Groundwater-flow model

Plans

This 24" x 9" x 1/2" Plexiglas groundwater-flow model can be built for $25 or less.

To learn more about the model, scroll through the present page.

To download plans and instructions for the model (gw_model.pdf), click the button below.

Experiments

To view photos of experiments, click any of the following buttons.

Other experiments will be added soon.

The groundwater flow model consists of the following components and parts:

2	24" x 9" x 1/4" Plexiglas sides
1	40" x 5/8" OD vinyl tube with 12 small holes and 2 larger holes
1	water supply tube (1/4" ID vinyl tube, 1/4" OD plastic tube, 2 1/4" T's)
1	water discharge tube (1/4" ID vinyl tube, 1/4" OD plastic tube, 1 1/4" T)
2	filter strips made of loose-weave fabric
14	#10 - 24 x 1 1/2" round-head machine screws
14	#10 - 24 wing nuts
14	1/2" nylon spacers for #10 screws (0.194" ID)
28	#10 flat washers
	extra vinyl tubing for various well configurations
	small basting bulb for water extraction and injection

STEP 1

Assemble the two Plexiglas sides of the model, as shown in the exploded view, using the fastening hardware provided. This will require the following:

13	#10 - 24 x 1 1/2 inch screws
26	#10 flat washers
13	1/2 inch nylon spacers
13	#10 - 24 wing nuts

Only start the wing nuts onto the screws. Do not tighten them at this point.

STEP 2

Slide the 5/8-inch (OD) vinyl tube into the top of the model, as shown. Be sure that the 12 small holes (6 at each end) face the center cavity of the model. Also, be sure that the 2 larger holes face the outside of the model and lie below the 3rd screw on each end.

STEP 3a

Install the 14th fastening screw, with nylon spacer, 2 flat washers, and a wing nut, in the center hole near the top edge of the model.

STEP 3b

Insert the water supply tube and the head adjustment tube into the larger holes in the 5/8-inch vinyl tube.

STEP 4a

Tighten all wing nuts, such that the 5/8-inch vinyl tube is compressed between the Plexiglas sides of the model and forms a water-tight seal.

STEP 4b

Fasten the water supply tube and the water discharge tube to the end of the model, as shown, using the 2 plastic ties. Be sure that these tubes will slide through the ties, such that the height of the head-controlling "T" is adjustable.

STEP 5 (not illustrated)

Carefully place fabric filter strips against the 5/8-inch vinyl tube such that they cover the 12 small holes and hold strips in place while filling the model with sand.

STEADY-STATE GROUNDWATER FLOW

The groundwater-flow model can be used to demonstrate steady-state groundwater flow, driven by a constant hydraulic gradient. In this case, a constant flow of water is supplied through the water-supply tube. This is most simply achieved by connecting the water-supply tube to a faucet and only slightly opening the faucet valve. Once the model has filled with water, water will begin to discharge through the water-discharge tube. The desired hydraulic gradient (Dh/Dl) can be achieved by careful adjustment of the faucet valve and the height of head-controlling T's in the water-supply tube and the water-discharge tube. The flow of supplied water should slightly exceed that required by the model such that there is a constant flow (drip) of excess water through the upper T in the water-supply tube. This is illustrated below.

To demonstrate the down-gradient flow of groundwater, inject dye-colored water to a position below the water table through an injection well (illustrated). The resulting plume will travel toward the discharge end of the model.

To demonstrate the problem of contamination in flowing groundwater, extract water from a well positioned downstream from the injection well. Ultimately, water from the colored plume will be extracted.

To demonstrate how a water table is determined, install 3 or 4 evenly spaced observation (piezometer) wells. Water will rise in each well to precisely the height of the water table at that position in the model.

PUMPING WATER FROM A WATER-TABLE AQUIFER, CONES OF DEPRESSION, AND RELATED GROUNDWATER FLOW

Alternatively, the groundwater-flow model can be used to demonstrate the effect on the water table of pumping water from a well. In this case, the model is set up with a horizontal water table, such that initially there is no hydraulic gradient. To accomplish this, simply fill the model with water, pinch off the water-supply tube, and adjust the head-controlling T's in the water-supply tube and the water-discharge tube to the desired level of the water table. This is illustrated below.

To demonstrate drawdown and the development of a cone of depression extract water from a centrally located pumping well. Observe the water levels in strategically placed observation wells. Water levels will be drawn down in observation wells, most significantly in observation wells closest to the pumping well. A "cone of depression" is defined by the drawn-down water levels.

To demonstrate that pumping water from a well induces groundwater flow toward the pumping well, inject dye-colored water into a well near the pumping well. The colored water will stream toward the pumping well and will be drawn into the bottom of the well if water is being extracted from it.