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.
Water covers the land surface throughout the year in all years.
Vegetation is composed of obligate hydrophytes. Surface water is present throughout the year except in years of extreme drought. Surface water persists throughout the growing season in most years. When surface water is absent, the water table is usually at or very near the land surface. Surface water is present for extended periods especially early in the growing season, but is absent by the end of the season in most years.