Monitoring of coastal morphodynamics using satellite imagery


This tool aims to use observed morphodynamical changes of any coastal system during the last 30 years to predict future morphological effects to coastal interventions. This is done by the analysis of LandSat satellite imagery using Google Earth Engine. This platform enables quick selection and analysis of satellite imagery, using Google storage space and processing capacity. Since the first useful LandSat imagery was recorded in the early 1980’s, over 30 years of imagery is available for every place on earth. By first assessing past morphological changes along the coast where an intervention is planned, the morphodynamical system can be understood and predictions of future effects to interventions can be better predicted. These observed changes in the past also provide a valuable dataset to test the performance of models.

Since the mid-seventies, Earth observation satellites have been collecting data from the Earth’s surface. Over the years, the quality and return frequency have improved considerably. Hence, the satellite images provide good coverage of the changes on the Earth’s surface, such as urbanisation, deforestation and morphological changes in rivers and along coastlines.

The data from many of these satellites is freely available. Until recently, the analysis of the images was difficult because of the huge amount of storage space and processing capacity necessary. However, several years ago, Google started the Google Earth Engine platform in which all freely available satellite imagery is accessible, and can be analysed using Google storage and processing facilities. This has greatly improved the applications of the satellite data. One such application is presented here, and involves the monitoring of morphological changes resulting from autonomous processes and interventions in the past.

For the Frisian coast along Lake Ijsselmeer, the satellite images provide interesting information about the larger scale morphological changes in the shallow foreshore. Over this period, several interventions have been executed, such as the development of islands, sand nourishments and dams. Most of these interventions were executed in the nineties. The morphological effects have not been monitored and are therefore not clear. The analysis of satellite imagery allows us to monitor the effects of these interventions in hindsight. In addition, it allows us to determine autonomous changes in the coastal system such as coastal erosion or progradation.

The understanding of the system at a decadal scale is essential for the planning and design of new interventions. It provides insight in the speed and magnitude of expected morphological changes and therefore also provides valuable data to test model outcomes.

The tool works best in sandy coastal settings in which interventions are planned. In the case of the Frisian Lake IJsselmeer coast it was used to monitor changes in the shallow foreshore, as this foreshore is visible in calm weather conditions. In more turbid settings, the tool can be best applied to monitor changes to the sandy coast.