Innovative Techniques Improve Safety at Lake Ponca Dam Spillway

The Lake Ponca Dam Spillway project was recognized with an Honor Award from ACEC Oklahoma.

About the Project

When a 2017 annual inspection identified worsening deterioration of the Lake Ponca Dam spillway, the City of Lake Ponca undertook a specific investigation of the concrete spillway. Investigators identified needed repairs, including replacing the spillway within two years.

Constructed in 1935 and modified in 1943, Lake Ponca defines the City’s northwest boundary and provides residents and visitors with opportunities to enjoy boating, swimming, fishing, hiking, camping and family picnics. Once the City’s primary source of drinking water, Lake Ponca is now becoming the City’s recreation center. Keeping the lake open as the spillway underwent rehabilitation exemplifies Lake Ponca’s commitment to residents and visitors for their uninterrupted enjoyment of this City asset.

Lake Ponca Dam is an earth-fill dam categorized as high-hazard due to habitable structures downstream. This rehabilitation and improvement project achieved Ponca City’s goal to repair and design improvements to the Lake Ponca spillway. The project enabled continued enjoyment of this municipal lake, furthering the vision of Lake Ponca as the City’s recreation center.

The Lake Ponca Dam Spillway Improvements project exemplifies an intentional, systematic approach to safety, users’ needs, and cost-effective solutions, allowing for continued use even during flood events.

With one change order for unanticipated ground conditions (due to lack of as-built information), design and repair were completed for $2 million by May 31, 2020, on time and within budget.

Complexity/Innovative Applications of New or Existing Techniques

While this project presents as a simple spillway improvement, the specific components of those improvements and their execution speak to the team’s attention to quality solutions and fulfilling the City’s commitment to lake access throughout the project.

The main tasks of this project were:

  • Installation of a phased, temporary cofferdam and flood bypass system so the lake could remain full and open to recreation during construction, and still be able to pass flood flows up to the 25-year storm event
  • Demolition and removal of the existing weathered concrete overlay on the crest section, approximately 19 ft. long and 245 ft. wide
  • Installation of rock anchors to resist uplift force during flood loading and improve structural integrity of the spillway crest
  • Construction of a reinforced concrete wall against the upstream side of the spillway’s vertical face to provide long-term protection
  • As a final step, a new reinforced concrete section was constructed and tied into the existing spillway walls and chute

The construction had two phases: Phase I repaired the western half of the spillway crest and Phase II addressed the eastern half. One half of this emergency structure remained in service throughout the entire process.

Additionally, design and installation of a temporary cofferdam with active dewatering and bypass system avoided lake lowering so that recreational activities were not affected during construction.

Successful Project Completion

Lake Ponca is the heart of Ponca City. These spillway improvements enable the City to continue and expand that role. Throughout planning, design and construction, this project accommodated current lake activities while significantly extending spillway life. Fishing, kayaking, boating, swimming and simply relaxing along the shore continue as fundamental family and community activities.

Lake Ponca has gained new significance as it offers a powerful outlet for families to navigate the impacts and uncertainties of COVID on family life. The lake is one of those City assets relied upon by many City residents, who assume Lake Ponca will be there for their enjoyment and as a refuge from daily stress. Thanks to this project, that is a safe assumption.