DESIGN OF BORDER

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DESIGN OF BORDER BASIN IRRIGATION

• 
  PRABHU.M
• 
  BTE-06-024

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BORDER IRRIGATION

• With border irrigation, water is diverted in a
  pre-constructed border, which is between 100 and
  1 000 m long and 3 to 30 m wide.
• The borders have a uniform slope away from the
  water canal so that the water flows into the
  borders by means of gravity while it infiltrates
  into the soil

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DESIGN OF BORDER IRRIGATION

• BORDER SPECIFICATION AND STREAM SIZE
• Width of border strip The width of border
  usually varies from 3 to 15 meters,depending on
  the size of the irrigation stream available and
  the degree of land levelling practicable.
• Border length The length of the border strip
  depends upon how quickly it can be wetted
  uniformly over its entire length.
• Sandy and sandy loam soils 60 to 120 meters
• Medium loam soils 100 to 180
  meters
• Clay loam and clay soils 150 to 300
  meters

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• Border slope The border should have a uniform
  longitudinal gradient.
• Sandy loam to sandy soils 0.25 to 0.60
• Medium loam soils 0.20 to 0.40
• Clay to clay loam soils 0.05 to 0.20
• Size of irrigation stream The size of the
  irrigation stream needed depends on the
  infiltration rate of the soil and the width of
  the border strip.
• Sandy soil 7 to 15 ( LPS)
• Loamy sand 5 to 10 ( ,, )
• Sandy loam 4 to 7 ( ,,)
• Clay loam 2 to 4 ( ,, )

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Design

• When border irrigation design as 2 types
• 1.design of open end border system
• 2.design of blocked end border system

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• 1.Design of open end border system
• The first four design steps for open-ended
  borders are the same as those outlined under for
  traditional furrow systems
• (1) assemble input data
• (2) compute maximum flows per unit width
• (3) compute advance time and
• (4) compute the required intake opportunity time

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• Hart et al. (1980) also suggest computing a
  minimum flow, Qmin, based on a value that ensures
  adequate field spreading. This relationship is
• Qmin 0.000357 L So.5 / n
• Where,
• Qmin is the minimum suggested unit discharge
  in m3/min/m and
• L, So, and n are variables

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• The depth of flow at the field inlet to ensure
  that depths do not exceed the dyke heights. For
  this
• where yo is the inlet flow depth in m.

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• After completing the first four design steps, as
  with furrows, open-ended border design resumes as
  follows
• v. Compute the recession time, tr, for the
  condition where the downstream end of the border
  receives the smallest application is,
• tr rreq tL

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• vi. Calculate the depletion time, td, in min, as
  follows
• 1. Assign an initial time to the depletion time,
  say T1 tr
• 2. Compute the average infiltration rate along
  the border by averaging the rates as both ends at
  time T1

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• 3. Compute the 'relative' water surface slope

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• 4. Compute a revised estimate of the depletion
  time, T2
• 5. Compare T2 with T1 to determine if they are
  within about one minute, then the depletion time
  td is determined. If the analysis has not
  converged then let T1 T2 and repeat steps 2
  through 5.

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• The computation of depletion time given above is
  based on the algebraic analysis reported by
  Strelkoff (1977).
• vii. Compare the depletion time with the required
  intake opportunity time. Because recession is an
  important process in border irrigation, it is
  possible for the applied depth at the end of the
  field to be greater than at the inlet. If td gt
  rreq, the irrigation at the field inlet is
  adequate and the application efficiency, Ea can
  be calculated using the following estimate of
  time of cutoff
• tco td - yo L /
  (2 Qo)

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• If td lt rreq, the irrigation is not complete and
  the cutoff time must be increased so the intake
  at the inlet is equal to the required depth. The
  computation proceeds as follows
• tco rreq - yo L / (2 Qo)
• and then Ea is computed
• Since the application efficiency will vary with
  Qo several designs should be developed using
  different values of inflow to identify the design
  discharge that maximizes Ea.

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• viii. Finally, the border width, Wo in m is
  computed and the number of borders, Nb, is found
  as
• Wo QT/Qo and,
• Nb Wt/Wo
• where Wt is the width of the field. Adjust Wo
  until Nb is an even number. If this width is
  unsatisfactory for other reasons, modify the unit
  width inflow or plan to adjust the system
  discharge, QT.

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2.Design of end block borders

• The suggested design steps are as follows
• i. Determine the input data as for furrow and
  border systems already discussed.
• ii. Compute the maximum inflows per unit width
  using with p1 1.0 and p2 1.67. The minimum
  inflows per unit width can also be computed using
  
• iii. Compute the require intake opportunity time,
  rreq.
• iv. Compute the advance time for a range of
  inflow rates between Qmax and Qmin, develop a
  graph of inflow, Qo verses the advance time, tL,
  and extrapolate the flow that produces an advance
  time equal to rreq. Define the time of cut off,
  tco, equal to rreq. Extrapolate also the r and p
  values found as part of the advance calculations.
  
• v. Calculate the depletion time, td, in min, as
  follows
• td tco yo L / (2 Qo)
  rreq yo L / (2 Qo)

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• vi. Assume that at td, the water on the surface
  of the field will have drained from the upper
  reaches of the border to a wedge-shaped pond at
  the downstream end of the border and in front of
  the dyke.
• vii. At the end of the drainage period, a pond
  should extend a distance l metre upstream of the
  dyked end of the border. The value of l is
  computed from a simple volume balance at the time
  of recession

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• where,
• Zo k tda fo td
• ZL k (td - tL)a fo (td - tL)
• If the value of l is zero or negative, a
  downstream pond will not form since the
  infiltration rate is high enough to absorb what
  would have been the surface storage at the end of
  the recession phase.
• In this case the design can be derived from the
  open-ended border design procedure.
• If the value of l is greater than the field
  length, L, then the pond extends over the entire
  border and the design can be handled according to
  the basin design procedure outlined in a
  following section.

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• The depth of water at the end of the border, yL,
  will be
• yL l So
• viii. The application efficiency, Ea, can be
  computed. However, the depth of infiltration at
  the end of the field and at the distance L-l
  metres from the inlet should be checked as
  assumes that all areas of the field receive at
  least Zreq.
• The depths of infiltrated water at the three
  critical points on the field, the head, the
  downstream end, and the location l can be
  determined as follows for the time when the pond
  is just formed at the lower end of the border
• Z1 k (td - tL-1)a fo (td -
  tL-1)

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• where,
• tL-1 (L-l) / p1/2
• It should be noted again by way of reminder that
  one of the fundamental assumptions of the design
  process is that the root zone requirement, Zreq,
  will be met over the entire length of the field.
  
• If, therefore, in computing Ea, one finds ZL-1 or
  ZL less than Zreq, then either the time of cutoff
  should be extended or the value of Zreq used
  should be reduced.
• Likewise, if the depths applied at l and L
  significantly exceed Zreq, then the inflow should
  be terminated before the flow reaches the end of
  the border.

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Design of basin irrigation

• Basin irrigation
• Basin irrigation is as good choice in cases where
  the natural gradient is relatively flat and even.
  
• Permanent orchards and grazing crops are
  especially well suited to basin irrigation.
• The farmer has to be prepared, however, to check
  that all the basin remain level throughout the
  season

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• First, the friction slope during the advance
  phase of the flow can be approximated by Basin
  irrigation design is somewhat simpler than either
  furrow or border design.
• Tailwater is prevented from exiting the field and
  the slopes are usually very small or zero.
• Recession and depletion are accomplished at
  nearly the same time and nearly uniform over the
  entire basin.
• However, because slopes are small or zero, the
  driving force on the flow is solely the hydraulic
  slope of the water surface, and the uniformity of
  the field surface topography is critically
  important.
•  
• Sf yo / x
• in which yo is the depth of flow at the basin
  inlet in m, x is the distance from inlet to the
  advancing front in m, and Sf is the friction
  slope.

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•  Utilizing the result of in the Manning equation
  yields
• or,

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• The second assumption is that immediately upon
  cessation of inflow, the water surface assumes a
  horizontal orientation and infiltrates
  vertically.
• In other words, the infiltrated depth at the
  inlet to the basin is equal to the infiltration
  during advance, plus the average depth of water
  on the soil surface at the time the water
  completes the advance phase, plus the average
  depth added to the basin following completion of
  advance.
• At the downstream end of the basin the
  application is assumed to equal the average depth
  on the surface at the time advance is completed
  plus the average depth added from this time until
  the time of cutoff.

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• The third assumption is that the depth to be
  applied at the downstream end of the basin is
  equal to Zreq.
• Under these three basic assumptions, the time of
  cutoff for basin irrigation systems is (assume yo
  is evaluated with x equal to L)

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• The time of cutoff must be greater than or equal
  to the advance time.
• Basin design is much simpler than that for
  furrows or borders.
• Because there is no tail water problem, the
  maximum unit inflow also maximizes application
  efficiency.

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• As a guide to basin design, the following steps
  are outlined
• i. Input data common to both furrows and borders
  must first be collected. Field slope will not be
  necessary because basins are usually 'dead
  level'.
• ii. The required intake opportunity time, rreq,
  can be found as demonstrated in the previous
  examples.

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• iii. The maximum unit flow should be calculated
  along with the associated depth near the basin
  inlet. The maximum depth can be approximated
• and then perhaps increased 10-20 percent to allow
  some room for post-advance basin filling.
• If the computed value of ymax is greater than
  the height of the basic perimeter dykes, then
  Qmax needs to be reduced accordingly.

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• As a general guideline, it is suggested that Qmax
  be based on the flow velocity in the basin when
  the advance phase is one-ninth completed.
• Usually the design of basins will involve flows
  much smaller than indicated .

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Cont.

• iv. Select several field layouts that would
  appear to yield a well organized field system and
  for each determine the length and width of the
  basins. Then compute the unit flow, Qo for each
  configuration as
• Qo QT / Wb
• where Wb is the basin width in m. As noted above,
  the maximum efficiency will generally occur when
  Qo is near Qmax so the configurations selected at
  this phase of the design should yield inflows
  accordingly.
• v. Compute the advance times, tL, for each field
  layout as discussed .the cutoff time, tco, from
  (if tco lt tL, set tco tL), and the application
  efficiency .
• The layout that achieves the highest efficiency
  while maintaining a convenient configuration for
  the irrigator/farmer should be selected.
•  

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• Thank u

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