PLT - Design of a New Riparian Conduit through an Active Embankment Using Innovative Techniques to Mitigate Risks

The Deloraine Dam, owned by Manitoba Transportation and Infrastructure (MTI), was constructed in 1962 by the Prairie Farm Rehabilitation Administration (PFRA). The dam is located approximately 10 kilometers (6 miles) southeast of the community of Deloraine in southwestern Manitoba. The facility consists of a 300 m long earthfill embankment dam with a riparian outlet structure, and an adjacent fixed crest concrete ogee spillway that transitions to a timber chute and ends with a 9 m vertical drop to a plunge pool. The riparian outlet structure consists of a 610 mm (24 in) diameter corrugated metal pipe culvert that runs through the base of the embankment structure and outlets to a concrete outfall structure. The gate of the riparian structure has been set in the closed position for at least 10 years. Attempts to raise the gate found that it was inoperable.
There are near-term plans to replace the existing spillway structure. As a first phase, the Owner has completed the detailed design for a new riparian conduit to be located through the Right Abutment of the dam. The new 1650 mm diameter riparian outlet has been designed to be capable of passing the construction design flood (CDF) of 14 m3/s.

During the detailed design phase, several risks were identified including deep, open trench excavations with high groundwater levels, long-term piping risks, and open channel flow at the downstream toe of the embankment. A trenchless option to construct the new riparian outlet structure was needed to avoid adverse soil and groundwater conditions along with dam safety risks otherwise associated with an open trench excavation. This presentation presents details of the risks associated with the installation of a new riparian conduit through an active embankment dam and the innovative trenchless technologies and design methods that were considered to mitigate the risks.