Alaska Department of Transportation & Public FacilitiesStormwater Best Management Practices (BMPs) for M&O

Renée Forque

November 2014

1. Environmental Effects:

a. Effect on fish – clogged spawning gravels, smothered eggs and fry, and gill abrasion b. Effect on streams – decreased photosynthesis, increased temperature, dirty water c. Effect on local area – clogged storm sewer systems, local flooding, dust pollution, and filled in reservoirs, shipping channels, and harbors

2. Financial Effects:

a. Legal liabilities for damage from sediment (EPA: $37,500 per day, per violation; ADEC: $500-100,000 plus $10,000 per day) b. Penalties from non-permit compliance (consent decrees, third party suits, stop work orders) c. Criminal sanctions (up to $10,000 fine and possible jail time)

Why Does Sediment and Erosion Control Matter?

1. Source Control – also called erosion control, the goal is to prevent stormwater from removing and transporting soil particles at your worksite. Source control BMPs work to prevent the problem.

Source control BMPs work to cover soil, stabilize soil, protect slopes, and preserve vegetation

2. Perimeter Control – also called sedimentation control, the goal is to prevent sediment-laden stormwater

runoff from leaving your worksite. Perimeter control BMPs work to treat the problem.

Perimeter control BMPs work to contain sediment-laden water, filter sediment-laden water, reduce runoff

velocity, and establish perimeter controls

What are the Goals of Sediment and Erosion Control?

04/17/2023 3Alaska DOT&PF

1. Silt Fence:

• Silt fence is designed for sheet flows• Silt fence is ineffective when it is improperly installed – it must be trenched in (at least 6 in. deep),

reinforced with stakes, and stakes must be positioned on the opposite side of the fence from where runoff will approach

• Silt fence often fails, so it must be checked regularly and maintained – clean out sediment when it backs up to 1/3 the height of the fence

• Often, one line of silt fence is ineffective; it takes multiple rows to effectively reduce the velocity of sheet flows

Remember: silt fence is not to be used on slopes or across concentrated water flows – it is a limited BMP best used for a temporary physical barrier to sediment and reducing the runoff velocities of overland flow

Proper Use of Common BMPs

2. Wattles:

• Wattles are designed to reduce slope flow velocities by breaking up slope length and directing water flow• Wattles are ineffective when installed improperly – they must be trenched and staked perpendicular to

the direction of runoff flow• Wattles should be tightly abutted together and the ends (at the edge of the slope) should be tilted upward

to form a ‘smiley face’ that keeps water flowing toward the middle of the slope• On low grade slopes, wattle can be spaced farther apart, but on steep slopes, wattle should be spaced

tightly in rows or replaced with a Rolled Erosion Control Product RECP (blanket or mat)

Remember: wattle on steep slopes is often not enough – wattles should be combined with another form of slope erosion protection

Proper Use of Common BMPs

3. Hydroseeding:

Hydroseeding is designed to grow new vegetation and to retain water and soil while protecting seeds Hydroseeding is much more effective on an uneven and slightly compacted soil surface – slopes

should be track-walked (with tracks perpendicular to the slope) and hydroseeded more than once and from more than one direction

Usually, more than one application from more than on direction is necessary to provide better cover The vegetation grown from hydroseeding will help reduce runoff volumes, runoff velocities, and raindrop

impact energy while filtering sediment, reducing pollution, and retaining soil

Remember that regular watering the first two weeks after hydroseeding is critical to the success of establishing vegetation!

Proper Use of Common BMPs

4. Check Dams:

• Check dams are designed to reduce channel erosion by restricting the flow velocity• Ideally, check dams should be made out of a material that helps to filter out sediment (loose rock [Type I or

II], fiber rolls, compost socks, bio bags, etc.)• The toe of the upslope check dam should be equal to the height of the next check dam• For a six foot or smaller (width) check dam, construct the center of the dam at least six inches lower

than the ends to act as a spillway for runoff and prevent water from flowing around the check dam and/or eroding the bank

• Remove sediment accumulation behind the dam as needed to prevent damage to channel vegetation and to allow the channel to drain through the dam

Remember to regularly inspect check dams to ensure they have not been breached, clogged with sediment, or otherwise damaged

Proper Use of Common BMPs

Proper Use of Common BMPs

5. Catch Basin Inlet Protection (silt sacks or witches’ hats):

• Catch basin inlet protection involves using a temporary barrier to prevent and filter the flow of sediment and debris into a storm drain or other stormwater conduit. An insert bag is a woven fabric bag installed below inlet grates that is designed to capture fine particles

• Inlet bag material will last between three months and one year without replacement, depending on traffic• Without regular maintenance (and removal of these devices when work is done), drains can

become blocked and cause flooding

Remember to check insert bags often – they don’t work when full of sediment. Insert bags can be cleaned and re-used, as long as they have not deteriorated

6. Sediment Cage:

• A sediment cage is designed to filter out sediment when placed over an open drain inlet • Cages should be placed over drain inlets on the concrete aprons surrounding the grates with the skirt

tucked under the grate• Water has to be able to pond around the cage and settle without over-topping the sediment cage or the

BMP will be ineffective• Sediment piled up around the cage is a good sign that the cage is working; there should be little to no

sediment inside the trap

Remember to inspect regularly - cages should be replaced or cleaned whenever they are 1/3 the cage height or become plugged with sediment!

Proper Use of Common BMPs

7. Riprap Outlet Protection:

• Riprap outlet protection is designed to dissipate energy at the outlet of a conduit to prevent excessive erosion (scour) from the discharge of high volume or high velocity runoff

• Riprap is ineffective unless installed properly – fill must be compacted, and then filter stone, fabric, or a blanket should be placed to prevent subgrade erosion before installing riprap large enough to prevent scour

• Use extra-strength filter fabrics, installed by continuously placing the upstream section of fabric a minimum of one foot over the downstream section of fabric

• The outlet protection apron should be constructed with no slope along its length. There should be no overfall at the end of the apron. The elevation of the downstream end of the apron should be equal to the elevation of the receiving channel or adjacent ground

• The outlet protection apron should be located so that there are no bends in the horizontal alignment

Remember to remove sediment when it fills the voids between rocks!

Proper Use of Common BMPs

8. Sediment Trap:

• Sediment traps are designed to allow sediment to settle out of runoff before entering receiving streams, lakes, drainage systems, or the surrounding area

• Sediment traps are formed by excavating an area or by placing an earthen embankment across a low area or drainage swale. An outlet or spillway is often constructed using large stones or aggregate to slow the release of runoff

• Per the EPA, the minimum storage capacity of a sediment trap should be 3,6003 per acre of total drainage area

• When excavating an area for a sediment trap, make sure the side slopes are no steeper than 2:1 and the embankment height no more than five feet from the original ground surface

• Check the depth of the spillway and maintain it at a minimum of 1.5 feet below the low point of the trap embankment

Remember to remove sediment when the basin reaches about 50% sediment capacity

Proper Use of Common BMPs

9. Sweeping:

• Sweeping is designed to remove fine particles from roads and other paved surfaces and trap them with an exhaust air filter to reduce discharges to air and stormwater

• Pre-wet roads and exposed soils to improve effectiveness• Treat areas early in the day if they appear dry and dusty. Early treatment prevents problems later in the

day as vehicle traffic and temperatures increase• Adjust brooms regularly to maximize efficiency of sweeping operations• If the filter is not fine enough or well-contained enough, materials that the vacuum picks up will be

dispersed into the air

Remember to check and change filters to make sure that fine particles are property contained!

Proper Use of Common BMPs

10. Material Site Ditches/Trenches:

• Ditches/trenches are designed to capture runoff before it leaves the material stockpile area• Dig ditches/trenches and then use the excavated material to construct a berm on the downhill side• The entrance to the material stockpile should be on the uphill side • Line ditches/trenches with permanent stabilization. Place riprap or line channel with blankets or plastics• Keep excavated sand/soil and other materials at least two feet from trench edges

Remember to remove accumulated sediment from ditches/trenches when they are 50% full!

Proper Use of Common BMPs

A flip book made to aid in choosing appropriate BMPs for field work has been developed and is being distributed to each station. The flip book divides BMPs by type/location:

1. Preservation and Use of Vegetation

2. Steep slopes

3. Inlets & Outlets

4. Flow Control

5. Dust Control

6. Material Stockpiles

7. In-water

BMP Flip Book

Features of the BMP flip book:

• BMP details and installation tips• BMP installation figures and drawings• BMP photos and recommendations• Contact information for central region

environmental staff• Waterproof pages

BMP Flip Book

• Often, the most effective stormwater control measures are a combination of two or more BMPs• Perimeter control BMPs are not nearly as effective as source control BMPs• Spacing for velocity control BMPs is dependent on the barrier height; the lower the barrier height, the

closer together the rows of BMPs should be installed• Wattles, fiber rolls, socks, etc. can float – they must be trenched and staked on bare ground and they must

be weighted or replaced with a more effective measure on asphalt/concrete/impervious surfaces• There is no such thing as a BMP that requires no maintenance or follow up!• If you’re not sure what BMPs to use, just call or email us – we’re happy to help

BMP Tips

Contact Info:

Questions?

Renée Forque

Environmental Specialist III Work: (907) 269-0714 Cell: (831) 682-8925 Jennifer Micolichek Environmental Specialist IV Work: (907) 269-5690 Cell: (907) 947-7529