Bay margin sand distribution, North Texas Coast: A model for sediment distribution in microtidal bays and lagoons
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Analyses of sediment from four bays on the north Texas coast reveal that sand distributions in microtidal bays and lagoons can be related to wind regimes and bay geometrics (ie., fetch and water depth). In order to examine this relationship, bottom profiles were constructed and sediment samples were collected along the profiles in Christmas, West, Trinity, and Galveston Bays. Grain-size analyses of these samples showed a point of marked change in the sand:mud ratio along each profile. This marked change from muddy bay center sediment to sandy bay margin sediment occurs at increasingly greater depths in the larger, deeper bays, and at greater depths along the southeast side of the bays than along the northwest side. The difference in the depth of the sand:mud break point between the northwest (76 cm) and southeast (92 cm) sides of Christmas Bay, the northwest (132 cm) and southeast (147 cm) sides of West Bay, the northwest (160 cm) and southeast (174 cm) sides of Trinity Bay, and the south side of Galveston Bay (220 cm) can be related foremost to the wind regime of the Texas coast. During nine to ten months of the year, moderate southeasterly winds dominate, creating waves that mainly affect the northwest side of the bays. During the winter months, however, strong northerly winds create larger waves, effectively winnowing sediments to a greater depth along the southeast side of the bays. In addition to the difference between break point depths on the northwest and southeast sides, minor differences in break point depths occur along the same side within a bay; such differences are related to variations in bottom geometry. On the basis of these preliminary analyses, it appears that sand distributions in analogous bays can be predicted using wind, fetch, and water depth data.