Soil and Water Conservation Engineering (UENGG 101) PDF

Soil and Water Conservation Engineering (UENGG 101 ) D. K. Singh Division of Agricultural Engineering ICAR-Indina Agricultural Engineering Soil Erosion Natural Erosion/ Geologic Erosion Anderson, https://www.slideserve.com/ morag/soil-erosion-by-water ...

Soil and Water Conservation Engineering (UENGG 101 ) D. K. Singh Division of Agricultural Engineering ICAR-Indina Agricultural Engineering Soil Erosion Natural Erosion/ Geologic Erosion Anderson, https://www.slideserve.com/ morag/soil-erosion-by-water  Accelerated Erosion Agricultural activities mainly cultivation Grazing in range and pasture Construction Traffic on uncarpeted roads (Plain and slopes) Soil erosion is maximum on bare soil exposed heavy rainfall Soil erosion involves three processes Detachment Transportation Deposition These processes are accomplished by mainly by action of water and wind Water erosion In this erosion is caused by raindrops, surface flow (sheet flow), channel flow (flow in rills and channels) and Wind Erosion gully flow Wind erosion mostly occurs in dry areas where soils are often bare high wind velocities are common Land Slide/ Land slippage Soil that is saturated with water, slips down the hillside or mountain slope. It is common along the roads in hills, streams (Stream bank erosion) and ocean fronts Glacier Erosion Glacier sometime may push soil, rocks, fallen trees, and other materials. This is not of much importance and occurs where glaciers exist  Soil Erosion Processes Detachment Transportation Deposition  Detachment Impact of raindrop Flowing water (Erosive velocity) Abrasive action of moving particles Weathering Animal and human interventions Burrowing Tillage Excavation Construction Mining Deforestation Settlements  Soil properties which resist detachment Adhesion Cohesion Binding forces of plant root systems Protective coverings such as plant material Anderson, https://www.slideserve.com/ morag/soil-erosion-by-water Soil properties affecting erosion Anderson, https://www.slideserve.com/ morag/soil-erosion-by-water  Transportation Raindrop splash Forces of flowing water Wind movement Gravity  Soil properties which resist transport Inertia Density Particle size  Action of raindrop Breaks soil aggregates into small particles Compacts the sub-surface soil layer thus increases overland flow Splashes small soil particles down the slope Increases the turbulence of overland flow and its transport capacity  Action of raindrop Eroding power of raindrop depends on Raindrop properties Soil properties Interaction properties (Park et al., 1982) Rainfall erosivity is described by kinetic energy and depends on raindrop properties (mass, size, shape, and terminal velocity) Kinetic energy is widely used indicator for estimating the potential ability of rain to cause erosion. (Torres et al, Kinetic Energy of Raindrops (KE) KE of raindrop can be easily expressed in terms of Diameter of drops (D) Terminal velocity (V) However, it is hardly used as the direct measurements of drop features is difficult and uncommon Hence, KE of a given storm has been generally computed from mean rain intensities using the formulae proposed in the literature Where P= the water density D= diameter of the equivalent spherical drop V= terminal velocity of raindrop KE of a rainfall event per unit of surface can be directly computed from D and the V of raindrop (Torres et al, Drop features are difficult to measure in erosion field studies Relations between KE and rainfall intensity (which is measurable) is used Wischmeier & Smith, 1958 Where, KE= Kinetic energy in J m-2 I = Rainfall intensity , mm h-1 t= time step, h Above formula associate rain intensity to Drop Size Distribution (DSD) to compute KE of rainfall Formulae using raindrop size distribution modelling to estimate Using theKE D50(I) relations from the literature the kinetic energy can be expressed as Where, V(D50) =Terminal velocity (in m s-1) of a raindrop of diameter D50 (in mm) (Torres et al,  Think and Discuss A parking lot had just been paved but the grading around it had not been completed. A heavy rain eroded the clay, and muddy water ran across the paved lot. About 0.5 inch of clay was deposited under each parked car, but the area between cars was washed clean. Discuss this event and try to explain why sediment remained under the parked cars, based on what you have learned about the erosion process. Anderson, https://www.slideserve.com/ morag/soil-erosion-by-water  Types of Soil Erosion by Water Splash erosion Sheet or inter rill Rill erosion Gully erosion Stream bank erosion Land slide Sea shore erosion Splash erosion It is the first process of erosion. When raindrop hit bare soil, it breaks up soil aggregates and soil particles are ‘splashed’ on soil surface These particles can bounce back up to height 60 cm and can move up to 1.5 m from the point of impact These particles block the pores, form crust, reduce infiltration and increase Sheet erosion overland flow Removal of a thin layer of top soil by sheet flow/overland flow Removes top soil congaing nutrient and organic matter It happens gradually and usually goes unnoticed, but in long term it accounts for large soil losses. Overgrazed and cultivated soils are more vulnerable to sheet erosion  Sheet erosion Sheet erosion depends on the depth and velocity of flowing and soil types www.soer.justice.tas.gov.au https://www.dpi.nsw.gov.au/__data/ assets/pdf_file/0003/255153/fact- sheet-1-types-of-erosion.pdf Anderson, https://www. slideserve.com/morag/soil- erosion-by-water  Rill erosiodrainage lines are developed when surface water Shallow concentrates n in depressions Water flows through these lines and carries soil Rill erosion is common in bare agricultural land, overgrazed land and cultivated lands where soil has been Loosened The rills can usually be removed with farm machinery Rill erosion can be controlled by reducing the flow velocity with grassed waterways and filter strips, mulchimg and contour drains. It is the intermediate stage between sheet erosion and gully erosion Anderson, https://www. https://www.dpi.nsw.gov.au/__data/ http://www. slideserve.com/morag/ assets/pdf_file/0003/255153/fact- kalkaskacounty.net) soil-erosion-by-water sheet-1-types-of-erosion.pdf Gully erosion Rills if not controlled become gully after sometime. Gullies are wider and deeper channels with depth more than 30 cm and can not be controlled/ removed by cultivation or farm www.soilsurvey.com. au machines. They apparently appear stable and over the time lose less soil than sheet Gullies areand rill erosion. formed when flow of water concentrates and cuts a channel through the soil upslope Head of the gully is continuously subjected to undercut and collapse Collapse and slumping of Anderson, https://www.slideserve. sidewalls usually contribute a com/morag/soil-erosion-by-water greater proportion of soil loss  Stream bank erosion Stream bank erosion is removal of soil and other material, such as rock and vegetation, from the stream bank It is a naturally occurring process, but anthropogenic or human activities such as urbanization and agriculture increase the rate of erosion http://www2.ca.uky.edu/ Stream bank erosion occurs When driving agcomm/pubs/AEN/AEN124/ forces of water and gravity become greater AEN124.pdf than the ability of the stream bank to resist Sea-shore them, stream erosion/Coastal bank erosion occurs Also known as shoreline retreat is the loss of erosion coastal lands due to the net removal of sediments or bedrock from the shoreline Coastal erosion is driven mainly by the action of waves and currents Mass wasting processes on slopes, and subsidence also cause coastal erosion https://diligentias.com/sea- It is often associated with extreme weather erosion/ events (coastal storms, surge and flooding) but also from(https://www.ga.gov.au/scientific-topics/community-safety/ tsunami coastalerosion) Land slide A landslide is the movement of a mass of rock, debris, or earth down a slope Landslides are a type of "mass wasting," which denotes any down- slope movement of soil and rock under the direct influence of gravity The term "landslide" encompasses five modes of slope movement: falls, https://indianexpress.com/article/ topples, slides, spreads, and flows cities/kolkata/fresh-landslide-cuts-off- These are further subdivided by the darjeeling-mirik-road-link/ type of geologic material (bedrock, debris, or earth) Debris flows (commonly referred to as mudflows or mudslides) and rock falls https://www.usgs.gov/faqs/what-a-landslide-and- are examples of common landslide what-causes-one?qt- types. news_science_products=0#qt- news_science_products  Universal Soil Loss Equation (USLE) The Universal Soil Loss Equation (USLE) was one of the most significant developments in soil and water conservation in the 20 the century. It is an empirical equation which applied world wide to estimate soil erosion by raindrop impact and surface runoff The development of the USLE was the result of decades of soil erosion experiments conducted by university faculty and federal scientists USLE wasthe across first published United in 1965 in USDA Agriculture Handbook 282 States. An updated version was published in 1978 in Agriculture Handbook 537 The Revised Universal Soil Loss Equation (RUSLE), a computerized version of USLE with improvements in many of the factor estimates was released in 1992 Work is continuing on a further-enhanced Windows version of the software, known as RUSLE2. USLE was the first empirical erosion equation not tied to a specific region of the United States, hence it was given the as "Universal" Soil Loss Equation. https://www.ars.usda.gov/midwest-area/west-lafayette-in/national-soil-erosion- research/docs/usle-database/research/  The USLE was developed at the USDA National Runoff and Soil Loss Data Centre at Purdue University led by Walter H. Wischmeier and Dwight D. Smith The USLE is based on extensive erosion data from studies throughout the USA, and provides a quick approach to estimating long-term average annual soil loss A=RKLSCP R - rainfall and runoff; K - soil erodibility; L - slope length; S -slope steepness; C - cover and management; P - support practice https://www.ars.usda.gov/midwest-area/west-lafayette-in/national-soil- erosion-research/docs/usle-database/research/  A=R×K×L×S×C×P Where A= Mean annual soil loss (metric tons per hectare per year) R= Rainfall and runoff factor or rainfall erosivity factor (megajoule millimetres per hectare per hour per year) K= Soil erodibility factor (metric ton hours per megajoules per millimetre) L= Slope length factor (unitless) S = Slope steepness factor (unitless) C= Cover and management factor (unitless) P= Support practice factor (unitless). USLE was developed at the farm plot scale for agricultural land in the USA but is used worldwide Name implies that the model can be applied to all soils, the original USLE is more accurate for soils with medium texture (Length 122 m, Slope range 3 % to 18 %, Consistent cropping practices that are well represented in plot-scale erosion studies (Wischmeier and Smith, 1978) Use of USLE family of models to soils and sites exceeding these limits requires careful parameterization of the model and being mindful of the increased uncertainty in model predictions. https://www.hydrol-earth-syst-sci.net/22/6059/2018/  USLE was developed for “unit plot” (22.1 m long, 1.83 m wide, 9 % slope (Wischmeier and Smith, 1978) Although the model accounts for rill and interrill erosion, it does not account for soil loss from gullies or mass wasting events such as Rlandslides factor (Thorne et al., 1985). Effect that rainfall on soil erosion and was included after observing sediment deposits after an intense storm (Wischmeier and Smith, 1978) The annual R factor is a function of the mean annual EI30 EI30 is calculated from detailed and long-term records of storm kinetic energy (E) and maximum 30 min intensity (I30) (Morgan, 2005; Renard et al., 1997) K factor Influence of different soil properties on the slope’s susceptibility to erosion (Renard et al., 1997) It is defined as the “mean annual soil loss per unit of rainfall erosivity for a standard condition of bare soil, recently tilled up-and-down slope with no conservation practice” (Morgan, 2005) K factor essentially represents the soil loss that would occur on the unit plot, which is a plot that is 22.1 m long, is 1.83 m wide, and has a slope of 9 % (Lopez-Vicente et al., 2008). https://www.hydrol-earth-syst-sci.net/22/6059/2018/  Higher K-factor values indicate the soil’s higher susceptibility to soil erosion (Adornado et al., 2009) In the (R)USLE, Wischmeier and Smith (1978) and Renard et al. (1997) used an equation that related textural information, organic matter, information about the soil structure, and profile permeability with the K factor or soil erodibility factor. LS factor Effect of the slope’s length and steepness on sheet, rill, and inter-rill erosion by water It is the ratio of expected soil loss from a field slope relative to the original USLE unit plot (Wischmeier and Smith, 1978) USLE method of calculating the slope length and steepness factor was originally applied at the unit plot and field scale, and the RUSLE extended this to the one-dimensional hill slope scale, with different equations depending on whether the slope had a gradient of more than 9 % (Renard et al., 1997; Wischmeier and Smith, 1978). LS factor was modified to incorporates contributing area and flow accumulation (Desmet and Govers, 1996) The USLE and RUSLE method of calculating the LS factor use slope length, angle, and a parameter that depends on the steepness of the slope in percent (Wischmeier and Smith, 1978). https://www.hydrol-earth-syst-sci.net/22/6059/2018/ Cover and management factor (C) Ratio of soil loss from a field with a particular cover and management to that of a field under “clean-tilled continuous fallow” (Wischmeier and Smith, 1978) The (R)USLE uses a combination of sub-factors such as impacts of previous management, canopy cover, surface cover and roughness, and soil moisture on potential erosion to produce a value for the soil loss ratio, which is used with the R factor to produce a value for the C factor (Renard et al., 1997) This requires extensive knowledge of the study area’s cover characteristics including agricultural management and may be suitable at the field or farm scale, but monitoring all these characteristics at the watershed scale may not be feasible. https://www.hydrol-earth-syst-sci.net/22/6059/2018/  Support practice factor (P) Ratio of soil loss under a specific soil conservation practice (e.g. contouring, terracing) to that of a field with upslope and down slope tillage (Renard et al., 1997) P factor accounts for management practices that affect soil erosion through modifying the flow pattern, such as contouring, strip cropping, or terracing (Renard et al., 1997) The more effective the conservation practice is at mitigating soil erosion, the lower the P factor (Bagherzadeh, 2014) Like the C factor, values for P factors can be taken from the literature P factor can also be estimated using sub-factors, but the difficulty in accurately mapping support practice factors or not observing support practices leads to many studies ignoring it by giving their P factor a value of 1.0 (Adornado et al., 2009; Renard et al., 1997; Schmitt, 2009). Hydrol. Earth Syst. Sci., 22, 6059–6086, 2018 www.hydrol-earth-syst-sci.net/22/6059/2018/ R. Benavidez et al.: A review of the (Revised) Universal Soil Loss Equation ((R)USLE)  Erosion index (EI) Erosion index (EI) for a given storm Product of the kinetic energy of the falling raindrops and its maximum 30 minute intensity R factorIntensity Rainfall = Σ EI over a year / 100 Rainfall intensity refers to the rate of rainfall over the land surface It is one of the most important factors responsible for the erosive nature of rainfall. The kinetic energy is related to the intensity of rainfall by the equation proposed by Wischmeier and Smith (1958) as follows: KE=tons per ha per cm I = rainfall intensity (cm/ EI 30 Index Method (Wischmeier (1965)) It is based on the fact that the product of kinetic energy of the storm and the 30-minute maximum rainfall intensity gives the best estimation of soil loss The greatest average intensity experienced in any 30 minute period during the storm is computed from recording rain gauge charts by locating the maximum amount of rain which falls in 30 minute period and later converting the same to intensity in mm/hour. This measure of erosivity is referred to as the EI30 index and can be computed for individual storms, and the storm values can be added over periods of time to give weekly, monthly or yearly values of erosivity.  Limitations of (R)USLE The uncertainties associated in erosion modeling/ prediction with the (R)USLE is complex due to its inability in capturing the complex interactions involved in soil loss Its applicability is limited by availability of long term reliable data for modelling, and the lack of soil erosion observational data for model validation, especially in datas carce environments Due to its simplicity, it is advisable to use (R)USLE allows usage in locations where there are insufficient data for more complex models that require large input datasets (de Vente and Poesen, 2005; Hernandez et al., 2012) (R)USLE does not account for all the complex interactions associated with soil erosion, predicted soil erosion rates should be taken as best estimates rather than absolute values (Wischmeier and Smith, 1987), Nigel and Rughooputh, 2012). https://www.hydrol-earth-syst-sci.net/22/6059/2018/  Limitations of (R)USLE Many researchers prefer to produce maps that show low, medium, or high areas of vulnerability instead of showing annual average amounts (Adornado et al., 2009; Schmitt, 2009) (R)USLE is a good first attempt at identifying vulnerable areas and estimating soil loss for a landscape at the baseline scenario due to the model’s relative simplicity and few data requirements (Aksoy and Kavvas, 2005) (R)USLE is also useful for doing scenario analysis to check whether changing land use or management practices would either exacerbate or mitigate soil loss, making it useful for comparison purposes (Merritt et al., 2004; https://www.hydrol-earth-syst-sci.net/22/6059/2018/  Wind Moving wind has energy which detaches, Erosion transports and deposits the soil to other places. This process is known as wind erosion Erosive wind energy increases by a factor equal to the velocity cubed A small increase in wind velocity results in a large increase in erosive wind energy Though the rough, cloddy, or vegetated surfaces reduce the wind speed and the energy available for soil erosion, many https://bookstore.ksre.ksu.edu/pubs/  Wind Erosion Processes Detachment When wind force acting on soil surface exceeds the force of gravity, detachment of soil particle is initiated. Detached, moving particles collide and detach other particles Transportation Detached soil particles are transported by wind Deposition When wind velocity decreases, soil particles are deposited at the surface away from the place of Threshold velocity: speed at which particle movement is detachment initiated Factors affecting threshold velocity on the condition of the soil surface Soil surface that are rough enough or well protected require higher velocity initiate particle movement compared to bare, smooth surface Soil type, Soil aggregate, https://bookstore.ksre.ksu.edu/pubs/ Roughness, Crop status,  Wind Erosion Processes Surface creep: Large particles (0.5 to 2 mm, diameter) roll over the soil surface, collide with other particles and dislodge them. Particles move only at surface Saltation: Middle-sized soil particles (0.05 to 0.5 mm, diameter) are lifted up, go under temporary suspension and fall on ground surface. They move through a series of low bounces over the surface, cause abrasion, break other particles into smaller particles. These are transported and deposited away from the point of https://www.qld.gov.au/__data/assets/pdf_file/0021/65217/wind-erosion.pdf detachment https://bookstore.ksre.ksu.edu/pubs/ Suspension: Very fine and tiny particles (0.1 mm, diameter or less) move into the air by saltation are taken further upwards by turbulence. Larger dust particles (0.05 to 0.1 mm) may get dropped within few kilometers. Finer particles (0.01 mm or less) travel hundreds of kilometers. Particle of 0.001 mm diameter may travel thousands of kilometers. These particles may remain in suspension until washed out by rainfall. https://www.qld.gov.au/__data/assets/pdf_file/0021/65217/wind-erosion.pdf  Principles of Erosion Control Protect the soil from impact of raindrop (Dissipate the energy of raindrop using Vegetative measures) This control the detachment- the first process Check the transportation Reduce forces of fluid Reduce flow velocity Increase forces holding soil Increase adhesion Increase plant root structure Separate soil from flow Pavement Mulch Residue  Wind Erosion Control Wind erosion control requires reduction of wind force at the soil and providing surface cover to resist wind forces Vegetation or Vegetative Residues Crop residue or keeps growing vegetation in the field are the most practical way to reduce wind erosion Plants and crop residues protect soil particles on the surface by absorbing part of the wind force, trapping moving particles and enhancing soil particle cohesion Crop rows perpendicular to the prevailing winds will control wind erosion more effectively than rows parallel with the wind Standing residues are more than twice as effective as flattened residues https://bookstore.ksre.ksu.edu/pubs/ MF2860.pdf Conservation practices to supplement vegetative cover Windbreaks Grass barriers Strip cropping Clod-producing tillage https://bookstore.ksre.ksu.edu/pubs/ MF2860.pdf  Residue Cropping systems that preserve surface residue are a Management practical approach to reduce the potential of soil erosion by wind No-till or strip Mulch till Ridge tillage till Permanent Vegetative Cover Permanent vegetative cover Pasture and hay planting Conservation cover Critical area planting Surface Roughening and Maintaining Stable Aggregates Soil crusts Crosswind ridges Clod-forming tillage https://bookstore.ksre.ksu.edu/pubs/  Crosswind Strip Cropping Practice of growing crops in strips, arranged perpendicular to the prevailing wind erosion direction Alternating the placing of strips susceptible to wind erosion with strips having a cover resistant to wind erosion This reduces the downwind avalanche effect by limiting the distance particles can travel before being trapped Designing strip-cropping systems requires consideration of soil aggregation, machinery size, exposure to knolls, residue management, and windbreaks in addition to the prevailing wind erosion direction. On extremely erodible soils where narrow strips are required, consideration should be given to permanent vegetation such as grass or grass-legume mixtures. https://bookstore.ksre.ksu.edu/pubs/ MF2860.pdf Barrie rs Wind, barriers alter the effect of the wind force on the soil surface. Barriers reduce wind speed on the downwind side of the barrier and trap moving soil. Windbreaks and shelterbelts Herbaceous wind barriers Crosswind trap strips Perennial grass barriers Annual crops Artificial barriers https://bookstore.ksre.ksu.edu/pubs/ MF2860.pdf  Reshaping the Land Reshaping the land by leveling and benching to shorten the unsheltered distance is an option for wind erosion control, but is usually not economical or practical Control measures, such as no-till or seeding to permanent grass, are usually more viable options Emergency Wind Erosion Control Emergency Addition tillage of crop residue Livestock Irrigati manure Temporary, on artificial wind Soil barriers stabilizers https://bookstore.ksre.ksu.edu/pubs/  Major Factors Affecting Soil Erosion Climate R Soil K Length and Slope (Topography) LS Vegetation C Conservation Practices P Anderson, https://www.slideserve.com/ morag/soil-erosion-by-water  Soil Erosion Units Mass per unit area per unit time Tons per acre per year Metric tons per hectare per year Natural Erosion Rate 1.0 to 5 tons/acre/year (2.47 tonne/ha/y to 12.35 tonne/ha/y) (Permissible rate of erosion) Erosion Rates in this Range are Sustainable Indefinitely For 1.0 ton / acre / year, it will take about 163 years to erode 1.0 inch of soil Anderson, https://www.slideserve.com/ morag/soil-erosion-by-water  Soil Loss Tolerance The maximum level of soil erosion that will permit a high level of crop productivity to be maintained both economically and indefinitely Anderson, https://www.slideserve.com/ morag/soil-erosion-by-water