Overview
Mormon Flat Dam is a concrete thin arch dam (380 feet long and 224 feet high) on the Salt River. Built in 1925, it is listed on the National Register of Historic Places and forms the ten-mile-long Canyon Lake. There are two hydroelectric units at the dam (Units 1 and 2). Unit 2 is a pump-back unit added to the project in the 70’s. After a previous dive inspection noted extensive damage to the draft tube and trashrack slots, the Salt River Project (SRP) quickly mobilized to work towards repairing the work. Extensive damage to the draft tube trashracks and slots was observed during a dive inspection.

Scope of Work
Ballard teamed with an engineer on the design-build contract to develop a system to de-water the work area and repair the system in the dry. Project objectives included: repair of the trashrack guide slots; replacement of the trashrack guide extensions; and re-establishment of the trashrack hold-down system. The work had a critical path design and construction schedule based on a limited, 17-day outage of the unit and the severity of the damage to the system. Ballard’s services included installing a new cofferdam bulkhead in order to de-water the draft tube and remove old trashrack slot guides to replace with new slot guides.

Innovative Solutions
Ballard transported and lifted a 12,000-pound bulkhead into place. To install the bulkhead safely and successfully, divers removed obstructions to facilitate the placement of the bulkhead.

Results
Divers removed, modified with new wedges, broken anchors with new epoxy anchors, and reinstalled the 15,000-pound trashrack.