Qualitative evaluation of organic envelopes on subsurface drainage performance*

Abstract

AbstractThe purpose of this study was to investigate the efficiency of organic matter such as rice husk and palm‐leaf stalk as envelopes in drainage pipes. For this purpose, to simulate field conditions in vitro, we used a physical model consisting of a plexiglass cylinder with a height of 200 mm and diameter of 100 mm, with five holes attached to the manometers and an inlet at the bottommost part and an outlet at the topmost part with a water tank which provided a fixed head. Experiments were carried out with five types of organic matter (i.e. rice husk, three types of powder and palm‐leaf fibres) on Ramshir agricultural soil which required envelopes according to existing standards. The results showed that among the envelopes utilized, the highest outflow (discharge) rate was related to powder No. 3 (the most coarse‐grained powder) in a gradient of 0.5. By increasing the gradient to 2, envelope hydraulic fracturing was observed, which means that it was unable to retain soil particles with finally an inadequate filtering function for this organic material. In gradient 2, the highest output discharge was related to palm stalk and leaf fibres, which is reflected in the proper hydraulic performance of this envelope and its high filtering properties. Finally, comparing the value of the gradient ratio in the higher gradients confirmed the results.