The Lugeon Test: Methodology, Interpretation, and Applications in Geotechnical Engineering

 Here’s a comprehensive set of viva questions with explanatory answers on Irrigation Engineering and Water Resources Engineering, written in exam-ready format:

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1. What is irrigation, and why is it necessary?

Irrigation is the artificial application of water to the soil to assist in crop growth. It is necessary in regions with inadequate rainfall, irregular rainfall distribution, or to increase crop yield, improve quality, and support multiple cropping. It also ensures food security in arid and semi-arid areas.

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2. What are the different types of irrigation systems?

Irrigation systems are broadly divided into surface irrigation, subsurface irrigation, sprinkler irrigation, and drip irrigation. Surface irrigation includes methods like furrow, basin, and border irrigation. Sprinklers distribute water in the form of spray, while drip irrigation delivers water directly to the root zone, conserving water.

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3. What is duty of water in irrigation?

Duty is the relationship between the volume of water supplied and the area irrigated with it. It is defined as the area irrigated per unit discharge of water flowing continuously during the crop period. Higher duty means efficient use of water.

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4. Define delta in irrigation.

Delta is the total depth of water required by a crop for its complete growth period. It represents the cumulative water depth applied to the field and depends on crop type, soil, and climatic conditions.

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5. What is crop period and base period?

Crop period is the time from sowing to harvesting of a crop. Base period is the actual duration in which irrigation water is supplied to the crop. Base period is usually shorter than the crop period.

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6. What is consumptive use of water?

Consumptive use is the total quantity of water used by a crop in evapotranspiration and metabolic activities during its growth. It excludes percolation losses and surface runoff.

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7. Explain canal headworks.

Canal headworks are structures constructed at the head of a canal, generally at a river diversion site. Their functions include diverting water from the river, regulating flow, excluding silt, and ensuring smooth entry of water into canals. Common components are weirs, barrages, regulators, and silt excluders.

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8. What is a weir, and how does it differ from a barrage?

A weir is a low-height structure built across a river to raise the water level and divert flow into canals. A barrage is similar but consists of gated structures that allow control of water levels and discharges. Barrages are more flexible and are preferred in modern irrigation systems.

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9. What is a distributary canal?

A distributary canal is a branch canal that carries water from the main canal to agricultural fields. It reduces waterlogging by delivering water in smaller channels closer to the fields. They may be major or minor distributaries depending on discharge.

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10. What is canal lining, and why is it important?

Canal lining is the process of providing an impervious layer (concrete, brick, or plastic) along the bed and sides of a canal. It prevents seepage losses, controls weed growth, reduces erosion, increases discharge capacity, and improves water efficiency.

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11. What are the main causes of waterlogging?

Waterlogging occurs when the water table rises close to the root zone. Causes include excessive irrigation, poor drainage, canal seepage, lack of natural slope, and heavy rainfall. Waterlogging reduces soil aeration and crop yield.

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12. How can waterlogging be controlled?

Waterlogging can be controlled through surface and subsurface drainage, lining of canals to prevent seepage, adopting efficient irrigation methods like drip irrigation, growing less water-intensive crops, and controlling excessive irrigation practices.

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13. What is the difference between gross command area (GCA) and culturable command area (CCA)?

Gross Command Area is the total area that can be irrigated from a canal system without considering land usability. Culturable Command Area is the part of GCA that is cultivable and can be actually irrigated. CCA excludes forests, urban areas, and barren lands.

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14. Define intensity of irrigation.

It is the ratio of area irrigated in a particular season to the total cultivable command area, expressed as a percentage. It reflects how intensively the available land is being used under irrigation.

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15. What are the types of spillways used in dams?

Spillways are structures provided in dams to safely release excess water. Types include ogee spillway (common in concrete dams), chute spillway, side channel spillway, shaft spillway (morning glory), and siphon spillway. Choice depends on topography and dam type.

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16. What is flood routing?

Flood routing is the process of predicting flood hydrograph changes as water passes through reservoirs or river reaches. It helps in flood forecasting and designing reservoir capacity to safely handle floods.

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17. Explain the concept of hydrologic cycle.

The hydrologic cycle is the continuous movement of water on earth through evaporation, condensation, precipitation, infiltration, runoff, and groundwater flow. It is the foundation of water resource engineering and determines availability of water for human use.

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18. What is the difference between confined and unconfined aquifers?

An unconfined aquifer has its water table exposed to the atmosphere, while a confined aquifer is bounded above and below by impermeable layers. Confined aquifers are under pressure, and water may rise above the top of the aquifer when tapped by a well.

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19. What are the different types of irrigation efficiencies?

Irrigation efficiency includes water conveyance efficiency (ratio of water delivered at the field to that released at headworks), water application efficiency (ratio of water stored in the root zone to that delivered at the field), water use efficiency (ratio of crop yield to water used), and overall irrigation efficiency (product of conveyance and application efficiency).

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20. What are the main objectives of water resources engineering?

Water resources engineering aims to plan, design, and manage water systems to meet demands for irrigation, domestic and industrial use, flood control, hydropower, navigation, and environmental conservation. It ensures equitable, efficient, and sustainable utilization of water resources.

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Formula Sheet – Irrigation & Water Resources Engineering

Topic	Formula	Description / Notes
Duty (D)	$D = \dfrac{A}{Q}$	Area irrigated (A) per cumec discharge (Q), usually expressed in hectares/cumec
Delta (Δ)	$\Delta = \dfrac{8.64 \times B}{D}$	Total depth of water required by crop, B = base period (days), D = duty (ha/cumec)
Relationship between Duty, Delta & Base Period	$\Delta = \dfrac{8.64 \times B}{D}$	Connects crop water requirement with irrigation supply
Crop Water Requirement	$W = \Delta \times A$	Water volume required for area A with delta Δ
Consumptive Use (Cu)	$Cu = ET_c = ET_0 \times K_c$	Evapotranspiration, where $ET_0$ = reference evapotranspiration, $K_c$ = crop coefficient
Irrigation Efficiency (Overall)	$\eta_o = \eta_c \times \eta_a$	Overall efficiency = conveyance efficiency × application efficiency
Conveyance Efficiency	$\eta_c = \dfrac{W_f}{W_h} \times 100$	$W_f$ = water delivered at field, $W_h$ = water released at headworks
Application Efficiency	$\eta_a = \dfrac{W_s}{W_f} \times 100$	$W_s$ = water stored in root zone, $W_f$ = water delivered at field
Water Use Efficiency	$\eta_u = \dfrac{Y}{W_u}$	Yield per unit water consumed, Y = crop yield, $W_u$ = water used
Irrigation Intensity	$I = \dfrac{A_i}{CCA} \times 100$	Ratio of irrigated area (Ai) in a season to culturable command area (CCA)
Gross Command Area (GCA)	$GCA = CCA + \text{non-cultivable area}$	Total irrigable area under a project
Capacity of Reservoir (Mass Curve Method)	Capacity = Max (cumulative demand – cumulative inflow)	Used in reservoir planning
Runoff (Rational Method)	$Q = C \cdot I \cdot A$	$C$ = runoff coefficient, $I$ = rainfall intensity, $A$ = catchment area
Hydraulic Radius (R)	$R = \dfrac{A}{P}$	A = area of flow, P = wetted perimeter (for canal design)
Manning’s Formula	$V = \dfrac{1}{n} R^{2/3} S^{1/2}$	Velocity in channels, n = roughness, S = bed slope
Discharge in Canal	$Q = A \cdot V$	A = area of flow, V = velocity from Manning’s formula
Kennedy’s Critical Velocity Formula	$V = 0.55 m D^{0.64}$	For unlined canals, m = silt factor, D = depth of flow
Lacey’s Velocity Formula	$V = \sqrt{ \dfrac{2}{5} f R }$	For regime channels, f = silt factor, R = hydraulic mean depth
Lacey’s Discharge Formula	$Q = \dfrac{2}{5} f A^{5/3} / P$	For canal design under regime conditions
Seepage Losses	$L = C \cdot P \cdot H$	$C$ = coefficient, $P$ = wetted perimeter, $H$ = head causing seepage

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This sheet covers irrigation water requirements, efficiencies, canal design, reservoir capacity, and runoff estimation – all the formulas you need at your fingertips.