(SEM VII) THEORY EXAMINATION 2022-23 IRRIGATION AND WATER RESOURCE ENGINEERING

SECTION A – Short Answers (2 Marks Each)

(a) Abstractions from precipitation

Abstractions from precipitation include evaporation, interception, infiltration, transpiration, and surface storage, which reduce runoff.

(b) Difference between precipitation and rain

Precipitation is the general term for all forms of water falling from atmosphere (rain, snow, hail, sleet), whereas rain refers only to liquid water droplets.

(c) Standard Project Flood (SPF)

SPF is the flood resulting from the most severe storm considered reasonably possible over a catchment.

(d) Base flow separation

Base flow separation is the process of separating groundwater contribution from total streamflow hydrograph.

(e) Limitations of Lacey’s theory

Lacey’s theory is empirical, applicable mainly to alluvial channels, ignores sediment size variation, and is unsuitable for non-regime conditions.

(f) Balancing depth

Balancing depth is the depth at which excavation of canal equals the filling required for embankments, minimizing earthwork.

(g) Deep open drains

Deep open drains are channels constructed below ground level to lower groundwater table and prevent waterlogging.

(h) Upstream approach

Upstream approach refers to the flow condition of water approaching a hydraulic structure from upstream side.

(i) Friction blocks

Friction blocks are devices provided in hydraulic structures to increase energy loss and reduce flow velocity.

(j) Water well

A water well is a structure constructed to extract groundwater from aquifers for irrigation or domestic use.

SECTION B – Long Answers (10 Marks Each)

(Attempt any three in exam; answers provided for all)

(a) Importance of hydrology

Hydrology helps in planning irrigation projects, flood control, water supply, hydro-power generation, and groundwater management. It enables estimation of runoff, floods, and droughts for sustainable water resource utilization.

(b) Single peaked hydrograph

A single peaked hydrograph consists of rising limb, peak discharge, and recession limb. Rising limb represents increasing runoff, peak shows maximum discharge, and recession limb shows gradual depletion of flow.

(c) Roughening devices and baffle walls

Roughening devices increase energy loss and reduce velocity. Baffle walls are vertical walls provided in stilling basins to dissipate kinetic energy and prevent scouring.

(d) Sections of groynes

Groynes consist of head, body, and tail. They project into river flow to control erosion, protect banks, and improve channel alignment.

(e) Selection of site for tube well

A suitable site should have adequate aquifer thickness, high permeability, good quality water, minimum interference from nearby wells, and accessibility for construction.

SECTION C – Long Answers (10 Marks Each)

3(a) Determination of φ-index and W-index

φ-index is the average rate of infiltration such that rainfall excess equals runoff.
W-index considers initial abstraction and represents effective infiltration rate during rainfall.
(Procedure: compute rainfall excess and equate to runoff depth.)

3(b) Flood discharge formulae for Indian catchments

Common formulae include Ryves formula, Dicken’s formula, Inglis formula, and Fuller’s formula, each based on regional rainfall characteristics.

4(a) Assumptions and uses of unit hydrograph theory

Assumptions include linearity, time invariance, uniform rainfall, and constant base flow.
Uses include flood prediction, reservoir design, and runoff estimation.

4(b) Discharge of water course (Numerical – Method)

Discharge is calculated using kor depth, kor period, intensity of irrigation, and commanded area.
Total discharge = sum of discharges for individual crops.

5(a) Design of irrigation canal (Numerical – Method)

Using given discharge, Lacey’s equations and assumed ratios, canal dimensions (bed width and depth) are calculated.

5(b) Canal breaches

Canal breaches are failures in canal banks caused by overtopping, piping, poor maintenance, excessive seepage, or structural weakness.

6(a) Groundwater flow to drains

Groundwater flows toward drains due to hydraulic gradient. Flow pattern depends on soil permeability, drain spacing, and water table level.

6(b) Sensitivity and flexibility of outlet

Sensitivity is change in outlet discharge due to change in water level.
Flexibility is ratio of change in outlet discharge to change in distributary discharge.
Relation: Sensitivity = Flexibility × Relative change in distributary discharge.

7(a) Yield of tube well (Numerical – Method)

Using Dupuit’s equation for artesian aquifer, yield is calculated based on permeability, drawdown, well radius, and radius of influence.

7(b) Shallow well vs deep well

Shallow wells tap unconfined aquifers, while deep wells tap confined aquifers.
Tube wells are deeper, more efficient, and suitable for high discharge compared to shallow wells.