Chapter 16: The Fluvial Processes 3. What factor determines the erosive effectiv

Question

Chapter 16: The Fluvial Processes

3. What factor determines the erosive effectiveness of streamflow?

4. Please describe some of the abrasive tools used by a stream in its erosive activities.

5. Please list & describe the components of a stream’s load.

6. How does a stream sort alluvial material?

7. Is it ever possible for a stream to erode below sea level? Please explain your answer.

8. What is stream capacity?

9. What is stream competence?

10. Why don’t all rivers form deltas?

11. Explain how a stream valley is lengthened.

Explanation / Answer

3) there are different types of factors that controls the erosion, and which varies with the environment in which the stream flows they are, the volume of the flow- as the volume increases the erosion increases.

gradient of the bed through which it flows- if the gradient is higher, erosion will be much larger. speed of the flow- erosion is also proportional to the speed of the stream flow, turbulance of the stream flow- if it flow more violently it will erode more sediments.

4)abrasive tool of the streams are the suspended debrises, they causes the abrasions. large sized debrises will hit the side walls and causes breaking of harder regions and suspended sediments will cause abrasion as the flow above these layers.

5)there are three types of stream loads,

* Dissolved load: these are dissolved chemical ions in the water solution, this occurs due to the chemical erosion of minerals and resulted ions mixed up with the stream flow, and this dissolved load materials are the smallest of the three loads.

*suspended load: these are the fine sediment particles suspended in the stream flow, this particles cannot dissolve in the water and also they will not deposit on the bed, and apperas as suspended in the water flow which include mainly clay and silt eroded by the water flow.

*Bed load: these load are much heavier so htey will roll along the floor of the stream flow,which includes sand gravel, cobbles and boulders.

6) sorting of the alluvial materials are based on their weight, more weighted materials will deposit close to the face of the flow, but less weight particles will travel more distance further as the speed of the flow decreases they will start to deposit, finally finest particles will deposit.

7)yes. when the water flows through the slope regios, even when it below the sea level it can cause erosion. it can erode the bottem of the river channel .

8) stream capacity is defined as the measure of the amount of sediment materials a stream can carry.as the velocity increases its ability to carry sediments also increases.

9)stream competence is the heaviest particle a stream can carry and it depends on the velocity of the flow. competence increases as the velocity increases.

10) the stream capacity of rivers varies, so when the river carry more sediments and reaches to the sea or a lake its speed decreases suddenly and the sediments deposit at the mouth of the river, when it is a huge deposit so that tides and waves cannot remove quickly they will form deltas. if the sediment content of a river is much less, they will not form deltas.

11)lengthening of the stream vally occurs through the erosion, as they start to flow across the steep slopes, they causes the large scale erosions, and the lengthening of the meanders also increases the lengthening process of stream.

uplift of land areas or lowering of the sea levels occurs rarely can trigger the same process, and which will causes the lengthening.

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