| Pipe irrigation is one of the main agricultural water-saving technologies for the future development in canal irrigation districts in China.It has led to much controversy which canals are suitable for replacing canals with pipes in the engineering practice,there have been qualitative analyses but lack of quantitative researches.Therefore,this paper took Dongfeng reservoir irrigation district which was in Jintang County,Sichuan province as a case and researched on which were the best canal-pipe methods in canal irrigation districts in southwest China,analyzing the feasibility and the reasonableness of using pipes replacing canals in the canal irrigation districts from the technical and economic perspectives.The research can provide technical support for the development of using pipes replacing canals when we make strategic decisions.The main contents and conclusions are as follows.(1)The application feasibility of different pipes in the field of water-saving irrigation was researched.It was appropriate to use PE pipe when the pipe diameters were less than 200mm,and reinforced concrete pipe was a relatively economical choice when the pipe diameters were more than 200mm in the research area.(2)The influence of using pipes replacing different canals for the transportation and distribution system was analyzed.In the present status of surface irrigation,the water-saving percentages were 3.57%,7.61%,11.84%and 24.43%,when we used pipes replacing canals from sublateral canals to the superior canals,comparing with the current irrigation system.Meanwhile,the increase rates of effective utilization coefficient of irrigation water were 3.70%,8.23%,13.43%and 32.33%.The result showed it was a remarkable water-saving measure to use pipes replacing canals.(3)The influence of different field irrigation methods on canal-pipe system was researched.On the condition of using sprinkler irrigation and micro-irrigation in the economic crops in the research area,the water-saving percentages were 11.04%,14.77%,18.67%and 30.29%,when we used pipes replacing canals from sublateral canals to the superior canals,comparing with the current irrigation system.Meanwhile,the increase rates of effective utilization coefficient of irrigation water were 12.41%,17.32%,22.96%and 43.45%.The improvement of effective coefficient of irrigation water utilization were all 8.40%,the water-saving values were 3.1,1.9,1.6 and 1.2 times successively,when we used pipes replacing canals at the same situations on the condition of using sprinkler irrigation and micro-irrigation in the economic crops in the research area,comparing with the current irrigation system.It showed the effect of water-saving was remarkable on the condition of using sprinkler irrigation and micro-irrigation in the economic crops in the research area.(4)The cost-benefit analysis method was used to evaluate the different canal-pipe systems.Either we used surface irrigation presently,or sprinkler irrigation and micro-irrigation in economic crops,the methods of replacing sublateral canals with pipes and replacing lateral canals with pipes were the best to develop canal-pipe irrigation,as the economic benefits of costs ratio and internal rate of return were the highest.(5)The principal component analysis method was used to research the main factors affecting the construction of canal-pipe irrigation projects.The results showed that there were two major factors which influenced the canal-pipe irrigation systems.The factors were hydraulic elements and operation management,and the bigger influence factor was hydraulic elements.Therefore,we should pay more attention to the hydraulic elements when we carry on the construction of canal-pipe irrigation engineering. |
