This article on Irrigation has been written by Rohit Sachdeva. He graduated from Delhi College of Engineering (now DTU) in 2012 (a gold medalist in his batch) in Civil Engineering branch. Then he appeared in Civil Engineering (CE) paper in GATE 2017 and secured an All India Rank (AIR) of 93.
In this blog, I will be discussing on how to prepare for Irrigation Engineering. This subject contains very few & small chapters and most of the questions asked can be easily answered if you focus on these chapters.
A rough breakup of questions of various chapters in last 30 years in GATE is as follows:
|Sl No||Topic||No. of Questions|
|1 mark||2 marks||5 marks|
|1||Water Requirement of Crops||7||15||2|
|2||Gravity Dams and Spillways||3||1||1|
|4||Design of Unlined & Lined Canals||4||–||4|
|5||Cross Drainage Works & Canal Regulation Works||–||1||–|
If we check the last 5 years GATE papers, we can see that Hydrology and Irrigation Engineering together carry 6-9 marks.
Time Required for Preparation (for Irrigation)
7 days (if you have 8-10 months of preparation) with 4 hours daily
3-4 days (if you have 4-5 months of preparation) with 7-8 hours daily
In this blog, I will be dealing with Irrigation and hydraulic structures (Hydrology is discussed in a separate blog). It is advisable to prepare separate notes for formulae and for working out numerical questions. The topic wise preparation strategy is given below, with the most important concepts in bold & italics. Approximate time required for each chapter is mentioned along with it. This can be varied according to individual interests. The textbook(s) to be referred are mentioned in a separate comprehensive blog which you should refer.
- WATER REQUIREMENT OF CROPS (2 DAYS)
This is the most important topic from which a numerical question (even NAT type) is frequently asked in many forms.
- Quality of Irrigation water, concentration of soluble salts, consumptive use of water, SAR;
- Basic definitions of soil moisture, Field capacity, wilting point, equivalent depth and readily available moisture depth, the frequency of irrigation, Duty-Delta & Base Period, Kor depth & period, time factor, crop period, Palao irrigation are some terms you should definitely study.
- The next very important concept that you should understand completely is Irrigation efficiencies. There are different types of efficiencies; some you can visualize easily (like conveyance, application), while some are just direct formula based (distribution), so note all of them down in formula sheet. Also remember what are Rabi and Kharif seasons, different cultivated areas, Net & Gross Irrigation requirements. Practice 10-12 numericals.
- Methods of Irrigation is also included in this chapter; only basic definitions about different methods are needed.
- GRAVITY DAMS AND SPILLWAYS (1 DAY)
Design of dam is itself a very big topic. But concepts important for GATE are how forces act on a gravity dam, modes of failures (crushing, overturning, tension and sliding) & their factors of safety, principle stresses. Practice 2-3 numerical questions in full length related to these topics.
- DIVERSION HEADWORKS (1 DAY)
Different types of diversion head works (weirs in detail), Creep theories (Bligh’s, Lanes), Khosla’s theory are important. Practice numerical questions related to creep coefficients, uplift pressure heads.
- DESIGN OF UNLINED & LINED CANALS (1-2 DAYS)
This is another very important topic, both from the theoretical and numerical point of view. Kennedy’s theory and Lacey’s theory are important; understand the basic difference/comparison (true, initial & final regime) b/w the two from theoretical point of view. They both use their own set of formulas for design, which are complicated but, unfortunately, you have to remember. Formula sheet! Practice 2 numericals for each theory.
In lined canals, just understand mechanics of sediment transport (tractive τo=γRS), Shield’s formula for non-scouring/no erosion of side banks (critical τc=γd/11) & stability of bed (τo11RS). You can practice these numericals while giving test-series directly.
- CROSS DRAINAGE WORKS & CANAL REGULATION WORKS (1 DAY)
In depth study of these chapters are not needed, read once. However give importance to canal modules.
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