Guam: A Biogeographic and Maritime Cultural Landscape Exploration of a World War II Amphibious Battlefield

January 27-February 25, 2023 // July 27-August 23, 2023

Measuring Elevation to Understand Coastal Change

Coastal elevation data allow scientists to document how the coastal environment is changing over time. At War in the Pacific National Historical Park (WAPA), such data is particularly important since past human activities, such as those related to World War II, and natural events, such as typhoons, have contributed to the current shape and structure of the coast. Understanding changes the park is now experiencing and may anticipate in the future due to climate change will help park managers identify the most effective management strategies for preserving its cultural and natural resources, both above the water and below it.

Erosion and bank undercutting along the shoreline at the Agat unit of Guam’s War in the Pacific National Historical Park immediately after 2023’s Typhoon Mawar.
Erosion and bank undercutting along the shoreline at the Agat unit of Guam’s War in the Pacific National Historical Park immediately after 2023’s Typhoon Mawar. Image courtesy of National Park Service via Guam: A Biogeographic and Maritime Cultural Landscape Exploration of a WWII Amphibious Battlefield. Download largest version (jpg, 6.2 MB).

During our January/February 2023 field expedition, we conducted elevation surveys to map and characterize the coastal environment at the Asan and Agat units of WAPA. We repeated a subset of these surveys when we returned to Guam in May/June 2023. These datasets provide "snapshots in time" of the coastal environment, and we will compare them to each other to evaluate short-term change. This comparison will be especially meaningful because it will illustrate how Category 4 Typhoon Mawar, which made landfall on Guam on May 24, 2023, changed the coastline. Noticeable impacts from the storm included shoreline erosion, redistribution of sand along the beaches and intertidal zones, and reconfiguration of the Asan River mouth.

Photographs of an area along the Asan River immediately before Typhoon Mawar (left) and after (right). The storm resulted in substantial bank erosion and removal of much of the existing vegetation.
Photographs of an area along the Asan River immediately before Typhoon Mawar (left) and after (right). The storm resulted in substantial bank erosion and removal of much of the existing vegetation.
Photographs of an area along the Asan River immediately before Typhoon Mawar (left) and after (right). The storm resulted in substantial bank erosion and removal of much of the existing vegetation. Images courtesy of National Park Service via Guam: A Biogeographic and Maritime Cultural Landscape Exploration of a WWII Amphibious Battlefield. Download largest version of the left image (jpg, 4.5 MB). Download largest version of the right image (jpg, 5.9 MB).
Point cloud data collected with a Trimble SX10 total scanning station of the mouth of Guam’s Asan River in February 2023 (left) and June 2023 (right). Comparison of the two datasets shows that the river has been redirected eastward and a delta has formed at its mouth as a result of Typhoon Mawar.
Point cloud data collected with a Trimble SX10 total scanning station of the mouth of Guam’s Asan River in February 2023 (left) and June 2023 (right). Comparison of the two datasets shows that the river has been redirected eastward and a delta has formed at its mouth as a result of Typhoon Mawar.
Point cloud data collected with a Trimble SX10 total scanning station of the mouth of Guam’s Asan River in February 2023 (left) and June 2023 (right). Comparison of the two datasets shows that the river has been redirected eastward and a delta has formed at its mouth as a result of Typhoon Mawar. Images courtesy of National Park Service via Guam: A Biogeographic and Maritime Cultural Landscape Exploration of a WWII Amphibious Battlefield. Download largest version of the left image (png, 680 KB). Download largest version of the right image (png, 700 KB).

We collected elevation data using a Trimble SX10 scanning total station and R12i global navigation satellite system (GNSS) equipment. The scanning total station provides high-density point cloud data. The point clouds are x,y,z datasets, where x and y represent coordinates (e.g., latitude and longitude or easting and northing) and z represents elevation. These data can be turned into geospatial surfaces, such as digital elevation models (DEMs). We collected this data for the entire visitor use areas of both park units, from the shoreline to the main road, including the beach, intertidal zone, rivers, parking lots, and facilities.


A project team member collecting high-resolution coastal elevation data using a Trimble SX10 scanning total station.
A project team member collecting high-resolution coastal elevation data using a Trimble SX10 scanning total station. Image courtesy of National Park Service via Guam: A Biogeographic and Maritime Cultural Landscape Exploration of a WWII Amphibious Battlefield. Download largest version (jpg, 2.9 MB).
Preliminary point cloud data from a Trimble SX10 scanning total station set up on boulders on the shoreline of Agat facing inland to measure bank erosion at the shoreline in February 2023.
Preliminary point cloud data from a Trimble SX10 scanning total station set up on boulders on the shoreline of Agat facing inland to measure bank erosion at the shoreline in February 2023. Image courtesy of National Park Service via Guam: A Biogeographic and Maritime Cultural Landscape Exploration of a WWII Amphibious Battlefield. Download largest version (jpg, 780 KB).

To complement the data from the scanning total station, we took thousands of measurements with the R12i GNSS receivers to document the location and elevation of specific features at each park unit. These features included the shoreline at low tide, shoreward bluff and vegetation lines, historic features (e.g., pill boxes, boulder wall), monuments, wayside signs, trails, parking bollards, and footprints of restroom facilities.

Collectively, these data will be used to provide a more holistic land-to-ocean understanding of the study areas, including insights of increased coastal vulnerability as a result of the blasting of the coral reefs during World War II.

By Monique LaFrance Bartley, National Park Service Ocean and Coastal Resources Branch
Published September 18, 2023