Grand Terrace receives storm drain master plan estimating $11 million and flags county constraints

Tom Ryan, a consultant with Q3 (speaker 12), told the Grand Terrace City Council on June 23 that a yearlong storm drain master plan used advanced 1D/2D hydrologic modeling to map flood-prone areas and propose regional improvements. The study produced a planning-level cost estimate of about $11,000,000 for proposed improvements and applied a 58% contingency to unit prices to reflect permitting, construction management, and likely overlay and rehabilitation costs. "We identify a 58% contingency. Actual cost may come in cheaper depending on when the construction is," Ryan said.

The presentation emphasized that the master plan is a funding and planning document, not a final construction design. Ryan said the modeling matched known flooded locations and allowed the team to see where surface flow would "jump" out of streets under a 100-year storm scenario. He also described coordination with an adjacent private "gateway" project whose developer has designed and agreed to build regional drainage infrastructure the city can extend. "Phase 1 improvements are already underway in final design," Ryan said, and the master plan recommends prioritizing those extensions, Pico Street storm-drain upgrades and Van Buren extensions before more localized maintenance items.

Council members raised questions about the plan's high contingency and whether county authorities would accept the consultants' advanced modeling approach. Councilmember (speaker 7) pressed whether San Bernardino County would agree to the 10-foot grid methodology and whether the $11 million estimate excluded street reconstruction and curb-to-curb work. Ryan replied that the contingency accounts for junctions, manholes, inlets, permitting and construction management and that unit prices were padded to reflect asphalt overlay and rehabilitation. He said the city would receive readable model files and accompanying pipe profiles to support future final-design civil engineering work.

Ryan told council the major constraints are county-owned storm drains and the Riverside and Gage canals, which limit where the city can add or redirect drainage without costly crossings or upsizing county facilities. He said the plan purposely avoids touching county facilities where possible and instead proposes parallel systems or localized solutions to limit impacts on county-owned infrastructure. "As long as you don't touch a county facility, you don't have to use their criteria," he said. The plan also identifies points where existing infrastructure ties into Southern California Edison (SCE) facilities for downstream discharge.

Council accepted the report by consensus for the purpose of pursuing funding and final design. The consultants said they would provide model files to the city so future engineers can convert model outputs into conventional pipe and profile drawings needed for permitting and construction. Next steps include detailed design, grant-seeking for the priority projects and coordination with county and regional partners.