Groundwater flows through an unconfined sand aquifer of porosity $n = 0.25$ and hydraulic conductivity $K = 15.0\text{ m/day}$. Two piezometers spaced $500\text{ m}$ apart in the direction of flow register a water table head difference of $2.5\text{ m}$. The actual seepage velocity ($v_s$) of groundwater is ________ $\text{m/day}$ (round off to two decimal places).
Answer Key:
0.30
Step-by-Step Solution & Explanation
Hydraulic gradient $i = \frac{\Delta h}{L} = \frac{2.5}{500} = 0.00500$.
Darcy velocity (specific discharge):
$v = K i = 15.0 \times 0.00500 = 0.07500\text{ m/day}$
Seepage velocity accounts for void space porosity:
$v_s = \frac{v}{n} = \frac{0.07500}{0.25} = 0.300\text{ m/day}$
Rounding to two decimal places: $0.30\text{ m/day}$.