The Village of Kitkatla, a Gitxaala Nation community of roughly 450 people on Dolphin Island, is reachable only by boat or float plane. Its raw water supply passes through a timber retaining structure that is about a hundred years old and still in service. As structural Engineer of Record, I delivered the structural feasibility scope for its replacement - under barge-only construction logistics and near-absent as-built records.

My Role

Structural Engineer of Record for the retaining structure. Authored the structural scope of the feasibility report: existing-conditions assessment, design criteria, proposed structure, and construction methodology.

The Proposed Structure

  • Reinforced concrete gravity retaining wall, 2 to 3 m retained height
  • Design water levels El. 30.7 to 32.6 m, with 1 m seasonal fluctuation
  • Twinned 200 mm HDPE transmission mains penetrating the wall with waterstops
  • Hydrostatic, earth-pressure, and surcharge loading criteria to CSA A23.3 and NBCC 2020

Construction Method

Trenchless directional drilling was considered and rejected. Open cut was selected to eliminate the risk of draining Kitkatla Lake or undermining the operational hundred-year-old earthen structure.

I defined a five-stage construction sequence that holds the community’s water supply in service throughout the replacement, and flagged the excavation zone-of-influence and setback as the governing construction risk requiring geotechnical analysis.

Designing Without Record Drawings

No original construction drawings exist. I reconstructed a defensible design basis by reconciling what does:

  • 2023-24 inspection reports
  • A 1991 drawing and 1995 record drawings
  • Hydrology data

Two unknowns govern and cannot be closed from paper: the below-grade structure depth (2 m versus 3 m) and the soil-rock foundation interface. I scoped the field survey and geotechnical investigation needed to resolve both before design proceeds.

Cost

Class D opinion of probable cost of approximately $250,000 at 25-30% accuracy, built from first-principles elemental quantities - 33 m³ of 30 MPa concrete, 155 m² of formwork, 2,400 kg of reinforcement - with a 1.75x remote-location factor for barge-only Dolphin Island access and 30% contingency reflecting early project definition. A risk and sensitivity analysis isolated concrete-supply logistics and wall height as the dominant cost drivers.

Delivery

Signed and sealed 2026-03-27, submitted to Indigenous Services Canada 2026-03-31 - on schedule, under budget, in under 40 billable hours, with close coordination maintained with the Gitxaala Nation client and the multidiscipline project team throughout.

Codes and Standards

CSA A23.3, CSA A23.1, NBCC 2020.