6.     Abstraction and flow regulation and water level regulation

6.1.        Introduction

The flow regime and water level fluctuations are one of the major determinants of ecosystem function and services in river and wetland ecosystems. Many European rivers have had their seasonal or daily flow regimes changed by various uses that have a significant impact on ecosystems.  Many lakes and rivers have their water level regulated.

The water level regulation depends on the uses. With hydropower production water levels are normally high or rising during summer period, while during the winter period, when the need for electricity is normally at its highest, the water level is strongly lowered.  Flood prevention regulation follows a similar pattern during winter time, but in summer time some storage capacity is left empty to catch flash floods.  When the major objective of the regulation is recreation or navigation, then regulated water levels are often more stable than natural ones.  If the water level is regulated for water supply use, the water level fluctuation is more irregular and depends on the specific use of raw water. In reservoirs used for storage of water for irrigation

Abstracted water is used for a diverse range of processes including public water supply, water for agricultural irrigation and livestock management, domestic supply for individual dwellings (Figure 6.1), cooling for power stations, water supply for industry as well as many other purposes.

Figure 6.1 A) Reservoire used for water supply (Hasznos, Hungary) and B) Dam on River Rába at Nick for irrigation water abstraction and partly hydropower generation

Irrigation reservoirs generally store water during wet seasons and release it during dry seasons. Release of water from hydropower reservoirs depends on electricity demand. Flows downstream of hydropower plants may fluctuate daily when increased water volumes are channelled through turbines during periods of high electricity demand (Figure 6.1b).  The effects of changes in the seasonal flow regime below dams and reservoirs and reduction in flow caused by water abstraction and diversion, upon lotic and riparian ecosystems have been demonstrated for rivers in a range of geographical regions.

The main challenge in managing abstraction is to meet the reasonable needs of water users, while leaving enough water in the environment to conserve river, lake and wetland habitats and species.

Dry river stretches may appear downstream of some reservoir dams; where whole streams are diverted into reservoirs; or during periods of dry weather in summer where abstractions can suck out the remaining river flow. More commonly, water abstraction during dry weather can reduce the wetted width of rivers. This loss of habitat can result in a loss of species and decreased abundance of others. It can also increase the vulnerability of water plants and animals to pollution and high summer temperatures.

Variation in flows and water levels is also important in all surface waters to maintain their characteristic ecological diversity. In lakes serving as reservoirs, extreme variation in water levels between winter and summer can result in the lake margins becoming a hostile environment for water plants and animals and the creation of a scar zone of bare sediments. In rivers, higher flows provide a trigger for migratory fish like salmon to make their runs upstream and successfully navigate waterfalls and other obstacles to migration. They also move fine and larger sediments around as well as detritus and other food sources. This creates the diversity of shifting habitats on which different water plants and animals depend. An estuary without the ebb and flow of the tide or inputs of river flows will not provide the conditions necessary for a natural complement of estuarine plants and animals.

6.2.        European overview of abstraction and rivers with regulated flow

WFD required river basin management plans report on hydromorphological pressures on water bodies.   Five groups of hydromorphological pressure on surface waters (rivers and lakes) were included in the WISE-WFD database, namely (1) Water abstractions; (2) Water flow regulations and morphological alterations of surface water; (3) River management; (4) Other morphological alterations; (5) Other pressures.    In the reporting system hydromorphological pressures comprised of several subcategories of pressures. In case of Water abstractions subcategories include pressures from Agriculture, Public Water Supply, Manufacturing, Electricity cooling, Fish farms, Hydro-energy, Quarries, Navigation, Water transfer, and Other; while in case of Water flow regulations and morphological alterations of surface water include pressures from Groundwater recharge, Hydroelectric dam, Water supply reservoir, Flood defence dams, Water Flow Regulation, Diversions, Locks, and Weirs.

6.2.1.      Key messages

• 8% of European river water bodies are affected by water abstraction pressures.
• The most water abstraction affected river basins are in Bulgaria, France, Italy, and Spain.
• Only 2% of the lake water bodies are affected by water abstraction pressures.
• The predominant HYMO pressure type in the EU coastal water bodies is coastal water management. Water flow regulation and morphological alterations of surface water are the second most important pressure type. Other pressures can be found in lower extent.
• Water flow regulation and morphological alterations of surface water are the most significant HYMO pressure type in the EU transitional water bodies, followed by transitional water management. Water abstraction and other morphological alterations are less important.

6.2.2.      Assessment

Out of 23 Member States that have reported to the WISE-WFD database three (Luxemburg, Romania and Slovakia) have not reported hydromorphological pressures.

Surface water bodies affected by direct water abstractions

17 out of 20 Member States reported river water bodies affected by water abstraction. Cyprus, the Czech Republic and Latvian did not report any river water bodies affected by water abstraction.  Nine percent of the river water bodies are affected by water abstraction. Overall, 8% of European river water bodies are affected by water abstraction pressures. Countries with the highest percentage of water abstraction pressure are Italy, Spain, France and Bulgaria; all of them belong to the Mediterranean region (Figure 6.1).

Most Member States (17 out of 20 Member States) reported lake water bodies being affected by water abstraction, however only 400 lake water bodies were identified as affected by water abstraction, which represent only 3% of the lake water bodies.  This fact maybe read in a way that only few lakes are used as source for water supply for public water supply or irrigation or fish farming. The highest percentage of water abstraction affected lake water bodies are located in Greece, The Netherlands, United Kingdom and Bulgaria while in Austria, Czech Republic, Finland, Latvia and Sweden no lake water body is under water abstraction pressure (Figure 6.2).

Four Member States (UK, France, Spain and Italy) have identified transitional water bodies being affected by water abstraction in the river basin district; accounting for 12 % of the transitional water bodies in these Member States. High water abstraction or water storage in the river basin district may markedly reduce the freshwater inflow, in particular in summer, and the dilution of pollutant discharges.

Figure 6.1:  Percentage of river (left panel) and lake (right panel) water bodies having water abstraction identified as a significant pressure, by countries

Note: Number of water bodies affected by water abstraction are given in parenthesis. Percentage of affected water bodies is calculated as percentage of water bodies with known ecological status/potential

Source: WISE-WFD database February 2012; fd.atkins.dk/report/WFD_aggregation_reports/SWB_pressure_status

Water bodies affected by water flow regulation and morphological alteration

Most Member States reported water bodies being affected by the pressure group water flow regulation and morphological alteration. Nearly 40 % of the river water bodies are affected by water flow regulation and morphological alteration. This pressure group includes impacts from storage of water in reservoirs, but also change in hydrological regime and impacts by weirs and locks. For lakes pressures from water flow regulation and morphological alteration were affecting 27 % of the lake water bodies. For transitional and coastal waters pressures related to water flow regulation and morphological alteration generally affected 18 % and 12 % of the water bodies.

In central Europe generally more than half of the river water bodies have water flow regulation and morphological alteration as a significant pressure (Figure 6.2). In Germany, Poland and Belgium Flanders more than three quarters of the river water bodies have water flow regulation and morphological alteration as a significant pressure.

In Belgium Flanders, the Czech Republic, United Kingdom and the Netherlands more than half of the lake water bodies have water flow regulation and morphological alteration as a significant pressure. In Sweden 2150 lake water bodies have water flow regulation and morphological alteration as a significant pressure; accounting for 30 % of the Swedish lakes.

Figure 6.2:  Percentage of river (left panel) and lake (right panel) water bodies having water flow regulation and morphological alteration identified as a significant pressure, by countries

Note: Numbers of water bodies affected by water flow regulation and morphological alteration are given in parenthesis. Percentage of affected water bodies is calculated as percentage of water bodies with known ecological status/potential

Source: WISE-WFD database February 2012; wfd.atkins.dk/report/WFD_aggregation_reports/SWB_pressure_status

6.3.         Case studies

We hope that Member States and relevant stakeholders will comment on the current case studies and contribute with updates and new case studies. The current case studies are partly copy and paste from RBMPs or other relevant documents

6.3.1.      Rivers being affected by high abstraction rates

Case: Water bodies affected by abstraction in Catalonia

Source: Catalonia Water Agency, 2010

The extraction of water for urban and agricultural use, the regulation of the rate of flow of rivers (in order to satisfy demand for water using reservoirs), and the proliferation of plantations of phreatophytic trees (with deep roots which reach down to the phreatic level) are all activities which reduce the quantity of available water and directly affect the quality of 8.9% of rivers and 58.8% of groundwater.

Those areas most affected by water extraction and river flow regulation are the basins of the Muga, the Ter, the Llobregat, the Cardener, the Noguera Ribagorçana, the Segre and the Ebro, with particular problems being experienced in the final sections of the Foix, the Gaià and the Riudecanyes stream, with practically non-existent flows as a result of reservoir regulation.

The groundwater systems most affected by extraction for irrigation, water supply or industrial uses include most of the aquifers close to the coast (but also inland areas, such as Carme-Capellades and the Moianès, the alluvial fan of Terrassa and the Tàrrega limestones), while the effect of phreatophytic tree plantations is particularly significant in the basins of the Tordera, the Onyar and the lower sections of the Ter.

Map 6.2 River and groundwater bodies at risk due to water abstraction and changed flow regime in the Catalonia RBMP

6.3.2.      Change in hydrological regime due to water transfer and reservoirs

Case: Change in flow due to canals

Source:

Opening of the Albert canal (1935) and the Juliana canal (1939) has resulted in a decrease of low-discharge levels. In 1990 the weir at Borgharen has been automized and discharges below 10 m³/s are mostly prevented

Figure 6.3: Lowest discharge per year on the river Meuse (Borgharen)

To prevent too low discharge in the Grensmaas, the Netherlands and northern Belgium ratified the Meuse Discharge Treaty in 1995, which comprises agreements on water distribution. This has since ensured the restriction of discharge into canals during periods of drought, and the surplus lockage water is pumped back into the river. The aim of this treaty is to prevent the Grensmaas discharge from falling below 10 m³/s. This minimal discharge seems to be sufficient to keep aquatic life in the Grensmaas healthy, provided that it does not occur too often.

Case: Changed low regime of the Júcar river

Source: Sánchez Navarro et al. 2007

The natural flow regimes of Mediterranean streams have strong seasonal and inter-annual flow variations. This pattern of flow contrasts with agricultural water needs. The Júcar River and its main tributary the Cabriel River provide a typical example of water management in Spain. The Alarcón Reservoir on the Júcar River and the Contreras Reservoir on the Cabriel River have been operated for irrigation water supply since 1954 and 1970, respectively. Flow regimes downstream of these reservoirs show an inverted seasonal pattern.

Case: Ebro River Basin – change in flow regime

Source: Bartalla et al.

The Ebro River and its tributaries (North-Eastern Spain) are regulated by over 187 dams, with a total capacity equivalent to 57% of the total mean annual runoff. Annual runoff did not show strong trends, but the variability of mean daily flows was reduced in most cases due to storing of winter floods and increased baseflows in summer for irrigation. Monthly flows ranged from virtually no change post-dam to complete inversion in seasonal pattern, the latter due to releases for irrigation in the summer, formerly the season of lowest flows.

Figure 6.4: Illustrative plots of mean monthly flows pre and post dam for Guadalope and Ebro (below Ebro Dam near headwaters)

Note: IR is the ratio of reservoir capacity to annual runoff; Φ is the correlation coefficient between pre and post dam monthly flows.

6.3.3.      Case: Regulated water levels of lakes

Regulated lakes in the Nordic countries

Source: Martunnen et al. 2006: 

There are hundreds of regulated lakes in Finland, Norway and Sweden (Table 2). For instance, in Sweden, there is 563 lakes larger than 1 km2 with water level regulation vary from 0.1 m to 35 meters. In Norway, there are approximately 800 reservoirs registered in NVE’s database, and a further 100 are assumed to exist without being registered so far. In half of these reservoirs, the water level fluctuation is more than 5 metres. The highest regulation amplitude is 140 m. In Finland, the water levels from 100 regulation projects of the total 350 projects have been analysed. Finnish regulations are usually relatively mild in terms of annual water level fluctuation. Half of these projects show that the annual water level fluctuation is less than 1 metre. The maximum water level fluctuation in the most heavily regulated lake in Finland is 7 metres.

Relative proportions of regulated lakes to the total number of lakes is the lowest in Finland (8 %) and the highest in Scotland (46 %), where the combination of high altitude and high precipitation favours establishment of reservoirs. However, in Finland, most of the largest lakes are regulated and consequently one third of the total lake area (about 11 000 km2) is regulated.

In summary, many Swedish and Norwegian reservoirs are much more heavily regulated than Finnish ones. However, the regulation amplitude itself does not directly describe the magnitude of ecological impacts of regulation. For instance, in Finland lakes are generally much shallower and their water is more coloured and consequently the productive zone is narrower than in Norwegian and Swedish lakes. Furthermore, there is a big difference in the use of regulated watercourses between Finland, Sweden and Norway. In Sweden and Norway most reservoirs are located in remote areas where recreational use of the watercourse is usually of minor importance, whereas in Finland the regulated lakes are almost always important for recreational purposes.

Finland – Regulated lakes and rivers

Source: Finnish Environment Institute

6.4.        Measures in relation water regulation and water level fluctuations

Measures to be described here, including

• Reduce demand for water and abstraction of water
• Evaluate impacts of water transfers
• Ensuring minimum flow/environmental flow
• Evaluate sector activities impacts such as inland navigation and hydropower operation
• Other measures to rehabilitate the flow regime
• Reducing human-induced peak flows
• Enhancing natural water retention
• Restoring wetland
• Reduce the impact of water level fluctuations in lakes

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Minimum flow

In order to meet the criteria of good ecological status or potential, the minimum flow should at least leave water in the river (except in naturally dry falling rivers) and aim at maintaining and restoring the river’s type-specific aquatic community; promote the continuity of the original river bed, as well as the bypass at its termination; achieve nearly natural flow dynamics and groundwater status in floodplain; and maintain distinct water exchange zones. Instead of gathering statical data on minimum flow, the feasibility of implementing an ecological control mechanism for minimum dynamic flow should be ascertained. This mechanism should maintain a constant and inflow-driven minimum flow, or should at least be seasonally controlled and meet the aforementioned criteria. A river’s ecological status or potential can be ameliorated through the realization of measures that upgrade watercourse structures along original riverbeds in the light of site-specific characteristics, management goals, and minimum flow data, consideration should be given to site-specific characteristics.

Discharge regime:

Rapidly varying flows can be generated in a hydropower facility (hydro peaking). This gives rise to conditions that are deleterious to watercourse hydromorphology and aquatic biota downstreams, thus jeopardizing the goal of achieving good ecological status or potential. Hence, such artificial discharge regimes should be avoided for ecological reasons. However, if artificial discharge regimes cannot be avoided entirely, the ecological status of the water body/water bodies affected can still be improved through operational modifications (e.g. downstream “buffer” reservoirs) that attenuate the volume and frequency of artificially generated abrupt waves and avoid unduly precipitous water level fluctuations.

References

Batalla, R.J., Gomez C., nd  Kondolf M. 200xRiver impoundment and changes in flow regime, Ebro River Basin, Northeastern Spain. Available at http://www2.uah.es/econ/Papers/BatallaGomezKondolf03.pdf

Finnish Environment Institute: Regulated lakes and rivers Available at  http://www.environment.fi/default.asp?contentid=356128&lan=EN

Martunnen et al. 2006:  http://www.ewaonline.de/journal/2006_05.pdf

Rafael Sánchez Navarro et al., “Hydrological impacts affecting endangered fish species: a Spanish case study,” River Research and Applications 23, no. 5 (June 1, 2007): 511-523.