Soil Erosion - Watershed Management - Lecture Slides, Slides of Business Management and Analysis

Download Soil Erosion - Watershed Management - Lecture Slides and more Slides Business Management and Analysis in PDF only on Docsity! Module 2 – (L6) Sustainable Watershed Approach & Watershed Management Practices 6 Soil Erosion & Conservation 1 1 L6 Soil Erosion & Conservation–  Topics Covered  Soil erosion: causes, processes, erosion factors, water erosion, types, estimation of soil loss wind erosion , , soil conservation practices  Keywords: Soil erosion, Water erosion, Wind erosion Soil conservation 2 , . Prof. T I Eldho, Department of Civil Engineering, IIT Bombay Soil Erosion Problem… India’s Land Degradation: Source: state of environment report 2009 MoEF  Soil erosion deteriorates soil quality & reduces productivity of natural , agricultural & forest ecosystem  Soil erosion deteriorates quality of water  Increased sedimentation causes reduction of carrying capacity of water bodies 5 . Prof. T I Eldho, Department of Civil Engineering, IIT Bombay Causes of Soil Erosion  Human Induced & Natural Causes  Land use - Over grazing by cattle Deforestation , , arable land use, faulty farming, construction, mining etc. l d d l C imatic con itions: precipitation & win ve ocity  Soil: soil characteristics - texture, structure, water retention and transmission properties.  Hydrology: Infiltration, surface detention, overland flow velocity, and subsurface water flow. L d f Sl di l l h d h f  an orms: ope gra ent, s ope engt an s ape o slope Soil erosion in a 6 watershedProf. T I Eldho, Department of Civil Engineering, IIT Bombay Types of Soil Erosion  Geological erosion, Natural erosion & Erosion from activities of human & animals – Geological erosion:-Soil forming and distribution Long time process – Human and animal:-Tillage, removal of plants and other vegetation accelerated erosion – Stream bank erosion – Landslide, Volcanic eruption, flooding – Water and wind: major factors of soil erosion Soil erosion in a 7Prof. T I Eldho, Department of Civil Engineering, IIT Bombay watershed Water Erosion  Detachment & transport of soil particles from land mass by water including rain runoff , , melted snow  Depends on: soil nature & capacity of water to transport  More on sloppy land  More velocity more transport  Water erosion  accelerated by agriculture, grazing and construction activities Soil erosion in a 10 watershed Prof. T I Eldho, Department of Civil Engineering, IIT Bombay Factors affecting Erosion by water  Climate Precipitation, temperature, wind, humidity and solar radiation  Soil size, type of soil, soil texture, structure, organic matter  Vegetation interception of rainfall-reduce surface sealing & runoff decrease surface velocity , , improvement of aggregation, increased biological activity and aeration, transpiration, physical holding  Topography degree of slope, shape and length of slope and size and shape of watershed 11Prof. T I Eldho, Department of Civil Engineering, IIT Bombay Types of Water Erosion  Water Erosion Types: Interrill (raindrop and sheet), rill, gully & stream channel erosion  Raindrop erosion (splash erosion) Soil detachment & transport - from impact of raindrops directly on soil particles or on thin water surfaces  On bare soil  about 200 t/ha soil is splashed into the air by heavy rains  Relationship - erosion, rainfall momentum & energy - by raindrop mass, size, shape, velocity & direction Relationship: Rainfall intensity & energy (F t t l 1981) os er e a .,  E = 0.119 + 0.0873 log10i ; E- kinetic energy in MJ/ha-mm; i = intensity of rainfall in mm/h 12Prof. T I Eldho, Department of Civil Engineering, IIT Bombay Gully erosion Advanced form of rill erosion –forms larger channels than rills – Four stages – Formation stage – Development stage – Healing stage – Stabilization stage  Gullies may be small 1m or less Gully & rill erosion in a watershed -  Medium-1m to 5m  Large-more than 5m – Stream channel Erosion: Removal of soil for stream banks or soil movement in channel Soil erosion in a 15Prof. T I Eldho, Department of Civil Engineering, IIT Bombay watershed Measurement of Soil Loss – Water Erosion  Measurement from runoff plots Size varies from 1/250 to 1/125 Hectare– – Runoff measured by Flume  Measurement from streams – Silt observation Posts (SOP) – Suspension, saltation and surface creep (bed load) – Both separately measured and added – Soil Sampler: S = p* q*86400/1000  S-amount of material transported in tones/day  p-amount of material (1m3 of water in kg),  q-rate of stream flow in m3/sec 16Prof. T I Eldho, Department of Civil Engineering, IIT Bombay Estimation of Soil Loss- Water E osionr  Universal soil loss equation (USLE) (th h i t ) (R j Vi Si h 2000)roug exper men s a r ng , PCSLRKA  – A-Average annual loss: in ton/ha/year – R-Rainfall & runoff erosivity index for location – K-Soil erodibility factor – L-slope length factor – S – slope steepness factor – C-cover management factor P ti ti f t 17 – -conserva on prac ce ac or Prof. T I Eldho, Department of Civil Engineering, IIT Bombay Slope Length Factor (L) mIL       Where, L-slope length factor; I-slope length in m 22 m- dimensionless exponent Sin 05.0)(269.0 8.0    SinSin m Where θ-field slope steepness=tan-1(s/100)  s-field slope in % 20Prof. T I Eldho, Department of Civil Engineering, IIT Bombay Slope Steepness Factor (S)  Slope Length shorter than 4m F l l th l th 4 d 9%   56.0sin0.3 8.0  S  or s ope eng onger an m an s< 030sin810  S  Slope length more than 4m and s >= 9% .. 5.0sin8.16  S 21Prof. T I Eldho, Department of Civil Engineering, IIT Bombay Crop management factor (C)  Combined effect of crop sequences, productivity level, length of growing season, tillage practices, residue management & expected time distribution of erosive rain t ith t t l ti & h t d ts orm w respec o p an ng arves a e Crop Soil loss Value of C Eg. Hyderabad (tn/ha) Cultivated 5 1 Grass 0.59 0.12 Bajra 2 0 38 22 . Prof. T I Eldho, Department of Civil Engineering, IIT Bombay Mechanism of Wind Erosion  Initiation of movement –due to turbulence and wind velocity  Transportation –depends on particle size gradation wind , , velocity and distance  Deposition—occurs when gravitational force is greater h f h ld l lt an orces o ing soi partic es in air  Types of soil movement by wind – Saltation- Fine particles lifted from surface and following specific path w.r.t wind and gravity – Suspension-floating of small particles – Surface creep -rolling or sliding of large soil particles along soil surface. 25Prof. T I Eldho, Department of Civil Engineering, IIT Bombay Estimation of Wind Erosion  Average annual loss )( VLCKIfE  Where, E-estimated average annual loss (tn/ha/year) ,,,, I- soil erodibility index (ton/ha-yr), K-ridge roughness factor, C-climate factor, L-unsheltered length of eroding field (m) V-vegetative cover factor, I-Soil erodibility index (ton/ha-yr) FI 05.0)7182(525  F-% of dry soil fraction greater than 0.84 mm . 26Prof. T I Eldho, Department of Civil Engineering, IIT Bombay Roughness Factor  A measure of effect of ridges made by tillage implements on wind erosion  Ridge roughness in mm h2160 h ridge height in mm; d ridge spacing in mm d Kr .  - - from Kr, roughness factor K   2610*2.6 18 1235.0 Kr K K r    27Prof. T I Eldho, Department of Civil Engineering, IIT Bombay Preventing Soil Erosion Photo, A.K. Singh, 2002  Preventing soil erosion requires political, economic & technical changes.  Aspects of technical changes include:  use of contour ploughing and wind breaks;  leaving unploughed grass strips between ploughed land;  making sure that there are always plants growing on the soil, and that the soil is rich in humus (decaying plant and animal remains).  avoiding overgrazing and the over-use of crop lands;  allowing indigenous plants to grow along the river banks en o ging biologi l di e it b pl nting e e l diffe ent  c ura ca v rs y y a s v ra r types of plants together;  conservation of wetlands. 30Prof. T I Eldho, Department of Civil Engineering, IIT Bombay Soil Conservation Practices  Conservation measures - reduce soil erosion by both water & wind.  Tillage and cropping practices, as well a land management practices, directly affect the overall soil erosion problem .  Combination of approaches (Eg. contour plowing, strip cropping, or terracing)  Other measures: Silt Fencing, Erosion Control Blankets, Sediment Traps, Plastic Covering/Bank Stabilization Pipeline Sand Bagging Check Dams , , , Drain Inlets, Filter Berms & Silt Dikes 31Prof. T I Eldho, Department of Civil Engineering, IIT Bombay Photo, A.K. Singh, 2002 Photo, A.K. Singh, 2002 Soil Conservation Practices - Types  Vegetative practices Contouring– – Strip cropping – Tillage operations – Mulching  Mechanical practices – Terraces – Bunds (graded & contour) – Check dams – Vegetated outlets & watercourses 32 Photos: Singh, 07. 2001 Prof. T I Eldho, Department of Civil Engineering, IIT Bombay Photo, A.K. Singh, 2002 References  State of Environment of India 2009: report of Ministry of Environment and Forest ( source: http://moef.nic.in/downloads/home/home-SoE- R 2009 df )eport- .p  Raj Vir Singh (2000), Watershed Planning and Management, Yash P bli hi Hu s ng ouse  http://www.geo.fu-berlin.de/fb/e- learning/geolearning/en/soil_erosion/types/index.html  http://iahs info/redbooks/a236/iahs 236 0531 pdf. _ _ .  http://www.ias.ac.in/currsci/25jan2010/213.pdf  G Das (2000): Hydrology & Soil Conservation Engg Prentice Hall of . , ., India, New Delhi 35Prof. T I Eldho, Department of Civil Engineering, IIT Bombay Tutorials - Question!.?.  Illustrate the possible soil conservation measures within the perspective of sustainable watershed management practices.  Identify the components soil erosion  Scientific interventions Identif the p oblems  y r  Identify vegetative & mechanical measures.  Importance of soil conservation. 36 Prof. T I Eldho, Department of Civil Engineering, IIT Bombay Self Evaluation - Questions!.  What are the causes and consequences of soil erosion?.  What is wind erosion & under what conditions does it occur?.  Enumerate measures adopted for control of soil erosion caused by wind. P f T I Eldh D t t f Ci il E i i IIT B b 37 ro . o, epar men o v ng neer ng, om ay