Kakhovka Dam Collapse: Medium-Term Consequences

By Hessel Winsemius, Fedor Baart, Ruben Dahm (Deltares)

This article discusses the aftermath of the Nova Kakhovka Dam collapse in Ukraine. The dam is the most downstream in a series of six, forming the largest reservoir in Europe. Its collapse resulted in significant flooding, widespread damage, and casualties. This article explores the consequences of its destruction, such as increased downstream flood risk, implications for agricultural activity, and the potential for pollution in the Black Sea. The article emphasizes the need for ongoing investigation and informed actions to manage these diverse impacts.

In the night of 6 June 2023, the Nova Kakhovka Dam in Ukraine collapsed after an explosion, causing very fast rising waters and vast flooding in the downstream river valley, resulting in casualties and the evacuation of residents as well as the destruction of infrastructure. The breached dam forms the most downstream part of the Dnieper reservoir cascade, a series of six dams. In addition to providing energy and water for domestic, industrial, and agricultural use, these dams help to manage high flows and reduce the flood risk. The water levels of the reservoirs are managed by controlled release of water through the dams until it reaches the Black Sea. One month on from the event, and with water retreating, several consequences for the coming years may now become more apparent, causing indirect societal and environmental impacts in Ukraine and beyond.

An initial analysis by the Water, Peace and Security partnership explored several key insights on short- and long-term impacts. This blog considers in more detail the three water-related concerns that will require future attention and potentially action: an increased downstream flood risk, consequences for agricultural activity, and pollution in the Black Sea. These consequences – and some of their potential impact on the local population, environment, and the wider region – have been assessed using publicly available satellite imagery and hydro-meteorological information. Before we examine these three water-related concerns, we first explore the various hydrological anomalies that have been observed in the months leading up to the incident.

Figure 1: Breach location with the main breach, the secondary breach that evolved further over time, and the now dried up connection to the North Crimean Canal. The image on the left reveals that prior to the breach, the Kakhovka dam had already been spilling for several months (situation 2023-06-19, source planet.com)

Hydrological anomalies before the collapse

Water levels in the Kakhovka reservoir had been stable for the past seven years. However, in recent months before the breach, satellite sources (Sentinel-3, Sentinel 6) reveal that several hydrological anomalies could be observed. Lake altimetry shows a decrease in water levels between November and February 2023, resulting in the lowest recorded reservoir level since the space altimetry observation became operational in March 2016.

This was followed by a period of filling until early May 2023. During this 3-month period, the reservoir level increased to more than 1 metre above normal levels. This high reservoir level was maintained for a month until the moment of the breach. Satellite imagery from Planet reveals that prior to the breach, the Kakhovka dam had been spilling for several months. This, together with the unusual pace of filling, suggests that the operators had to deal with a very large inflow.

A hydrological analysis of previous years can help to determine the cause of this large inflow into the Kakhovka reservoir. We investigated the water level variation further by performing a model run with a distributed hydrological model (Wflow) that simulates the naturalised river flow throughout the basin. We used 20-year climatology data to establish average naturalised flow conditions with an empirical probability distribution. The naturalised river flow is the amount of flow that would occur at given locations in the basin if there would be no man-made controlled water use.

We compared the flow of the 2022/2023 winter and spring season with the normal expected flow during the season. This analysis demonstrated that the naturalised flow was extremely high during the past year, visualized in Figure 2 below, and often even exceeded the 95% flow.

We then accumulated the total naturalised flow over time, starting from 1 January 2023. In figure 3, we demonstrate how the accumulated flow compares against the total storage capacity of all 6 reservoirs in the Dnipro cascade. This shows that the anomaly is severe, and that the difference between normal situations is comparable to the total amount of storage in the entire cascade. This anomaly very likely has contributed to the extreme high water levels just before Kakhovka collapsed.

Increased downstream flood risk in the coming years

With the Kakhovka dam destroyed and unlikely to be rebuilt any time soon, a large part of the catchment area of

the Dnipro is now uncontrolled. The potential occurrence of flow anomalies in the coming years (until reconstruction of the dam or other measures that provide storage, or additional conveyance capacity) may pose new danger to settlements in the Dnipro floodplain as the entire basin area in between Dnieper reservoir and the coast is now uncontrolled. Several settlements on the south bank are low-lying and therefore may be under risk of future uncontrolled flood flows.

Whether the flood risk increase is indeed significant has not yet been investigated. If, following investigation, such risks are deemed to be significant, modification of the flood rule curves in the still existing upstream reservoirs may be considered. This is a temporary flood prevention measure as long as no new impoundment or other means to prevent flooding have been established.

Consequences for agricultural activity

We expect significant future pressure on agricultural activity in the region. This is due to several factors. Firstly, the available maximum storage of the reservoir has been greatly reduced, from about 44 km3 to 25.5 km3 ^[1], which reduces the amount of water available for irrigation on which several regions depend for agricultural production. Secondly, agricultural land which has been flooded may face contamination. This is likely to affect agricultural productivity and the quality of any agricultural produce. Finally, the Kakhovka reservoir was feeding several irrigation channels serving the South-East of the country, such as the North Crimean canal and the Kakhovsky canal, which are now likely no longer in service.

An adapted water management plan, aimed at increasing supply from alternative water sources, decreasing water demand from all sectors, prioritizing water use and increasing awareness by users will therefore be required. Low water availability is likely to prevail for several years as long as no new impoundment is available. This may put agriculture-dependent jobs at risk. And it might not only influence Ukraine’s domestic food security, but also potentially its ability to export foods.

Figure 4: The Zaporizhzhia power plant before and after the collapse of the Kakhovka dam (situation 2023-06-20, source planet.com)

Black Sea delta pollution

Finally, we have identified a very large plume of likely contaminated sediments which spread along the Black Sea coastline. Using satellite imagery (MODIS, see also the Figure below) dated from June 17, we estimate that an area of approximately 4,500 km2 might be affected by this plume. The plume has evolved out of the Dnipro River.

The impact of this plume on local biodiversity, ecosystems, and livelihoods is still unknown. Neither is the extent to which the plume contains contaminants from industrial sites. The plume can potentially reduce the availability of oxygen near the seabed, affecting benthic ecosystems. This is particularly relevant as this part of the Black Sea and adjacent coastal areas also host important natural sites, including the Danube Delta Transboundary Biosphere Reserve and the Black Sea/Chernomorskiy Biosphere Reserve, both inscribed on UNESCO’s World Heritage List.

Although precautionary actions at this scale are very difficult, it is essential that water quality data is gathered continuously so that local authorities can act with the best available information. Beyond the immediate effects on the Ukrainian coastal areas, it is also important to note that the Black Sea borders several other countries, who may also be impacted by these environmental consequences.

In the aftermath of the Kakhovka dam breach, the challenges faced by first responders to provide support during an active conflict became clear to the international community. Now the water is receding, the focus will shift towards longer term impacts of the breach on people, ecosystems, and the entire region. In this blog, we identified three such impacts. First, an unregulated flow regime will potentially put lives and livelihoods at recurring risk of flooding. Second, the impact on the agricultural sector due to the limited availability of irrigation water. And finally, the ecological consequences of pollution in the Black Sea.

The actual impact of these consequences will become clearer over the coming months and years. The situation will continue to require further investigation and quantification, so that informed actions can be taken. An example of such action could be re-assessing the upstream reservoir operations considering the regional water demand and risk of flooding given the uncontrolled downstream situation.

^[1] It should be noted that this is the total storage from bottom to top. The so-called “live storage” (i.e. water available under control) is lower.

The WPS blogs provide insights into recent developments relating to water, conflict, security and peace. These blogs reflect the opinion of the authors and not necessarily of the WPS partnership or its donors.