Study On Hydraulic Characteristics Of Water Conveyance System Of Cascade Pumping Stations In Jingtai Irrigation Area

The water conveyance system of cascade pumping stations redistributes the water resources with uneven spatial distribution and low utilization rate,which plays an indispensable role in the development of human society and the protection of ecological environment.During the long-distance operation of the water conveyance system,it is necessary to study the hydraulic characteristics of the water conveyance system of cascade pumping stations through densely populated areas such as cities and villages,so as to provide theoretical support for the safe and stable operation of water conveyance projects.In this paper,the method of combining theoretical analysis and numerical simulation is used to study the hydraulic characteristics of the water conveyance system of the first pumping station to the sixth pumping station of the second phase of Jingtaichuan Electric Power Irrigation Project in Gansu Province.The main conclusions are as follows :(1)The horizontal gradient of water surface line with concave bank and high convex bank and low convex bank appears in the water surface line of trapezoidal channel in the curved interval.With the increase of curvature or flow rate,the backwater area of concave bank increases,and the maximum water surface superelevation point of concave bank moves upstream,but the curvature has little effect on the maximum water surface superelevation value of concave bank.The corresponding flow velocity in the backwater area of the bend is small,and the corresponding flow velocity in the drop area is large.z/H = 0.7 is the maximum flow velocity depth.(2)The trapezoidal cross section in Jingdian Irrigation District is gradually transformed into rectangular cross section,and the water surface line decreases along the way;Mainstream changes along the way down first and then rebound;The thickness of the mainstream zone at the exit of the gradient section is the smallest,about 0.6H.(3)In the filling stage of water conveyance system,the flow rate is small and the water depth is low.The flow capacity of channels with different cross-sections is in the order of rectangular stone channel > aqueduct > trapezoidal stone channel > trapezoidal soil channel.When the flow reaches the trapezoidal soil channel,backwater will occur.For the same channel,the larger the water filling flow is,the smaller the water filling duration is;Under the maximum water filling flow of the channel,starting from a pumping station,the fastest 2 hours 11 minutes,the flow can reach the front pool of six pumping stations.(4)In the normal water conveyance stage of the water conveyance system,the water level line in the channel shows a downward trend along the channel;With the increase of the same flow rate,the larger the proportion of rectangular channel length in the channel form,the greater the rise of the water level line in the channel,and the rise of the water level line in the first section and the aqueduct section is the largest.The flow velocity along the channel is affected by the channel section form and channel trend,which is not uniform change and will appear larger value in the aqueduct.(5)Under the accident condition of water conveyance system,overflow mainly occurs in the front pool of pumping station.The stronger the water storage capacity of the channel itself,the longer the channel overflow occurs.In the channel form,the larger the proportion of trapezoidal channel length with large slope coefficient,the stronger the channel water storage capacity,and the longer the accident overflow time;The backwater wave in the channel propagates from the front pool of the pumping station to the upstream,and the water depth of each section does not change significantly before the backwater wave reaches.