion will result. In this worse case scenario of culvert plugging, you want to make sure that the water at least stays in its watercourse.
Lastly, for all culverts, inspect the culvert outfall. Is water hitting an exposed hillside and causing erosion? If so, you can place large rocks at the outfall to minimize this damage.
Special Cases: While you want to pay the most attention to culverts, also be aware of some special situations. Unfortunately, roads have been and will continue to be constructed across dormant and active landslides. In these situations, you want to make sure that no storm runoff is hitting the landslide. In these cases, it is best to route water off to either side of the ditch.
Sometimes road cuts expose springs that well up in the middle of the road. These should be gently channeled off the road to a stable spot.
Lastly, remember that most roads require regular inspection and maintenance. Even if your road has been storm-proofed, outsloped, and otherwise upgraded, it will benefit from regular winter-time inspections. Please remember that sediment runoff from roads has the potential to harm fisheries habitat, and that it is largely preventable with proper design and maintenance.
This is the last of a four-part series on roads. Previous issues discussed why roads are important, culverts, and in-sloping/out-sloping. If you have any questions or comments, please contact the author at 629-3514. If you live in the Mattole River watershed, you can learn more about the Mattole Restoration Council's Good Roads, Clear Creeks Program by calling (707) 986-1078 or visiting www.mattole.org.
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- by Chris Larson Of The Mattole Restoration Councel
- about Good Roads, Clear Creeks
- by Mattole Restoration Council
TOC for Forest & River News, Summer 2003