For Garcia and Associates, San Francisco District Army Corps of Engineers, and Santa Clara Valley Water District

Questa provided assistance  in the final design of the Llagas Creek Flood Control Project channel geometry. The conceptual channel design included an in-channel riparian bench at the elevation of the 2-year flood level, as established by hydraulic modeling. The mitigation plan for the reach  required that the riparian bench plantings meet certain  height and canopy cover targets, and that the final plan demonstrate a self-sustaining established riparian community. Since the channel bank materials are predominantly non-cohesive sandy soils, stable channel design and erosion protection were important design elements. The proper elevation of the bench, with respect to creek peak flows, channel forming and flushing flows, summer base flow, and depth to first encountered groundwater, was an important consideration in ensuring project success.  Questa's work scope included completion of soils, hydrologic, and geomorphic studies along the creek.  The final report made recommendations regarding the elevation and width of the terrace, planting zones, and bank stabilization needs, considering channel hydraulics, stream-groundwater interactions, and soil:soil moisture conditions with respect to native plant materials' edaphic requirements.