Real Risk

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directly to, and discussed with, national authorities, and will be

used to guide technical plans and support national and regional

strategies for disaster preparedness. But since such risks exist in

all ocean basins to varying degrees, UNESCO is promoting the

establishment of tsunami early warning systems not only in the

Indian Ocean but also in the Caribbean, the Mediterranean and

the North East Atlantic, and for their reinforcement in the South

West Pacific and the South China Sea.

Flood mitigation in Lagos, Nigeria: the case of Ikoyi and

Victoria islands

Victoria and Ikoyi islands constitute the two main barrier island

complexes in Lagos State. The islands are made up of residen-

tial, commercial and tourist facilities and are surrounded by the

Lagos Lagoon and the Atlantic Ocean. The islands usually expe-

rience annual flooding during the rainy months, May to October.

Even though the islands have a network of drainage channels

consisting of both ancillary and main channels with outfalls to the

Lagos Lagoon, flooding hazards are worsened when heavy rains

or storm surges coincide with high tides. When this happens,

large areas of the islands are flooded, causing a disruption of

socio-economic activities on the islands with concomitant adverse

effects on the economy of Lagos State and the entire nation of

Nigeria.

As a contribution to the UNESCO Disaster Reduction

Programme, the Coastal Regions and Small Islands (CSI) plat-

form of UNESCO supported a project to study the drainage

channels in Victoria and Ikoyi islands, Lagos, Nigeria. This was

followed by a public enlightenment programme.

Aim of the study

– The study examined the causes of flooding

in Victoria and Ikoyi islands and the implications of tidal and sea

level changes, and anthropogenic activities. The study also

focused on the effectiveness of the main drainage channels built

to discharge runoff into the Lagos Lagoon.

Activities

– The study, which was carried out by the Nigerian

Institute for Oceanography and Marine Research (NIOMR)

between July 1998 and September 2000, examined the efficiency

of the main drainage channels in the face of tidal and sea level rise

and other anthropogenic activities by:

• Surveying eight main drainage channels to estimate their

capacity to discharge storm waters to the lagoon

• Analysing historical tide gauge data to determine sea level

rise variations

• Conducting a bathymetric survey of the outfalls of the

drainage channels

• Collecting and analysing meteorological data and storm surge

data

• Determining the efficiency of the present channels and giving

recommendations to government

• Organizing a public enlightenment campaign through the

media and a public forum.

Data collection and analysis

– Data used in this study comprised

primary water level, wind parameters and barometric pressure

records from the Next Generation Water Level Measuring System

(NGWLMS) acoustic tide gauge between 1992 and 1996; daily

rainfall data for Lagos from 1980 to 1998; and public opinion

sampling through the use of a questionnaire.

Statistical analysis of rainfall data, primary water level, wind

parameters and barometric pressure records from the NGWLMS

was carried out. Topographic levelling of the eight selected main

drainage channels was done to determine their gradient from the

head to their outfalls. During this levelling, particular attention

was paid to the state of the channels, namely deposits of solid

waste, sediment and other physical obstructions.

A questionnaire was used to collect information about flood-

ing, refuse disposal, and drainage channel patterns from local

residents in flood-prone areas. The answers were statistically

analysed and used to determine residents’ opinions on the

problem of flooding. In addition, an awareness campaign was

conducted using a public forum and the media to inform the

public about the results of the study.

Results

– A report on the case study detailed several problems

that had been identified through analysis of levelling records for

the eight major drainage channels:

• Clogging of the drainage channels by domestic waste and

blocking of some channels by buildings

• Low gradient of the channels and variable channel width

from head to outfall

• Collapsed drainage channel walls

• Reverse gradients in most channels such that, when heavy

rains coincide with high tides, tidal waters flow back into the

channels through the outlets causing excessive flooding.

Analysis of the questionnaire showed that few people were well

prepared to tackle the problems; that the drainage channels were

ineffective because they were either blocked by sand or refuse;

and that refuse containers are inadequate, leading to dumping of

refuse in the drainage canals by residents.

A successful media and public forum was conducted on 6 June

2000. More than 200 participants attended, representing several

government agencies, print media, radio and television stations.

The report, which was submitted to the Lagos State Ministry

of Environment and Physical Planning, made several recom-

mendations, including the rerouting, repairing, fencing and

screening of several channels; construction of new channels;

increasing beach height; and a public awareness campaign to

discourage the dumping of solid refuse in drainage channels.

Flood mitigation: wise practices

Working with CSI, flood mitigation measures were categorized

into two groups: engineering and social. The engineering solu-

tion may require rerouting, fencing and screening of several

channels; construction of new channels; increasing beach height;

and removing solid waste and structures erected on the channels.

These may not represent all available engineering options, as there

is a need for further studies.

The social solution requires a determined effort towards aware-

ness creation, environmental education and behavioural

modification to encourage good waste disposal practices. The

‘wise practices’ social solution was implemented by NIOMR,

UNESCO and the Clean-up Nigeria NGO. This consisted of

public enlightenment campaigns to educate local residents on

the adverse effects of dumping their waste in drainage channels

in the belief that storm waters will transport it to the lagoon.

Residents, government officials, print and electronic media took

part in the public enlightenment effort, which targeted at least

50 per cent of the population of Lagos. Posters, handbills,

brochures, street theatres and meetings with relevant stakehold-

ers were organized. Market women, the taxicab operators’

association, residents and all groups of citizens whose activities

impact flooding in Lagos were also involved. This was reinforced

with electronic media jingles and media chats. The activities are

still ongoing, and constitute a part of the wise coastal practices.