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The water that buoys up Bryggen in Bergen, Norway
Beneath the suite of picturesque historic buildings of the Bryggen World Heritage Site in Bergen lies a unique archaeological environment. When excavations started after the fire in 1955, which consumed the northern half of the remaining settlement built after the fire in 1702, the archaeologists were unprepared for the enormity of the task awaiting them. The excavations brought to light a formidable array of mainly wooden constructions, including houses, thoroughfares, wells and quays, along with myriad artefacts of both perishable and inorganic material. The archaeological remains were among the best preserved in Europe. So why is that preservation conditions at Bryggen are so good? The answer is water!
The extensive archaeological remains on which the heritage buildings rest are known as cultural deposits and reach thicknesses in excess of 10 meters. The deposits consist of varying mixtures of refuse such as woodchips, twigs, moss, leather off-cuts and textile strips, along with the remains of buildings, quays, passages, latrines and wells – and all manner of artefacts. As long as these organic materials remain permanently inundated in water, preferably fresh and with as little flow as possible, the outlook for their preservation is good. But if the water is removed, oxygen concentrations skyrocket and the microorganisms that break down organic matter can go into a feeding frenzy, accelerating the process of decomposition to an alarming degree. As a result, the cultural deposits are literally eaten away.
Intensive monitoring has shown damaging settling rates. Low groundwater levels caused by redevelopment of the area next to the heritage site in the late '70s has led to an increased flux of oxygen in the subsurface. This currently threatens the heritage site due to decomposition of organic material. Both mechanical settling of the terrain and oxidation of organic material occur, thereby not only removing irreplaceable archaeological values, but also taking away the bearing structure of the buildings above. One of the main goals at Bryggen is therefore to establish a stable hydrological environment, so that the heritage site will be safeguarded for future generations.
Since the start of the monitoring in 2001, numerous investigations have been undertaken to map the problems and identify causal relationships. When the pattern from the settling data was compared with the map of groundwater levels, the conclusion was very clear - the worst settling resulted from a substantial lowering of the groundwater table. Based on earlier records, it was possible to ascertain that the groundwater level in the affected area had been stable up until 1980, but the construction of a building with an underground basement and associated drainage system subsequently caused the level to drop by almost three metres. Once this had been determined, it was vital to initiate a monitoring project capable of making sense of the complex interplay of the factors and mechanisms that govern preservation conditions underground.
A long-term strategic restoration project (2001-2031) aims to bring Bryggen to a state of repair that is in accordance with the status as a World Heritage Site, and where only regular maintenance is necessary. Bryggen has since 2001 received considerable funding from the government for restoration of buildings and monitoring of the cultural deposits. In 2011, the government granted an extraordinary endowment of 45 million NOK for re-establishing the groundwater balance.
The protection of the archaeological heritage is based upon effective collaboration between professionals drawn from many disciplines. It also requires the cooperation of government authorities, academics, private - and public sector enterprises and, not least, the general public. The Directorate for Cultural Heritage in Norway (Riksantikvaren), leads the project in cooperation with regional and local heritage authorities of Hordaland County Council and the City of Bergen in line with the UNESCO requirements.
A range of research disciplines is involved in the project in order to find optimal solutions for preserving both buildings and the archaeological remains. At Bryggen, it involved the participation of, at one time or another, of archaeologists, architects, carpenters, chemists, conservators, engineering and geotechnical consultants, microbiologists, mycologists, tree scientists, wood anatomists and hydrogeologists. A variety of methods for monitoring the cultural deposits have been developed, and at the same time the authorities have invested heavily in the formulation of proposals for mitigation strategies aimed at reducing the dewatering of the Bryggen area.
Currently, the biggest problem is to stop the loss of groundwater towards the redeveloped hotel area next to Bryggen. Experts have developed different innovative solutions to cope with the problems. This process has been facilitated through transnational cooperation and workshops organised in the SKINT project. The mitigation solutions are based on creating a hydrological division between the hotel area and the heritage site and involve improvement and extension of the existing sheet piling as well as hydrological measures to actively control ground- and surface water flow. Today, the solutions are being implemented through a stepwise-approach, where the effects of each step are monitored before implementing the next measure. It is expected that this approach will lead to the most sustainable and long-lasting package of solutions that will reduce the loss of cultural deposits to a minimum and reduce the settling to a natural rate.
An important change will be the transformation of large parts of the surface water drainage system at Bryggen and surroundings from a piped system towards a sustainable urban drainage system (SUDS) with different infiltration facilities. Solutions that currently are being implemented are swales, infiltration-transport pipes, storage crates and a stepwise subsurface infiltration system (photo).
A transnational knowledge exchange program has been set up with other SKINT partners in order to ensure that the design of SUDS is being done according to best international practices. The implementation of SUDS is expected to increase and stabilize the recharge of groundwater towards the cultural deposits and recreate the "natural" hydrological balance before construction of the underground parking. All measures will be monitored and evaluated. If continued monitoring shows that the hydrological situation is not effectively restored, further geotechnical measures will be necessary to physically divide the historic site of Bryggen from the neighbouring modern underground constructions, such as repair or renewal of the existing sheet piling.
Directorate for Cultural Heritage in Norway