The Big Flush

It’s been about a month since Hurricane Matthew unleashed devastating flooding on eastern North Carolina. According to news reports, that flooding inundated swine waste lagoons, farm fields, chicken houses, wastewater treatment plants, and even a coal ash pond, washing the resulting mix of pollution downstream to our sounds and estuaries.

Typically, freshwater flows from the Neuse and Tar rivers feed the estuaries but have a long residence time once they get there.  In part, that’s because these waterbodies are large and the State’s barrier islands impede the ability of  river water to quickly exit to the ocean.

With all the pollutants in the water, however, a lazy trip to the ocean is not ideal.  It results pollutants settling to river bottoms and banks.

Enter the big flush.  This is the result of the extreme flooding pushing downstream.  That pressure helps push water more quickly through the sounds and out into the ocean.  You still get settling of pollutants, just less of it.

The above effect can be seen in monitoring data from UNC. The graphic below shows a monitoring of several parameters in the Neuse River Estuary during similar timeframes in October of this year (2016) with that of last year (2015). At the top of the graph is salinity in October.  Salinity in the river typically rises in the summertime and pushes upstream as freshwater flows are reduced. Those levels then gradually decrease as fall moves into winter and river freshwater flows increase.

On the lower graph from late-October 2016, however, you see how the flooding from upstream has quickly lowered salinity pushing freshwater far down the estuary out to the ocean.

Is the pollution damaging to the ecosystem?  It must be. The effect of coal ash, pig and human waste, oils, and other pollutants lingering in the estuary will be something to study in the coming months. The flushing, however, helps mitigate the harmful effects of all these pollutants in the estuaries by flushing much of them out to the ocean.