(Rounded off to two decimal places)
Soil Water Depth Calculation Basics
The question asks for "water depth (in metres per metre depth of soil)", which is equivalent to the volumetric water content ($\theta_v$). This represents the volume of water present in a unit volume of soil.
Core Cylinder Dimensions and Properties
The given dimensions of the core cylinder are used to determine the total volume of the soil sample.
- Internal Diameter ($D$): $60\text{ mm}$
- Radius ($r$): $D/2 = 60\text{ mm} / 2 = 30\text{ mm} = 0.030\text{ m}$
- Length ($L$): $100\text{ mm} = 0.100\text{ m}$
- Weight of Moist Soil ($W_m$): $0.48\text{ kg}$
- Weight of Oven-Dried Soil ($W_d$): $0.44\text{ kg}$
- Density of Water ($\rho_w$): $1000\text{ kg.m}^{-3}$
Step-by-Step Soil Water Content Calculation
The calculation involves finding the volume of water and the total volume of the soil sample.
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Calculate the Weight of Water ($W_w$):
The weight of water is the difference between the weight of the moist soil and the weight of the dry soil.
$W_w = W_m - W_d$
$W_w = 0.48\text{ kg} - 0.44\text{ kg} = 0.04\text{ kg}$
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Calculate the Volume of Water ($V_w$):
Using the density of water, the volume of water can be determined.
$V_w = \frac{W_w}{\rho_w}$
$V_w = \frac{0.04\text{ kg}}{1000\text{ kg.m}^{-3}} = 0.00004\text{ m}^3$
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Calculate the Volume of the Soil Sample ($V_{soil}$):
The volume of the soil sample is the internal volume of the core cylinder.
$V_{soil} = \pi r^2 L$
$V_{soil} = \pi \times (0.030\text{ m})^2 \times (0.100\text{ m})$
$V_{soil} = \pi \times 0.0009\text{ m}^2 \times 0.100\text{ m}$
$V_{soil} = \pi \times 0.00009\text{ m}^3 \approx 0.000282743\text{ m}^3$
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Calculate the Volumetric Water Content ($\theta_v$):
This is the ratio of the volume of water to the total volume of the soil sample.
$\theta_v = \frac{V_w}{V_{soil}}$
$\theta_v = \frac{0.00004\text{ m}^3}{0.000282743\text{ m}^3} \approx 0.141421$
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Round the Result:
The value needs to be rounded to two decimal places.
$\theta_v \approx 0.14$
Result Verification
The calculated value of 0.14 is within the provided correct answer range of 0.12 to 0.16.
Important Questions from Soil Moisture Measurement
- In-situ volumetric soil moisture content measuring method(s) is/are:
- The elevations of pressure gauge and porous cup of the tensiometer installed in unsaturated zone are 145.8 m and 144.2 m, respectively. Pressure measured at the gauge is $-19.62\times10^3$ $N$ $m^{-2}$. The specific weight of water is 9810 $N$ $m^{-3}$. The estimated pressure at the porous cup is ________ $N$ $m^{-2}$.
- Tensiometer installed in the soil measures
Undisturbed soil sample is collected from a field when the soil moisture is at field capacity. The inside diameter of the core sampler is 7.5 cm with a height of 15 cm. Weight of the core sampling cylinder with moist soil is 2.81 kg and that with oven dry soil is 2.61 kg. The weight of the core sampling cylinder is 1.56 kg. Assuming $\pi = 3.14$, the water depth in centimeter per meter depth of soil (rounded off to two decimal places) is__________.
- Match the following items between Column-I and Column-II with the most appropriate combinations:
Column-I Column-II 1) Neutron Probe P) Open channel flow 2) Pressure Plate Apparatus Q) Deep percolation 3) Tipping Bucket R) Aquifer parameters 4) Current Meter S) Soil moisture 5) Pumping Test T) Rainfall intensity 6) Lysimeter U) Soil-moisture characteristic curve
