Hydraulic Model Study of the Fuse Plug Spillway at Hagneck Canal, Switzerland

The importance of fuse plugs for spillways along embankments and levees has become very important in flood management. The present case study summarizes a series of laboratory tests conducted at the Laboratory of Hydraulics, Hydrology, and Glaciology, ETH Zurich, to examine the feasibility of a fuse plug spillway along the River Aare at the Hagneck Canal. This fuse plug will prevent uncontrolled overtopping of the existing levees for extreme flood scenarios and discharge the surplus water into a destined flood plain. The fuse plug is 300 m long and 1.2 m high, and should provide a spillway discharge of approximately $300{\mathrm{m}}^3/\mathrm{s}$. Two fuse plug designs were tested at both laboratory and prototype scales and analyzed in detail regarding the breach development. Design A, with an inclined clay core, was successfully adopted from a previous study. Design B consisted of a nearly homogenous sand body. Both designs are sufficiently impermeable to prevent seepage failure for water levels below the trigger water level. Both designs erode rapidly once they are overtopped. The fuse plug with the inclined clay core erodes progressively due to undercutting and collapse of the core; the homogenous sand body breaches continuously. The fuse plug Design B with homogeneous sand body was finally chosen for the Hagneck Canal spillway, primarily because of its simple structure and ease in constructional effort.