POINT BAR RESPONSE TO UPSTREAM CHANNEL CUT OFFS, THE LOWER TRINITY RIVER, TEXAS

Rules governing meander development are largely understood, but do not always hold true downstream of recent cut offs. Cut offs alter the course of the river, forcing downstream adjustments. These changes are reflected in the channel and bank geometry. This study investigates the relationship between meander cut offs and channel and bar geometry. In doing this we examine two point bars in the lower Trinity River of Texas, a coastal river which is cut into primarily sandy Quaternary fluvial deposits. One bar has been relatively stable and shows only a small amount of migration in the past 60 years. In planview, this bar shows a crescent-like shape. The second bar is downstream of a recent meander cutoff (less than a decade ago) and displays a tear-drop morphology in planview. The two distinct shapes are evidence that the bars are being geomorphically altered by different manners. We will synthesize time-lapse planimetric maps, high-resolution topographic and bathymetric surveys, cross sectional trenches of the bars and sedimentology of bar deposits to: 1) evaluate the cause-and-effect relationship between cut offs and meander adjustments, and 2) describe the relationship of channel planform and bar morphology to sedimentation style.