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- 2066 Jestha (old course) · 4 marks
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Confined versus unconfined aquifer
Short answer
In an unconfined aquifer, the water table forms the upper boundary, pressure is atmospheric, recharge occurs over the entire area, and it is prone to pollution. A confined aquifer is between impermeable layers, water is under pressure above atmospheric, recharge is limited to outcrops, and it has lower pollution risk.
Differentiate between confined and unconfined aquifer.
| Point | Unconfined (water-table) aquifer | Confined (artesian) aquifer |
|---|---|---|
| Boundary | Permeable above; open to the surface | Between two impermeable layers (aquicludes) |
| Upper surface | Water table, free surface | Piezometric surface above the aquifer top |
| Pressure | Atmospheric | Greater than atmospheric |
| Water in well | Stands at the water table | Rises above the top of the aquifer, may flow (artesian) |
| Recharge | Direct from rain over the whole area | From the outcrop area only |
| Pollution risk | High | Low |
| Level fluctuation | Large | Small |
| Storage | Specific yield | Storage coefficient (small) |
ground ~~~~~~~~~~~~~~~~
unconfined: water table . (sand)
--------------------------
clay (aquiclude)
confined: sand under pressure
clay (aquiclude)
✓ Answer checked by Claude Opus 5.5 (high effort)
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