A Research On Calculation Methods And Irrigation Patterns Of Return Flow In Irrigation Districts

In China,the total water resources is shortage and the water environment pollution is extremely serious.The amount of available water couldn't meet the demand of current agricultural irrigation.The irrigation district is an important grain production base,so it's important to develop and utilize its water resource rationally.In irrigation field,water resource can be divided into three parts:rainfall?irrigation water?return flow.In order to exploring an effective way to solve the contradiction of agricultural water use,this study chooses the return flow as an object,expecting to provide some meaningful suggestions for the sustainable development of irrigation area water resources in the future.The existing researches at home and abroad mostly focus on the mathematical model studies of fields in small scale.Those studies spend long experimental period and their findings are limited to field scale.Therefore,this research tries to discuss calculation methods and using patterns of return flow,which could provide practical suggestions and plans for the future using of irrigation return water.The main results of this paper are as follows:(1)This study chose Yangxi irrigation district as study area,which was a representative irrigation district with multi water source and medium size of Zhejiang province.With analyzing hydraulic engineering situation and canal system the study area was divided into 9 parts including 7 parts of north and 2 parts of south.(2)The traditional water balance equation just took water supply and demand into account,but it ignored the water recycling in irrigation district.Consequently,this paper proposed a new balance equation with many factors,like evapotranspiration,seepage,irrigation amount and return amount etc,then described each parameter in detail.(3)First of all,with analysing the structure of irrigation area,water source projects in district were classified into different types.Secondly,via a series of traditional methods the calculating results of water quantity for each irrigation field can be got.Thirdly,the value of crop water requirements would be calculated by Penman equation in each zone.The results of crop water requirements and irrigation coefficient can be used to count the total number of irrigation water in whole district.Finally,the computing method of return flow was established by distinguishing the difference between water consumption and water requirement.(4)This paper analysed the influence factors of return water,mainly including:water volume,meteorological factors,irrigation system,crop structure,canal structure,soil texture,soil surface parameters etc.In order to carry out a more comprehensive evaluation of the seven factors,this study made a regression analysis by SPSS statistical software.It was found that irrigated crops planting structure and the canal construction had significant effect on the return water.(5)Judging with the value of parameters of the return flow,this paper gave some suggestions to the reuse of return flow.These advice were mainly aiming at how to reform water resource project and canal project.