Laboratory Study Of Scour In Stone Beds Downstream Triangular Plan Form Weirs

Abstract

In this research, the phenomenon of scour downstream triangular plan form weirs on stone beds were studied experiment ally. The study deals with the measurement of maximum scour depth and the length of scour hole downstream the weir. The shape of scour hole was also studied. One hundred and eight runs were conducted in a laboratory channel. Three sizes of crushed stones of diameters (0.7142, 1.111, 1.5875)cm were used. Four weir-heights (10,15,20,25)cm were tested for all sizes of crushed stones. The effect of tailwater depth on scour depth was studied for all weir-heights except 10 cm because submergence appeared, while, total number of tailwater depths tested were thirty six. Experimental results of this study showed direct relation between scour depth and scour hole length with the densimetric particle Froude number, but the scour depth and scour hole length had inverse relations with both relative tailwater depth and relative drop. Two empirical equations were obtained; the first for the estimation of relative scour depth and the second for the estimation of relative length of scour hole. A simple design method was presented to obtain the length and thickness of rock protection downstream triangular plan form weirs depending on field data and size of available rocks. Key words: scour , stone beds , triangular weirs.