Metro Hub Reservoir

WestLand provided a design to the Metropolitan Domestic Water Improvement District for their HUB Reservoir and Booster site.  The existing site which is located in a high end development on the northeast side of Tucson consisted of two existing reservoirs (186,000 and 250,000 gallons) and a booster station that served the remote service area.  The existing site is set into the surrounding area with a retaining wall that is as high as 25 feet. In addition to the need to remove the smaller reservoir and replace it with a 900,000+ reservoir for system storage, an interconnect between Metro Water and Tucson Water was designed to provide back up supply to the system.  As part of the reservoir design, a ringwall for the tank which was also required to be a retaining wall for part of the span was designed to help fit the tank in this difficult site. Part of the design challenges was to build a large reservoir inside of an existing site with retaining walls on two sides as well as rock below the surface.  A solution to working so close to an existing retaining wall was to complete an analysis of the soils and the current wall configuration and then develop a specification for what can be excavated. In the area where the new tank ringwall footer was getting close to the existing retaining wall, the Contractor was only allowed to expose a set length and had to backfill it every day to avoid any open trenches in that vicinity.  This approached worked and the ringwall and tank were built without any issue. After relocation of security systems, drainage improvements and new paved access, Metro was provided with a reservoir providing them with 5 times the storage of the old one and a back up connection for system reliability.