November 30, 2021

Coastal Flooding Visualization

Written by: Mackenzie Mills

 

Using the 2D and 3D visualization and analysis methods in Global Mapper, changes in water levels and flood risks can be modeled and explored to aid in understanding the risk of flooding in local areas. Flooding is often thought to be caused by storms with extreme amounts of precipitation, but as Earth’s climate changes and seas warm and rise, routine flooding with high tides is an increasing concern. 

Recently Portland, Maine, a city not far from the Blue Marble headquarters, experienced flooding due to the rising levels of natural tides. As a coastal city, the risk of minor flooding has always been a concern, but king tides rising high enough to cause water to run through the streets were only an annual or biannual occurrence. Using Global Mapper and publicly available terrain and tide predictions and data, coastal flooding for this area can be modeled and analyzed. 

From the Tides and Currents predictions from the National Oceanic and Atmospheric Administration (NOAA), the high and low tides for the current month are charted.

Looking at the tidal chart for Portland over the month of November, the high and low tide marks are seen. The king tides, cycles that occur during the full moon, are most extreme and can be seen in this chart as well. For any given date, the water level can be visualized in Global Mapper using the Water Level Display option in 2D and 3D. With this visualization and the reference data loaded, areas likely to be impacted by high tides can be seen. 

The water level shown in 2D shades the covered portion of the terrain data blue. This shading is also reflected in the elevation legend.
Shown in 3D the water is shown as a shaded surface intersecting the terrain at the water level elevation.

A more complex analysis utilizes the Simulate Water Level Rise/Flooding tool in Global Mapper. This tool models how an increase in water level from a starting elevation will flow over the terrain in a given area. Using an elevation of zero as the start point and raising the water to the high tide measurement, the areas impacted by a specific tide are created as polygons in the workspace. 

To quickly analyze multiple tide periods, predicted or measured, over the study period, data for only high tides from NOAA’s tide predictions can be extracted as a table. Using this table of high tide values in a Global Mapper script, layers modeling each high tide can easily be generated. 

Using the table of high tides as a variable table, a new layer is created in the workspace, modeling the water level at each high tide.

Using the Animate functionality in Global Mapper, each layer can be viewed in succession showing the variation in high tides, including recent king tides, over the beginning of November. 

Looking ahead, the tide predictions for the month of December are downloaded from NOAA and in reviewing the data it appears tides are expected to approach and even exceed two meters. This is higher than what was seen in November and will likely result in some coastal flooding. Using the same script format as above the generated December tides table is used to create water level rise layers for the high tides through the first half of December.

Displaying multiple water level rise layers for December shows the total predicted high tide impact.

Identifying the highest predicted tide, the generated flood model can be used in the Spatial Operations tool with local municipal data to determine the parcels and roads that may see some flooding, as a result of this particular tide. Using the intersect predicate with the parcels data and then the roads data to create two new vector layers, lists of potentially flooded roads and land areas are generated. 

Spatial Operations is used to identify the roads and land parcels at risk of flooding during the highest predicted tide in December.

With Global Mapper’s ability to model the impact of local tides and predict affected areas, local officials and businesses can better prepare for these higher tides. After assessing the current situation of coastal flooding this information can be used to discuss and model flood mitigation strategies in Global Mapper and other programs. 

If you would like to model tides and coastal flooding in Global Mapper, download a 14-day free trial today! If you have any questions, don’t hesitate to get in touch

 

References:

“Tide Predictions – NOAA Tides & Currents.” Tides & Currents, National Oceanic and Atmospheric Administration, https://tidesandcurrents.noaa.gov/noaatidepredictions.html?id=8418150. 

Weber, Sam, and Christopher Booker. “Barely a Cloud in the Sky and Portland, Maine, Is Flooding.” PBS, Public Broadcasting Service, 14 Nov. 2021, https://www.pbs.org/newshour/show/barely-a-cloud-in-the-sky-and-portland-maine-is-flooding. 

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