Agriculture Reference
In-Depth Information
(i) Investigate the soil profile and geo-hydrologic condition including groundwa-
ter quality
(ii) Measure the quality of proposed irrigation water
(iii) Estimate the sources of drainage water other than irrigation
(iv) Review and analyze the climatic data of the area
(v) Select appropriate crop(s)/cropping pattern
(vi) Measure the hydraulic conductivity of the root zone soil
(vii) Estimate drainage requirement or drainage coefficient
(viii) Optimize the depth of drain placement and lateral drain spacing (considering
permissible mid-way water-table depth for the selected crop/cropping pattern,
in situ crop water-use plan by capillary rise , and cost of drain).
Different combinations of drain depth and spacing will result in same
drainage coefficient. But the water quality of drainage may be different. For a
particular drainage intensity, shallow depth of drains requires narrow spacing,
thus drainage cost increases with decreasing drain depth.
First, a drain depth is specified and the spacing is calculated based on the
recharge schedule and the mid-point water-table depth criteria. Subsequently,
the drain depth will be varied to calculate a range of depths and spacing, and
economic analysis should be performed for each case. The most economic
drain depth and spacing is then selected from analyses of several drain system
configurations.
(ix) Determine lateral pipe size and main pipe size (capable of carrying the
maximum drainage rate)
(x) Design the drain envelop material
(xi) Design the drainage disposal system, or decide regarding reuse of drainage
water for irrigation
(xii) Design the pump size to pump the maximum drainage discharge from the
field (if need to be pumped)
In situ use by the crop will affect the drainage design by reducing the irrigation
requirement and the deep percolation losses that will be included in the drain system
design procedure.
The USBR recommends installation of drains at a depth of 2.4 m, if possible, to
provide a balance between the system cost and spacing.
9.6.4.3 Estimation of Drainage Requirement or Drainage Coefficient
For estimation of drainage requirement (or drainage intensity, or drainage coeffi-
cient), following steps may be followed:
collect long-term rainfall and other weather data for the project area
calculate daily average rainfall, evaporation, and evapotranspiration rate for the
target crop season
perform water-balance
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