It’s all too easy for sheet and gully erosion to develop while no one’s watching. You can clear some trees and undergrowth away one day, then return after a weekend to find half of the exposed soil, or more, missing from its original location. This kind of damage requires careful repair since the original stability of the soil is weakened and disrupted. It’s especially important to properly repair any erosion occurring around or under the area a structure is being built, but even erosion in a remote part of a property can have long reaching effects. Don’t let mining or roadway erosion damage continue to worsen when these repair techniques are available.
As with erosion control, stabilization of the existing soil and slope is always the first step in repairs. This can be harder than it looks when there’s a major channel or gully carved into an area. While the channel may look like it can be simply filled it with gravel and covered, it creates a fast drainage zone under the gravel that continues to erode. You’ll find your fill material settling lower and lower over time, creating dangerous conditions under a building that needs a stable base. If you try to toss in stumps or other debris from site clearing, to fill in erosion damage, the problem occurs much faster as the organic material decays. Soil stabilization requires an engineer’s approach, filling and stabilizing any cuts and depressions, and often includes adding drainage to control how water flows under the surface. Steep slopes and unstable areas must also be removed and reshaped as much as possible during the repairs for the patches to stay in place.
Geotextiles play an important role in stabilizing rills, gullies, and other cuts and cracks in the soil surface. Even when packed with the right fill material, these zones are susceptible to the erosion that occurs between two different materials. Covering the repaired area, with a layer of geotextile, helps hold the edges together and discourages water from seeking a gap between dissimilar materials. The tensile strength of the textile prevents spreading; especially if the damage occurs in or under a roadway that is constantly subjected to downward forces.
Encouraging Natural Growth or Covering Entirely
Badly eroded areas should be transitioned into natural vegetation whenever possible. If a slope is simply too unstable or steep for this effort, the most serious repair method of hard armoring may be necessary. Hard armoring is covering the entire hillside in a carefully built layer of concrete or a similar impervious material. It creates other runoff and drainage issues, but it’s often the last measure possible for a hillside that is too damaged for planting and too close to roads and structures to remove. Hard armoring relies on multiple, geotextile layers under the surface, to keep the inflexible surface from losing contact with the softer soil beneath. Even if you manage to follow a vegetation plan as part of your repair, you may need to start with geotextiles to keep the soil from washing out from around the new roots.
Cover Materials for Actively Eroding Areas
Active erosion, that needs repair rather than just control, will also demand a larger and heavier cover material than other areas. Rip rap is the usual recommendation for covering slopes that have begun to rill or tear in sheets. Due to the larger size of these pieces of rock, they exert a lot more stabilizing force than mulch or gravel. Rounded stones may offer a more appealing look, but they’re not usually recommended for covering active erosion. Uneven and sharp-edged pieces are a better choice because they lock together and resist the forces of gravity that could slide them off of the slope. Make sure to use a reinforced geotextile under larger and sharper pieces of stone, since rock blankets put a lot of wear and tear on polymer materials.
Controlling Traffic Levels
Traffic should be minimized as much as possible when dealing with an actively eroding area. If the erosion is occurring due to a paved or gravel road, consider redirecting traffic if possible. This is often helpful at mining sites, where it’s not too much work to cut in a new road, so older tracks can be repaired and stabilized. If there’s no way to get people and equipment off of the ground, try using temporary track panels and boards that protect the soil from mechanical erosion. Even if these tools add more compaction, it’s better than physically disturbing and dislodging soil with every footstep.
While all forms of erosion are best handled with the help of a soil engineer, they’re downright required for developing repair projects. An existing erosion problem can become much worse if your repair and control attempts fail. Don’t add any stone, or start stretching out geotextiles across a loose hillside, until you have guidance on the best methods to use and how to apply them specifically to your particular problem.