The work of rivers
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The document discusses the three main functions of rivers: erosion, transportation, and deposition. It describes the four primary ways that rivers erode the landscape: abrasion, attrition, hydraulic action, and solution. It also outlines the four methods that rivers transport sediment: traction, saltation, suspension, and solution. Finally, it explains that rivers deposit their sediment loads when their volume or speed decreases, such as when entering a lake or plain with a gentler slope.
The work of rivers
- 1. The Work of Rivers The erosional work of streams/rivers carves and shapes the landscape through which they flow. 3 functions of rivers c. Erosion d. Transportation e. Deposition
- 2. The Work of Rivers A. Erosion •A river may erode in 4 ways 3.Abrasion/corrasion Load carried by a river will grind against its bed and sides. This process slowly wears the bed and sides away.
- 3. The Work of Rivers A. Erosion 2. Attrition When thrown against the sides and bed of rivers, the load gets broken into smaller pieces.
- 4. The Work of Rivers A. Erosion 3. Hydraulic action The work of turbulence in the water. Running water causes friction in the joints of rocks in a stream channel Joints may be enlarged Loosened fragments of rocks get swept away.
- 5. The Work of Rivers A. Erosion 4. Solution/Corrosion Certain minerals in rocks like limestone can be dissolved in water. Rocks are then eroded.
- 6. The Work of Rivers Relationship of velocity and sediment size to erosion
- 7. The Work of Rivers B. Transportation (4 ways)
- 8. The Work of Rivers B. Transportation (4 ways) •Traction Larger and heavier rocks/gravels are dragged or rolled along the bed.
- 9. The Work of Rivers B. Transportation (4 ways) 2. Saltation (saltim: by leaps/jumps) Smaller and lighter rock fragments and sand hop and bounce along the river bed. At times, the distinction between traction and saltation may be difficult to determine.
- 10. The Work of Rivers B. Transportation (4 ways) 3. Suspension Some of the load like silt and clay (fine- grained) will float along. They may only be deposited when stream velocity reaches near 0. Turbulence in the water is crucial in holding a load of sediments.
- 11. The Work of Rivers B. Transportation (4 ways) 4. Solution Some minerals are transported in dissolved form. Especially chemical solution derived from minerals like limestone or dolomite.
- 12. The Work of Rivers C. Deposition A river will drop its load when: c. Volume decreases d. Speed decreases
- 13. The Work of Rivers C. Deposition A river’s volume decreases when • Dry season • Dry region with high evaporation • Presence of permeable rocks • Receding flood waters
- 14. The Work of Rivers C. Deposition A river’s speed decreases when • It enters a lake • It enters a calm sea • It enters a gently sloping plain
- 15. The Work of Rivers The work of a river depends on its energy Energy a function of c. Volume of water d. Speed of water flow (dependent on gradient)
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