# Relationship of delta, duty & base period

#### # 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