Grand Terrace Focused Area Master Plan Update

Project Description

Client: Lewis Management Corporation
Location: Grand Terrace, CA

Q3 Consulting, a PROACTIVE company, provided engineering services to update the “Pico” area of the City’s master plan of drainage. The City’s draft master plan update was never completed and lacked the necessary information for the required storm drain sizes associated with new development projects. The update for the Pico area included an advanced hydrology/hydraulic SWMM model that used a combination of 2-d surface flow analysis with a 1-d subsurface (storm drain) analysis. Due to the steep terrain, and gridded street network, a rain-on-grid approach was used for the developed urban areas to more accurately determine the stormwater runoff patterns. The rational method and unit hydrograph hydrology for the hillslopes tributary to the urban areas were prepared in accordance with San Bernardino County hydrology methods and incorporated into the advanced models.

The update included the evaluation of the existing watershed conditions to identify the deficiencies and flood prone areas. These areas were confirmed through discussions with City staff and review of historic flooding documentation. Q3 identified a set of potential alternatives and evaluated the effectiveness in the hydrology/hydraulic model. The results of the alternatives analysis runs were used to determine the most cost-effective solutions for the deficient areas. Alignments and facilities sizes were prepared for the recommended storm drain systems.