Agriculture Reference
In-Depth Information
Because of the many design and management controllable parameters, furrow irri-
gation systems can be utilized in many situations, within the limits of soil uniformity
and topography (<2% slope). With runoff return flow systems, furrow irrigation can
be a highly uniform and efficient method of applying water. However, the uniformity
and efficiency are highly dependent on proper management, so mismanagement can
severely degrade system performance.
3.4.6 Furrow Design Considerations
Furrow systems may be designed with a variety of shapes and spacings. Optimal
furrow lengths are primarily controlled by the soil intake rate, furrow slope, set
time, and stream size. For most applications the stream size should be as large as
possible without causing erosion.
When the intake rate is slow, the maximum application efficiency can be attained
providing a relatively longer furrow length. For soils with high intake rate, the length
of the furrow should be selected shorter. The maximum slope of 0.1% (0.1/100 m)
should be maintained for block ends furrow.
Optimal furrow irrigation performance requires understanding of application effi-
ciency and distribution uniformity and the methods for improving both. Improving
the efficiencies involve careful management of flow rates and irrigation duration and
appropriate timing (scheduling) of irrigation events:
•
Select a stream size appropriate for the slope, intake rate, and length of run. Or
alternatively, optimal furrow length and irrigation cutoff can be determined, as
related to soil infiltration characteristics, by the time ratio.
•
With the proper cutoff ratio and gross application, you can achieve uniform water
application and minimize deep percolation and runoff. Try different combinations
of furrow stream size and set time. The best combination is the one which moves
water to the end of the furrow within the requirements of the cutoff ratio, is less
than the maximum erosive stream size, and results in gross applications that are
not excessive.
3.4.7 Modeling of Furrow Irrigation System
3.4.7.1 Theoretical Considerations
Surface irrigation processes are governed by general physical laws such as conserva-
tion of mass, energy, and momentum, which are expressed as a function of physical
quantities. Simulation models of furrow irrigation rely on the knowledge of furrow
infiltration and hydraulic characteristics. These models solve equations of mass and
motion conservation which describe unsteady, nonuniform surface flow over a per-
meable bed. Flow rate, slope, hydraulic roughness, and geometry affect flow depth
and therefore wetted perimeter in time and space. Wetter perimeter and flow depth,
Search WWH ::
Custom Search