Hydroseeding
An industry evolving
With stricter regulations under the National Pollutant Discharge Elimination System requirements and tougher mandates from local governments, contractors everywhere are looking for effective and economical ways to control erosion and establish vegetation. A plethora of choices is available, but for many projects, hydroseeding is the way to go. The mixture of mulch, tackifier, seed, and soil amendments sprayed onto slopes is often more economical than applying blankets and, under many circumstances, is as effective.
Here are some criteria for choosing hydroseeding over other techniques:
- Slopes steeper than 2.5:1 or along a waterway
- Rough or inaccessible areas
- Require stabilization even before vegetation can sprout
- Need quick establishment of vegetation, but not enough budget for sod
- Not enough budget for blankets
- Need soil stabilization during a rainy season or winter, before vegetation can be established
- Require moisture retention without having to resort to heavy irrigation
As the hydroseeding industry has matured, companies are offering more choices of mulch types. The most common applications are wood and paper, with newcomers also in the mix. However, the basic wood and paper mulches mixed with guar tackifier have evolved into cross-linked applications. Cross-linking fibers provide more strength and stability to the mulch. Many of the manufacturers of hydraulically applied materials claim that their products rival blankets for stability and growth of vegetation.
Soft Wood Mulches
The Seattle-Tacoma International Airport’s third runway project, a massive billion-dollar earthmoving project, required erosion control measures that could withstand jet blast even on stockpiles of dirt and steep slopes. EcoAegis II was applied, including seed, and has held up well for 18 months.
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Photo: Dietz |
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Photo: Dietz |
The product is one of three classes of wood mulch developed by Canfor (Canadian Forest Products Ltd.) of British Columbia. Each product can be applied with a conventional hydroseeding machine with as little as 10 minutes’ mix time.
The first, EcoFibre, is a mulch appropriate for general seeding purposes. With added tackifier, it can be used for slopes as steep as 2.5:1. It can hold 10 times its weight in water. For moderate to severe slopes, EcoMatrix is stabilized fiber matrix (SFM). It is recommended for slopes from 4:1 to 2:1 and lasts three to six months. The third class of mulch is EcoAegis, a bonded fiber matrix (BFM). Wood fibers of varying lengths cross-link into a mat that will retain water, prevent erosion and rilling, and hasten seed germination. After curing, the mulch forms a “hydromat” that absorbs rainfall but still allows penetration of moisture and air.
Each of these products is made from soft wood. Joe Hargitt of Canfor explains that the tubular cell structure holds moisture better than hardwood mulches. These preparations need water for about 10 minutes, three times a day. The mulch is prepared with a thermomechanical process, rendering the mixture sterile and taking away the threat of disease or weed seed. The wood used is waste from wood mills, not reclaimed wood that might be contaminated.
Steve Jones of Fiber Marketing Inc. in Renton, WA, a distributor for Canfor, notes that in many instances, EgoAegis performed as well as erosion control blankets but at a cheaper cost. In a test plot, EgoAegis was put down at a rate of 3,000 pounds per acre on a 1:1 slope. Dry weather lasted during application, but within three or four hours, torrential rain fell. The slope held even though no vegetation was started.
The Washington Department of Transportation has approved Canfor products for use on state projects. According to the testing, the products met all requirements for stability and for nontoxicity to aquatic life.
Jones notes that one advantage of hydroseeding is that the mixture has closer contact with the soil than erosion control blankets. Labor cost with hydroseeding is lower than that of installing blankets. Another option, blowing straw to be used in place of mulch, can come up against dust control regulations in some locations.
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