Channel Bar Development in a Poorly Sorted Sand-Bed River

In order to better understand the development of channel bars in a poorly sorted sand-bed river, field investigations were conducted at four bars along the lower San Antonio River. This was complemented by analysis of aerial orthoimagery using GIS. Local topographic features and stratigraphic evidence indicated the development of two features, presently considered side bars, had occurred primarily from lateral accretion; aerial orthoimagery showed no migration of these bars. The other two features, both mid-channel bars, appeared to have developed mainly through vertical accretion, while aerial orthoimagery showed downstream migration along with significant surficial expansion of one of the mid-channel bars. Aspects associated with the evolution of bars located in both sand- and gravel-bed rivers were observed, although the presence of gravel seemed to have a disproportionate influence on development, especially in regard to the prospect of bar movement over time.