Brule Creek Watershed Site 1A Dam

Challenges

The Brule Creek Watershed Site 1A Dam is a high-hazard dam located approximately 2 miles north of Brule, Nebraska in Keith County.  The dam is owned and operated by the Twin Platte Natural Resources District.

A longitudinal crack on the upstream slope was first observed during an inspection in April 1988 and measured at 7 inches wide, 4 feet long, over 6 feet deep, and about 20 feet upstream from the dam crest.  The crack was not observed during subsequent inspections.  However, multiple holes were observed in this general vicinity in inspections following 2011.

The Natural Resources Conservation Service (NRCS) and RJH identified that a large longitudinal crack along the upstream slope was the primary potential failure mode at the dam.  A secondary potential failure mode was internal erosion into the principal spillway conduit through one of the reinforced concrete pipe steel joints.

Solution

RJH implemented a geotechnical investigation program with a specific focus on understanding the causes and mechanisms of the crack, and to obtain data needed to evaluate repair alternatives.  Based on the geotechnical investigations and subsequent analyses, RJH concluded that the embankment cracking is likely associated with collapse of the alluvial fan deposit beneath the upstream portion of the embankment.

The embankment remediation consisted of overexcavating the crest and downstream portion of the embankment, installing a filter zone, and reconstructing the embankment with a flatter downstream slope.  A toe drain pipe was also installed along the downstream toe to safely collect and convey potential seepage through the dam.

The principal spillway remediation consisted of extending the principal spillway discharge pipe downstream approximately 5 feet, lining the entire discharge pipe with a cured-in-place pipe liner, and installing a concrete impact basin in the discharge channel at the downstream end of the discharge pipe.

RJH advanced the design process from conceptual design through final design.  The National Design, Construction, and Soil Mechanics Center in Fort Worth, Texas approved the final construction documents.  RJH also provided full-time resident engineering services during construction.