Forest Park Low Tank

Portland Water Bureau/Murray Smith and Associates

Portland, Oregon

Forest Park Low Tank

Water is the life blood of any city. While no city can operate without water, treatment systems are not always aesthetically pleasing. This project addressed that conundrum by rendering form invisible. The Forest Park Low Tank was embedded into the sloping hillside site to preserve the natural character of the area and leave unfettered views. While this preserved the aesthetics, it presented a number of engineering challenges that had to be overcome. The American Council of Engineering Companies (ACEC) of Oregon awarded Hart Crowser a Grand Award for the Forest Park Low Tank for overcoming these challenges.

Hart Crowser led the geotechnical design for this 2-million-gallon AWWA D110 Type 1 water storage tank. Hart Crowser completed explorations of the hillside site to depths of 100 feet. Rather than encountering hard volcanic rock as expected, volcanic cinder (scoria) extended the full depth explored. This unexpected material complicated support of a tank of this size. Design and construction were further complicated by an extremely constrained site that left little room to work. Hart Crowser completed detailed analyses and testing of the scoria soils, so economical recommendations could be made to support the tank foundations and membrane slab on these soils. The firm also made recommendations for construction excavation and shoring, retaining walls, and stormwater infiltration.

During construction, the project team worked closely with contractors and the Portland Water Bureau to confirm the foundation soils were properly prepared, evaluate and develop performance criteria for shoring wall submittals, and design retaining walls to stabilize landsliding on the site. The project team was able to meet the project requirements and complete the engineering design and construction on time and under budget for the spring opening.