Erosion Control Mulch (ECM) berms can be used in place of silt fence in many locations. ECM is also very useful for the home and camp owner.
Mulching is one of the most effective and cost efficient Best Management Practices (BMP's) we have to work with. For stabilizing construction sites, eroded banks, and topdressing buffer plantings, mulch can work wonders when it comes to protecting water quality. First a short discussion on why mulch is such an effective BMP. When bare soil is exposed to the elements, erosion begins to occur. Rain and wind can remove topsoil very quickly and deposit soil particles in the water. As these particles are transported in stormwater, they act like little magnets picking up pollutants and nutrients along the way. Once in the lake (or river or stream) these pollutants are deposited causing a whole host of problems including algae blooms and elevated levels of toxins.
Mulch applied to an exposed site in the right amounts will serve several functions. A primary function is to protect the underlying soil from erosion and keep soil out of a water body. A secondary function occurs when a mulched area is located on the down side of a slope between a hill and the water. The mulch will filter out most soil particles, fertilizers or toxins found in storm water runoff. It can serve to “lock up” those particles and materials. In some cases, a mulch berm between a driveway, lawn or parking lot and the water can be added to provide this filtration even if there is no exposed soil to cover. Another major benefit to mulching is the moisture holding capabilities of this product. Mulching landscaped areas with tree and shrub plantings ensures that water, either from rain or a hose, will percolate to the roots and keep the soil cool and moist.
While simple enough the confusion begins when you start shopping for the right type of mulch for a specific kind of job. Mulch comes in many textures and colors. Sorting out the differences between "conservation mulch", "erosion control mulch", "bark mulch" and "wood chips" can become a daunting task when everyone has a slightly different name for these items.
"Wood chips" are simply trees or brush that have been run through a chipper. Wood chips are NOT the best choice to protect against soil erosion. These chips are generally 1-2 inches square and have not yet been exposed to the elements or begun to decompose. Given their shape, chips do not weave together or hold much water. Some mulch is sold as "conservation mulch". Usually these mulches are standard pine or cedar bark mulch just like that used for landscaping flower or shrub plantings in your yard. This mulch may hold soil in place in fairly flat areas and retains moisture well. Because this type of mulch is often used for landscaping and around plantings, 3-4" is recommended. Because it is referred to as "conservation mulch" people may think this product is like Erosion Control Mulch. IT IS NOT!
Erosion control mulch (ECM) was developed to protect soil from erosion in areas that receive high traffic, exposure to the elements or occur on steep slopes. ECM, sometimes called slope stabilizer, is not your standard landscape bark mulch. The best way to describe ECM is "chunky". While regular bark mulch is fairly fine with strands of bark no longer than 6", ECM has larger pieces of woody material, bark and small stones. These small rocks mixed in with the bark provide additional structure to the product and add weight for keeping slopes intact. One key to the effectiveness of ECM is the size and shape of the bark material. When applied, the long and fairly thin material essentially weaves itself together and creates a kind of blanket over the soil. ECM traps plenty of moisture, similar to standard bark mulch. Thickness of application can vary depending upon several factors but 4-6" is average. Sites with extreme exposure to wind and water may need more while mulch berms may be 18-24" tall.
Buffer plantings are ideal sites for ECM. When installing a watershed buffer planting, use ECM. One important thing to remember is that 4" is too much mulch around the trunk of a tree or shrub. Remember to pull back the top 2" of material leaving 1-2" around plants. If the look of the ECM is too chunky for your taste, topdressing with an inch of standard landscaping bark mulch is fine. The reverse technique can also be used to create walking paths with ECM through your mulched beds.