4.1 THE RATIONALE OF RANKING
An Oil spill sensitivity ranking of potentially threaten resources is usually an
integrated part of a national oil spill contingency planning. It helps deci-
sionmakers to prioritize the available resources and tOFocus the emergency
response on the most valuable areas.
The sensitivity ranking system provides oil spill responders with a useful
tool during several steps in the contingency process:
· during the prespill planning, in order to prepare appropriate response
strategies for e.g. particularly threatened or vulnerable areas or other
areas that deserve special attention.
· during an oil spill combat in order to plan and continuously optimize
the response strategy under the given conditions and limitations (oil
type, weather, equipment, crew).
· during the cleanup operation to avoid postspill damages, minimize cost
Sensitivity ranking is one of several considerations during oil spill contin-
gency. Oil type and behaviour, weathering of the oil, meteorology, hydro-
graphy, safety of crew and equipment are other topics to consider.
The goal of oil spill response is to minimize the overall impacts on natural
and economic resources as well as cultural assets, but some features will be
of greater concern than others. The sensitivity ranking includes therefore
the actual sensitivity of the features and a more subtle valuation of impor-
tance or value.
4.2 THE CONCEPT OF RANKING SENSITIVITY
The concept of mapping coastal environments and ranking them on a scale
of relative sensitivity is more than thirty years old. Since then, different ran-
king system have been developed, refined and expanded to cover all types of
The ranking should integrate a multitude of information on geological pro-
perties, wave exposure, biological diversity and productivity, oil behaviour,
ease of cleanup, human use and cultural assets - properties that are not
directly comparable or quantifiable within the same scale of values. The
outcome should ideally be a simple statement, a numerical index value, or a
Comparing and valuation of incomparable features is a matter of interest
and negotiation, and no true or perfect system can be established. A com-
The Oil-spill Sensitivity Ranking System
plicated systems is not necessarily better and more accurate than a simple
system or qualified judgements. But it is a requirement that the level of
details matches the purpose and leaves the decisionmakers with some alter-
natives. e.g. 20 km coastline with exactly the same sensitivity index value is
not of much help. Another requirement is that the system is transparent
and generally accepted by the stakeholders.
We have applied a relatively simple system including three types of features:
Coastal type, Biological resource, and Human use. The coastal type feature
is derived from the well known ESI-index. The sensitivity index is calcula-
ted from the indices for each of the features.
4.3 SENSITIVITY RANKING USED IN THE
ATLAS - RANKING OF COASTAL FEATURES
The sensitivity index is assigned to an index line running parallel to the
shoreline at a distance of 500 m offshore.
The three different groups of coastal features are projected onto the index
A - Coastal type
B - Biological resource
C - Human use
The Oil Sensitivity Index (SI) for each point or segment of the coast is cal-
culated simply as the sum of index values from the three groups:
SI = A + B + C
The coast type index value forms the basics of the index line; there is always
a coast type assigned to the coastline. If there is more than one coastal type
present, only the type with the highest index value is considered.
The index value assigned to each type of feature is based on the description
in Chpt. 2 and 3, but finally calibrated and balanced during a stakeholder
seminar where al major stakeholders were invited
The final Oil Sensitivity Index shows values from 2 to more than 20. These
values are then represented along the index line by a colour code of 5
It is important to note that the index value does not represent a sort of
absolute value at any scale. It is mostly a matter of making changes of sensi-
tivity visible along the index line. An important use of the index will be to
select which areas to protect and where to let the oil strand within a coastal
strip of few kilometres, and not to compare the sensitivity of e.g. northern
and southern Kenya.
Environmental Sensitivity Atlas for Coastal Area of Kenya
Three types of features
Sheltered sand beach
Exposed sand beach
Tidal mud flat
Coral reef and reef flats
3 - 5
River mouth or creek
Important bird area, IBA
Turtle breeding site
Low/high density of nests
Coral reef, priority
Small scale fishery
Fish landing site
Cooling water intake
Proposed natural reserve
Table 4-1 Sensitivity Index Values of features
considered in the Coastal Resource Maps.
The index values were fixed and agreed
among all major stakeholders during a sta-