EFFECT OF DIFFERENT TRAPPING PATTERN OF FLOATING DEBRIS AT LARGE FLOOD EVENT ON THE CHANGE IN RESISTANCE

Abstract

 In recent years, flood damage has frequently occurred due to the increase in memorial heavy rainfall. At a large food event, resistance by vegetation is greatly changed by trapping floating debris that is produced through the washout phenomenon in upstream. This study classified the trap pattern into three, and examind the resistance characteristics by modeling a trapped material and a forest using real tree branches. I-type trap that debris is only trapped in front of forest can increase the water depth locally. U-type trap that each tree in the forest traps debris can increase the whole water depth and the influence is large. Doubling the thickness of the trap object, the drag coefficient increases around 1.2 to 2.1 times for the I type and 1.3 to 1.6 times for the U type. This is because the flow velocity in the trap object is assumed constant, however it is not constant and decreases while passing, and the resistance from rear side of the object decreases because of the shielding effect.