(50 years remained and ended in a historic tragedy)

Dr. Abdel Moneim Saeed

Derna is a city located on the banks of a large valley “Wadi Derna” . This valley is more than 60 km long and the area of ​​its catchment basin is 575 square km. As a result of the frequent occurrence of floods in the city due to the valley passing through its centre, studies conducted in the 1960s recommended the necessity of constructing more than one dam in order to protect the city and to reserve the huge amounts of water that flows through the valley at the time of flood and ends up in the sea.

inAt the beginning of the 1970s, a Yugoslav company built two aggregate dams (the core is made of compacted clay, and the sides are made of stones and rocks) on the valley’s course, the Al-Bilad Dam, which is about 1 km south from the heart of the city, with a storage capacity of about 1.5 million cubic metres, and the Abu Mansour Dam, which is about 1 km south of the heart of the city. 13 km south of the first dam, which is a large dam with a capacity of about 22.5 million cubic metres. Throughout my life, I have never seen the Boumansour Dam fill due to its large storage capacity.

The construction of these dams ended the city's flood problem, which was causing huge losses of life and property. These include the 1941 flood, which caused great losses to the German army, the 1956 flood, the catastrophic flood of 1959, the 1968 flood, and the 1986 flood, which, although large, the dams played their role in preventing damage to the city. The 1959 flood remains the most painful in the city’s memory due to the number of victims and material losses before the flood occurred yesterday, September 11, 2023.

The September 2023 flood is the most severe, destructive, destructive and painful in the history of this city for several reasons, including:

(1) The amounts of rain that fell in a period of less than 24 hours exceeded 200 mm in the valley’s catchment basin. This means that the catchment basin received more than 115 million cubic meters of water, an amount much greater than the combined bearing capacity of the dams. These quantities have not been recorded previously in all recorded floods (what is meant is rainfall over several hours).

(2) The presence of dams during the past fifty years created a state of reassurance among people, which made them crawl with buildings, roads, and facilities on the banks of the valley that were not intended throughout history to construct roads and buildings.

(3) Unlike previous floods, where water was flowing freely through the stream, yesterday’s dawn flood was due to the large quantities that had accumulated behind the dams, in addition to the huge additional amounts of water brought to the valley, which made this flood historic and unprecedented. One of the evidence for this is that the shrines of the Companions of the Messenger of God have remained there since the Islamic conquest, despite all the floods throughout history, until yesterday’s dawn flood that swept away them and several meters below them, and the location of those shrines is now in the air several meters above the surface of the ground.

There is no doubt that this flood has never been seen before in the city throughout its history. Everything has changed, including the city’s landscape. The valley has now expanded to include several streets and neighborhoods on its sides and along its course in the city. Today, the city is without protection from any other flood, even if it is minor. Therefore, the way we deal with this valley must change from the roots.

We always say that trying to manage nature has disastrous results, and what is always correct and safe is to work with nature with its laws and reality, and not to try to control it. What happened yesterday morning will have major impacts on people’s lives and their presence in the region. These dams have remained in place for 50 years in full and complete, and they collapsed yesterday. This is a period that must be studied carefully, and all its positive and negative aspects must be known, not only for the sake of purely academic aspects, but also in order to anticipate different ways of dealing with dams and valleys throughout Libya.

Source :https://www.newslibya.ly/%D8%B3%D8%AF%D9%88%D8%AF-%D9%88%D8%A7%D8%AF%D9%8A-%D8%AF%D8%B1%D9%86%D8%A9%D8%8C-%D8%A7%D9%84%D8%A8%D8%AF%D8%A7%D9%8A%D8%A9-%D9%88%D8%A7%D9%84%D9%86%D9%87%D8%A7%D9%8A%D8%A9/