Solution to Exercise 9

William W. Woessner; Eileen P. Poeter

Solution to Exercise 9

9) A confined aquifer underlies a 10 km² area. The average water level in a number of wells penetrating the confined system rose 2.5 m from April through June. An overlying unconfined aquifer showed an average water table rise of 2.5 m over the same period of time.
Assume the storativity for the confined system is 3.6 × 10^-5, and specific yield is 0.12 for the unconfined system. How much water (in m³) recharged each aquifer based on the responses of each potentiometric surface?

Assume the storativity, S, for the confined system is 3.6 × 10^-5, and specific yield, S_y, is 0.12 for the unconfined system. How much water (in m³) recharged each aquifer based on the responses of each potentiometric surface?

Unconfined aquifer
Applying Equation 48 in this book to compute the volume of water recharged:

Volume of Unconfined Water for a change in head = S_yA∆h

Unconfined Volume = $\displaystyle 0.12\ 10\ \textup{km}^2\frac{1,000,000\ \textup{m}^2}{1\ \textup{km}^2}\ 2.5\ \textup{m}=3\times{10}^6\ \textup{m}^3$

Confined aquifer
Applying Equation 50 in this book to compute the volume of water recharged:

Volume of Confined Water for a change in head = SAΔh

Confined Volume = $\displaystyle 3.6 \times {10}^{-5}\ 10\ \textup{km}^2\frac{1,000,000\ \textup{m}^2}{1\ \textup{km}^2}\ 2.5\ \textup{m}=900\ \textup{m}^3$

The unconfined aquifer received 3,333 times as much water as the confined aquifer.

Return to Exercise 9

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