A Major Coastal Concern
A number of studies indicate that the sea has been rising 1-2 millimeters each year for the last century. This is not all due to global warming, though, because the land itself rises and subsides over time due to natural processes. But if atmospheric CO2 concentrations double, the Intergovernmental Panel on Climate Change (IPCC) estimates that planetary warming could cause global sea level to rise from 3-11 inches (8-29 centimeters) to 39 inches (1 meter) in the next 50 to 100 years. This action, which would result from water's tendency to expand when heated as well as from melting of glacial ice and polar ice caps, would send hundreds of meters of seawater encroaching over gently sloping coastal land. This would permanently flood hundreds of square miles of low-lying coastal areas along the Gulf. For those of us who live in the Lake Pontchartrain Basin, it means that barrier islands, tourist beaches, fishing centers, cultural and historical sites, business and industry, groundwater supplies, wildlife habitat, and residential areas would be severely impacted. Coastal wetland habitats might be lost or greatly reduced. We could probably prevent these negative effects from happening, but it would cost over $50 billion for bulkheads and levees to hold back the sea.
WHEN SEA LEVEL RISES OR FALLS?
A Topographic Model
The current concerns with global warming have made us wonder what will happen if there are changes in water levels of Lake Pontchartrain and the Gulf of Mexico. This activity is meant to increase our awareness of the effects of changing water levels on a coastal landscape.
- Construct a model of a contour map
- Use a contour map model to study changes in water levels and land elevations
- Understand the impact of sea-level rise on the Lake Pontchartrain Basin
Materials: per group
- Clear plastic shoebox
- Brown and green clay
- Acetate transparency sheet
- Metric ruler
- Transparency marker or grease pencil
- Use the clay to form a coastal landscape in the bottom of the shoebox. Don’t forget to leave room for water representing the Gulf of Mexico!
- Using the metric ruler, mark one-centimeter increments starting from the bottom to the top on the outside of the shoebox.
- With the marker or grease pencil, record the level of the coast/clay, according to the marks on the side.
How many centimeters does your clay coastline rise from the bottom of the
- Slowly pour water into the container and on to the clay coastline until it becomes level with the first centimeter mark from the bottom of the shoebox.
How much of the clay coastline is covered with water?
- Continue adding water to the next centimeter mark.
- Place the clear transparency sheet over the top of the shoebox. Have members of your group hold the sheet as flat as possible. Look straight down into the shoebox. With the marker or grease pencil, draw a line where the water meets the clay as you look straight down upon the coastline.
- Continue steps 5 and 6 until you have several lines on your transparency, marking each line with the corresponding centimeter mark on the side of the shoebox. The lines formed are called contour lines, and they are used on topographic maps to indicate elevation of land and water.
Once your map is completed, answer the following questions:
- How can contour maps be used to determine impact of sea-level rise on a
- If the water level decreased one centimeter in elevation on your model, how
much more land would be exposed? How can you determine this by using
your math skills? Explain your answer.
- What are problems associated with sea-level rise in the Lake Pontchartrain
Basin? What can we do about it?