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To Show the Interface Between Salt and Freshwater

Use the preparation shown at the right before proceeding.

When the model is completely saturated with freshwater, stop draining the water from the lake.  Siphon blue water out of the right recharge channel with the piece of tubing and a syringe.  Place the freshwater bottle on the left, the saltwater bottle on the right.  Place two extra syringe tips inside of each other, in the artesian well outlet.  Make sure the top of the tips are above the water table to stop flow from the artesian well.  Insert a third tip on the end of the piece of tubing, and create a siphon from the shallow pumping well with the tubing and syringe.

Contamination of saltwater should be seen in the lake in 5 minutes.

The interface (the point at which salt and freshwater meet) should be evident in another 5 minutes, depending on the rate of flow in each model.

Saltwater is more dense than freshwater, thus pushing under the freshwater.  A wedge will form where saltwater and freshwater meet.  Saltwater contaminates the piezometers.  The water that is being pumped out of the shallow well will be purplish, from the mixing of the waters, forming brackish water.  If this water appears clear, you may wish to add more food coloring in future uses for a darker effect.

To Show Three

Distinct Layers

This exercise show the difference in densities between salt and freshwater.

Use the preparation shown at the right before proceeding.

When the model is completely saturated with blue water, siphon water out of the left recharge channel.  Place the saltwater bottle into the left channel, with freshwater in the right.  Pump from the shallow pumping well again, but do not plug the artesian well.

A saltwater interface will be seen coming from the left side of the model in a wedge shape.  The saltwater also contaminates the lake via the artesian well.  The lake water from the three layers according to their densities - saltwater on the bottom, a layer of brackish water, and freshwater on the top.

The constant pumping through the shallow well pulls the salt water from the lake back into the system, showing the cone of depression. (the vertical movement of saltwater at a discharging well), resulting in saltwater contamination before the interface wedge reaches the pumping well.

Supplies

Needed:

Preparation:

 (20 minutes)

Fill both jars with water.  Add 15-20 drops of blue food coloring to one to distinguish freshwater.  Flow through model to completely saturate model with blue water.  Drain the water from the lake into a container.  This water can be reused through the model to save on dye and water.  Pull water from wells with syringes to ensure all water in model is blue for best visual effect.  This may take up to two bottles of "freshwater", depending on how dry the model is.  The more water that is initially in the model, the longer it will take to displace it with blue water.  

Add 50 mL of salt to the second jar with 15-20 drops of red or yellow food coloring.  Red is a little more visible against the sand.  Stir with stick until all salt is dissolved.  Do not exceed 75 mL of salt - the water won't flow through the model.

Clean Up:

(20 minutes)

Flush the model from both ends with 3-4 bottles of clear, distilled water, until all dye is out of the model, while draining from the lake.  Using the syringes to draw dyed water out can speed up this process.  Be sure to flush out the model completely.  Salts may form deposits, slowing down the flow rate of the model.  A vinegar rinse may help to dissolve such deposits.

Total Time:

 Approximately 1 hour