Oregon Sea Grant

Dikes are elevated earthen embankments raised along tidally influenced channels in estuaries and coastal sections of rivers to keep low-lying lands from being flooded during high tides. Flood boxes are installed in dikes to control the flow of upland water into estuaries or rivers. The doors of these flood boxes are called tide gates, structures that are effective at maintaining low water levels on the upland side of dikes but that have some undesirable side effects as well.

It is these physical, chemical, and biological side effects that the authors of this publication explore, describing changes in channel morphology, water temperature, water salinity, and heavy-metal concentration in water; tide gates as physical barriers to fish passage; and the effects of tide gates on salmon nursery habitats.