Experimental Study On Controlled Drainage In Paddy Fields Of The Yinnan Irrigation District, China

Controlled drainage is a water management practice that reduces drainage discharge by adding a control structure such as a weir, at drainage outlet. By adjusting the wier depth according to crop water requirement, drainage discharge receiving waters can be reduced to achieve water quality benefit. This thesis presents an experimental study on controlled drainage application in the Yinnan Irrigation District, China. The Irrigation District has been reported with excessive drainage problem and discharges its drainage water to the downstream of the Yellow River. Based on international research on controlled drainage, a 4 months controlled drainage experiment was conducted in rice fields in XiWei village of the YongNing county; field observations included drainage discharges, groundwater salinity, and nitrogen distribution. Monitoring data from the controlled drainage plots were compared with those in the conventional drainage plots. Major conclusions are drawn as below:1) The effect of controlled drainage on drainage dischargeWith controlled drainage, drainage discharge from field ditches is significantly less than that in the conventional drainage plots; the reduction is about 50% .2) The effect of controlled drainage on salinity of groundwaterThe controlled drainage clearly changed the distribution of groundwater salinity. The shallow groundwater salinity decreased, and the deep groundwater salinity increased. In the whole growing season, there is no indication of salt accumulation. The experimental results also show that the "intrinsic drainage" may have diluted the salinity growth due to drainage reduction of field ditches.