Deposition of Sediments Lab #5

Background Information: Rivers, ocean currents and wave action work constantly in a cycle of erosion and deposition that produces a variety of landforms. As streams work their way to the ocean they are constantly carrying sediment. When a stream enters a large body of water, the speed of the water decreases and sediment is dropped to the bottom. Larger, rounder, and denser particles are dropped first which end up closer to the mouth of the stream. Smaller, flatter, and less dense particles are carried further out into the body of water. Deposition occurs anywhere water current is slowed. Water moves slower along the inside curves of meanders depositing sediment. Man-made dams also slow the velocity of stream flow and sediment is deposited, which eventually fills up the reservoir behind the dam.

Problem: How does the size of sediment affect the rate of which sediment settles in still water?

Hypothesis: Write a hypothesis based on stream velocity and the rate of sediment deposition.

Materials:

Clay

Pebbles

Sand

Flat stone

Round stone

Stopwatch

Procedure:

  1. Obtain a small amount of clay, pebbles and sand.
  2. Drop a small amount of clay sediments in a beaker of 100 ml of water.
  3. Time how long it takes for the sediments to reach the bottom.
  4. Repeat steps 2-3 two more times
  5. Calculate the average time using all three trials.
  6. Repeat for the other two sediment types and the flat and round stones.

Data Table:

Title:

Sediment / 1st Trial / 2nd Trial / 3rd Trial / Average Time
Clay
Sand
Pebbles
Flat stone
Round stone

Graph: bar with the average time of each sediment type

Analysis and Conclusion Questions: Don’t forget full sentences.

  1. Which particles settled the fastest? Which settled the slowest? Why?
  2. Where in the environment would large quantities of sediment settle in water?
  3. Which particle would settle faster: A round pebble or a flat pebble? Why does one settle faster than another?
  4. Which size sediment would be found closer to the mouth of a river? Why?
  5. What would happen if you dumped a cup of mixed sediment into the water tube? Why?
  6. Why would a lead ball of the same size and shape as an aluminum ball fall faster to the bottom of your tube?
  7. What are the three factors that affect the rate at which sediments settle in water?

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