Sheetflow

November 25, 2010

Straw Bales Don’t Work as Check Dams

Filed under: Video — Sheetflow @ 12:33 pm

Straw bales installed in ditch lines with water flows is a mistake. Water goes under and around, causing erosion, rather than backing up behind to allow sediment to settle. Check dams need to have a center point that is 6 to 12 inches lower than the outer edges so that water flows over the top, rather than around the sides. You can’t do this with straw bales. For this reason, these are not allowed to be used as check dams in the state of Washington.

November 13, 2010

Inspecting Plastic Sheet Installed on Slope

Filed under: Video — Sheetflow @ 12:07 pm

Plastic sheet is a good, temporary practice you can use to protect soil from soil erosion and sediment loss from a slope. When used, you need to make sure that the plastic is installed so that all the clean rainwater that runs off doesn’t end up dirty because it ran onto bare soil. The clean water needs to be collected and piped away from the bare dirt, or the plastic needs to be run all the way to the bottom of the slope into a stable ditch covered with grass, erosion control blanket, rock or other soil erosion prevention measure.

November 6, 2010

Grass and Dirt Berm Instead of Silt Fence

Filed under: Video — Sheetflow @ 11:43 pm

Most erosion plans show silt fence installed around the project perimeter. This makes sense when a project has some risk of eroded sediment leaving the project. When the risk is low, the area is small, the soil is loose with high infiltration, silt fence is overkill, wasted expense, and creates landfill waste. When possible, alternative methods of perimeter protection should be considered: berms, straw wattles, vegetation, buffers. In this example, existing grass and vegetation was pushed to the edge of the project and covered with straw. Since the project involved tilling compost 12″ into the native soil with a 12″ bark cover, the risk of erosion was very low this worked well and was left in place. The seed and root mass in the soil will grow fairly quickly and become part of the overall native plant mitigation area.

November 2, 2010

Diverting Clean Water Away From Work Area Part 1

Filed under: Video — Sheetflow @ 10:15 pm

The less dirty water you have to manage the less cost and hassle to your project. One of the easiest and cheapest ways to keep water out of your project is to identify areas that drain clean water into the project, such as from asphalt roadways, parking lots, roof drainage, etc. and divert the water away. The rule is “Keep Clean Water Clean”. Once clean water enters your construction site and becomes dirty, you “own” it. Sometimes, the only way to keep the clean water clean is to use berms, sand bags, pipes or other material to contain, divert and convey the water. In this case, the contractor made the decision to hold off demolishing the existing curb and gutter until the new, widened section was nearly completed with the new curb and gutter installed, then waited until they had a few dry days to remove the old curb and pave the first lift of asphalt. This reduced the volume of dirty water they had to collect and treat with chemicals, which in turn saved them money.

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