Study On The Influence Of Daily Regulation Of Power Stations On Navigation Conditions At River Junctions

In recent years,with the rapid development of river canalisation,the daily regulation of large power stations has led to the increasingly significant characteristics of nonconstant flow,and the discharge of water from power stations has transformed the downstream river channel from a natural channel into a non-constant-flow channel with high and low water levels,which has had a certain impact on the conditions of navigable water flow at the confluence of the downstream channel,the safety of port terminals and the evolution of the channel topography.The flow and topographic conditions in the river confluence area are more complex than those of a normal river,with the tributaries topping each other as they swell into the main stream,causing high water levels and reduced flow velocities,and affecting both the longitudinal and lateral specific drops of the river surface.Therefore,this study carries out the propagation law of non-constant flow in the confluence area under the influence of daily regulation of the power station.By means of a three-dimensional numerical model,the flow combination of non-constant flow in the main stream and constant flow in the tributaries is used to analyse in detail the effects of non-constant flow period,flow variation,angle of confluence of the main stream and tributaries and the magnitude of tributary flow on the surface line along the centre of the asymmetric straight confluence area,surface variation,centreline specific drop,flow velocity distribution and The characteristics of longitudinal flow velocity changes in the separation zone.On the basis of this,the current conditions of navigable water flow at the confluence under the typical flow process of daily regulation of the Hegemun are combined and optimized working conditions are given.This study reveals the hydrodynamic processes at the confluence of the dry and tributary streams affected by the daily regulation of the power station,and provides a scientific basis for the study of the propagation of non-constant flow in the confluence zone of the dry and tributary streams and its impact on the navigable flow conditions,resulting in the following conclusions:(1)Under the conditions of non-constant incoming flow in the main stream and constant flow in the tributaries,the water flow in the confluence and the tributary section upstream of the confluence both show similar and obvious non-constant flow characteristics.(2)The effect of the non-constant flow cycle on the water level at the confluence is different in the rising and receding stages;the difference in water level between the upstream and downstream reaches of the confluence decreases with the increase of the non-volatile cycle.The area of the crescent-shaped high-velocity flow area is affected differently by the non-constant flow cycle in the rising and receding water stages.(3)The change in water level in the confluence area increases with the increase in flow variability,with the maximum water level variability occurring near the peak of the flood.The ratio drop at the confluence increases with increasing non-constant flow variability.Both the longitudinal flow velocity in the separation zone and the flow velocity gradient between different water layers increase with increasing flow variability.The area of the crescent-shaped high-velocity flow area is affected differently by flow variation in the upstream and downstream phases.(4)Upstream and downstream water level changes are influenced by the confluence angle,which is different in the upstream and downstream stages;the water level variation at the confluence decreases with the increase of the confluence angle;the specific drop of the river channel increases with the increase of the confluence angle;the area of the high velocity flow area becomes narrower and longer with the increase of the confluence angle.(5)The overall water level at the confluence of dry and tributary streams and the difference between the upstream and downstream water levels,the specific drop of the water surface at the confluence and the surface of the high-speed water flow area in the separation area all increase with the increase of the tributary flow,and the size of the tributary flow affects the time of the maximum water level;the area of the high-speed water flow area changes in the opposite trend during the rising and receding stages;the variation of the water level in the confluence area decreases with the increase of the tributary flow.(6)The water level variation in the confluence area is mainly influenced by the multiplicative variation of the main channel flow and the tributary flow;it increases with the increase of both,in addition,the water level variation at each measurement point decreases with the extension of the period,and the decrease is more significant in the short period.The correlation between the angle of confluence on the water level variation at each measurement point is smaller,but still shows a general trend of weakening water level fluctuation as the angle of confluence increases.(7)The water surface drop in the confluence area shows a significant linear correlation with flow variability,confluence angle and tributary flow,and increases with each factor.(8)Based on the changes in the hydrological runoff of the Jinsha and Min rivers and the dispatching operation mode of the power station,an analysis and calculation of the conditions of navigable water flow under typical daily regulation conditions at the confluence of the Hegemun River was carried out.The daily and maximum hourly water level variation at the confluence is reduced by the optimal regulation process of increasing the base discharge flow and reducing the peak flow.