Apex Engineering Group was hired by the North Dakota Game and Fish Department to evaluate Camel Butte Dam, located in western North Dakota. The Camel Butte Dam embankment also serves as the corridor for Interstate 94. Previous studies and inspections have identified numerous deficiencies, including outlet pipe conditions, sinkholes, and vegetation overgrowth. Apex authored a preliminary engineering report that outlined the original dam design, watershed and site conditions, historical improvements, proposed alternatives to address the issues, maintenance requirements to extend the dam’s life, and construction cost estimates.

Background

The dam was designed by the North Dakota Department of Transportation with the assistance of the North Dakota Department of Water Resources. Construction was completed as part of the I-94 construction in the late 1960s, as the dam embankment consists of I-94 eastbound and westbound lanes. The purpose of the dam was to impound water for fish and wildlife habitat and to provide recreational facilities to the public.

Geotechnical Investigation

Terracon served as a subconsultant to conduct a geotechnical analysis of the dam’s downstream face. These services included subsurface soil conditions, groundwater conditions, slope stability, seepage analysis, and conceptual level alternatives to address existing issues. This information was compiled into a Geotechnical Engineering Report.

Results of the geotechnical report and inspections:

• The existing toe-drain system is not functioning as designed
• The existing toe-drain system is deteriorating and collapsing in areas
• Sinkholes were present along the 30” CMP drawn down pipe from Interstate 94
• Excess erosion at the outfalls.
• Excess vegetation growth on the face and toe of the dam.

Proposed Improvement

Camel Butte Dam is a nearly 60-year-old rolled-earth dam with aged infrastructure.

1. The principal spillway has been lined twice, and seepage near the toe of the dam has been noted since shortly after the construction of the dam.
2. A geotechnical reconnaissance showed excessive seepage present at the downstream toe of the dam. It is recommended to install a new filtered exit for the dam to reduce seepage and lower the piezometric surface at the dam toe.
3. Sinkholes along the NDDOT drawdown pipe have been noted in past inspections and have worsened over time. It is recommended to replace the pipe.
4. It is recommended to plug the 12” low-level outlet.

5. It is recommended to address the minor deficiencies outlined in the inspection reports, which include tree removal, sediment removal, and inlet apron repairs.