Division 2 - Sitework
Erosion Control
Erosion Control:
In most municipalities, a preconstruction meeting will be held with regulators to receive a grading permit.
Erosion protection must be in place and maintained throughout construction. Install the measures as
shown on the approved plans, including constructing the measures per the construction details. Ensure
measures are installed before any other areas are disturbed on the site.
The measures need to be installed in the field as shown on the plans. If for some reason the measures
shown on the plans will not work (or can't be constructed as shown) in the field, you need to contact the
erosion control site inspector to let them know of the problem. It is best if you have a couple solutions
of how you think the problem could be fixed. The flip side to this is if the plans do not show a measure
below the disturbed area, you should contact the erosion control inspector if you think it could cause
sediment damage to other property and/or streams/lakes.
If you have a large site or sensitive areas to protect (e.g. streams, wetlands, ponds, etc.), I would
recommend having a site inspection conducted by the erosion control inspector before disturbing any
other areas. That way, if something does not look proper in the field, it can be fixed before the measures
don't work properly or fail. Sometimes the plan reviewer can miss items during the plan review process.
Look at the measures once they are installed in the field. Check to see that the measures will function in
the field as they were designed to function. Erosion control is not very complicated. Just remember
water always flows downhill and takes the path of least resistance. Try to visualize where the water will
flow during a rain event. Common problems we observe in the field are: berms of sediment traps too
low and water flows over the berm before it flows over the stone spillway; weirs not provided in stone
spillways; diversion berms that do not have positive drainage to traps/basins; silt fence installed across
ditches or swales; rock check dams (in ditches) too high in the center and water flows around the stone;
inlet protection not installed properly for yard/curb/pipes or the wrong type of protection is installed;
temporary inlet protection not installed for stubbed out pipes awaiting box installation; rip-rap in ditch
lines and below culvert outlets installed too high; wrong type of ditch liners installed and/or not
installed/stapled to channels properly; diversion berms not provided at the top of fill slopes with slope
drains; slopes drains that do not outlet at toe of slopes or into an adequate measure, etc.
Maintain the erosion control measures at all times even if it does not rain. As site construction
progresses, damage to measures usually occurs. The measures need to be in proper working condition
all the time. I would recommend walking and inspecting the measures every couple of days during
periods of no rain. The NPDES permit requirements actually require an inspection of the measures at
least once a week (twice per week for some areas). If the measures are damaged, have them fixed. I
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Division 2 - Sitework
Erosion Control
would recommend inspecting the measures after every rain event (NPDES requires an inspection after
each rain event >0.5 in/24 hr period). If the measures are damaged, have them fixed. If the weather
forecast calls for a high probability of rain, inspect the measures and be sure they are ready to function
during the rain. Most of the time, contractors are shut down from construction when it is raining.
It is good practice to actually inspect the site during a rain event, especially the first decent rain event
after the measures are first installed. This allows you to follow the water to see where it is draining and
ensure it is flowing to the measures properly.
Stabilize disturbed areas as soon as possible. Providing ground cover and stabilizing disturbed areas
(placing stone on roads/parking lots/building pads, etc.) reduces the run-off from the site to the
measures. This in turn, reduces the maintenance on the measures. Disturbed slopes must be stabilized
within 21 calendar days of completion of any phase of grading. If you clear and grub a slope and do not
plan to grade the slope, it needs to be temporarily stabilized until construction work progresses. If you
grade a slope (rough, final, etc.), you have 21 calendar days to stabilize it. For sites with building
construction, you should provide a stabilized surface for material staging areas/construction
trailers/access roads, etc.
Ground cover for all other disturbed areas must be provided within 15 working days or 90 calendar days
following completion of construction or development, whichever period is shorter. Basically, stabilization
of disturbed areas that are completed or where construction work ceases should be completed along
with building construction. The common problem is that contractors leave the disturbed areas exposed
throughout the life of the project (eroded gullies and all) and then try to provide ground cover (in June &
July of course when fescue is unlikely to survive) after all the site work is completed (building done,
parking lots/roads, etc.). Disturbed areas need to be seeded & mulched as the construction progresses.
Once construction is completed in an area, seed and mulch the areas to begin establishing the ground
cover. The ideal planting season for fescue is August 15th thru October 25th and February 1st thru April
15th. If you are outside the fescue planting dates, at least temporary seed and mulch disturbed areas.
You should monitor the germination of the ground cover and re-seed or over seed areas that do not
survive or germinate properly at the next planting season (e.g. seed in September/October, over seed in
March or seed in March/April over seed in August/September). Land Quality cannot close out a site until
all areas that were disturbed have an adequate stand of permanent ground cover. It should be noted
that NPDES monitoring still has to be conducted until the project is closed out by Land Quality (even if
the building construction has been completed for 1+ years).
Ensure proper types of seed are planted on the disturbed areas. Contractors like to use the "Contractors
Blend" which is basically 70-80% annual rye grass (which is not a permanent ground cover) and 30-20%
fescue. The annual rye grass comes up quickly and is nice & green until June/July when it dies and turns
Samet Corporation | Building Structures. Building Relationships.
Division 2 - Sitework
Erosion Control
brown. I would guess the "Contractors Blend" is cheaper in the beginning, however, after you have to
seed & mulch 4-5 times to provide a permanent ground cover, it is probably more expensive (not
counting labor intensive). In addition to providing proper seed, the proper seedbed preparation needs
to be completed prior to seeding/mulching. The ground needs to be tilled 4-6 inches and all foreign
debris removed (e.g. roots, rocks, etc.). Nurse crops (e.g. millet, rye grain, etc.) are recommended to add
to the fescue blends to obtain a temporary ground cover before the fescue germinates. Applying the
proper mulching rate is important, as well as, properly anchoring the mulch to the ground to keep it from
blowing away. Seeding types, notes, and rates are normally on your erosion control plan. It should be
noted that volunteer weeds is not providing an adequate ground cover.
Ensure ditch lines/swales are stabilized per the approved plan. Typically, ditch lines with a slope equal to
or greater than 2% will require a liner, however, it depends on the amount of flow in the channel. Install
the proper types of liners in the ditches/swales. If a ditch/channel is lined with rip-rap, ensure the rip-rap
is placed in the channel properly. A common field mistake is the rip-rap is too high in the middle of the
channel and/or the top of the rip-rap channel is not lower than the surrounding ground. The water will
flow along the top edge of the channel and erode.
For example, if a channel shows 18" depth of rip-rap, you have to excavate 18" below grade of the
channel so that the rip-rap will be placed at the correct elevation. This is also true for rip-rap lined
emergency spillways of basins, outlet protection below culvert outlets, stream bank stabilization for utility
crossings, etc.
Once adequate permanent ground cover has been provided for all disturbed areas, the erosion control
measures can be removed. I would recommend obtaining approval from the erosion control inspector
prior to removing the measures. Once the measures can be removed, the resulting disturbed areas (from
the measures) need to be adequately stabilized.
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