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

Visual AssessmentUncertainty

± 0.45

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

Blekusu

Atorkor

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

Acknowledgements

Thank Youmerci