Quantification and differentiation of delta and fluvial fan channel network morphometrics

Abstract

Deltas and fluvial fans are two fan shaped landforms with complex channel networks. Accurately differentiating between these two landforms is crucial to identifying and understanding these two landforms on Earth, as well as on other planetary bodies like Mars and Titan. Differentiating between these landforms is critical for infrastructure planning and sea level rise resilience as deltas and fluvial fans will react differently to sea level rise. One significant difference between deltas and fluvial fans is that deltas only form along shorelines where a river enters an ocean or lake. Fluvial fans may form hundreds of kilometers inland from a shoreline and are predominantly controlled by upstream controls. Fluvial fans form by channel avulsions whereas deltas primarily build by mouth bar deposition and consequent channel bifurcations. Here I present an ensemble of quantitative metrics to differentiate morphologically fluvial fans from deltas. To achieve this, I quantify channel bifurcation/divergence angles, channel lengths and widths between these bifurcation/divergence nodes, channel orders, and the number of terminal channels. Previous research on delta channel morphometrics strongly suggest that delta s exhibit an average channel bifurcation angle around 72 while maintaining a distinct downstream non linear decrease in channel lengths and widths for successive bifurcations. Our results show that fluvial fans differ from deltas by exhibiting a considerably smaller divergence angle, and down fan channel length shortening that is not associated with divergence orders. Our results further suggest there exists a statistically significant difference between deltas and fluvial fans channel networks. These results indicate that channel network assessments show a difference between deltas and fluvial fans, and that the channel networks need to be carefully assessed if used for paleo shoreline estimations on planetary bodies. Additional evidence is needed for the presence of shorelines as fluvial fans may occur at shorelines.