Lab Exercise 9 Coastal Processes GEOG 221 Name _____________________ Lab Section ________________ Lab Instructor ______________ Background: The purpose of this lab is for you to explore coastal processes. A streamtable is modified to represent a coastal zone. The streamtable is set to a very low slope, which is representative of conditions in many coastal zones, including in the south-central United States where the Mississippi River enters the Gulf of Mexico. Coastal Terrace Formation When the relationship between mean sea level and the land surface is relatively stable over long periods of time (i.e. no sea level changes, and no uplift or subsidence of the land), the energy dissipated by waves is concentrated at one elevation along the land-sea interface. This produces an erosional feature that was shown in class called a wave-cut terrace, or coastal terrace. Exercise 1: Terrace formation 1) Pay close attention to where sediment is being eroded and deposited from. Your TA will start generating medium size waves at a high sea level stage. Describe what happens as the waves encounter the coastline. Where is sediment eroded and deposited? 2) Next the wave size will decrease. How does the sediment in the system respond? Soon your T.A will increase the size of the waves. 3) What are two ways that the size of waves can naturally increase in nature? 1 4) Before the wave size increases, what hypothesis can you develop regarding how the coastline will evolve? 5) While the demonstration is occurring take note of how increased waves size alters the beach. Describe how the beach has changed with increased wave size. Did large waves erode or build the beach? 6) How will large storms such as hurricanes impact a beaches sediment supply? Soon your TA will lower the sea level stage and repeat the wave generation process. 7) Write a hypothesis describing what you think will happen. 8) Describe how the system responded. Where was sediment eroded and deposited? 2 Wave Refraction and Coastal Straightening Exercise 2: Wave Refraction and Coastal Straightening 1) Your TA will increase the irregularity of the coastline by developing two headlands. Make a quick sketch of the coastline. 2) Before wave generation resumes, what hypotheses can you develop regarding how the coastline might evolve over time? Remember to think in testable terms. Write your hypothesis. 3) How will you test this hypothesis? 4) While the wave demonstration is occurring, make notes on the processes you are observing. Where is deposition occurring? Where is erosion occurring? 3 Next you will dredge sand from the beach. Sand dredging is the removal of sand typically for supply of construction material or to provide additional sand for another section of beach. 5) Write a hypothesis describing what will happen to the beach near the mined area. 6) Your T.A will now dredge a portion of the beach and continue wave simulation. Describe how the beach has responded to the mined area. Where did deposition occur? Where did erosion occur? EXERCISE 3: Delta Formation Next your T.A will set up the streamtable in order for a delta to form. Before the simulation begins, what hypotheses can you develop regarding what will happen at the point where the river meets the ocean? What will happen to the velocity of the water as it meets the ocean? What will happen to the sediment? Remember to think in testable terms. 1) Hypothesis: 2) How will you test this hypothesis? 4 3) Your TA will now turn on the streamtable. Observe the delta formation demonstration that your TA has started in the streamtable. Describe what is happening to the water’s velocity and river sediment when it reaches the sea? 4) What shape of delta is being formed (Draw and describe)? 5) Is sediment added to the entire delta surface uniformly, or does the location of deposition shift through time? Describe how deposition varies throughout the delta through time. 6) Soon we will increase the sea level. Write a hypothesis on how a sea level rise may influence the formation of the delta. 7) Your T.A will now increase the sea level. Observe how the delta formation changes. How has the delta changed? 5 8) Soon we will decrease the sea level. Write a hypothesis on how a sea level decrease may influence the formation of the delta. 9) Your T.A will now decrease the sea level. Observe how the delta formation changes. How has the delta changed? Exercise 4: Nutrient runoff and the dead zone Excessive nutrient pollution is currently creating record setting “dead zones” (areas of very low oxygen concentration in water) in many areas of the world, including the Gulf of Mexico around its confluence with the Mississippi River. Simulate fertilizer application on a farm in the upland area (away from the stream) within the watershed. Now repeat the experiment but this time apply the fertilizer on a farm near a stream. 1. What happens to the fertilizer? Does it influence the water within the stream? 2. What differences did the location of the farm make? 6 3. What happens to the fertilizer once it reaches the coast? 4. Do you think that on days when fertilizer runoff does not occur (for example during dry seasons) the coastal water is still impacted? Why or why not? 5. What can be done to reduce the area of the dead zone? 7
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