Part II: Unconfined and Confined Aquifers

Part II: Unconfined and Confined Aquifers


[ Music ]>>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. [ Music ]

13 thoughts on “Part II: Unconfined and Confined Aquifers

  1. Really nice model. Did you guys build it? Im working on something similar and me and my university colleagues are wondering if we can buy those piezometric plastic tubes (wells). Can you tell me which are dimensions of the aqcuifer?

  2. really awesome model but please explain what a hydraulic head is and why there are different levels in the wells. Why is the confined aquifer under pressure and how are the 2 springs working?

  3. A 2-dimensional enclosure is not a cross-section view of what really takes place in nature. The glass side makes it a completely different situation, and a two-square-foot 2-d model is nothing like what happens in, let's say, an area of 500 x 500m, going 100m deep; the ratios are just incomparable !!!

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