 |
Environment
and development in coastal regions and in small islands |
 |
|
Environment
and development in coastal regions and in small islands |
|
 |
Coastal region and small island papers 12: papers
FLOOD
MITIGATION IN LAGOS NIGERIA THROUGH THE WISE MANAGEMENT OF SOLID WASTE: THE CASE
OF IKOYI AND VICTORIA ISLANDS
Nigerian Institute for Oceanography and Marine Research
P.M.B. 12729 Victoria Island, Lagos, Nigeria
Introduction
Victoria and Ikoyi Islands constitute the two main barrier island complexes in Lagos State. The islands are made up of residential, commercial and tourist facilities and are surrounded by the Lagos Lagoon and the Atlantic Ocean. The islands usually experience 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 Disaster Reduction Programme, the Coastal Regions and Small Islands (CSI) platform of the United Nations Educational, Scientific and Cultural Organization (UNESCO) funded 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 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 give recommendations to government;
organising a public enlightenment campaign through media and 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 from 1992 to 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 flooding, refuse disposal and drainage channel
patterns from local residents along flood prone areas. The answers to the
questionnaire 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 of the case study was prepared entitled ‘Study of main drainage channels of Victoria and Ikoyi Islands in Lagos, Nigeria and their response to tidal and sea level changes’. The report showed that flooding of Victoria and Ikoyi Islands predominantly occurs during the rainy season May to October. Flooding is more serious when rains or storm surges coincide with high tides.
Analysis of the eight major drainage channels levelling records revealed several problems namely:
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 6th 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 recommendations, including rerouting, repairing, fencing and screening of several channels; construction of new channels; increasing beach height; and a public awareness campaign to discourage dumping of solid refuse in the drainage channels.
Flood mitigation: wise practices
Working with CSI, flood mitigation measures were categorised into two groups: engineering and social. The engineering solution 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 awareness creation, environmental education and behavioural modification to encourage good waste disposal practices. The ‘wise practices’ social solution was implemented by NIOMR, UNESCO and Clean-up Nigeria, a non-governmental organisation. This consisted of public enlightenment campaigns to educate local residents on the adverse effects of dumping their wastes in drainage channels in the belief that the storm waters will transport the wastes to the lagoon. Residents, government officials, print and electronic media took part in the public enlightenment, which targeted at least 50% of the population of Lagos. Posters, handbills, brochures, street theatres and meetings with relevant stakeholders were organised. Market women, the taxicab operators association, residents and all groups of citizens whose activities impact on flooding in Lagos were also involved. This was reinforced with electronic media jingles and media chats. These activities are still on going and constitute a part of the wise coastal practices.
Conclusion
Recommended long-term wise practices included rehabilitation of drainage channels. This should include the development of a comprehensive master plan for the rehabilitation of the drainage system in Victoria and Ikoyi Islands. A project proposal for external funding will be developed in collaboration with the Ministry of Environment and Physical Planning of Lagos State, the Nigerian Institute for Oceanography and Marine Research, and CSI.
While awaiting the preparation and implementation of a comprehensive drainage rehabilitation plan, certain critical ‘wise practices’ will continue to be targeted, in particular the reduction of garbage disposal in the drainage channels.
Acknowledgements
The authors of this paper are grateful to UNESCO-CSI and the UNESCO Office in Nigeria – Abuja for the financial and moral support. The assistance and cooperation of Lagos State Ministry of Environment, all media houses and Clean-up Nigeria is also hereby acknowledged.
