Sustainable Land Development Today - October 2008 - (Page 16)

inches on the sides and 18 inches downslope. Rolls are secured to the ground with lawn staples at a density defined by the Erosion Control Technology Council of 1.5 staples per square yard. Staples are generally put a foot apart across the top and every three feet along the sides on both overlapping and non-overlapping portions. Staples should also be installed down the middle of the roll in a diamond or square pattern. When installing ECBs, good contact with the soil surface is important to reduce soil bridging and washouts under the ECB. Correct installation—making sure the blanket is flush with the soil surface—is important for long-term erosion control and vegetative establishment. Hydromulches Like ECBs, there are many types of hydromulches available for erosion control. The selection of a hydromulch for a particular purpose depends on the slope and soil type where the mulch is being applied, the price of mulch application, and the effectiveness of a particular mulch type under a unique set of circumstances. The wide variety of hydromulches allows the applicator to select the optimum mulch for a job. Unlike straw and ECBs, hydromulching requires specialized equipFigure 2. Hydromulching a large slope. This process should be repeated from the bottom of the slope. Note the berm at the top of the slope to prevent runoff from the upper areas onto the slope. ment, including a water tank with a mixer and a high-powered pump to apply the mixture to a slope. A water source, such as a pond, stream, or fire hydrant, near the site is also needed. The amount of water needed is based on the manufacturer’s recommended amount of material in the tank and the recommended application rate. Hydromulch application does not require advance site preparation or direct access to the slope, making it suitable for large slopes (figure 2). In addition, hydromulch does not contain netting that could entangle wildlife or degrade slowly. Lime, seed, and fertilizer are sometimes mixed with the mulch, but this Slope Ratio ≤ 2:1 ≤ 2:1 ≤ 2.5:1 Material Stabilized mulch matrix Bonded fiber matrix Fiber reinforced matrix Rate (lbs/ac) 1500-2500 3000-4000 3000-4500 Description Organic fibers with soil flocculants or cross-linked hydro-colloidal polymers or tackifiers. Used to provide erosion control and facilitate vegetative establishment on moderate slopes. Designed to be functional for a minimum of 3 months. Organic fibers and cross-linked insoluble hydro-colloidal tackifiers. Used to provide erosion control and facilitate vegetative establishment on steep slopes. Designed to be functional for a minimum of 6 months. May need 24 h cure time. ≤ 6:1 Hydraulic mulch 1500 Organic defibrated fibers, cross-linked insoluble hydro-colloidal tackifiers, and reinforcing natural or synthetic fibers. Used to provide erosion control and facilitate vegetative establishment on very steep slopes. Designed to be functional for a minimum of 12 months. Paper, wood or natural fibers that may or may not contain tackifiers. Used to facilitate vegetative establishment on mild slopes. Designed to be functional for up to 3 months. Table 3. Various types of hydromulches, adapted from Erosion Control Technology Center descriptions. 16 October 2008 Sustainable Land Development Today

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Sustainable Land Development Today - October 2008

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