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Environmental Sensitivity Atlas for Coastal Area of Kenya, March 2006

 
Contents and overview, Environmental Sensitivity Atlas for Coastal Area of Kenya, March 2006
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45
Environmental Sensitivity Atlas for Coastal Area of Kenya
The Environmental Sensitivity Atlas for the Coastal Area of Kenya devel-
oped through the KenSea project contains three types of maps:
·
Logistic and Topographic Maps
·
Coastal Resource Maps
·
Environmental Sensitivity Atlas
which has been reproduced in 16 map sheets in scale 1: 50,000 to cover the
whole coastline. In addition, 4 map sheets in 1: 25,000 have been produced
for the Mombasa Creek Area.
5.1 LOGISTIC AND TOPOGRAPHIC MAPS
5.1.1 Description of the production of the maps
These raster maps are based on the scanning, cropping (cutting off everyt-
hing but the actual map) and georeferencing of a total of 34 topographical
paper maps from the Survey of Kenya at a scale of 1:50,000 and three maps
in scale 1:100,000. The latter covering the very north of the country where
no 1:50,000 maps could be obtained from the Survey of Kenya. Due to
this, areas between Kiunga and the Somali border contains a slightly lower
degree of detail on the logistical maps.
Upon being scanned and georeferenced, all of these 37 maps where then
put together as a single seamless raster layer in the GIS. Consequently a
system of 16 map frames was constructed with the objective to render the
entire coastline in scale 1:50,000 on a minimum of map sheets in size A1
including sufficient parts of the inland areas.
5.1.2 Description of features on the maps
The natural resources and coastline features on the topographical maps have
formed the basis for the Coastal Resource Maps. These features should now
be read from these maps, as they represent the most upto-date dataset. The
topographic maps are used for terrestrial features which are not all transfer-
red to the resource maps, as contour lines, tracks and buildings. The topo-
graphic maps are the maps to use for planning oil combat and cleanup
actions from land
5.2 Coastal Resource Maps
5.2.1 Description of the production of the maps
Following the production of the Topographical and logistical maps, all the
analoug topographical maps were put into digital format and the raster layer
containing all the topographical information was used as the very founda-
tion for the process of creating Coastal Resource Maps. Through the digiti-
Map frame construction
5
Description of Maps Produced
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zation of a number of features from the topographical maps, as series of
new vector layers were created. These include:
·
Administrative Boundaries (District Admin Level 3 and coast line)
·
Contour lines
·
Hydrology (rivers and inland water bodies)
·
Utilities (health clinics, schools, hotels and ports)
·
Railways (lines and stations)
·
Airfields (airports and landing strips)
·
Towns (major, minor and settlements)
·
Pipelines
·
Roads (3 classes)
·
Mangroves
·
Mudflats
·
Plantations
·
Forests
·
Corals
The 1:50,000 topographical maps from Survey of Kenya were lacking for
the area north of Pate Island. Therefore, features were digitized from the
1:100,000 maps covering the same area. The digitized features now occur-
ring as point, line, and polygon layers have undergone an intensive quality
assurance (QA) with respect to their topology and attributes. Further, each
vector file is associated with a metadata file created in ArcCatalog to ensure
that it is compatible with the Contents standards of the Federal Geographic
Data Committee (FGDC) allowing the data to be located via the National
Geospatial Data Clearinghouse (NGDC) mechanism. All of this work were
accomplished at DEPHA in Nairobi supervised by the KenSea Team and in
a dialogue with staff of the UNEP GRID-Nairobi facility.
Another substantial source of data for the Coastal Resource Maps was the
project database containing the data behind the Eastern Africa Atlas of
Coastal Resources (EAF-14).
The EAF-14 datasets includes a variety of information with high relevance
to the KenSea context, wherefore some of the datasets from the EAF-14
have been incorporated in the KenSea either directly or as guideline for
further investigations. The main challenge of the EAF-14 in this context is
the fact that it has been produced in scale 1:250,000 implying that it has a
lower degree of spatial precision than data created in 1:50,000. Especially
features digitized from the 1:250,000 topographical maps under EAF-14 do
not show compliance with the level of detail necessary for reproduction in
scale 1:50,000. This inherited lack of precision is particularly pronounced
for polygon and line features. Point features that indicate a certain feature
or activity with finite spatial extent such as for instance hotels have been
included without any manipulation because of their indicative nature. All
features occurring in the EAF-14 that have not been supported by our own
information sources have been completely omitted from the KenSea databa-
se like for instance the occurrence of Dugongs.
46
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Quality Assurance
EAF-14
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Environmental Sensitivity Atlas for Coastal Area of Kenya
Aerial photo missions
Other data holders
A significant amount of new data was also created during the three aerial
photo missions. This dataset provided the KENSEA project with an excel-
lent tool for documenting near coast features such as coastal morphologies,
extent of corals, mangroves and fishing sites. A point layer containing an
exact GPS position of each photo acquisition locality was also created enab-
ling the use of a hyperlink function embedded within the ArcGIS software
allowing an effortless look up of pictures from a certain area of interest. In
addition to this all pictures were tagged with coordinates of were they were
taken and the KenSea name.
Apart from creating the above mentioned new layers and reusing modified
versions of data from the EAF-14 database a very large effort was put into
harvesting all existing GIS layers with relevance to the project from other
data holding institutions or organizations.
Much information was acquired through consultations with the NMOSCP
partners and other stakeholders during the Inception Phase. This was an
ongoing process that continued to add information to the KenSea database
throughout the entire project. Much information was acquired through the
consultative dialogue between the KenSea team and the various partners,
since much of which can be considered to be geographic information in
that it has a spatial character, wherefore it was distilled into new spatial
datasets and included in the database. Good examples of this is information
on the importance of the coastal shallows for small scale fishing, areas with
high priority corals, turtle breeding sites and fish landing sites.
The following layers were included in the Coastal Resource Maps
Feature Name
Type
Source
Waders
point
KenSea
Turtle breeding area
point
KenSea
Fish landing site
point
KENSEA
Historical site
point
EAF-14 (modified)
Hotels
point
EAF-14
Air strip
point
KENSEA/SoK
Water intake
point
KENSEA
Towns
point
KENSEA
Coastal Morphology
line
KENSEA/SoK
Coral reefs
line
KENSEA
Rivers
line
KENSEA
Roads
line
KENSEA
Importance of small scale fishing
line
KENSEA
Protected areas (parks and reserves)
Polygon
EAF-14 (modified)
Priority corals
Polygon
KENSEA
Mangroves
point
Polygon
KENSEA/SoK
5.2.2 Description of features on the maps
The Resource Maps represent all available data and are the basis for the cal-
culation of the environmental sensitivity index. The features are grouped
according to Human Use, Coastal Types and Biological resources.
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Feature
comment Oil
sensitivity
Town and settlements
From topographic maps
Not considered
Roads, tracks,
air-strips and ferries
From topographic maps
Not considered
Historical sites
Virtually none of the
None are
sites are in contact with
found to be
the inte rtidal zone.
sensitive to oil,
Data from EAF-14
but deserve
attention
during a clean-
up operation
Hotels
Data fro EAF-14,
Very sensitive.
Most hotels in
the coastal zone
are tourist hotels
with clean beaches
and marine activi-
ties as major assets
Fish landing sites
Usually small landing
Sensitive, mostly
sites, without a pier or
due to lost fishing
other facilities in the water
opportunities
dept of fishery.
during the spill,
Data from Dept. of Fishery
and reduced
catch during
recovery of the
fishing grounds
Fish traps
Constructed by mangrove
Sensitive to
poles and nets.
smothering by
Data from air photos,
oil and to redu-
May 2005.
ced catch if the
mangrove is
destroyed.
Tainting of fish
Small scale fishing
Local fishermen depend
Moderate sensitive
on subsistence fishery
due to possible
all along the cost.
destruction of local
The three levels of impor-
fishing grounds and
tance reflects the density
of breeding and
of fishermen, but also
nursery areas.
some seasonal fishing
grounds in Lamu District.
Data from Dept. of
Fishery and Sam Weru,
WWF
Salt works
Only the evaporation
The evaporation
ponds are marked on
ponds are not sen
the maps.There are no
sitive, but the
indications of the water
industry depends
intakes. Data from satellite
heavily on clean and
and aerial photos
untainted water as
the sole resource.
Water intake may
be via the mangro-
ve, and not from
open water - which
enhance the sensiti-
vity
Water intake
Industrial use of seawater
Highly sensitive,
for cooling purposes
is but small in time
only known from Mombasa.
and space
Data from the port authorities
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Table 5-1 Human use features on the
Coastal Resource Map.
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Feature
comment Oil
sensitivity
Mangrove
Data from topographic maps
Very sensitive due to
and field observations
the sensitivity of
the trees, the difficult
clean-up, and the
slow recovery
Sheltered rias
Data from topographic maps
Medium sensitive
and field observations
Tidal mud flats
Data from topographic maps
Very sensitive and
and field observations
difficult to clean-up.
Good capacity for
recovery
Sheltered sand
Data from topographic maps
Sensitive if untreated,
and field observations
but fairly easy to clean
Exposed sand
Data from topographic maps
Sensitive if untreated,
and field observations
but fairly easy to clean
Rock
Data from topographic maps
Less sensitive,
and field observations
and good self-cleaning
ability of exposed cliffs
Coral
Data from topographic maps
Highly sensitive and
and satellite photos
slow recovery.
Only intertidal part
directly exposed
Feature
comment Oil
sensitivity
Turtle
Data from KESCOM.
Very sensitive, but the
Positions are not very precise.
turtles only stay
Each point represent 1000 m coastline.
in the risk zone
Importance/relative density of
in a very short period.
nests by expert assessment by KESCOM
The nests may be at risk
during clean-up,
and should be moved
Waders
Data from EAF-14 and
Sensitive but ephemeral.
the National Museum of Kenya.
Can avoid the oil
Importance/relative density
to a certain degree
of nests by expert assessment
Mangrove
Data from topographic maps
Very sensitive
and field observations
due to the sensitiv-ity
of the trees, the difficult
clean-up, and the
slow recovery
Priority coral
Coral reefs of particular importance.
Highly sensitive and
Expert assessments by David Obura
slow recov-ery,
and Tim McClanahan
but the most important
reefs are sub tidal
end therefore less
exposed
Forest or thicket
From topographic maps.
Not considered
Not in contact with the coastline
Plantation
From topographic maps.
Not considered
Not in contact with the coastline
Papyrus swamp
From topographic maps.
Not considered
Freshwater swamps,
Not in contact with the coastline
Sand or mud
Data from topographic maps
Mudflats are
and field observations
sensitive and
difficult to clean-up.
Good capacity for
recovery
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Environmental Sensitivity Atlas for Coastal Area of Kenya
Table 5-2 Biological resources on the
Coastal Resource Map.
Table 5-3 Coastal types on the Coastal
Resource Map.
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Feature
comment Oil
sensitivity
Seasonal swamp
Data from topographic maps
Not considered
Marine national
Data from KWS
Fishery and
park
other resource
extraction are prohibited
and therefore in a
better state and more
valuable than the reserves.
Marine national
Data from KWS
Only traditional
reserve
fishery allowed
therefore regarded
as more valuable
than surrounding areas
Proposed marine
Data from KWS
Regarded as more
national reserve
valuable than
surrounding areas
5.3 Environmental Sensitivity Maps
5.3.1 Description of the production of the maps
After the development of the Coastal Resource Maps the data layers contai-
ning geographic information about these resources were used as the founda-
tion for the calculation of the environmental sensitivity index and the ren-
dering of the index values in a separate set of maps: The Environmental
Sensitivity Maps, with the sum of all index values illustrated by a colour
coded line along the coast containing five classes or index levels ranking the
coastal sensitivity to oil spills from a low sensitivity to a high sensitivity.
The notion of having three different groups of features A- Coastal type; B-
Biological resource; C- human use was all carried on from the Coastal
resource maps. The individual index values for each feature are illustrated in
table 5-4.
Feature
Index
Length/width
Shape
A
Rocky Coast
1
Line
A
Sheltered sand beach
2
Line
A
Exposed sand beach
2
Line
A
Tidal mud flat
3
Line
A
Sheltered rias
2
Line
A
Coral reef and reef flat
3/4/5
Width:
200-1000 m/> 1000 m
Line
A
Mangrove
3/5/7/10
Width:
> 200 m, inlet
Line
A
River mouth or Creek
8/10/12
Small-large-creek
Line
B
Important BIRD Area
1
Polygon
B
Waders
0.2/0.6/1
2000 m
Point
B
Turtle breeding site
0.5/1
1000 m
Point
B
Coral reef
1
Line
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Table 5-3 (Cont.)
Table 5-4 Agreed Index values and
properties for coast types and other
features.
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C
Hotel
1
500 m
Point
C
Small scale fishery
0.2/0.6/1
Low-medium-high
importance
Line
C
Fish trap
0.5
500 m
Point
C
Fish landing site
1
500 m
Point
C
Harbour
1
500 m
Point
C
Cooling water intake
2
200 m
Point
C
National park
1
Polygon
C
Natural reserve
0.5
Polygon
C
Proposed natural reserve
0.5
Polygon
Values for each feature representing the same geographic locality were added
up into the final index value for that locality. Since the features are all either
point, line or polygon features a method for bringing all these features onto
the line had to be developed. Therefore all points were buffered to a certain
distance, so that they no longer only represented a point in space but an
interval along the coast. Then all line intervals, lines and polygons were pro-
jected onto an individual index sub-line for each feature containing index
values for that feature. Finally, all of the individual index values along these
identical sublines were added into a single line running 500 m off-shore
representing the sum of all index values.
Since the outline of certain areas of the coast is very complex in having
numerous estuaries, inlets, archipelagos and individual islands, the projec-
tion of features onto a separate index sub-line was done partially manually
and partially in an automated manner. It was often necessary to manually
project features from its actual location onto the index sub-line. In areas
where the coast line had a more unanimous pattern the projection of featu-
res onto the sub-lines was done using a search based on the proximity of the
features to the line.
Figure 5-1 Figure Illustrating how segments from the index sub-lines are added up on the final Index Line.
The process of adding up segmented values along identical lines largely
depends on the capacity of ArcGIS to work with so called linear referencing
where lines have a measure attribute or address that describe locations along
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Environmental Sensitivity Atlas for Coastal Area of Kenya
Table 5-4 cont.
Semi automatic
Linear referencing
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the line. This feature of ArcGIS was used to appoint a system of compatible
line addresses to each index segment of each of the identical index sub-lines
and then add up all these segments into resulting segments on the final
index line Each segment then have an index attribute attached to it contai-
ning the sum of indexes from the index attribute of each sub-line.
In order not to distort the comprehensiveness of the Index Line, the linear
features illustrating the coast types were omitted from the Environmental
Sensitivity Maps. Also the line representing the importance of small scale
fishing was left out. Other than that, environmental sensitivity maps con-
tain the same layers and symbols as the Coastal Resource Maps.
5.3.2 Description of the representation of the sensitivity
The Sensitivity Index is calculated as described in chapter 5.3, by use of the
agreed index values listed in Table 5-4 . The Sensitivity Index values range
from 1 to 20.6 and the colour code cut-off values are chosen to give as
many details along the index as possible. The values do not represent any
absolute value, and is best used when comparing parts of the coastline close
to each other e.g. while selecting which areas to protect by booms and
where to let the oil strand, when a large spill is approaching.
The final products of the project are the 56 map sheet. In the Annex has
some of these map sheets been presented in an A4 format to provide the
reader with an impression of the final product. The map sheets presented
are:
Map sheet 1 (1:50,000) of the Logistic and Topographic Maps
Map sheet 1 (1:50,000) of the Coastal Resource Maps
Map sheet 1 ­ 16 (1:50,000) of the Environmental Sensitivity Maps
covering the coastal are of Kenya
Map sheet 17 -20 (1:25,000) of the Environmental Sensitivity Maps
covering the Mombasa Creek Area
All map sheets in full scale as A1 maps can be ordered from Kenya Marine
and Fisheries Research Institute (KMFRI), P O Box 81651, Mombasa,
Kenya, Tel/Fax: + 254 41475157, http://www.kmfri.co.ke.
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5 - KenSea, Environ. Sensitivity Atlas for Coastal Area of Kenya