Erosion is the process of soil being removed by physical processes. The most common processes are water erosion and wind erosion. Less frequently, animals can make significant contributions to erosion. In urban areas, the real culprit is almost always water.
If you live on a property with steep slopes, you are a prime candidate for erosion. The ability of water to carry particles increases as the square of its velocity. In other words, for a given volume of water, when the water speed doubles, the soil carrying ability goes up four times. Steeper slopes mean faster rates of water flow which means more erosion.
Water that causes erosion normally comes from three sources: rainfall, drainage from other peoples’ property (or perhaps your own yard), and water leaks. If you do not have gutters, heavy rainfall can dump huge amounts of water around the edges of your foundation. To illustrate the problem, consider a peaked roof over a 20-foot wide garage with 2 foot wide soffits (the part of your roof that sticks out beyond your walls.) From the peak of the roof to the edge is 12 feet. So during a light rain of ½ inch, six inches of water ( 12 X ½) will fall off of the roof onto the ground next to your foundation. During a moderate rain of 2 inches, TWO FEET of water will fall on the ground at the edge of your foundation. If it rains 6 inches (which happens in north Texas every couple of years) SIX FEET feet of water will pour onto the ground next to your foundation. As water pours off of a roof, it can certainly carry away soil.
Occasionally, a plumbing leak can cause significant erosion. For a leak to cause erosion, there has to be a significant flow of water, and there has to be a place for the water to flow. If there is a big leak, and the water is trapped in the soil, then there will be no erosion. This is why under-slab leaks do not cause erosion. (If fact, under a slab, leaking water that is trapped is absorbed by the soil which, in the presence of expansive clays, can cause a foundation to be lifted up.) On the other hand, leaking sprinkler systems (or overwatering) can contribute to erosion.
The general approaches to controlling erosion are: reducing water velocity, capturing water, and diverting water. If space and regulations allow, one of the best ways to deal with steep slopes and to reduce water velocity is retaining walls. Where conditions allow, a series of low retaining walls can create a terraced slope. The flat surfaces between the walls will not be subject to erosion. For areas with expansive soils, retaining walls need to be constructed with proper drainage and with enough strength to resist the pressure created by expanding soils. If not properly constructed, retaining walls can be damaged or overturned by expansive soils. A beautiful example of terraced slopes for both construction and agriculture is the Longji or Longsheng terraces in China.
Water velocity can also be reduced by forcing water to flow through obstacles that break up the flow. Most commonly, areas that are exposed to significant water flow are covered in decorative rocks or gravel.
Gutters and downspouts help to capture and divert water. It is very important to have splash blocks, or better, underground pipes, to carry away the runoff. If your downspouts dump water right at the edge of your foundation, the water can carry away a significant volume of soil. In addition, an area that is frequently saturated with roof runoff can lead to clay soils expanding and then lifting a home. It is always important to keep water from standing around your foundation.
For many urban lots, where homes have narrow side yards, retaining walls are not a suitable option. For closely spaced homes, particularly where the narrow side yards (sometimes only five feet) have significant slopes (which can be as steep as 30 degrees) there are two common approaches. The first and most common is vegetation, most frequently grass. There are other suitable ground covers, all of which will cover the surface of a slope with roots and plants. For shaded areas, mondo grass works well as does jasmine. Rocks or gravel placed over a filter fabric also works well.
Drainage that concentrates water in an area where the soils are not properly protected can cause significant erosion. If a swale between two homes receives significant volumes of water, it needs to be covered by a thick layer of grass or some other ground cover. If you live next to a drainage feature, such as a drainage ditch or a stream, you should ensure that the side slopes or banks are properly protected. When a stream is involved, this may require a substantial investment in walls or other features.
Insects are attracted to water. Some insect-eating animals, in particular armadillos, can do a lot of damage while digging for insects. One homeowner in Arlington Texas, who lives next to a wooded area, replaced the entire back yard with varieties of vine ground covers (jasmine, Virginia creeper, and honeysuckle) after armadillos repeatedly tore up the grass. Other animals, such as skunks, opossums, rabbits, and raccoons can cause some damage, but generally only do so when digging burrows (often under foundations.) If an animal burrow is in an area where water accumulates, such as next to a gutter downspout, the burrow can direct water under a foundation, a process that can cause a great deal of damage.
In some cases, lots are so flat that water simply stands and does not drain off. In such cases, erosion is not a problem. Gutters, downspouts, underground pipes, and pumps are generally the solution.
Sometimes, it is pretty obvious that your house needs some work done on drainage or grading. Whether or not there has been related foundation damage is often not so clear. To ensure your home stays safe and sound for you and your loved ones, it’s important to leave this work to the professionals. Contact Advanced Foundation Repair today for a free, precise inspection. With years of experience, a transferable lifetime warranty, and the willingness to work with you on a payment plan to make sure your home gets the repairs it needs, you won’t be disappointed.