GEOL: SURFACE WATER HYDROLOGY

 

 

Material Properties of Soil Water in the Unsaturated Zone

 

1. Material Properties of Soils

We have collected a soil sample using a  20cm long cylindrical tube having a 5cm diameter. Wet weight of the soil sample was  760g. After oven-drying at 105ºC the sample weighed 620g. Assume the particle density ( ) was 2.65g/cm³.

 

Q1) What was the bulk density?

Q2) What was the porosity?

Q3) What was the water content?

Q4) What was the wetness (or degree of saturation)?

 

2. Pressure Head and Volumetric Moisture Content

 

The following table is pressure head and volumetric moisture content data obtained from a fine sand. Data like this are typically obtained from laboratory experiments.

 

Head	Water
meters	Fraction
-0.6	0.05
-0.55	0.06
-0.5	0.08
-0.47	0.1
-0.45	0.14
-0.43	0.2
-0.42	0.25
-0.4	0.32
-0.38	0.34
-0.35	0.35
-0.3	0.35
-0.25	0.35

 

Q5) Graph pressure head (meters of water; x-axis) versus volumetric moisture content (fraction; y-axis).

Q6) At what volumetric water content does the soil wetness (S) equal 1? How did you figure this out?

Q7) Is the volumetric water content of 0.05 less than, equal to, or greater than the permanent wilting point? How did you figure this out?

 

3. Volumetric Moisture Content and Hydraulic Conductivity

 

Q8) Graph volumetric moisture content (x-axis) versus hydraulic conductivity (y-axis), using this data from a fine sand. Use a linear-log plot, with hydraulic conductivity (y-axis) plotted on a log scale.

 

water      conductivity

fraction       m/s

0.05       0.00000005

0.10       0.000001

0.15       0.000006

0.20       0.00002

0.25       0.00007

0.30       0.00015

0.35       0.0002

0.40       0.0002

 

Q9) How does the hydraulic conductivity change with increasing water content?

Q10) What is the hydraulic conductivity at Ksat?

Q11) What is the hydraulic conductivity at a pressure head of -0.35 m? 

Q12) What is the hydraulic conductivity at a pressure head of -0.55 m?

 

4. Tensiometers are installed at 0.4 m and 0.5 m above the water table in a uniform sandy soil with the moisture characteristic and hydraulic conductivity curves from the two problems above. The tensiometer readings are -0.45 m at 0.4 m above the water table and -0.6 m at 0.5 m above the water table.

 

Q13) What is Darcy’s Law? Give the equation and an interpretation of each parameter. What is Darcy’s law used for?

Q14) What is the hydraulic gradient (estimated from the tensiometer measurements)?

  Q15) Is the water movement up (towards the surface) or down? Include your reasoning.

 Q16) What is the moisture content at the 0.4 tensiometer?

Q17) What is the moisture content at the 0.5 tensiometer?

Q18) What is the hydraulic conductivity at the 0.4 tensiometer?

Q19) What is the hydraulic conductivity at the 0.5 tensiometer?

Q20) Calculate the specific discharge at the 0.4 tensiometer.

Q21) Calculate the specific discharge at the 0.5 tensiometer.