Investigating Daniel Floods through Satellite Images

 Research question

How did "Daniel" floods evolve and why? Which actions can our community take to avoid similar issues in the future?

Abstract

In this case study we downloaded satellite images from the EO Browser with the appropriate visualization to see the evolution of the Daniel effect. Through the satellite images, we found the severity of the phenomenon throughout Thessaly. The amounts of water that fell with the rainfall within four days were equivalent to the amount that falls in a year for many regions of our country. The amount of water in the first few days made the neighboring Plastira lake seem insignificant. From the discussion with self-administrative agents, the incomplete anti-flood planning and the failure of local dams became apparent. The water not being able to find a sufficient outlet to the sea, created a lake in the area between Volos and Larissa, where the lake Karla used to be. We come to the conclusion that the policy of maximizing agricultural land must be changed so that widening projects of the banks of the Pinios River along its entire length are carried out. We also adopt the solution of creating small waiting reservoirs at various points to reduce the flow of water in similar conditions so that it can be drained gradually. Also, the drying up of Lake Karla created problems for the region's ecosystem and we propose its gradual restoration.

Main Results and Conclusions

We downloaded satellite images of our area from EO Browser. To make the visualization of the water volumes more intense we used wavelengths in the near-infrared SWIR (Short wave Infrared composite). So bodies of water are depicted as black areas as they absorb infrared. With the images we collected, we created short videos (which we also converted into gifs) to highlight the evolution of the phenomenon. They show the severity of the phenomenon that covered a huge area of Thessaly. The comparison of the flooded areas with Lake Plastira is typical.

We collected data on the amount of precipitation of those days (Meteo). The maximum amount of rain in Zagora of Pelion shows us that in five days 1096 tons of water fell per 1000 square meters!
The average precipitation for the city of Larissa (1955-2010) is 424.6mm, i.e. 424.6 tons of water per 1000 square meters!
Calculating an average precipitation of 400 mm and given that the area of Thessaly is about 14000 square kilometers, Thessaly received about five and a half billion tons of water in five days.

 The water not being able to escape to the sea created a lake in the area between Volos and Larissa in the place where Lake Karla used to be. Karla Lake was drained in 1962 to increase agricultural land. According to the study by Sidiropoulos et al, 2012, the desiccation created serious problems in the ecosystem, such as lowering the water table and salinization of the soil. So it was decided in the 80s, to create a smaller reservoir that can be seen in the related images. The current size of the lake makes it the largest in Greece. Due to the small possibility of draining into the sea, the lake maintains its size even today with a reduction of approximately 10-15%.

It is clear that the disasters that occurred were largely unavoidable. The expert autopsies showed the lack of large-scale flood protection works and the poor management of local dams. The above made the effects of weather phenomena worse, exacerbating the consequences. According to Professor Mr. Nikitopoulos (University of Thessaly) https://bit.ly/4apq9Aa  , there were studies, but the risk was underestimated, with the result that very few projects were carried out. In an article by Mr. Koundourakis http://bit.ly/3JaZMSU  , according to the Risk Management Theory (Domingo, 2020), the steps that must be followed in order to successfully manage such situations are presented.

Prognosis, prevention, accurate and timely information, and preparedness, are important factors influencing and managing the risk.

The expert suggestions  https://bit.ly/3VPTJuy that currently exist are summarized in the following suggestions:

Change in the policy of maximizing agricultural land. Large tracts of land near the Pinios river must be converted to be used in such emergencies.

The widening of the river beds, the disposal of flood plains, the removal of embankments, the demolition of riverside structures, the redesign of railways, roads, bridges, anti-flood works, the creation of alternative diversion channels for the Pinios, and creating small waiting reservoirs at various points to reduce the flow of water.

The above design leads to the creation of alternative flow paths of the water volumes and the time delay of the water flows so that there is no congestion of the system and there is enough time for its drainage. Also important is the redesign of the early warning system.

Phenomena like Daniel's have happened in the past and will surely happen again in the future. Their frequency may even increase, as a result of climate change. Therefore, we should highlight the issue in our local community, so that we can be part of the solution and the change of mentality, in our region.