Agriculture Reference
In-Depth Information
W
=
width of the section
or
unit plot
N
=
roughness coefficient of flow for the plot (Manning's
N
)
S
0
=
longitudinal slope of the plot
I
n
=
infiltration characteristics of the soil
t
cutoff
=
time of cutoff
S
w
=
soil water status at the time of irrigation (i.e., condition of deficit)
D
ru
=
reuse of drainage runoff (if applicable)
=
P
pressure of the flow system (specially for sprinkler)
R
d
=
root zone depth of the crop during the irrigation event
ET
atmospheric water demand or evapo-transpirative demand (specially for
sprinkler)
=
W
=
wind factor or windy condition (specially for sprinkler)
Irrigation performance may vary from irrigation event to event, based on the
dynamics of some factors such as infiltration characteristics, roughness coefficient,
root zone depth, soil water deficit.
4.2.3 Performance Indices
or
Indicators
Activities of irrigation systems start at the point of water supply head-work or pump.
Impacts of irrigation are not limited to the field but also extend to the socioeconomic
conditions of the target audience. In general, a set of indices or indicators are used
for evaluating the performance of an irrigation scheme. The indicators are termed
as performance indicators. No single indicator is satisfactory for all descriptive pur-
poses. Moreover, there are uncertainties about the exact values of some indicators.
Several indicators can give an overall picture of the irrigation project.
For convenience in understanding and application,
the indicators can be
grouped as
•
Engineering
•
Field water use
•
Crop and water productivity and acreage
•
Socioeconomic
4.2.3.1 Engineering Indicators
Engineering indicators are those which are related to pump, water headwork, water
supply, water conveyance system, and energy use. Indices under this category
(i) Pumping plant efficiency
(ii) Headworks efficiency
(iii) Water conveyance efficiency
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