LINCOLN, Neb. - The U.S. Army Corps of Engineers, Omaha District, Dam Safety Section performed the first of two periodic tributary dam inspections scheduled for 2025 beginning with the Branched Oak Dam located northwest of Lincoln, Nebraska June 2.
A periodic inspection of the dam is conducted every five years while a periodic assessment is conducted every 10 years. The inspection and assessment are conducted to identify potential defects and to ensure the dam is functioning as designed.
“We look for any issues that might affect the performance of the dam, especially during extreme conditions where the reservoir rises above the normal pool,” said Matthew Borys, who is the Omaha District dam safety engineer for the 10 Salt Creek dams.
The periodic assessment is led by the Institute for Water Resources, Risk Management Center, while the Omaha District is the technical lead. The inspection team includes geotechnical, structural and hydrologic engineers as well as an economist who analyzes the consequences of a dam breach and the potential effects to downstream communities in the event of a flood.
The team walked the entire length of the spillway, abutments and embankments looking for any deficiencies including cracking, active erosion or settlement, depressions where erosion could start, and unwanted vegetation. A structural engineer also inspected other features of the dam including the intake structure and outlet works conduit where they looked for deteriorating concrete.
Following the inspection, a week-long potential failure mode analysis was conducted to review inspection observations and existing data to brainstorm potential failure modes for the project.
According to Borys, the most common failure modes identified for the system of Salt Creek dams are overtopping of the dam that may result in a dam breach, followed by spillway erosion that may cause a breach through the spillway, and finally, concentrated leak erosion along the conduit which is an internal seepage failure mode.
“We are brainstorming any possible ways the dam could have an unintentional release of water,” Borys said. “We discuss the existing conditions of the outlet works, consisting of the intake, conduit, and stilling basin, along with the embankment, foundation, and abutments and how these features will perform at various pool elevations.”
Branched Oak Dam was built in 1967 by the U.S. Army Corps of Engineers as part of the Salt Valley Lakes flood control project. It captures water from Oak Creek, a tributary of Salt Creek, during high runoff events to help control flooding. It is one of 10 Salt Creek dams that work together to help reduce flood risk for the city of Lincoln and surrounding communities.
The 1,800-acre Branched Oak Lake sits behind the dam and is part of the Branched Oak State Recreation Area managed by the state of Nebraska’s Game and Parks Commission. The 5,595-acre recreational area provides fish and wildlife habitat, water resource benefits, and recreational opportunities to include fishing, boating and camping.
Borys emphasized that while there hasn’t been any significant flooding from Salt Creek in recent years, dams cannot prevent all floods. Residents who live near a dam or river should have a plan in place for a flood event. He also wants to remind recreators to avoid restricted areas and to use life jackets while recreating on lakes.
To learn more about Branched Oak Dam or to view flood inundation maps for other dams, visit the National Inventory of Dams at https://nid.sec.usace.army.mil/#/.