Nearshore changes at jettied inlets, Texas coast.

In recent years, two artificial channels with jetties were constructed to provide access to port and industrial sites. Jetties several kilometers in length were required because of shallow water depths and broad ebb-tidal deltas, especially along the upper coast. These jetties greatly alter littoral processes at the inlets and navagation channels, but the extent of their effect along the shoreline is not fully known. Futhermore, their total effect on sediment budget is unknown but they do represent the greatest sediment sink along the Texas coast. Patterns of deposition and erosion attendant with jetty construction illustrate the shoreline and shoreface response to altered littoral processes and the disruption of sediment by-passing along the shoreface and around former ebb-tidal deltas. Similar nearshore changes have documented in other coastal areas. In addition to offering some examples of nearshore changes, the present study provides alternate interpretations and a partial classification scheme for many observed nearshore changes. General conclusions based on this study apply to similar coastal settings with (1) relatively simple jetty designs and channel configurations (2) relatively low wave energy and tidal range, and (3) low to moderate littoral drift. The study confirms that shorelines accrete updrift and erode downdrift from jetties constructed across straight shorelines with shore parallel depth contours, but paired jetties that permanently disrupt sediment by-passing at ebb-tidal deltas and river-mouth bars may cause updrift and downdrift shoreline accretion related to adjustment of offshore profiles and landward transport of sediment.