A Time Line of Cedar Bayou




Ward, George H.

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Center for Research in Water Resources



Exchanges with the sea are an important feature of the hydrography of an estuary. For San Antonio Bay, the principal exchanges occur through the Pass Cavallo complex (including the Matagorda Entrance Channel) and through Aransas Pass. The closest inlet to the bay, however, is Cedar Bayou, which separates Matagorda Island and San Jose Island. When open, Cedar Bayou is an effective passage for migratory organisms, so analysis of long-term organism abundance data requires knowledge of the state of the pass. Cedar Bayou has existed as a channel crossing the barrier island for nearly 2500 years. Authoritative surveys establish that its gross physiographic features, notably its NNE-SSW trend across the island and the washover fan to its west, have not substantially changed since before the Civil War. This project constructed a chronology for Cedar Bayou for 1900-2009. Overall, Cedar Bayou has tended to diminish in size from the surveys of the early twentieth century to the aerial photography of the twenty-first century. The largest recorded cross sections of Cedar Bayou were attained in the late 1960’s to early 1970’s (during which Texas Parks and Wildlife performed an intensive study of migratory organisms using the inlet), but the inlet has been greatly reduced in cross section, or completely closed in the years since. While determination of the causes of shoaling of Cedar Bayou is beyond the scope of this study, the chronology includes natural or human activities that could potentially affect the inlet. The mechanisms that scour and maintain Cedar Bayou seem to be operating at roughly the same intensity and frequency during the past three decades except perhaps for freshwater inflow, which is trending upward. Nonetheless, during this period the inlet has been chronically closed, or just marginally open, despite two dredging projects, several hurricanes, and record floods.

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