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Published bydaniel gebrehiwet Modified over 7 years ago
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Chapter-3 CWR
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Duty – Delta relation ship Base period (B): the base period is the period between the first watering and the last watering. Duty of water (D): -I s its capacity to irrigate land. - It is expressed in hectares / cumecs Delta ( ): is the total depth of water supplied to the crop during the entire base period. - expressed in m
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1*B*24*60*60* = (D*10 => D = 8.64 B = 8.64 B D Where D = in ha/cumec = in m B = in days
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Factors affecting Duty - Type of soil - Type of crop and base period - structure of soil - Slop of ground - Climatic condition - Method of application of water - Salt content of soil
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Example The base period, duty of water and area under irrigation for various crops under a canal system are given in the table below. If the losses in the reservoir and canals are respectively 15%, 25%, determine the reservoir capacity.
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Definitions of important terms Crop water requirement - Evapotranspiration (ET) - Unavoidable application losses - Other needs such as leaving & land preparation WR=IR +ER + S +GW IR= WR-(ER+S+GW)
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CWR estimation methods Direct method Empirical formulas A) Lysimeter experiment B) Field experimental plots C) Soil moisture studies D) Water balance method Blaney- Criddle method Thornthwaite method Hargreaves class A pan Evaporation Modified Penman Method
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