# Why the sediment delivery ratio decreases as contributing area increases

This is a paper that focuses on why the sediment delivery ratio decreases as contributing area increases. The paper also provides further questions that you are to follow in this assignment.

## Why the sediment delivery ratio decreases as contributing area increases

1) Firstly, define the sediment delivery ratio. Then, explain why the sediment delivery ratio generally decreases as contributing area increases.

2) Secondly, the slope of an alluvial fan is often very similar to the slope of the river that drains into it. Given that there is not a large change in slope, explain why deposition tends to occur on alluvial fans.

3) Thirdly, describe how an alluvial channel responds to a change in base level. Focus on how the longitudinal profile of the river will change with time following the base level change.

4) Fourthly, list three of the factors that control the rate of recession of waterfalls in bedrock channels. In a few sentences, explain how these factors control the rate of recession. Make sure to mention the processes that drive bedrock channel erosion (abrasion, plucking, and, rockfalls in channels with vertical cliffs).

5) Also, list 4 controls on suspended sediment flux and, for each control, state whether an increase in that quantity leads to an increase or a decrease in suspended sediment flux.

6) Using shear stress or Shields stress as a starting point, explain why alluvial channels tend to have concave longitudinal profiles (i.e., steeper near the headwaters with a decreasing slope with increasing distance downstream).

7) In a short paragraph, explain the rating curve approach to estimating the long-term suspended sediment load in a channel.

8) In a few sentences, describe how channel meanders develop in alluvial channels.

9) In a few sentences, describe the critical flow hypothesis. This hypothesis is used to relate bankfull water velocity to channel depth in alluvial rivers.

10) List four variables that can control alluvial fan area. State whether alluvial fan area tends to increase or decrease with an increase in each controlling variable.

### Why the sediment delivery ratio decreases as contributing area increases

11) In a few sentences, describe how climatic changes can lead to pulses of pulses of aggradation on alluvial fans.

12) In a sentence or two, explain why many deltas are sinking faster than global sea level is rising.

13) What variables control the size of deltas? Also, discuss how these two factors influence delta size.

14) In a few sentences, explain how marine terraces form along a tectonically uplifting coastline. Hint: your answer should involve tectonic uplift, wave-cut erosion, and sea level.

15) What is a “drowned coast” and what are the patterns in the topography that are used to identify drowned coasts?

16) In a few sentences, describe the law of the wall and also its significance for aeolian sediment transport.

17) List three factors that control dune type, and list how each of the major dune types relate to those factors.

18) In a few sentences, explain how glacial valleys tend to develop U-shaped cross-sectional profiles.

19) In a few sentences, explain why mid ocean ridges are ridges. List two factors that control the width of mid-ocean ridges.

20) Describe the shape of the hypsometry of Earth (the frequency distribution of elevations of Earth’s surface, including elevations above and below sea level). In a few sentences, explain the shape of the graph.

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