INTERPLAY BETWEEN RIVER DISCHARGE AND LAKE BOTTOM TOPOGRAPHY IN A HYPERPYCNAL LACUSTRINE DELTA, RED RIVER, LAKE TEXOMA, TEXAS/ OKLAHOMA, USA

This paper studies the influence of basin topography with progradation direction and changes in delta morphology of the hyperpycnal Red River Delta. The Red River water creates a hyperpycnal plume, which is the main process that builds the delta. Because the river plume is hyperpycnal, topography has a strong influence on deposition. Higher river water density is created by higher total dissolved solid values in Red River water than Lake Texoma into which it builds. In addition, the density contrast is increased by high suspended sediment concentration during high discharge events. The presence of steep basin lateral slopes deflects hyperpycnal river plumes and subsequently changes overall delta progradation direction before the delta is able to reach the opposite bank. This study of multi-temporal aerial and satellite images indicates that the hyperpycnal delta follows the steepest gradients, which correspond to the pre-dam river talweg, bypassing shallow parts of the lake. A numerical model for the hyperpycnal plume trajectory indicates plume deflection during low or high discharge events, toward the deepest part of the basin. The magnitude of plume deflection is a function of river discharge and basin-side gradients. Plume deflection can vary between 10 and 80 degrees from the channel axis toward the old river talweg. The high deflection appears in the case of maximum basin side-gradients of 12.8 degrees and in conditions of low river discharge. During low discharge periods the Red River Delta had a lobate shape with multiple terminal distributary channels while during high discharge periods the Red River Delta had an elongate shape with a single large distributary channel.