Delivery of Strategically Placed Sediment through Tidal Creeks to Adjacent Coastal Wetlands
In the summer of 2021, instrumented platforms were deployed at Seven Mile Island Living Laboratory, New Jersey to conduct time series measurements of tidal velocity, turbidity, surface elevation, sediment concentration, and suspended sediment characteristics. The collected data will be used to provide decision support to the U.S. Army Corps of Engineers as they plan dredging activities in the Gulf Intracoastal Waterway.
The Science Issue and Relevance: Sediment-poor wetlands benefit from mineral sediment input to maintain elevation and to support root biomass production that allows wetlands to keep pace with relative sea level rise. Strategic placement of dredged material along the marsh edge may provide two benefits to such systems: 1) reduction of edge erosion by vessel- and wind-generated waves, and 2) increase in sediment supply to tidal creeks. Increasing sediment supply through the tidal creek network may provide mineral sediment far from the wetland edge, a present limitation of thin-layer-placement spraying applications, which purposefully place dredged material in marshes with the intent to restore or maintain their elevation relative to sea level. Additionally, the supply of sediment may occur over a much longer duration, generating widely dispersed, thin deposits of mineral sediment through the tidal creek network. The success of such an approach is likely related to the tidal prism, flood or ebb dominance of the tidal flow, vertical mixing of the system, sediment characteristics (such as size, density, and settling velocity) of mobilized sediment, and the characteristics of vegetation in the system. Research is required to determine if this strategic placement approach offers substantial benefit of sediment delivery to tidal wetlands.
Methodology for Addressing the Issue: Net sediment import/export and the associated sediment and tidal hydrodynamic parameters will be measured at two tidal creeks in Seven Mile Island Living Laboratory (SMILL), New Jersey. Strategic placement of dredged material will occur near the mouth of one tidal creek; the other site will serve as a control. Instrumented platforms were deployed in the summer of 2021 for 8-12 months to conduct time series measurements of tidal velocity, turbidity, surface elevation, sediment concentration, and suspended sediment characteristics (size, settling velocity, and density). and Plots will be established to measure vertical accretion and sediment deposition. Recently placed dredged material at the SMILL provides a prime opportunity for such an assessment. The net transport measurements will determine if the strategic placement case produces greater import of sediment than the control case.
Future Steps: After collecting 8 – 12 months of hydrodynamic and sediment data to empirically quantify impacts of strategic dredged material placement, modeling approaches will be used to provide decision support to U.S. Army Corps of Engineers as they plan dredging activities in the Gulf Intracoastal Waterway.
In the summer of 2021, instrumented platforms were deployed at Seven Mile Island Living Laboratory, New Jersey to conduct time series measurements of tidal velocity, turbidity, surface elevation, sediment concentration, and suspended sediment characteristics. The collected data will be used to provide decision support to the U.S. Army Corps of Engineers as they plan dredging activities in the Gulf Intracoastal Waterway.
The Science Issue and Relevance: Sediment-poor wetlands benefit from mineral sediment input to maintain elevation and to support root biomass production that allows wetlands to keep pace with relative sea level rise. Strategic placement of dredged material along the marsh edge may provide two benefits to such systems: 1) reduction of edge erosion by vessel- and wind-generated waves, and 2) increase in sediment supply to tidal creeks. Increasing sediment supply through the tidal creek network may provide mineral sediment far from the wetland edge, a present limitation of thin-layer-placement spraying applications, which purposefully place dredged material in marshes with the intent to restore or maintain their elevation relative to sea level. Additionally, the supply of sediment may occur over a much longer duration, generating widely dispersed, thin deposits of mineral sediment through the tidal creek network. The success of such an approach is likely related to the tidal prism, flood or ebb dominance of the tidal flow, vertical mixing of the system, sediment characteristics (such as size, density, and settling velocity) of mobilized sediment, and the characteristics of vegetation in the system. Research is required to determine if this strategic placement approach offers substantial benefit of sediment delivery to tidal wetlands.
Methodology for Addressing the Issue: Net sediment import/export and the associated sediment and tidal hydrodynamic parameters will be measured at two tidal creeks in Seven Mile Island Living Laboratory (SMILL), New Jersey. Strategic placement of dredged material will occur near the mouth of one tidal creek; the other site will serve as a control. Instrumented platforms were deployed in the summer of 2021 for 8-12 months to conduct time series measurements of tidal velocity, turbidity, surface elevation, sediment concentration, and suspended sediment characteristics (size, settling velocity, and density). and Plots will be established to measure vertical accretion and sediment deposition. Recently placed dredged material at the SMILL provides a prime opportunity for such an assessment. The net transport measurements will determine if the strategic placement case produces greater import of sediment than the control case.
Future Steps: After collecting 8 – 12 months of hydrodynamic and sediment data to empirically quantify impacts of strategic dredged material placement, modeling approaches will be used to provide decision support to U.S. Army Corps of Engineers as they plan dredging activities in the Gulf Intracoastal Waterway.