Impacts of a Major Mississippi River Freshwater Diversion on Suspended Sediment Plume Kinematics in Lake Pontchartrain, a Semi-enclosed Gulf of Mexico Estuary

Abstract

MODIS satellite imagery and in situ water measurements were used to quantify inorganic sediment concentration (ISC) and, subsequently, sediment plume motion and evolution during the 2016 diversion of the Mississippi River through the Bonnet Carre Spillway (BCS) within Lake Pontchartrain (LP) estuary in Louisiana, USA. Satellite images revealed that sediment plume areal distribution was closely linked to BCS discharge rate. The plume flowed eastward along the southern LP coastline at an average speed of ~ 0.3 m s−1 during the first week of the event and attained its maximum areal extent (~ 1117 km2; 68% of the total LP area) on 23 January. In an attempt to examine the plume kinematics and potential sediment resuspension impacts, wind information was also assessed. Following BCS closure, the prevailing wind direction, but not wind speed, corresponded to significant differences in LP ISC. LP was further subdivided into four separate quadrants to assess relationships between ISC within each quadrant to BCS discharge rate and winds. While the BCS was open, the plume’s eastward motion was associated with a high correlation (r2 = 0.93) between BCS discharge and ISC in the southeast quadrant. However, the weak relationship (r2 = 0.42) between BCS discharge and ISC in the northwest quadrant was attributed to influences from other tributaries. These results will benefit future research regarding impacts of freshwater diversions on coastal and estuarine processes that are sensitive to sediment influx by providing a satellite-based sediment map time series that can be used to help validate numerical circulation and sediment transport models.