Brisbane unveils three engineering options to shield lagoon from rising tides; residents press dredging and contamination concerns

Brisbane City on Thursday presented a Caltrans-funded study of adaptation options for the Brisbane Lagoon, outlining three concept alternatives — a self-regulating tide gate, raising the lagoon edge, and a pump station — and fielding extended public questions about dredging, contamination and habitat impacts.

Oz, the city’s public works director and city engineer, opened the meeting and introduced the consulting team before turning the presentation over to Robin Lee. Lee described the Brisbane Lagoon Sea Level Rise Adaptation Plan as a concept-level study intended to identify engineering approaches and to position the city to seek construction funding.

The technical team ran combined tide-and-runoff scenarios in a two-dimensional model using LIDAR topography. "The lagoon water surface elevation is really primarily driven by the tide," Robin Lee said, summarizing the model results. Presenters told the room that the model projects roughly a one-foot increase in lagoon elevation by mid-century under the study assumptions and that some end-of-century combinations of extreme tides and sea-level…