The City of Odense is under big pressure – from above: because annual mean precipitation has gone up around 100 mm since measurements started 140 years ago. Extreme rains are occurring more often and they are becoming more intense. There is also pressure from surface water: because of flooding due to extreme runoff in the rivers through the city or flooding from the Odense Fjord. Sometimes both occur at the same time. Thirdly, there is pressure from the subsurface: due to a rise in groundwater level caused by increased recharge, diminishing needs for potable water / lesser water abstraction and the sealing of previous leaky sewers which hereby stop acting as drains.
Read more about Odense City in case study report TU1206-WG1-011
During the last 100 years the area of the city has grown greatly. The water supply was primarily based on local groundwater abstraction sites. Today, it is still based on groundwater, but most of the groundwater abstractions within the urbanized areas have been stopped and the total amount of abstraction of groundwater has been reduced by 50%. Furthermore the majority of our potable water are being abstracted in the surrounding municipalities The effect of these changes has meant that the groundwater level within the city limits has risen dramatically over the past 25 years. In some areas the water table has risen 12 meters. Today, the water level in some areas, are close to what the water level used to be at the turn of the last century (early 1900’s).
The areas that are drained and urbanized are becoming increasingly waterlogged again. This is of great concern for the inhabitants and constitutes a major conflict of interest. The development in urbanization also causes other challenges. The natural seepage of rain into the ground is drastically reduced due to the increase in total area of impermeable surfaces.
Historically, sewage pipes were established as common sewage systems for both rain run-off and raw sewage. Expanding sewage pipe systems to accommodate future heavy rains/climate change is very expensive and sometimes an almost impossible task, but we try. Within the city limit we have used more than 1 billion Euro establishing large diameter sewage pipes for delaying or storing storm water during extreme rains, in order to meet the EU-legislation by hindering/decreasing the amount of sewage water that though “overruns” are led untreated into the Odense Å and Odense Fjord (Å means river and Fjord means Inlet).
Instead of building larger and bigger storage pipes/pools there is a growing interest in securing local infiltration. The need for artificially/naturally enhanced infiltration of rainwater in urban areas is growing. This, again, - is putting further strain on the water level and saturation beneath the city. New large scale suburban infrastructure projects like tunnels and underground parking facilities also puts further strain on the groundwater saturation challenge and may alter the nature of groundwater flow patterns etc.
In order to meet the above mentioned growing demands, the Municipality of Odense together with VCS Denmark (one of the biggest water/waste water companies in Denmark), GEUS (The Geological Survey of Denmark and Greenland) and The Region of Southern Denmark have started building a detailed 3D geological and hydrogeological model. A model to study the groundwater resources, the climate change impact on the water cycle and also covering subjects of archaeological and historical interests.
Denmark is a small country that covers 43.100 km2 – less than 1/10th of Sweden. Denmark consists of the peninsula of Jylland (Jutland), and an archipelago of 406 islands of which 78 are inhabited. The coastline stretches more than 7300 km in total length. The land is mainly used for agriculture (67%) and forests (12%) and semi-natural areas (11%), also urban areas and infrastructure installations (10%).
The Kingdom of Denmark also includes the Faeroe Island and Greenland. Denmark has a population of 5.6 million inhabitants and the population density is 130 persons per km2. 85% of the population lives in cities and villages with more than 200 inhabitants and 15% live in the countryside and smaller villages. One third of the population lives in Greater Copenhagen.
The Municipality of Odense only covers an area of 305 km2. This place it in the center part of the 98 Danish municipalities –The municipality of Copenhagen – the Capital of Denmark – only covers 88 km2, which is roughly the same area as the City of Odense.
The City of Odense is one of the oldest in Denmark, dating back to the Vikings and their ring fort “Nonnebakken” south of the Odense Å. Archaeological excavations have uncovered pavements, buildings and crafts dating back to the first millennium and the first time Odense is mentioned in a written reference is in year 988. The oldest parts of St. Alban’s Priory and The Cathedral for Canute the Saint are dating back to the 11th century. During the 12th century the building of another church, several monasteries and nunneries and a moat testifies strong urban growth.