Effect Analysis of Increasing Throwing Strength and Change Law of Characteristic Indexes under River Closure by Vertical Blocking

During process of river closure in mountain areas，combination of multiple adverse factors would lead to greater closure difficulties.Especially，scouring of riverbed near closure gap and dike collapse can have a negative effect on safety of dike.Model test was carried out to study if increasing throwing intensity could reduce difficulty of colure.Firstly，time effect and space effect of rising throwing intensity were analyzed，and then hydraulic index and scouring law caused increase and loss ratio variation law were also studied.Research results showed that increase of throwing intensity had relatively significant effect on drop of closure gap，but less on average flow velocity in closure gap.During period of using large stone throwing，time and space effects of increasing intensity of throwing were gradually significant，and drop and loss were significantly reduced.In difficult period of river closure，effect of increasing casting strength on scour depth was relatively weak，but it could reduce quantity and times of berm collapse，and then speed up rate of berm closure.Finally，by dimensional analysis method，a formula for calculating loss rate of riprap grain based on throwing intensity and hydraulic characteristics was obtained.Research results could enrich engineering measures to reduce difficulty of river closure，and provide technical reference for river closure in mountainous areas.