Thursday, February 22, 2024

NewsHorizon

Where your horizon expands every day.

Science

became a major issue in 2014 The malfunctioning dams located in Wadi Derna, Libya were a significant problem in 2014.


One of the dams that collapsed at Wadi Derna

Dave Petley, widely acclaimed as a global authority on landslides, authors The Landslide Blog.

Image of a landslide partially covered with a transparent sand-colored overlay and the words “The Landslide Blog,” centered, in white

The media has been reporting on the destruction caused by the severe flooding in Derna, a port city in Libya. The focus has been on the devastation in the urban area and the heartbreaking stories of loss. Satellite images before and after the event, as well as some photos taken on mobile phones, are now available to show the extent of the disaster. It is evident that the damage was not just caused by heavy rainfall and a river flood, as two dams further up the Wadi Derna (also known as Darnah) are being blamed for exacerbating the situation.

The two dams are clearly visible on Google Earth. The first is located at 32.658, 22.578:-

The upper dam in Wadi Derna, as shown on Google Earth.

The image from June 2023 depicts the upper (Al-Bilad) dam located in Wadi Derna, visible on Google Earth.

The second point is located approximately 1 kilometer above the city at coordinates 32.752, 22.631.

The lower dam in Wadi Derna, as shown on Google Earth

The image from June 2023 depicts the Abu Mansour dam in Wadi Derna, located on Google Earth.

An Arabic article on the News Libya website details the origins of dams in Derna. It mentions that the city has experienced multiple floods from the Wadi, with notable occurrences in 1941, 1959, and 1968. The flood in 1959 was especially devastating.

During the 1960s, research suggested that building dams would be necessary to safeguard the city. In the 1970s, a Yugoslavian company was commissioned to construct the dams. The first dam, named Al-Bilad Dam, could hold 1.5 million cubic metres of water, and the second dam, called Abu Mansour Dam, had a capacity of 22.5 million cubic metres. Both dams were composed of a central layer of compacted clay covered with a layer of stone.

The recent disaster has led to the release of planet images depicting the locations of the two dams. Specifically, the upper dam, also known as Al-Bilad dam, is shown.

Satellite image of the site of the Al Bilal Dam in Wadi Derna, Libya.

The photograph of the Al Bilal Dam location in Wadi Derna, Libya taken by a satellite. The image is copyrighted by Planet and was taken on September 12, 2023.

The picture is evident in demonstrating the dam’s collapse and subsequent washing away, along with a significant flood downstream. The evidence suggests this was a disastrous breakdown.

The lower dam, also known as Abu Mansour, has been lost. However, the current Planet image is partially obscured by clouds.

Satellite image of the site of the Boumansourl Dam in Wadi Derna, Libya.

The picture taken by a satellite shows the location of the Abu Mansour Dam in Wadi Derna, Libya. The image is owned by Planet and was approved for use. It was captured on September 12th, 2023.

The most probable event is a chain reaction of danger in which the initial dam was overpowered and gave way, causing a surge of water and debris to flow downstream. This would have combined with water in the channel to overpower the lower dam, resulting in an obvious catastrophic collapse. This scenario requires additional investigation.

The placement of the lower dam, only 1 km before the city, played a role in the flooding. The close proximity meant that the flood had little time to disperse, resulting in Derna being hit with the full force of the rush of water.

Efforts are required to comprehend the reasons behind the calamity. Evidently, the precipitation brought by Storm Daniel was exceptionally high – with reports of over 200 mm. This significant amount may have surpassed the intended capacity of the structures. It would be intriguing to determine if this total can be linked to climate change. In 1986, Derna experienced floods, but the dams were able to effectively manage the water and prevent significant damage to the city. It will be crucial to compare the 2023 event with past storms.

There have been allegations that the maintenance of the dams may have been inadequate. These structures are relatively old, being around 50 years old, and therefore would likely require upkeep.

Inevitably, a population that has experienced conflict and a dysfunctional government will be more vulnerable, ultimately resulting in a higher number of casualties.

It should be acknowledged that Derna remains vulnerable to future flooding. However, securing the necessary resources to reconstruct the dams is expected to be extremely challenging due to the current state of civil society in Libya.

.

Go back to the main page of The Landslide Blog.

Text © 2023. The authors. CC BY-NC-ND 3.0
Unless stated otherwise, all images are protected by copyright. Reproduction without explicit consent from the copyright holder is not allowed.