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The Park Science Podcast

Insightful conversations about science, nature, history, and "wicked problems" in our national parks. Hear the stories behind the headlines. Produced by Park Science, a digital magazine of the National Park Service.


1. Swept Away


INTRODUCTION [WITH MUSIC]: Welcome to Park Science Podcast, a podcast of Park Science magazine that highlights milestones and contributions to science made by parks and programs of the National Park Service. Find our podcast series as well as the full Park Science magazine online at nps.gov/parkscience.

BROOKE: U.S. national parks with coastlines are on the front lines of climate change. They’re seeing the effects of sea level rise, storm surge, and coastal erosion firsthand. But science is helping our national parks meet these challenges. I’m Brooke Bauman, a Scientists in Parks intern with the NPS Coastal and Ocean Advisory & Support Team (COAST). I’m here with Dave Hallac, superintendent of the National Parks of Eastern North Carolina. For him, the park with the most coastal challenges in Eastern North Carolina is Cape Hatteras National Seashore. He recently published a study [1] [http://doi.org/10.34237/10089211] on predicting how the seashore’s shoreline will change.

Cape Hatteras is a big, sandy island, 75 miles long, just off the coast of North Carolina. Because it is a barrier island, it’s formed and reformed by waves constantly removing and depositing sand parallel to the shoreline. It has sandy beaches and dunes, which provide food and shelter for animals like sea turtles and shore birds. It also has a lot of private homes. Hallac says when sand erodes from the island or accretes—accumulates—it has an impact on those habitats and structures.

DAVE: As you can imagine on a large, sandy barrier island [2], having an incredible amount of erosion or accretion can really affect the amount of habitat that we have, but it can also affect the vulnerability of many of the structures that we have, or assets, everything from roadways to lighthouses to parking lots.

BROOKE: Think how often we see footage of houses under water or collapsing into the ocean after a storm. If you don’t live near the coast, you may think coastal erosion is caused by things like sea level rise or more frequent storms. But Hallac says it’s natural for sand to move along the coast on barrier islands like Cape Hatteras.

DAVE: Many of the challenges we have related to erosion, structures, and roads being threatened would be occurring without any sea level rise or climate change. And that’s because most barrier islands are dynamic landforms. Generally, the barrier islands in Eastern North Carolina here would be sustained through a process of frequent overwash and some transport of sand from the Atlantic-facing ocean across the island, which would build some island height but also in some cases shift the island westward.

BROOKE: How has that natural process of sand movement changed since people began building roads or living there?

DAVE: So that normal process of migration has been altered in many ways because for decades, we built large sand dunes that prevented that island overwash. Those sand dunes were required to protect a highway that extends more than 50 miles through the seashore. And then interspersed within the seashore we have a number of developed villages where there are beach homes and homes behind the dunes. Those homes also have had to be protected and the dunes have had to be maintained over the years to protect those private properties.

BROOKE: How else has coastal development affected the natural movement of sand?

DAVE: Because we have halted some of these processes, we have islands that are now eroding both from the Atlantic-facing side and from the sound side. And the islands are becoming smaller and smaller, and there is less habitat available for wildlife, there are fewer areas for people to recreate on, and other important structures that support society on the islands, whether they be roadways or waterlines, or powerlines, are increasingly threatened.

BROOKE: Okay. But climate change and sea level rise play a role here too, don’t they?

DAVE: As I said earlier, all those issues—erosion, island breaches—those have been happening for hundreds and hundreds of years, prior to some of the modern climate change that we are seeing on earth, and the sea level rise that’s coming from that. But what we do know is that sea level rise and climate change are probably exacerbating those coastal hazards, and that is likely to continue to become an increasingly difficult problem.

BROOKE: The National Oceanic and Atmospheric Administration—NOAA—has been monitoring sea level at Cape Hatteras since the late 1970s. NOAA scientists determined that sea level rose by one and a quarter feet from 1920 to 2020 [3]. But Hallac says sea level rise isn’t the only concern.

DAVE: NOAA is also expecting that we should have more damaging flooding. And so these are the types of flood events that you know sometimes you might hear to as king tides, but they’re just simple flood events that are caused by tide and storm surge increased water levels; they expect those types of events to increase in frequency on average by as much as 10 times over the frequency we see today. So when you combine just having a higher sea level in addition to having this large increase in the frequency of these damaging flood events, I think it’s a recipe for greatly accelerated erosion and further instability of the barrier islands.

BROOKE: In 2021, Hallac and a colleague, Michael Flynn, published a scientific study [1] in Shore and Beach Journal. The study evaluated how well an updated version of a shoreline change forecasting model worked at Cape Hatteras. The forecasting model uses something called the Digital Shoreline Analysis System [4], which was developed by the U.S. Geological Survey.

DAVE: So what we did was to look at a couple of decades of high-tide shoreline data. In other words, how far does the water line come up onto the beach at high tide on average, and we looked at that over multiple years. Not surprisingly, we found, in most areas of the seashore, a continuous trend of erosion. In other words, that high tide line was coming higher and higher up on the beach, and we were losing dry sand beach over time. We took multiple shoreline high-tide depictions and performed a statistical analysis.

BROOKE: Right, and you found that the rate of shoreline change was about 10 was 14 feet per year. What does that mean in real-world terms?

DAVE: We found that the shoreline would be perhaps within a neighborhood, it might be on the west side of a road, in other words, completely overtaking a road in a certain area or village, or it might be breaking in the middle of, the waves might be breaking in the middle of a parking lot. So that information is extremely helpful. Because, as you can imagine, in a place like Cape Hatteras Seashore, we have damages from storms, tropical storms, nor’easters, and hurricanes regularly. And we wanted to know, following these storms, does it make sense, if a parking lot is damaged, to invest in rebuilding that parking lot in the same location?

BROOKE: In light of this information, what did you end up doing?

DAVE: It gave us the opportunity to think differently, to find another location, a substitute location, for that parking where the investment would likely be able to be used and we could realize those benefits for at least a 20-year period. So that’s an example of how we used the work from that publication and how we’re still using the results from that publication to inform our planning and management decisions.


BROOKE: OK. So now we know a little bit more about how the sand on barrier islands moves naturally and what that means for the people, plants, and animals there. It’s obvious that the boundaries in a national park like Cape Hatteras are constantly shifting, unlike inland parks like Shenandoah or Yellowstone.

DAVE: So our eastern facing boundary at Cape Hatteras National Seashore along 75 miles of beach is actually the mean low tide line. In some cases of the park, the boundary is from the mean low tide up to the high tide line. And then, as that area, which is referred to as the foreshore, continues to migrate to the west, there are some circumstances now where that high tide line to low tide line is right next to or maybe essentially straddling a home that is on the beach. Because of that moving foreshore boundary, it is possible that there could be homes that were once built in a high and dry location behind the dunes that are now between the high tide line and the low tide line.”

BROOKE: With shorelines and park boundaries encroaching upon homes, that must create some challenging park management situations.

DAVE: We’ve actually had three collapse [5] since the beginning of the year 2022. But on a daily basis, pieces and parts of these homes are also falling off. Sometimes septic systems are exposed and also break apart. So this has created some really unique and difficult challenges for the park where we are of course trying to maintain pristine beaches that are available for our visitors to enjoy and also for wildlife to use.

BROOKE: I know that in the aftermath of collapsing homes, Cape Hatteras has led extensive clean-up efforts. To help remove particularly small pieces, the park even purchased a mechanical beach rake. There are a lot of concerns for wildlife. I understand the park also drafted a plan for what to do if more homes collapse, and park staff have also been working with the local communities. Can you tell us more about that?

DAVE: We have made some significant communication efforts to work with and encourage house owners in the area to do something to prevent the ongoing and potential future impacts to the seashore up to and including moving or removing their homes if feasible. So we work very closely with the Dare County Building Inspector and Planning Department, and they have kept us in the loop when it comes to the status of homes that may be at risk.

BROOKE: What do you do if you find a home that’s at risk of collapsing into the ocean?

DAVE: We would typically follow up with a communication in the form of a letter to the house owners if Dare County notified us that there was some type of a risk or instability of one of the structures in this area of the seashore and offer to work with and communicate with the house owner and to encourage them to do things to avoid a home collapse or any significant damage.

BROOKE: And how have homeowners responded?

DAVE: There have been several, I believe about a half dozen homeowners, who have looked at the situation and worked with us and with Dare County, and they’ve actually lifted their house up, put it on beams and on a truck, and moved it across the street.

BROOKE: Cape Hatteras has obviously been dealing with some really sticky issues. But as sea level continues to rise, more national parks may face issues like these. So, what advice do you have for other parks and public land managers in general?

DAVE: Yeah, the number one recommendation I have is don’t just focus on water levels, also focus on erosion. We have worked quite a bit with colleagues from Eastern Carolina University and others, and I’ve been here for eight years now, and I’ve realized that sea level rise is a very important factor; we need to be aware of it, we need to consider it, but before the sea level rises a foot and becomes a big issue, the ongoing erosion that occurs without sea level rise is a much bigger factor.

BROOKE: I imagine your scientific studies help a lot with that.

DAVE: So studying erosion and erosion transit, being able to forecast changes in the morphology and the dynamics of the barrier islands I think is a really important thing that is sometimes missed because we have such a large focus just on water levels themselves. And I think the second thing of course to focus on in terms of trying to predict future concerns really relates to storm surge. Storm surge modeling is really important. You can have very few impacts on a day-to-day basis, but once you have surge that is associated with certain storm events, and they might not even be hurricanes, those episodic stressors can really have a very large impact on coastal barrier island systems.

BROOKE: What kind of impacts are we talking about?

DAVE: They can result in large losses of sand, almost overnight; they can sometimes result in a large accretion of sand, but they can really have impacts on habitats, neighboring properties, and other assets that the parks use to support operations. So the more science that I think you can bring to bear, the better.

BROOKE: But don’t models like the one you used have limitations?

DAVE: When it comes to studying these things, and making these forecasts, that there’s also no substitute for experience and empirical observations. In some cases, we have some really good predictive models. They tend to sometimes just illuminate the obvious, the things that we already know are going to happen from watching our beaches day to day, month to month, year to year, and seeing the patterns and the trends. So really meshing those observations from our staff, from our community members, with scientific monitoring data and modeling I think really helps to inform our decisions.

BROOKE: OK. It looks like using the best available science, taking into consideration real-world conditions is key. And working with local communities. Are there any other things that public land managers in situations like yours should consider?

DAVE: Yeah, the one thing that I think when it comes to coastal hazards and sea level rise and climate change that we don’t talk about enough is the human dimension of managing these challenges. In some cases, the physical science side of it in terms of what’s happening with erosion and water levels and changes to national parks in coastal communities is the easy part. It can be easy to see what’s happening, make those projections, but finding ways to work with staff and nearby communities and park stakeholders and partners and come to consensus on the best way to manage those changes is the hard part.

BROOKE: Why is working with stakeholders harder than figuring out the science?

DAVE: And that’s because in many cases, there are communities and cultures that have thousands of years of history around these areas and have a really deep connection to the land. And those cultural connections are challenging and interesting to try to navigate through and dovetail with sometimes the harsh reality of the scientific predictions that we have. So I think that the area of social science and the human dimension of climate change and sea level rise management is something that’s really important for us as an organization to continue to build our capacity to study and understand.

BROOKE: That was Dave Hallac, superintendent of the National Parks of Eastern North Carolina and author of a recent study on predicting how the shoreline will change at Cape Hatteras National Seashore. Thanks for listening.

CONCLUSION [WITH MUSIC]: This has been Park Science Podcast. Catch up on more podcasts and articles at nps.gov/parkscience. ______________________________________________________


About the author: Brooke Bauman is a Scientists in Parks intern with the NPS Coastal and Ocean Advisory & Support Team (COAST). Her expertise is in environmental science, geospatial data, environmental journalism, and coastal restoration/resilience.

[1] See http://doi.org/10.34237/10089211

[2] See https://www.usgs.gov/geology-and-ecology-of-national-parks/geology-cape-hatteras-national-seashore

[3] See https://tidesandcurrents.noaa.gov/sltrends/sltrends_station.shtml?id=8652587

[4] See https://www.usgs.gov/centers/whcmsc/science/digital-shoreline-analysis-system-dsas

[5] See https://www.nps.gov/caha/learn/news/after-house-collapses-contractors-volunteers-national-park-service-clean-miles-of-beach-at-cape-hatteras-national-seashore.htm]

Barrier islands move constantly, but people build houses on them anyway. Cape Hatteras superintendent-scientist Dave Hallac explains why good data can only do so much. See the transcript for more about publications mentioned in the podcast. A production of Park Science magazine, Winter 2022 issue (December 30, 2022), https://www.nps.gov/subjects/parkscience.