Knowledge Bank

Coastal rivers can experience tidally-induced stage fluctuations due to their close proximity to the ocean. Information about the extent of tidal influence is essential because an increasing number of people rely on tidal rivers for both drinking water and recreation, and sea-level rise will likely alter river levels and water quality in the coming decades. While previous studies have examined the ecology of tidal rivers, this study analyzes locations of tidal influence in the continental United States using USGS stream hydrographs and the National Hydrography Dataset. Of the 4,834 coastal gauges surveyed, approximately 8% (383) are tidally influenced. Tides extend up to 47km inland. Tidal gauges have a mean elevation of -0.29m below sea level. Dams and other manmade structures as well as natural riffles and waterfalls obstruct the flow of tides. Due to the scarcity of data for tidal rivers, more expansive stream-gauging networks are needed in coastal regions to better document tidal influence on rivers.