Wetland Delineation by Means of Tide Gauge, South Padre Island, Texas

Elevations of mean high water (MHW) and the high tide line (HTL) were determined at four wetlands located along the southern end of the Laguna Madre, Texas, by applying standard Section-404 procedures of the Clean Water Act and by reference to water level at a nearby tide gauge. The Section-404 evaluation involved visual identification of vegetation and saturation of the soil. The average of five visual estimates of the MHW elevation agreed within 2 cm (0.8 inch) with MHW given by the tide gauge. The elevation of the HTL was found to lie 0.31 m (1 ft) above MHW, corresponding to an annual exceedance between 2.8 and 7.7 percent for each of 3 recent years. It is concluded that experienced personnel can apply visual indicators at tidal wetlands adjacent to the southern Laguna Madre to estimate reliably MHW and the HTL. The procedure of referencing the elevation of the HTL to MHW determined by a local tide gauge appears applicable to other tidal wetlands.