Impact of Land Use Change on Shoreline Erosion and Mangrove Dynamics in Watamu Mida Creek, Kenya
Abstract
Watamu Mida creek coastal area is a major attraction site for tourists and also a
source of income for the local people. The key identified anthropogenic pressures in
the mangrove forest are; encroachment into the forest (from a growing number of
hotels, cottages and private holiday houses) and, high dependence from the
surrounding villages which has resulted in clearing and selective cutting. The
shoreline is also equally affected by human induced change such as physical alteration
of the beach through clearing the vegetation, development close to the High Water
Mark, and the construction of sea walls. This research assessed the impact of land use
change on mangrove dynamics and shoreline erosion as well as the main driving
factors that cause these changes in Watamu Mida creek. The study had four
objectives; (i) to assess the land use change and, mangrove dynamics (ii) measure the
rate of shoreline change and define the drivers, (iii) determine the natural and human
induced drivers of land use change, mangrove dynamics and shoreline change (iv)
assess the role of relevant government and community level polices on land use and
shoreline management.
This study used old aerial photographs (1969 and 1989), current high resolution
satellite images World view (2010) and ground truthing to analyze the patterns and
dynamics of Mida creek mangrove forest changes, shoreline erosion rates and land
use change over 41 years between 1969-2010. The data were generated for the
mangrove cover by on screen visual digitizing and interpretation using the mosaic
aerial photographs and satellite image. In order to assess the biomass of the
mangrove, a non-destructive method was used to collect data on 25 sample plots and
934 trees were measured to estimate the above ground biomass and carbon stock of
the forest. This study also investigated the trend of shoreline changes, and the factors
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attributed to these changes. The Digital Shoreline Analysis System (DSAS) in ArcGIS
environment was used to create transects and statistical analyses for the shoreline. The
9.8 km long Watamu shoreline was divided into 245 transects with 40 meter spacing
in order to calculate the change rates. To identify the primary driving forces of land
use change, a multiple regression model was used. For the household questionnaires,
a stratified random sampling method was used. The household survey included 60
respondents from different resource users groups and villages.Five Focused Group
Discussions (FGDs) were conducted with representatives of the community and
eleven Key informants interviews were conducted with the key leading government
office representative’s, non-governmental organization, hoteliers, and old residents
along the beach.
The greatest land use change rate observed between 1969 and 1989 was in,
miscellaneous coastal vegetation cover at 2.5%, while coastal bush experienced a
significant negative change rate of -6.5%. The main land use changes observed
between 1989 and 2010 were; increasing coastal bush, an expansion of town and
urban areas, hotels, and private holiday houses. The results of the mangrove analysis
showed a decline in mangrove cover (16%) between 1969 and 1989, while between
1989 and 2010 an increment in mangrove cover (9%) was observed. The total above
ground biomass and carbon estimated was 296.14 ton·ha-1 and 148.07 ton·ha-1
respectively. Mida creek mangrove forest is largely dominated by the presence of;
Rhizophora mucronata and Ceriop tagal and the regeneration of these two species is
very high. The result of shoreline erosion from WLR indicated a mean of -0.89
m/year where 69.7% of transects fall under erosion and 30.3% accretion. Shoreline
erosion was mainly attributed to anthropogenic factors. These include; construction
near the High Water Mark, defensive structures and sea walls, and, destruction of
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vegetation along the beach front. The main drivers of land use change were human
population growth and policy. The research found that the policy instrument review of
the existing policy and legal framework indicated a number of gaps and opportunities
for the protection of the coastal environment in the study area.
The most unique aspect of this research was that it has analyzed a 41 year period of
human and naturally induced changes in the study area through a combination of
GIS/RS tools and community/key informant interviews, enabling a robust
triangulation of the results to be made. As a result the research recommendations
provided a firm foundation for improved County/multi stakeholder management in the
Watamu Mida creek area. The integrated methodology developed as part of this paper
offers other researchers a clear pathway for future comparative studies
Publisher
University of Nairobi
Rights
Attribution-NonCommercial-NoDerivs 3.0 United StatesUsage Rights
http://creativecommons.org/licenses/by-nc-nd/3.0/us/Collections
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