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A steady state drain spacing equation for two-layered soils, or three-layered soils with the drains located at the interface of the top two layers, has been developed based on the equations of Hooghoudt and Ernst. This equation can be solved by the direct trial-and-error approach, which is very convenient to use. It has been compared with the equation ofToksoz and Kirkham (1971a, 1971b). Under the same conditions, the new equation yields larger, and possibly more accurate results.
G. Wu and S.T. Chieng 1991. A convenient drain spacing formula for layered soils. Canadian Agricultural Engineering 33(2):239-243.
Canadian Society for Bioengineering