Series 23 - Soil Erosion III - Erosion by Water

Summary

This video from Cornell University explains the process of soil erosion, highlighting how rainfall can dislodge and transport soil particles, leading to various forms of erosion such as sheet, rill, and gully erosion. It explores the role of overland flow and runoff, and how poor land management accelerates these processes. The video introduces the Universal Soil Loss Equation (USLE), a tool for quantifying erosion, and discusses methods for managing it, including the use of cover crops, contour farming, and conservation tillage. Effective erosion control is crucial for maintaining soil health and preventing further environmental degradation.

Takeaways

• 🌧️ Raindrop Detachment: Raindrops act as a powerful force during erosion, hitting the soil and breaking it down into smaller particles, which are then transported by water.
• 🚰 Overland Flow: Overland flow occurs when water flows over the surface faster than it can infiltrate, increasing the potential for erosion and runoff.
• 🌱 Infiltration and Sealing: When raindrops break down soil aggregates, the smaller particles can clog pores, reducing infiltration and increasing surface runoff.
• 🌾 Vegetation Impact: Sealing the surface reduces not only water infiltration but also vegetation growth, as it hampers seedling emergence.
• 💧 Erosion Stages: The stages of erosion begin with sheet erosion (thin flow), progress to rill erosion (small streams), and culminate in gully erosion (deep, wide channels).
• 🔬 Soil Loss Equation: The Universal Soil Loss Equation (USLE) is used to estimate soil erosion based on factors like rainfall, soil type, slope, and land cover.
• ⛰️ Slope and Water Energy: Water’s erosive potential increases with steeper slopes and longer water flow paths, which means controlling slope can reduce erosion.
• 🌿 Vegetation Cover: Vegetation slows water flow and anchors the soil, reducing both the speed of runoff and its erosive energy.
• 🚜 Mechanical Solutions: Practices like contour farming and strip cropping alter the landscape and water flow, reducing the energy of moving water and preventing erosion.
• 🌾 Conservation Tillage: Leaving crop residues such as corn stubble in place helps reduce the speed of water flow and the resulting erosion, even if not as effectively as other methods.

Q & A

What is the primary cause of accelerated erosion?

Accelerated erosion is primarily caused by poor land management practices that disturb the natural processes of soil formation and protection, such as inadequate vegetation cover, improper tillage, and ineffective water management.

How does raindrop detachment contribute to erosion?

Raindrop detachment occurs when rain hits the soil surface with force, breaking up soil aggregates into smaller particles. These particles can then be transported by water, contributing to the erosion process.

What is Overland flow, and when does it occur?

Overland flow is the movement of water across the land surface when the rate of water delivery (e.g., rainfall) exceeds the rate at which the soil can absorb it. This causes water to flow across the surface, increasing the potential for erosion.

What is the relationship between surface sealing and erosion?

Surface sealing occurs when soil particles, broken down by raindrops, accumulate and clog the pores of the soil. This decreases infiltration, leading to more water flowing over the surface, which increases the risk of erosion and runoff.

How does soil sealing affect seedling growth?

Soil sealing not only reduces water infiltration but also prevents seeds from entering the soil and emerging as seedlings. This limits vegetation growth, which further exacerbates erosion, as there is less plant cover to protect the soil.

What are the three main types of erosion described in the script?

The three main types of erosion are sheet erosion (thin layers of soil removal), rill erosion (formation of small, concentrated channels), and gully erosion (large, deep channels that can cause significant landscape changes).

How does the Universal Soil Loss Equation (USLE) help in managing erosion?

The USLE helps estimate soil erosion by considering factors like rainfall intensity (R), soil erodibility (K), slope length (L), slope steepness (S), vegetation cover (C), and erosion control practices (P). It provides a way to quantify and predict erosion risk, allowing for better land management.

Why is vegetation cover important in preventing erosion?

Vegetation cover is critical because it anchors the soil, reducing its vulnerability to water erosion. Plants slow down water runoff, lowering its energy and erosive potential, while also improving soil structure through their root systems.

What are some effective land management practices to reduce erosion?

Effective practices include planting cover crops to protect the soil, contour tillage to change the slope of the land and reduce runoff speed, strip cropping to alternate crops and grasses, and conservation tillage to leave crop residues on the soil surface.

What role does water speed play in the erosion process?

The speed of water plays a crucial role in erosion. Faster-moving water carries more energy, increasing its ability to detach and transport soil particles. By slowing water down through vegetation or land modifications, its erosive power is reduced.