A Research On The Scale Effect Of Irrigation In Multi-source Irrigated Area

With the development of society and economy and the improvement of urbanization,the amount of domestic water use and urban water use keeps increasing,laying an increasingly heavy stress on water resource.Since the balance between water use and supply is about to break,as a huge water use sector,irrigation water use is attracting more and more attention:the"three red lines" policy,the work of total water use calculation have made strict standard to regulate irrigation water use.Besides,counting irrigation water use accurately is also beneficial for water resource planning.However,in multi-source irrigated area,too many water sources are used to irrigate,spying on each source is not possible,and the over-irrigate problem makes typical field method inaccurate because of the reuse of irrigation return flow.Under these circumstances,it is necessary to study the scale effect of irrigation water,which can be helpful to the calculation of multi-source irrigated water use.Using adapted SWAT model,this article simulates the nature-human water cycle in Tongjiqiao irrigated area and makes irrigated water cycle models of different scales,the main results are as follows:(1)The adapted SWAT model can precisely simulate the nature-human water cycle,the irrigating process and water cycle process are basically similar as reality.In multi-source irrigated area,ponds are the most important source which provide more than 50%of total irrigation water,and they can collect return flow upstream as well as rain water.(2)The distribution of return flow is mainly affected by rain.In low-flow year and month,the thickness of return flow in river and ponds and the reuse of return flow are relatively high.Even in accurate irrigation mode,the reuse of irrigated return flow at irrigated area scale is adorable:the ratio of reuse return flow to total irritation water of cash crop is 30%,which of rice is 20%.(3)The ratio of crop area to total area and irrigation system are the main factors which affect area irrigation water use.At the circumstance of three times over irrigation,return flow ratio of total irrigation water almost doubles,cash crop increases from 30%to 56%,rice rises from 20%to 40%.(4)With the increase of area scale,the thickness of return flow keeps increasing,the irrigation water use keeps decreasing.The average irrigation water use of cash crop decreases from 485.5mm at scale 1 to 389mm at total irrigated area scale,which of rice drops from 555mm to 496.2mm,which indicates that the reuse of return flow will make irrigation water use decrease as scale goes up.