Terracing is an agricultural and engineering practice that involves constructing earthen barriers or ridges across slopes. Its primary purpose is to control soil erosion, making sloped land suitable for cultivation and preserving environmental health.
The Problem of Soil Erosion
Soil erosion is the process by which natural forces detach and transport soil particles, leading to land degradation. Water erosion, a primary concern on sloped terrain, occurs when rainfall runoff gains speed and volume as it flows downhill. This moving water detaches valuable topsoil, reducing soil fertility and carrying sediment into waterways.
Water erosion manifests in different forms. Sheet erosion involves the uniform removal of a thin layer of topsoil across a wide area. When runoff concentrates, it can carve small channels known as rills. If these rills deepen and enlarge, they can develop into gullies.
How Terraces Manage Water Flow
Terracing works by physically altering the landscape to control the movement of water across sloped surfaces. The constructed terrace ridges act as physical barriers, intercepting rainfall runoff as it flows down the hillside. This interception prevents water from accumulating speed and volume over long distances.
By breaking the slope into shorter segments, terraces reduce the velocity of water flow. Slower moving water has less erosive power. The slowed water has more time to soak into the soil within the terrace channels, a process known as infiltration. Increased infiltration conserves water within the soil profile, making it available for plant growth, and reduces surface runoff. Some terrace designs are engineered with a gentle grade to safely divert excess water along the terrace to a stable outlet, preventing the formation of gullies.
How Terraces Preserve Soil Quality
Terraces preserve soil quality by managing water flow. As water slows within the terrace channels, suspended soil particles have an opportunity to settle out. This process, known as sediment trapping, prevents the loss of valuable topsoil. By keeping soil in place, terraces help maintain soil structure and prevent the loss of organic matter and essential nutrients. This contributes to long-term soil fertility.
The enhanced infiltration promoted by terraces boosts soil moisture content. Increased soil moisture is beneficial for plant growth, particularly during drier periods. By preventing soil and water runoff, terraces also minimize the loss of valuable nutrients and fertilizers applied to the land. This keeps these resources within the cultivated area.
Variations in Terrace Design and Function
Different types of terraces are designed to suit varying terrains and agricultural needs, each contributing to erosion control through specific structural features. Bench terraces, resembling a series of level steps, are built on steep slopes. These designs are suitable for intensive cultivation by completely breaking the original slope into flat platforms.
Broad-base terraces consist of wide, gently sloping ridges and channels. They are designed for cultivated land where farm machinery can operate over them, managing water by diverting it slowly along a gentle grade. These terraces are often used on gentler slopes and can be designed for moisture conservation or runoff removal.
Narrow-base terraces feature narrower, steeper ridges. These are used on pasture or woodland where heavy machinery is not a primary consideration. Conservation bench terraces combine a level bench with an upslope contributing runoff area. This design is specifically engineered not only for erosion control but also for water conservation by capturing and holding runoff water.