Evaluating current drainage practices and feasibility of controlled drainage in the YinNan Irrigation District, China

The YinNan Irrigation District (YNID) is located in the upper reaches of the Yellow River in NingXia, China. Its drainage system was constructed between the 1950s and 1970s to maintain salt and water balances in the district. The system, however, has been reported draining the agricultural lands excessively, resulting in frequent irrigations and large amount of drainage discharge into the Yellow River each year. This paper presents a comprehensive analysis of current drainage practices in the YNID and discusses the feasibility of controlled drainage in order to mitigate the negative impact of agricultural drainage. Based on historical records and available information, drainage discharge has been estimated for different crop fields and ditches. The results show that for the major water use crop, rice, controlled drainage may reduce subsurface discharge through field ditches up to 94%. For wheat and corn, the benefit of controlled drainage is not significant because the major drainage discharge is directly through the main ditch system and the Yellow River channel. The rotational cropping nature and local water management tradition, however, make controlled drainage a very attractive option for water savings and reducing water pollution to the Yellow River.