DELTA ISLAND CONSTRUCTION – MATCHING GENERIC MORPHOLOGY METRICS TO SEDIMENTOLOGICAL REGIMES (Invited Presentation)

River deltas consist of a co-evolving channel and island network with feedbacks between both features. We seek to understand the construction of a simple end-member deltaic island evolving from an initial river mouth bar deposit with little to no influence from channel avulsion. We impose a simple theoretical framework for construction of these islands, from initial deposition to full island maturity. These developmental paradigms relate island morphology to the ratios of sand, mud, and organic soil within this structure. Our theory is tested by extracting transects from a Digital Elevation Model from Wax Lake Delta along Bezier curves. These elevation transects are spaced evenly along the bank line, from the channel apex to the periphery; each transect connects the channel/island edge to the channel centerline, and the approaches to channel edge and island centerline are forced to be perpendicular. This method prevents biased cross-cutting of the levee, and represents a 2D slice of island morphology adjacent to any location along the delta channel. The centroid and relative area of each slice are extracted. We relate these values to our imposed theoretical framework, so as to identify the developmental regime associated with each 2D slice. Our theoretical framework suggests that these two metrics should be sufficient to distinguish between four developmental stages. The sedimentological composition of cores previously extracted from Wax Lake Delta islands are compared against the rough partitioning estimates suggested by our theory. The validation of this result would imply a quantitative relationship between the relative ratios of sand/mud/organic soil and stage of development, which itself is related to island morphology.