Geomorphic Process from Topographic Form: Automating the Interpretation of Repeat Survey Data to Understand Sediment Connectivity for Source-Bordering Aeolian Dunefields in River Valleys

Aeolian geomorphologists can readily describe landscape change by contrasting repeat topographic surveys, a method termed geomorphic change detection, thanks to the ubiquity of high resolution topographic data. However, change detection alone does not attribute changes to geomorphic processes; that is, the reasons why change occurred are not explicitly revealed. This process attribution, known as `mechanistic segregation' is typically completed via manual attribution, a method that is time consuming and may be quite subjective. Here we present a novel, automated, two-part method for mechanistic segregation of changes in DEMs of Difference (DoDs) that is both reproducible and computationally efficient. Part 1 employs a landscape-based approach (LBA), wherein we use topographic characteristics from repeat surveys to predict primary and secondary geomorphic transport mechanisms for an area of interest. Part 2 uses morphometry of geomorphic change in a DoD-based approach (DBA) to predict a single geomorphic mechanism. The results of both methods are then evaluated for commonality to assess our confidence in each prediction. We evaluated this approach at 113 discrete sample points within seven source-bordering aeolian dunefields undergoing a combination of fluvial, aeolian, and hillslope geomorphic processes along the Colorado River in Grand Canyon, Arizona. The LBA and DBA performed well independently, but the combined results provided the greatest degree of agreement with field observations (>90%). These methods have proved useful for sediment budgeting, where we confirm spatial and temporal patterns in sediment flux consistent with previously published results. We anticipate that this approach will be reproducible at multiple spatial scales (e.g., 102-106 m2) and adaptable to other river valleys where the interactions of aeolian, fluvial, and hillslopes processes drives sediment connectivity for source-bordering aeolian dunefields.