IMPORTANT ADDENDUM 2023-06-06: The model have been further developed and water should start rising at Cherson city after three hours. The actual waterlevel in the dam is also higher than in the model below. Media enquires about the modelling of a dam breach at Nova Kakhovka should contact UNICEF in Ukraine who took over the initial model from Dämningsverket. THE MODELLING BELOW SHOULD NOT BE USED FOR DECISIONMAKING OR INFORMATION ON WHEN TO EVACUATE. THE UKRAINIAN AUTHORITIES WILL HAVE CORRECT INFORMATION.
This blogger is not an expert on hydrology, dam breaches or flooding. This blog just published a first prelminary modelling of a dam breach at Nova Kakhovka. Any interview requests will be declined.
A worst case modelling for a russian demolition of the Nova Kakhovka Dnipro river dam show that the worst flooding will take place on the left (south east) side of the river bank. A 4 – 5 m wave will hit the Antonovsky bridge east of Cherson city after 19 hours, and there will be a backswell flooding up the Inhulets river, and after 4 – 5 days there would be some flooding up the river Bug to Mykolaiv. The demolition of the Nova Kakhovka dam is a war crime according to the Geneva Convention, but Russia has already systematically broken the Geneva convention during it’s illegal war in Ukraine.
Clarification: The worst case here is that all the floodgates are blown, ie 200 meters. The entire dam is 3500 meters and in the event that 400 m or 1 800 m would be torn down the modeled time for the water to hit Cherson City would be almost halved. There would be some more flooding.
First off, dams like the Dnipro dam in Nova Kahkovka are protected by the laws of war and the Geneva convention. Destroying it would be considered a weapon of mass destruction and an indiscriminate war crime. Article 56 of the 1977 Additional Protocol I provides:
“Works and installations containing dangerous forces, namely dams, dykes and nuclear electrical generating stations, shall not be made the object of attack, even where these objects are military objectives, if such attack may cause the release of dangerous forces and consequent severe losses among the civilian population. Other military objectives located at or in the vicinity of these works or installations shall not be made the object of attack if such attack may cause the release of dangerous forces from the works or installations and consequent severe losses among the civilian population.”
The following modelling of the worst-case dam break have been done by the Swedish hydrological engineering company Dämningsverket.
It is modeled using the US Army Corps of Engineers (USACE) software HEC-RAS 6.3, which is available here. The terrain data comes from Nasa.’s Shuttle Radar Topography Mission (SRTM) and are available from the United States Geographical Survey (USGS) here.
A model is a model. It is not reality. The CEO of Dämningsverket writes:
“As you know, all models are wrong, but some models are useful. This one is guaranteed to be wrong as I have nothing to calibrate it against, plus a host of other unknown parameters that I’ve just come up with, but I’d say it gives a picture of a worst-case scenario in case the Russians get around to blowing up the dam . I find it hard to see how it could get any worse than this, although it’s probably bad enough.”
The model is thus not based on actual measurements of the current state of the Dnipro flow, waterline, temperature, humidity, air pressure, wind speed and anytning else which would affect the model, but on assumptions for a worst case.
Assumptions include that the water-level in the dam is 13 meters above the Dnipro downstream, and that the dam break over an hour expands to a width of approximately 200 meters break in the dam.
When the wave hits the Antonivsky Bridge it will be between 4 and 5 meters of height. Wheter the severly damaged bridge would withstand the increased waterflow is not modeled.
The wave will be higher further upstream, and both speed and height of the wave is higher closer to the dam. It will take approximately 19 hours for the wave to hit Cherson City in this model, as the water spreads out over the lowlands and does not just rush forwards. The flooding will be much worse on the left side of the river (left/right side is when you are looking in the direction of the river flow, in this case towards the Black Sea – generally in this case the left side is the south or east side of the Dnipro). Most of Cherson City will not flood, but the harbour and the docklands including the island in the south of the city will be flooded.
Several smaller towns or villages on both sides of the Dnipro will be flooded and when the wave hits it will probably be very dangerous and lives will be lost.
There will be a backswell up the Inhulets river. In 4 – 5 days the swell will cause some flooding up the river Bug up to Mykolaiv. The isthmus at the end of the bay outside the Dnipro delta will be severly flooded and almost completely drowned, although this will start approximately 50 hours after the dam break.
The modelled flow will peak at 14 000 cubic meters of water per second (m3/s), which could be compared to the Niagara Falls average flow of 2 400 m3/s the Dnipro average according to Wikipedia of 1 670 m3/s. The flow will diminish over time.
This model is a worst case model and a simplification of reality as all models are. The reality will be something else if this war crime were to be commited by Russia.
Animation of the dam break below.
The model would be an indication of which areas should be evacuated if Russia were to commit the war crime of blowing the Nova Kakhovka dam. There would also be probable secondary effects including the cutting of cooling water for Europe´s largest nuclear power plant ZPP, which requires cooling even for the shut down reactors. A radiological disaster is a separate model, but with prevailing winds blowing eastwards it would generally be worse in the by Russia temporarily occupied territories or even within Russia itself if any fallout reaches the internationally accepted borders of Russia east of the Donbas. Exact results would be highly dependent on the weather conditions.
Clarificitation. In the case that 400 – 1800 meters width of the dam would break – the worst-worst-worst case and considering how the rest of the dam is constructed requiring an extremely large amount of destruction, one of the possibly biggest non-nuclear demolitions in history – the modeled time for water to reach Cherson would be almost halved and there would be some more flooding. The difference in flooding is seen below in magenta.
A video with 200, 400 and 1800 meter break below.
Comments are disabled on this post in order to avoid russian trolls and russian propaganda. I ordinarily only write articles in Swedish, but make an exception in this case. The article could be discussed after the post on Twitter.
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