- Slides: 19
UNIT 3 SOIL EROSION APARAJITA MUKHERJEE THK JAIN COLLEGE
WHAT IS SOIL EROSION Soil erosion is a type of soil degradation in which there is wearing away or displacement of the upper layer of soil (topsoil). § Soil erosion is a global threat in the current world scenario. § Apart from all natural agents the most fearful reason is human activity which is increasing the rate of soil erosion by 10 -50 times §
Soil erosion: physical processes 1. Rainfall and surface run off cause the following types of soil erosion: Ø Splash erosion- the impact of a falling raindrop creates a small crater in the soil ejecting soil particles Ø Sheet erosion- it is the transport of loosened soil particles by overland flow Ø Rill erosion- refers to the development of small and ephemeral concentrated flow pats which function as both sediment source and sediment delivery system for erosion on hill slopes Ø Gully erosion- when runoff water accumulates and rapidly flows in narrow channels during or immediately after heavy rains or melting snow, removing soil to a considerable depth
SURFACE RUNOFF BY RAINWATER
SOIL EROSION IS A PHYSICAL PROCESS 2. Rivers and streams cause erosion in three ways: Ø Downward erosion- deepening the valley Ø Head ward erosion- erosion at the origin of the stream causing it to move back away Ø Bank erosion- creating steep banks 3. Floods are formed by large volumes of rapidly rushing water which can cause extreme local erosion. 4. Wind erosion is a major geomorphological force which causes extensive soil erosion mostly in arid and semi-arid regions. 5. Mass movement is another physical process leading to soil erosion which involves outward or downward movement of rock and sediments on a sloped surface, mainly due to the force of gravity
SOIL EROSION BY RIVER
SOIL EROSION BY FLOOD: TOPSOIL IS WASHED AWAY
AFTER FLOOD SCENARIO
SOIL EROSION BY WIND
SOIL EROSION BY MASS MOVEMENT
OTHER FACTORS AFFECTING SOIL EROSION 1. Climate: § The amount and intensity of precipitation is the main climatic factor governing soil erosion by water in areas where sufficient amount of precipitation occurs and where the soil surface is not protected by vegetation. § In areas of dry climate, wind causes soil erosion as mentioned earlier. 2. Climate change: Climate change can increase the amount of soil erosion: § Increased global temperature causes increased evaporation leading to more vigorous rainfall which itself is a causative factor of soil erosion § Glacier melting leading to more water flow in oceans which is causing habitat loss and coastal erosion. § Pattern of rainfall may change leading to change in plant canopy and biomass storage, changes in soil moisture, changes in evapotranspiration rate which are all contributing factors to soil integrity
OTHER FACTORS AFFECTING SOIL EROSION 3. Soil structure and composition: The composition, moisture content and compaction of the soil are major factors in determining the erosivity of rainfall in that region. § Clayey soil tends to be more resistant to erosion than soil with more sand or silt because clay helps to bind soil particles together. § Soil containing high organic matter are more resistant to soil erosion as organic matters coagulate with soil colloids and create a stronger , more stable soil structure § Moisture of the soil prior to rainfall is important as soil which is more saturated undergoes more erosion and surface runoff with further rainfall.
OTHER FACTORS AFFECTING SOIL EROSION 4. Vegetative cover: § Vegetation acts as an interface between the atmosphere and the soil. § It increases the permeability of the soil to the rainwater § Reduces surface runoff § Roots of the plants bind soil particles strongly and reduces soil erosion by both water and wind. 5. Topography: Steeper slopes are more susceptible to soil erosion, mudslides, landslides and gravitational mass movement. 6. Human activities: § Unsustainable agricultural practices involving the followings cause soil degradation – Ø Mono cropping Ø Farming on steep slopes Ø Pesticides and chemical fertilizer usage Ø Surface irrigation § Over grazing: This leads to topsoil removal § Deforestation: In an undisturbed forest, the topsoil is protected by leaf litter and humus. Deforestation exposes the topsoil and makes it prone to erosion.
OTHER FACTORS AFFECTING SOIL EROSION § Roads and urbanization: Urbanization has major effects on soil erosion Ø Firstly it causes the denuding of land vegetative cover and exposes the soil to the factors that can lead to soil erosion Ø Compacting the soil during construction Ø Covering the land with impermeable layer of concrete that increases surface runoff (containing fuel, oil, cement and chemicals) and this layer also increases wind speed Ø This add chemical filled sedimentation to the adjacent watersheds also and contaminate them leading to increased flow of water through them which in turn cause increased bank erosion.
PREVENTION OF SOIL EROSION Followings are the preventive measures of soil erosion: 1. Maintaining a healthy perennial plant cover 2. Plantation of cover crop, such as annual grasses, small grains, legumes to provide a temporary vegetative cover and they can also serve as green manure 3. Placing crushed stones, wood chips and other similar materials in heavily used areas where vegetation is hard to establish and maintain 4. Mulching is another process which reduces soil erosion, reduce weeds, conserve soil moisture