Using ADCIRC to extend the time period of the Neuse River Estuary eutrophication model

Abstract

The previously developed two-dimensional, laterally-averaged mechanistic CE-QUAL-W2 was updated and extended with all the input files needed to run the model through to the end of calendar year 2016. In order to extend the previous model past 2009, a new method had to be created to estimate the elevation downstream head (EDH) of the Neuse River Estuary. A meteorological forcing ADCIRC model of the Pamlico and Albemarle sound was created to predict the needed elevation time history. However, the ADCIRC model was only able to predict known EDH values with a coefficient of determination of 0.03 and a correlation of -0.187. This level of performance was considered inadequate for simulating the downstream elevation boundary condition for the model. An alternative method had to be used to extend the elevation time history. Known water elevations from Oregon Inlet were manipulated using a variance factor and a time shift to predict the needed water level time history. A two-year time period of elevation data were available to test the method. Over the 2006-2008 time period, this method was able to predict the EDH with a coefficient of determination value of 0.078 and a correlation of 0.28. This was a significantly higher level of prediction accuracy that was considered suitable for generating the necessary elevation boundary condition. Additional work was done to develop the other model input files for the 2012 – 2016 time period. With updated input files, two new CE-QUAL-W2 model time periods were created: 2012-2014 and 2015-2016. Model predictions of temperature, salinity, nitrate, ammonia, orthophosphate, dissolved oxygen and chlorophyll-a were compared to available monitoring data. Additional work is needed to fully calibrate the model. Once calibrated, the model may be used to simulate nitrogen reduction scenarios in the estuary.