When the Road Runs, Drain It
Have you ever been on a dirt road in New Mexico when it started to downpour? Most likely, you watched storm water rush down ruts in the road, quickly turning the silt and clay around your tires into a gooey mess. Perhaps you even left your truck there for the night and walked off with a few extra inches of mud on your boots
Your vehicle is not the only thing that suffers because of poorly functioning roads. Such roads trap water that would normally spread out over the land surface and would slowly nourish plants that anchor the soil in place. Poorly located, designed, or maintained rural roads intercept this water and concentrate flow down the road instead. Land below the road dries out more quickly, and the concentrated overland flow accelerates soil erosion and gully formation. Ruts form more easily in the road and exacerbate the problem.
Poor road drainage is common in the Rio Puerco watershed. Steve Carson, who specializes in riparian and dirt road restoration, notes that the "Rio Puerco watershed, not unlike a lot of other watersheds, has been severely impacted by road infrastructure, both planned and unplanned." Poorly functioning dirt roads are a main cause of accelerated surface runoff in the watershed and a major source of sediment to the Rio Puerco. With careful assessment and planning, though, many of these low-standard rural roads can be converted to well-drained, functional roadways, even when it rains.
To begin to address this issue, the Rio Puerco Management Committee (RPMC), in cooperation with the Bureau of Land Management (BLM), private landowners, permittees, and the State Land Office, contracted with Carson to restore rural dirt roads in an approximately 100-square-mile area within the watershed. Carson and his crew - which included Van Clothier, Robin Kibler, and Carson's daughter, Gennie - initially surveyed about 100 miles of road in Torreon Wash, Penistaja Arroyo, branches of San Isidro Wash, and branches of Arroyo Chijuilla. The extensive project, funded by the Rio Puerco Watershed Initiative, focused on treating areas where roads deposited runoff directly into stream channels without a buffer zone of vegetation.
Planning for the project began in 2005, and construction began in May of 2006. Over a six-week period, the crew installed over 300 cross drains at key locations in roads to diffuse the captured, concentrated flow and redirect water to areas where it can infiltrate. The most common type of cross drain used in this project was the rolling dip, which includes an excavated drain (the "dip") on the upslope side and a raised "roll-out" on the downslope end that stops water from continuing down the road and guides it into a lead-out ditch. Rolling dips and other drainage features are designed to accommodate the amount of water draining into them as well as the vehicle types that use the road. For example, on a road that semi-trucks use, a rolling dip would have a long and gently sloped dip and roll-out so that a long truck could drive over it at an appropriate speed with little or no "bump." The areas disturbed are also seeded with native grasses to help offset the impact of heavy equipment. With properly designed and constructed drainage features in place, these dirt roads will stay intact with minimal maintenance, and valuable water will be harvested off the road and onto the surrounding landscape.
The restoration crew also treated a few problematic stream and arroyo fords, which pose a continual challenge to maintaining good channel and road condition. Rather than install culverts, which would require higher maintenance, Carson's crew built boulder cross vanes just downstream of road crossings to control grade in the stream channel. Large boulders are dug into the channel for permanence, are keyed in, and arc upstream so that pressure from a high flow will make the structure stronger. The rocks are also set a foot higher than the existing bed, which will cause the channel to aggrade slightly rather than downcut and possibly take out the road above. At another location, a rolling dip was used to redirect a diverted arroyo back into its original channel and across the road at an angle. Here, the water will be able to spread out in its natural flow pattern across the valley.
Although a variety of restoration techniques can be used to help a road function better after it is built, many problems could be avoided if roads were created with more forethought. "A lot of people don't really consider if it's ... necessary to have a road there" before putting one in, says Robin Kibler. Lack of consideration often creates multiple roads that all lead to the same place, or roads in the bottom of a valley where it seems easiest to drive in the dry season. Unfortunately, a valley bottom cannot be drained, and when it rains, vehicles end up either deeply rutting these roads or creating additional routes on higher land. Moving the entire valley-bottom road upslope allows the road to drain properly and can limit the number of braids created en route. This type of treatment was used in the Valle San Isidro, where a road that was encroaching on the arroyo was moved up on the hillside.
How well will all of these treatments work? Only water can tell. And if Kibler's experience on the job a few weeks ago is representative, the outlook is hopeful. Kibler had just finished constructing the drain of a rolling dip when a large storm sent water streaming down the road. With just enough time to move her equipment out of the way, she turned around to see her cross drain work perfectly.
But even people out on the road without heavy equipment can play a crucial role in maintaining good road condition. Drivers can avoid creating new roads where a road already exists. And as Steve Fischer, Rio Puerco Watershed Coordinator at the BLM, put simply: "If roads are really sloppy and you're making ruts, it's good not to drive on them."