1. Chapter-3 CWR

2. 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

3. 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

4. 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

5. 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.

6. 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)

7. 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