Modification of the hydrological regime of surface waters

4.3.1. Modification of the hydrological regime of surface waters

Modification of the hydrological regime refers to an increase or decrease in the discharge of streams and rivers as a result of human interventions on a local/regional scale. The transboundary status of the issue is reflected in Table 4.1. A detailed causal chain reflecting the links between this issue its immediate and underlying causes is shown in Figure 4.2.

Environmental impacts

The impacts of this issue are linked closely with those of a number of other issues including changes in the groundwater regime (Section 4.3.2), flooding events and elevated groundwater levels (Section 4.3.3), water resource pollution issues such as chemical and microbiological pollution, and eutrophication (Section 4.4) and modification and loss of ecosystems ands ecotones (Section 4.5).

Modification of riparian habitats

Changes in the temporal and spatial pattern of flooding in the floodplains of the Dnipro Basin have led to a modification of riparian habitats. More details on this impact can be found in Section 4.5 on the modification and loss of ecosystems, Section 3.1.6 on nature reserves and protected areas and in the Basin Passport.

Changes in water quality

A number of other Issues including chemical pollution (Section 4.4.1) microbiological pollution (Section 4.4.2) and eutrophication (Section 4.4.5) are closely linked with this issue. Modification of the hydrological regime can significantly increase the impacts of these issues. Generally, water quality in the Dnipro Basin greatly depends on water releases from the Kakhovka reservoir. Salinity levels in the Dnipro-Bug Estuary tend to increase if discharge rates at the reservoir dam fall below 1,000 m³/s.  More details on changes in water quality can be found in and Section 3.2.8 on the sanitary situation in the Basin and the 2000/2001 field survey results discussed in Section 3.3.2.

Immediate causes

Significant changes in the hydrological regime of watercourses in the Dnipro Basin are a result of the following immediate causes (also refer to Table 4.17):

- Flow regulation, including required releases from the Dnipro reservoirs;

- Flow diversions between the river basins or within the basin;

- Flow abstraction for industrial and domestic purposes;

- Land drainage activities;

- Flow abstraction for irrigation;

- Returns/runoff of water;

- Flow diversion for aquaculture.

1. Extent of the river flow regulation

There are 102 reservoirs in the Belorussian part of the Dnipro Basin with a total water surface area of 345 km², and volume of 1,044 million m³. Of that, 55 reservoirs (with a water surface area 206 km² and a capacity 585 million m³) and 730 ponds (water surface area 93 km² and capacity 164 million m³) are located in the Pripyat River Basin. The overall flow regulation ratio is 2-3%. In the Russian part of the Dnipro Basin there are 25,000 artificial impoundments with a total area of 18,000 hectares with an overall flow regulation ratio of about 3%. In Ukraine, the overall flow regulation ratio for reservoirs and ponds was about 22%, as of 1990. More details on the extent of hydro-engineering activities in the Ukrainian part of the Basin can be found in the Basin Passport and in Section 4.3.3 on flooding events and elevated groundwater levels.

2. Flow diversion schemes

There are two major flow diversion schemes in the Republic of Belarus with an annual capacity of 0.2-0.3 km³/year. The first scheme (the Western Dvina/Berezina flow diversion system) supplies 0.2 to 0.25 km³/year of water from the Viliya river basin. The second scheme (the Western Bug Basin/the Dnipro-Bug Channel) redistributes the flow within the Dnipro Basin and diverts part of the flow (0.04-0.06 km³/year) to the Western Bug Basin. In Ukraine there are 6 major channels and 5 water conduits in operation, diverting 3.14 km³ of flow (2000 figures) to supply Dnipro water to water-scarce areas in the country (e.g. the Crimea). Further details on flow diversion schemes can be found in Section 3.2.10 on water uses in the Basin.

3. Flow abstraction for industrial and domestic purposes

In 2001, the total flow abstraction for industrial and domestic purposes within the Belorussian part of the Dnipro Basin (excluding the Pripyat River) was 0.24 km³, with a maximum annual abstraction rate of 0.7 km³ between 1985 and 2001. In the Pripyat River Basin, flow abstraction was 0.18 km³ in 2001, with a maximum annual flow abstraction of 1.26 km³ between 1985 and 2000.

In the Russian part of the Dnipro Basin, annual flow abstraction was 0.77 km³, in 2000. The proportion of non-returnable flow abstraction in Ukraine is over 75%, with the Dnipropetrovsk (14%) and Kherson (23%) Oblasts being the major water consumers. In 2000, the total annual flow abstraction for industrial and domestic purposes in the Ukrainian part of the Dnipro Basin was 6.17 km³, and the total flow abstracted in the Pripyat River Basin in that period was 1,086 million m³. Further details on flow abstraction can be found in the Basin Passport and Section 3.2.10 on water uses in the Basin.

4. Land drainage and flow abstraction for irrigation

Large areas of land have been drained and irrigated in the 3 riparian countries. The extent is shown in Table 4.3. In Belarus, the total length of the surface drainage/irrigation network has reached 64,000 km, or twice the length of the natural drainage network. More details on irrigation activities can be found in Section 3.2.5 on agriculture in the Basin.

Table 4.3 Extent of drained and irrigated land in the 3 riparian countries

The highest levels of flow abstraction for irrigation in the Dnipro Basin occur in the Ukraine with 0.86 km³ abstracted per year. The levels in Russia and Belarus are significantly lower (0.003 km³/year and 0.004 km³/year, respectively. Refer to Section 3.2.10 on Water uses in the Basin for more information on flow abstraction.

5. Returns or runoff of water

In 2000, return flows as a result of industrial effluent discharges were 0.43 km³ in the Russian Federation, 0.4 km³ in the Republic of Belarus, and 0.5 km³ in Ukraine.

Underlying sectoral causes

The underlying causes of this issue arise in the following key sectors; energy (hydropower), agriculture, transport (river), urbanisation, industry and aquaculture. The effects of the resource uses and practices associated with industry, urbanisation and fishery/aquaculture are less significant. A list of the priority sectors for all issues is presented in Table 4.18 (Section 4.7)

A detailed causal chain reflecting the links between the immediate and underlying sectoral causes of this issue is shown in Figure 4.2 and a detailed description of terminology used in this causal chain is given in the definition of terms in Annex 2.

Priority inter-sectoral issues

Based on the causal chain in Figure 4.2, the priority sectoral resource uses and practices and the underlying political, economic and governance causes of this transboundary issue can be identified. These are shown in the Strategic Action Programme (SAP) decision making management tool (Figure 4.3).

The SAP decision making management tool shows the priority sectors for this issue (colour coded with the causal chain) together with three hierarchical levels of concern. These levels are:

Within each level the priority resource uses and practices and the underlying political, economic and governance causes for each transboundary issue are listed. These can either cut across all sectors (e.g. Lack of finance) or be sector specific (e.g. unsustainable agricultural practices).

Justification for sectoral prioritisation

Construction of the Dnipro reservoir chain has had a profound effect on the hydrological regime of the river. The need for this major development project was mainly driven by a growing demand for hydroelectric power. As a result of the reservoir construction, river flow in the middle and lower reaches of the Dnipro has become fully regulated by water releases from the reservoir dams.

Agriculture is the second significant sector affecting the hydrological regime of surface waters. As a result of the development of large-scale drainage schemes in the Pripyat River Basin, many smaller rivers have been canalized, partially or completely. Numerous hydroengineering facilities and polders regulate and divert a significant part of the river flow in the Pripyat Basin. The remaining flow is regulated and redistributed by major flood-protection schemes during the spring and summer/autumn high flow period.

In Ukraine, especially in the southern regions, irrigated agriculture is a major user of water. A dense network of irrigation channels has been constructed to deliver water to drier areas of the Basin, resulting in the significant redistribution of flow over time and space.

Water transport is the third largest contributor to the issue of modification of hydrological regime, where river flow is affected by channel-clearance and dredging activities to enable navigation, especially during the low-water period. A significant amount of water is diverted to the Dnipro-Bug Channel, a major inter-basin water route, affecting surface water levels in the Upper Pripyat Basin. The contribution of other sectors (industry, urbanisation, and fishery/aquaculture) is relatively minor.

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