Abstract
Although the Mississippi River deltaic plain has been the subject of abundant research over recent decades, there is a paucity of data concerning field measurement of sediment erodibility in Louisiana estuaries. Two contrasting receiving basins for active diversions were studied: West Bay on the western part of Mississippi River Delta and Big Mar, which is the receiving basin for the Caernarvon freshwater diversion. Push cores and water samples were collected at six stations in West Bay and six stations in Big Mar. The average erodibility of Big Mar sediment was similar to that of Louisiana shelf sediment, but was higher than that of West Bay. Critical shear stress to suspend sediment in both West Bay and Big Mar receiving basins was around 0.2 Pa. A synthesis of 1191 laser grain size data from surficial and down-core sediment reveals that silt (4–63 μm) is the largest fraction of retained sediment in receiving basins, larger than the total of sand (>63 μm) and clay (<4 μm). It is suggested that preferential delivery of fine grained sediment to more landward and protected receiving basins would enhance mud retention. In addition, small fetch sizes and fragmentation of large receiving basins are favorable for sediment retention.
Highlights
Deltas occupy only 5% of the Earth’s surface, but nourish over a half billion people around the world
We focus on the fundamental sedimentary processes in seaward parts of receiving basins for diversions
West Bay, which is downstream of Sediment Retention Enhancement Devices (SREDs) (Figure 2A) and close to the emerging subaqueous delta developed after the 2011 flood
Summary
Deltas occupy only 5% of the Earth’s surface, but nourish over a half billion people around the world. Specific objectives of this research are: (1) to quantify the high-resolution grain sizes of both surficial and down-core sediment in two existing diversion receiving basins: West Bay and Big Mar, and to compare with other grain size datasets from Louisiana coast; (2) to measure the erodibility of bed sediment in the field at West. In order to restore vegetated wetlands and create land, since 2003 water and sediment have been diverted from a non-gated crevasse at a 120 ̋ angle along the west bank of the Mississippi River 7.6 km upstream of the Head of Passes of MRD (Figure 2A). Lopez et al [31] reported approximately 4 km of new emerging land and about 201,800 m3 of sediment retention in Big Mar pond
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