Preparing for the Rainy Season
David S. Jenkins
WSDOT Statewide Erosion Control Coordinator
September 1997
Now that the El Nino has ended and the La Nina has begun, the National Weather Service is predicting a much wetter fall and winter than normal. So, what are some things you can do now to prepare? How about: (more…)
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 clean water from asphalt roadways, parking lots, roof drainage, etc. and divert the clean 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.
On this I-66 highway project, the main cause of the slope erosion and rills is clean runoff from the highway. I assume there were curbs along the road edge that at some point were removed. I would restore permanent or temporary curbs to direct clean water to catch basins.
I might leave the slopes uncovered. This would depend on what phase of construction this project is in. If it is in shutdown, I would cover with plastic ( I hate using plastic because it ends up in the landfill), or some type of erosion blanket. I might even consider spraying the slope with polyacrylamide and not covering it.
I do like how the area at the base of the slope is lower than the road to the left so it acts like a sediment pond. Rather than pump to a geotextile bag, I would set up a chitosan-enhanced sand filtration (CESF) treatment system, treat and discharge clean water to the catch basin. Or, if the state environmental agency allows, I would use a gel-floc passive treatment system instead.
All photos may be used for teaching and training purposes with attribution to: David Jenkins, sheetflow.com
Photos may not be used for commercial purposes without prior express permission from David Jenkins, sheetflow.com
I know there’s a catch basin in there somewhere. Can you identify all of the materials? I think there are five or six types.
Inspecting Soil stockpiles: they need to be covered when not being used. This helps both with keeping the soil dry in the case of reusing it for backfill and with preventing rain from washing soil into the storm drainage system.
In addition, fugitive dust is prevented from blowing off of the stockpile in windy areas. If the stockpile is to remain in place for longer than a few weeks, black plastic, (at least 6 mil thickness) should be used, as the black plastic is UV (ultraviolet light) stabilized and won’t break down as quickly in sunlight as will clear plastic, which is not UV stabilized.
The plastic needs to completely cover the soil. If soil is exposed at the base of the pile, clean rainwater will run off of the plastic and into the exposed soil causing erosion of the soil and will generate dirty water runoff that can flow into the storm drainage system. In order to keep the plastic in place and prevent it from blowing off in the wind, plenty of sandbags or some other heavy material needs to be used to hold it in place.
As with the plastic itself, sandbag fabric should be UV stabilized if they will be in place for longer than about a month. White sandbags will deteriorate fairly quickly in strong sunlight.
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