Specifications include, but are not limited to: Napa County requires technical assistance to design the replacement of a flapgate including a new slide‐gate on an existing culvert passing under Milton Road. The culvert is located roughly 1000 feet South of the Napa Valley Marina. It is connected to a ditch along Milton Road as well as a drainage channel coming from the properties to the west which both drain to the Napa River. The culvert is tidally influenced with up to an eight foot daily swing between high and low tides. The culvert outlet to the Napa River is often fully submerged, becoming exposed to roughly half its height during low tide. A flapgate is currently fitted to the outlet and a trash rack is on the inlet side. Due to the age of the flapgate (circa 1959) and deterioration of mating surfaces, the structure no longer provides the desired level of tide muting which has prompted its replacement. An inlet slide gate is also needed to provide maintenance and emergency operational capability. Napa County is open to exploring alternate improvement configurations that accomplish the project goals to an equal or greater extent at a lower cost.