Using our expertise in Earth Observation at Mallon, we are exploring how readily available satellite data can assist in detecting and tracking environmental issues.
In our latest blog, we look into the recent breach of the Nova Kakhovka dam in Southern Ukraine and the subsequent flooding of vast areas of land downstream. Mallon colleague Rafal Marciniak compiled the following case study using data captured from the European Space Agency’s (ESA) Sentinel–1 satellite.
Case Study – Mapping the Floods Following the Nova Kakhovka Dam Breach
The Nova Kakhovka Dam is located on the Dnipro River in Southern Ukraine, an area that has come under renewed focus due to the ongoing war in Ukraine. The dam helped to power the Kakhovka hydroelectric plant, holding back a reservoir containing 18 cubic km of water. Following the breach of the dam, water from the reservoir was released, resulting in a flood that covered 230 sq. miles of land.
Our flood maps were produced using ESA’s Sentinel–1 Synthetic Aperture Radar (SAR) satellite. Radar images are perfect for mapping the presence of water, as calm water reflects the signals away from the sensor, resulting in areas that appear contrastingly dark. Radar images are especially helpful when weather conditions are far from perfect or if suitable cloud–free scenes are unavailable for the concerned region.
The first radar image acts as a reference to show how the river and dam looked before the breach. The Nova Kakhovka dam can be seen at the top of the image, with the large reservoir behind it. The red areas on the map represent urban areas, and the blue areas water. It is clear from the map that the river levels are steady and that the urban areas are free from water.
The second map was created using imagery captured on 9th June 2023, 3 days following the breach of the dam. From this map, it is easy to see the effect the breach has had on the downstream areas. The river is now broader and higher, while the reservoir is starting to reduce. It has also affected rivers and streams that flow into the Dnipro River, which have also become swollen with the additional water. However, it is the city of Kherson at the base of the map where the effects of the dam breach are at their most stark. Large areas of the city can be seen to be underwater, affecting tens of thousands of people.
The final flood map is similar to the one above but with the urban areas affected by the flooding highlighted. This makes it easier to see how much land has been flooded. The map shows that approximately 109 sq. km of urban land and about 273 sq. km of other land had been flooded up to 3 days following the dam breach.
What can we learn from this?
Earth Observation has almost limitless potential for remote monitoring of global flood and water levels, especially in hard–to–reach areas or regions that are inaccessible due to war or conflict. With SAR, satellites such as Sentinel–1 can capture imagery in any weather condition, day or night. This means that any area of interest can be studied over long periods to assess meaningful changes.
The only current drawback to the use of Sentinel–1 is the limited revisit times which have increased to 12 days from 6 following the failure of one of the Sentinel–1B satellites. However, the advantages of using Earth Observation to monitor and map flooded areas, especially in remote locations, are clear.
For more information about the methods used in this study or to discuss your Earth Observation project requirements, contact us below.