Changes to Subaqueous Delta Bathymetry Following a High River Flow Event, Wax Lake Delta, USA
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Changes to Subaqueous Delta Bathymetry Following a High River Flow Event, Wax Lake Delta, USA Amanda Whaling 1 & John Shaw 1 Received: 6 February 2019 / Revised: 28 February 2020 / Accepted: 6 March 2020 # Coastal and Estuarine Research Federation 2020
Abstract The construction of the subaqueous delta front is foundational to deltaic land building and field data is needed to validate conceptual models of delta front evolution. The bathymetric change that occurred across the entire delta front (~ 75.9 km2) of the Wax Lake Delta (WLD) in coastal Louisiana was measured between February 2015 and July 2016. Sediment removal (− 9.85 × 106 m3) exceeded sediment accumulation (7.64 × 106 m3), making the delta front net-erosional (− 2.21 × 106 m3) despite the occurrence of a flood. These results factor in an estimated 4.28 cm of subsidence during the survey period. Deposition on the delta front was localized around channels and the northern and eastern flanks of the delta whereas erosion was more spatially uniform. This erosion coincides with an anomalously strong winter storm season that may have exported this sediment offshore and is consistent with a growing body of research that identifies winter storms as a significant mechanism for sediment removal from Atchafalaya Bay. Winter storm erosion is crucial to understanding and predicting volumetric growth of the WLD and has important implications to land building from sediment diversions. Future models of deltaic growth need to account for significant volume export and erosive episodes on the delta front. Keywords River delta . Bathymetry . Delta morphology . Subaqueous delta growth . Subaqueous distributary channel . Winter storm
Introduction At the large scale, subaerial portions of deltas have been the primary focus of studies regarding network and land growth, ecology, human sustenance, and land-loss mitigation strategies (Kim et al. 2009; Edmonds et al. 2011; Nyman 2014; Chamberlain et al. 2018). Comparatively, much less is known about the subaqueous portions of deltas, the region encompassing the delta front lying below low-tide level bayward of the subaerial delta. Studies of subaqueous deltas around the world have shown that their morphology can generally be described as sigmoidal-shaped deposits on the continental shelf (clinoforms); however, their morphology at smaller scales is highly variable in space and time due to
Communicated by Mead Allison * Amanda Whaling [email protected] 1
Department of Geosciences, University of Arkansas, Gearhart Hall, 340 N Campus Dr, Fayetteville, AR 72701, USA
differences in coastal marine energy, discharge, and even latitude (Prior et al. 1986; Alexander et al. 1991; Nittrouer and DeMaster 1996; Walsh et al. 2004; Swenson et al. 2005). Even though the growth of the subaqueous delta is fundamental to subaerial land growth (Cahoon et al. 2011), there are few studies that monitor subaqueous delta change at the channel scale because it is generally less accessible with remote sensing and conventional surveying (Shaw et al. 2018).
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