Oder/Odra estuaryDescription of case study area:
The Odra river (German: Oder; Polish and Czech: Odra) in the Baltic region is an outstanding example to show the interrelations between river basin and coast and to prove the dependency of coastal management on river basin management. Therefore, the Odra became a case study of the ASTRA project. The Odra activities are also supported by the project IKZM-Oder (www.ikzm-oder.de).
Short geographical description and problems, which were addressed during the project:
River and basin
The Odra (854 km length) is one of the most important transboundary rivers in the Baltic region. Its basin (118,000 km²) is shared between Poland (89 %), the Czech Republic (6 %) and Germany (5 %). The Odra is a lowland river with its origin in the hilly Polish-Czech boundary region. Due to the warm-temperate climate with sufficiently rain in all seasons, the water discharge shows only a limited annual cycle with an average discharge of 530 m³/s. Floods are a rare phenomenon and are not necessarily linked to snow melting. The last extreme flood with a discharge up to 2,800 m³/s took place during late summer 1997 and caused severe damage.
The coastal region is a complex pattern of lagoons and islands and shared between Germany and Poland. With about 840,000 inhabitants (414.000 in the city of Szczecin) the estuary region is only sparsely populated. Neglecting Szczecin and Swinoujscie, the population density is around 50 inhabitants per km². The Odra river flows through Szczecin and enters the large, shallow Szczecin (Oder) Lagoon. The river and its loads are responsible for the poor water quality in the lagoon and its highly eutrophic state. Through the lagoon runs the waterway, which links the Baltic Sea with the city of Szczecin, its large harbour and important ship-building industry. The water way is permanently dredged to maintain a depth of more than 10 m. In average, dredging removed about 1.5 million m3/a sediment during the last decades. Most of the entering Odra sediment as well as large amounts of nutrients are removed with this dredging and stored at land. Intensive denitrification removes about 15 % of the entering nitrogen load. Therefore, the lagoon serves as a storage pond for sediment, nutrients and heavy metals and protects the Baltic Sea from pollution. The water flushing time is only 55 days and the lake-like salinity around 1.5 0/00 shows that the lagoon is only to a minor degree influenced by the Baltic Sea. The landscape around the lagoon is flat and dominated by agricultural land and forests. In some areas sand, gravel, oil and gas are exploited. Broad reed belts and artificial sandy beaches near the few small towns characterize the coastline. Due to its outstanding ecological value and beauty, most of the coastal area is under nature protection. A detailed description of the lagoon's ecology is given in Radziejewska & Schernewski (in press).
Overview map and photos of the case study area:
The Odra river basin and the adjacent coastal area
The quiet Odra lagoon suffers from severe eutrophication.
The Baltic Sea coast (Ahlbeck, Usedom) with traditional architecture and flourishing tourism.
Future threats and challenges
Climate change: Climate change scenarios predict an increased risk of extreme weather events. Ongoing sea-level rise and a sinking coast as well as changes in precipitation in the catchment, with subsequent changes in river discharge, will increase the flooding risk in the river basin and at the coast. Along the Baltic Sea coast, an increased risk of storms and storm surges will have immediate negative effects on coastal erosion, protection measures and tourism infrastructure (sport boat harbours, beaches, piers, promenades).Flooding: The Odra is a lowland river with only a low hydraulic gradient. The tides in the Pomeranian Bay are in the range of only one decimetre. Strong northerly wind can cause storm water levels at the Baltic Sea coast of one meter and more. During these situations backwater in the Odra is observed far south of Szczecin and a temporary intrusion of Baltic Sea water with a salinity of 6 0/00 into the lagoon is observed. A sinking coast and climate change caused a relative water-level rise of about 1 mm/a during the last century in the region. An even faster increase is assumed for this century. Therefore the effect of storm surges on the river water level will increase, backwater will penetrate even farther into the river basin and cause a hazard. Climate change will affect not only the coast but also the river basin itself. Recent calculations do not suggest a significant increase in precipitation in the Odra basin, but the likelihood of extreme events and floods might become higher. The region has to face danger from two sides, due to sea-level rise as well as due to increased floods. Therefore, an integrated coastal and flood protection is needed.
Eutrophication and water quality: Intensive agriculture, industries and cities cause loads of heavy metals and organic pollutants and especially high loads of the nutrients nitrogen and phosphorus. The river water quality suffers from these loads, but the major consequences are visible in the coastal area. The lagoon can be regarded as a hypertrophic, degraded ecosystem. It largely lacks a submerse vegetation, suffers from severe algae blooms (partly of toxic species) and the water transparency in summer is often below 50 cm. On sunny days without wind, anoxic situations temporary occur and cause fish kills as well as a damage of benthos. Untreated sewage water of the city of Szczecin is source of human pathogenic viruses and has potentially negative impacts on the hygienic (bathing) water quality. Due to regular dredging of the canal and denitrification processes, the lagoon still serves as a retention pond for nutrients and protects the Baltic Sea to a certain degree from pollution, but the poor water quality hampers bathing tourism and nature protection. Water quality will gain importance because most parts of the coastal zone became Natura 2000 sites and EU-Water Framework Directive (WFD) demands a good water quality. The WFD further asks for a river-basin coastal water management plan.
Results from the case study area:
The impacts of climate change on water quality within the Oder/Odra river catchment as well as within coastal waters and effects on economic development, e.g. tourism, have been published in several articles and publications and have been discussed on regional workshops and meetings with regional stakeholders, authorities and partners. Articles which are available online can be found with this link to ICZM Oder.
Within the case study a flood risk assessment was done. The results are available online within the GIS ICZM Oder Estuary.
To keep the public, especially stakeholders, informed a lot of articles in scientific papers as well as in known national and international newsletters were published and several presentations have been given. For interested laymen an online learning module "Climate Change and Coasts" has been prepared in German language and a glossy magazine as been launched, which is available here.