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HAZARDMAPPING IN GHANA

A PROJECT REPORT SUBMITTED TO

NATIONAL DISASTER MANAGEMENT

ORGANIZATION

(NADMO)

EDITED BY


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CONTENTS

PREFACE

PROJECT TEAMS

ACKNOWLEDGEMENT

INTRODUCTION

SECTION A:

SECTIONB

SECTIONC

GEOLOGICAL HAZARDS

EARTHQUAKE

LANDSLIDE

COASTAL EROSION

FLOODS

FIRES

PAGE

III

IV

v

1

4


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The adverse effects of disasters on the economies and the overall development of nations

is well known. History abounds with reported cases of human causalities, destruction ofstrategic infrastructure, complete disruption of economic and social facilities resulting in

severe hardships on communities.

It is in this light that the United Nations Organisation (UNO) and the African Union (AU)

and other International Agencies have taken disaster management issues so seriously that

they have now become integral parts of the planning process of many nations. Disaster

management activities encompass preparedness and mitigation, emergency response,

rehabilitation and reconstruction.

The current global trend now is to place emphasis on the pre-disaster phase, where

communities are encouraged to identify risks to their lives, properties and livelihoods as a

means of preventing or minimising the effects of such disasters. With the NationalDisaster Management Plan (NDMP) and the National Standard Operating Procedures

(SOP) in place it is fitting that hazard maps for the various hazards are also prepared to

guide planners to take steps to include in their planning measures that would prevent or

reduce the risk of disasters.

The support of UNDP as well as the devotion of the Technical Teams in the preparation

of this document is highly appreciated.


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PROJECT TEAMS

(1)

(2)

(3)

GEOLOGICAL HAZARDS

MR. P.Y.O. AMOAKO

MR. MA WULI AKOTO

MR. JOHN FOSU PINKRAH

HYDROMETEOROLOGICAL

MR. O.K. ANAOLATE

MR. BEN BROWN

MR. P. OYAU BOAKYE

FIRES

DCFO A.B. OAISIE

ACFO AMPONSAH TETTEH


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ACKNOWLEDGEMENT

We acknowledge some organizations and individuals without whose efforts and

contributions this report could not have been produced. We wish to mention the Ministry

of Food and Agriculture, the Geological Survey Dept, Geology Dept University of

Ghana, the National Fire Service, the Forestry Commission and their staff at

headquarters, regions and districts.

We are particularly thankful to the UNDP who supported the project financially and

NADMO for giving us the opportunity to this pioneer project of Hazard Mapping in

Ghana. The support and encouragement of the Ag. National Co-ordinator (DCOP

Douglas Akrofi Asiedu) and Deputy National Co-ordinator (Finance & Administration)

ofNADMO, Dr. Kwaku Osei-Akom are well appreciated.

Our special appreciation goes to Dr. Duah- Yentumi of UNDP for his personal interest

shown in the project and encouragement given to us. Messrs Alexander Appau-Akoto,

Eugene Asamoah Ayew and Mrs. Diana Boakye, (Acting Deputy National Co-ordinator,

Disasters) of NADMO who assisted in preparation of the project document and Mrs.

Diana Boakye, in particular, who assisted administratively in its execution are well

recogni ed


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HAZARD MAPPING IN GHANA

Introduction

The United Nations declared the period 1990 - 1999 as the International Decade for

Natural Disaster Reduction UN/IDNDR: UN RES 42/169/1987) with the following

goals

to achieve:

I. to increase worldwide awareness

II. foster prevention and reduce the risks of natural disasters through the

widespread application of modem science and technology.

Consequently, international demonstration projects (hazard mapping) designed to

improve the assessment of natural hazards (earthquakes, floods, volcanoes, tropicalhurricanes etc) were initiated.

These demonstration projects served as an international platform for promoting aregionally co-ordinated homogeneous approach to hazard evaluation. Such hazardmaps are actually needed for alerting countries to their vulnerability potential andshould stimulate some policy initiatives especially for the developing nations

which sometimes apply for loans from the World Bank and other such financialinstitutions that may need accurate hazard assessment.


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Objectives

The broad objectives of this project; supported by the UNDP are to support.

(i) NADMO to prepare a long term National Risk Reduction Policy and

Programme.

(ii) The development of a system of hazard reporting and early warning.

(iii) The strengthening ofthe institutional structures in the country.

The specific objectives for which the terms of reference have been drawn are :

(i) To prepare hazard maps for the four major hazard types

that are prevalent in Ghana.

(ii) To prepare Vulnerability Assessment maps for the four major hazard

types that are prevalent in Ghana.

(iii) To prepare disaster risk zonation maps for each of the four majorhazards to guide the development processes countrywide.

Due to time and resource constraints the Vulnerability and Risk Assessment mapscouldnot be prepared.

Methodology

In order to achieve this, four teams of three specialists each were tasked to prepare


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Hazard Maps

The following hazard maps have been prepared: and presented in the

report.

GEOLOGICAL

Seismic Hazard Map

Coastal Erosion Hazard Map

Landslides Hazard Map

PESTS AND INSECTS Maps on incidences of:

Grasshopper

Anthrax

Black Pod

ArmyWorm

Cape St Paul Wilt Disease

African Swine Fever

Avian Influenza

Invasive Fruit fly

Larger Grain Borer

HYDRO METEOROLOGICAL Floods Hazard Maps for:

The Whole Country


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SECTION A

GEOLOGICAL HAZARDS

1.0 Seismic (Earthquakes)


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Executive Summary

This report has been prepared to cover three of the geological hazards namely ,

earthquakes, landslides and coastal erosion. Each hazard has been treated separately. The

purpose of the exercise is to prepare maps depicting the levels of hazards for each hazard

and in such a way as to be beneficial to the various stakeholders.

Hazard mapping has, in the past, not been taken seriously in Ghana even though the

country has been known to suffer from the effects of hazards such as earthquakes, floods,

landslides and coastal erosion. The UNDP has been particular since 1990, about the needfor member countries to prepare hazard maps for the various hazards that affect them. In

view of this, and realizing that Ghana has not carried out any coordinated hazard

mapping program, the UNDP has supported NADMO in this exercise. The main

objective is to prepare hazard maps for four hazard types namely; Geological hazards

(earthquakes, landslides and coastal erosion), hydro meteorological (floods), Biological

(pests and insects infestation) and Fires.

This section deals with three of the geological hazards, that is earthquakes, landslides andcoastal erosion. The main method used was to gather information, analyze them and

prepare the appropriate hazard maps. Sources of information included government

institutions (e.g. Geological Survey Department), the Universities, the Building and the

Road Research Institute (BRRI), the Council for Scientific and Industrial Research,

individual geoscientists, published and unpublished reports and / or papers. With regard

to landslides and coastal erosion, some Regional and District NADMO coordinators were

helpful. The local communities also volunteered useful information. Along the coast,

some fishermen, opinion leaders and assembly members enthusiastically assisted the

team in information gathering.

With d t th k i ti th t l t th i t it th l l


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The maps show that earthquakes, landslides and coastal erosion hazards are potentially

dangerous in the identified zones or areas. They could cause extensive damage toproperties and loss of lives when they do occur.

The following recommendations have therefore been made:

Development in such zones or areas should be made with reference to the

maps.

The National Building Code should incorporate seismic design and

construction requirement to ensure that buildings are earthquake resistant in

zones 4, 3 and 2.

There should be effective collaboration between and amongst the relevant

organizations / institutions for proper documentation on landslides.

There should be enforceable documentation to

1. Discourage individuals or developers from building along hazardous

beaches, where necessary setback distances should be set.

2. Ensure that human activities such as sand winning are curtailed.

In all cases, there should be a coordinated program for a comprehensive studyof the various hazards to enhance periodic revision of the hazard maps.

NADMO should take the initiative and prepare the program with input from

the relevant stakeholder institutions / organizations and or individuals.


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1.0 SEISMIC HAZARD MAPPING

CONTENTS

1.1 Introduction

1.2 Seismic Hazard

1.3 Seismicity in Ghana

1.4 Geology of Ghana

1.5.0 Methodology

1.5.1 Source Characterisation

1.5.2 Hazard Computation Method

1.6 Results and Discussions1.7 Conclusions

1 8 R d ti


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1.1Introduction

Seismic hazard maps depict the levels of seismic risk in a given area. The mapping is a

useful tool for presenting information on seismic hazards essential for preparation of

seismic codes needed for proper design and construction of buildings and infrastructure,

general land use planning, and policy decision making with regard to disaster

management.

The basis of seismic hazard analysis is the analysis of seismicity or the occurrence of

earthquakes in space and time. Information generally used in the hazard map preparation

include:

Instrumental Seismicity: Earthquakes for which actual instrumental records exist.

Historical Seismicity: Records of earthquakes that occurred during the hundreds of years


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Thepeak ground acceleration (PGA) relates directly to the dangerous, earthquake related

phenomena such as ground shaking, fault rupture or soil liquefaction which could result

in the destruction ofbuildings, loss oflife or other adverse consequences to society.

PGA values denote maximum horizontal acceleration on competent soil. With soft or

unconsolidated soil and clays of appreciable depths, the ground accelerations will be

different from those indicated in PGA hazard maps.

Under the GSHAP, the hazard map shows the PGA which is virtually "a standardised" or

common measurement of ground shaking. The seismic hazard map of Ghanaprepared

under this project has been presented in PGA values.

The information used includes:

Instrumental Seismicity: Epicentral and isosismals data, of instrumentally recorded

earthquakes (from 1973).

Historical Seismicity: Epicentral and isosismals data of historical earthquakes (from 1615

to 1969)

Geology and Major Fault Maps.


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The historical seismic data so far collected in the country since 1615 is sparse and apartfrom the 1939 historical earthquake, almost all the historical earthquakes in Ghana have

not been properly documented.

Based on the available information / data and within the limits of such uncertainties, five

seismic hazard zones [ZONE 4, ZONE 3, ZONE 2, ZONE 1, ZONE 0] have been

delineated. ZONE 4 has the highest level of risk and ZONE 0 the lowest level of risk.

The PGA values for the zones have been calculated usmg the regression equation

provided by Murphy and O'brien as stated in Leiter (1990). The equation relates the

intensity, the local magnitude and the epicentral distances to thepeak horizontal ground

acceleration. It is expected that the PGA map and the supporting documentation willprovide a useful seismic hazard framework for Ghana and serve as a resource for

improved and or detailed studies by the appropriate agencies and the individual research

scientists. It should therefore serve as a guide to all users including developers, land use

planners, engineers and policy makers.


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1.2 Seismic Hazards

Seismic hazard is basically the probability of the occurrence of an earthquake with

potential for dangerous, seismogenic (earthquake related) phenomena such as ground

shaking fault rapture and soil liquefaction. The phenomena could result in the destruction

of buildings and other man made structures along with the loss oflife (Reiter 1990).

The earthquake motion and consequent effects can be very dependent upon local surface

conditions which depend largely on the geology of the area.

The effects of earthquakes on soft sediments have been known to be greater than those on

harder rocks. As the sedimentary rocks get younger and less consolidated, the relative

intensity of earthquake ground shaking increases with respect to the harder granitic,

metamorphic and volcanic rocks.

Seismic hazard assessment is the first step in the evaluation of the seismic risk obtained

by convolving the seismic hazard with local site effects (anomalous amplifications tied to

soil conditions local geology and topography) and with the vulnerability factors (type


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The basic elements of modem probabilistic seismic hazard assessment as implemented by

the GSHAP can be grouped into the following four categories:

>- Earthquake catalogues and databases (historical seismicity, instrumental

seismicity).

>- Earthquake source characterisation (creating seismic sources usmg evidence

from earthquake catalogs, seismotectonics,paleo seismicity , geomorphology,

mappmg of active faults, geodetic estimates of crustal deformation, remote

sensing, and geodynamic modelling).

>- Strong seismic ground motion - the evaluation of ground shaking on a function of

earthquake size and distance.

>- Computation of seismic hazard - the computation of the probability of occurrence

of ground shaking in a given time period to produce maps of seismic hazards and

related uncertainties at appropriate scales.


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The following table and maps indicate the type of information used.

Table 1 (Appendix Al.1)

Fig.Al.1

Fig.Al.2, Fig Al.3, FigA1A

Fig Al.5

List of all known historic earthquakes

Map showing historic earthquakes and

their maximum intensities(1615-1669)

Isoseismal maps of 1862, 1906 and 1939

earthquakes respectively

Map showing earthquakes in Ghana

(1615 2003)


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3.4.5.Fig.A1.1 Historic Earthquakes (1615-1969)

EARTHQUAKES IN GHANA (1615 - 2003)

4 .;J -2

V-1

+

+

+


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Fig.A1.2 Isoseismal Map of 1862

tsoselsmal Map of the 1862 Earthquake (after Quaah, 1982)

If)....-l",


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1.3 Seimicity In Ghana

Ghana, by location, does not lie along any of the well known tectonic plate boundaries

which mark the recognized global earthquake zones. However, Ghana has a well

documented history of damaging earthquakes around Magnitude 6 occurnng mostly

along the coastal zones. Junner (1941); Adams and Ambraseys (1986).

The historical catalogue for Ghana begins m 1615 and the most significant historicdamaging earthquakes are, Elmina (1615), Axim(1636), Accra(1862), Ho(1906), andAccra(1939).

Less damaging ones have occurred in 1858, 1863, 1883, 1907, 1911, 1923, 1925 and

1930.

Earthquake swarms occurred in 1918-1919 and 1933-1935.

In more recent times earthquakes of magnitude 3.5 or higher have been felt in 1964,1967,1969, 1978, 1985 and 1995.

Instrumental recordings of earthquakes (with analogue equipment) started in August,1973. The instrumental catalogue includes all micro earthquakes (those with magnitudeless than or equal to 3)

It has been observed from both historical and instrumental recorded data that all the

earthquake activity in Ghana can be associated with three major tectonic zones of


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Finally there is the north-east trending Akwapim fault which intersects with theCoastal Boundary fault just to the west of Accra. Blundell (1976).

Most, of the micro-earthquake epicentres have been located in the area where the

Akwapim fault intersects the coastal boundary fault. Numerous intersection faults are

also present in this area which can compound the earthquake effects. This is the reasonwhy Ambrasseys and Adams (1986) indicated that this area (Accra) is the most

seismically active in West Africa.

From the instrumental seismicity records so far, there is very little micro seismic activity

outside south eastern Ghana. This could be due to the fact that seismological stations are

skewed towards the east.

According to Essel (1979) the seismic activity in Ghana is related to deep seated active

faults. Also, earthquakes in Ghana are purely intraplate, and unlike the interplate

earthquake found along the well known tectonic plate boundaries, the origin of

intraplate

earthquakes is still poorly understood and because of their unexpectedness and

infrequency, they result in major disasters.


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11.12.13.

4

Fig.A1.5 Earthquakes in Ghana (1615-2003)

EARTHQUA KES IN GHA NA (1615 - 2003)

- ., -1

+

Cote d' Ivoire

~-~-~

?~-~\ill;>!)!I)t"utr,)

\ \\

\\Mt,mnr~~~-2

r~;;::;:~~:: ..

Bronqa-Ahafo

Ash

stern

"~O i\.

"

-

W " , '~

'~I

Magnitud e (Richter Scale)

) 1"" 2 2.1 - 4 4.1 +Convex polygon of total activity

+

(IS de Trd ~Jl93~

b'J90 1

Western

A,m f't


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14.15.16.FigA1.6 Instrumental Recorded (1973-2003)

Instrument Recorded Earthquake Activity in Ghana (1973-2003)

oJ

-

2

-1

----


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17.

Fig AI. 7 Instrumental Recorded Earthquakes (20% outlier removed)

Instrument Recorded Earthquake Activity in Ghana (1973-2003)

(After 20% outlier removal)0"35' 0"30' 0"25' 0"20' 0"15'

5"20- IliJINNEBA

"

0"10' 0"6' 0";'

-0 "45'

-0 "40'

0


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18.

Fig.A1.8 Instrumental Recorded Earthquakes (50% kernel density view)

-


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1.4 Ceology of Ghana

According to (Kesse, G. 0, 1985), Fig A1.9 Ghana falls neatly within the Precambrian

Guinean Shield of West Africa. The country is divided into five main geological

provinces; namely:

The shield area (or western unit);

The south eastern unit which belongs to the Precambrian Mobile Belt;

The central unit mainly of the sediments of the Voltaian System;

The coastal basins and

The Tertiary to Recent deposits

The shield area (western unit) consists of Birimian metasedimentary (volcaniclastics,

greywacke and argillite); Birimian metavolcanics (basaltic flows, volcaniclastics and sub

volcanic rocks);the Tarkwaian Group(a slightly younger, unconformable unit of

sandstones and conglomerates which overlies the Birimian volcanic rocks); belt

granitoids and basin granitoids which intrude respectively the Birimian metavolcanics

and metasediments ..


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The Accraian Series: They are Devonian Sedimentary rocks which occur in

several places around Accra and are made up of upper sandstone and shale

formation, middle shale formation and lower sandstones with a basal grit.

The Amisian Formation: This outcrops at a number of places along the

coast

near the mouth of River Amisa between Saltpond and Winneba and are made

up

of a series of interbedded, soft,pebbly grits, conglomerates, micaceous

sandstones, arkose and greenish grey clay.

The Sekodian Series: Consists mainly of sandstones and shales with

conglomerates,pebble beds, grits and mud stone resting with major

unconformity

on a complex of granites, gneisses and schists. They occur in several

disconnected

outcrops along the coast between Cape Coast and the mouth of the Butre river

near Dixcove.

The Appolonian (Tano Basin) Formation: They are Cretaceous - Eocene

marine sedimentary rocks which occur at the southwest comer of Ghana and


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Fig.A1.9 Map of Ghana showing the Shield Area, the Mobile Belt, the Voltaian

Platform, the Coastal Basins, and Tertiary to Recent Deposits (After Kesse, 1985)


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1.5.2 Seismic Source Characterisation

The earthquake catalogue for Ghana served as the source of data for characterization for

the seismic hazard map. The zoning has been done based primarily on

The isoseismals (maximum intensity).

The geology and the geological faults,

The distribution of cities, towns and other human settlements.

The characterization of seismic sources actually seeks to obtain robust answers to these

questions; where do earthquakes occur? How often do they occur?, and how big can

we expect these earthquakes? Seismicity catalogs are the fundamental tools used to

determine where, how often and how big earthquakes are likely to occur. The results

from seismic monitoring, the historic record, geodetic monitoring and the geologic record

are therefore combined to characterize seismic sources.

With the data at hand an approach was chosen based on the assumption that any

earthquake that has occurred in the past may happen again in the future. To this end,

isoseismals of past major earthquakes were used and areas around faults that had

produced earthquakes in the past demarcated as the most probable area to be affected by

earthquakes in future.


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Fault zones where a controlling earthquake of magnitude 6.5 could originate:

The Cote d' Ivoire fault which cuts through the south western edge of Ghana.

Coastal Boundary fault, a major fault almost parallel with the coast just a few

kilometers off shore and trending east-west. To the east, this fault most probably

strikes inland and continues as the faulted northern margin of the Keta Basin.

The north-east trending Akwapim fault which intersects with the Coastal

Boundary

The intersection of the Coastal Boundary Fault and the Akwapim fault zone.

1.5.3 Hazard Computation Method

There is no strong motion equipment III Ghana for direct measurement of various

elements of actual ground movements. Ground motion estimations for the purpose of

seismic hazard analysis can only be made using models based on measurements fromother parts of the world. Reiter (1990) refers to a model based on regression computed by

Murphy and O'brien for the Western United States This model relates the intensity


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Log a =0.14 I MM + 0.24 ML -0.68Log(~)+0.6

This has been adopted for estimating the Horizontal Component Peak GroundAcceleration (PGA) in the various hazard zones demarcated in the zonation map(Akoto,1998).

ZONES

Seismic Parameter 4 3 2 1 0

Max. Intensity (I MM) IX VII V IV III

Max Magnitude (ML) 6.5 6.5 6.5 6.5 6.5

Avg. Epicentral Distance (M 20km 40km 100km 250km 400km

PGA (a) cm see" 347 112 32 12.3 6.5

a/g 0.35 0.12 0.03 0.01 0.006

g = 980 em sec-lis the Gravitational

Acceleration

PGA f Z 4 0 35


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Fig.A1.10 Map showing Geology, Geological faults and EarthquakeEpicentres

Earthquake(i615-200

3)

Rir;hterScale

t

-

2

2


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Fig. A1.11oJ

11

1

0


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Ghana (1615-2003)

Fig.A1.12 Earthquake Epicenter Map and Computed Intensity Distribution for

Triangles: felt earthquakes. Earthquake data from LEYDECKER &AMPONSAH (2004),

AMPONSAH (2002) and Geological Survey Dept.

Ghana - Earth quake epicenter map and computed intensity distribution (16152003)

10

FigA1.12

~QA'IINO)Il

r

.TlltMiLE

Ghana

(j'lvoire

A

SUllYANI

-4 -2

00 0 00 100 150 200 Kilome! . s

E3 ~ ~ IDot. from LEYDECKER& A MPONSAH (2004) ,AMPONSAH (2002)& Geological SurveyDept""ccra.

__ .

(ls cs etsrnals)

cc(l)

m

N

~'ll ~.

MM

Legend

Magno" de Intensity

1 1.9 14

2-2.9 4.1 -5

~3- 3.9

~5.1 -6

.. 4- 4.8 6.1 -7A 7.1 -8

-I.&. 8.1 -9

Fe~ Earthquakes

Inten sity Zones

7.

5

7.5

.5


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1.6 Results And Discussion

The prepared seismic hazard map Fig AI.II of Ghana depicts the PGA values. Five

distinct PGA zones have been identified with the areas in and around Accra, Wejia and

Ho as those with the highest PGA value of 0.35g. The areas to the north of Ashanti

including the Brong Ahafo, Upper East, Upper West and Northern Region are virtually

aseismic with a PGA value of 0.006g

The highest PGA values are coincident with the Akwapim fault zone and the intersection

of the same fault zone with the coastal boundary fault. These fault systems are active and

these highest values imply the possibility of the occurrence of magnitude 6.5 earthquakes

with the strongest ground shaking.

The seismic hazard map depicts the shaking hazard that will have the largest effects on

one and two storey buildings/ structures (the largest class of buildings/structures in

Ghana). There are no instrumentally recorded strong motion data in the country. This

hazard map has therefore been derived from the maximum intensity and maximum

magnitude data. It is therefore to serve as a guide for the design and construction of

earthquake resistant buildings and structures.


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some areas north of Ho and areas in and around Accra including Weij a. In Reiter (1990),

Murphy and O'Brien stated that the best model relating to intensity and ground motion

would be one that took into account epicentral distance~)and local magnitude(ML) and

geographic region as has been used in the preparation of the PGA value hazard map.

From past and present records, areas in and around Accra continue to be the most seismic

in the country; and all things being equal, should have the highest potential for the next

devastating earthquake as the present map depicts. The PGA value hazard map should be

preferred. However Leydecker's 'isoseismal' hazard map gives food for thought.

Earthquakes in Ghana are shallow and the hypocentres lie at depths of less than 20

kilometres. Shallow earthquakes can be very destructive, because the geometrical

damping is low and the earth's crust is brittle and snaps very rapidly when stress is

relieved.

Microseismic activity is concentrated in south eastern Ghana where the seismograph

network is installed. Activity outside the network may go unnoticed. Also written

records of historic earthquakes are concentrated along the coast where European settlers

were located (1600 - 1900).

Conclusions


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Zone 2 has a PGA value of O.03g,

Zone 3 has a PGA value of O.12g,

and

Zone 4 has a PGA value of O.35g

Development in these areas must involve an earthquake disaster mitigation plan.

Zone 0 has a PGA value ofO.006g

Zone 1 has a PGA value ofO.Olg

Zones 0 and 1 can be regarded as areas of low risk.

Earthquakes in Ghana are intrapalate and of shallow depth. Because intraplateearthquakes are low frequency/low probability but high impact phenomena, even policymakers invariably are tempted to ignore the inherent danger. It is expected that thisseismic hazard map will influence the thinking and policy direction of the governmentwith regard to earthquake related issues; more so now that the international financinginstitutions such as the World Bank may require such a map to facilitate loanapplications.

The PGA map and the supporting documentation are designed to provide a useful hazardframework for Ghana and serve as resource for proper detailed studies by the appropriateagencies and the individual research scientists. Such proper detailed studies will involveappropriate ground motion relationship, proper digital monitoring of instrumental

earthquakes (at least to avoid the subjectivity factor in calculating for the ML andepicentral distances) and inclusion of scenario events for Ghana. Hopefully, this willimprove the seismic hazard map which should be updated periodically, say every tenyears!


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1.7 Recommendation

1. Twelve Station Seismic Network with the state of the art technology should be

established in Ghana for the purpose of proper monitoring of earthquake

activities.

2. The Geological Disaster Technical Committee of NADMO should be made to

draw up and supported to execute a program for site specific seismic risk

assessment in the country for selected cities such as Accra This should be done in

collaboration with appropriate agencies

3. The National Building Code should incorporate seismic design and construction

requirements.

4. The active faults, fault zones or fault systems in Ghana should be properly

mapped for authentic seismotectonic maps to be prepared.

5 The National seismological team should be revived for a coordinated effort in

handling seismic issues in the country.


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References

Akoto M. A; 1998: Impact of Sea Level and adaptation strategy for the coastal zone of

Ghana; Seismicity and seismic hazards; Environmental Protection Agency of Ghana

Report

Ambraseys, N. N and Adams R. D; 1986: Seismicity of West Africa" Annales of

Geophysics 4B (6) 679-708

Amponsah P.E 2002: Seismic activity in relation to fault systems in southern Ghana.

Journal of Africa Earth sciences 35 (2002) PP. 227 -234

Blundell, D. J., and Banson, J.K.A.;197S: Interpretation of Seismic reflection survey

across the continental shelf of south of bAccra and its bearing on earthquakes in the area.

Rep. Geol. Survey, No. 7511, Accra.

Blundell D. J; 1976: "Active faults in West Africa" Earth and Planetary science letters

Vol 132 . pp. 287-290.


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Giardimi Dominico; 1999:Annali Di Geofisica - The Global Seismic Hazard

Assessment Program (GSHAP) 1992-1999; Summary Volume ICP Publication No. 350

and IG/ETHCPublication n 1104

Junner, M. R, 1941:"The Accra Earthquake of 22ndJune, 1939". Gold Coast GeologicalSurvey Bulletin No 13,

Kesse, G. 0; 1985: The Mineral and Rock Resources of Ghana. A.A.

BALKEMAIROTTERDAM/BOSTON

Leydecker, G. and Amponsah P. E. 2004: Earthquake Catolog for Ghana, GeologicalSurvey Department, Accra, Ghana.

Muff R, Okla R, Anokwa Y.M, Brakohiapa E,Brown R,Edifor D.R, Efa E,Abel Th,

Leydecker G; 2006: Geoinformation for Land Use Planning and Urban development inthe Greater Metropolitan Area with Schematic Map of suggested Land Use 1: 1 00,000and Geohazard Map 1: 100,000: Ghana- Germany technical Cooperation Project;Environmental and Engineering Geology for Urban Planning in the Accra- Tema Area.

Quaah, A.O 1980: Microseismicity, Past Seismic Activity and Seismic Risk m

Southern Ghana. PhD Thesis University of London.

Reiter, L; 1990:"Earthquakes hazard analysis, issues and insights" Columbia University


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Viccari Franco; 1998: Lecture notes for Training Workshop on earthquake hazard

mitigation in Ghana: Council for Scientific and Industrial Research (CSIR), Building and

Road Research Institute (BRRI).

Appendix Al

Table 1: Historical Earthquake Occurrences In Ghana

DATE EPICENTER CAUSE MAGNITUDE(M)

EFFECTS AND FELT AREAS

1615Near CapeCoast

Damage to Fort St. George in Elmina.

1812/1636 Near Axim 5.7 The Axim district was badly shaken. The

buildings and underground workings of the

Portuguese gold mine at Aboasi, which was

situated near the Duma River, north -east of

Axim, collapsed and many of the workers

were buried. Damamge along Axim coast,

Fort Sa Antonio at Axim was cracked.

1858 First reported earthquake known to have

shaken Accra strongly. Caused panic but

probably little or no damage.


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1871 4.5 Severe shocks felt in Accra, caused panic.

15/04/1872 4.9 Several violent shocks occurred in Accra,

considerable damage, many houses

destroyed, few senous but no senous

accidents occurred.

1883 4.6Felt along the coast, walls of ChristianborgCastle and nearby houses cracked, causedpanic in Accra and Winneba, felt in CapeCoast

20/11/1906 Near Ho AkwapimFault

5.0Greatest damage m Ho area, some

government buildings were badly damaged

or partly destroyed, many houses badly

cracked and uninhabitable. In Accra Castle, James and

Usher Fort suffered much damage, some houses

cracked but none seriously. Abnormal fluctuations of

sea level observed in Togo, coast flooded a number of

times but no damage.

09/02/1909 8km South ofTema

Coastalfault

4.9 Felt in Accra and Tema


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08/01/1997Weija

Akwapim

Fault

3.8 Felt in McCarthy Hill, Aplaku, Madina,

West Legon, Kasoa, Tema. Panic no

injuris.

14/02/1997 Weija AkwapimFault

4.1 Kasoa, Bortianor, Mallam, Ashaiman,Legon, Cape Coast, Koforidua, Cracks werenoticed in buildings west of McCarthy Hilland Bortianor and one building In theAdweso Estate, Koforidua

06/03/1997 Weija AkwapimFault

4.8 Felt in Cape Coast, Apam, Akwapim Ridge

towns, Ho, Koforidua, Obuasi. Stampede at

national theater fire outbreak; Kaneshie

North Industrial area, cracks In some

buildings in Accra.


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Appendix AI:2

Relation of Earthquake Effects to Geology

Detailed studies of earthquakes in various parts of the world have shown that the effects

of earthquakes on buildings and other structures vary greatly with the nature and structure

of the underlying rocks, and also to an appreciable extent with the topography. (Junner

1941). Generally structures that are built on solid rocks are more stable than those built

on soil or unconsolidated sediments, especially if they are poorly drained or if they

compress when shaken by an earthquake. Buildings and infrastructure founded on such

soils may collapse due to phenomena such as liquefaction, landslides and subsidence.

Other things being equal the effects are least:

(a) Where the underlying rock is homogenous and particularly where it IS

weathered and free from fractures.

(b) on flat ground underlain at shallow depth by solid rock or underlain by sand

and clay containing little or no water, and

(c) where foundations are on solid rock, or are deep and massive and greatest:

(a) on swampy alluvial ground such as waterlogged sands, gravels, clays, silt or

made-up ground;


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infrastructure in seismic zones. The Birimian metavo1canics are good conductors when

fresh and strong,but could bepoor conductors within unconsolidated saprolite horizons.

The Birimian metasediments are relatively good conductors when they are strong and

fresh;but they are poor when weathered and especially within soft argillites. The Togo

quartzites and quartz-schists within the Mobile Belt are good conductors when hard and

fresh; but in areas where they contain bands of softphyllites and are fractured and faulted

(eg. In Weija), they are relativelypoor conductors. Hard, fresh and strong sandstones

within the Central Unit (The Voltaian System) could be good conductors, but they are

generally poor conductors where they are interbedded with soft shales and mudstones and

are extensively weathered. The rocks within the coastal basins are not generally good

conductors except in areas where they are hard, compact, homogenous and strong. For

instance, alternatingbeds of sandstone and shale of variable hardness, texture and degree

of weathering, such as the Accraian beds at Accra, arepoor conductors of seismic waves.

The Tertiary and Recent deposits are generally loose and unconsolidated and are

relativelypoor conductors of seismic waves.


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2.0 Landslide Hazards in Ghana

2.1 Introduction

2.2 Types of landslide

2.3 Geology

2.4 Causes of landslides

2.4.1 Causes of Landslides In The Voltaian System

2.5 Methodology

2.6 Landslide Hazard Map Preparation

2.7 Results And Discussions2.8 Conclusion

2.9 Recommendation

References

Appendix


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2.0 Landslide Hazard in Ghana

2.1 Introduction

Landslide and related phenomena can cause substantial damage and loss of life and

property. In Ghana, landslides have been known to occur on hill tops/side and especially

during heavy rains. Unfortunately, most of them have not been properly documented

even though they have been destructive at times; blocking main roads, destroying farms,

and settlements, damning of rivers down slope. In July 1968, 1500m3of rock, soil and

vegetation blocked the Kumasi - Mampong road for 10 days (Ayetey, 1989). In April,

2007, the same Kumasi -Mampong road was blocked and closed to vehicular traffic for

almost a month. This was because of a serious landslide that occurred on the Mampong

scarp. In October 2007, fourteen people were displaced and two autoparts stores were

affected by a landslide that occurred at Elubo in the Jomoro district of the Western

Region. Landslides have been reported to occur in places such as Pokuase in the Greater

Accra Region; Kumawu and the Ejura scarp in the Ashanti Region, Abansu in the Brong

Ahafo Region; Nakpanduri in the Northern Region and some other places. At


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landslides in Ghana occur mostly on escarpments, especially on the Voltaian escarpment.

Some of the landslides have affected roads, farms, forest and a few settlements.

2.2 Types of Landslides

The types of landslides can be classified as slide, slump, flow, fall, topple or complex

slides.

Slide - Occurs when there is movement along aplanar surface e.g. Joint,bedding

plane. It is typical of rocks and is varied in size and depth.

Slump -It is also referred to as rotational slide. Here the failure surface is arc-shape.

It is common in soils and deeply weathered rocks; it is varied in size and

depth.

Flow - This could be dry or wet; in the wet flows, saturated materials also flow out

of the slope e.g. debris flow. The flow failure is shallow and is common on

steep slopes. It can pose high hazard due to highly erosive nature, major

damage can be caused if the velocity of flow high.


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2.3 Geology

The Geology of Ghana is as shown in Fig A2.1 Most of the western and northern parts of

Ghana are underlain by Paleoproterozoic metabasaltic and metasedimentary rocks of the

Birimian Supergroup. The metabasalts form a NE-SW trending volcanic belts which are

separated by metsedimentary basins. The metavolcanics are made up of greenstone,

mainly metamorphosed basic and intermediate lava and pyroclastic rocks with

interbedded bands of phyllite and greywacke; whilst the metasediments are made up

of slate, phyllite, greywacke, tuffa and lava together with schist and gneiss derived from

these rocks. The Birimian rocks are isoclinally folded with dips generally greater than

60. Overlying the metevolcanis is the" Tarkwaian group" which is an unconformable

unit of mainly sandstone and conglomerates. Many granitoids intrude the Birimian

super group.

The central part of the country is the V oltaian System which is made up of a thick

succession of undeformed Neoproterozoic to early Paleozoic sedimentary rocks mainly

sandstones, shale and mudstone. The Voltaian form a lot of a escarpment especially in


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Fig A2.1 Geological Map of Ghana

GHANA Simplified Geology


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2.4 Causes of Landslides

An increase in driving force or decrease in resisting force in earthen materials are often

masked by immediate causes such as earthquake shocks, vibrations or sudden increase of

water entering the slope. In road construction or housing development, for instance, the

real cause of landslides could be the poor designed slope but the immediate cause could

be earthquake shocks, vibrations or heavy down pour of rains. Landslides at Highway

sides along hills could be attributed to poor designs of cut slopes. Such poor designs

could trigger off successive slides along incipient failure planes in the slope.

Other causes are the occurrence of weak rock/soil overlying failure planes, slope

undercutting, earthquake, or blast vibrations and water. In effect, the geology,

geomorphology and climate contribute to landslides where there is weak rock/soil,

foliated/fractured rocks, steep mountainous terrain, high drainage density; warm tropical

climate and high seasonal rainfall.


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2.4.1 Causes of Landslides in the Voltaian System

A study conducted by Ayetey (1989) around the Mampong escarpment indicates that

within the Voltaian System of Ghana three major causes of slope failure have been

identified. These are:

a. Structural discontinuities - The Voltaian System along the Kumasi - Mampong road

consists of massive, extensively jointed sandstone with interbedded shale and mudstone.Differential weathering of the softer shale and mudstone undercut the sandstone as much

as 4m. Tension cracks developed in the massive sandstone which eventually failed.

b. Texture of Soils - the particle size distribution of the debris was important m

subsequent failures of the decomposed Voltaian material. After the rockfall, huge

boulders decomposed into smaller particles, the strength changed considerably and the

slope became unstable and failed again.

c. Vegetation - The landslide in the Kumasi - Mampong road section is in the rain

forest area of Ghana. Large roots of trees in this area penetrate deeply into the rock

through joints, acting as wedges, and in time, pushing over the shattered rocks. During

windstorms, tree and root movement may also cause the widening of rock joints with

subsequent release ofthe boulders down slope initiating landslides and rockfalls ..


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in some of the communities have ideas of occurrences but are not sure of the exact

spots and the time of occurrence or recurrence ..

2.6 Landslide Hazard Map Preparation

Ayetey (1989) produced a landslide hazard map of Ghana. The original map was

digitised and prepared and as shown in Fig.A2.2 .Information gathered from the field

work and other sources could not be used in the preparation of the map because the spots

could not be properly georeferenced. The recent landslide potential map prepared by

Muff R. et al (2006) covers only a section of the Akwapimian escarpment as part of the

Greater Accra Metropolitan Area. This map has been presented separately as Fig. A2.4

Information gathered during the working visits could not be used since the reported

landslides could not be properly located.


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Fig.A2.2 Landslide Hazard Map of Ghana

GHANA - Relief & Land Slide hazard map


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FigA2.3 Soil Erosion Hazard Map of Ghana

1II

I

"

TI+

I j

f1


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Fig A2.4 Environmental and Engineering Geology Map of Accra Metropolitan Area

Urban Erosion and Potential Rockfall Zones 1: 100 000

o.no.n

r-~--~'"'-"~_~_~-'--'-

After Muff R, et al (2006)

mo,,,,,,,...,

\) \.. yo

G

OfG\)\~f.p..

Potenllal rockfall 2.one

_Higl'lsu,ceP~oiIil1

_MOClIun.,uIoOl,OP~bi~(

Y

[.

"

Intensity of &rosfol1

"~m


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2.7 Results And Discussion

The landslide hazard Fig.A2.2 map shows that the areas where they have occurred are on

the highlands or escarpments with levels above 630 meters (about 2000 feet), above mean

sea level. They are more prominent in the Voltaian System where scarps have formed and

in areas where the Voltaian unconformably over-lies the Birimian. In most of the cases

they have occurred in places with little development. However, at times, farms are

destroyed, roads are blocked and commercial activities are affected.

Within the Voltaian System, and along the main landslide potential areas, there have been

reported rockfalls on the Kwawu scarp. The fall occurred in 1991, and the process seems

to be progressive ...

The map also shows that there have been landslide occurrences in the Togo Series (and

the Buem Formation) in the South-Eastern part of the country. This covers areas such as

Honuta, near Kpedze in the Volta Region. Here, quartzites and phyllites covered the road

and affected settlements sometime in 1994 (Ghartey, 1994)

The areas underlain by the Birimian System are the most developed and populated.Landslide events have not been prominent so as to cause any havoc; a few slope failures

have however been reported in surface mines Generally landslides in the Birimian


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Landslide hazard maps should be revised every five years. This should be part

of a wider NADMO program for hazard mapping in the country.

The landslide hazard mapping should be part of a wider program

encompassing landslide vulnerability and risk assessment.

There should be effective collaboration between and amongst the relevant

Organisations/Institutions for proper documentation on landslides. These may

include the Ghana Geological Survey, the Building and Road Research

Institute(BRRI),The Universities, the Ghana Institution of Engineers, the

Ghana Institution of Geoscientists, the Environmental Protection Agency, the

Council for Scientific and Industrial Research,(CSIR), the Ministry of Water

Resources, Works and Housing, the Town and Country Planning department,

the asse4mblies(District, Municipal, Metropolitan).

References

Anon- Natural Hazard Mapping And Vulnerability Assessment-Landslides

Carribean Disaster Mitigation Project for the USAID Office Of Foreign Disaster

Assistance And The Carribean Regional Program.

Anon- 2003 :Landslides Disaster Reduction through Landslide Hazard Zonation

Mapping.


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Kesse, G.O. 1085: Mineral and Rock Resources of

Ghana.

A.A. BALKEMAIROTTERDAMIBOSTON

Muff R, Okla R, Anokwa Y.M, Brakohiapa E,Brown R,Edifor D.R, Efa E,Abel Th,

Leydecker G; 2006: Geoinformation for Land Use Planning and Urban development in

the Greater Accra Metropolitan Area with Schematic Map of suggested Land Use

1: 100,000 and Geohazard Map 1: 100,000: Ghana- Germany Technical Cooperation

Project; Environmental and Engineering Geology for Urban Planning in the Accra-Tema

Area.

Ofori, H.; 1971: Soil Erosion Hazard Map of Ghana; CSIR, Kamasi, Ghana


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3.0 Coastal Erosion

3.1 Introduction

3.2 Occurrences and Causes of Coastal

Erosion in Ghana

3.2.1 Occurrences

3.2.2 Causes

3.3 Geology

3.4 Seismicity

3.5 Objectives and Methodology

3.6 Map Preparation

3.7 Results and Discussions

3.8 Conclusion

3.9 RecommendationReferences


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3.0 Coastal Erosion

3.1 Introduction

The coastal zone of Ghana occupies less than 7% of the total land area but is home to

about 25% of the population. (Armah, A. K; Amlalo, D. S, 1997). This apparently

severe stress has resulted in problems such as fisheries degradation,poor sanitation,

wetland degradation, coastal erosion, industrial pollution,poor land use planning and

development. Under the Large Marine Ecosystem Project of the Gulf of Guinea (1997)

an action plan was developed to critically look at these problem areas. With regard to

coastal erosion, twenty five spots or communities were identified along the entire

Ghana coast line with various degrees of coastal erosion hazard; that is measured as

low, mild, moderate, high and very high.

The present work involved data gathering, field visits to all these identified hot-spots

and other spots, reappraisal of the situation and preparing a coastal erosion hazard map

or improving on the existing one. The idea was to examine the erosion problems with

regard to the causes, geology, human settlements and human activities. Causes of


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Evidently coastal erosion in Ghana is a persistent problem. In many instances the

communities are worried. However, the negative socio-economic consequences, the level

of severity of the problem and the attempts either made or being made for its mitigation

on communityby communitybasis vary considerably. Some of these havebeen

discussed in the report.

The hazard map, and for that matter the report, has been prepared in a way as to be of

great help in the overall management of the coastal beaches.

3.2 Occurrences and Causes of Coastal Erosion in Ghana.

3.2.1 Occurrences

Manyplaces or spots along the beaches of Ghana experience some degree of coastal

erosion at various times. In all, over twenty five spots have been located with varying

degrees of coastal erosion. These include, from the west to the east coast, Half-Asini,

Bakanta, Axim, Princess Town, Aketekyi, Dixcove, Adjua, Shama, Komenda, Elmina,

Senya Bereku, Langma, Old Ningo, Anyamame, Azizanya, Dzita, Keta, Horvi, Brekusu,

Adina, Adafianu, Hevienu and Aflao. Some of these places are shown on the hazard

map(Fig A3.2). Many of the areas have been known to be experiencing serious erosion


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3.2.2 Causes

Causes of coastal erosion for some of the identified spots have been given in appendix

C3 .1. However the general causes of coastal erosion in Ghana which are both natural

and anthropogenic (man made) have been summarized as below.

Natural Causes:

These include:

Global sea level rise and tidal waves

Geology: Rock type, faulting and possible subsidence. For instance,

Akpati(1978) reports that the Keta basin is a graben that is modified by

basement faulting.

Severe storm surges which occur normally during the beginning and end of the

dry season

Anthropogenic Causes:

Poor siting and design of maritime structures

Harbour construction: an example is the erosion caused at Tema New Town as


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The Amisian Formation: This outcrops at a number of places along the coast

near the mouth of River Amisa between Saltpond and Winneba and are made up

of a series of interbedded, soft, pebbly grits, conglomerates, micaceous

sandstones, arkose and greenish grey clay.

The Sekodian Series: Consists mainly of sandstones and shales with

conglomerates,pebble beds, grits and mud stone resting with major unconformity

on a complex of granites, gneisses and schists. They occur in several disconnected

outcrops along the coast between Cape Coast and the mouth of the Butre river

near Dixcove.

The Appolonian (Tano Basin) Formation: It is made up of Cretaceous - Eocene

marine sedimentary rocks which occur at the southwest comer of Ghana and

consists of alternating sands, clays and limestone.

The Tertiary to Recent deposits: These deposits consist of river, marine, and lacustrine

gravels, sands and clays, laterite, bauxite and surface ironstone.


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FigA3.1 Map of Ghana showing the Shield Area, The Mobile Belt, The Voltaian

Platform, The Coastal Basins, and Tertiary to Recent Deposits (After Kesse, 1985)

C

oast

al

basi

n,

Terti

ary

to

rece

nt

dep

osits

_

Mobi

le

belt-

Sout

h

east

ernunit

S

h

i

e

l

d

a

r

e

a

-

I

J

U


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3.6 Map Preparation

Some of the spots visited including those already identified (Armah, A. K; Amlalo, D.

S;

1998) were indicated on a digitized map of southern Ghana showing some regions and

all

the districts along the coast. The spots were classified in terms of severity of coastal

erosion as low, low to moderate, moderate, high and very high.

FigA3.2 Coastal Erosion

Hazard Map


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r:

N

W*E

GHANA COASTAL EROSION - HAZARD MAP

0

ID;E!.gb~ 1fJJ,:.

1. C - r

l

.

x

' s t~~ ;.~e,pl'er A~

Jc m o tc \ ~\j ~~""

/ '\ ,'"'"~ ~ ~ nzm a I Accra, ' "'

, '. ""_"" " a ~ ~


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3.7 Results and Discussion

The coastal erosion hazard map shows the spots that are being affected by coastal erosion

and the relative severity. Generally, the severity is more to the east coast from Ningo to

Aflao than to the west coast.

The reasons are varied but typical to specific segments and may include:

The geology of the area, (e.g. Ningo where the coastline is made of recent, loose

and unconsolidated sediments)

Removal of the hydraulic groyne effect and littoral current that wash away loose

sands (e.g. Ada Foah)

Combination of wave action and geology (e.g. Keta).

Some of these cases have been given in appendixC3.1

However there are areas on the west coast such as Shama, Axim and Dixcove which are

of moderate to high in severity.

In some of the beaches, for example Axim, Dixcove, Langma (Kokrobite), human

habitats are very close to the shore line and this makes the coastal erosion situation more

serious. At some places (e.g. Kokrobite), individuals are,out of desperation, using boulder

rocks as defence structures to protect their individual properties; this is not properly doneapparently because of the high cost involved.

I h W k b A i d H i B k l d i b i l


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In rocky beach areas such as Dixcove, Adjua, Elmina, Senya Breku, Tantum (Otuam) and

others, the heights of the waves can increase due to bending or refraction of the

wavefront. As the wave height increases, the wave energy (this is approximately

proportional to the square of the wave height) expenditure at the shoreline also increases.

This obviously increases the effect of erosion in the areas.

The Keta sea defence wall and the groins have been recently constructed. These have

virtually curtailed the hitherto very high coastal erosion which for years have taken over

about 2 - 5 km of land (built environment).Unfortunately since the completion of the

Keta sea defence, the community from Horvi to Brekusu immediately after Keta along

the east coast has been experiencing unprecedented high rate of erosion. It is also on

record that sea erosion being experienced at Prampram is as a result of the "end effects"

of the breakwaters of the Tema Harbour. These examples suggest that the practicewhereby the beach is protected or developed on community by community basis may not

be the best since it could affect the sediment budget of the adjoining beaches or areas.

Erosion normally occurs whenever more sediment is transported out of a particular area

(or littoral cell) than is delivered to that site.

Unfortunately, the causes of coastal erosion in Ghana, the sediment budget, the wave

climate, the coastal geology and seismotectonics of the beaches and the coast are not very

well researched into These have to be known in details for proper remedial actions and


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This requires systematic studies (research) of the coast including the geology, sediment

deposition, wave action and global sea level rise. The problems can then be understood

better and appropriate and lasting measures taken.

Apart from building sea defences, damages from coastal erosion can be prevented by

showing setback distances which must be evaluated on a case by case basis for each

object of development. It is anticipated that this map will serve as a guide for developers

and planners; and also as a first step to more coordinated studies in coastal erosion in

Ghana.

In almost all the coastal communities the common belief is that the high tides or strong

destructive waves come only when the sea is disturbed; that is when somebody dies in

the

sea. This belief seriously affects their understanding of the problem and their regard for

defence structures.

3.8 Conclusion

Coastal erosion in Ghana is common along the entire shoreline of Ghana and it can be

very severe at some places especially at the east coast. Unfortunately, measures taken to

address these issues are done in piecemeal or on community by community basis. Since


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Spots such as Axim, Azizanya and Brekusu should be critically examined,

evaluated and remedial action taken on time. Areas such us Komenda and Senya

Breku where wave action impedes fishing activities should be conceded as

special cases.

Holistic approach to the coastal erosion problem should be adopted and

encouraged. The entire coastline of Ghana should be divided into littoral cells or

segments for a better understanding of the problems and solutions.

A historic database I record on the coast should be built.

Since it is not practical for public funds to be spent to restore or protect

uninhabited beaches, individuals or developers should be discouraged by

legislation from building along such hazardous beaches. Where it becomes

necessary setback distances should be set.

The Assemblies (District, Municipal, and Metropolitan) should ensure, by

enforceable legislation that human activities such as sand mining are curtailed.

The communities should be educated on the scientific reasons why there are tidal

waves, coastal erosion and the remedial measures that are to be taken.

References:


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Kesse, G. 0; 1985: The Rock And Mineral Resources Of Ghana.

A.A BALKEMAJROTTERDAMIBOSTON

Muff,R. et a12006: Geoinformation for Land Use Planning, and Urban Development in

Greater Accra Metropolitan Area with Schematic Map of suggested Land

Usel : 1 00,000. Ghana-Gerrnany Technical Cooperation Project. Environmental and

Engineering Geology for Urban Planning in the Accra- Tema Area.

Appendix A3.1 Some Coastal erosion hotpots, their locations, type of

erosion/problem(s)

SECTION OF LOCATION TYPE OF EROSIONIPROBLEM

COASTLINE LONG. LAT.

A. Western Region

1. Axim 2 16' W 4 53' N 1. The sea has penetrated the rocky coast

and formed a cove in the softer material

in the centre of the Axim town.


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4. Adjua

5. Amanful Kuma

6. Funko

7. Nkotonopo &

Essaman

8. Essipong

1 48' W 4 52'N4.

4 52' N

1 47' W 4 52' N

1 42' W 4 59' N

1 42' W 4 59' N

. 4. The sandy beaches are being eroded by the

headland.

5a. The sandy beaches are being eroded by

the headland

5b. The erosion problem are been heightened

by the winning of sand on commercial

basis on the beaches

6. The sandy beaches are being eroded by

heavy waves reaching this coast. The

problem has been exacerbated by the

wmmng of sand on the beaches for

building purposes

7. This coastline lies on the leeward side ofthe Takoradi harbour and as a result

suffering from the 'end effect' of the

breakwaters of the harbour. The problem

has been worsened by the winning of

sand and shingle on beaches for building

purposes.

8. This beach used to be a very wide sandy


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SECTION OF

COASTLINE

B. Central Region

11. Elmina

LOCATION

LONG. LAT.

54' N

caused by the headland immediately on

the west of the Town.

TYPE OF EROSIONIPROBLEM

11.There is an acute erosion problem

between the Castle and the Motel. The

problem is caused by the headland on

which the Castle is located. There isalso an observed erosion problem due

to shoaling at the mouth of the Elmina

Fishing Harbour. This may be due to

the complex hydronamic changes

imposed on the entrance to the lagoon

by the building of the breakwater. Sea

defence measures are in progress.


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15 . Jamestown

16. Rivera Beach(Mensah gunea

0 13' W 5 33 N

0 10' W 5 33 N

currents of the Densu River which

debauches immediate east of Bortianor.

With the building of the Weija Dam, this

process stopped nd littoral currents and

the refractive action of the waves by the

headland, on which Ama Hotel sands,

took over and wiped out the sands.

15. This beach came under serious threat of

erOSIOn after the construction of the

Korle Lagoon outfall. A revetment and a

groyne filed has now been put in place to

contain the erosion. These measures

have proved so effective that, the

accreted sands are threatening to block

the mouth of the lagoon.

16. The coastline extending from Mensah

Guinea to the Osu Castle is under serious

threat of erosion. This problem is partly


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18. Teshie (Acapulco

beach)

19. Nungua (Regional

Maritime Academy

0 8' W 5 35 N

0 8'W 5 35'N

of the mouth of the Kpeshie lagoon by a sand

bar, the erosion problem set in. This coast has

now been successfully protected with a

gabion revetment.

18. The coastline in front of the Acapulco

beach resort has suffered severe sea erosion.

This problem has been caused by extraction of

rock, shingle and sand from the adjacent

beaches. With the exposure of outcrops,

refraction of the seas waves has worsened the

erosion problem. This is now being protected

with a rubble mound revetment.

19. The stretch of coastline m front of

Regional Maritime Academy IS

undergoing serious erosion. This stretch

of land which used to be a promontory

has now been reduced to a cove by the


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2. The stretch of beach from the Tema

Beach Club to the Harbour

The cause of erosion in the coastline (l)

are the headlands at Nungua and

probably the geology of the sea bottom

and bathymetry. The cause of erosion in

the case of coastline (2) are the rocky

outcrops exposed to sea waves at Tema

Beach Club. These rocks reflect as well

as refract waves to produce more

powerful and destructive waves to cause

serious erosion on the beach east of the

Tema Harbour where accretion should

naturally be expected. A close study of

the problem reveals that the activities of

sand winners on this beach caused the

exposure of the outcrops and set the stage

for the erosion of the beach.

Prapram which is only 16 km from Tema is experiencing


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23. Ada-Foah

D. Volta Region

24. Dzita

S048'N

0 47'E SO 4S'N

of Tema Harbour is being continued

without any resistance in the easterly

direction

23.The Ada-Foah erosion is one of the well

known in the country. It started in the

193 Os, at a very slow rate and

accelerated In the 1970s. At the

moment the rate of erosion is about

4m/yr. This erosion is caused by the

removal of the hydraulic groyne effect

of the flow of the Volta River by a

sand bar. Littoral currents then washed

away the loose sandy materials whichform the beaches.

.24 Dzita is a fishing town IS km from the

mouth of the Volta. The stretch of


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some natural frequently. The Keta town

is located on a sand bar whose geology

makes it too vulnerable to the deep sea

waves that break on beaches. At present,

waves breaking on these beaches appear

to come from the Cape St. Paul, near

Woe. The south -westerly waves are

refracted by the cape in the southerly

direction to interact with the unaffected

in-coming waves that which would have

arrived there without refraction. These energy laden waves

are responsible for the characteristic and

devastating coastal phenomenonalong this coast.


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Appendix A3.2

AXIM :BROKEN SEA DEFENCE WALL

AXIM :BROKEN SEA DEFENCE WALL


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WEKUMAGBE: NEAR ADA


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SECTIONB

HYDROMETEOROLOGICAL


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HYDROMETEOROLOGICAL HAZARD MAPPING IN GHANA

1.0 Introduction

Ghana suffers from the under listed hydrometeorological (hydromet) hazards.

1. Floods

2. Thunderstorms/Windstorms

3. Dam Failures

4. Tidal Waves

5. Drought

6. Desrtification

Among these hazards, floods have proved the most extensive and destructive.

Floods occur frequently due to various factors. River floods are mostly as a result

of rainfall during rainy seasons.

Urban floods on the other hand occur due to a combination of factors, most of

which are man-made, e.g. building in flood basins, choking drain with solid


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In developing countries scarce vital resources are diverted from other

equally important development needs to rescue and relief operations

which may set back their development by as long as a decade.

The current thinking is that with Global Warming, it is possible that the

occurrence of floods will become a phenomenon to contend with more

frequently.

Floods as natural event need not be seen as hazards only. They are part of

a natural hydrological cycle and do have some beneficial effects,

providing much needed water resources for use during non flood periods.

Floods are regarded as natural cleansing mechanisms of the environment.

In developing countries with primarily agricultural economies, flood

plains contribute substantially to food production. Proper flood plains

management could take advantage of floods for sustainable development.


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1.1.1 Floods in Ghana

Records show that flood disasters suffered in Ghana have resulted fromabnormally heavy rainfalls which cause rivers to overflow their banks thus

flooding the flood plains. Urban floods also occur in Ghana as a result of human

activities such as settlements in water courses, chocking of drains with solid waste

and concreting of large areas around settlements.

Of late, the flood incidences in Ghana have shown a certain amount of cyclicity of

9 - 10 years, however this is only statistical.

Project Objectives

The objectives of this report are to prepare:

(i) Hazard Maps for flood prone areas in Ghana

(ii) Vulnerability Maps for the flooded communities in these areas

(iii) Help NADMO prepare Disaster Zonation Maps for Long Term

National Risk Reduction.

2.0 Methodology

(i) With Fig. B.l as a guide the hydromet team visited as many river basins as


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FigB1 Flood Hazard Map Of Ghana

GHANA

FLOOD HAZARD MAP

FLOODPRONERIVERS---ROADS


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3.0 Results and Discussion

3.1 Upper West Region

The Black Volta serves as the natural border between Ghana and La Cote

D'Ivoire on the southern part and Burkina Faso on the northern part. The source

is in the Burkina Faso.

Almost all the flood prone areas in the region lie on the Black Volta (Fig. B2).

Some of the communities visited are:

Lawra

Dikpe

Takpo

Weinchau - The Hyppo Sanctuary

These communities are all farmers. Their farms get flooded and their houses

which are mostly built with mud or laterite are washed away.


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FigB2 Upper West, Upper East and Northern Regions


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3.2 Upper East Region

This Region was visited at the time when the recent floods in September 2007

were at their peak. All the rivers, especially the White Volta, were in floods.

The communities listed below lying between the Red Volta to the west and the

White Volta were flooded (Fig. B2)

Kupeliga

Mognori

Sapeliga

Kunbugu

Teshie

Zebilla

Tonga

Kusanamba

Tinonde

Zongoyivi

The above communities are farmers whose farms and some of their settlements


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Bangi

Yalugu

Bazua

Azum Sapeliga

Sakpari

Nafloliga

These communities, like those on the west of the White Volta, are all farmers.

Their farms get washed away and in some cases part of their settlements are also

affected.

The flooding situation on the White Volta could become aggravated by the

spillage from the Bagri Dam in the Burkina Faso which lies upstream on the

White Volta.

The mainstay of these communities is farming. The socio-economic lives of the

communities become adversely affected as the floods normally wash away their

farms.


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Kulpawn River

A major tributary to the White Volta is the Kulpawn River which flows from the

Upper West and joins it in Northern Region. The road network could not allow

for pursuit.

3.3 Northern Region

3.3.1 The main basin (White Volta) enters the region atNayeri having run along the

boundary between the Upper East and the Northern Regions (Fig B.2). The

following communities were identified in the White Volta basin as flood prone .

:. Kpesenkpe

.:.Nawuni (Tamale Water Works Intake)

.:. Daboya (A large market town)

.:. Lingbisi

.:. Yapei (A port on the Volta Lake)

These areas are subject to flooding as was evidenced during the September 2007

floods; and especially at Nawuni where the inhabitant had to be evacuated from

the intake area on the White Volta.

3.3.2 The Oti Basin


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These communities, apart from Saboba, are mainly itinerant fisherman whose settlements

are virtually on the river banks. As a result of their locations, their settlements get

flooded when the river bursts its banks. The socio-economic activities of these people

are seriously disrupted.

The flood prone areas within the river Oti basin are shown in Fig B2a.


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Fig B2a

N

Flood Prone Areas of the River Oti (Saboba to Sabari)

Ghana - Flood prone areas of the river Oti (Sabari to Saboba)

Cf20'


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3.4 Volta Region

The following four basins were visited in the region. These are the Oti River

basin to the north, Kpasa river basin, the Volta Lake basin and the Todzie river

basin to the extreme south.

3.4.1 The Oti River Basin

This basin enters the region from the northern region at Damanko in the Nkwanta

District (Fig. B3).

Settlements located in the river basin include the following:

~ MolaNo.1

~ Mola No.2

~ Jobosu

~ Obonja

~ Sibi Bator No.1

~ Sibi Bator No.2

~ Mama Akura


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3.4.2 Kpasa River Basin

A relatively smaller river Kpasa also floods its banks during the rains affecting

the following communities.

y" Jombo

y" Azua

y" Kpasa

y" Kofi Kura

These areas are on higher grounds and therefore less vulnerable than the

communities along the Oti basin.

3.4.3 The Volta Lake Basin

The Volta Lake forms a substantial part of the Volta region. Communities which

get flooded during heavy rains include the following:

Tepa Amanya

Tepa Abotoase

Kwami Krom

Kpando Tokor

Avenue


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Fig B3 Flood Prone Areas in Volta, Greater Accra and Eastern RegionsLegend


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3.5 Eastern Region

3.5.1 In the Eastern Region, apart from the area along the Volta Lake, the most affected

flood area is Nsawam in the Densu basin. Some settlements close by the river get

affected during floods (Fig B.3).

The commercial activities of Nsawam town are very seriously disrupted during

this period.

3.5.2 Birim River Basin

Other areas the team visited were along the Birim basin and the flood prone area

includes:

Abodom

Kade

Wenkyi

However, the flooding situation in these areas is relatively lower than that of

Nsawam mentioned above.


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3.6 Central Region

There are in the region, the Ayensu,Nakwa, Arnisa and Kakum river basins

besides the Pra River basin which is considered the most active during floods (Fig

BA). The rest are rather minor and ofless significance.

3.6.1 Pra River Basin

The communities identified along the Pra river are the following, (Fig. B4)

Twifo Breman

Twifo Praso

Brefoyedura

Enyinabirimu

Abetwusu

Sekyere Heman

Daboase

Beposo

ShamaKedzi

These communities are mostly cocoa farmers. Their farms get affected during

i 4 l d A i h C l A h i d i


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Fig B4 Flood Prone Areas in the Central, Western, Ashanti and Western Regions

N


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3.7 Western Region

Two major basins were identified in the Western Region namely the Ankobra and

the Tano River basins (Fig BA).

3.7.1 Ankobra River Basin

On the Ankobra river, the affected communities include:

Apatan

Asanta

Ashien

Enyinase

These people depend mostly on their coconut plantations and farms. Their

settlements which are of thatch are mostly flooded. The Asanta village at the

estuary is awaiting resettlement from the Distirct Assembly.

3.7.2 Tano River Basin

Along the Tano basin to the far west, the towns that are mostly affected by floods

i l d h f ll i


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Urban Flooding

In Ghana, some of the cities such as Accra, Kumasi and Sekondi- Takoradi do experience

urban floods. In the Greater Accra Metropolitan area, flooding in the eastern and western

lowlands is mainly of short duration and is caused by heavy rains in June-July rainy

season.

Major floods which lead to loss of lives and extensive damage and in some cases

prompted international help occurred in the rainy seasons of 1973, 1986, 1995, 1999,

2001 and 2002.

Types of Flooding

The Greater Accra Metropolitan Area is affected by four broad types of flooding:

(i) Out-of-bank river flooding: It occurs after long periods of heavy rains and

inundates large tracts of land for a long time because of low gradients of the

river beds and land surfaces in the coastal plains. Out-of-bank river flooding

occurs predominantly in the areas mapped as Natural Prone Areas. (Fig. B.S)


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(iii) Sheet Flow is a loosely defined term which refers to any form of unconfined

run-off that occurs over broad, expansive area with low relief and a gentle

slope and lack of defined stream channels. Sheet flooding is restricted to the

Eastern lowlands which are underlain by clayish soils.

(iv) When flooding follows immediately or within a short time of thunderstorm,

one speaks of "Flash Flood". Urban flooding and sheet flooding often takes

the form of flash floods. Flash floods have also occurred in the Densu River

below the Weija Dam when the gates were opened to release the pressure on

the dam.

The Geohazard Map (Fig B.5) shows types of flood prone areas. These are:

,. Frequently flooded urban area

R. Natural flood prone areas'. Marshes and swamps

Frequently flooded urban areas become flooded either by degenerated urbanized

rivers,by obstructed drainage systems or by sheet floods caused by impervious

t"-O


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Environment and Engineering Geology Map of Greater Accra Metropolitan Area

Areas of Frequent Flooding 1: 100 000

O.----.

;.SE;RAKU'4E.i"G \.\\

l~rsh.!W lIfTlp

mas 'I'.tllctJ ere water-sa:l;r/l~~ e- ~ M:;f.-~.-~y"' .,!.:.,,.:;>:tmd

because lh9y ar& lo'~.10n~./\~ oc 'i"+>~'''' ''. v;:,< ;'i:'iern,.,

Flood areas

Fnsqventtyfloodedultltlnernas

~lenS(l rainfalls 8Ild tnundcrs:(;'1"'-,S ;'


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Recommendations

~ There should be intensive education to make the communities aware of the

implication of developments in flood prone areas.

Weather Warnings from the Ghana Meteorological Agency should be more

seriously utilized by communities so as to be able to mitigate effects of floods.

Regular monitoring of rainfall in the catchment areas should be carried for the

building of a database for forecasting flood.

There should be enforceable laws by the Assemblies to regulate building in flood

prone areas.

The Bagri Dam in Burkina Faso could be used as an Early Warning for floods in


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References

Annon, WMO Annual Report No.1000 2005

Annon, WMO Bulletin Volume 55 (1) January 2006

Annon, WMO Bulletin Volume 55 (3) July 2006

Annon, Emergency Preparedness Plans for Water Supply Dams

The Norplan - Royal Haskoning - ABP

Annon, 1995 Geopeference Database for all African Countries.

World Resource Institute; World Conservation Monitoring Centre;PABCO

Incorporated Digital Mapping

Robinson Projection Grid; 1: 1 ,000,000

Aboagye M.A. (2005) - NADMO Workshop on Floods Management and Industrial

Accidents 2005


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SECTION C

FIRE HAZARDS


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TABLE OF CONTENTS

Introduction

Data collection

Results for Northern Region

Results for Upper East Region

Results for Brong Ahafo Region

Results for Upper West Region

Results for Eastern Region

Conclusion and Recommendations


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Introduction

The UNDP in collaboration with NADMO are conducting a survey to assess the bushfire

and lightning situation in Ghana. This assessment is being carried out to produce

geographical information on the four major hazards i.e. geological, hydrometeorological,

Pest and insects infestation bushfires and lightning. The objectives of this assessment are

to support;

NADMO to prepare a long term National Risk Reduction Policy and Programme

The development of a system of hazard reporting and early warning

The strengthening of the institutional structures in the country

In view of this objective, a team of three (3) led by Mr. Albert Brown Gaisie

(consultant), undertook the above exercise for bushfires and lightning in Brong Ahafo,

Upper West, Upper East, Eastern Ashanti and Northern Regions. However work done in

the Ashanti Region was not completed within the time limit and is therefore not reported

here.

Methodology

Questionnaire administration was carried out in twelve (12) districts in the Ashanti


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Data available at the Ghana National Fire Service (GNFS) collected over five (5) years

(2002 - 2007) in the regions covered were added to the results from the questionnaire for

the analyses. A Program known as 'Statistical Package for Social Scientists' was used in

the analysis of the data collected based on the number of respondents in each region. The

information presented covers the District analysis of fire prone areas within selectedregions of the country namely, Upper West, Upper East, Northern region, Brong Ahafo

region, Ashanti and Eastern regions respectively. The results of the analyses of the data

were used to prepare bushfire hazard maps for the regions covered.


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Results for Northern Region

In all there were 38 respondents covering eleven districts in the Northern Region (Table

C.1, Fig C.1). Yendi,Nanumba North and Saboba/Chereponi Districts recorded the

highest number of bush fires per year, followed by ZabzuguiTatale, Central Gonja and

Walewale. The district with the least number of bush fires per year is Tamale Metro. (Fig

C. 7 Table C. 7).

Twenty-five (25) percent of the respondents agreed that bush burning is the greatest

environmental problem in the region (Table C.2, Fig C.2). However, as much as 36.8%could not recollect the number of fire outbreaks experienced in the five year period

studied while 23.7% said there were over 39 fire outbreaks (Table C. 3,

Documents

Hazard Maping in Ghana222