5 - Transient

Question 1

What is storativity?

Answer 1

Applies to confined aquifers.
• Volume of water released per unit area over the entire aquifer thickness of the aquifer as a result of a unit fall in the potentiometric surface.
• The water arises from the small reduction in the aquifer porosity and fluid density which result from the drop in fluid pressure.
• Storativity is taken to be
S = HSs
where H [L] is the aquifer thickness and Ss [L-1] is the specific storage coefficient.

Question 2

What is specific yield?

Answer 2

Applies to unconfined aquifers.
• Volume of water released per unit area as a result of a unit fall in the water table elevation.
• The water arises from the dewatering of the pores as the watertable is lowered.

Question 3

Key assumptions for Thiem

Answer 3

Darcy’s law.
• Confined aquifer.
• Homogenous and isotropic aquifer.
• Uniform initial condition.
• No recharge.
• Infiniteaquifer.
• Infinitesimal well.
• Fully penetrating well.
• Constant pumping rate.
• If used for an unconfined aquifer, S = Sy. This is valid providing s « h.