Erosion control measures
Preparing the soil topography for the designed construction purpose while taking erosion and sediment control factors into consideration.
To leave the surface soil in a roughened condition to provide temporary soil stabilization and augment future erosion and sediment control practices.
So some extent, on most construction sites that require land disturbing activities, and in particular where there are critical, erodible slopes.
Designing surface roughening techniques into the project is determined by:
- Site conditions
- Available equipment (i.e. bulldozers, tractors, etc.)
- Supplemental BMP application (i.e., hydraulic mulch, erosion control blanket, etc.)
- Final landscape design.
Types of surface roughening techniques include
- Use vertical tracking instead of horizontal tracking on slopes
- Sheepsfoot rolling and/or disking
Erosion control accomplished by constructing benches or large steps across the land slope.
Reduce the length of slope and thereby the potential for soil erosion
On steep slopes where erosive factors are very high and gully erosion is likely to take place
Terrace spacing and slope maintenance need to be considered.
Reduce slope length proportional to the steepness of the slope. Control outlets from terraces so erosion is eliminated.
Slope Interrupter Devices
Tube-like devices composed of a mesh or netting enclosing a biodegradable plant fiber that are installed on the slope contour.
To reduce runoff water velocities and trap sediment particles, thereby ameliorating the impact of slope length and steepness on erosion.
On slopes steeper than 5:1.
Follow manufacturer's instructions as to design and specification, particularly in terms of spacing.
Employ slope interrupter devices as a complementary practice to supplement:
- Surface roughening techniques
- Surface mulches, including hydraulic applications and rolled erosion control products
- Removal after slope stabilized is optional.
Planting fast growing vegetation to provide temporary erosion control.
To provide stabilization on bare soil areas that will not be brought to final grade for a period of more than will not be in/on for a period of more than 21 days.
May be used on cleared unvegetated areas where temporary erosion control is needed.
Selection of appropriate plant species, use of quality seed, proper bed preparation, and seed application method are important.
The area to be seeded should be uniform and loosened to a minimum depth of 3 inches. The area should be cleared of stones, roots, and other debris.
Use of a protective layer of straw, hay, wood chips, wood fibers, gravel, or synthetic materials on the soil surface to reduce rainfall impact and dislodgment of soil particles.
To protect the soil surface from the erosive forces of raindrop impact and overland or sheet flows. A secondary benefit of surface mulch is to retain soil moisture and moderate soil temperatures, aiding plant establishment.
As a temporary, non-vegetative surface erosion control treatment and/or in conjunction with a temporary or permanent revegetation technique, such as broadcast or hydraulic seeding.
Application of temporary or permanent mulch materials should be planned to coincide with schedule of disturbance and final landscape design.
Organic mulches are most effective when uniformly spread and secured to the soil structure. Benefits include:
- Ease of installation
- Erosion control effectiveness
- Runoff versus infiltration characteristics
- Compatibility with revegetation strategy
- Water quality impact
Types of surface mulching materials/techniques include:
- Stray or hay fibers
- Recycled paper or wood fibers
- Wood chips
- Hydraulic matrices of cellulose fiber and tackifying agent
- Bonded fiber matrices (BFM)
- Rolled erosion control products (RECP)
Turf Reinforcement Materials (TRM)
Three-dimensional fabrics of synthetic materials placed in areas of concentrated flow to provide plant reinforcement.
To provide increased shear strength to allow plant material usage in drainage channels as a functional substitute for hard armoring.
Installation of TRMs is critical to their performance in the field. Follow manufacturer's recommendation as to design, specification and installation of the material in conjunction with its vegetative component.
Stripping off, storing, or spreading the upper layers of soil over disturbed areas.
To provide a suitable medium for vegetation establishment and growth.
Wherever it is economically practical, this technique should be considered. Recommended for use in areas where subsoil is infertile and other methods will not produce or maintain a desirable stand of vegetation. Recommended for placement on soils that do not have a deep rooting zone to support plants and that may contain material toxic to plant growth, and where exposed subsoil is not suitable to produce adequate vegetation.
Should be applied on slopes 2:1 or flatter. Sample topsoil or duff material and apply lime and fertilizer as appropriate.
Permanent Seeding Planting of Grasses
Control of runoff and erosion with permanent vegetation.
To economically control erosion and sedimentation.
Used on graded or cleared areas where soil is unstable because of texture, structure, high water table, or slope.
Selection of appropriate plant species, use of quality seed, and proper bed preparation are important.
Planting required to occur within 14 days of final grading.
Permanent Ground Cover Plants
Control of runoff and erosion with trees, vines and shrubs by stabilizing soils in areas where vegetation other than grasses or legumes is preferred.
To economically control erosion and sedimentation.
Used on steep banks, graded cleared areas, and shady areas where turf maintenance is difficult. Also, can be used between terraces.
Selection of species should match soil characteristics. Quality stock should be selected and kept moist from time of receipt and planted as soon as possible.
Usually more effective when planted in clumps or blocks. Competitive vegetation should be pulled out of the area where the plants are to be planted.
Use of grass sod to permanently stabilize an area.
To rapidly prevent erosion and sedimentation
May be used in areas requiring immediate and permanent vegetative cover, particularly in landscaping applications.
More costly than seeding, but can be established during times of the year when grass seed may fail. Irrigation may be necessary.
On slopes, sod should be applied with the long dimension perpendicular to the slope and pegged or stapled sufficiently to prevent movement.
Riprap or Aggregate
Permanent layers of loose angular stones or aggregate with a filter fabric or granular underlining placed over an erodible soil surface.
To protect the soil surface from the erosive flow of water, slow water flow velocity, and stabilize slopes.
Used when soil may erode under design flow conditions and cannot be protected by vegetative cover or other means.
Riprap can be used at:
- Storm drain outlets
- Channel banks and bottoms
- Roadside ditches
- Drop structure
- Toe of slopes
- Channel transitions
Graded riprap contains a mixture of stone sizes while uniform riprap is made up of stones of similar sizes. The size of stone used is directly related to the deign flow velocity of the channel. Typically should be used for velocities in excess of 15 ft/sec.
The minimum riprap thickness is 2 times the maximum stone diameter but not less than 6 inches. The specific gravity of the individual stones should be at least 2.5. Maximum bank slope for application should not be steeper than 1.5:1
Structurally lined aprons or other acceptable energy dissipation devices placed at the outlets of pipes or paved channel sections.
To protect the soil surface from the erosive flow of water, slow the water flow velocity, and stabilize slopes or channels.
Use where the flow velocity at the design capacity will exceed the velocity of the receiving channel or area.
Geotextile fabrics in conjunction with vegetation create a natural outlet protection. Riprap aprons are relatively low cost and easy to install. Riprap silting basins or plunge pools are used where overfalls exit the ends of pipes where high flows would require excessive apron lengths.
Capacity: 10-year peak runoff or design discharge of conveyance, whichever is greater. Geotextile fabrics should be designed to handle peak flow rates and tractive forces. The depth of a riprap apron should be 2 times the maximum stone diameter but not less than 6 inches.
Actions or methods which reduce the erosive effects of wind on dry soils.
To prevent soil particles in the form of dust from becoming airborne.
Used where open dry areas of soil, particularly in dryer climates or during the dry season, are exposed to the erosive factors of the wind.
The direction of the prevailing winds and careful planing of clearing activities are important.
Minimize the period of soil exposure through use of temporary ground cover and other temporary stabilization practices. Some of the possible dust control measures are:
- Vegetative cover
- Spray-on adhesive
- Calcium chloride