ABSTRACT

Historical progradation rates of the Laguna Madre shoreline at Padre Island National Seashore have varied considerably, largely in response to rainfall fluctuations and perhaps grazing pressure. Analysis of aerial photographs indicates that near the northern margin of the National Seashore the shoreline prograded into Laguna Madre at an average rate of 26 ft/yr between 1941 and 1950. The average progradation rate increased to 42 ft/yr between 1950 and 1964. Average rates then slowed in the late 1960's and 1970's, and since 1979 the shoreline has retreated. Rates of retreat have slowed since the early 1980's, but some parts of the shoreline continue to erode. Early maps and accounts suggest that a century ago North Padre Island was largely vegetated. Overgrazing and a series of droughts in the late 19th and early 20th centuries denuded the island, and prevailing winds blew sand westward across the island into Laguna Madre. With higher than average rainfall in the past two decades and less grazing the island has significantly revegetated. Winds now carry less sand to Laguna Madre; reduced sand supply is a major cause of present-day shoreline retreat.