The specific yield Sy of an unconfined aquifer is:
Choose the correct answer
Equal to the porosity n
The fraction of groundwater that drains by gravity from the aquifer when the water table drops by one unit (Sy = n - Sr, where Sr = specific retention)
The artesian pressure divided by depth
The transmissivity divided by thickness
Correct Answer
B. The fraction of groundwater that drains by gravity from the aquifer when the water table drops by one unit (Sy = n - Sr, where Sr = specific retention)
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Specific yield Sy = n - Sm (Sr = specific retention = moisture held against gravity). Sy typically 0.1-0.3 for sand. Specific retention: 0.02-0.05 for gravel, 0.06-0.12 for fine sand, 0.10-0.20 for silty soil. Sy represents storativity of unconfined aquifer. Storage coefficient S = Sy (unconfined) or << Sy (confined, typically 0.0001-0.001).
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