Research Training Program

The morphology and controls of meandering in alluvial rivers have been extensively studied, but this knowledge has not been applied to meandering channels on deltaic plains. Sinuosity, the ratio of channel distance to valley distance, is related to slope, bank material, tectonic activity, and other features of the deltaic environment. The Rio Grande delta in Texas makes an interesting case study because it has numerous meander scars dating from about 150,000 years ago to the present. The delta has a lobate form and Holocene deposits are protected from wave action by an extensive barrier beach. The modern delta is being eroded, because the mouth of the river has breached the barrier system and is exposed to a high energy coastline. This research examined the sinuosity of river channel meanders on the Rio Grande delta, used the meander forms to interpret delta evolution, and explored factors influencing meander development on twenty deltas. Sinuosity was measured in modern, Holocene, and Pleistocene channels, and spatial and temporal trends were analyzed. Rio Grande deltaic sinuosity (2.1) is significantly higher than the mean of the other deltas studied (1.6), and the Rio Grande is unique in being a meandering river with higher sinuosity in the delta than the alluvial valley. A high sinuosity belt crosses several Holocene channels and suggests the influence of seismic motion, dissipation of tidal control, or changes in bank material. Channels in the Rio Grande delta have become more sinuous since the mid-Pleistocene. This shift may be related to increasing aridity or decreasing slope. Sinuosity of delta channels is not correlated with ten other parameters examined, suggesting that a combination of factors or an unstudied control may influence meander development in deltas.