SALT WATER INTRUSION EXERCISE

NAME: ________________________

Now that you have been introduced to groundwater processes, this exercise will allow you to see the effects of saltwater 
intrusion in coastal areas. We will use a simulation again, so when you are ready to start the simulation press 

What you are looking at is a simulated cross-section through a coastal area. The blue represents groundwater, the  
green - seawater.

The bars at the bottom of the cross-section control aspects of the simulation. 
	Precipitation refers to the rate of recharge from above. 
	Permeability sets the condition of the aquifer. 
	Pump Rate controls how fast water is pumped from the well.

Note that the green sea water is intruding the portion of the aquifer near the coast. The boundary between the two water 
masses is not vertical - it dips to the left. This is because fresh water, being less dense, "floats" on top of seawater. The 
boundary is about 40 cm below sealevel for every cm of fresh water above sealevel. Of course the real boundary is 
somewhat mixed, but we will illustrate it as a sharp division. 

You may notice that the level of fresh water in the aquifer is declining. This is because there is no precipitation right now. 
Where is the water in the aquifer going?

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Begin pumping water from the well. What happens?


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Sea water is undrinkable, so shut off the water when the well starts pumping green. You have just experienced a problem 
common in many coastal areas - saltwater intrusion. As well as being unpotable (undrinkable), saltwater corrodes pipes 
and fixtures. You can probably still see the boundary below the well. Try to pump at a very slow rate to avoid pumping 
saltwater. Not easy is it? 

Now turn off the pumping and add a little precipitation. What happens to the fresh/salt water boundary?


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Try pumping at a slow rate that avoids the salt water. Summarize the relationship between precipitation and useable 
pumping rate.


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What you are experiencing is the same thing Miami often experiences during dry summers. Reduced recharge, either 
from rainfall or water flowing into the aquifer from Lake Ockochobee and the Everglades, allows the boundary to move up 
and inland. Then coastal wells start to pump seawater and must be shut down. In severe cases, water rationing soon 
follows.

Shut off the pumping and increase precipitation to half-way. What happens to the boundary?


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This is analogous to what happens along many parts of the Florida Gulf coast. Here recharge and flow rates are high, 
and the boundary is sometimes "pushed" offshore. At Spring Creek, Florida, fresh water escaping from the submerged 
aquifer forms a "boil" on the ocean surface, a short distance from shore. 

Although the simulation doesn't support this option, what do you think the effect of sea level rise would be on the 
fresh/salt water boundary?



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This is one aspect of Global Change that has many coastal communities worried.

SUBMIT TO STUDENT DROPBOX