3 Flooding
Water, that essential elixir for life-on earth, can pose a serious threat to artworks and cultural artifacts in archives, libraries and museums. This may be as a result of technical malfunctions (discussed in a separate section) or of extreme weather events and the resulting flooding of flood plains. Cultural property is at risk from surface water, sewer backup or rising or discharging groundwater. The questionnaire facilitates the analysis of threats and provides initial pointers to the steps to be undertaken. The topic is discussed in greater detail in the introduction.
I. Introduction
Flooding caused by rising water poses a serious threat to cultural property. Not only artifacts stored in basements are at risk, flooded basements can damage technical building services such as electrical, heating and telecommunications equipment. As a result, cultural objects in areas of the building not directly affected by flood waters are also at risk. Flooding may even cause structural damage that, at worst, could endanger the stability of the building as a whole.
Recent years have seen a rise in the occurrence of flooding events in Europe, often triggered by unusual weather patterns with heavy rainfall (Vb-track cyclones, low-pressure systems coming from the Mediterranean). Examples include the Oder floods of 1997, the flooding of the Elbe and its tributaries in 2002, and floods in Rhône/Provence in France in 2003. The devastating impact of the 1966 flood of the Arno in Florence should also not be forgotten. Globally speaking, flooding is prevalent above all in Asian countries (Bangladesh, India, China).
The most frequent scenario encountered is the flooding of buildings as a result of major rivers breaking their banks (Oder, Elbe, Rhine, Arno, Rhône), mainly following heavy rainfall or as a result of melting snow. Spring floods are a regular occurrence when temperatures rise rapidly and snow melts. When water levels in major rivers start to rise, this often gives considerable advance warning and it is possible to estimate the water levels to be expected. This advance warning period can then be exploited to take protective action (dams, barriers, evacuation). Objects can be damaged by surface water (water that does not drain away into the ground), backed up wastewater from the sewer network and rising groundwater.
Even relatively small watercourses can be a threat if they are unable to cope with a large volume of water and consequently break their banks. In particular, smaller rivers close to mountain regions can rapidly become a threat as rainwater flows down from the mountains towards larger rivers or lakes. Such a situation in Saxony in 2002 resulted in serious flooding within a very short space of time. When the volume of water increases rapidly, the lack of advance warning is a problem, especially when at the same time a natural gradient results in a high flow rate. There is then almost no time at all to warn people (with sirens for example) or take protective measures for the buildings or assets. This type of threat is not so frequent, and consequently not so established in the public’s awareness. Thus institutions often have a plan in place to deal with a once-in-a-century flood of a major river, but not to deal with “water coming through the back door” (cf. the damage suffered in Dresden on August 12, 2002). Threats are posed by surface water, backed up sewers and rising groundwater.
Buildings located in low-lying areas can also be flooded in the event of heavy rain. However, this is often taken into account when the building is erected and during its subsequent use.
Museums, archives and libraries around the world are taking the threat of flooding increasingly seriously. For instance, the Standard Facilities Reports used in the USA and Europe to determine the security of loaned items or touring exhibitions include questions on flooding. Before offering a policy, art insurance companies will also ascertain any risk from flooding events.
Given some advance warning, it is possible to take certain steps to protect property from the risks of flooding. This applies not only to the cultural assets themselves (if they are kept in areas directly at risk from flooding), but also to ensuring the continued operation of building services and reducing damage to the building itself.
These measures should be outlined in a flood response plan and should be set out in clear procedures. Two questions need to be answered: Where can I obtain information about the water levels expected? And: What specific threats to the building do these levels then pose and what actions follow as a consequence? Thinking through such hazard scenarios in advance makes it easier to take the necessary action in the event of an actual incident, as following a set of established guidelines in a crisis situation, when hectic activity, stress and adrenalin are the order of the day, requires fewer decision and coordination processes. It is also expedient if the flood response plan includes a list of contacts for assisting organizations (fire service, Federal Agency for Technical Relief (Technisches Hilfswerk THW), removal firms, storage facilities, partner institutions).
Key partners for answering questions relating to potential treats to cultural property are the local fire service, water utility companies, environmental agencies, building inspectorates and, if applicable, any central flood alert services.
Institutions faced with similar threat profiles, such as museums, archives and libraries, should form a preparedness network. Members of these networks can then cooperate in the event of an emergency and pool their resources and expertise. The ability to exchange know-how is also an important benefit of these networks (no “reinventing the wheel”).
II. Protective measures
General
As part of a risk assessment, it should be determined whether there is a flood risk for the building in question. If so, no cultural artifacts should be stored in any areas that might be affected (exhibition galleries, storage areas, packing rooms, workshops). A specific policy setting out the technical/structural and organizational measures to be taken to avoid or mitigate risks should be drawn up. The steps necessary to implement these technical/structural and organizational measures should be summarized in a flood response plan.
Precautions against surface water
If rivers break their banks, surface water is the most common threat to buildings and assets. Depending on the advance warning time, it may be possible to protect premises with sandbag dams or mobile flood barriers that can be quickly erected. The costs of mobile barrier systems (often made of aluminum) are reasonable. Regular training in assembling the barriers and maintaining the seals is also essential. In advance of flooding events, building apertures such as ducts for energy utilities and telecommunications systems should be inspected to ensure they are watertight. Doors and windows with a high resistance to external water penetration can also be fitted.
Many municipalities and cities in areas at risk hold barrier systems that can be installed quickly when needed (e.g. Cologne, Dresden, Prague). It is advisable to consult the relevant municipal authorities on the nature and timing of the deployment of such protective measures.
The states are responsible for reservoirs and flood retarding basins. These are vital defenses for smaller rivers in particular. However, a conflict of interest is increasingly emerging between their protective function of lowering the water table and their use for tourism activities. It is therefore advisable to consult the respective reservoir administration and water authorities on the operation and levels of such reservoir facilities.
Protection against sewage backup
Depending on the location of the building, if there is a large volume of surface water there may be a risk of wastewater from the sewer network backing up. During the 2002 flood, this led to the initial water ingress into the storage rooms of the Dresden State Art Collections. The only feasible course of action is to shut off the drain system, with all the resulting consequences. To do this, non-return or shut-off valves must be installed at the point where the building’s wastewater drainage system enters the sewage mains. When necessary these can then be closed to prevent sewage backing up. It is advisable to provide two such shut-off systems since they may malfunction if they are dirty or if there is a mechanical blockage (e.g. by stones). Be aware that shutting off the wastewater drainage system will immediately result in serious technical problems in the building. The toilets will no longer work for instance. They must therefore be closed immediately and replaced by mobile WC systems. Air-conditioning units with humidification elements (spray chamber, steam humidifier) must be switched off immediately as these system discharge into the drains.
In the case of rain, note that gutters may overflow. This will lead to water running down the sides of the building, and rainwater may flow from the downpipes. If they are within the building, any leaks in downpipes can result in damage to the building. In view of the water column that can be expected, these rainwater pipes should therefore not simply be slotted together, but should be pressure-sealed.
Protection against rising groundwater
In connection with heavy rain and surface water, but also when the level of major rivers is high, a rise in the groundwater table can be expected. This can give rise to a range of threats. Some buildings are “tanked”, i.e. a watertight foundation slab is used to prevent the ingress of rising groundwater. However, the groundwater exerts strong pressure against this impermeable slab and this can pose a structural risk (if the slab splits or rises). In the case of such tanked buildings, therefore, it is necessary to know what the critical groundwater levels are. These values can be obtained from architects or structural engineers. If necessary, the local building inspectorate will be able to provide the information. In the event of a threat to buildings, the groundwater table can be lowered by means of flood relief wells. For instance, 15 relief wells are installed around the city center of Dresden which provide a local “funnel” for the groundwater and reduce the threat to some of the city’s significant historic buildings. The operation of the wells requires the consent of the water authority and a secure electricity supply.
The extra load on the foundation slab as a result of sandbags, other heavy materials, or even clean water, can however also cause damage to a building.
In the case of buildings without tanking, the groundwater may infiltrate the foundation slab or the bottom of the walls. However, owing to the high resistance of the building envelope, the volume of water is usually limited and can be drained off locally. In this case it is expedient to plan for sumps (see below) or a drainage system to deal with the seepage and facilitate the removal of the water from the building.
Standby power systems and systems for removing water from buildings
As water can find its way into buildings, especially basements, not only as a result of seepage through flood defenses, but also because of technical systems malfunctioning, it is always worthwhile having a concept for removing water from the building. Installing sumps or a drainage system facilitates the removal of any water that has penetrated, as pumping systems often require an effective water height of 2 cm. A sump is a depression, small ditch or hole, usually in a corner of the basement, from which the pump can then extract the water. It is expedient to have a prior plan for laying the hoses and electrical connections for the pump locations. It is also advisable to include a defined building aperture (such as a basement window or door) through which hoses for siphoning off the water are to be passed. In this case it is of course also necessary to consider protection from any surface water. The pumps, hoses and electrical cables should be planned and procured in advance. They should also be numbered in order to simplify response in an emergency. Note that a secure electricity supply must be available, since in a crisis situation both the institution’s own electrical systems and the supply from the energy provider may be out of action. It is therefore advisable to have an independent standby power system (emergency power supply) that can supply power to the pumps if necessary.