3.8 Erosion Prevention Methods
Erosion of ground surfaces in the roadway and ROW threatens the stability of the pavement and structures, increases costs for cleaning of drainage structures, and contributes to siltation and turbidity of nearby streams and lakes. The costs associated with the control and repair of eroded surfaces can be significant and sometimes directly impact driver safety.
The areas most susceptible to erosion are slopes associated with embankments and drainage channels. Embankments often receive concentrated runoff from pavement surfaces that, depending on soil and slope conditions, may lead to significant erosion problems.
Erosion prevention begins with the roadway’s design and adherence to best practices per TxDOT’s
and the
. Aesthetic treatments to prevent erosion include intercepting sheet flows, whether from paved surfaces or adjacent slopes, and utilizing various techniques to minimize, divert, and disperse the intercepted flow.
Additional training for TxDOT employees to become more familiar with erosion prevention methods is available through TxDOT’s PeopleSoft/Training & Development. The list of courses can be found in the
that is managed by ENV. TxDOT’s EMS courses are available externally for contractor and subcontractor employees through the
and through the
.
3.8.1 Slope Configuration
The percentage of slope and shape of slope can be manipulated to minimize sheet flow over the slope face.
- Design slopes as flat as economically practical (max. 3:1, 6:1 preferred);
- Create rounded tops and bottoms of slopes;
- Step cut-slopes where suitable rock is encountered; and
- Use streamlined cross-section design techniques to help reduce wind erosion.
3.8.2 Surface Protection
Every effort should be made to cover bare ground after disturbance by construction or maintenance activities. A stand of good quality vegetation is the best long-term solution to potential erosion. The use of mulches or compost can be used on gentle slopes (1:4 V:H) orflatter. Temporary erosion control material may be necessary depending on soil type as slopes increase. These two primary considerations, soil type and slope, determine the selection of the appropriate temporary erosion control measure. Highly erodible channel areas may require more permanent channel liners or possibly riprap.
- Soils with higher percentages of fine sand or silt particles are increasingly more erosive, while soils with minimal percentages of sand or clay particles are considered cohesive soils or clays.
- As the degree of slope increases, the potential for sheet erosion increases.
- The includes approved products for hydro mulch, roll products and hydraulically applied (spray-on) products for temporary erosion control, and temporary and permanent channel protection.
- Products are approved based on soil types and for slopes for temporary erosion control and shear stress for channel protection products.
3.8.2.1 Compost or Mulch
The primary function of mulch is to maintain moisture in the soil and foster seed germination and plant development. Coordinate preferences for use of compost and mulch with each specific District. There are three types of mulch used for erosion control:
- Straw and hay mulch:Straw and hay mulch are used as surface covers in conjunction with some type of tacking agent (tackifier). The tackifier helps form a uniform mat and prevents migration of the material down the hill. Straw can also be crimped to help prevent material loss or migration. Refer to the and on the for additional information.
- Hydromulch:Hydromulches are hydraulically applied. Cellulose mulches may be applied with the seed mix and a tacking agent to form a more consolidated mat on the surface. TxDOT maintains a list of approved cellulose mulch materials. Depending on the soil type and side slope, hydraulically applied mulches have varying rates of application. Refer to the on the for additional information. TxDOT maintains an approved list for cellulose fiber mulches at .
- Compost:Compost may be blended to make compost manufactured topsoil in flat areas. Slopes up to 1V:3H should utilize Erosion Control Compost. Erosion Control Compost may be pneumatically applied on slopes 1V:3H or flatter. This material not only provides short term erosion control with mulch chips but also works to improve the existing soil. Refer to the on the for additional information.
3.8.3 Channel Liners & Soil Retention Blankets
TxDOT maintains an Approved Materials List for channel liners/soil retention blankets at
. This list describes the conditions for application and provides a list of materials approved based on its resistance to tensile stress. Refer to the
on the
for additional information.
- There are two broad types of channel lining material: organic/organic composites and synthetics.
- In general, organic and composite lining materials are used for vegetation establishment and offer no long-term channel protection.
- The synthetic materials are longer lived and work with the root matrix of the vegetation to provide long term protection of the channel. Synthetic materials are preferred in ditches and channels that will have frequent flows at depths greater than 8 in (200 mm).
3.8.4 TxDOT Standards
- Standard Details & Specifications (Temporary Erosion Control Measures, Details, & Standard Spec Book); and
- Environmental Forms & Processes (Stormwater Program, EMS, Stage Gate, and Construction BMPs).
3.8.5 Vegetation
Consider the planting material installed for erosion control on slopes and embankments (seeding, sod, shrubs, trees, etc.). Specify material with deep and strong root systems, known to tolerate the extreme roadway conditions. Refer to
for specific material preferred in each District. Refer to
for the appropriate seed mix for each District, based upon Urban or Rural conditions.
3.8.6 Bioengineering Streambank Stabilization
Consists of lining channels and streambanks with live plant materials. In addition to the use of appropriate plants, mechanically stabilized earth, riprap, and natural boulders are frequently used to stabilize eroding streambanks.
- Plant materials:As much as possible, use native grasses and forbs with deep roots systems, and woody plants that root easily from cut root stock.
- Bioengineering techniques:Multiple techniques are available, with two being the most successful in Texas: Live Stakes and the Vegetated Geogrid.