Porosity Practice problem 2
Porosity Practice problem 2 by Donald G. McGahan is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.
A large raised container has a total volume (to the top of the soil) of 3.64 m3. The soil is dry and your boss wants you to calculate how large of a water container is needed to bring the soil to a volumetric water content of 0.27. Calculate first in m3, then convert to liters (L), and finely convert to gallons.
Solution
Let VT equal the volume total (VA + VW + VS ): VT = 3.64 m3.
Let θv represent the volumetric water content
Let VW equal the volume of water: unknown to solve for
Since θv = (VW / VT)
VT x θv = (VW / VT) x VT [ multiply both sides by VT and then since VT / VT = 1]
VT x θv = VW
Plug in measured values.
3.64 m3 x 0.27 = 0.9828 m3
1 m3 = 10,000 cm3
3.64 m3 x (10,000 cm3 / 1 m3 = 36,400 cm3
1 cm3 = 1 ml
1,000 ml = 1 L
1 gallon = 3.78541 L
36,400 cm3 x (1 ml / 1 cm3) x (1 L / 1,0000 ml) = 36.4 L 36.4 L x (1 gallon / 3.78541 L) = 9.62 gallons
Note: Use the unit conversions you know. Remember significant digits and rounding rules. Keep up with populating units throughout the calculations. Don’t skip calculation steps not matter how simple. In a time crunch, when you are tired, and perhaps stressed being able to step through even the simplest conversion or calculation as a recheck is invaluable.