The delicate water balance of Bryggen

Size: px

Start display at page:

Download "The delicate water balance of Bryggen"

Joel Wright
7 years ago
Views:

1 The delicate water balance of Bryggen Cultural heritage and water management at the World Heritage Site Bryggen in Bergen, Norway Hans de Beer, Geological Survey of Norway Ann Christensson, Directorate of Cultural Heritage Norway Henning Matthiesen, National Museum of Denmark

de Beer, Geological Survey of Norway Ann Christensson, Directorate

2 Bryggen

3 Bryggen In 1979, Bryggen in Bergen was listed on the World Heritage List on the following selection criterion: to bear a unique or at least exceptional testimony to a cultural tradition or to a civilization which is living or which has disappeared (ICOMOS, 2008 (rev.))

least exceptional testimony to a cultural tradition or to a

4 Artist impression old remaining part new part excavated hotel built 1980 Illustration: Riksantikvaren

5 Aims The Norwegian Ministry of the Environment states: to preserve the underground archives and at the same time establish conditions for continued development of vital inner cities Governments strategy document White Paper Nr. 1, states Groundwater situation at Bryggen is out of control and will be dealt with by national and international experts

inner cities Governments strategy document White Paper Nr.

6 Fires (?) Photo and drawing: Riksantikvaren

7 What are we trying to preserve? A 54 m long section of historic waterfront, preserved for almost 800 years Photos: A. Herteig, 1969, Riksantikvaren

8 What are we trying to preserve? 1000 year old timbers from the southern part of Bryggen Photos: Riksantikvaren

9 Why is water so important? In situ preservation is only a viable strategy if the archaeological deposits are lying in a steady, balanced burial environment, with no or negligible decay going on. This is threatened by: urban development climate change Most variables influencing the preservation conditions are closely related to the presence or absence of water, and its chemical composition.

steady, balanced burial environment, with no or negligible decay going on.

10 Urban development, 1979 Map: Geological Survey of Norway Photos: Riksantikvaren

11 A delicate water balance m below terrain now future Middle photo: Riksantikvaren, drawing right: Nationalmuseum Denmark, Top drawing: Geological Survey of Norway, based on E. Mørk.

5 now future Middle photo: Riksantikvaren, drawing

12 Rising seawater levels Levels Year when surface level is exceeded Sea level rise* 0 (3) mm/year settling 2 mm/year +0.3 m for meteorological conditions +0.3 m for meteorological conditions +0.5 m for wave heights mean spring tide (0.63 m above msl) 2135 (2060) 2009 (2009) 2009 (2009) mean high tide (0.46 m above msl) 2215 (2091) 2065 (2032) 2009 (2009) Mean sea level (msl) 2440 (2182) 2165 (2122) 2040 (2022) *Average sea level rise estimations from satellite measurements last 15 years in the worlds oceans (Poseidon/Topex). Due to isostatic uplift the relative sea level change in Bergen has been approximately approx. 0 over the last 1000 years ( Estimations on the expected sea level rise along the Norwegian coast vary from 0.15 m up to 1.0 m for the year 2100, dependant on different C0 2 scenario s. (IPCC (2007), Rhamsdorff (Science, 2007), Drange et al (Klima, 2007)). Edited photo: (Bergens Tidene), sea level at appr. 4.5 m above current msl. Table based on: Multiconsult AS

46 m above msl) 2215 (2091) 2065 (2032) 2009 (2009) Mean sea level (msl) 2440 (2182) 2165 (2122) 2040 (2022) *Average sea level rise estimations from satellite measurements last 15 years in the

13 Falling groundwater levels settling Bryggestredet Bredsgården Bugården Drawings and graphics based on: Multiconsult AS ( )

14 Falling groundwater levels settling Drawings based on : Multiconsult AS ( ) Graphics: Geological Survey of Norway (2008)

15 Waterlogged archaeological deposits preservation conditions water air O 2 diffusion in air O 2 diffusion in water anorganic material organic material organic material Immobile: Fe(III) oxides Fe(IV) oxides Fermentation Other oxides (NO 4, SO 4 ) conductive flow of O 2 in water Source: Henning Matthiesen, National Museum Denmark waterlogged deposit mechanical settling deterioration of organic material

Fe(IV) oxides Fermentation Other oxides (NO 4, SO 4 ) conductive flow of O 2 in water Source:

16 Varying preservation conditions Water is decisive for the preservation conditions on Bryggen. Drainage and settling ( no water ) Dynamic conditions (O 2 rich rainwater) Flooding (with seawater) Stagnant, waterlogged (anoxic water)

Drainage and settling ( no water ) Dynamic conditions (O

17 State of preservation (conditions) excellent 1979 condition lousy time past present future

18 Holistic approach Drawing: Marcin Gladki (2009)

19 Towards a sustainable solution Infiltration of seawater to restore the water balance is no option due to sulphate reduction processes that have a large destructive potential for the cultural deposits. Solution will focus on creating a physical and hydrological division between the drained hotel area and Bryggen. Use of SUDS to improve infiltration and reduce variable conditions may contribute to an integrated and sustainable solution in the long term.

Solution will focus on creating a physical and hydrological division between the drained hotel area and Bryggen.

20 Interdisciplinary collaboration The protection of archaeological heritage must be based on effective collaboration between professionals drawn from many disciplines. maintenance reconstruction legislation urban planning documentation research conservation water treatment monitoring survey

21 Why change what works? Keep the system in balance: the deposits are non renewable resources once destroyed, they can never be replaced. The buildings at Bryggen have survived for over 300 years, the underground remains for up to 1000 years, largely due to the long existance of favourable preservation conditions. Repair and renewal works have been based on traditional methods and know how. We need to understand the areas wider environment and try to establish a sustainable system in balance.

22 Bryggen is NOT a unique case! Urban hydrology has a major effect on archaeological preservation conditions. This is particularly the case in Medieval cities with large reservoirs of organic deposits (list is not exhaustive). Oslo York Stockholm Trondheim Gdansk Lübeck Stavanger Szczecin London Bergen Copenhagen... Tønsberg Amsterdam Kristiansand Ribe

Toll ring around Oslo: How car owners help paying for improved mobility, and better environment too

Toll ring around Oslo: How car owners help paying for improved mobility, and better environment too Kristian Wærsted City Hall Chief Engineer (NPRA) Road tolling in Norway Trondheim Bergen (1986) (1991)