Water Application Methods - Practices of Irrigation and On-farm Water Management - page 42

Soil and Topography
For basin irrigation, basin size should be appropriate for soil texture and infiltration
rate. Basin lengths should be limited to 100 meter (m) on very coarse textured soils,
but may reach 400 m on other soils. Flat lands, with a slope of 0.1% or less, are best
suited for basin irrigation: little land leveling will be required. If the slope is more
than 1%, terraces can be constructed. However, the amount of land leveling can be
considerable.
In areas of high intensity rainfall and low intake rate soils, surface drainage
should be considered with basin irrigation, to reduce damage due to untimely
inundation.
Water Quantity
It is important that irrigation stream size be properly matched to basin or border
size for uniform irrigation. Basin systems are suitable for leaching of salts for soil
reclamation, since the water can be held on the soil for any length of time. Under
normal operating conditions, leaching fractions adequate for salinity control can be
maintained with basin.
Required Depth of Irrigation Application
When the irrigation schedule is determined, it is known how much water (in mm
depth) has to be given per irrigation application. It must be checked that this
amount can indeed be given. Field experience has shown that the highest water
can be applied per irrigation application when using basin irrigation. In practice,
in small-scale irrigation projects, usually 40-70 mm of water is applied in basin
irrigation.
Attainable Efficiencies
The system designer and operator can control many of the factors affecting irri-
gation efficiency. Properly designed and maintained basin systems are capable of
obtaining moderately high efficiencies. Some basins are typically designed to pond
the water on their surfaces and prevent tail water; they are usually the most efficient
surface irrigation method. Design efficiencies should be on the order of 70-85%.
With reasonable care and maintenance, field efficiencies in the range of 80-85%
may be expected.
Labor and Energy Requirement
Basin irrigation requires accurate land leveling. Some labor and energy will be nec-
essary for land grading and preparation. Basin irrigation involves the least labor of
the surface methods, particularly if the system is automated. With surface irriga-
tion, little or no energy is required to distribute the water throughout the field, but
some energy may be needed to bring the water to the field, especially when water is