The cost of protection works at circular pipe outlets can be reduced using a suitable appurtenance to dissipate the excess energy in an efficient manor within a shorter length of the stilling basin. Some of the energy dissipators used for pipe oulets are the USBR type VI stilling basin, hydraulic jump type stilling basin and Garde's stilling basin. The stilling developed in these tests is an impact-type energy dissipator, contained in a relatively small box-like structure, which requires no tail water for successful performance. The model used in this test has a pipe outlet (5cm in diameter), Froude number varied from 1.5 to 3.7, with different type of bed material. The results demonstrate that the location of end sill at ten times a pipe diameter from pipe outlet gives minimum scour hole depth. Also, the results show that the decrease of median grain size by 75% will cause the scour hole to be deeper by 65%. |
