Erosion Control

Erosion Control

The Scope of the Problemerosion1_ykpj

The high desert is one of extreme climates. In one day, it can experience 50 mph wind gusts followed by a summer thunderstorm that can drop a ¼ of its yearly average rainfall in an afternoon. Even in undisturbed areas, these elements have a huge impact on the environment which can result in soil loss. Soil erosion is visible almost anywhere in the state but is usually highest in construction areas. The biggest factor is soil disturbance and the loss of native vegetation. The use of heavy machinery during construction activities often leaves tracks that may concentrate water flow and create accelerated erosion of the already disturbed soils. It is inevitable that a portion of the ground be disturbed in developing areas, but it can be stabilized and reclaimed. By stabilizing the ground, native or other perennial vegetation can become established, which creates a vegetative canopy that intercepts and slows water before it hits the ground and reduces wind speed along the surface of the soil. The root systems of plants create an underground matrix, helping to stabilize soils and prevent erosion. Without native vegetation, soil loss rates increase 200 times or more. When soils are disturbed, it takes many years for vegetation to re-establish itself. After the first rains, invasive pioneer species such as Russian thistle start growing. The native vegetation cannot compete with the fast growing invaders.

Why Is Erosion Bad?

Soil erosion results in sediment in waterways, air pollution, expensive reclamation of eroded areas, loss of native vegetation and destruction of infrastructure such as bridges and roads. Soil also carries pollutants with it. Uncontrolled surface water movement is destructive; yet that same water stored safely in the soil is productive. Extreme storm water runoff will destroy buildings down-slope and deposit large amounts of soil on roads. Such erosion costs the home construction industry, local government, and homeowners millions of dollars a year.

How Do We Stop Erosion?

Soilutions has trained erosion control specialists. Owner Jim Brooks is an erosion control expert and member of the International Erosion Control Association who, specializes in Stormwater Management for Urban Environments. He has received numerous soil and water conservation awards. How he can help depends on your stage of construction. If you are in the planning stages of building we suggest you have us come out and design an erosion control plan. The best time to address erosion is before it happens. We consider site specifics when deciding appropriate erosion control techniques. Countless land owners rely on contractors untrained in hydro-dynamics to implement erosion control plans that inevitably fail. In the end they spend twice as much. So why not do it right from the beginning?

If you have erosion problems at an existing site, we can help, too. We have a long list of earthwork techniques that we use to control surface water and prevent soil erosion.

What we offer:

  • Slope stabilization
  • Soil stabilization
  • Earthworks
  • Gabion
  • Streambed crossings
  • Mulching to prevent erosion
  • Stormwater retention
  • Move water safely from built areas
  • Arroyo reclamation

Contours

Contours are imaginary lines created by connecting points of equal elevation contour_swale2_kbp7across a landscape. We use contoured earthworks to intercept and stabilize the flow of water. A ditch (swale) made along a contour will stop the flow of whatever water enters it from above. Water will spread laterally within the ditch, allowing soil particles to drop out of the water. The water will then infiltrate the soil.

Contour Swale

A swale is a depression or ditch dug on contour, or slightly off, to move surface water to a desired location. The soil excavated from the swale is used to make a berm downslope. Swales are used to intercept and slow surface water on a slope, which in turn allows it to infiltrate the ground. Swales direct water laterally across a slope instead of vertically. The water harvested behind swales creates an ideal place to plant.

Berms

Berms are swales but without the depression. They also move water on contour berm1_v8mmto a desired location. Berms can be made out of mulch, soil, wood chips, or brush.

Surge Basins


The faster water flows, the more destruction it causes to our delicate soils. When water collects and funnels, as it does out of downspouts and in culverts, its velocity and destruction increases. Surge basins are high-volume capacity depressions in the ground placed to receive high-velocity surges, usually under canales/downspouts and before and after culverts. Their primary function is to slow high-velocity water before it overflows and moves, controlled and benevolent now, through the rest of the landscape.

Most commonly, after creating a basin in the appropriate place, we line it with a geo-synthetic fabric and staple the fabric down securely. The fabric’s main purpose is to keep moving water from undercutting the soil beneath the rocks placed on top.

In the next step, we cover the fabric with rock. Rocks absorb and dissipate the energy of violently flowing water. The more violent the water flow, the larger the rock size required to properly dissipate the energy.  Rocks also protect the fabric from photo-degradation. If water enters the basin fairly slowly or at the slow end of the basin, one can choose organic mulches instead of rock. However, if we use an organic mulch, we will generally avoid using the geo-synthetic fabricin order to all it to interface with the soil.

Finally, before we call the surge basin complete, it must contain an overflow. A surge basin without an overflow is a dam. The elevation of the overflow determines how much water the basin can retain. We place overflows deliberately to take water directly where we want it in the landscape. Because we are dealing with concentrated, moving water, they require fabric and rock. Overflows usually connect the surge basin to a functioning arroyo or other such earthworks.

Sponges

Sponges are buried organic matter used to improve water absorption and retention in the soil. We can make sponges out of straw-bales, straw-bale flakes, mulch, compost, phonebooks, or a multitude of other recycled materials.

To understand why, we will look at two principles of water: adhesion and cohesion. Adhesion is water’s tendency to stick to something. It causes the last of our drink to stick to the glass bottom even when we tip it up-side-down. Organic matter in soil gives water something to adhere to. The less organic matter found in the soil, the more likely it is that rain water will run-off instead of into our soils. Sponges create preferred points of entry for surface water.
Cohesion is water’s tendency to stick to other molecules of water. Ever notice how it is more difficult to make dry fabric wet than it is to make a damp cloth wet? Dry soils often fail to absorb water well because water is looking for more water. At the first sign of rain, dry soils, despite their needs, repel water like a dry piece of fabric.

A sponge acts as a port of entry for ground water, holding many times its weight in water. In addition to that, water soaks into the soil around the sponge making the entire area more absorbent.

Just as sponges increase soils ability to absorb rain water, the same principles of adhesion and cohesion allow sponges to decrease water evaporation from the soil. When the hot sun reappears after a storm, it quickly begins drawing the water out of the soil back into the atmosphere. If the water has nothing to adhere to, i.e. organic matter, it gives up the fight quickly. Under our desert sun, unprotected soils can dry up to six feet below ground surface. Next fall, when grasses begin to loose their lively color, notice how the grass around the base of trees remains greener longer than other grass. This is in part due to the shade of the tree, but also may be due to the increase of organic matter and root structure near the tree.

Mulch

Time and time again, organic mulch has been disregarded as an effective method of erosion control. We have used mulch successfully in many projects where it was thought that it could not perform. We use our Native Mulch which is a coarsely ground woody material with a shredded look. Mulch has many characteristics that make it ideal for slope stabilization.

The millions of shredded fibers in mulch interlock forming a blanket of mulch that holds the slope while intercepting water flow. When rain falls on the site water is spread laterally thru the mulch as a result of the surface area and airspace. The shredded material acts as millions of tiny dams forcing the water to slow down and spread out. Mulch will also absorb water, trapping it thus allowing it to percolate into the soil underneath. Because mulch holds water effectively through adhesion and cohesion, it keeps the soil surface cool and moist longer, thus promoting favorable conditions for beneficial organisms to thrive and further develop the soil profile. Over time, the soils will become more and more aggregated, increasing their ability to hold, percolate and exfiltrate water.

Lack of moisture keeps native vegetation from re-establishing, but with mulch, moisture is kept in the soil longer allowing vegetation to establish and stabilize the slope. Native vegetation on mulched areas grows healthier and is more drought resistant than on bare soil. Invasive weeds love bare, dry, disturbed soil. When organic mulch is used to cover disturbed soil, it prevents sunlight from reaching the soil surface thus inhibiting the germination of many invasive weed species. When wind blows, it carries soil along the surface of the ground resulting in air pollution and damage to buildings and cars. Mulch has a textured, rough surface that allows it to trap wind-blown soil (and seeds). To restore the appearance of the mulch and to reduce the germination of unwanted seeds, you can lightly rake the mulch every 1-2 years. Soilutions’ Native Mulch resists wind erosion and will stay in place much better than smaller sized mulches.

Mulch will not erode during large rainstorms nor will it roll down the slope. Mulch forms a bond with the soil and is eventually held in place by vegetation. Our organic mulches are made from recycled materials, creating a sustainable product that is not mined or petroleum based. It will biodegrade over time, resulting in an organic layer that will continue to provide soil stabilization and a growing medium for vegetation. Our Native Mulch™ is made of recycled green waste brought to us by New Mexico citizens.

Straw Wattles

Straw wattles are tubes filled with either straw or mulch and are up to 20 feet long. They are staked down on contour to “shorten” slope length and provide slope stabilization. We then apply mulch on top of the wattles to prolong their life. They are normally not used in areas of high water flow but along slopes. Wattles may be used in conjunction with other techniques such as swales and berms.

Gabions

You may have seen a gabion along the highway, a wire basket filled with stone, usually placed in an arroyo or drainage. Gabions are “leaky dams” mainly used in areas of concentrated water flow, such as streambeds and arroyos, to create a check dam or drop structure. They are filled with stone so water can filter through. Because gabions are porous, water will only backup temporarily while draining through in a non-erosive velocity. Gabion mattresses can be installed in roads or driveways instead of culverts to create a stable stream crossing that will protect the road from erosion.

Examples of Erosion Control

In the photos below, you can see the area that mulch was not applied. You will notice the numerous rills and erosion. The swale at the bottom of the slope is now full of sediment and not functioning. Water creates channels (rills and gullies) and over time will continue to use the same channels resulting in high soil erosion and sediment transport.

In the pictures below, the slope has been stabilized and a swale installed that still continues to function. The mulched slope helped retain moisture in the ground resulting in more and healthier native plants than compared to the bare slope.