Dynamic coastline at the Nile Delta
Background
The coastline at the Nile mouth near Alexandria is defined mainly by the balance of sediment deposition by the Nile River and its removal by the Mediterranean Sea.
The sediment load of the Nile River was significantly reduced by the Aswan High Dam located about 1000 km upstream, which was completed in 1970. Before the construction of the dam, the Nile Delta received an annual sediment load of approximately 130 million tons. Today, this figure has dwindled to around 16-20 million tons, leading to reduced natural replenishment of the coastline.
Over the past century, the Mediterranean Sea has seen an average sea level rise of about 3.4 millimetres per year due to global warming. This leads to an additional substantial increase in coastal erosion and vulnerability to storm surges.
Based on satellite data, coastal erosion around Alexandria has been estimated at around 1 meter per year in certain areas. This rapid rate of erosion threatens infrastructure, coastal communities, and agricultural lands. Alexandria is Egypt’s second-largest city and home to over 5 million people. Many of the residents rely on agriculture, fisheries, and tourism, all of which are directly or indirectly affected by changes in the coastline. Therefore, Egypt combats coastal erosion around Alexandria and has, for example, spent 21 million Euro in 2018 for this task.
Exercises
- Satellite Map:
- Look at the satellite image maps and click on the layer selector in the upper right. Deselect all layers except the satellite image from 1985 by unticking the respective boxes.
- Describe the satellite image and try to identify land cover classes.
- Add the satellite images from 2002, 2016, and 2023 one by one and try to identify differences. What is happening with the coastline?
- Can you find structures along the coast, which might have been made to slow the retreat of the coast down?
- Toggle between the satellite images from 1985 and 2023. Where are the changes in the landscape most prominent?
- Comparing these two images, which changes in the landuse can you identify?
- Go back to the satellite image from 1985 again.
- Add the layer “coastline” and compare the changes visible here with your findings.
- EO Browser:
- Open the EO Browser.
- Find the most recent Sentinel-2 dataset covering the area displayed in the satellite map. Is it easy to find (more or less) cloud-free images? Why/why not?
- Select a true colour visualisation.
- Can you identify additional, recent changes in the area (check e.g. forests and agricultural land)?
- Compare with the Satellite Map. Can you identify additional substantial changes?
- Select the false colour infrared representation. Can you identify the land-use of the most intensely vegetated areas (represented by bright red colours)?
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