128-22 Time Distribution in the Abandoned Channel Belts of the Rio Grande Delta

Abstract:

The Rio Grande delta (RGD) in south Texas, USA, and northern Tamaulipas, Mexico, preserves numerous abandoned channel belts, locally known as resacas, that contain many oxbow lakes and record the evolution of the fluvial-deltaic landscape. Despite their abundance, the timing and spatial distribution of channel-belt abandonment remain poorly constrained, limiting our understanding of avulsion dynamics and floodplain evolution for the RGD. Thus, this study investigates the temporal distribution of abandoned channel belts by quantifying the geomorphic characteristics and spatial arrangement of oxbow lakes throughout the RGD, using metrics of normalized oxbow distance, abandonment, and cutoff timescales. High-resolution satellite imagery and digital elevation models were used to map abandoned channels and associated oxbow lakes in the RGD using ArcGIS Pro. For each oxbow lake, geomorphic attributes including centerlines, neck midpoints, endpoints, lengths, nearest-neighbor spacing, distance to the modern active channel, and meander radius were extracted and analyzed. A total of 38 abandoned channel-belt segments were identified, with 17 containing preserved oxbow lakes. Preliminary mapping indicates a greater abundance of oxbows on the northern (U.S.) side of the delta compared to the southern (Mexico) side, suggesting spatial differences in channel-belt preservation and abandonment history. The extracted morphometric dataset is then  used to evaluate the spatial organization of oxbow lakes as a proxy for the relative timing of channel-belt abandonment. Distances between neighboring oxbows and their position relative to the active Rio Grande channel belt are compared with theoretical relationships describing meander-belt evolution to reconstruct floodplain time distributions. These analyses provide a quantitative framework for assessing whether channel-belt abandonment occurred as isolated events or in temporally clustered episodes associated with avulsions and channel migration. This work represents the first systematic application of oxbow-lake morphometry and spatial statistics to reconstruct the relative chronology of abandoned channel belts in the RGD, providing new insights into channel migration and floodplain development. 

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