When it comes to stabilizing disturbed soils it is important to do the job well the first time. When properly applied and monitored for germination and establishment temporary and permanent vegetative stabilization will protect the soil from erosion. However, if the stabilization is not applied correctly and/or the project is not monitored failure will likely occur.
Failure of vegetative stabilization practices in this case typically means erosions of the soils, sediment-laden discharges, and additional expenses. The added expense results from having to re-grade the site to correct erosion issues, reapply product, and paying people to do the work.
Traditionally, contractors have used grass seed and straw mulch as the primary method of vegetative stabilization. This method is adequate providing that the application is closely monitored and maintained. Lately, there has been an increase use of new and innovative products to aid with stabilization efforts. These products have a higher initial cost but they stand up better to the punishing conditions of a construction site. They provide a fast growing, less maintenance intensive alternative to tradition seed and mulch. Below I briefly highlight a couple of these products.
Cast grass seed with erosion control matting:
In this method seed is cast over the bare soil. An erosion control mat/blanket is rolled over top of the seed and pinned in place. This method works well to intercept and break up raindrops which dislodge soil particles upon impact. The key to installation is ensuring the erosion control blanket is in intimate contact with the soil surface. If not properly secured to the soil surface water that is sheet flowing over the surface will go under the blanket causing unintended erosion which is often not visible until the problem is serious.
Pelletized seed and mulch (with polymer):
This product is cast over bare soil in pellet form. The dried pellets contain seed, cellulose mulch, fertilizer, and polymers. After the product is wetted (either rainfall or watered) the dried pellets expand and form a blanket that is totally in contact with the soil surface. The fertilizer provides nutrients to the seed, the cellulose mulch provides moisture control and erosion resistance, and the polymers provide enhance erosion resistance through water repellency; water simple rolls off the product. Grass eventually grows and any residual polymers bio-degrade.
Hydro-seeding w/ polymer additives:
This method is very similar to what was previously mentioned with the pelletized product. The difference here is that the stabilization products (seed, cellulose, nutrients, and polymers and mixed with water and sprayed onto the bare soil. This creates a shell over the soil which remains until the grass germinates.
The take away from this post is to develop a stabilization plan that is appropriate and feasible for your job site. If there are enough resources and labor to provide sufficient monitoring and maintenance then the more cost effective tradition methods may be appropriate. If the project deadlines are such that there is no time for a ‘re-do’ and you’re looking for a product that is less maintenance intensive extra money spend on the initial application can save money on subsequent costly fixes.