Author(s): Adriano Lais; Alice Schroeder; Peter Billeter; Yves Keller; Adrian Stucki; Robert Boes

Linked Author(s): Robert Boes

Keywords: Energy dissipation chamber; slotted-grating drop-type dissipator; diversion tunnel; culvert; air-water two-phase flow; physical model

Abstract: The flood diversion tunnel Gattikon-Thalwil is designed to protect the city of Zurich from extreme flood events by diverting the flood peaks from the Sihl River to Lake Zurich in open channel flow. Due to its location in an urban agglomeration and restricted site conditions in Thalwil, a special solution had to be found for the outlet structure to ensure energy dissipation in the limited available space. The centerpiece of the outlet structure consists of a drop-type energy dissipation chamber. Downstream of the energy dissipation chamber follows a culvert that crosses under a road and discharges peak flows at moderate velocities into Lake Zurich below the lake level. The challenge for the drop-type dissipation chamber is to fix the hydraulic jump above the lake level despite low supporting forces and at the same time to minimize air entrainment into the pressurized culvert flow. Using physical model tests, a hydraulic optimization of the outlet structure was carried out and a special solution for the structure was developed. The objectives of stabilizing the hydraulic jump in the chamber and minimizing air entrainment into the culvert were achieved by four box beams installed at the drop which are completely submerged thanks to an additional backwater effect caused by a series of rectangular-shaped bluff bars in the culvert. The findings of this case study provide clues for future designs of drop-type dissipation chambers and outlet structures.

DOI: https://doi.org/10.3929/ethz-b-000675921

Year: 2024