Irrigation and Drainage Engineering- ICAR JRF/SRF 2024

• Wind Velocity Profile with Height:
• Power-Law Velocity Profile:

where $\alpha$ is the Hellmann exponent (typically $\approx \frac{1}{7} \approx 0.143$ for neutral atmospheric stability over agricultural surfaces).

• Calculation:
• Velocity at $z_1 = 2\text{ m}$ is $v_1 = 5.0\text{ km/h}$.
• At height $z_2 = 9\text{ m}$:

• Conclusion: Wind velocity is approximately 6.2 kmph (Option 1).

Correct option: (1) 6.2 kmph

• Water Advance Rule in Check Basin Irrigation:
• The One-Fourth Advance Rule:
• In check basin irrigation design, water advance across the entire basin floor should be completed within one-fourth ($t_a \le \frac{1}{4} t_n$) of the time required for the net irrigation depth to infiltrate into the soil.
• Hydrologic Rationale:
• Restricting advance time to $\le \frac{1}{4}$ of net infiltration time ensures that the contact opportunity time is nearly equal between the inflow edge and the far end of the basin, achieving a distribution uniformity ($DU$) exceeding $85 - 90\%$ and preventing excessive deep percolation losses near the inlet.
• Conclusion: One-fourth of the time required to infiltrate the net depth of irrigation water (Option 1).

Correct option: (1) One-fourth of the time required to infiltrate the net depth of irrigation water

• Streamflow Measurement via Constant-Rate Tracer Dilution:
• Mass Balance Principle:

Since stream background concentration $C_0 = 0$ and tracer injection rate $q \ll Q$:

• Calculation:
• Tracer concentration $C_1 = 20\text{ g/L} = 20 \times 10^6\ \mu\text{g/L} = 20 \times 10^6\text{ ppb}$.
• Injection rate $q = 5\text{ cm}^3\text{/s} = 5 \times 10^{-3}\text{ L/s}$.
• Downstream equilibrium concentration $C_2 = 4\text{ ppb}$.

• Conclusion: Stream discharge is 25 m$^3$/s (Option 2).

Correct option: (2) 25 mls