Contour Bunding, Graded Bunding, and Bench Terracing

These soil and water conservation methods are especially useful in areas prone to soil erosion, particularly on sloped lands where runoff water can easily wash away topsoil. These techniques help manage water flow, reduce soil erosion, conserve moisture, and improve the productivity of agricultural land.

1. Contour Bunding

Definition:
Contour bunding involves constructing embankments (bunds) along the natural contours of the land. These bunds are designed to intercept water runoff, slow its movement, and allow water to infiltrate into the soil. They are generally used on land with a slope to prevent water from washing away the fertile topsoil.

Key Features:

• Land Survey: The land is surveyed to determine the contour lines (i.e., lines of equal elevation). Bunds are constructed along these lines.
• Embankments/Bunds: The bunds are embankments or small dikes made of locally available materials like soil, stones, or a mix of both. They can be built to various heights, depending on the slope of the land and the volume of water expected.
• Shape and Alignment: Bunds are typically continuous lines that follow the slope contours of the land, ensuring that water cannot run downhill unchecked.

Purpose:

• The main goal is to reduce the speed and volume of water flowing downhill, allowing more time for water to infiltrate the soil.
• Bunds create barriers to stop the erosion caused by water flow and sediment displacement.
• These barriers effectively trap water, reducing the risk of soil loss and improving moisture retention in the soil.

Steps for Construction:

1. Survey and Marking: The first step involves surveying the land and marking the contour lines with the help of tools like A-frames or leveling instruments.
2. Excavation: Shallow trenches are dug along the contours, where bunds will be placed. These are typically 30 cm to 1 meter deep.
3. Building Bunds: Soil is piled up along the contour lines to form the bund. The bunds are often reinforced with vegetation or stone to improve their stability and longevity.
4. Drainage Channels: Small drainage channels are built at regular intervals to direct excess water from the bunds to lower areas without eroding the land.

Benefits:

• Prevents Soil Erosion: By reducing the speed of water flow, contour bunding helps prevent soil from being washed away.
• Improves Water Infiltration: Bunds slow down water runoff, giving the soil more time to absorb moisture.
• Increases Land Productivity: The soil stays moist and fertile for a longer period, benefiting crops.

Challenges:

• Requires regular maintenance to ensure the bunds do not break or collapse.
• Can be labor-intensive, particularly on large areas.

2. Graded Bunding

Definition:
Graded bunding is a variation of contour bunding where the bunds are constructed with a slight grade or slope along their length, facilitating the flow of water to specific outlets. This allows water to drain effectively, reducing the chances of waterlogging behind the bunds while still slowing down the runoff.

Key Features:

• Slight Slope: The bunds have a slight slope (usually 0.1% to 1%), directing water towards drainage outlets or lower areas.
• Incorporating Drainage: Graded bunding also includes provisions for drainage, unlike contour bunding, where water is often trapped behind the bund.
• Water Flow Control: Graded bunds ensure that any excess water that might accumulate does not cause erosion or damage the bunds.

Purpose:

• The purpose of graded bunding is to allow water to flow gently along the bunds and direct excess water to drains or lower lying areas, preventing waterlogging.
• The slight slope helps maintain a manageable water flow, avoiding erosion while encouraging drainage.

Steps for Construction:

1. Surveying and Slope Design: The first step is to survey the land and design the slope of the bunds. A slight gradient (usually about 0.1% to 1%) is maintained along the bund’s length.
2. Construction of Bunds: Bunds are constructed similarly to contour bunds but with a gradual slope instead of a level alignment.
3. Drainage and Outlet Design: Drainage outlets are incorporated into the design to direct excess water away from the bunds. These outlets could be small ditches or culverts.
4. Monitoring: After construction, the bunds should be monitored to ensure that the water is flowing as intended, and no waterlogging occurs behind the bunds.

Benefits:

• Effective Drainage: Water can flow more freely and is channeled into drainage systems, preventing accumulation behind bunds.
• Prevents Soil Erosion: Graded bunding still reduces the risk of soil erosion by slowing down water and allowing more time for infiltration.
• Improves Land Efficiency: By managing water flow and preventing waterlogging, graded bunding allows more consistent crop production.

Challenges:

• Requires careful design to ensure that the slope is not too steep, which could cause erosion.
• Maintenance of drainage systems and outlets is necessary to prevent clogging.

3. Bench Terracing

Definition:
Bench terracing is a technique where the slope is cut into a series of horizontal steps or terraces. Each terrace is typically surrounded by a bund or embankment to hold soil in place and prevent erosion. It is especially useful for areas with steep slopes, converting difficult-to-use land into arable land.

Key Features:

• Terrace Structure: Each terrace is a level area that serves as a platform for planting crops. These terraces are separated by bunds that help in retaining soil and water.
• Steep Slope Conversion: Bench terracing is primarily used on steep lands, where traditional farming would not be possible due to the risk of erosion.
• Water Management: The terraces hold water in place, and the bunds prevent it from flowing down the slope, allowing for gradual infiltration into the soil.

Purpose:

• Bench terracing is used to conserve soil and water on steep terrains.
• It helps in reducing the velocity of water runoff by creating multiple barriers and level areas, where water can be absorbed and where soil erosion is controlled.

Steps for Construction:

1. Planning: The slope is analyzed, and the number and size of terraces are determined based on the slope gradient and soil type.
2. Terrace Cutting: The slope is cut into steps, where each step is a flat area designed to hold water and prevent runoff.
3. Bunding: Each terrace is separated by bunds made of soil or stone, ensuring that water does not erode the soil between the terraces.
4. Drainage Systems: Proper drainage channels are designed to ensure water does not accumulate behind the terraces, preventing waterlogging and further erosion.

Benefits:

• Reduces Soil Erosion: By breaking the slope into steps, bench terracing effectively reduces water flow and prevents soil erosion.
• Improves Land Use: Steep, unusable land is converted into productive agricultural land, which was previously too steep for farming.
• Increases Water Retention: The flat terraces hold water, allowing for better moisture retention in the soil.

Challenges:

• High Labor and Cost: The process of cutting terraces into steep land can be labor-intensive and costly.
• Long-Term Maintenance: Terraces and bunds need regular maintenance to ensure their stability and prevent erosion.