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>> Welcome back.
Thanks for joining me for the second segment covering unconfined
and confined aquifers using a physical model.
For our first demonstration, we'll look at an unconfined aquifer composed of gravel and sand.
In the model, you can see the aquitard at the base of the unconfined aquifer
and open to the surface at the top.
We will use dye to show how water flows through the aquifer.
On the right side of the tank, we have higher elevations.
And to the left, we have a lake and a river.
As we start to inject the dye, where you think it will go?
Let's watch.
Did you figure it out?
The dye flows from high head to low head.
Head essentially means the height of the water surface.
There is more horizontal movement than vertical movement.
You can also see that the low permeability aquitard is restricting the dye
from flowing into deeper aquifers.
Eventually, groundwater flow paths discharge the dye into the river.
For that confined aquifer, you can see it is kept by an aquitard and an aquiclude,
a type of aquitard that allows no water to flow through.
Watch what happens when we inject the dye.
The dye follows a similar path of the unconfined aquifer.
There is little vertical movement yet lots of horizontal movement.
As the dye reaches the artesian wells, the dye flows up and discharges onto the land surface.
Again, this is because confined aquifers are under pressure.
In a fractured bedrock aquifer,
a type of confined aquifer commonly called a [inaudible] aquifer,
the surrounding rock has very low, if any permeability.
Thus, it is kept by an aquiclude, a layer of rock which will not transmit water.
As we inject the dye, where do you think it will go?
Think about the speed of the water too.
Will it slow faster or slower than the other aquifers?
Let's watch.
Look at that.
The dye flows only through the fractures, not through the rock matrix.
And it flows much more quickly than the other aquifers.
Again, once it reaches an artesian well, the dye discharges
onto the land surface and flows into the river.
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