Flow Movement Laws Of Compound Trapezoidal Diversion Canal And Siltation Rate Of Canal Before Sluice During Gate Closing

Damless canal work is widely applied for its simple configuration and the low cost.There are systemic theories on characteristic of rectangular diversion canal. To analyze flow movement laws of compound trapezoidal diversion canal and suspended sediment deposition rate of canal before sluice, flow field of the open channel and area near the entrance were observed, while siltation mechanism and deposition rate of suspended load of canal before sluice during the gate closing were analyzed by fix bed model tests at typical diversion conditions, according to the scheduling intake pumping station in South Asia. The main research results are as follows:1. At the condition of equal diversion discharge, intense turbulence and mixture is taken place in area near the entrance, whether at flood, medium or low flow rate, three-dimensional flow field of compound trapezoidal diversion canal. The velocity gradient reaches to the maximum at the interface. Water near the entrance presents conspicuous 3D characteristic.Along the water depth, flow velocity distribution shows relatively uniform characteristic,even velocity of surface layer is less than that of bottom layer.2. About intake head of compound trapezoidal channel, the phenomenon of plane circulation is outstanding. Width of water diffusion into the channel transversely contracts,while hydrodynamic axis focuses on the right bank. By the turbulent mixture in front of the open channel, flow pattern gradually transits to one-dimensional conventional motion along the channel, and the extent of one-dimensional hydraulic features is inversely proportion to the depth of canal.3. Entrance of trumpet-shaped cross section, which connects compound trapezoidal canal to the main stream, results in development of sorts of secondary circulation. Owing to much lower speed of diversion canal than the main stream, water in front of channel shows circulation of closed channel in cecum branch in the main, secondary circulation of different sizes as deputy. The flow field of intake head is similar to that of closed channel in cecum.Besides, there is a positive correlation between the intensity of circulating and incoming flow rate.4. At different conditions of combination of all levels of stage discharge and incoming sediment, suspended sediment carrying capacity is quite low for small velocity of the open channel, and suspended load movement presents typical supersaturated sediment transport.Besides, suspended load concentration decreases along the channel, causing serious deposition.5. In view of extremely adverse conditions in actual operation, it is studied that sediment deposition of canal before sluice during the gate closing. Referring to research thoughts on movements of sediment carrying capacity of circulating zone in closed channel, an estimation method of accretion rate of canal before sluice was proposed with Zamlion E.A. formula of sediment carrying capacity for channel.