Performance Evaluation of Irrigation Projects - Practices of Irrigation and On-farm Water Management - page 115

uniformity coefficient and low-quarter distribution uniformity (or simply distribu-
tion uniformity).

4.1.3.1 Uniformity Coefficient

Uniformity coefficient, introduced by Christiansen ( 1942 ) , is defined as the ratio
of the difference between the average infiltrated amount and the average deviation
from the infiltrated amount, to the average infiltrated amount. That is,

⎡ ⎤

i

i = 1 |

= N

Z i − Z av |

⎣ ⎦ ×

UCC = 1 − 100 (4.6)

Z av × N

where

UCC = Christiansen uniformity coefficient (or simply uniformity coefficient)

Z i = infiltrated amount at point i

Z av = average infiltrated amount

N = number of points used in the computation of UCC

Christiansen developed uniformity coefficient to measure the uniformity of sprin-
kler systems, and it is most often applied in sprinkler irrigation situation. It is seldom
used in other types of irrigation. Values of UCC typically range from 0.6 to 0.9.

4.1.4 Low-Quarter Distribution Uniformity (or Distribution
Uniformity)

Low-quarter distribution uniformity (DU lq ) is defined as the percentage of the aver-
age low-quarter infiltrated depth to the average infiltrated depth. Mathematically,

LQ
M

DU lq = 100 × (4.7)

where

DU lq = distribution uniformity at low quarter (or simply distribution unifor-

mity, DU)
LQ

= average low-quarter depth infiltrated (mm)

M = average depth infiltrated (mm)

The “average low-quarter depth infiltrated” is the average of the lowest one-
quarter of the measured values where each value represents an equal area.