Atlantic Rim Dam

Challenges

Atlantic Rim Dam and Reservoir is an off-channel reservoir that provides municipal water for the Town of Rawlins, Wyoming.  The reservoir is impounded by an earthen embankment that is about 2,200 feet long and has a maximum height of about 33 feet.  The embankment was constructed in 1979 and, since its first filling in 1980, has had significant seepage issues.

Items that required remediation included excessive and uncontrolled seepage at the downstream toe, inadequate downstream slope stability, a lack of filter compatibility of toe drain materials, and seepage collars along existing pipe penetrations.  The reservoir was not able to store water because of the excessive seepage. During the past 30 years, multiple repairs were attempted but were relatively unsuccessful.

Solution

RJH performed a site reconnaissance, dam safety inspection, and geotechnical investigations to evaluate the existing compacted clay liner and embankment.  Based on the investigations and analyses, the existing compacted clay liner was likely being compromised by repeated freeze-thaw cycles.  Additionally, the site is on the side of an anticline, which results in locations of high groundwater pressures, which was likely leading to uplift of the liner.

RJH performed seepage and stability analyses to develop a preferred rehabilitation alternative.  The selected concept included a HDPE geomembrane underlain by a geosynthetic clay liner, underlain on the embankment slopes by a filter drain.  A toe drain was installed on the inside of the reservoir and connected to the filter drain to collect both groundwater seepage and seepage through the liner, and reduce uplift pressures.  RJH prepared issued for construction drawings, assisted with bidding, and provided part time technical support during construction to confirm the filter and liner were constructed in conformance with the drawings and specifications.