155
Identifying Sites for Flood Protection
the land and the depth to which flooding occurred. It was intended that the index
values could be used to identify the critical areas where flood management schemes
would be of greatest benefit. The matrix for calculating the index values was created
using an EXCEL spreadsheet. The use of a spreadsheet allows for rapid and easy
changes to be made in any of the parameters used to calculate the flood index values.
This method avoids the problem which has plagued some earlier work in which the
values used for calculating flood scenarios have been overtaken by new global warming
projections.
Calculation of the flood index values required the allocation of weightings
that were based on the temporary ‘loss’ of specific land use during periods of flooding.
Five weighting were used. In each grid square the land use with the highest value was
applied to the entire cell. The five categories are listed below:
land providing services such as main transport links, pipelines and utilities
were considered of regional importance and were weighted with a maximum
value of 3.0. Severance of any of these services would result in maximum
disruption to a population throughout the region. The disbenefit due to
flooding would be major and the consequential losses to society great
residential property, local transport links and agricultural land of grade 3.i
and better were grouped together and weighted with a value of 2.0. This
group contained land use types of considerable difference. Although flooding
of residential property would bring maximum personal disruption and
economic loss to the general public it has not been given the highest weighting
because losses can be compensated by insurance cover. Even though personal
tragedy levels can be high the loss to society has been judged to be less than
that experienced by landuses contained in Category 1. Similarly, local
transport was judged to cause minor inconvenience while flooding of the
better quality agricultural land was given a weighting of 2
land used for industry and designated conservation zones received a weighting
of 1.5. The industrial land category may justify further analysis. Industrial
types along that part of the Clyde Estuary included in this study were of
relatively low value, such as scrap metal yards, boat yards, storage areas,
unloading wharves. Installations such as oil and chemical works or electrical,
telecommunications or computer plants would justify a higher classification.
Designated conservation zones include S.S.S.Is, National Trust property etc.
and were included in this category because of their statutory definition
areas with no human habitation, no industry, non designated conservation
areas, agricultural land lower than class 3.i and communication confined to
tracks and paths received a weighting of 1.0 and their inundation was thus
considered to have no lasting significance. This category would not normally
receive priority in terms of flood protection
the final category differed from all the previous categories in that it
represented land which could be used as a ‘buffer area’ and be deliberately
allowed to flood. These areas would be sacrificed on either a temporary or
1)
2)
3)
4)
5)
Identifying Sites for Flood Protection
the land and the depth to which flooding occurred. It was intended that the index
values could be used to identify the critical areas where flood management schemes
would be of greatest benefit. The matrix for calculating the index values was created
using an EXCEL spreadsheet. The use of a spreadsheet allows for rapid and easy
changes to be made in any of the parameters used to calculate the flood index values.
This method avoids the problem which has plagued some earlier work in which the
values used for calculating flood scenarios have been overtaken by new global warming
projections.
Calculation of the flood index values required the allocation of weightings
that were based on the temporary ‘loss’ of specific land use during periods of flooding.
Five weighting were used. In each grid square the land use with the highest value was
applied to the entire cell. The five categories are listed below:
land providing services such as main transport links, pipelines and utilities
were considered of regional importance and were weighted with a maximum
value of 3.0. Severance of any of these services would result in maximum
disruption to a population throughout the region. The disbenefit due to
flooding would be major and the consequential losses to society great
residential property, local transport links and agricultural land of grade 3.i
and better were grouped together and weighted with a value of 2.0. This
group contained land use types of considerable difference. Although flooding
of residential property would bring maximum personal disruption and
economic loss to the general public it has not been given the highest weighting
because losses can be compensated by insurance cover. Even though personal
tragedy levels can be high the loss to society has been judged to be less than
that experienced by landuses contained in Category 1. Similarly, local
transport was judged to cause minor inconvenience while flooding of the
better quality agricultural land was given a weighting of 2
land used for industry and designated conservation zones received a weighting
of 1.5. The industrial land category may justify further analysis. Industrial
types along that part of the Clyde Estuary included in this study were of
relatively low value, such as scrap metal yards, boat yards, storage areas,
unloading wharves. Installations such as oil and chemical works or electrical,
telecommunications or computer plants would justify a higher classification.
Designated conservation zones include S.S.S.Is, National Trust property etc.
and were included in this category because of their statutory definition
areas with no human habitation, no industry, non designated conservation
areas, agricultural land lower than class 3.i and communication confined to
tracks and paths received a weighting of 1.0 and their inundation was thus
considered to have no lasting significance. This category would not normally
receive priority in terms of flood protection
the final category differed from all the previous categories in that it
represented land which could be used as a ‘buffer area’ and be deliberately
allowed to flood. These areas would be sacrificed on either a temporary or
1)
2)
3)
4)
5)