Author(s): Vankayalapati S. Ramarao; Amit Kulhare

Linked Author(s): Amit Kulhare

Keywords: Slotted roller bucket; tailwater level; bucket teeth; apron; ground roller; surface roller; ski jump bucket

Abstract: Slotted roller bucket type energy dissipators are provided for spillways when the tailwater depth is 1.2 times the sequent depth required for the formation of a hydraulic jump. In slotted roller buckets, the dissipation of energy occurs by the lateral spreading of jet passing through bucket slots in addition to the formation of two complementary rollers as in the solid bucket. These are provided for spillways where the downstream river bed is of sound rock. However, when the tailwater levels are not realised during the release of floods over the spillway and surface and ground rollers are not formed, it results in a possible sweep of the flood out of the bucket. Deficient tailwater levels during the initial period of operation of the bucket leading to ski action, generation of high hydrodynamic pressures during roller formation due to very high incoming velocities and occurrence of negative pressures on the bucket teeth, are some of the hydraulic parameters that lead to damage to the slotted roller bucket. Indira Sagar Dam is 653 m long and 92 m in height and was built on the River Narmada in Madhya Pradesh. The main and auxiliary spillway comprises 12 and 8 spans respectively of size each 20 m x 17 m and is designed to dispose of a Probable Maximum Flood of 83,400 m3/s. The energy dissipator provided was original in the form of a slotted roller bucket. The project is in operation from 2004-2005. Discharges of the magnitude 30,000 m3/s were released during the monsoon of 2013 and then it was observed that the entire slotted roller bucket in front of spans 6 to 12 was washed away. The teeth of the roller bucket were overturned and thrown away by the flood waters. Theoretical analysis for actual discharges passed over the spillway from 2006 to 2012 indicated that the roller action was not forming for these conditions and instead ski action was taking place due to deficient tailwater levels. There was also a transition from ski action to roller action for increasing discharges till the tailwater build was realised. In fact, this is the inherent shortcoming of roller bucket type of energy dissipators and damages to the bucket have been reported elsewhere also. In this paper, the authors account for the causes that damaged the slotted roller bucket of Indira Sagar dam, M.P and recommendations suggested for improving the performance of energy dissipation

DOI: https://doi.org/10.26077/8d2a-290f

Year: 2022