GATE Agricultural Engineering Irrigation and Drainage Engineering Syllabus

Irrigation and Drainage Engineering syllabus — full chapter and topic list

Expand any chapter to see its topics and sub-topics. This is the whole examinable outline for Irrigation and Drainage Engineering in GATE Agricultural Engineering, not a summary of it.

1. 1

   Soil-Water-Plant Relationship

   4 topics

   • Water requirement of crops
   • Consumptive use and evapotranspiration
   • Measurement of infiltration
   • Soil moisture and irrigation water infiltration
2. 2

   Irrigation Water Conveyance and Application Methods

   7 topics

   • Design of irrigation channels and underground pipelines
   • Irrigation scheduling
   • Surface irrigation methods
   • Sprinkler irrigation methods
   • Micro irrigation methods
   • Design and evaluation of irrigation methods
   • Irrigation efficiencies
3. 3

   Agricultural Drainage

   5 topics

   • Drainage coefficient
   • Planning, design and layout of surface and sub-surface drainage systems
   • Leaching requirement and salinity control
   • Irrigation and drainage water quality and reuse
   • Non-conventional drainage system
4. 4

   Groundwater Hydrology

   4 topics

   • Groundwater occurrence
   • Darcy’s Law, steady and unsteady flow in confined and unconfined aquifers
   • Groundwater exploration techniques
   • Overview of groundwater recharge estimation and artificial recharge techniques
5. 5

   Wells and Pumps

   6 topics

   • Types of wells
   • Steady flow through wells
   • Design and construction of water wells
   • Classification of pumps
   • Pump characteristics
   • Pump selection and installation

Irrigation and Drainage Engineering flashcards for GATE Agricultural Engineering

21 of 51 cards from the Irrigation and Drainage Engineering deck — real questions with worked answers.

1. Define consumptive use (CU) of water by a crop.

   Consumptive use (evapotranspiration) is the total water used by a crop in transpiration plus that evaporated from the adjacent soil and plant surfaces, in any specified period. It does not include water used for metabolic activity (which is negligible).

2. What is the difference between potential evapotranspiration (PET) and actual evapotranspiration (AET)?

   PET is the ET that would occur from a short green crop completely shading the ground with no shortage of water. AET is the ET that actually occurs under the existing soil-moisture supply; $AET \leq PET$, and $AET = PET$ only when soil moisture is non-limiting.

3. State the Blaney–Criddle equation for monthly consumptive use.

   $$u = k \cdot p \cdot \frac{(0.46\,T + 8.13)}{100}$$ (SI form) where $u$ = monthly CU (mm), $k$ = crop coefficient, $p$ = monthly percentage of annual daytime hours, $T$ = mean monthly temperature in $^{\circ}\mathrm{C}$.

4. In the FAO Penman–Monteith approach, how is crop evapotranspiration $ET_c$ obtained from reference $ET_0$?

   $$ET_c = K_c \cdot ET_0$$ where $K_c$ is the crop coefficient (varies with growth stage: initial, development, mid-season, late season) and $ET_0$ is the reference (grass) evapotranspiration.

5. What is the field water requirement of a crop and how does it relate to consumptive use?

   Field water requirement = consumptive use (CU) + application/conveyance losses + special needs (leaching, land preparation, frost protection) $-$ effective rainfall $-$ contribution from groundwater/soil moisture.

6. Define effective rainfall in the context of crop water requirement.

   Effective rainfall is that portion of total rainfall which is actually stored in the root zone and is available for crop consumptive use; it excludes deep percolation below the root zone, surface runoff, and evaporation losses.

7. Define infiltration and infiltration capacity (infiltration rate).

   Infiltration is the process of water entering the soil surface. Infiltration capacity ($f_p$) is the maximum rate at which a given soil can absorb water; the actual infiltration rate equals the supply rate when supply $< f_p$, and equals $f_p$ when supply $\geq f_p$.

8. State Horton's infiltration equation.

   $$f_t = f_c + (f_0 - f_c)\,e^{-k t}$$ where $f_t$ = infiltration rate at time $t$, $f_0$ = initial rate, $f_c$ = final (constant) rate, and $k$ = decay constant ($T^{-1}$).

9. State the Kostiakov infiltration equation.

   Cumulative infiltration: $F = a\,t^{b}$, and infiltration rate: $$f = \frac{dF}{dt} = a\,b\,t^{b-1}$$ where $a$ and $b$ are empirical constants ($0 < b < 1$) and $t$ is time.

10. State the Philip two-term infiltration equation.

    Cumulative infiltration: $F = S\,t^{1/2} + A\,t$, so the rate is $$f = \tfrac{1}{2}S\,t^{-1/2} + A$$ where $S$ is sorptivity and $A$ relates to gravity/saturated conductivity. As $t \to \infty$, $f \to A$.

11. Name two field instruments used to measure infiltration and the key difference.

    Double-ring (concentric ring) infiltrometer and the flooding/basin method. In the double-ring infiltrometer the outer ring acts as a buffer to force vertical (one-dimensional) infiltration in the inner ring, eliminating lateral spread error.

12. Define field capacity (FC) and permanent wilting point (PWP).

    Field capacity is the soil moisture content after gravitational water has drained (about $-\tfrac{1}{3}$ bar, i.e. $-33$ kPa). Permanent wilting point is the moisture content at which plants can no longer extract water and wilt permanently (about $-15$ bar, $-1500$ kPa).

13. Define available water capacity (AWC) of a soil.

    AWC is the water held between field capacity and permanent wilting point, available to plants: $$AWC = \theta_{FC} - \theta_{PWP}$$ usually expressed as depth of water per unit depth of soil (e.g. mm/m).

14. How is the depth of water stored in the root zone between FC and PWP computed?

    $$d = \frac{\gamma_d}{\gamma_w}\,(\,FC - PWP\,)\,D = (FC - PWP)\,D \quad (\text{mass basis})$$ where for volumetric content $d = (\theta_{FC} - \theta_{PWP})\,D$, $D$ = root-zone depth, $\gamma_d$ = dry bulk density, $\gamma_w$ = density of water.

15. Define readily available moisture (RAM) and management allowed depletion (MAD).

    RAM is the fraction of available water the crop can use without stress: $RAM = p \times AWC$, where $p$ (= MAD, management allowed depletion) is the allowable depletion fraction (typically $0.4$–$0.6$). Irrigation is scheduled when soil moisture drops to this level.

16. What is the relationship between volumetric water content $\theta$, gravimetric water content $w$, and dry bulk density?

    $$\theta = w \cdot \frac{\rho_b}{\rho_w}$$ where $w$ = mass of water / mass of dry soil, $\rho_b$ = dry bulk density, $\rho_w$ = density of water. $\theta$ is dimensionless (volume of water / volume of soil).

17. State the general formula for irrigation interval (frequency).

    $$\text{Irrigation interval } (\text{days}) = \frac{d_{net}}{ET_c} = \frac{(\theta_{FC} - \theta_{PWP})\,p\,D}{ET_c}$$ where $d_{net}$ = net depth of irrigation, $p$ = allowable depletion, $D$ = root depth, $ET_c$ = daily crop ET.

18. What are the three main approaches to irrigation scheduling?

    (1) Soil-based — irrigate when soil moisture/tension reaches a threshold; (2) Plant-based — based on plant indicators (leaf water potential, canopy temperature, stress); (3) Climate/water-balance based — using $ET_c$ and a soil-water budget (e.g. IW/CPE ratio approach).

19. Explain the IW/CPE ratio method of irrigation scheduling.

    Irrigation is applied when the cumulative pan evaporation (CPE) since the last irrigation reaches a value such that the ratio of a fixed irrigation water depth (IW) to CPE equals a chosen value (commonly $IW/CPE = 0.75$–$1.0$). A fixed depth IW is applied each time CPE reaches the threshold.

20. Define the Manning's equation used in the design of irrigation channels.

    $$V = \frac{1}{n}\,R^{2/3}\,S^{1/2}$$ where $V$ = mean velocity (m/s), $n$ = Manning's roughness, $R = A/P$ = hydraulic radius, $S$ = bed slope. Discharge $Q = AV$.

21. What is the condition for the most economical (best hydraulic) trapezoidal channel section?

    For a given area, the section is most efficient when the hydraulic radius is maximum, i.e. half the top width equals the sloping side ($\tfrac{b + 2my}{2} = y\sqrt{1+m^{2}}$) and the hydraulic radius $R = y/2$. The section is then tangent to a semicircle.

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