Forcing uncertainty and salinity response to dredging in a tidal freshwater river

ABSTRACT

This study evaluates the salinity response to dredging under different forcing regimes for a 75-kilometer segment of the flood-prone Vermilion River located in coastal Louisiana, USA. The Vermilion is a tidal freshwater river affected by baseflow regulation, rapid urbanization, and hydromodification. This river also serves as major freshwater resource for the region. An efficient one-dimensional model calibrated previously for stage and water temperature is used to analyse the salinity impacts due to a large-scale flood control dredging. The analysis is based on 200 alternative scenarios based on combinations of uncertain key forcing variables for a critical 13-day intrusion period. The analysis reveals a nonlinear effect on mean salinities and position of the brackish water limit as a function of uncertain forcing variables. Dredging also increases the variability of salinity encroachment effects due to uncertainty in future forcing conditions (e.g. relative sea level rise, baseflow diversion volumes, and salinities at the river mouth). The robust analysis presented here provides a foundation for future model-based assessments of under-studied tidal freshwater rivers and provides key insights for coastal management and sustainability efforts in general.

KEYWORDS:

• Dredge effects
• salinity intrusion
• uncertainty
• forcing conditions
• tidal freshwater river

Acknowledgements

The author would like to thank two anonymous referees for their helpful comments which led to an improved manuscript. Salinity measurements were for calibration were furnished by the Coastal Protection and Restoration Authority Coastwide Reference Monitoring System (CRMS) available online at (https://lacoast.gov/crms_viewer/Map/CRMSViewer). The water level data for the site shown in Figure 3 was furnished by the United States Geological Survey (USGS) and the station location is available online at (https://waterdata.usgs.gov/la/nwis/uv?site_no=07386980). The salinity boundary condition was provided by in part by the USGS Fearman Bay location available online at (https://waterdata.usgs.gov/nwis/uv?site_no=07387050) and the downstream stage was furnished by the USGS Cypremort Point with data available online at (https://waterdata.usgs.gov/la/nwis/uv?site_no=07387040). Channel survey data for the Vermilion River study reach was provided by the United States Army Corps of Engineers (USACE) and the latest survey data is available online at (https://hydrosurvey.mvn.usace.army.mil/navpgs/n_vermilion.asp). This research was supported in part by the Louisiana Board of Regents Support Fund LEQSF (2020-23)-RD-A-25.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Additional information

Funding

This work was supported by the Louisiana Board of Regents: [grant number LEQSF (2020-23)-RD-A-25].