Cornerstone provided engineering services for the design of a new box culvert and multiple retaining walls for the Gasser District in the City of Napa. The new structures are part of the Residual Overland Flow project, which provides flooding improvements to Tulocay Creek, a tributary to the Napa River. The culvert consists of a four-cell, precast concrete box culvert and cast-in-place concrete retaining walls along Gasser Drive. To maintain the desired architectural treatment, the headwalls of the culvert were designed to be cast-in-place.