Read the following statements about economization of irrigation water in rice
(A). Physical characteristics of infiltrating water have no effect on infiltration rate
(B). The depth of wetting increases the infiltration rate
(C). Viscosity of water increases infiltration rate hyperbolically
(D). Pore sizes increase infiltration rate parabolically
Choose the correct answer from the options given below:
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Remember the Hagen-Poiseuille Equation: flow rate is highly sensitive to pore radius (\(r^4\)). This is why puddling is performed in rice fields to destroy macro-pores, reducing infiltration and percolation to conserve water.
Step 1: Understanding the Concept:
Infiltration is the downward entry of water into the soil surface. Minimizing excessive infiltration and percolation is a key strategy to conserve water in flooded rice cultivation. Step 2: Detailed Explanation:
Let us analyze the validity of each statement:
Statement (A): Physical properties of water, such as temperature, viscosity, and solute content, directly affect the infiltration rate. Warmer water has lower viscosity, which increases the rate of infiltration. Thus, Statement (A) isfalse.
Statement (B): As the depth of wetting (the wet front) increases over time, the hydraulic gradient (the driving force) decreases, causing the infiltration rate to decrease, not increase. Thus, Statement (B) isfalse.
Statement (C): Viscosity represents resistance to flow. An increase in the viscosity of water reduces the flow rate through soil pores, decreasing the infiltration rate. Thus, Statement (C) isfalse.
Statement (D): Soil water flow through pores can be modeled using the Hagen-Poiseuille equation:
\[ Q = \frac{\pi \cdot r^4 \cdot \Delta P}{8 \cdot \eta \cdot L} \]
This indicates that the flow rate (\(Q\)) is proportional to the fourth power of the pore radius (\(r^4\)).
Therefore, even a small increase in pore size (such as cracks or macro-pores) dramatically increases the infiltration and percolation rates.
The statement that pore sizes increase infiltration rate is structurally and physically valid. Thus, Statement (D) istrue.
Since only Statement (D) is true, Option (B) is the correct choice. Step 2: Final Answer:
The correct option is (B), representing D only.
