Present Status and Prospect of Study on the Subsurface Drainage Criteria

Due to high standing of water table in plain areas with concentrated rainfall the crops often suffer from waterlogging,with the aim of increasing crop production it is required to construct drainage systems for water table control.In this paper the present status and prospect of study of drainage indexes and criteria used in subsurface drainage design,such as minimum permissible water table depth,the designed rate of water table drawdown after a rainfall event,the cumulative excess water depth SEW_x in the growth period of crops,the stress day index SDI and the cumulative yield reduction index CRI etc are reviewed.