CUT BANK STABILIZATION, Exercises of Geology

Download CUT BANK STABILIZATION and more Exercises Geology in PDF only on Docsity! 742-1 Conservation practice standards are reviewed periodically, and updated if needed. To obtain the current version of this standard, contact the Natural Resources Conservation Service. NRCS, CA July, 2000 NATURAL RESOURCES CONSERVATION SERVICE CONSERVATION PRACTICE STANDARD CUT BANK STABILIZATION (feet) CODE 742 CA INTERIM DEFINITION To stabilize and treat cut banks of bare earth with vegetation and/or structural measures to protect against erosion by wind or water. Scope This standard applies to measures used to stabilize and protect bare earth or decomposed rock banks usually associated with the construction of roads, parking lots, storage yards, building pads or other similar disturbed areas. It applies to naturally occurring banks but NOT to streambanks which are cover by Practice Standard 580-Streambank and Shoreline Protection. PURPOSES To treat cut banks for one or more of the following purposes: 1. To reduce erosion and the resulting sediment loads causing downstream damage. 2. To maintain or enhance water quality. 3. To improve the conditions to sustain vegetative growth. 4. To improve the wildlife habitat. 5. To improve the visual appearance of the area. CONDITIONS WHERE PRACTICE APPLIES This practice applies to natural or excavated earthen cut banks where erosion can be reduced by the establishment of vegetation, or a combination of structural measures and vegetation, and where the failure of structural measures will not result in loss of life or serious damage to property. CRITERIA Because each cut bank is unique, treatment will be designed for the specific site conditions, and installed according to a plan. Designs shall address the following: 1. Geology exploration; determination of the extent and stability of the cut bank. 2. Soils investigation; determination of soil profile, and any alternations needed for plant growth, and also evaluation of the soil mechanics of soil loadings and stability of footings. 3. Hydrology investigation; determination of runoff, for both before and after treatment with intent of reducing runoff; determination of peak runoff at bottom of cut bank. 4. Erosion study; determination of soil erosion rates for both before and after treatment, using USLE, and noting the existing "C"; the aged "C" values; and determination of allowable slope to maintain plant growth. 5. Hydraulics analysis; determination of peak flows at bottom of slope for various frequency storm events, and of needed conveyance system to dis- charge the flow to the same watercourse. The design discharge should be compatible with the project life, and with other risk factors. 6. Structural analysis; insure structural measures are adequate and serviceable for the project life, given proper scheduled maintenance and repair. 7. Vegetation evaluation; vegetative practices must be consistent with the project objectives. The seedbed preparation, species, fertilizer, mulch and other vegetative requirements shall be as set forth in Practice Standard 342-Critical Area Planting. Irrigation may be needed to establish, and maintain vegetative growth. 742-2 NRCS, CA July, 2000 8. Maintenance; specify any and all maintenance requirements needed for the project to reform as designed. Protection Measures Guidelines: The following is a partial list of elements that may be included in a plan for Cut Bank Protection: 1. Scaling and grading of the slope, and the removal of fallen or hazardous trees, rocks, and other debris. 2. Flattening of slope of the bank to provide a suitable condition for establishment and maint- enance of vegetative growth. 3. If bank can be sloped to a 2:1, then establish vegetation. 4. If bank cannot be sloped to a 2:1; then construct retaining walls to a height needed to provide a 2:1 slope from the top of bank, and then establish vegetation. 5. Installation of structural measures to provide for stable conditions, so that vegetation can be established on the modified slope. Structural measures may include: a. timber retaining walls b. gabion retaining walls c. Rock Toe-walls d. Rocked slopes, or slopes reinforced with screen blocks, or other geotextile materials. e. Concrete curb and gutter at toe of bank. f. Grassed waterways, or lined channels. Lined channels maybe loose rock, grouted rock, modular block, shotcrete, or concrete. 6. Diversion of excess runoff away from the upper edge of the bank, and providing for toe protection. 7. Conveyance system downslope for concentrated flows, including drop inlets and culverts as needed. 8. Provide irrigation as may be need for plant establishment. Wildlife Special attention shall be given to improving the habitat for wildlife. Landscape Consideration shall be given to the use of construction materials, grading, and vegetation, that either improves, or minimizes the visual impacts, and maintains or complement the existing landscape. CONSIDERATIONS Water Quantity 1. Effects on the water budget, especially on volumes and rates of runoff, infiltration, deep percolation, and ground water recharge. 2. Effects on downstream flows and aquifers that affect other uses and users. 3. Effects on the water table of adjoining fields. 4. Effects on the interflow discharge into streams. 5. Effects on soil moisture storage, and rooting depths and transpiration of vegetation. Water Quality 1. Filtering effects of vegetation on movement of sediment, and sediment-attached and dissolved substances. 2. Effects on erosion and movement of sediment, and soluble and sediment-attached substances carried by runoff and streamflow. 3. Effects on the visual quality of onsite and downstream water resources. 4. Effects of construction and vegetation establishment on quality. 5. Effects of changes in water temperatures. 6. Short-term and long-term effects on wetlands and water-related wildlife habitats. 7. Effects on the visual quality of the water resource.