Geodetic Science Snapshots - Environmental & Hydrogeodesy

Geodetic stations at two coastal sites in Hong Kong were able to measure storm surge from Typhoon Hato in 2017 and Typhoon Mangkhut in 2018, using GNSS Interferometric Reflectometry (GNSS-IR). Adding more satellite signals and GNSS ground stations would provide greater coverage in space and time and greater accuracy to geodetic, storm-resistant, ground-based measurements of sea level, storm surge and even tsunami height.

A new method to measure relative sea-level rise in low-elevation coastal zones combines global navigation satellite system (GNSS) data with measurements from rod surface-elevation table–marker horizons (RSET-MHs) and satellite altimetry. Combining these measurements shows that the sediments in coastal Louisiana are subsiding faster than previously recognized and thus relative sea level is rising at a higher rate.

GPS measurements of surface motion near four dams in India, show that the surface moves when the water volume of the dam changes. These observations show that the water volume of the dam affects the stress of the surrounding rock. Thus the dams may contribute to stress changes and deformation, particularly triggering earthquakes nearby.

Ground displacements caused by wastewater injection near Cushing, Oklahoma determined from remote sensing showed between 4 to 6 centimeters of uplift across Cushing over 17 months. Remote sensing provides a significant new way to understand near-surface deformation caused by humans or nature, especially near critical infrastructure such as the Cushing Hub, among the largest of oil storage facilities.

Vertical surface motions measured by GPS sites in Idaho, Montana, Nevada and Wyoming can be combined to measure water load over local to regional scales that is useful for water resource management and our understanding of the water cycle. Users can use this technique and the many available geodetic networks to track precipitation, water quantity changes, and the state of aquifers.

A colluvial hollow in Fourmile Canyon, Colorado that was present after the 2010 Fourmile Canyon wildfire transitioned to a fluvial channel with steps and pools while retaining the original hollow roughness after an intense 2013 flood. The changes were measured with a terrestrial laser scanner from UNAVCO and can help understand future risks in a changing landscape.

The health of wild vegetation during the California drought of 2012 to 2014 was measured with reflected Global Positioning System (GPS) measurements from hundreds of sites that are part of the EarthScope Plate Boundary Observatory. The geodetic data is compared to optical-wavelength measurements at collocated sites. These methods can help gauge future conditions and inform environmental impacts on humans and nature.

Satellite and GNSS observations show that parts of the San Francisco Bay area are underlain by artificial fill and old mud deposits that are undergoing subsidence at a higher rate than previously appreciated. Combining the rate of subsidence with the potential sea level rise suggests that much more of the bay area could be inundated with water.

GPS sites in California measure the changing water load due to rainfall, snowfall, groundwater, and drought. The vertical motions are shown to influence the state of stress on shallow faults. The rise and fall of the surface due to water loading and unloading creates a small amount of additional stress on the faults and can trigger small earthquakes.

Groundwater withdrawal during the 2007 to 2010 drought in the San Joaquin Valley in California caused a great deal of subsidence. Geodetic, water level and geologic data were used to determine the amount of inelastic deformation. The results suggest that most of the deformation was inelastic during the drought and thus the volume of the aquifer has been reduced, leaving less storage capacity for water in the future.

Vertical motions measured by GPS ground stations can be used to track water loads related to precipitation in Ethiopia and Eritrea. The network monitors the seasonal East African monsoon and a smaller regional rainy season. The GPS network is an effective water monitor for the region, where most of the population is agriculture-based.

Eight years of observations of millimeter-level vertical surface changes from a dense network of Global Positioning System (GPS) receivers in the Pacific Northwest tracks a fluctuating water load due to varying precipitation. The observations track seasonal variations (i.e., more rain or snow in the fall and winter) and the drought of 2008-2010.

The Plate Boundary Observatory in the western United States is being used as a hydrological monitor. From 2013-2014, the western U.S. lost about 240 gigatons of water, equal to the amount of annual ice loss in Greenland.

Analysis of GPS stations, many that are part of the Plate Boundary Observatory, reveals uplift of the California Coast Ranges and Sierra Nevada Mountains. Much of this uplift comes from groundwater depletion for irrigation. These changes may increase the rate of seismicity on the San Andreas Fault.

About 900 GPS stations, most of which are part of the Plate Boundary Observatory in the western United States, recorded the Earth’s surface response to snow and rain loading. The analysis indicates the seasonal water storage in the mountains in California and shows another way to use GPS for water resource management.

The Mississippi Delta along the Gulf Coast of the United States is a major site of sediment deposition from the Mississippi River and conversely a major site of wetland loss from rising seas and subsidence. There is debate about how much and when the delta has risen or fallen due to deposition, subsidence, sea level change, and erosion.

Measurements of snow depth are important to climate modelers, meteorologists, and water resource managers, but in the past there has not been both an accurate and widespread method of obtaining these data.

Subsidence, or sinking, is becoming a big issue for coastal towns that are also dealing with the threat of rising sea-level. A sinking city becomes more susceptible to flooding over time, and knowing the rate of subsidence can help a city prepare for future floods.