Surface irrigation

• Surface irrigation


  Small open channels or overland flow is used to distribute the water over a cropped field
• Surface irrigation


  • Convey water from the source to the fields in lined or unlined open channels and/or low-head pipelines
  • Smaller investment is normally required for surface systems than for sprinkler and trickle systems, except possibly when extensive land smoothing is needed
  • Suited to soils with low to moderate infiltration capacities and lands with relatively uniform terrain and slopes less than 2-3%
• Basin irrigation


  Type of surface irrigation where water is applied to the basin through a gap in the perimeter dike or adjacent ditch; water is retained until it infiltrates into the soil or the excess is drained off
• Basin irrigation


  1. The field to be irrigated is divided into units surrounded by small levees or dikes

  2. Gated outlets, siphon tubes, spiles and hydrants conduct water from delivery channels or pipelines into each basin

  3. Water is introduced into the basin as rapidly as possible and then held until it infiltrates or is drained away
• Basin irrigation


  • May either be level or graded
  • High application efficiencies are possible primarily because runoff losses are minimized
• Types of Basin Irrigation

  • Closed Single Basin
  • Multiple/Sequential Basin
• Closed Single Basin


  1. Water applied to an individual basin and all of that applied water is allowed to infiltrate

  2. Each basin in the irrigation block is hydraulically independent

  3. Water advances from the inflow point towards the downstream end of the basin in a regular pattern, which may be distorted by surface irregularities

  4. Inflow is normally shutoff before the water reaches the downstream end of the basin
• Multiple/Sequential Basin


  1. Each basin is irrigated separately by a supply channel running along the boundary with a number of adjacent basins

  2. In each basin, the water level in the supply channel controls the water application. When a basin is irrigated, the water level in the channel is raised higher than the soil surface elevation and overflows onto the basin

  3. When the irrigation is completed, the water level in the channel is lowered below the soil surface elevation of the basin and supply is diverted to the next basin. The excess water from the first basin drains back to the supply channel

  4. The next basin is irrigated with the supply discharge plus the drainage water from the upstream basin (or basins)
• Basin irrigation design criteria


  • Topography - The basin shall be nearly if not completely level to prevent tailwater. A difference of 6 cm to 9 cm between the highest and lowest elevations may be allowed such that it is less than one-half of the net depth of application
  • Soil type - Sandy soils or fine-textured soils that crack when dry shall be avoided to maintain adequate basin ridge height
  • Application rate - Irrigation water shall be applied at a rate that will advance over the basin in a fraction of the infiltration time
  • Irrigation volume - The volume of water applied shall be equal to the average gross irrigation application
  • Intake opportunity time -The intake opportunity time at all points in the basin shall be greater than or equal to the time required for the net irrigation to infiltrate the soil. The longest intake opportunity time at any point in the basin area shall be sufficiently short to avoid scalding and excessive percolation losses
  • Depth of water - The depth of water flow shall be contained by the basin dikes
  • Design application efficiency - The minimum design application efficiency shall be 70% thus, the minimum time required to cover the basin shall be 60% of the time required for the net application depth to infiltrate the soil
  • Basin dikes – Top width of the basin dike shall be greater than or equal to the height of the dike. The settled height shall be at least equal to either the gross application depth or the design maximum depth of flow plus a freeboard of 25%, whichever is greater
  • Supply ditches – Supply ditches shall convey the design inflow rate of each basin or multiples of the design flow rate where more than one basin is irrigated simultaneously. The water surface in the ditch shall be 15 cm to 30 cm above the ground surface level in the basin depending on the outlet characteristics. The ditches shall be constructed with a 0.1% grade or less to minimize the number of check structures and labor requirements
  • Outlet location – One outlet shall be installed for basin widths of up to 60 m and flow rates up to 0.4 m3/s. Multiple outlets at various locations may be installed depending on the rate of flow required and the width of the basin
  • Drainage – Surface drainage facilities shall be provided for basins with low or moderate intake soils and in high rainfall areas
  • Erosion – The maximum water flow velocity into the basin shall be less than or equal to 1 m/s to avoid scouring and erosion
  • Agricultural practice – The width of the agricultural machinery or implement to be used in the basin shall be considered in finalizing the width
• Basin irrigation design procedure


  The design procedure is based on the objective to flood the entire area in a reasonable length of time so that the desired depth of water can be applied with a degree of uniformity over the entire basin
• Basin irrigation design procedure

  • Table 2 shows the suggested basin size for different soil types and flow
  • Table 3 shows the maximum basin width based on slope
• Basin irrigation operation


  1. Direct Method - Irrigation water is led directly from the field channel into the basin through siphons, spiles or bundbreaks

  2. Cascade Method - Irrigation water is supplied to the highest terrace, and then allowed to flow to a lower terrace and so on
• Border irrigation


  Border irrigation is a method of irrigation which makes use of parallel border strips where the water flows down the slope at a nearly uniform depth. Border strip is an 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
• Types of Border Irrigation System

  • Open-end Border System
  • Blocked-end Border System
• Border irrigation design criteria

  • Crop – All close-growing, non-cultivated, sown or drilled crops, except rice and other crops grown in ponded water can be irrigated by border irrigation
  • Topography – Areas shall have slopes of less than 0.5%. For non-sod crops, slopes of up to 2% may be acceptable and slopes of 4% and steeper for sod crops
  • Soil Type – The soil shall have a moderately low to moderately high intake rate which is 7.6 mm/hr to 50 mm/hr. Coarse sandy soils with extremely high and those with extremely low intake rate shall be avoided
  • Stream Size – The stream size shall be large enough to adequately spread water across the width of border
  • Irrigation Depth – A larger irrigation depth shall be aimed by making the border strip longer in order to allow more time for the water to reach the end of the border strip
  • Cultivation Practices – The width of borders shall be a multiple of the farm machinery used in the field
• Border irrigation design procedure


  Detailed steps for designing border irrigation system
• Border irrigation operation


  Borders are irrigated by diverting a stream of water from the channel to the upper end of the border where it flows down the slope. When the desired amount of water has been delivered to the border, the stream is turned off which may occur before the water has reached the end of the border. The following may be used as guidelines: On clay soils, the inflow is stopped when the irrigation water covers 60% of the border. On loamy soils it is stopped when 70 to 80% of the border is covered with water. On sandy soils the irrigation water must cover the entire border before the flow is stopped.
• Furrow irrigation


  Furrows are small parallel channels, made to carry water in order to irrigate the crop. Furrow irrigation is a method of irrigation where water runs through small parallel channels as it moves down the slope of the field
• Types of Furrow Irrigation

  • Corrugation Irrigation
  • Zigzag Furrow
• Furrow irrigation design criteria

  • Slope – The minimum grade shall be 0.05% to facilitate effective drainage following irrigation and excessive rainfall. If the land slope is steeper than 0.5%, furrows shall be set at an angle to the main slope or along the contour to keep furrow slopes within the recommended limits
  • Soil Type – Furrows shall be short in sandy soils to avoid excessive percolation losses while furrows can be longer in clayey soils
  • Stream Size – If the furrows are not too long, 0.5 L/s of stream flow shall be adequate for irrigation but the maximum stream size shall largely depend on the furrow slope
  • Irrigation Depth – Larger irrigation depths shall allow longer furrows
  • Cultivation Practice - Compromise shall be made between the machinery available to cut furrows and the ideal plant spacing while ensuring that the spacing provides adequate lateral wetting on all soil types
• Furrow irrigation design procedure


  Detailed steps for designing furrow irrigation system
• Furrow irrigation design procedure

  • Furrow Length
  • Gross depth of irrigation
  • Required Discharge from Source
  • Furrow shape - Narrow, deep V-shaped furrows shall be made in sandy soils in order to reduce the area through which water percolates. Wide, shallow furrows shall be made in clay soils in order to obtain a large wetted area
• Furrow irrigation design procedure

  1. Determine furrow length

  2. Determine gross depth of irrigation

  3. Determine required discharge from source

  4. Determine furrow shape

  5. Determine furrow spacing
• Furrow shape


  • Furrows shall be large enough to contain the expected stream size
  • Narrow, deep V-shaped furrows in sandy soils to reduce percolation area
  • Wide, shallow furrows in clay soils to obtain large wetted area
• Furrow irrigation operation


  Direct application - water supplied to each furrow from field canal using siphons, spiles or gated pipe
• Performance evaluation of furrow irrigation should refer to Annex A of PAES 607:2016
• Water spreading


  Turning a stream of water onto a relatively flat field and allowing the water to spread naturally
• Water spreading


  • Inefficient method providing little or no control of water distribution over the field
  • Employed in low-lying areas with a stream or small river where water can be diverted during periods of high water
  • Allows use of short term, excess supplies of water that would otherwise be lost
• Contour ditch irrigation


  • Water is released onto the field from a series of slightly sloping ditches spaced 25-200m across the field contours
  • Water is released onto the land between ditches using large siphon tubes or over downslope ditch banks
• Contour ditch irrigation


  • Application uniformity is reduced as water is channeled by depressions in the land surface
• Delivery systems for surface irrigated farms

  • Convey water from the farm water source to the fields in open canals and/or pipelines
  • Include structures for measuring, regulating flow, controlling head and erosion, and diverting water
• Open channel delivery systems

  Lined canals and unlined ditches are widely utilized for on-farm conveyance of irrigation water
• Unlined ditches


  • Low capital cost and ease of construction
  • Best suited for flat lands with cohesive soils and low infiltration
  • On steep lands or unstable soils, ditch erosion can be serious
  • In porous, high infiltration soils, large water seepage can reduce conveyance efficiency
  • Weed control is essential for efficient operation
• Lined canals


  • Reduce seepage and potential for drainage problems
  • Smooth surface reduces friction losses and increases carrying capacity
  • Steeper slopes possible due to resistance to erosion
  • Reduce water losses from burrowing animals
  • Generally have lower maintenance costs
• Open channel design


  1. Determine design discharge

  2. Determine flow velocity

  3. Determine roughness coefficient

  4. Determine canal cross section

  5. Determine bottom slope

  6. Determine freeboard
• Design discharge


  For main canal, equal to diversion water requirement

  For main farm ditch, equal to farm water requirement
• Flow velocity


  For unlined channels, shall not exceed max permissible velocity to avoid erosion

  For lined channels, shall be above min permissible velocity to avoid sedimentation and weed growth
• Roughness coefficient


  Value shall be based on surface condition after years of operation, not original finish

  For farm ditches, 0.03 may be adopted due to lack of maintenance, non-uniform section, and grass/weed growth
• Canal cross section


  • Recommended shapes are trapezoidal or rectangular due to stability and resistance to scouring
• Velocity of flow


  Should be low enough to prevent erosion, but high enough to prevent deposition

  Flow velocity in excess of 0.6 m/s will normally minimize deposition