The Role of Coastal Processes

cp1Barrier islands like those found on the Outer Banks of North Carolina represent land forms that are subjugated to an array of environmental factors including variable winds, waves, and episodic storm events.  Rodanthe is a back-barrier area, meaning it is on the sound side of the islands.  This makes it susceptible to different conditions or processes than the ocean side.  These environmental conditions impact what goes on both above and below the water and have the capacity to bring about rapid change to the habitats that are found therein.

 

A team of geologists at the UNC Coastal Studies Institute are evaluating wave and current processes with regards to sediment dynamics in the research area at Rodanthe.  This area is referred to as Hatteras Flats and is characterized by being both very flat and shallow.  What these researchers want to know is how the processes of wind and waves move sediment on the Hatteras Flats.  Scientists are trying to discover what options there are to mitigate the refilling of the channel due to these processes.

PSES

 

 Sound Science: The Pamlico Sound is the largest of North Carolina’s estuaries measuring 80 miles in length and 15-20 miles in width, providing a water surface area of 3,000 square miles.

 

Sediment Dynamics

 

When geologists talk about sediment dynamics, they are talking about particles that are transported by water flow.  Sediment dynamics is the attempt to understand how these particles move around, what causes them to move and also what contributes to their retention.  If scientists can figure out a way to inhibit sediment dispersal, then it paves the way for understanding a way to disrupt the degradation of shoreline caused by back-barrier erosion.   By understanding the sediment dynamics unique to the defined research area in Rodanthe, scientists hope to offer suggestions to the NC DOT about their options for dredging and spoil deposition.

Research Methods: Field and Lab Work

IMG_6064cj  sediment (1 of 1)

 

 

 

 

 

The first step in the approach to understanding sediment dynamics in the research area is to first understand the sediment.  That means recording its type (whether its sand or silt), size (medium or fine), and the amount of organic material present (lots of vegetation, little or none).  All of these factor into the capacity for the sediment to be re-suspended, or swept up into the water column and able to be carried away.

In addition to knowing the characteristics of the sediment, scientists need to know the characteristics of the processes.  That means they need data on the wind, water depths, tide movement, water clarity and the rate of erosion.  If you combine knowledge of the variety of sediment present with knowledge of processes, then an educated suggestion can be offered concerning where to place the sediment, where not to place it, or how long DOT can expect to re-dredge a particular area.

Before conducting any field research, the geologists spent time in the lab pouring over maps like the one below, which use aerial images of the coastline going back decades.  By looking at these images and comparing how the coastline looked and changed over the years, the scientist can learn a lot about the effects tides, wind, and weather have historically wrought on the back barrier.  In getting a sense for this past, the scientist are better informed to make judgements based on modern data about what is going to happen in the future.

aerialimage copy

This map details shoreline change in the study area at Rodanthe spanning nearly 70 years.

 

Research in Rodanthe is on going, check back in for future updates and results from the project.