Investigation of Hydraulical and Chemical Behavior of Dual Drain Envelopes (Organic and Synthetic) in Paddy Conditions with Two Different Water Qualities

Drain envelopes have significant roles in performance of drainage systems due to reduce sediments into the drainpipes and also increase the hydraulic conductivity of soil around the drainpipes. In this research، the effect of 1000 hours flow on dual envelopes consist of geotextile as improving the hydraulic gradient and rice husk as bio-sorbent، on the hydraulic and chemical trends under paddy field conditions without rice، was considered. To do so، drainpipe with two different thicknesses of geotextile at depth of 40 cm on a physical model was installed. Then the drain pipe filled using 5 cm thickness of rice husk. Thousand hours flow test under two different water qualities with 0. 7 and 1. 9 dS/m was done and flow of drainage، EC، sodium absorption ratio and pH of drained water was measured. Results showed that the reduction of flow rate of treatments of rice husk & thin geotextile with saline water (RNs)، rice husk & thin geotextile with ordinary water quality (RN)، rice husk & thick geotextile with ordinary water quality (RV) and rice husk & thick geotextile with saline water (RVs) was 44، 94، 21 and 75 percent، respectively. But totally، RN and RNs treatments had maximum and minimum clogging، respectively. Thickness of geotextiles affected on flow rate and chemical trends، and performance of rice husk among all treatments، didn’t perform properly for saline conditions.