Owned and operated by the Water Security Agency, Gardiner Dam is the third largest embankment dam in Canada and is located on the South Saskatchewan River. Completed in 1967, Gardiner Dam is 64 m high and approximately 5 km long one and is one of two dams that impound Lake Diefenbaker. The Dam is equipped with a service spillway and five low-level outlets: Tunnels 1 – 3 serve as power penstocks operated by SaskPower; Tunnel 4 is decommissioned and is available for future expansion needs; and Tunnel 5 is used as a low-level outlet to augment riparian flows as needed.

Tunnel 5, along with Tunnels 1-4, was used in the 1960s to divert South Saskatchewan River flows during construction of the Dam. Damages to the stilling basin likely occurred during those diversion operations. Since then, the tunnel has been rarely operated. The Water Security Agency is currently planning to repair the structure so that it can be used as intended to provide riparian flows when the other low-level outlet tunnels are taken out of service for upgrades.

NHC was retained by the Water Security Agency to undertake a computational fluid dynamic (CFD) study to identify likely causes of the observed damages to the Tunnel 5 outlet structure; identify the range of flows for safe operation of Tunnel 5 in its current state; and to recommend remediation measures to enable safe operation of Tunnel 5 at its original maximum design discharge, 527 m3/s.