Sheetflow Construction Erosion and Sediment Control

June 14, 2019

Horizontal Silt Fence

Photo: David Jenkins

Walking around South Congress district south of downtown Austin, I discovered a new best management practice-horizontal silt fence. This makes access to the work area so much easier than if vertical silt fence was used. Fortunately no rain in the near future.

March 8, 2019

Curb Inlet Protection

According to the Minnesota Stormwater Manual:

“Inlet protection devices intercept and/or filter sediment before it can be transported from a site into the storm drain system and discharged into a lake, river, stream, wetland, or other waterbody.

These devices also keep sediment from filling or clogging storm drain pipes, ditches, and downgradient sediment traps or ponds.

Inlet protection may also include placement of a barrier to create a bypass of an inlet transferring flow downstream to a sediment trap, basin, or other inlet discharging to a non-critical area.”

Nothing wrong with sediment control BMPs, as they are necessary tools in an effective erosion and sediment control system.  However, these do not “filter” sediment. 

When properly installed, these allow for ponding of water which allows larger sediment to settle out, keeping it out of the storm system.  This is a good thing, but doesn’t necessarily prevent water quality non-compliance.   

I do like this statement in the manual : “Caution: To the extent feasible, erosion prevention practices such as stabilization are preferred to sediment control practices.”

In my world, where we have to meet a turbidity effluent limit of 25 NTUs, stabilization and stormwater management are the primary methods used to meet strict turbidity limits.  

February 16, 2019

Vacuum Sweeper Maintenance

If I specify a vacuum sweeper on a construction project, I expect it to be operational.

I require all systems to be functional per manufacturers specifications.

If not, the sweeper goes away, maybe the job is shut down, until a working sweeper is brought to the site.

Specifications:
1) Power brooms shall not be utilized without prior approval by
the Engineer.

2) Contractor shall have sufficient working vacuum sweepers on
site at all times work is being performed.

3) All sweepers shall have on-board water spray systems that
shall be operating at all times.

4) systems shall function per manufacturer specifications
including, but not limited to, spray water systems, blowers,
vacuum nozzles, hoses, debris hopper, hydraulics and
electrical.

5) At no time shall debris hopper seals leak debris and liquids.

September 19, 2013

Lessons in Solving Big Weather-Related Problems

Grading and Excavation Contractor
September-October 2003

When it comes to controlling erosion and sediment in bad weather, construction of a third runway at Seattle-Tacoma International Airport, near Seattle, WA, qualifies as a genuine challenge. Providing a foundation for the 8,500-ft.-long, 150-ft.-wide runway in the hilly terrain will require an estimated 17 million yd.3 of fill. Since construction began in 1997, about 5 million yd.3 have been placed. It will take a large fleet of dump trucks, running 20 hours a day, three and a half years to bring in the rest. Then there’s all that wet weather the area is famous for, especially in late fall and winter. Two years ago, for example, the project was drenched with about 5 in. of wind-driven rain in one 36-hour period. (more…)

September 4, 2012

Prepare for Fall and Winter Rains

Winter is approaching, now is the time to get construction projects ready. Here are some things to consider:

Cover bare soil. Final grades can be covered with hydroseed, erosion blankets, topsoil, bark or whatever final cover is planned for the project.

Get your hydroseed contractor lined up now and avoid the October rush.

Don’t open up more than a few acres after September 1st.

Grades that aren’t being actively worked can be covered with straw at a rate of 1500 pounds per acre. This is a very cheap and effective way to protect bare soil from raindrop impacts and erosion. Hand seed before spreading the straw. Spray it with water to help hold it in place.

Track your slopes with a Cat: up and down slope, not across slope. The first helps prevent erosion, the second speeds it up.

Use flex pipe drains at bridge ends if your permanent drainage system and curbs are not in place. Collect the water from the bridge using sand bags and divert it to the pipe. Make sure the pipe is long enough to reach the bottom of the slope.

Use a water truck and water seeded areas weekly to get quicker growth. The better the growth going into winter the better.

If you have to open up a large area, only clear and grub small areas. You can clear larger areas if you don’t grub. Roots and slash help protect the bare soil.

Walk the site looking only at erosion controls, thinking ahead of areas that could have a problem. Identify them and start making additions and corrections.

Locate all existing water flows in and around your project and find out where they drain to.

Think about maintenance and regular inspection of erosion controls. When are silt fences going to be inspected and who does it? Who removes mud from check dams? Who covers slopes with straw or other mulch?

Get materials on site now. Again beat the rush for materials in October and November when everyone is in a panic to get plastic and straw. Stockpile enough straw, plastic, silt fence, flex pipe, sand bags, seed, rock, now to cover all areas that are bare.

Set up emergency procedures now. Who should be called in emergencies? Do you have a WSDOT certified Erosion and Spill Control Lead? Brief your personnel on what to do if they see muddy water and who to go to.
Make sure that erosion control material installers know proper installation methods.

Make sure all your silt fence is installed on contour with the ends flared up slope a few feet. If it is not on contour, identify the lowest points of the fence as these will be the failure spots. Install a double row of silt fence at these low spots before you have a failure. Double up your silt fence in areas where eroding slopes could flow into wetlands or streams.

Do you have bare spots where previous seeding hasn’t grown? Cover it with seed and straw if the area is small, remobilize the hydroseeder for larger areas.

Make sure all catch basins within the project boundary are protected with inserts, fence surrounds, or other methods to keep mud out. Locate any catchbasins outside project boundaries that may receive water from your site and protect them.

Make sure that you have a copy of the Stormwater Site Plan (SSP) and Temporary Erosion and Sediment Control plan (TESC) and any grading or environmental permits on site in the job shack. Know what they say. Give each inspector a copy of the SSP and TESC to keep in their truck. These are working copies that can be adapted to site conditions.

Modify your permanent stormwater ponds into temporary sediment ponds by installing a standpipe and blocking the outlet with sand bags. Cut a few small holes in the standpipe to allow for slow release of water. You can also use perforated pipe as the standpipe and hold it in place with “T” posts, wire, and gravel piled up around it.

Use geotextile fabric as a temporary ditch lining to protect bare soil from erosion. Hold the fabric in place with rock check dams, wooden stakes, or sand bags.

Make sure that all check dams are installed so that the top center point is lower than the bottom end points. This prevents endcutting. You may have to add more material to the dam to increase the width, especially on wide ditches with shallow grade side slopes

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