الفهرس 
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Abstract
The objective of this thesis is to develop a new method for determining the spacing between the tile drains and their depths underground taking into consideration the parameters of the soils, crops, climate, salinity and rate of irrigation. from the results obtained, it is concluded that the most effective and economic method for drainage is the subface drains which consists of tile drains laid under the ground surface at certain depths and spaced by certain distance apart. many equations exist for the determination of the spacing between the drains for the steady and transient conditions. the dupuit-forchhemer theory is a simplified method for obtaining some apprxrimate, theoretical solutions for some cases, but such theory has some physical disadvantages