Kentuck Slough Tide Gate Replacement Project (OR)
The Kentuck Slough Bridge is located along the northeastern side of Coos Bay near North Bend, OR. The existing bridge did not meet current design standards and needed to be replaced. Attached to the downstream side of the existing bridge was a set of three 7.5-ft wide by 10-ft high top-hinged tide gates. One of the tide gates was wedged in the gate slot and completely inoperable. The other two gates functioned, but leaked significantly during flood tides. Additionally, the gates were frequently overtopped during high tides.

The leaky gates have allowed for salt-water intrusion into the slough, which has re-created an important estuarine habitat. However, this has also resulted in an increase in the amount of salt water that intrudes into adjacent land via groundwater flow. This has negatively affected the quality of the soil during the summer months when there is little freshwater inflow to the slough to help dilute the salt concentrations from the bay water. The local landowners have indicated that the current volume of saltwater influx to the slough is tolerable, but any increase would not be acceptable. WEST developed an HEC-RAS unsteady flow hydraulic model of the tide gate designs to accommodate and improve upon conditions that encourage the estuarine habitat, while at the same time, will not increase the volume of salt-water influx to the slough over the existing conditions.

Kentuck Slough is considered an important salmonid habitat. Therefore, the hydraulic parameters for the replacement tide gates were developed in close consultation with the National Oceanic and Atmospheric Administration Fisheries (NOAA Fisheries), U.S. Department of Fish and Wildlife (USFW), and the Oregon Department of Fish and Wildlife (ODFW).