Olariu, Cornel¹, Janok Bhattacharya¹ 
(1) University of Texas at Dallas, Richardson, TX

ABSTRACT: Basin Topographic Influence on Delta Progradation, in the Modern Lacustrine Red River Delta, Lake Texoma, Texas/Oklahoma

Lake Texoma is a man made lake impounded in 1944 which flooded the Red River valley approximately 45 km upstream of the dam. The lake shape is “meandering” and the banks have gradients between 0.01 and 0.2. Knowledge of pre-deltaic basin topography and observation from air photos and satellite imagery show delta progradation rates of approximately 250 m/ year over a 60 years period and indicate a high control of topography on delta progradation direction. The Red River inflow is hyperpycnal most of the time because total dissolved solids and suspended sediment concentrations are higher in the river water than in the lake water. When the inertial-hyperpycnal delta started to fill the lake, it prograded straight. When reaching the first original channel meander, the delta followed the main valley, bypassing some parts of the lake, despite the relatively narrow lake width. This phenomenon can be explained by the tendency of the river effluent to follow the steepest gradient which in this case is the talweg of the previous river. During high discharge periods, the hyperpycnal delta prograded straight and the influence of slope gradient is minimal. During low discharge periods, inertial flows are redirected toward the steeper slopes. These observations, although commonly made in theoretical experiments, are difficult to observe in natural system because the predeltaic topography is usually unknown and long time observations are necessary. The results show that delta progradation direction is a result of the interplay between the inertial and gravitational forces which act on sediment load.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.