Flooding forces thousands to flee their homes in southeastern Ghana.

As many as 26 000 people have been forced to flee their homes in southeastern Ghana, following a flood caused by an emergency release of water from the Akosombo Dam on the Volta River. The water was released after the water level in the dam reached 84.5 m following months od unusually high rainfall this summer. The maximum safe water level in the dam is 84.6 m, above which there is considered to be a risk of the dam failing catastrophically. 

Residents of the Volta Basin in southern Ghana flee their homes following an emergency release of water from the Akosombo Dam on Friday 13 October 2023. Ariana Cubillos/AP.

The Akosombo Dam was built in the 1960s as a hydroelectric dam, intended to generate power for the aluminium industry. The dam crosses the Volta River at Akosombo Gorge, creating behind it Lake Kariba, the largest man-made lake on Earth, covering 3.6% of Ghana's land area. Today the dam provides much of the electricity used in Ghana, as well as neighbouring Togo and Benin. 

Water being released from the Akosombo Dam. Ghanaian Times.

See also...

Follow Sciency Thoughts on Facebook.

Follow Sciency Thoughts on Twitter. 

Thousands forced to flee their homes as much of southern Norway affected by flooding.

Thousands of people have been forced to flee their homes, and at least one person has died, in flooding which has affected much of southern Norway. The country received about three times as much rainfall as would usually be expected in the month of July, with no sign of a let-up in the first part of August. Many rivers have burst their banks, and a series of landslides have been triggered as sediments became waterlogged, impacting transport networks and other infrastructure. Landslides are a common problem after severe weather events, as excess pore water pressure can overcome cohesion in soil and sediments, allowing them to flow like liquids. Approximately 90% of all landslides are caused by heavy rainfall. On Wednesday 9 August the Braskereidfoss Hydroelectric Dam on the Glomma River partially collapsed under the weight of water that had built up behind it, sending floodwaters across the border into Sweden. One woman is reported to have died after falling into a flooded stream on Tuesday 8 August.

Floodwaters from the Storelv River pouring through the centre of Hønefoss, to the northwest of Oslo, on 9 August 2023. Annika Byrde/NTB/Reuters.

Summer rainfall in Norway is usually driven by evaporation over the North Sea, leading to rain when westerly winds prevail, and drier spells when the wind blows from the east. However, much of this summer's rain has been driven by the exceptionally high temperatures in the Baltic Sea this July, which have led to higher rates of precipitation, and high levels of rainfall when the wind blows from the east. The average annual rainfall in Norway has risen by 18% in the past century, with much of that increase happening in the past four decades. Should high summer temperatures in the Baltic become a regular feature of a warming climate, then it is likely that Norway, and Scandinavia in general, could shift towards a much wetter climate.

Flooding at Aurdal in southeast Norway on 11 August 2023. Ole Berg-Rusten/NTB/AFP/Getty Images.

See also...

Follow Sciency Thoughts on Facebook.

Follow Sciency Thoughts on Twitter.

Flooding and landslides kill at least 37 people in South Korea.

Thirty seven people are known to have died and another ten are missing in a series of flooding and landslide related events in southern South Korea.  The highest number of fatalities occurred in Osong in North Chungcheong Province, where a river burst its banks, causing an underpass to flood, and trapping 15 vehicles, including a bus on the evening of Saturday 15 July 2023. Nine bodies have now been recovered from the site of this incident, with nine people receiving hospital treatment, and five still unaccounted for.

An underpass in Osong, North Chungcheong Province, which flooded on Saturday 15 July 2023, trapping fifteen vehicles and resulting in at least nine deaths. Korea National Fire Agency/AP.

At least seventeen people have died in landslide events in North Gyeongsang Province on Friday 14 and Saturday 15 July, with another nine missing. A rail engineer was injured when a landslide derailed a train, although fortunately no passengers were on the train at the time. Landslides are a common problem after severe weather events, as excess pore water pressure can overcome cohesion in soil and sediments, allowing them to flow like liquids. Approximately 90% of all landslides are caused by heavy rainfall. 

The aftermath of a landslide caused by heavy rains in Yecheon County in North Gyeongsang Province, on Saturday 15 July 2023. Yonhap/Reuters.

Many of the country's hydroelectric dams are struggling after 75 cm of rain fell of much of the country on Saturday, with the Goesan Dam in North Chungcheong Province reporting an inflow of 2700 tonnes of water per second - equivalent to its maximum outflow. This has led to many dams releasing water at high rates, further raising the risk of flooding. More than 7800 people have been evacuated from homes in low-lying areas since Thursday. Thirty two stretches of road are reported to have been swept away by flooding or otherwise destroyed, as are 33 homes. Forty nine rivers are reported to have burst their banks. Two hundred and sixteen roads and the entire national rail network were closed for at least some time, although most of the roads and some of the rail lines have now re-opened. Twenty of the country's national parks have been forced to close.

A collapsed river embankment in Cheongyang County in South Chungcheong Province on 15 July 2023. Yonhap.

The events are associated with the annual monsoon rains, which fall in Korea between mid-June and mid-August. Flooding and related incidents are not unusual during this season, but such large-scale problems have not happened in recent years. This years rains have been exceptionally heavy, with the country receiving an average of 30% more rain than would be expected, rising to 38.8% additional rain in the south of the country.

A rescue Dog and handler searching for survivors following a landslide in South Korea this week. Yun Kwan-shick/Yonhap/AP.

Monsoons are tropical sea breezes triggered by heating of the land during the warmer part of the year (summer). Both the land and sea are warmed by the Sun, but the land has a lower ability to absorb heat, radiating it back so that the air above landmasses becomes significantly warmer than that over the sea, causing the air above the land to rise and drawing in water from over the sea; since this has also been warmed it carries a high evaporated water content, and brings with it heavy rainfall. In the tropical dry season the situation is reversed, as the air over the land cools more rapidly with the seasons, leading to warmer air over the sea, and thus breezes moving from the shore to the sea (where air is rising more rapidly) and a drying of the climate.

Diagrammatic representation of wind and rainfall patterns in a tropical monsoon climate. Geosciences/University of Arizona.

See also...

Follow Sciency Thoughts on Facebook.

Follow Sciency Thoughts on Twitter.

Dinosaur trackway discovered beneath reservoir in Argentina.

A Dinosaur trackway has been discovered in an area usually covered by the waters of a reservoir in Neuquen Province, Argentina. The footprints were discovered by officers of the Argentine Naval Prefecture while on patrol on the shores of Lake Ramos Mexia in Villa El Chocon, an artificial lake created by the El Chocon Hydroelectric Dam. The footprints are in an area where they would usually be covered by the waters of the lake, but have been exposed by low water levels caused by a prolonged drought in Argentina. Following the discovery, the officers contacted scientists at the National Scientific and Technical Research Council, and Ernesto Bachmann Paleontological Museum, who hope to arrange an expedition to study the footprints.

 

Officers of the Argentine Naval Prefecture inspecting a Dinosaur trackway revealed by subsiding waters at Lake Ramos Mexia in Villa El Chocon. Prefectura Naval Argentina/Real Press.

The footprints are found within the Candeleros Formation, which has been dated to the Cenomanian stage of the Late Cretaceous Period, i.e. between 96 and 100 million years old. They are thought to have been created by an Iguanodontid Dinosaur about six metres in length and about three metres high at the shoulder.

 

One of the footprints revealed by the subsiding waters of Lake Ramos Mexia in Villa El Chocon. Prefectura Naval Argentina/Real Press.

See also...

Online courses in Palaeontology. 

Follow Sciency Thoughts on Facebook.

Follow Sciency Thoughts on Twitter. 

Thousands forced to flee their homes as two dams fail in MIchigan.

Around 10 000 people have been forced to flee their homes in parts of central Michigan following the failure of two dams on the Tittabawassee River. The eastern part of the Edenville Dam in Gladwin County collapsed at about 5.45 pm local time on Tuesday 19 May 2020 following days of heavy rain in the area, causing thousands of people to be evacuated from homes in the city of Edenville, about 6 km downstream, as water levers three metres above normal surged towards the town. Shortly after the Sanford Dam, 4km downstream of Edenville and 10 km downstream of the Edenville dam overtopped, sending floodwaters towards the city of Midland, another 9.7 km downstream, where mass evacuations are again underway.

The failure of the Edenville Dam on the Tittabawassee River in Gladwin County, Michigan, on Tuesday 19 May 2020. Dave Petley/Landslide Blog/American Geophysical Union/MLive/Youtube.

The Edenville Dam, a hydroelectric project built in the 1920s, had its licence revoked by the Federal Energy Regulatory Commission in October 2018, following the failure of it's owners Boyce Hydro Power to comply with an order to rectify multiple breaches of safety regulations, including an inability to cope with a potential maximum flood. The dam was subsequently purchased, along with three other hydro-electric projects, including the Sanford Dam, by the Four Lakes Task Force, a 'Delegated Authority' formally created by resolutions passed in Midland and Gladwin counties to administer and oversee the maintenance and operations of the projects.

Flooding on the Tittabawassee River in Michigan following the failure of the Edenville Dam on 19 May 2020. WXYZ Detroit.

Many parts of the eastern United States have suffered extremely high levels of rainfall this week due to the passage of Tropical Storm Arthur, which swept up the eastern coast of the United States without making landfall, and eventually turned east and headed out into the central Atlantic.

Flooding in Sanford, Michigan, following the failure of the Edenville and Sanford dams on 19 May 2020. Michael Connell/TC Vortex.

Tropical storms are caused by solar energy heating the air above the oceans, which causes the air to rise leading to an inrush of air. If this happens over a large enough area the inrushing air will start to circulate, as the rotation of the Earth causes the winds closer to the equator to move eastwards compared to those further away (the Coriolis Effect). This leads to tropical storms rotating clockwise in the southern hemisphere and anticlockwise in the northern hemisphere. These storms tend to grow in strength as they move across the ocean and lose it as they pass over land (this is not completely true: many tropical storms peter out without reaching land due to wider atmospheric patterns), since the land tends to absorb solar energy while the sea reflects it.

 The failure of the Sanford Dam in Midland County, Michigan, on 19 May 2020. CitadelofRick/Twitter.

Despite the obvious danger of winds of this speed, which can physically blow people, and other large objects, away as well as damaging buildings and uprooting trees, the real danger from these storms comes from the flooding they bring. Each drop millibar drop in air-pressure leads to an approximate 1 cm rise in sea level, with big tropical storms capable of causing a storm surge of several meters. This is always accompanied by heavy rainfall, since warm air over the ocean leads to evaporation of sea water, which is then carried with the storm. These combined often lead to catastrophic flooding in areas hit by tropical storms.

See also...

Follow Sciency Thoughts on Facebook.

Explaining the failure of the Xe-Pian Xe-Namnoy Dam in southern Laos.

On 23 July 2018 the Xe-Pian Xe-Namnoy Project, a recently-opened hydro-electric dam on the Bolaven Plateau in southern Laos collapsed suddenly, releasing approximately half a million cubic metres of water onto villages bellow. Forty people have been confirmed dead following this incident, with another 65 still missing and over 6600 made homeless. Within hours of the failure disagreements had emerged between the Korean contractors who built the dam and the Thai investors who provided the financial backing for the project, with one side claiming that the project had failed due to poor construction, and the other that excessive and unexpected levels of rainfall were to blame, and despite a plea from the Lao Prime Minister for a collaborative approach to investigating the cause of the failure, including globally recognised experts in the field, both parties have appointed their own teams to investigate the failure of the dam, and requests from outside parties for information on the design and construction of the dam have been blocked by lawyers representing these teams.

In a report published by the Blume Earthquake Engineering Center at Stanford University on 26 October 2018, Richard Meehan of the School of Earth Sciences and Blume Earthquake Engineering Center at Stanford University presents a theoretical cause of the dam’s failure, based upon satellite ground elevation data and previous geological surveys of the region carried out by the Japan International Cooperation Agency.

Meehan asserts that the western arm of the dam was built over a dry basin, in which a sinkhole system made up of caves, lava tubes and cracks in the basaltic rock had been infilled by soil, and were quite incapable of supporting the weight of the water behind the dam. He believes that when the dam was filled, water penetrated these systems soaking through or washing away the soil within the sinkhole system, and in some cases causing the surrounding rock to fissure abruptly as the pressure within built up rapidly.

Progressive failure scenario: (a) 20 July 2018, when 11 cm of subsidence was noted. (b) 22 July, when a warning of engineering failure was issued. (2) 25 July, post failure with fissured basalt rock exposed. Meehan (2018).

This theory is supported by cloud-piercing satellite images from the Sentinel 1 Satellite, which show a series of rising springs developing as underground conduits fill with water, followed by the superstructure of the dam beginning to sink into the void beneath, before being overtopped by the waters behind and failing completely.

See also...

Follow Sciency Thoughts on Facebook.