An extraction well on a large river
island has been considered for a temporary lowering of the
piezometric surface for construction purposes.
The island's sandy aquifer, which is naturally confined, will have to
undergo a change to unconfined conditions at the construction site because of
the requirement that the piezometric surface must be kept at 1.5 meters below
the aquifer top during the construction.
A. Use an analytical approach to determine the pumping rate at the well
that will satisfy this requirement for safe constriction. The well diameter is 500 mm. The hydraulic conductivity of the aquifer is
3.73xl0-5 m/s. Other elements needed for
the calculation are shown in the provided figures.
B. Solve the problem numerically using MAGNET. Compare your results with the analytical result.
MAGNET/Modeling Hints:
- Use 'Synthetic mode' in MAGNET to create a model domain with the same approximate dimensions as described above.
- Overlay the provided SiteMap image file included in the problem description (use the .jpg file). Choose 'Use Domain Extent' to fir the image to the established domain size.
- Use a relatively large grid size (e.g., NX=100)
- Represent the river as a prescribed head zone feature
- Conceptualize the model as a 1-layer aquifer system, using the aquifer elevations given in the figure.