Shoreline Change Analyses along the Eastern Coast of Ghana ...
Transcript of Shoreline Change Analyses along the Eastern Coast of Ghana ...
Shoreline Change Analyses along the Eastern Coast of Ghana using
Landsat and ASTER Images
Philip-Neri Jayson-Quashigah (Mphil. Environmental Science Programme, UG)Dr. K. Appeaning Addo (Department of Marine and Fisheries Science, UG)
Outline
• Introduction
▫ Objectives of study
• Study Area
▫ Erosion & Interventions
• Approach
• Results and Discussion
• Conclusion and Recommendations
Introduction• Coastal zones are facing intensified disturbances▫ SLR▫ Coastal erosion (70% of the worlds beaches )▫ Increase in population (Appeaning Addo et al., 2008;
Zhang, 2010)• Hence accelerated efforts to assess, monitor and
mitigate stressors (Boak and Turner, 2005)• Shoreline change portray a cumulative outcome of the
processes that altered the shoreline for the periods analysed▫ Facilitates formulating effective coastal management
strategies and planning by revealing trends (AppeaningAddo, 2009).
• Coastal management/engineering require such information (Alves, 2007)
Ghana’s Coast• Ghana’s coastal zone represents about 6.5% of the
land area▫ 25% of the nation’s population▫ 80% of the industrial establishments (Armah and
Amlalo, 1998)• 540km of shoreline to be managed sustainably▫ Some of this is not easily accessible
• Erosion is a serious problem along the entire coast▫ Studies by Nai et al., 1993 and Armah, 1991 also Ly,
1980; Appeaning Addo et al. 2008
Motivation
• Part of efforts for continuous monitoring of Ghana’s shoreline
• The impacts of interventions such as the KSDP
• Expensive high resolution data and field work
Armah and Amlalo, 1998; Appeaning Addo, 2009
Study Objectives
Identification of Change (medium resolution data)
Rate Estimates
Shoreline Management
Evolution Trend
Objective 1
Objective 2 Objective 3
KSDP
Other Factors
informsinforms
Study Area• Between 5º25' and 6 º 20' N and 0 º 40' and 1 º 10' E
• East of the Volta Estuary
• Keta Lagoon Complex
• Soft geology; unconsolidated beach sands and lagoon clays •Waves reach as high as 3m
o South west
• Tidal range of 1m
• Presence of canyons offshore
• Narrow spit with high population density: 164-500 p/km2
Allersma and Tilsman, 1991; Sorenson et al., 2003; GSS, 2005; Boateng, 2009
Erosion & Intervention• Erosion rates had
reached 4-8m/yr▫ 1970-1980
• Destruction of infrastructure
• Keta Sea Defence Project (2000-2004)▫ 6 groynes▫ Revetment▫ Beach nourishment▫ Flood control
Ly, 1980
MethodologyData Landsat
TMASTER VNIRLandsat ETM+
Landsat 8
Resampling Pan‐Sharpening
Overlay of Extracted Shorelines
Registration
BandRatioing
Digitizing
Maps
Visual Interpretation
Change Rate Estimation (LRR) DSAS
Accretion & Erosion Statistics
Raster to
Vector
• The dry-wet boundary (approximate HWL) was extracted as shoreline▫ 1986, 1991, 2001,
2007 and 2013 • Band Ratio▫ B5/b2 (mid-
infrared/green)• Raster to vector
conversion• Digitization of
shoreline in ArcMap
Analysis• Development of Database▫ Shoreline attributes
• DSAS (Extension for ArcGIS)▫ Computes rates at specified
intervals▫ Various statistical methods
• Baseline construction▫ About 500m onshore
• Casting of Transects▫ 50m spacing
• Linear Regression Rate of change (LRR) was used
• Error estimation▫ 30m▫ Annualized: ▫ Ea = √( E1
2 + E22 + E3
2 + E42 + E5
2)/ T
DSAS 4.3; USGS
Results/Discussion
• A total of 5 shorelines 1986, 1991,
2001, 2007, 2013
• 1986 to 2001 pre KSDP
• 2001 to 2013 post KSDP
Pre and Post KSDP1986-2001
2001-2013
KSDP SiteReversal of Situation
3.04m/yr
3.40m/yr
Estuary
72% erosion before 47% erosion after Higher rates at around Blekusu and
Atorkor
•Individual transect reach 11m/yr
Overall Rates of Change
KSDP Site
Estuary
Period Erosion(m/year)
Accretion(m/year)
1986-2013 2.04 2.31
1986-2001 3.04 5.80
2001-2013 3.40 5.15
Rates consistent with other studies
Angnuureng et al. 2013
Possible Factors • Wave action▫ Prevailing southwesterly winds▫ High energy waves (1.3m 10.9s;
Max:2.82m, 19.68s)▫ Presence of Canyons on sea bed
• Shoreline Orientation• Bathymetry (relatively deep)• Human Activities▫ KSDP▫ Sand Mining, mangrove
destruction• Land squeeze▫ coastal development ▫ prevents coasts from adapting
Conclusions and Recommendations
• The methodology is useful and replicable
▫ Detect and monitor shoreline at a medium resolution
• KSDP has a “knock off” effect
• Integrated shoreline management (rather than site specific
interventions)
• Use of higher resolution image to assess accuracy of results
• Extending the study to the national and regional level