New Technique Enhances Coastal Water Level Monitoring

Researchers at the Technical University of Munich (TUM) and the University of Oxford have developed a new measurement method that captures the variability of tidal levels more accurately than previously used methods. Using this method, they were able to demonstrate tidal differences of up to one meter within a bay 90 kilometers long. The results could improve coastal protection and navigation in areas where measuring stations are lacking.

Anyone who has ever been to the beach, especially on the North Sea, has experienced how the water can spread out or recede in a very short time-a phenomenon caused by the tides. Accurate and reliable knowledge of these movements is essential for coastal protection, flood forecasting, and safe ship navigation. However, in many coastal regions the data are lacking: while local tide gauge stations provide data only at individual points, the satellite measurements typically used near the coast often has too low a resolution.

Variability in water levels at 100-fold resolution

The newly developed method by researchers at TUM and the University of Oxford also uses satellite data, but in a new way: Instead of measuring water depth along the coast, they use the beach itself as a "ruler". They combine the visible waterline on satellite images with the known slope of the beach. They can thus monitor sea levels and calculate tidal variations from these observations.

The method provides data accurate to within 100 meters. Previous satellite data could only provide this information at a resolution of about ten kilometers-a difference of a factor of 100. With this level of accuracy, they found, for example, tide differences of nearly one meter along a 90-kilometer stretch of coastline on a beach in New Zealand.

Better predictions even without a tide gauge

Thomas Monahan, one of the study's authors and a research associate at the University of Oxford, says: "Our research shows that tides can vary significantly even over relatively short distances. This has major implications for the risk of coastal flooding. Small-scale differences in tides can determine whether two neighboring regions are spared or flooded during the same storm. Once these methods are further refined, they could enable significantly more precise local tide forecasts. People would then no longer just learn about tide patterns in their region, but specifically what to expect on their beach."

"Our method combines the precision of local tide gauge stations with the coverage of satellite imagery," says Michael Hart-Davis of the German Geodetic Research Institute at TUM. "This also allows us to close the data gap in coastal regions without their own tide gauge stations." These are currently areas in parts of Africa or Southeast Asia. This opens up new possibilities, particularly for navigation along the coastline. " It also offers an opportunity to better assess flood risks involving a combination of factors-such as heavy rain, storm surges, and high tides-or to determine when saltwater threatens to seep into the groundwater."

In developing the method, the researchers relied on satellite imagery spanning more than forty years, provided by NASA's Landsat program and the U.S. Geological Survey. They hope this will enable them to make more reliable forecasts in the future. Additional data from programs such as Copernicus Sentinel-2 could further increase spatial and temporal coverage in the future.