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LAWTON – The Lake Ellsworth spillway repair project will be readvertised for bids, and a project to repair or replace Gondola Dam below Lake Lawtonka is being evaluated.
Only one bid was received on the project to reconstruct the Lake Ellsworth spillway, and it was rejected because it came in 155% higher than the engineer’s estimate.
Shimmick bid $61,585,000 for the job. The engineer’s estimate was $24,150,175.
The repair project cost will be financed with a $925,251 high-hazard dam grant from the Federal Emergency Management Agency, $11 million in American Rescue Plan Act grants from the Biden administration, and up to $8 million in city matching funds, records reflect.
Lake Ellsworth’s concrete spillway was damaged after heavy rains in 2015 forced the city to open the floodgates to release runoff water that otherwise would have topped the dam.
City officials knew from the outset that heavy runoff damaged concrete panels in the spillway. However, further analysis revealed other problems, such as empty spaces beneath the spillway that were identified after geotechnical and engineering analyses. The spillway “floated” during the water releases, Public Utilities Director Rusty Whisenhunt told Southwest Ledger. Rehabilitation measures, the Oklahoma Water Resources Board reported, will include adding more robust rock anchors, additional drains beneath the apron, sealing cracks and casting a reinforced concrete slab over the existing apron, repairing concrete on the 363-foot-long spillway, retrofitting the spillway retaining walls, adding chute blocks on the spillway stilling basin, and adding riprap along the east side of the spillway.
The Ellsworth Dam is labeled a high-hazard structure because more than 5,200 people downstream would be atrisk if the dam failed, the OWRB explained.
According to the state agency, the dam is a combination earth fill and concrete structure 3,900 feet long, 96 feet high, and 30 feet wide at the top. It has 15 gates, each 10 feet high and 20 feet wide.
Lake Ellsworth provides approximately 20% of Lawton’s water, Lake Waurika about 10%, and Lake Lawtonka is the city’s primary source of fresh water, Whisenhunt said.
Lake Ellsworth is northeast of Lawton, between Elgin and Apache, and straddles the Comanche/ Caddo county line. It was built by the City 1.66” X 5.7” of Lawton in 1962 as a source of drinking water and for recreation. The reservoir, an impoundment of East Cache Creek, encompasses 5,100 surface acres and has 53.5 miles of shoreline.
• City-owned Gondola Dam is downstream of Lake Lawtonka and is used to create a small tilling pool.
The dam is approximately 100 years old and, “There is no as-built information, maintenance records, or previous inspection records” for the dam,” Whisenhunt informed the city council.
The Gondola Dam’s overflow spillway has been damaged and requires rehabilitation,” Whisenhunt said.
The scope of services to be performed by Jacobs Engineering Group includes work to develop a high-level condition summary of the dam, feasibility assessment for rehabilitation or replacing the existing dam at the same location, concept development for the recommended alternative, and a cost estimate.
“The intent of this dam evaluation is to assist the City of Lawton in making an informed decision to either retrofit the existing dam or replace it,” Whisenhunt wrote.
The total project cost is estimated at $2.5 million to $2.8 million, he said. Two American Rescue Plan state designated grants were awarded for this project, records indicate.
1.5” X 6.2”