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NOAA's Sea Level Rise Viewer Uses CoNED, EROS for Challenging Mapping in Louisiana

An old economics axiom holds that a rising tide lifts all boats. That may be, but a Sea Level Rise Viewer that has used elevation provided by the USGS’ Earth Resources Observation and Science (EROS) Center in parts of the U.S. suggests that rising tides have the power to impact a lot more than just the plight of ships.

Doug Marcy with NOAA's Office of Coastal Management
Doug Marcy with NOAA's Office of Coastal Management (Public domain.)

Created within the National Oceanic and Atmospheric Administration’s Office for Coastal Management (OCM), the Sea Level Rise Viewer web-mapping tool visually projects how sea level rise and coastal flooding may one day impact communities, local landmarks, and infrastructure. The underlying premise behind what the viewer projects is simple enough, says Doug Marcy, who works for OCM in Charleston, SC.  When sea leveIs go up, the current high tides go up with them.

“It looks at the difference in tide range. It’s like, we take what happens now at high tide, and then we add what’s going to be the high tide in the future,” Marcy said of the viewer. “We start with where our base level is and say, ‘OK, if we have three more feet of sea level, this is where high tide will be.”

In Louisiana, the Sea Level Rise Viewer relied in part on Topobathymetric Digital Elevation Models (TBDEMs) provided through the work of the Earth Resources Observation and Science (EROS) Center and the Coastal National Elevation Database (CoNED) Project. CoNED scientists use high-resolution point clouds from light detection and ranging (lidar) to produce enhanced topographic (land elevation) datasets, along with sonar and other existing data to produce bathymetric (water depth) datasets. Once integrated into seamless elevation products, those TBDEMs are useful for such science application studies as shoreline delineation, coastal inundation mapping, sediment transport, sea level rise, storm surge models, and tsunami impact assessment.

Jeff Danielson, the CoNED Applications Project Chief and a physical geographer at EROS, said the vertical accuracy of his projects today are within an impressive 10 centimeters in some places. Honing in on elevation accuracy is key to the Sea Level Rise Viewer’s mapping tool, Marcy added, especially as his office seeks out the best available elevation data when it goes into new places to map.

'The CoNED DEMs Were Important to Us'

“The CoNED DEMs were important to us in Louisiana,” Marcy said, “because they enabled us to accurately map different water levels to show the impacts of inundation or flooding in a very flood prone state.”

The Sea Level Rise visualization tool averages around 15,000 hits a month, Marcy said. Floodplain managers use it. So do municipal planners. It’s a source of information for officials with the Department of Energy who want to check on the vulnerability of nuclear sites. The Environmental Protection Agency can project impacts on one-source pollution sources or, say, a solid waste facility, using the viewer.

“Are those sites going to be vulnerable? That’s what they’re interested in,” Marcy said. “And it gets used all the time by the media. It one is of our most popular tools”

OCM began developing the Sea Level Rise Viewer in roughly 2010 to 2011. At first, the elevation data used weren’t always that good, Marcy said. But as new data emerged and were collected, the potential of the viewer expanded and became even more useful. In time, modeling for sea level rise came to encompass everywhere in the U.S. and its territories with sufficient data.

Across the coastlines of the United States then, the web-mapping tool projects community-level impacts from sea level rise and/or coastal flooding. Though it doesn’t look at storm surges, it does visualize the impacts of future levels of high water—from increases as little as knee-high all the way up to 10 feet.

The elevations within the TBDEMs don’t take into account the height of trees or structures, but rather projects how water is going to flow over bare earth, Danielson said. Photo simulations of how such events may impact local landmarks are also provided with the viewer, as well as data related to water depth, connectivity, flood frequency, socio-economic vulnerability, wetland loss and migration, and mapping confidence.

Sea Level Rise not the Same Everywhere

Of course, sea level rise isn’t the same everywhere. Though NOAA’s National Ocean Service (NOS) has reported that global sea level rises at a rate of about one-eighth of an inch per year, levels at specific locations may be more or less than that because of many local factors: the gradual settling or sudden sinking of the Earth’s surface, upstream flood control, erosion, regional ocean currents, and variations in land height.

Today in the United States, almost 40 percent of the population lives in relatively high-population-density coastal areas where sea level plays a role in flooding, shoreline erosion, and hazards from storms, NOS officials say. In such scenarios, rising seas threaten infrastructure necessary for local jobs and regional industries. Roads, bridges, subways, water supplies, oil and gas wells, power plants, sewage treatment plants, landfills—virtually all human infrastructure—are at risk from sea level rise, NOS reports.

While the CoNED work is important in helping to measure the impacts of sea level rise on all of that, Marcy said working with the CoNED team has been a two-way street for his agency. OCM not only has used the TBDEMs for its work in Louisiana, but it also reviews elevation products from CoNED, assesses their value to the work of NOAA and the OCM, and points out issues where it finds them to make improvements on those products.

One such improvement Danielson and CoNED are working on now is taking a wide variety of elevation datasets available from many different sources and pulling them together into one product. If they succeed, Marcy said, it will make mapping and modeling all that much easier.

“We look forward to what (CoNED) is trying to do to bring all these datasets together,” he said. “If they can do that, and we can use it, it’s going to save us a lot of work.”

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