How is soil eroded?

Soil erosion happens all over the world.

What is Soil Erosion?  Soil erosion is the detachment, transport and deposition of soil particles on land surface.  Also termed as Loss of soil.  Wind, water, ice and gravity are also known as the agents of erosion.

Soil Erosion is caused by: Natural Processes  Wind  Water  Ice  Gravity Human Activities  Overcropping  Overgrazing  Deforestation  Inappropriate farming techniques  Lock of crop rotation

Accelerated Erosion ● Water Erosion ● Wind Erosion Types of Soil erosion Geological Erosion

Types of Soil erosion Geological Erosion  Also referred to as “normal” or “natural” erosion.  It is a “natural” process responsible for the formation of and the loss of soil simultaneously.  Relatively slow, continuous process that often goes unnoticed.  Responsible for the formation of topographical features such as stream channels, valleys, etc.

Example of geological erosion Grand Canyon, Arizona, USA  One of the geologic wonders of the world.  Formed by the entrenchment of Colorado River  The Grand Canyon displays rock from about 200 million to 2 billion years old.

Types of Soil erosion Accelerated Erosion  Also referred to as anthropogenic or man-induced erosion  It is activated by human activities that bring changes in natural cover and soil conditions.  Soil removal is much faster than the natural soil formation process ● Leads to serious environmental damages

Accelerated Erosion ● Water Erosion ○ Sheet erosion ○ Rill erosion ○ Gully erosion ● Wind Erosion Types of Soil erosion

Lets start with wind…

Wind Erosion In dry areas wind causes erosion by picking up and carrying loose particles and dust away. These flying particles crash into the land and break off more particles.

Severe dust storms. An example of wind erosion.

Dust storms can carry loose unprotected soil into cities, too.

Now lets talk about water…

Even a single rain drop can dislodge soil, and start erosion

Water Erosion Can change the shape and texture of mountains

Note the color of the river water….Why?

Sheet erosion Sheet erosion is the removal of the thin layer of topsoil by raindrop splash or water run-off. It typically occurs gradually and goes unnoticed until most of the productive topsoil has been lost. Overgrazed and cultivated soils are most vulnerable to the sheet erosion. Water Erosion

Rill erosion If sheet erosion occurs with full force, the run off water moves rapidly over the soil surface. Its erosive action results in the formation of shallow channels, known as “rills”. The removal of soil by concentrated water running through rills is “Rill erosion ”.

Gully erosion If rills are not destroyed and the detachment continues, then these become wider and deeper. This results in the formation of Gullies. Gully erosion is the removal of soil along drainage lines by surface water runoff.

Stages of Gully erosion  Formation Stage Channel erosion by a downward scour of the top soil (Rill → Gully)  Development Stage Consists of u/s movement of the gully head and enlargement of gully in width and depth  Healing Stage Vegetation growth begins in gully  Stabilization Stage Vegetative cover spreads over the gully surface such that Gully reaches a stable gradient, and walls reach a stable slope.

Classification of gullies  Based on size Small (Depth < 1 m; Drainage area < 2 ha) Medium (Depth 1 – 5 m; Drainage area <2 – 20 ha) Large (Depth > 5 m; Drainage area >20 ha)  Based on shape ● U-shaped – formed where both the topsoil and subsoil have the same resistance against erosion. ● V-shaped – formed where the subsoil has more resistance than topsoil against erosion.

GULLY EROSION RILL EROSIONSHEET EROSION Channels are deepShallow channelsNo channel for soil erosion It is the soil erosion caused by a stream or river. Rainwater runoff through a gentle sloping land. It creates temporary channels. Impact of raindrops mainly cause erosion.

Ice Erosion Glaciers wear down the landscape; by picking up and carrying debris that moves across the land along with the ice.

Gravity Erosion is better known as Mass Movement and is defined as the transfer of rock and soil down slope by direct action of gravity without a flowing medium (such as water or ice). Gravity Erosion (a) Rockfall (b) Landslide(C) Avalanche

Effects of Soil Erosion Reduced the crop production Eroded soil is deposited on riverbeds, raising their levels and leading to devastating floods. Plant productivity decline. Desertification

So what can we do?

METHODS OF CONSERVATION Various methods of soil conservation may be broadly categorized into two types: (1) Agronomic Practices (2) Engineering Practices

(1) Agronomic Practices This method involves protection of the top soil by special methods and schemes of crop cultivation. These are- (a) Crop Rotation - It is a method of growing a series of dissimilar crops or different types of crops in the same area in sequenced seasons. Here different crops are grown in the same area by rotation, that is, one after another. Crop rotation also helps in the improvement of soil structure and fertility.

(b) Strip Cropping – In this method, the cultivated crops and the cover crops are sown in alternate strips during the same period in the same field.

(2) Engineering practices (a) Terraces construction – Terraces are large steps cut into a hillside. This reduces slope length and steepness to control the energy of running water and its ability to carry soil away.

(b) Check Dams – Small(sometimes temporary) check dams are constructed out of various materials like stones, timber, steel etc. to control erosion by reducing the velocity of water flow. Fig. 1 – A steel check dam Fig. 2 – A concrete check dam

CONSERVE THE SOIL, SAVE THE EARTH. THANK YOU. SOIL EROSION INDIRECTLY CAUSES POVERTY.