EVALUATING THE MORPHOLOGICAL CONTROLS ON CHUTE CHANNEL LATERAL MIGRATION USING GOOGLE EARTH ENGINE

Chute channels form via scour and incision from overbank flow across point bars in meandering river systems; in some cases, chute channels persist as smaller, laterally migrating bifurcations without causing bend cutoff. Recent work has shown that laterally migrating chute channels can deposit scroll bars with similar spacing and dimensions as main channel scrolls. However, controls on chute channel lateral migration rate and the morphodynamic connection between main channels and chute channels remain unclear. Here we analyze the lateral migration rates of main channel reaches and associated chute channels to understand the relationship between channel width and curvature on migration rate and to test the degree of coupling between main- and chute-channel migration

Using Google Earth Engine to process Landsat imagery from 1991-2022, we created active channel binary masks for paired main- and chute-channel sites for a range of chute-dominated rivers worldwide. These masks were analyzed with RivMap, a MatLab package used to calculate lateral migration rates of single-thread river channels.

Preliminary results from the middle reaches of the Paraguay River (Paraguay/Brazil border) show that main and chute channel migration rates have different magnitudes but are the same when normalized by channel width. Main channel sites have migration rates ranging from 0.26-10.93 m/yr (mean: 4.25 m/yr), while migration rates at chute channel sites range from 0.82-6.9 m/yr (mean: 2.87 m/yr). Paraguay River chute channels are consistently narrower and have less curvature than main channel sites; mean channel width is 107.45 m for chutes and 199.99 m for main channel stretches. The average width-normalized migration rates are the same for main and chute channel stretches (mean: 0.022 yr^-1).

Further analysis shows that main channel sections have a significantly more variation in migration rate compared to their associated chute channels, which move more slowly overall but at more consistent rates. Additionally, years with the maximum and minimum channel migration are the same for chute and main channels in most cases. Overall, these preliminary findings suggest that channel width is a key control on chute channel lateral migration, and that main and chute channel reaches are morphodynamically coupled.