River Processes

River Processes Overview

Focus on three main processes: Erosion, Transportation, and Deposition, crucial for river and stream ecology.

Learning Objectives

Understand and explain:

  • Erosion

  • Transportation

  • Deposition

Erosion Processes

Key Processes:

  1. Abrasion (Corrasion): Load acts like sandpaper, scraping rocks from riverbed and banks.

  2. Hydraulic Action: Water force removes particles, most effective in high-velocity areas.

  3. Solution (Corrosion): Effective on specific rocks like chalk and limestone.

  4. Attrition: Load chunks collide, eroding and rounding each other.

Types of Erosion:

  • Lateral Erosion: Sideways erosion in lower, gentler gradients.

  • Vertical Erosion: Downward erosion deepening channels in steep upper courses.

Notes on Erosion:

  • Faster flow increases the erosion rate, with different types contributing at various stages.

Transportation of Material

Mechanisms:

  1. Traction: Heavier rocks rolled along the bed, reduced size downstream.

  2. Saltation: Larger particles bounce along the bed.

  3. Suspension: Smaller particles kept afloat, increasing in concentration downstream.

  4. Solution: Dissolved minerals carried invisibly in water.

Influence of Flow:Faster rivers can carry larger loads due to increased energy.

Deposition

Occurs when river energy decreases, leading to sediment dropping.

Conditions for Deposition:

  • Volume Decrease: Dry seasons, high evaporation, permeable rocks, receding floodwaters.

  • Speed Decrease: Entering lakes, calm seas, gentle slopes.

Questions for Review

  1. Distinguish between Corrasion and Corrosion.

  2. Compare Attrition and Hydraulic Action regarding bed load effects.

  3. Anticipate deposition in slightly sloping terrain during dry seasons.