HOW TO: PREVENT EROSION DURING CONSTRUCTION
The U.S. Department of Agriculture estimates that one billion tons of topsoil are lost to erosion every year. Not only does erosion take away precious topsoil, but also clogs waterways and damages adjacent properties. The National Pollutant Discharge Elimination System (NPDES) Phase II provides federal guidelines for preventing erosion. These guidelines are regulated by state and local agencies, making it imperative to research the guidelines for your area.
What can you do to prevent erosion on your projects? The solution can be quite easy or difficult, depending on the site. You might have to be creative. Use these tips to get started.
Water, along with wind, is a primary agent of erosion. Water will, obviously, always run downhill; however, it will run uphill when the volume of water flooding an area moves the water out of its banks and up into higher ground. Prior to the onset of construction, make a plan to slow the movement of water. If you have the luxury to do so prior to construction, observe the site in a rainstorm and see where the water runs.
Observe the property for potential slope problems, affected areas adjacent to the site and access to waterways. Plan accordingly.
Disturb as little area as possible. Try to disturb only one area at a time. It may seem more expensive to bring in equipment more than once, but the cost of remediation caused by excess sediment (and possibly being fined for causing the mess) may more than make up for the initial cost-savings.
Once disturbed, if an area will not be impacted by further construction, go ahead and seed the area with a temporary cover. Check with local experts to find a groundcover that can be easily converted, if necessary. Chances are, some construction process will overrun into the seeded area, but that is to be expected.
Hydroseeding can work on some slopes, but is not effective on slopes greater than 4:1.
Plastic sheeting to shield the soil from rain and irrigation can be effective in small, erodible areas only. Don't use it in large areas.
If you're removing trees from the site, consider chipping them on site and using the chips to form erosion-control swales or apply a 2- to 3-inch layer over the soil to slow water movement and catch sediment. The chips can be incorporated into the soil when complete or hauled away. If you leave them in place, be sure to apply an extra dose of nitrogen fertilizer to help break down the wood chips and prevent nitrogen deficiency on installed plantings.
Silt fencing is often a part of erosion control. This consists of wire support covered with filter fabric and staked into the ground using 36-inch T-posts or hardwood posts. In order to work properly, you should dig an 8-inch trench along the area where you will install the fence. You should drive the fence posts at least 16 inches into the soil. Once upright and tight, backfill the trench with the soil. You should inspect the fence after each rain event for breaks in the system and for sediment accumulation. Once sediment reaches half the height of the fence, you should remove the sediment. Silt fences can be installed across slopes to help slow water movement and catch sediment. You should not install them across waterways, ditches or other areas with concentrated water flow — these fences were not designed to handle this much pressure and will fail.
Straw wattles, which resemble long, straw logs, are another means to slow water and catch sediment, and seem to be more versatile than silt fencing. These must be installed in a trench, as well, and staked and backfilled on the upper side. You should not be able to see daylight under the wattle once installed, and you should turn down the ends slightly to prevent ponding on the back side of the wattle. These are made with either UV resistant netting, which holds for three to five years, or with biodegradable burlap, which lasts approximately one to two seasons.
You may need to also install erosion control mats or blankets along streamways and ditches to help catch sediment.
A relatively new product, the Silt-Saver, consists of a plastic frame with filter fabric covering that you can place over basins to catch sediment before it enters the drainage system. If you use this method, you'll need to monitor and remove sediment to insure that the system keeps working.
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