APPROPRIATE DRAIN ENVELOPE FOR PROBLEMATIC CALCAREOUS SOILS IN EGYPT

Abstract

Agricultural subsurface drainage systems are commonly used to remove the excess water and salts from the root zone to enhance crop production and to ensure irrigated agriculture sustainability. In Egypt, drain pipes installed in soils with limited cohesion (clay content is less than 30%) should be provided with envelopes to prevent the entry of soil particles into the drains (filter function) and to reduce entrance resistance by creating a more permeable zone around drains (hydraulic function). Calcareous soils with calcium carbonate (CaCO3) content of more than 15% are considered hazardous problematic soils that cause envelope clogging and sedimentation in the subsurface drainage network. Earlier testing of synthetic drain envelopes in Egyptian calcareous soils has revealed poor performance. Therefore, the main objective of this study is to determine the most appropriate locally available envelope material(s) that can be used in calcareous soils under Egyptian conditions. Both theoretical and experimental (laboratory as well as field) investigations were conducted to assess the performance of the locally available synthetic envelope (polypropylene with pore size 400 microns – PP400) alone and combined with granular materials. The assessment results (theoretical and experimental) indicated that the currently used synthetic envelope PP400 is not performing well when used alone (too thin with low porosity). Treatments that have a gravel material, either alone or in combination with the locally available synthetic envelope revealed good performance and consequently gravel envelopes alone are recommended.