Developing a Truly Global Delta Database to Assess Delta Morphology and Morphodynamics

Abstract:

Delta morphology reflects the interplay of various environmental parameters, though these relationships have only been tested on small datasets with 30-50 deltas. These datasets are biased toward the largest deltas, which typically have compound morphologies, form on passive margins, and may not be representative of the full breadth in delta morphology. With the goal of building more robust predictions of delta morphology to enhance hazard mitigation and resiliency planning, we have developed a truly global delta database including every delta on the world’s marine coastlines. Using Google Earth imagery, we first identified all fluvial river mouths (≥ 50 m wide) connected to an upstream catchment. Deltas are defined geomorphically as river mouths that split into two or more active or relict distributary channels, end in a depositional protrusion from the shoreline, or do both. In our database we identified 5,801 river mouths, and 1,426 of those coastal rivers (~25%) have a geomorphic delta. ~75% of deltas exhibit an active or relict distributary network, while the remaining ~25% are single channel deltas with a basinward protrusion. Preliminary morphometric analysis (ratio of shore-parallel width, W, to shore-perpendicular length, L) on a subset of 159 deltas suggests W:L values range from 0.52 (elongate) to 23.6 (broad/cuspate). The median W:L value is 2.68, suggesting the majority of deltas are roughly semi-circular (W:L = 2), and the distribution is heavily skewed to the broad/cuspate deltas (~28% are >4 times wider than they are long). Preliminary comparison to downstream significant wave height data shows that the ‘wider’ deltas relate to higher wave heights (R² = 0.42), though the data are scattered. Ultimately, the database will include additional measured morphometrics, including number of channel mouths and delta area, and morphodynamic data derived from serial Landsat imagery.