Soil and Water Conservation Engineering- ICAR JRF/SRF 2024

• Specifications for Tubewell Gravel Packs:
• Desirable Physical Properties:
• Must be clean, washed, and free from silt, clay, and organic matter.
• Rounded to sub-rounded particles (well-rounded gravel ensures high, uniform pore volume).
• Hard, durable, and chemically insoluble siliceous gravel (quartzite with $\lt 5\%$ calcareous matter).
• Uniformity: Must be uniformly graded (uniformity coefficient $C_u = d_{60}/d_{10} \lt 2.0 - 2.5$) rather than well-graded, because well-graded mixtures allow smaller grains to pack between larger particles, drastically reducing gravel pack permeability.
• Conclusion: It should not be well graded (Option 4).

Correct option: (4) It should not be well graded

• Steady-State Condition in Open Channel Flow:
• Mathematical Definition:
• Flow is in a steady state when hydraulic parameters such as velocity ($v$), depth ($y$), and discharge ($Q$) at any given cross-section do not change with respect to time:

• In contrast, uniform flow requires that parameters do not vary with distance along the channel ($\frac{\partial v}{\partial x} = 0$).
• Conclusion: $dv/dt = 0$ (Option 1).

Correct option: (1) dvidt =0

• Dupuit-Thiem Assumptions for Steady Radial Well Flow:
• In Dupuit's classical formulation for steady flow toward a fully penetrating well in a confined aquifer:
• Steady flow: Water table and piezometric surface remain stable with time ($\frac{\partial h}{\partial t} = 0$). (Correct)
• Isotropic and homogeneous aquifer: Hydraulic conductivity is identical in all directions. (Correct)
• Fully penetrating well: The well extends across the full saturated vertical thickness of the aquifer. (Correct)
• (C) Areal extent: Dupuit assumes the aquifer has an infinite areal extent; therefore statement (C) (The aquifer is not of infinite areal extent) is incorrect.
• Conclusion: (A), (B), (D) only (Option 2).

Correct option: (2) (A), (B), (D) only.

• Channel Expansion in Subcritical Open Channel Flow:
• Specific Energy Dynamics:
• In subcritical flow ($Fr \lt 1$), specific energy is dominated by potential depth ($y$).
• As channel width expands ($B_2 \gt B_1$), discharge per unit width decreases ($q_2 = Q/B_2 \lt q_1$).
• Under frictionless ideal channel expansion, depth increases. However, in actual transitions where expansion creates significant eddy separation and head loss, the downstream surface profile undergoes backwater adjustments resulting in water surface drops.
• Conclusion: at a D/S section will drop (Option 1).

Correct option: (1) ata D/S section will drop