Dam diversion tunnel and low level outlet facility investigation

July 26, 2017

The right technology and the right team, together with a solid relationship with the client, successfully met the requirement for non-destructive analysis methods of the Broken Bow diversion tunnel and the low level outlet facility investigation, even when unexpected weather threatened the timeline.

The Tulsa District of the U.S. Army Corps of Engineers owns and operates 38 multi-purpose projects, among them the Broken Bow Dam, which includes a diversion tunnel and low level outlet facility. The district’s comprehensive dam safety program supports USACE’s nationwide dam safety program.

In response to concerns regarding Broken Bow’s diversion tunnel and low level output facility, the district wanted to confirm safety and stability to ensure that facility operations could continue effectively without risk to operations staff or to downstream life and property. As an initial step in the risk assessment process, Tulsa District engaged the MH+MH Joint Venture to investigate the tunnel using only non-destructive testing methods to estimate the critical geologic parameters and tunnel performance.

The investigation involved the structural, geological, mechanical and electrical condition and performance of the 44-year-old diversion tunnel and LLOF. Originally, the tunnel was designed to carry flow from the river until completion of the dam, and then be sealed with a concrete plug.

However, in 1967, plans changed to convert the tunnel into an LLOF to meet new USACE requirements. The retrofit was finished by 1974 with the new structure incorporating the LLOF and a slide gate system at the dam’s centerline.

Although the downstream side of the LLOF service gates was regularly inspected, the upstream tunnel and gate structure are 170-ft below water and flooded. As a result, the emergency gates, upstream side of the service gates, stop log structure, and upstream segment of the tunnel had not been inspected since they were constructed. Despite the service gates being regularly exercised during the 1980s and early 1990s, periodic inspection reports listed the LLOF as requiring an increased level of rehabilitation.

READ MORE in The Military Engineer. July-Aug 2017 issue (PDF)