Principle of erosion control- Introduction to contouring,strip cropping,contour graded bund and bench terracing(1).pptx

Principle of erosion control

1. MEASURES FOR WATER EROSION CONTROL Er . Mukesh Seetpal Assistant Professor, ITM University, Gwalior (MP)

2. Agronomical Measures of Water Erosion Control Contour Cropping Contour Cropping is a conservation farming method that is used on slopes to control soil losses due to water erosion. Contour cropping involves planting crops across the slope instead of up and down the slope . Use of contour cropping protects the valuable top soil by reducing the velocity of runoff water and inducing more infiltration. On long and smooth slope, contour cropping is more effective as the velocity of flow is high under such situation and contour cropping shortens the slope length to reduce the flow velocity. Contour cropping is most effective on slopes between 2 and 10 percent.

3. Contour cropping. (Source:  www.studyblue.com )

4. Strip Cropping Strip cropping is the practice of growing strip of crops having poor potential for erosion control, such as root crop ( inter tilled crops), cereals, etc., alternated with strips of crops having good potentials for erosion control, such as fodder crops, grasses, etc., which are close growing crops. Strip cropping is a more intensive farming practice than contour farming. The farming practices that are included in this type of farming are contour strip farming, cover cropping, farming with conservation tillage and suitable crop rotation. A crop rotation with a combination of inter tilled and close growing crops, farmed on contours, provides food, fodder and conserves soil moisture. Close growing crops act as barriers to flow and reduce the runoff velocity generated from the strips of inter tilled crops, and eventually reduce soil erosion. Strip cropping is laid out by using the following three methods : i)    Contour strip cropping:  In contour strip cropping, alternate strips of crop are sown more or less following the contours, similar to contouring. Suitable rotation of crops and tillage operations are followed during the farming operations. ii)    Field strip cropping:  In a field layout of strip cropping, strip of uniform width are laid out across the prevailing slope, while protecting the soil from erosion by water. To protect the soil from erosion by wind, strips are laid out across the prevailing direction of wind. Such practices are generally followed in areas where the topography is very irregular, and the contour lines are too curvy for strict contour farming. iii)  Buffer strip cropping:  Buffer strip cropping is practiced where uniform strip of crops are required to be laid out for smooth operations of the farm machinery, while farming on a contour strip cropping layout. Buffer strip of legumes, grasses and similar other crops are laid out between the contour strips as correction strips. Buffer strips provide very good protection and effective control of soil erosion.

5. Mechanical Measures for Water Erosion Control Contour Bunds Contour bunds are laid out in those areas which have less rainfall and permeable soils. The major requirements in such areas are prevention of soil erosion and conservation of rain water in the soil for crop use. To maximize the conservation of rainwater in the soil, no longitudinal slope is provided to the field strip. In such a system of bunding , the bunds are designed to be laid out on contours with minor adjustments, wherever necessary. The main functions of contour bunds are: It reduces the length of slope which in turn reduces the soil erosion. The water is impounded for some time and gets recharged into the soil which helps in crop cultivation. The limitations of contour bunds are: The contour bunds are suitable for those areas, which receive the annual rainfall less than 600 mm  It is not suitable for clayey soils Contour bunding is not suitable on the land slopes greater than 6%.

6. Graded Bunds Graded bunds are laid out in areas where the land is susceptible to water erosion, the soil is less permeable and the area has water logging problems . A graded bund system is designed to dispose of excess runoff safely form agricultural fields. A graded bund is laid out with a longitudinal slope gradient leading to outlet. The gradient can be either uniform or variable. The uniformly-graded bunds are suitable for areas where the bunds need shorter lengths and the runoff is low. The variable-graded bunds are required where bunds need longer lengths, owing to which the cumulative runoff increases towards the outlets. In these types of bunds, variations in the grade are provided at different sections of the bund to keep the runoff velocity within the desired limits so as not to cause any soil erosion . The limitations of the system are: Due to crossing of farm implements, the bunds are disturbed and some soil is lost. Proper maintenance is required at regular interval.

7. Bench Terracing The original bench terrace system consists of a series of flat shelf-like areas that convert a steep slope of 20 to 30 percent to a series of level, or nearly level benches . In other words, bench terracing consists of construction of series of platforms along contours cut into hill slope in a step like formation. These platforms are separated at regular intervals by vertical drop or by steep sided and protected by vegetation and sometimes packed by stone retaining walls. In fact, bench terrace converts the long un-interrupted slope into several small strips and make protected platform available for farming. In several hilly areas bench terraces have been used for the purpose of converting hill slopes to suit agriculture. In some areas where the climatic conditions favour the growing of certain cash crops like potato, coffee etc., the hill slopes are to be bench terraced before the area is put for cultivation of these crops. Bench terraces have also been adopted for converting sloping lands into irrigated fields or for orchard plantations.

8. Bench terrace and its different components.

9. 4 PRINCIPLES OF EROSION CONTROL 1. Erosion control measures Your primary course of action is to keep the soil on your site in place. In order to do that, you need to limit vegetation removal when possible. You can also try to cover bare soils by seeding and covering with straw. Additional provisions are necessary when working in a sensitive habitat, or on a steep slope. Erosion control blankets are typically best applied on steep slopes and can be used to cover soil after seeding has taken place. 2. Sediment control measures Think of sediment control as a back-up, or secondary defense, to erosion control. Should the erosion control measures fail, sediment control measures are designed to capture eroding soil and keep it on site. This can be done be using straw rolls on slopes or at the bottom of slopes. Or, silt fences can be placed at the bottom of slopes, provided they don’t impact drainage. Gravel bags, particularly around drainage inlets are also commonly used. Finally, rocked driveways and entrances prevent soil and sediment from being tracked onto adjacent roads. Remember, none of these measures are meant to initially stop erosion. Rather, they’re intended to capture soil that has eluded erosion control measures before it can cause any damage. 3. Runoff control measures The primary enemy in erosion control is water. That means controlling stormwater , and keeping it away from bare soils, is essential to preventing soil erosion. Your first option will be to find a vegetated area that can withstand increased runoff. This can be done by diverting the runoff from any bare soils and newly disturbed areas. When dealing with a large concentration of water, it’s unwise to concentrate all of your runoff to one area. Find multiple locations for drainage and ensure your development won’t cause additional erosion after construction is completed. It’s also important to avoid fill slopes in favor of cut slopes for drainage. If that’s impossible, try breaking up drainage in order to create sheet flows over the slope. If you’re implementing pipe, conduits or channels for runoff, be sure to install energy dissipators such as a collection of rocks, which reduces flow velocity and helps prevent scour and downstream erosion. 4. Maintenance Because there’s typically no sure-thing in erosion control, it’s important to continually check on the measures you’ve put in place, particularly when it rains. You should be able to spot areas that may need additional reinforcement, or need a new plan all together. In order to help the ability of the erosion control measures, try to regularly clear out silt that has built up around silt fencing or drainage inlets.