Hydrodynamic and geomorphic controls on mouth bar evolution

While river deltas are one of the major repositories for sediments and carbon on Earth, there exists a paucity of field data on the formation of distributary mouth bars—one of their key features. Here we present results from an experiment that tested a model of mouth bar development using hydroacoustic, optical, sedimentary, and geochemical tools on a mouth bar in a crevasse splay near the mouth of the Mississippi River. Our results validate an existing model for mouth bar development, which we extend to explain mouth bar stratigraphy. We propose that changes across a hydrological cycle are important for mouth bar development, resulting in a stratigraphy that has alternating fine and coarse grain sediments. Results also indicate that sand is carried up to 6 km from the main stem of the Mississippi River, despite repeated channel bifurcations, which has important implications for our interpretation of the rock record, understanding of coastal sedimentary systems, and the restoration of large deltas. Key Points We show field data showing seasonal sedimentation and transport on a mouth bar Sedimentation in mouth bars occurs across the hydrographic cycle Crevasse splay channels can transport sand long distances