If Palustrine, Riverine, and Lacustrine wetlands are only irregularly flooded by tides, we designate them by the appropriate nontidal Water Regime Modifier with the word tidal added, as in seasonally flooded-tidal . The water regimes are largely determined by oceanic tides. The substrate is permanently flooded with tidal water. The land surface is exposed by tides less often than daily. Tidal water alternately floods and exposes the land surface at least once daily.
Tidal water floods the land surface less often than daily.
The periodicity and amplitude of tides vary in different parts of the United States, mainly because of differences in latitude and geomorphology. Therefore, though no hard and fast rules apply, the division between regularly flooded and irregularly flooded water regimes would probably occur approximately at mean high water on the Atlantic Coast, lowest level of the higher high tide on the Pacific Coast, and just above mean tide level of the Gulf Coast. The width of the intertidal zone is determined by the tidal range, the slope of the shoreline, and the degree of exposure of the site to wind and waves. Nontidal Though not influenced by oceanic tides, nontidal water regimes may be affected by wind or seiches in lakes. The rest of the year is defined as the dormant season, a time when even extended periods of flooding may have little influence on the development of plant communities.