Agriculture Reference
In-Depth Information
advance
wetting (or ponding) and
recession
The advance phase starts when water first enters the field plot and continues up
to the time when it has advanced to the end of plot (Fig. 3.2 ) . The period between
the time of advance completion and the time when the inflow is cut off or shut off is
referred to as wetting or ponding or storage phase. After termination of the inflow,
the ponding water or the water-front recedes from the field by draining and/or into
the next field by infiltration. This is the recession phase.
Recession curve
Recession phase
Water
stopped/
cutoff
Wetting or
ponding phase
Opportunity
time
Advance curve
Time of
advance
Advance
phase
Distance from inlet
Fig. 3.2 Schematic presentation of phases of water-front in surface irrigation system
Unsteady overland flow analysis is required for the design and management of
surface irrigation systems. When sufficient water is released over a porous medium
in surface irrigation, part of this water infiltrates into the soil (Fig. 3.1 ) and the
remainder moves over the field as overland flow. Hydraulic analysis of surface
flow during all the phases of irrigation from advance to recession is important for
successful design and operation of a surface irrigation system.
3.2 Border Irrigation System Design
3.2.1 Definition of Relevant Terminologies
Border strip : The area of land bounded by two border ridges or dikes that guide the
irrigation stream from the inlet point of application to the ends of the strip.
Cutback : Reduction of flow rate (partially or fully) is referred to as cutback. The
objective of cutback is to reduce runoff from the field.
Cutoff time : Cutoff time is the time at which the supply is turned off, measured
from the onset of irrigation. Cutoff time has no impact on advance as long as the
 
 
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