DESIGN OF BORDER _ BASIN IRRIGATION by malj

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									DESIGN OF BORDER & BASIN
       IRRIGATION

               PRABHU.M
               BTE-06-024
          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
  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.
1. Sandy and sandy loam soils: 60 to 120 meters
2. Medium loam soils           : 100 to 180 meters
3. Clay loam and clay soils    : 150 to 300 meters
                             Cont..
• Border slope: The border should have a uniform longitudinal
  gradient.
1. Sandy loam to sandy soils : 0.25% to 0.60%
2. Medium loam soils           : 0.20% to 0.40%
3. 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.
1. Sandy soil : 7 to 15 ( LPS)
2. Loamy sand : 5 to 10 ( ,, )
3. Sandy loam : 4 to 7 ( ,,)
4. Clay loam : 2 to 4 ( ,, )
                   Design
• When border irrigation design as 2 types;
1.design of open end border system
2.design of blocked end border system
                     Cont..
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
                   Cont…
• 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
                    Cont…
• 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.
                     CONT…
• 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
                    Cont…
• 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:
                   Cont…
3. Compute the 'relative' water surface slope:
                        Cont…
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.
                           Cont…
• 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 > 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)
                      Cont…
• If td < 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.
                     Cont….
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.
      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)
                    Cont….
• 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:
                          Cont…
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.
                              Cont..
• 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)
                        Cont…
where,
            tL-1 = [(L-l) / p]1/2
• 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.
       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
                              Cont…
•  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.
                    Cont…
• Utilizing the result of in the Manning
  equation yields:




        or,
                        C ont…
• 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.
                   Cont….
• 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):
                   Cont…
• 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.
                     Cont…
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.
                       Cont….
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.
                    Cont…
• 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 .
                                   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 < 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.
Thank u
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