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could be minimised by identifying such areas via a Flood Mapping Programme, learning the flood history of the area
from older residents and respecting the natural water courses (Anonymous, n.d., b).
Another major cause of flooding is blocked drainage. During periods of heavy rainfall the refuse that blocks the
drains has a damming effect and prevents the water from flowing freely, thus creating overflows and ultimately
giving rise to flooding. Deforestation can be another well-known reason for floods. Without the tree root system the
rainwater runs freely down the slopes carrying everything, inc luding soil and debris with it (Anonymous, n.d., b).
Flood mitigation measures in general deal with two main areas: control of the river and control over the land,
including land use policies. Control over the river includes measures like channel improvement and the construction
of reservoirs to store excess amounts of water. Control over land includes the construction of terraces and
reforestation. These are just a few of the p ossible measures (CDERA website). The only totally effective protection
against flooding caused by a river overflowing is to choose a site that is sufficiently high up to rule out this danger
(Duchein, 1988).
At a workshop of the UN Economic and Social Commission for Asia and the Pacific (UNESCAP) at Bangkok
in 1991 a delegate noted that 80% of all victims of water-related disasters live in Bangladesh, China or India. It
appears that the low-income countries are the worst effected by flood disasters. It also became clear that most flood
disasters victims live in rural areas and belong to the poorest section of the population (UNESCAP , 1990).
Preparing for a disaster is the best defence. Thus, when choosing a site for an archive, library or museum it is
important to investigate the risk of a flood. The building itself requires a structure that can withstand water pressure
or the velocity of flowing water. Proper anchorage of the building prevents floatation of the foundation. In several
countries traditional houses are built on poles to diminish the damage of flooding. For institutions of cultural heritage
the elevation of the basement may be a solution (CDERA website). Needless to say that the roof is important to
prevent invasion of water (see section on Damage – W ater). Roof coverings must be able to resist heavy rainfall and
the covering should be fixed tightly so that the wind is not able to tear it off. Flat roofs and skylights are a hazard,
as are walls made of non-waterproof materials e.g. porous stone. A double thick wall with a void between them is
advisable in flood-prone areas. All openings in the walls like doors, windows, vents, air holes, etc. are a risk. They
must be watertight and shutters are a good protection against heavy rain. All windows must be placed well above
the ground level (Duchein, 1993). Metal flood shields bo lted into place will reduce water penetration through doors
and windows, alternatively old sandbags or sheet metal coverings can be used (Fortson, 1992). T he sandbag has a
modern version: the water absorbent cushion. It absorbs the water and when swollen acts as a sandbag. After the
disaster checks must be made for water accumulation in hidden areas like attics, false ceilings and compact shelving.
Water can also damage the fire detection or fire suppressing systems (Fortson 1992).
Alarms can be installed to detect water in storage rooms water. They can be connected to a central response
facility but if that is not possible self-contained units last up to 72 hours. Archival boxes, again, are a good protection
for paper and books. Most boxes resist water and give som e protection even when the water is contaminated with
salt or other deposits of floodwater. As mentioned before (see section on Damage – Water) shelves must be at least
four inches off the floor. Collections stored temporarily must never be placed directly on the floor, but always on
a pallet. If there is not enough time to move a collection out of a vulnerable area, the shelving units should be
covered with plastic sheets. They must not be covered longer than 48 hours and they should be checked every 12
hours for mildew. Always keep a supply of plastic sheets, heavy-duty tape and scissors in the storage rooms ready
for use (Fortson, 1992).
The disastrous flood in Florence in 1966 severely damaged the holdings of the National Library. However, it
also brought the concept of the conservation of library materials to the attention of the library public (Lan, 1990).
The river water, channelled through narrow streets, travelled at up to 80 miles p er hour and poured into Italy’s
National Library, drenching thousands of manuscripts (Nelson 1991). The 1997 flood in Poland affected about 80
libraries and destroyed around 300,000 volumes, the value of which is estimated at US $700,000. On top of that,
the material losses in buildings and furnishings are estimated at US $1 million (Wolosz, 1999).
Water-related natural disasters bring confusion and destruction to a large segment of the community. This
complicates the recovery. Staff may have other problems at home, lack of assistance from local authorities or
shortage of supplies (Fortson, 1992).
Today the effects of water on documents are well known. Seawater is more dam aging than fresh water due to
the corrosive effects of sea salt. Flood water can be polluted and can cause particular damage to paper (see section
on Damage – Water). Paper and books may also be covered with mud and dirt (Duchein, 1993; Waters, 1993). For
the recovery of wet paper and books see section on Disaster Preparedness – Recovery. Audio-visual materials,
photographs, microforms, magnetic media and other discs, are also vulnerable to water, and the damage depends
on the type of the material, the length of exposure to water, its temperature, etc. (Brandt-Grau, 2000).
For websites on water-related disasters see Dartmouth Flo od Observatory, Flood Hazard Research Centre
(FHRC), International Tsunami Information Centre (ITIC).
An online bibliography on floods called El Niño and flooding, a global resource is published on the website of
the Center for Ocean and Atmospheric Prediction Studies.
For further reading see Anonymous, 1992; Corning Museum of Glass, 1977; Ezennia, 1995; Lucchitta et al.,
1999; McCann et al., 1995; Rees et al., 2000; UNESCAP, 1990; Wolosz, 1999.
6.3.6.1 Tsunami
Tsunami is Japanese for a tidal wave and is consid ered a special kind of flood often caused by an earthquake. T his
wave can move over the ocean at a speed of 800 km /h. Tsunamis remain an ever-present threat to lives and property
along the coasts of most oceans of the world.
Most of the websites o n natural disasters will also cover floods. For information exclusively on tsunamis see
the National T sunami Hazard M itigation Programme website hosted by the NOAA (National Oceanic and
Atmospheric Administration), and the websites of the National Tidal Fac ility, the International Tsunami Information
Center, Tsunami hosted by the Earth and Space Sciences at the University of Washington.