Abstract
This study was conducted to evaluate the performance of subsurface drainage and a rice husk envelope in Behshahr, a coastal region in the northern part of Iran. The subsurface drainage system was monitored in the rainfall seasons of 2006 and 2007 (22 November to 19 March). Various parameters such as daily groundwater table fluctuations and drain discharge rate were measured. To evaluate the drainage envelope, the gradation curve, bulk density and natural durability of rice husk and also the head loss of the groundwater table in the vicinity of the drain were measured. The large difference between the approach‐flow head and entrance‐flow head could be related to clogging of the external part of the rice husk envelope. The overall conclusion of this study was that subsurface drainage system performance was not satisfactory due to poor control of groundwater table depth, which could be related to clogging of the rice husk drain envelope. Hooghoudt's equation is not recommended to be used for evaluation of design parameters in this case. The basic uncertainty in application of a rice husk envelope was its durability, which was found to be very variable and depended on soil environmental conditions. Copyright © 2010 John Wiley & Sons, Ltd.