CHANGES IN CHANNEL PATTERNS ACROSS FAULT SCARPS - A COMPARISON BETWEEN THEORY AND OBSERVATIONS

Rivers, especially those of low order, are thought to respond to even subtle tectonic changes by changing their channel patterns. For instance, a meandering river may adapt to a gradient drop by lowering its sinuosity, i.e. undergo straightening, or by changing into a braiding river. If the gradient increases downstream, on the other hand, this may cause a meandering river to increase its sinuosity, or cause a braided river to change into a meandering one. Due to this, changes in the channel pattern downstream have been widely used as an indicator of deformational changes in the underlying strata. The literature on this topic is mainly based on experiments and field observations where the deformational changes have been inferred from channel pattern variations downstream.

This study utilizes high resolution LIDAR data to examine the active Baton Rouge growth fault, in southern Louisiana. Vegetation is removed from the dataset, which exposes numerous fault segments and the rivers that flow across the fault system. This dataset provides an excellent opportunity to compare theory with field observations of an active fault scarp.

The sinuosity (P=Channel length/ Valley length) has been carefully measured for rivers and creeks that cross segments of this clearly active fault system. The sinuosity for the rivers in this area vary between 1.2 and 2.7. We find that, while some changes are observed at faults, in general there is not a clear relationship between the changes in sinuosity and the location of the fault scarps. We conclude that other measures, such as the gradient-slope index, may be better indicators of subtle tectonic activity.