The impact of commercial vessels on coastal hydrodynamics and sediment movement has been measured and simulated in shipping channels and rivers. However, little empirical data exist on the temporal variation in vessel-generated forces in addition to the ecological implications for natural waterways such as tidal creeks and bayous. Along the U.S. Gulf of Mexico coast, these ecosystems may be highly susceptible to unnatural currents created by commercial vessel traffic. We sought to characterize and quantify the impact of large vessel traffic in the Gulf Intracoastal Waterway (GIWW) on tidal creek hydrodynamics at Aransas Wildlife Refuge (ANWR). Creek water level was monitored at 1-minute intervals in three different tidal creeks at ANWR during the summer of 2004. We also conducted preliminary measurements of bedload sediment flux associated with vessel passages. Vessel-induced fluctuations in water level in at least one site were the equivalent or greater than the diurnal tidal range (about 0.1 m) and were driven by distance to the GIWW, presence of islands as barriers, and baywide water levels that affected the attenuation of drawdown currents across a shallow bay. Bedload sediment flux during barge-induced outflow (mean = 9.3 g dry weight [dw] min−1) was nearly twice the mean measured during normal ebb outflow (5 g dw min−1). Our results identify a potentially important factor that may affect the long-term sustainability of the marsh and tidal creek systems at ANWR, which serve as wintering habitat to the endangered whooping crane (Grus americana L.).
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Vol. 2009 • No. 252