The Dnieper River
A Geomorphological Case Study
Introduction
The Dnieper river is the 3rd largest river in Europe, and flows through three different countries: Russia, Belarus, and Ukraine [1]. It has a catchment area of more than half a million sq. kilometers as it flows for 2200 km towards the Black Sea (Fig 1), and joins with up to 32 000 tributaries, 90 of which are longer than 100 km [1] .
Fig 1: The Map of the Dnieper River [3]
The river has unique characteristics as it can be broken down into three parts [1]. Within the last several centuries, the river has also been severely impacted by human activity, specifically through the construction of artificial structures and water pollution.
Despite everything however, the Dnieper remains an extremely beautiful river, with many unique ecosystems and wildlife.
Channel and Floodplain Characteristics
Valdai Hills, Russia
The Dnieper originates in the Valdai Hills in Western Russia in the Smolensk Region. The hills have an elevation of approximately 200-300 m above sea level and mark the beginning of Upper Dnieper [1]. Many other major Eastern European Rivers originate from these uplands, including the Volga (the longest river in Europe), the Lovat, and many more. This region thus separates three separate drainage basins: the Caspian Sea, which is the outlet for the Volga, the Black Sea, the outlet for the Dnieper, and the Baltic Sea, the outlet of the Lovat [1].
This region is predominantly characterized by hills, uplands, plateaus, and glacial moraines, intersected by lakes and river systems [1], creating a heavily vegetated area with lots of excess moisture and a well developed river network [3]. The Upper Dnieper River, originating at a height of 220 m, is a small sinuous river, at most 30 m wide, with low banks flowing in a narrow 2 km valley through forested and swampy areas (Fig 2). Further downstream, near the city of Dorogobuzh, Russia, the river widens to 40-150 m wide, with the valley widening to 3-10 km. The river is flowing southwest [1].
Belarus
Near the city of Orsha in Belarus (Fig 3), the river crosses a Devonian limestone ridge forming the Kobelyaksk Rapids as the river narrows to 20 m and the flow velocity increases up to 1.0 m/s [1].
The river, now going south, then flows through a wider valley, up to 15 km in width, with steep forested banks. Within this stretch, the river is mainly straight until Mahilyow (Fig 4) where it splits into several channels creating a series of islands and sandbanks [1].
Further downstream, the Dnieper confluences with some of its major tributaries including the Sozh River, marking the point the Dnieper crosses into Ukraine, and the Prypiat River, which it meets further downstream along the border [1]. In this area, the river also passes through the Polessian Lowlands (Fig 5) as the floodplain grows to up to 14 km in width. The floodplain is characterized by sandy lowlands and marshes. From the mouth of the Prypiat to the mouth of the Dnieper, the width is 490 to 610 m [1], a significant increase from the small beginnings of the Dnieper in Valdai Hills.
Kyiv, Ukraine
The capital city of Ukraine marks the end of upper Dnieper, which flowed for 1300 km, and the beginning of the Middle Dnieper [1]. Here it also meets with the Desna River, a major left-hand tributary, and the floodplain width increases to 12-14 km. It is characterized by swampy land intersected by oxbow lakes and streams while the channel remains sinuous and is composed of ripple-pool sequences [1].
The middle Dnieper flows through the boundary between the Dnieper uplands (Fig 6) on the right bank and the Dnieper lowlands (Fig 7) on the left bank [1]. This results in a highly asymmetrical valley of the river. The steep and high slopes on the right bank form cliffs and escarpments up to 80 m above the river, while the left bank, which is mostly sandy, is made of gently sloping, rolling hills and ancient river terraces. Kyiv (Fig 8), which has grown around the river, was originally built on the right bank of the river, sitting on the steep hills of the Dnieper Uplands [1].
Within this reach, the Dnieper flows through the forest-steppe vegetation region, which is an area of grasslands with intermittent forests. The river network is much less dense compared to the Upper Dnieper, with only a few major tributaries [3].
Further downstream the river becomes more wide, and reaches widths of up to 1200 m near the city of Cherkassy, as the floodplains widens to 9 km [1].
Dnipro, Ukraine
As the Dnieper continues flowing downstream, it then cuts across exposed Ukrainian Shield, ridges of basaltic and gneissic rocks [1]. This created the Dnieper Rapids (Fig 9) as the river flowed though a narrow unterraced valley bounded by high rocky cliffs. The water levels dropped about 50 m within a span of 66 km. The rapids began below the city of Dnipro and ended at Zaporizhzhya (which literally means beyond the rapids) [1].
The rapids, 6 major (or 9) and over 50 minor (Fig 10), were a major risk for ships and prevented continuous navigation across the river for centuries. With the construction of the Dnieper Hydroelectric dam above Zaporizhzhya in 1932, the water level rose by over 130 m, creating the Dnieper reservoir (Fig 13) and covering the rapids [3].
Zaporizhzhya, Ukraine
Zaporizhzhya marks the end of the middle Dnieper, which flowed for 555 km, and the beginning of the lower Dnieper [1]. The lower Dnieper flows through the Black Sea lowlands (Fig 12), black-soil area of natural steppe which has almost completely been plowed up, irrigated, and used for agriculture [1]. This results in very little moisture being left in the ground as the river network is mostly composed of intermittent and ephemeral streams [3]. Here, the river flows slowly towards the Black Sea, .
Slightly downstream of the Dnieper dam, the river splits into two channels and forms the large island Khortitsa (Fig 13), an important cultural location [1]. It is 12.2 km long and 2.5 km wide and has unique vegetation and wildlife. While the northern part of the island is rocky and steep, the southern part is slightly sloping, highly vegetation, and often gets flooded by the Dnieper [1].
The river valley narrows to 4 km before expanding and widening to 25 km. Downstream near Nikopol (Fig 14), the river valley once again narrows to 4 km, then expands to 3-7 km creating sets of lowlands on the shore [1]. Before the Kharkovka reservoir was developed, the Dnieper split into many channels, with swampy and flat island between the streams vegetated by floodplain flora like reeds. Today, most of this is hidden under the reservoir which greatly raised the water levels [3].
Kherson, Ukraine
Downstream past Kherson (Fig 15), the Dnieper splits into many streams creating a delta with an area of about 350 km2 with numerous lakes and islands [1]. The delta is part of the Dnieper-Bug Estuary (Fig 16) as it meets the Black Sea. An estuary is a unique aquatic environment forming in the mixing fresh and salt waters and is inhabited by both freshwater and marine life [1].
Climate
The climate of the Dnieper River basin is temperate, and when compared to regions in Russia at the same latitude, much milder and damper [3]. Upstream in the northeastern parts of the basin, the winters are cold and persistent, with annual mean air temperatures of 5 degrees. Going downstream winter become shorter and milder (Fig 17), and the climate is slightly warmer, with mean air temperatures near Kyiv (middle Dnieper) being around 7 degrees and lower Dnieper around 10 degrees [3].
Fig 17: Temperature Distribution along the Dnieper in Ukraine [20]
While temperatures increase going downstream, precipitation increases upstream (Fig 18), probably due to the elevation [3]. In the Upper Dnieper basin in the Valdai Hills - a range of uplands, the annual precipitation is 760-810 mm. Above Kyiv, the annual precipitation is about 710 mm while in the lower Dnieper, which is found in lowlands, the precipitation is 460 mm. Precipitation typically peaks in the late summer to early fall while the minimum is in the late winter to early spring [3].
Fig 18: The precipitation distribution near the Dnieper in Ukraine [20]
Land Use
The land use of the area around the Dnieper River varies spatially and is tied to both human and physical geography [1]. Most of modern-day Ukraine and Belarus, which make most of the Dnieper basin, were populated by nomadic tribes up to the 17th century. These tribes would use the land for hunting, pasture, and agriculture, cutting down and burning the wood and using it as fertilizer for crops. This process eliminated a large amount of native coniferous forests that were found in areas as far south as Kyiv. With the appearance of cities, the nomadic lifestyle disappears, and the land became more urbanized and colonized very quickly [1].
Today, about 65% of the total area of the Dnieper drainage basin is used for agriculture, pasture, and urban cities [1]. This is especially the case for the lower Dnieper as the soil is extremely rich in nutrients and is good for agriculture. The soil is known as chernozem (Fig 19) , which means “black soil” [1].
Fig 19: The distribution of chernozem within the middle and lower Dnieper Areas [21]
A large part of middle Dnieper became home to several hydropower stations that provide energy to the manufacturing industry that emerged in cities like Zaporizhzhya and Dnipro [1]. These stations created reservoirs that flooded a total of 6900 km2, withdrawing that area from agriculture. More industrialization of the area increased the water demands, which resulted in the construction of several water canals between neighboring watersheds, like the North-Crimea canal systems [1].
About 3.2% of the drainage area is protected in natural reserves, while the population density is 64 people/km2. There are more than 20 cities found along the Dnieper, and more than half of them have a population of greater than 100 000 [1].
Hydrology
The hydrology of the Dnieper River is mostly associated with the landscape and climatic processes [1]. The river is known to have spring high flows, and summer and winter low flows. During the spring from March to May, snow melt contributes up to 50% of annual runoff while about 27% is made up of groundwater and subsurface flows. The rest is made up of floods due to precipitation events [1].
Starting from the upper Dnieper, spring high floods come in around early April and peak at around mid April [1]. In the the lower catchment, the spring floods last much longer and peak at around mid May. While water levels increase immensely in the upper catchment, little to no water rise is seen downstream in the lower Dnieper. Near the city of Smolensk in the upper Dnieper region, the maximum yearly water amplitude is 5.7 m while downstream near the city of Kherson in the lower Dnieper, the water amplitude lowers to 2.5 m [1]. This is most likely due to the significant widening of the floodplain near the outlet.
Mean discharge in the upper catchment is approximately 97 m3/s, and it increases to about 1310 m3/s near Kyiv, the beginning of the middle reach, and 1670 m3/s at the mouth of the river near Kherson [1]. At the same, the specific discharge, the rate of discharge of groundwater per unit area, decreases from north to south, starting at about 6.9 L/s km2 near Smolensk, and ending at 3.5 L/s km2 near Kherson [1].
The Dnieper itself is a relatively low-gradient river as the difference in elevation between the mouth and the source of the river is only around 220 m.
The hydrology of the Dnieper was greatly affected by the construction of dams and reservoirs on it [1]. Originally, the river had high flows during the spring and low flows during the summer and fall. Due to the reservoirs created by dams, of which there are 6 in total, it now has diminished flows during the summer and more pronounced high flows during the spring. The reservoirs also brought a reduction of the average runoff of the river in general [1].
Ice cover (Fig 20) is also very important for the hydrology of the Dnieper [1]. In the upper catchment area, ice develops at around mid may, and breaks apart by late March early April in a process that takes about 5-7 days. Downstream in the lower catchment area, the ice covers forms at around late December, and melts within 1-3 days by early March. The ice cover itself is relatively unstable as it freezes and thaws periodically during the winter [1].
Fig 20: Ice covering the Dnieper in Kyiv [23]
Human Impacts
Dnieper River Cascade System
The Dnieper Reservoir cascade (Fig 21) is the name given to the systems of reservoirs within the middle and lower Dnieper in Ukraine [25]. These reservoirs were formed because of the 6 hydroelectric dams on the river: Kyiv, Kaniv, Kremenchuk, Kamianske, Dniepro, and Kakhovka. They were constructed between 1958 and 1973. These reservoirs have a total volume of 43.8 km3 and occupy an area of 6974 km2. The whole cascade system stretches for over 800 km, covering almost 40% of the total river length [25].
Fig 21: The Dnieper Rive Cascade system [25]
In total, the Dnieper cascade generates about 9255 GWh of energy as water passes through the dams and spins the turbines, generating electricity [25]. At the same time, a volume of approximately 17-18 km3 is extracted from the Dnieper and used for agriculture, irrigation, and in the industrial and energy sectors. Also, over two thirds of the population of Ukraine, about 30 million, are supplied with water taken from the reservoirs [25].
While extremely beneficial and useful for the cities and areas nearby, these reservoirs have affected the hydrology and flow regime of the Dnieper River [1]. Due to the damming, the spring high-flow outflow near the mouth of the river in the Black Sea decreased by a factor of 1.9. Within the reservoirs, the average velocity decreased from 0.6-0.8 m/s to 0.3-0.02 m/s [1]. This change in velocity has tremendous impacts on the erosion and transportation of sediment, one of the most critical factors behind the formation of river channels. As a result, river channel morphology downstream of the dams has changed a lot over the past several decades [25].
A Closer Look: The Kaniv Dam
One of the most studied regions along the Dnieper Cascade is the Kaniv hydroelectric plant which has radically changed the river pattern along this reach.
The Kaniv Dam, which is part of the Kaniv Hydroelectric Power Plant (Fig 22) is the last commissioned dam in the Cascade, being built in 1973 [25]. It is found near the city of Kaniv which is in the Kyiv region. The dam is 15 m tall, 5 km long, and the reservoir holds about 2.3 cubic km of water. The management of the Kaniv reservoir is primarily determined by the water supply from the upper reaches of the river, specifically from the Kyiv Reservoir. This water supply was those prone to variability. The average inflow into the Kaniv reservoir from the upper river between 1985 and 2013 was about 1429 m3/s, while the flow through the dam was approximately 1395 m3/s [25].
During the years of operation, the dam was controlled using two different operating systems: hydropeaking system between 1973 and 1990, and the run-of-river system, which has been up to present day [25]. With the hydropeaking system, the Kaniv HPP was working only during times of high demand for electricity while in the run-of-river system, the plant was working constantly, where some part of the running water goes through a guided channel and generates electricity. This system was also utilized during spring-high flows before 1990. This change in operating systems was done to primarily cut down operation costs and improve the ecological state of the river [25].
Both operating regimes have had their own impacts of the river hydrology (Fig 23) [25]. Until the year 1994, there were huge variations between the daily flow rate through the dam. The maximum difference reached up to 6000 m3/s, and for almost 50% of this period, the difference was greater than ±200 m3/s. Between 1994 and 1997, the difference in flow rate began to decrease, which marked a certain kind of transition period, as the change in operating systems began to take affect. Between 2000 and 2015, the difference in daily flow decreased tremendously from the values before 1994, with 80% of days having a flow of less than ±200 m3/s. This change and variability in the daily flow through the Kaniv Dam had large morphological effects on the river channel downstream [25].
Fig 23: On the left, mean monthly discharge. On the right. difference in daily discharge [25]
Before the construction of the Kaniv Dam, this stretch of the river, 3 to 14 km below the dam, would be characterized as a sand-bed dominated, laterally active island-forming fluvial system [25]. From around the 1940s to 1970s, before the Kaniv Dam was built, the river was stable with widening of the river accompanied by deposition of sediments, with a slow build-up of sandy inter-channel forms (islands), and decomposition of larger channel forms [25].
Everything changed when the dam was built. Now the flow was entirely regulated by the management of the dam which resulted in highly variable daily flow, especially under the hydropeaking operating regime [25]. Rapid and frequent changes in daily flow result in the water having a higher shear stress, thus intensifying the erosion near the dam and increasing the bed and suspended sediment movement. As a result, during the 70s and 80s, the main channel of the Dnieper began to incise into the bed, thus narrowing the channel and making it deeper. The side channels, which were now higher than the main channel, became shallower as they lost flow to the deeper main channel. Islands that were separated by these channels now combined (Fig 24) to form larger inter-channel areas [25].
Fig 24: Changes in the channel of the Dnieper over the years of study [25]
This process is evidenced by measurements taken along this stretch of river [25]. In 1962, there were 10 island forms within this part of the river that had a total area of 5.9 km2 and an average form area of 0.53 km2. By 2015, there were 3 forms, 2 islands and 1 inter-channel area, with a total form area of 7.9 km2 and the average form area was 2.6 km2. This shows the evolution of the Dnieper River fluvial system as a direct response to erosional changes caused by Kaniv Dam [25].
Pollution
Unfortunately, the Dnieper River is extremely polluted [28]. There are many sources of pollution affecting the river. Firstly, there is waste from cities. In Ukraine, only 3 major cities are not situated on the Dnieper, and as such, there is massive waste from the cities and the people in them. Industrial sources, like the countless factories found on the river, also dump a lot of industrial waste into the Dnieper. Finally, pesticides and fertilizer runoff from farms is another major source of pollution [28].
In early spring of 2021, the Dnieper was unusually green due to more algae (Fig 25) caused by a much higher concentration of phosphates in the river [28]. In the past year, it is estimated that approximately 6000 tonnes of phosphate were released into the river. Water samples were taken and tested, and a total of 161 pollutants were found, 19 of which were identified as particularly dangerous [28]. Some of these were pharmaceuticals drugs like antibiotics and antidepressants, but there was also some amounts of atrazine, which is a herbicide that has been banned by the European Union because of its effects on humans and animals [28].
This cocktail of drugs and chemicals all culminated in a massive build up of algae, which bloomed unusually early this year [28]. The massive algal bloom is destabilizing the ecology of the river as it depletes oxygen from the water, killing off plants and animals. On June 29, 2021, the Ukrainian government labelled the ecological state of the river as catastrophic, and further banned swimming in the river due to health hazards [28].
While Ukraine does have environmental and laws and regulations in place, the institutions in charge of monitoring pollution are not strong enough to enforce the laws [28]. Many businesses are not willing to change their practices, and the environmental authorities do not have enough influence and power to change or force anything. The government also continually neglects proper management of the basin [28]. Wastewater is barely treated due to outdated water utilities and old sewage treatment plants. The river has changed forever, and even with proper treatment, which would cost the state about $85 million if water quality continues to decline, the river will not go back to normal for decades [28].
