CHAPTER TWO: BASICS IN IRRIGATION ENGINEERING. 2.1. IRRIGATION ENGINEERING: This involves Conception, Planning, Design, Construction, Operation and Management of an irrigation system.
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iii) Water Supply: Consider
(a)Sources of water
(b) Quantity and quality of water
c) Engineering works necessary to obtain water e.g. if underground, pumping is needed
e.g. Surface (90% worldwide),
Trickle and Sub-irrigation(5%).
Total water demand of crops is made up of:
Weather parameters, Crop Characteristics, Management and Environmental aspects are factors affecting ET
ETc = Kc . ETo where Kc is crop coefficient
Heat Transfer Mechanisms Involved In Heating Of Water In The Standard Pans (diameter D) And Their Walls (After Jagroop,2000).
Incoming Radiation q’ Absorbed By Water
Incoming Radiation Heats Pan Wall q’’ rad
q’ conv absorbed by the water
Conduction Through Walls of pan
Convection q”conv heats uppan walls
Ec acceptable = 4 mmhos/cm. For water quality, Ec of 0.8
Mmhos/cm is medium, quality while Ec of 4 mmhos/cm is saline.
Note: This is the actual water needed to be pumped for irrigation.
It is equivalent to:
120 /1000 mm x 10,000 m2 = 1200 m 3 per hectare.
Assuming water is applied in a border in a day,
the total period of irrigation is then 11 days.
Ea is inadequate in describing the overall quantity of water
since it does not indicate the actual uniformity of irrigation,
the amount of deep percolation or the magnitude of
under-irrigation. See diagrams in text.
Water lost by evap
= 38/45 = 84%
This measures the uniformity of irrigation
W here: is the summation of deviations from the mean depth infiltered
m is the mean depth unfiltered and
n is the number of observations.
m = 5.9 cm; n = 13
ET is Evapotranspiration;
Wl is Leaching Requirement;
Re is Effective Precipitation;
is change in storage;
Wi is water diverted, stored or pumped for irrigation.
Irrigation Plan: Apply 30 mm of water at 30 mm deficit.
Parameters are measured in ME/litre.