Morphologic Examination of the Stability of Pass Cavallo, Texas
2008
Kraus, Nicholas C. | Batten, Brian K.
The study concerns the cross-sectional area stability of Pass Cavallo, a natural coastal inlet located in the southwest corner of Matagorda Bay, Texas. The width of Pass Cavallo has decreased since opening of the Matagorda Ship Channel (MSC) entrance to Matagorda Bay in 1966. The process of narrowing began after separation of Matagorda Bay into East Matagorda Bay and the present Matagorda Bay by formation of the Colorado River delta during 1929 1935. The deep-draft MSC enters the bay 3.5 miles (5.6 km) to the north of Pass Cavallo and is a more efficient tidal channel by joining with a deeper and more central portion of the bay. Tidal inlets are maintained in a dynamic equilibrium through a balance of coastal and inlet processes. Conceptually, longshore transport of sediment by waves and the wave-induced current tends to fill an inlet, whereas the ebb-tide and flood-tide currents through the inlet scour its channel. The most reliable approach for examining inlet stability, and that taken here, is based upon accepted empirical predictive relations, supported by measurements made at Pass Cavallo. Collapse of a portion of the ebb-tidal shoal at Pass Cavallo after construction of the MSC entrance is posited as being responsible for much of the reduction in cross-sectional channel area of Pass Cavallo. Since the mid-1990s, the width of Pass Cavallo has been stable, suggesting the sediment load to the inlet from collapse of its ebb shoal has declined. Subject to the uncertainties that enter all coastal sediment processes studies, it is concluded that Pass Cavallo will remain open at its present dynamic cross-sectional channel area or undergo a moderate increase in channel area.
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