Elbe catchment fact sheet
1 Catchment characteristics
The Elbe River basin is shared mainly between the Czech Republic upstream, which has approximately a third, and Germany downstream, which has the remainder.
Large parts of the Elbe river basin (Figure 1) have characteristics of a lowland river with a wide alluvial valley downstream of Dresden (Grossmann, 2012). More than a half of the river basin is located at altitudes lower than 200 m alt., mainly forming the Northern German Plain, almost 33% of the catchment has altitudes between 200 and 500 m alt., representing the hilly land, and almost 17% of the drainage area belongs to the low mountain ranges, of which only 2% is located at altitudes of more than 800 m above sea level (IKSE, 2005).
Figure 1: Location and topography of the Elbe river Basin and its three largest tributaries Vltava, Saale and Havel (including the Rhin catchment) and location of the most important cities (C. Hesse, 2019)
2 Elbe climate and discharge regime
The average annual precipitation levels in the Elbe catchment range from 1,700 mm at the ridges of the Giant Mountains and the Jizera Mountains as well as in the Upper Harz Mountains and 450 mm in areas located in the rain shadow of the low mountain ranges. The average annual precipitation level of the complete Elbe River basin is 628 mm. Compared with the Rhine, Danube, Weser, and Ems basins, the Elbe is the driest of the drainage basins in Germany. However, the map shows significant differences in the individual regions. For about one third of the Elbe River basins the precipitation level is below 550 mm. These are mainly parts of the Vltava, Ohře, Saale and Havel river basins. These central parts of the Elbe river catchment in Germany as well as in the Czech Republic are located in the rain shadow of several mountainous ranges, and receive only little precipitation amounts during the cyclonic westerly and north‐westerly weather situations. (Cornelia Hesse, Integrated water quality modelling in meso- to large scale catchments of the Elbe River Basin under climate and land use change, 2019, https://publishup.uni-potsdam.de/opus4-ubp/frontdoor/deliver/index/docId/42295/file/hesse_diss.pdf ) As a result, the Lower Saale region with an average of approx. 430 - 450 mm per year, the Žatec basin in the Ohře region and the Thuringian Basin in the Unstrut region with 450 mm per year are the driest areas. By contrast, annual precipitation of more than 1,000 mm is only to be found at the higher elevations of the lower mountain ranges.( https://www.ikse-mkol.org/en/themen/die-elbe )
Figure 2: Average annual precipitation in the Elbe catchment (https://www.ikse-mkol.org/en/themen/die-elbe/)
Resulting from these climate conditions, the Elbe river is characterized by a rain‐snow‐type runoff regime, typical for such transitional climate. The discharge regime of the Elbe river (861 m3·s−1 on average) usually shows high water levels in winter and spring, and low water levels in summer and autumn (Figure 2.2). Due to snow melt in the low mountainous regions the runoff maximum is usually observed in the months of March and April. The lowest runoff can be registered in September. Additionally, extreme floods can be caused by regional heavy precipitation events in summer, such as the flood events in August 2002 and June 2013 (Hesse, 2019). (Cornelia Hesse, Integrated water quality modelling in meso- to large scale catchments of the Elbe River Basin under climate and land use change, 2019, https://publishup.uni-potsdam.de/opus4-ubp/frontdoor/deliver/index/docId/42295/file/hesse_diss.pdf)
Figure 3: Long-term (1931 / 1946 -2000) average monthly discharges (m3/sec) at the downstream gauges of the Elbe river, its three largest tributaries, and the Rhin river (1980 – 2005) (C. Hesse, 2019)
The three main Elbe tributaries show quite similar runoff regimes on the long‐term as the Elbe river (Figure 2.2). However, the maximum discharge can be observed earlier, in March, in the Vltava and Saale rivers, and the Havel has a more prolonged period of high discharge, from January to April. The longer high flow period in the Havel is caused by the lowland character of its catchment, with more rain and less snow cover in winter, and by a high share
of dammed river reaches with low flow velocities. The meso‐scale Rhin river is characterized by average monthly discharges lower than 10 m³·s‐1. The relation between the highest discharge in March and the lowest one in September is larger than for the large‐scale rivers presented in Figure 3 (Hesse, 2019). Additionally, the summerly low flow period starts earlier and lasts longer than in the large‐scale Elbe tributaries due water. (Cornelia Hesse, Integrated water quality modelling in meso- to large scale catchments of the Elbe River Basin under climate and land use change, 2019, https://publishup.uni-potsdam.de/opus4-ubp/frontdoor/deliver/index/docId/42295/file/hesse_diss.pdf)
management impacts, water consumption and a higher evapotranspiration potential in this lowland catchment with vegetation connected to the groundwater. In the Elbe river basin, 71% of the average annual precipitation is lost by evapotranspiration (FGG‐Elbe, 2005). With the reference to the Neu Darchau gauge, which represents 89% of the whole Elbe drainage area, the average annual runoff rate amounts to 5.4 L·s‐1·km‐2. Thus the Elbe basin belongs to the river catchments with the lowest runoff rates in Europe (IKSE, 2005).
Table 1 gives an overview on the main natural characteristics of the Elbe river basin and the four selected sub catchments
Table 1 Natural conditions of the total Elbe river catchment and, in comparison, differentiated for four of its sub catchments (discharge and climate parameters for the time period 2001‐2010), Hesse 2019
3 Flood risks
The Elbe River is experiencing all three major water-related problems: too much water once in a while, i.e., floods; too little water from time to time, i.e., droughts; and water of inadequate quality, although a notable improvement in water quality was achieved over the last 15 yr (Krysanova et al. 2006). There was a destructive flood in August 2002, followed by a severe drought in 2003. Because of the disastrous flood in 2002, general public attention has strongly shifted to the flooding problem (Krysanova et al. 2008).( Valentina Krysanova et al, Practices and Lessons Learned in Coping with Climatic Hazards at the River-Basin Scale: Floods and Droughts, 2008, https://www.ecologyandsociety.org/vol13/iss2/art32)
The Elbe river flows through three major cities before it reaches the North Sea. Prague (Czech Republic), Dresden and Hamburg (Germany) all contain more than 1 million inhabitants and have all experienced flooding of the Elbe river in the past. In 2002 Prague and Dresden both suffered from flooding after a week with extreme rainfall in central Europe. Many people were evacuated and damages were up to billions of euros. Risk of flooding in Hamburg is seldom caused by heavy rain (only). The water level in the Elbe river can rise dramatically with heavy storms at sea. Such an event caused floods in 1962.
Preventive measures against flooding (German Committee for Disaster Reduction (DKKV), 2004) combine engineering facilities, river-basin planning, and financial and social measures. These include:
Due to climate change the Elbe catchment is likely to receive more rainfall in the winter period( https://ec.europa.eu/regional_policy/sources/docoffic/working/regions2020/pdf/regions2020_climat.pdf).
Study shows that there is a moderate certainty that most German rivers will experience more extreme 50-year floods and more frequent occurrences of 50-year droughts. Projected changes with a high certainty include an increasing trend of floods in the Elbe Basin( Shaochun Huang et al, Projections of climate change impacts on floods and droughts in Germany using an ensemble of climate change scenarios, 2014, https://link.springer.com/article/10.1007/s10113-014-0606-z).
4 Droughts
The Elbe catchment has a long history with droughts. Ancient ‘hunger stones’ surface when water levels reach ex
tremely low levels, like recently in 2018. In all of the recent years 2014 to 2019 the Elbe catchment has experienced droughts, during exceptionally dry periods (Low Water Stage Marks on Hunger Stones: Verification for the Elbe River in 1616 – 2015, Elleder et al, 2019, https://www.researchgate.net/publication/337088602_Low_Water_Stage_Marks_on_Hunger_Stones_Verification_for_the_Elbe_River_in_1616-2015). Statistically significant trends in dry indices were found for the lowland part of the basin( Valentina Krysanova et al, Practices and Lessons Learned in Coping with Climatic Hazards at the River-Basin Scale: Floods and Droughts, 2008, https://www.ecologyandsociety.org/vol13/iss2/art32)
The rock, below Tyrs Bridge, is marked in Czech and German, with one message from pub owner Franz Mayer in 1904 saying: “If you see me, weep”. Drought uncovers once-dreaded 'Hunger Stones' in Czech river | Reuters
Higher average temperatures and lower precipitation in the summer months are projected for the basin under future climatic conditions. Thus, the water scarcity problem in this densely populated area will likely grow, and the risk of droughts will increase; this will possibly have adverse consequences on several sectors, including water supply, agriculture, forestry, navigation, and recreation. (Becker and Grunewald 2003).
5 Land use, water quality and biodiversity
According to the data analysed within the framework of the CORINE Land Cover project in 2006, 42.8% of the area in the Elbe River basin is used as agricultural land. Forests cover 30.6%, among them is 21.9% coniferous and 8.7% deciduous and mixed forest.
The land use patterns in the Elbe river basin reflect the orographic, climatic and soil conditions. Forests can be found in the mountain ranges and on less fertile sandy soils. Predominantly agricultural use prevails on fertile brown and black soils in the middle and lower courses of the Saale basin and in the central Czech part, and grassland is widespread on wetland soils with a high groundwater table, as in the Havel catchment, and in the lower Elbe part close to the mouth. The map of the soil properties in the Elbe river basin in Figure 4 is based on two main features important for water and nutrient behavior in a river catchment: a) the sand content and b) the easy connection to groundwater (wetland soil). The sand content in soil is one essential parameter reflecting the water and nutrient retention potential in a landscape: the higher the fraction of sand in soil texture, the lower is its retention potential (Scheffer & Schachtschabel, 2002; Zotarelli et al., 2006). The wetland soils shown as grids in Figure 4 mark those lowland areas (e.g. fens, floodplains) characterized by an increased evapotranspiration (and nutrient uptake) potential due to a higher percentage of plant roots reaching the groundwater (Cornelia Hesse, Integrated water quality modelling in meso- to large scale catchments of the Elbe River Basin under climate and land use change, 2019, https://publishup.uni-potsdam.de/opus4-ubp/frontdoor/deliver/index/docId/42295/file/hesse_diss.pdf).
Figure 4. Spatial distribution of land use classes, point source emissions of total nitrogen (TN) and total phosphorus (TP), soil properties, and fertiliser application levels (as used in the study for the entire Elbe river basin), Hesse 2019 .
Point and diffuse nutrient sources in the Elbe basin are mainly connected to human activities in the catchment. Large cities or industrialized regions usually come along with intensive point‐ borne pollution to the river network originating from water treatment plants and industrial sites. The diffuse pollution is linked to agricultural areas, and additionally depends on soil types and climatic conditions.
Fertiliser application on agricultural fields is usually recommended to be increased with increasing crop yield expectations (TLL, 2011a), which can be defined by soil quality, water availability and climate conditions. Following this rule, the very fertile soils in the lower Saale basin can be expected to receive more fertiliser than the sandy less productive soils dominating in the Havel river basin (Hesse 2019). Resulting from the maps and facts described above several additional characteristics of the Elbe river basin and its four sub catchments under consideration can be calculated, summarized and comparably listed. The comparison can be found in Table 2(Cornelia Hesse, Integrated water quality modelling in meso- to large scale catchments of the Elbe River Basin under climate and land use change, 2019, https://publishup.uni-potsdam.de/opus4-ubp/frontdoor/deliver/index/docId/42295/file/hesse_diss.pdf)
Table 2 Comparison of land use composition, selected soil conditions and point and diffuse nutrient sources of the Elbe river catchment and four of its subcatchments for the time period 2001‐2010 (Hesse, 2019).
A water quality monitoring network was established along the Elbe river and its main tributaries in the last decades, and data can be found online and used for evaluation of the former and recent water quality status of the Elbe river and selected subcatchments (FGG‐Elbe, http://www.fgg‐elbe.de/elbe‐datenportal.html). This was done for the most downstream stations of the Vltava (Zelčin), Saale (Groß Rosenburg) and Havel (Toppel) rivers and the last tide‐unaffected Elbe river gauge (Schnackenburg) representing the subcatchments, which were already analysed above. The analysis of NO3‐N and PO4‐P values for the meso‐scale Rhin basin (gauge Kietz) based on measurements provided by the LUA is also added (Figure 2.4). The upper graphs of Figure 5 depict the development of the annual average concentrations of nitrate nitrogen, ammonium nitrogen, phosphate phosphorus, and dissolved oxygen for the time period 1991‐2010. As one can see, the nutrient concentrations in the Elbe river basin are mainly decreasing with time, whereas the dissolved oxygen is mostly increasing. This indicates on an overall improvement of water quality in the Elbe river.
Figure 5 Water quality of the Elbe river, its three largest tributaries, and the Rhin (most downstream gauges): annual average concentrations
in 1991‐2010 (above) and monthly average concentrations in 2001‐2010 (middle) of nitrate nitrogen (NO3‐N), ammonium nitrogen (NH4‐N), phosphate phosphorus (PO4‐P) and dissolved oxygen (DOX) and comparison of their 90th percentiles for nutrients and 10th percentiles for dissolved oxygen (below) with the German water quality classes for surface waters according to LAWA (1998) (data sources: FGG Elbe, http://www.fgg‐ elbe.de/elbe‐datenportal.html, December 2012; LUA), Hesse 2019
However, some tributaries show a different behaviour and pollution classes for several substances. In subcatchments with dominating agricultural land use (e.g. Saale), the nitrate and ammonium nitrogen concentrations are higher than in the Elbe and in other rivers, resulting probably from a larger fraction of arable land characterised by fertiliser application and leaching. ( Cornelia Hesse, Integrated water quality modelling in meso- to large scale catchments of the Elbe River Basin under climate and land use change, 2019,https://publishup.uni-potsdam.de/opus4-ubp/frontdoor/deliver/index/docId/42295/file/hesse_diss.pdf) These high nutrient concentrations have also negative effects on the Elbe river. It has been already observed that the ecological status of the Elbe river declines after the confluence of the Saale river, especially due to increase in nitrate nitrogen concentration (Arge‐Elbe, 2008).
In contrast, the catchments of the Havel and Rhin rivers are less used for agriculture, and show the lowest nitrogen pollution. The slowly flowing lowland rivers with a lot of lakes and wetlands within their catchments additionally facilitate the retention of nutrients (FGG‐Elbe, 2010). Nevertheless, the highest phosphorus level can be observed in the Havel river. Besides phosphate leaching processes in the mainly sandy soils of the catchments, the high phosphate concentrations in the rivers can be additionally explained by desorption from historically polluted sediments (Bronstert & Itzerott, 2006). Such processes mainly occur in times of high temperatures and low oxygen availability, as it can be seen in the monthly average values for the late summer in the Havel river (Figure 5 middle).( Cornelia Hesse, Integrated water quality modelling in meso- to large scale catchments of the Elbe River Basin under climate and land use change, 2019,https://publishup.uni-potsdam.de/opus4-ubp/frontdoor/deliver/index/docId/42295/file/hesse_diss.pdf)
According to the German classification of water quality (LAWA, 1998), which uses the 90th percentile for nutrients and the 10th percentile for dissolved oxygen to compare with certain water quality thresholds, the highest nitrate level in the Elbe basin results in water quality class III (Saale), the highest ammonium value belongs also to the Saale (class II‐III), the maximum phosphate phosphorus level represents water quality class III (Havel), and the lowest dissolved oxygen concentration results in water quality class II (Havel). There are some diversities between the rivers in this respect, and no river exists which has the worst or best status for all components (Figure 5, below).
In general, the long‐term observations of surface water quality in Germany (1955‐2011) show an increase of nutrient pollution with growing industrialisation and intensification of agriculture from the 50ies until the 70ies or 80ies, and then a decrease in nutrient concentrations (or rather 90th percentiles) for PO4‐P and especially NH4‐N, but only slightly for NO3‐N. For the Elbe river the same behaviour could be observed, but only from the beginning of the 90ies, after the German reunification (UBA, https://www.umweltbundesamt.de/en/topics/water/rivers).
Due to former political and socio‐economic conditions, until the 90ies the Elbe was one of the most polluted rivers in Europe with a low ecological potential. The improvements in water quality could be recognised after the political change due to closure of industrial enterprises and upgrading of sewage treatment plants in the basin, as well as due to a substantial decrease in fertilisation rates on agricultural land (Lehmann & Rode, 2001; Hussian et al., 2004). However, nutrient pollution is still an important problem in the Elbe basin, as the availability of nitrogen and phosphorus is the main factor for the riverine primary production, often causing a moderate to bad status of the biological quality components according to the WFD.( Cornelia Hesse, Integrated water quality modelling in meso- to large scale catchments of the Elbe River Basin under climate and land use change, 2019,https://publishup.uni-potsdam.de/opus4-ubp/frontdoor/deliver/index/docId/42295/file/hesse_diss.pdf) The main reason for the heightened loads is the still excessive diffuse input of nutrients to rivers, mainly caused by time‐delay in leaching from agricultural fields, as well as remobilisation from the heavily nutrient‐loaded sediments. The high nutrient pollution loads carried with rivers to the seas are especially dangerous for the coastal ecosystems (FGG‐Elbe, 2010).
Therefore, the Elbe river management plan of 2009 requested by the WFD mentions the reduction of diffuse nutrient pollution as one of the most important management points for the national and international water management strategies. It is assumed there that the nitrogen and phosphorus loads have to be reduced within three 6‐year periods by 24% (based on the values of 2006 at the gauge Hamburg‐Seemannshöft), in order to reach a good ecological status of the coastal waters (FGG‐Elbe, 2009). ( Cornelia Hesse, Integrated water quality modelling in meso- to large scale catchments of the Elbe River Basin under climate and land use change, 2019,https://publishup.uni-potsdam.de/opus4-ubp/frontdoor/deliver/index/docId/42295/file/hesse_diss.pdf) In the actualisation of this management plan published in 2015 target values regarding the average annual nitrogen and phosphorus concentrations are defined (TN: 2.8 mg L‐1 (Seemannshöft), 3.2 mg L‐1 (Schmilka); TP: 0.1 mg L‐1). These values are still exceeded at the majority of the Elbe river water quality gauges, at some stations by up to 60% (IKSE, 2015). According to IKSE (2015), a total of 91% of all river waters in the Elbe basin do not reach the good ecological status as requested by the WFD. The main pressures counteracting to reach the aims of the WFD in the intensively used Elbe river catchment can be summarised as follows:
• diffuse sources (42%),
• regulation of discharge and/or morphological changes (35%),
• point sources (20%),
• water abstraction (1%),
• others (2%).
The influence of urbanization (e.g. ground sealing), potamalisation (impoundment of water courses), and erosion-prone, agricultural land-use types (e.g. root crop, maize) are significantly related to the fish community com
position of the Elbe catchment. These terrestrial effects of land-use and urbanization need to be more strongly considered in the conservation of endangered stream fishes, ideally including combined measures of erosion control, restoration of environmental flows and mitigation of structural degradation (A.M. Bierschenk et. al. 2018). ( A.M. Bierschenk et al, Impact of catchment land use on fish community composition in the headwater areas of Elbe, Danube and Main, 2019
)
6 River structures impact
The natural flow regime of the Elbe river and its tributaries is influenced by several anthropogenic measures, such as creation of reservoirs, regulation of rivers, drainage of wetlands and brown coal mining (Klöcking & Haberlandt, 2002). A large number of dams with a reservoir volume of more than 0.3 million m³ can be found in the Elbe river basin, 175 of them are located in Germany and 137 in the Czech Republic. They comprise a total reservoir volume of approximately 4.12 billion m³ (IKSE, 2005). The hydraulic engineering measures can influence water quality, discharge regime, structural diversity, particulate matter and groundwater, often seriously affecting the vulnerability of the ecosystem (Rode et al., 2002). For example, in the upper course of the Saale basin, the river morphology and hydrological regime is modified by a series of five reservoirs for water harvest, flood protection and a salt‐ load control system in order to dilute high industrial and mining salt emissions downstream in the low flow seasons. The natural water flow in the lower reaches is influenced by several weir and lock systems to store water for enabling inland navigation also in the drier summer months.
The meso‐scale Rhin river basin is characterised by an intensive water regulation system including more than 300 small dams and weirs. The large fens and wetland areas in this lowland catchment are meliorated for agricultural purposes and for use as pastures. Water storage, irrigation practices and water transfer to and from adjacent catchments influence the natural hydrological cycle, and have significant impacts on river discharge. The extensive brown coal mining activities, as e.g. in Southern parts of the Havel river catchment (Lusatia), led to a wide‐spread decrease in groundwater level and an artificial increase in river discharge by dewatering. After closure of the open‐cast mining the pits are often refilled with river water causing a decrease of discharge. A temporary decreased groundwater level usually induces oxidation processes in the soils of the influenced regions, and often causes ferric sulphate pollution problems in the draining rivers after the rerise of the groundwater table.
Nevertheless, large parts of the main Elbe river in Germany are still free‐flowing and are not influenced by barrages. Especially the areas around the middle course of the Elbe river in Germany contain several protected natural areas with a high diversity of flora, fauna and landscape types. But the originally broad floodplain areas around the middle and lower courses of the Elbe river are reduced and influenced by flood protection measures for settlements and agricultural or industrial activities. During the last two centuries approximately 84% of the floodplain along the Elbe river course in Germany has been protected by dikes, and cut off from the natural river ecosystem, whereas the narrower upstream valleys have experienced lower losses of floodplain than the wider lowland valleys downstream of Dresden (Grossmann, 2012). The reduced flooding area around the river reaches causes problems not only in times of very high water levels (e.g., during the last decades when immense flood events and damages occurred), but also hinders the natural nutrient retention capacity of the river. The water engineering measures and construction of dams also influence the eutrophication status of a water body. They lower the river’s flow velocity, impact sediment transport and planktonic growth rates and reduce oxygen concentrations in the river reaches. This often induces an intensification of nutrient pollution problems in the river waters.
7. Climate mitigation / carbon storage
Study results indicate that recently (1991–2000) croplands are a net source of carbon (net annual flux of 10.8 g C m-2 year-1 to the atmosphere). The recent temperature trend for the years 1951–2000 (+0.8 K in summer and +1.4 K in winter mean temperature) alone have already caused a significant net flux of 1.8 g C m-2 year-1 to the atmosphere. Future climate change (2001–2055) derived from regionalised meteorological properties driven by the IPCC-SRES A1 scenario results in an increased net C flux of an additional 4 g C m-2 year-1 in comparison to the reference period (1951–2000).
Besides climate-induced alteration of net C fluxes, considerable impacts on groundwater recharge (−45.7%), river flow (−43.2%) and crop yield (−11% to −15% as a basin-wide average for different cereals) were obtained. Recent past and expected temperature changes within the Elbe basin predominantly contribute to the increase of net C fluxes to the atmosphere. However, decreased crop growth (crop yields) and decreased expected water availability counteract even higher net C losses as soil C turnover is reduced through less C input (less crop growth) and drier soil conditions (decrease in water availability). Based on this study, present-day and potential future development of net C fluxes, water components and crop yields were quantified. This allows integrated assessment of different ecosystem services (C storage, water availability and crop yield) under climate change in river basins. ( Joachim Post, Integrated assessment of croplands soil carbon sensitivity to recent and future climate in the Elbe river catchment (central Europe), 2008)
8 Further information