Irrigation, Drainage & Pumping Systems

Comparison Between Cut-Throat and Parshall Flumes (Skogerboe et al., 1973):

• Statement (A) is True: The cut-throat flume was developed specifically by removing the parallel throat section of the Parshall flume, connecting the converging inlet section directly to the diverging exit section over a flat horizontal floor.
• Statement (B) is True: Under free-flow conditions, cut-throat flumes provide discharge measurement accuracy comparable to standard Parshall flumes (within $2 - 5\%$ error).
• Statement (C) is False: In cut-throat flumes, the geometry is standardized such that the angle of convergence ($3:1$) and angle of divergence ($6:1$) remain CONSTANT across all flume sizes; only the throat width and overall length vary.
• Statement (D) is True: Having a completely flat bottom without the depressed floor of a Parshall throat makes cut-throat flumes significantly simpler and cheaper to fabricate and install in irrigation channels.

Hydraulics of Sprinkler Jet Throw:

• Governing Parameters: The radius of throw ($R$) of a sprinkler jet depends exclusively on jet discharge mechanics:
• Operating pressure head ($H$), dictating exit velocity $v = C_v \sqrt{2gH}$.
• Nozzle orifice diameter ($d$) and streamlined geometry.
• Trajectory angle of inclination ($ heta$, typically $23^\circ - 27^\circ$).
• External Field Layout: The distance between lateral pipelines ($S_l$) is a layout design parameter chosen by the engineer to ensure overlap and uniform application, but it has no physical effect on the hydraulic throw distance of the nozzle itself.

Water Saving Mechanisms of Drip Irrigation:

• True Mechanisms:
• Partial wetting: Wets only the plant root zone ($20 - 60\%$ of soil surface), drastically cutting non-productive inter-row soil evaporation.
• Deep percolation minimization: Low discharge matched directly to crop consumptive rate eliminates gravity drainage beyond root depth.
• Zero runoff: Controlled application rate prevents surface ponding and runoff.
• Statement 4 is Incorrect: The physiological crop water requirement ($ET_c$) is determined by atmospheric evaporative demand and crop growth physiology; drip irrigation optimizes APPLICATION EFFICIENCY and reduces conveyance/evaporation losses, but does NOT reduce the crop's intrinsic biological transpiration demand.

Preponderance of Surface Irrigation in Indian Agriculture:

• Assertion (A) is Correct: Surface irrigation (furrow, border strip, basin, flooding) covers more than $85 - 90\%$ of irrigated area in India and continues to dominate Indian agriculture.
• Reason (R) is Correct: It requires no pressurized energy inputs, minimal capital equipment, utilizes gravity head, and conforms to indigenous traditional agronomic skills practiced across generations of small and marginal farmers with limited financial resources.
• Causal Link: The low capital requirement, lack of power demand, and generational familiarity directly explain why surface methods continue to dominate the Indian agricultural landscape.