RIP RAP SCOUR BELOW PIPE OUTLETS

Abstract

Most of the studies on the riprap scour below pipe outlet have been done using the discharge, riprap size, tailwater depth and drop height as variable in prediction of scour hole dimensions. In the present study an experimental program was undertaken to determine how pipe outlet diameter affected the scour hole geometry. The discharge, drop height and tailwater depth were also used as variable. A 'total number of 60 experiments were performed. Three pipe outlets of different diameters were used. A set of 20 experiments were done on each pipe outlet. The diameters of pipel, pipe2 and pipe 3 were 1.275 cm, 2.55 cm and 5.1 cm respectively. The d50 of riprap used was 4.6 mm and a- = 1.218. The scour hole dimensions were recorded for tailwater depth of 1,2,3, and 4 times the pipe outlet diameter. The scour hole dimensions were recorded after 30, 60, 180, 300, 600, 1200, 1800, 3600, 7200 and 10800 seconds from the beginning of the run. The relationships were developed for the estimation of scour hole dimensions. These relationships were also verified for the data of other investigators. The agreement was good between observed and computed values. The relationships of other investigators were also tested using present study data and data of other investigators. The need for further study on nonuniformity of riprap was also felt.