*# DUTY: *

* The area of land that can be irrigated with a unit volume of water supplied is called duty. It is denoted by D.*

*# DELTA: *

* The depth of water required to raise a crop over a unit area is called delta. It is denoted by Δ.*

*# BASE PERIOD:*

* The time between the first watering of a crop at the time of its sowing to its last watering before harvesting is called the base period. It is denoted by B.*

*# RELATIONSHIP AMONG DUTY, DELTA AND BASE** PERIOD.*

* *

* Let us consider a crop having base period B days. Assume that 1 cumec of water is supplied to this** crop for B days to provide delta Δ m depth of water.*

* Now the volume of water supplied by unit discharge to this crop during B days is given by:*

* V=Q (m³/s)*B (days)*

* V= 1*24*60*60*B m³*

* V=8.64*10000 m³ …………………(1)*

* Also, the volume of water applied to the field can be calculated as:*

* V=Area of land irrigates by unit discharge*depth of water applied*

* V=D(ham)*Δ (m)*

* V=D *A*10000(m³) ………………….(2)*

* From Eqn(1) and (2), we get*

* 8.864*10000=D*Δ*10000*

* D=8.64*B/Δ *

*EXAMPLE:*

* Calculate delta based on the following data*

* Base peroid=110 days*

* Duty=1400ha/cumec*

* Delta=?*

* solution,*

* Δ =8.64*110/1400*

* Δ=0.68m*

* Δ =68cm*

* *