Erosion And Sediment Control

DESCRIPTION

Soil preparation and roughening involves the assessment and preparation of surface soils for BMP installation. This preparation should include soil testing and recommendations for correcting compacted soils. Roughening surface soils by mechanical methods maybe required to prepare soil for additional BMPs or break up overland flow. Soil preparation can also involve tilling topsoil to prepare a seed bed and incorporating soil amendments to enhance vegetative establishment.

APPLICABILITY
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GUIDELINES
MAINTENANCE AND INSPECTION

Check the seeded slopes for signs of erosion such as rills and gullies. Fill these areas slightly above the original grade, then reseed and mulch as soon as possible.


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GUIDELINES

When choosing a product appropriate for the specific site condition consider:

  • Effectiveness of reducing erosion, flow velocity and runoff;
  • Compatibility with native plants, wildlife, moisture retention;
  • Durability, longevity and projected maintenance; and
  • Plastic products are not allowed in areas that protect wildlife such as the San Francisco Garter Snake and the California Red-legged Frog.
TYPES OF RECPs
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INSTALLATION

Remove all rocks, clods, vegetation or other obstructions and grade to allow the blanket or mat to come into consistent contact with the soil surface. Improper installation allows rain runoff to flow under the blanket.

Ensure RECPs are adequately overlapped and securely anchored to resist the effects of wind and water.

If the area is to be mowed at a later date, the anchoring staples or stake pins should be driven flush to the soil surface to avoid a potential hazard during the mowing.

Install in accordance with manufacturer’s instructions.

MAINTENANCE AND INSPECTION

RECPs should be inspected periodically and after rainstorms for signs of erosion or undermining. Failures should be corrected immediately. Material should be reinstalled following any tears or separations, and the slope or channel should be backfilled and stabilized.





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APPLICABILITY

Hydroseeding may be performed on:

  • Disturbed areas requiring temporary protection until permanent stabilization is established.
  • Disturbed areas that will be re-disturbed following an extended period (6 to 12 months) of inactivity
  • Cleared and graded areas exposed to seasonal rains or temporary irrigation.
  • Areas not subject to heavy wear by construction equipment or high traffic.
INSTALLATION

Where appropriate, soil should be prepared (See Soil Preparation BMP on pg. 36).

  • Hydraulic seed can be applied using a multiple step or one step process.
  • In a multiple step process, hydraulic seed is applied first, followed by mulch or a RECP.
  • In the one step process, hydraulic seed is applied with hydraulic mulch in a hydraulic matrix. When the one step process is used to apply the mixture of fiber, seed, etc., the seed rate should be increased to compensate for all seeds not having direct contact with the soil, or as specified by the landscape architect.
  • All hydraulically seeded areas should have mulch, or alternate erosion control cover to keep seeds in place and to moderate soil moisture and temperature until the seeds germinate and grow.
MAINTENANCE AND INSPECTION

Regularly inspect the area to ensure seed germination and vegetation establishment. Where seeds fail to germinate, the area must be re-seeded, fertilized, and mulched within the planting season, using not less than half the original application rates. Physical inspection should be performed following rain events to observe gully and displaced mulch.


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GUIDELINES

Soil binders can be effective for periods of 3 months or longer, depending on the requirement of the specifications. Soil binders are categorized as: short-lived plant based materials, long-lived plant based materials, polymeric emulsion blends (acrylic polymers), and cementitious-based binders.

The less durable stabilizing emulsions are called tackifiers. Short lived plant based materials, highly diluted polymeric emulsions and cementitious binders are tackifiers. They are applied directly to the soil surface or are used as the stabilizing emulsion in hydraulic and straw mulches for disturbed soil areas that require short term stabilization.

The more durable stabilizing emulsions are heavy duty soil binders. Heavy duty soil binders are applied directly to the soil surface or used as the stabilizing emulsion in hydraulic and straw mulches for disturbed soil areas that require long term stabilization. Long lived plant based materials, less diluted polymeric emulsions and cementitious binders are considered heavy duty soil binders. Soil binders are also used to stabilize temporary roads during construction. Use only those binders specified in the plans, for each application.

INSTALLATION

After selecting an appropriate soil binder, the untreated soil surface must be prepared before applying the soil binder. The untreated soil surface must contain sufficient moisture to assist the agent in achieving uniform distribution. In general, the following steps should be followed:

  • Follow manufacturer’s written recommendations for application rates, pre-wetting of application area, and cleaning of equipment after use.
  • Prior to application, roughen embankment and fill areas.
  • Consider the drying time for the selected soil binder and apply with sufficient time before anticipated rainfall. Soil binders should not be applied during or immediately before rainfall.
  • Avoid over spray onto roads, sidewalks, drainage channels, sound walls, existing vegetation, etc.
  • Soil binders should not be applied to frozen soil, areas with standing water, under freezing or rainy conditions, or when the temperature is below 40°F during the curing period.
  • More than one treatment is often necessary, although the second treatment may be diluted or have a lower application rate.
  • Generally, soil binders require a minimum curing time of 24 hours before they are fully effective. Refer to manufacturer’s instructions for specific cure time.
MAINTENANCE AND INSPECTION

Inspect BMPs prior to forecasted and rain, daily during extended rain events, after rain events, weekly during the rainy season, and at two-week intervals during the non-rainy season. Repair eroded areas and reapply BMP as soon as possible. Minimize damage to stabilized areas while making repairs. The binder will be reapplied as needed to maintain effectiveness.


DESCRIPTION

Sodding is a permanent erosion control practice and involves laying a continuous cover of grass sod on exposed soils. Sodding can stabilize disturbed areas and reduce the velocity of stormwater runoff. This BMP can provide immediate vegetative cover for critical areas and stabilize areas that cannot be readily vegetated by seed. It also can stabilize channels or swales that convey concentrated flows, and reduce flow velocities.

INSTALLATION
  • In the area to be sodded, clear all trash, debris, roots, branches, stones and clods larger than 2 inches in diameter.
  • If a soil test determines the need, prepare the soil, and add lime and fertilizer.
  • Lay strips of sod:
    • Beginning at the lowest area to be sodded.
    • Perpendicular to the direction of water flow, and stagger it in a brick-like pattern.
  • On slopes steeper than 30%, staple the corners and middle of each strip firmly. Place jute or plastic netting over the sod to protect against washout during establishment.
  • Roll the sodded area and irrigate.
  • Ensure that sod is harvested, delivered, and installed within a period of 36 hours. If it is not transplanted within this period, inspect and approve the sod before its installation.
MAINTENANCE AND INSPECTION

When mowing, do not remove more than one-third of the shoot. Maintain a grass height between 2 and 3 inches. After the first growing season, determine if additional fertilization or liming is needed. Permanent, fine turf areas require yearly maintenance fertilization. If the grass is unhealthy, the cause shall be determined and appropriate action taken to re-establish a healthy ground cover.


DESCRIPTION

Diversion structures are structures that intercept, divert, and convey surface runoff around or through the project site in a non-erosive manner.

GUIDELINES

Dikes and drainage swales are suitable for use, individually or together. When properly placed and maintained, dikes used as temporary diversions can control the velocity and direction of stormwater runoff. Used by themselves, they do not have any sediment removal capability. They must be used with an appropriate sediment-trapping device at the outfall of the diversion channel. It may be necessary to use other erosion and sediment control measures such as check dams, plastic sheeting or blankets to prevent scour and erosion in these swales, dikes and ditches. In some cases, the swale may need to be constructed of concrete or rock. Diversion structures may be used:

  • To convey surface runoff down sloping land;
  • Along paved surfaces to intercept runoff;
  • Along the top of slopes to divert surface flow from slopes;
  • To divert and direct runoff towards stabilized drainage systems; and
  • Below steep grades where runoff begins to concentrate.
INSTALLATION
  • A combination dike and swale is easily constructed by a single pass of a bulldozer or grader, and compacted by a second pass of the tracks or wheels over the ridge.
  • Diversion structures should be installed when the site is initially graded and remain in place until post construction BMPs are installed and the slopes are stabilized.
  • Temporary diversion dikes should not adversely impact adjacent properties, and should not be used in areas with slopes steeper than 10%.
  • Provide stabilized outlets.
  • Divert sediment laden runoff into sediment traps.
MAINTENANCE AND INSPECTION

Check channels, embankments and ditch beds for erosion, washout and accumulation of sediment and debris. Remove sediment accumulation and debris, and repair or replace lost riprap, linings or soil stabilization, as needed.



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GUIDELINES

Check dams are generally used in:

  • Small open channels;
    Steep channels where runoff velocities exceed five feet per second;
  • Ditches or channels where grass linings are being established; or
  • Temporary ditches where short term service does not warrant establishment of erosion resistant linings.
INSTALLATION
  • Install check dams approximately 20 feet from the intake structure and at regular intervals along the channel. Space dams closer together where there is a high potential of erosion (steep grades and/or high flows).
  • Embed structure sufficiently in sides and bottom of channel to prevent undercutting.
  • The dams should be placed at a height and distance allowing small pools to form behind them but also allowing high velocity runoff (typically a two year storm or larger) to safely flow over them without an increase in upstream flooding or damage to the dam.
  • Stabilize channel immediately downstream of check dams to prevent erosion at the toe of the structure.
  • If using a prefabricated check dam, follow manufacturer’s recommendations and installation instructions.
MAINTENANCE AND INSPECTION

Perform maintenance as required. Inspect following rainfall events and at least daily during prolonged rainfall. Maintain to provide an adequate sediment holding capacity. Remove debris daily and remove sediment when it accumulates to 1/3 of the dam height.


DESCRIPTION

Drain inlet and catch basin protection reduces sediment entering the storm drain system carried by runoff from a construction site. Effective storm drain protection allows sediment to settle out of water or filters sediment from the water before it enters the drain inlet. All inlets and basins that are connected to the storm drain system must be protected. Inlet protection is the last line of defense for water quality prior to water entering the drainage system.

There are several types of inlet and catch basin protection measures:

GUIDELINES
    MAINTENANCE AND INSPECTION

    Check all temporary control measures before and after each storm event. During extended storm events, inspect at least once every 24 hours.

    • Remove accumulated sediment from the area around the drop inlet and catch basin when the capacity is reduced by half.
    • Remove additional debris from the shallow pools periodically. The weep holes in excavated areas around inlets can become clogged, preventing water from draining out of the pools.
    • Clear sediment build around barrier.


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    GUIDELINES

    If more than one fiber roll is placed in a row, the rolls should be overlapped by at least one foot.

    The diameter of the stake should be approximately 1” for ease of driving through the roll. Refer to manufacturers’ installation instructions for proper installation.

    MAINTENANCE AND INSPECTION

    The maintenance requirements of fiber rolls are minimal, but regular inspection is recommended to ensure that the rolls remain firmly anchored in place and are not excessively crushed or damaged by equipment traffic.

    • Inspect fiber rolls before and after rain events, and at least daily during prolonged rainfall.
    • Repair or replace split, torn, unraveled, or slumping fiber rolls. Fiber rolls are typically left in place on slopes after construction is complete as part of site stabilization. If they are removed, collect and dispose of the accumulated sediment.
    • After removal, fill and compact holes, trenches, depressions or any other ground disturbance to blend with the surrounding landscape.
    LIMITATIONS
    • Difficult to move once saturated. Some saturated fiber rolls may require a crane or other machinery to remove from site.
    • If not properly staked and trenched in, fiber rolls could be displaced by high flows.
    • Fiber rolls have a very limited sediment capture zone.
    • Fiber rolls should not be used on slopes subject to creep, slumping, or landslide. Use RECP with stronger soil stabilizing properties.
    ALTERNATIVES

    Polyethylene sediment-filtration fencing can be used as a substitute for the traditional fiber roll. This reusable and recyclable product is used for slope protection and stabilization. It slows the velocity and spreads the flow of runoff. The filter removes pollutants and sediment from the runoff. These products are easy to install, highly resistant to vehicle and foot traffic, and are lightweight.


    MAINTENANCE AND INSPECTION

    Silt fences can be maintenance intensive. Perform inspections before and after every rain event, and every 24 hours during extended rain events. Also, weekly inspections throughout the rainy season are recommended. Remove sediment deposits when they reach 1/3 of the fabric height. All torn or decomposed fencing should be replaced. Do not allow water or sediment depth to exceed 1.5 feet at any point. The fence should remain in place until the disturbed area is permanently stabilized.

    ALTERNATIVES

    Temporary high density polyethylene sediment-filtration fencing can be used as a substitute for the traditional silt fence. This reusable product which is made from recycled materials, is used for slope and perimeter protection. It slows the velocity and spreads the flow of runoff while handling larger floods and pressures. The filter removes pollutants and sediment from the runoff. These products are easy to install, durable, and are lightweight.

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    DESCRIPTION

    This is a temporary settling area formed by shallow excavation, perimeter construction of an earthen embankment or an embankment constructed across a waterway or low drainage area. It includes a controlled release structure like a sump pump or overflow structure.

    The sediment trap is used as a pretreatment measure for entry of the runoff into the storm drain system or natural waterway. This BMP allows sediment to settle out of runoff prior to the discharge of the water into the local storm drainage system or natural waterway.

    GUIDELINES

    The trap should be excavated where breech of the perimeter would not pose a risk to life or property. Access should be provided for maintenance including sediment removal.

    The length of the trap should be more than three times the width. Traps with levees greater than five feet in height should be designed by a professional civil engineer. The trap inlet should be located as far as possible from the outlet structure in order to allow maximum sediment settlement. Traps may require protective fencing to ensure safety.

    MAINTENANCE AND INSPECTION

    Traps should be inspected before and after every rain event, weekly during the rainy season, and at 24-hour intervals during extended storms. Check inlet and outlet structures and spillways for signs of erosion, damage or obstructions. Examine trap banks for seepage and structural soundness. Remove accumulated sediment when the storage trap is 1/3 full.

    To assist with vector control, vegetation should be removed from the basin frequently.


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    APPLICABILITY

    Use this BMP, per the design criteria and requirements described in the SWRCB Construction General Permit (CGP) when:

    • Discharging to turbidity sensitive waters, and turbidity reduction by other BMPs are insufficient
    • Where site constraints limit the ability to construct a properly sized sediment trap; or
    • Where use is required by the CGP.
    GUIDELINES

    Chemically treated stormwater discharged from construction sites should:

    • Be designed and approved by a Certified Professional In Erosion and Sediment Control (CPESC), a Certified Professional in Stormwater Quality (CPSWQ), or a California registered civil engineer.
    • Meet residual chemical and toxicity requirements as defined in the CGP.
    • Include a filtration step between the coagulant treatment train and the effluent discharge.
    • Be done in accordance with all local, state, and federal laws and regulations.
    • Should be equipped with instrumentation that automatically measures and records effluent water quality data and flow rate.
    • Comply with all provisions and prohibitions in the CGP.
    • The project shall have a site-specific Operation and Maintenance (O&M) manual covering the procedures required to install, operate and maintain the ATS.

    • Operators shall have training specific to using an ATS and liquid coagulants for storm water discharges.

    • Any discharger who deploys an ATS on their site shall conduct the daily visual monitoring and record findings in the project data log.

    MAINTENANCE AND INSPECTION

    Daily on-site visual monitoring of the ATS operation and performance shall be done by a qualified person as required. The name and phone number of the qualified person assigned the responsibility of operation and monitoring of the system, and documentation of the qualified person’s training as required by the statewide General Construction Stormwater Permit will need to be provided on site.

    ATS require continuous monitoring when operating. Special attention needs to be given to ATS whenever they are being started up for the first time, restarted after an extended down time, and after maintenance or repair work has been done on the system.