EU EDF 8 – SOPAC Project Report No ER0095:
Reducing Vulnerability of Pacific ACP States
SUMMARY REPORT: Integrated Flood Management, Apia, Samoa
SOPAC Secretariat
SOUTH PACIFIC APPLIED GEOSCIENCE COMMISSION
c/o SOPAC Secretariat
Private Mail Bag
Flooding in Apia 2006
SOPAC Secretariat
SOUTH PACIFIC APPLIED GEOSCIENCE COMMISSION
c/o SOPAC Secretariat
Private Mail Bag
GPO, Suva
FIJI ISLANDS
http://www.sopac.org
Phone: +679 338 1377
Fax: +679 337 0040
www.sopac.org
director@sopac.org
Important Notice
This report has been produced with the financial assistance of the European Community; however,
the views expressed herein must never be taken to reflect the official opinion of the European
Community.
BACKGROUND
The South Pacific Applied Geoscience Commission (SOPAC) is currently implementing an EUfunded project Reducing Vulnerability of Pacific ACP States.
The goal of the Project is to address vulnerability reduction in the Pacific ACP States through the
development of an integrated planning and management system, Island Systems Management.
The objective is to strengthen integrated development by concentrating on three key focal areas in
the island system: Sustainable coastal zones including the identification of alternative aggregate
sources to that of beach mining and coral shore extraction; Improved planning practices installed
for safe water and sanitation; and Implementation of comprehensive hazard risk management
tools. The Project is addressing problems such as: unavailability of accurate and timely data; weak
human resource base; limited resources (money and infrastructure); and lack of appropriate
management plans, policies and regulatory frameworks to deal with these three focal areas.
With respect to the Hazard and Risk component of the Project, the Government of Samoa during
the stakeholder consultations had requested an assessment of the river flooding and erosion
problems of Apia [WS 3.5.4].
INTRODUCTION
River flooding, especially flash floods, are a serious and frequent problem in Samoa and in
particular Apia where steep catchments with rapid flood onsets are subject to frequent heavy
rainfall events. The April 2001 flood event inundated large parts of Apia urban area within a
negligible time lag from the beginning of the intense rainfall. The surrounding watersheds
responded to the flash floods with combined overbank/overland flow. Approximately 5,000 local
residents were directly affected by the flood and resulting damages were estimated in excess of
WST$ 11 million. Such events are not rare for Samoa.
The Vaisigano catchment was selected for the study due to its impacts on Apia during flood
events. It is also the best-monitored watershed in Samoa with discharge records available between
1973 and 1990 and precipitation records from several locations on Upolu with two records dating
back some 100 years.
In addressing flood risk management, previous studies have concluded that technical mitigation
measures such as channel or detention basins are only be of local and thus limited effect. As the
development described above is mainly caused by urban extension activity only considerate flood
plain management strategies and urban development planning strategies adapted to flood
drainage are sustainable and therefore of high importance for the future protection of Apia, the
principal centre of population, administration and commercial activity in Samoa.
0 km
30 km
Samoa
Vaisigano
River catchment
Savai’i
Apia
Pacific Ocean
Upolu
Apia
Harbour
0 km
Vaisigano
catchment
boundary
5 km
Figure 1 Location of Vaisigano River in Apia, Samoa
GOAL
The overall goal of the study is to reduce flood risks for urban Apia by enhancing flood risk
management capacity within Samoa.
PROCESS
To address the goal the Project first focussed on the capacity needs of the Meteorological Division
Water Resources Division and the Planning and Urban Management Agency (PUMA) in
understanding flood hazards of Apia urban area by identifying areas prone to flooding and
quantification of flood hazard, extent and intensity. The training and ensuing modelling and
mapping served as guides for improved urban planning and floodplain management.
The process taken by the Project
is depicted
below
(Figure
Process
to Reduce
Flood
Risk in2).
Samoa
Capacity building
and information development
and management
flood hydrology
river modelling
flood plain mapping
Flood Plain Guidelines and
Action Plan
policy review
consultation
mitigation
options
Cost Benefit Analysis
of flood plain mitigation
options
Figure 2 Steps undertaken by Project to address Flood Risk in Samoa
Interventions
In meeting the goal of the study the following missions were carried out:
Phase 1:
Phase 2:
Phase 3:
Phase 4
Activity
Dates
Training in data capture and 25 April - 01 May 2006
topographic river survey
Training in flood hydrology, 12 July - 03 August 2006
flood modeling and flood plain
mapping
Calibration of hydraulic model 31 October - 02 December
and production of inundation 2006
and flood hazard maps,
Development
of
Flood
Guidelines and Action Plan
Presentation
of
Draft 15 – 30 March 2007
Guidelines and Action Plan,
Socie-economic survey for
Benefit-Cost Analysis
Michael Bonte- Grapentin
Shane Cronin
Darren Lumbroso
Michael Bonte- Grapentin
Litea Biukoto
Alena Lewadrau
Darren Lumbroso
Netatua Pelesikoti
Litea Biukoto
Alena Lewadrau
Allison Woodruff
Netatua Pelesikoti
Michael Bonte-Grapentin
The activities that the Project undertook to address the goals of the study included:
Capacity Building in Flood Risk Assessment and Management
A rainfall/runoff model for Vaisigano watershed was developed based on hydro-meteorological
records and historical evidence. Using this storm water hydrographs were calculated at distinct
points along the main river channel, design events were defined, inundation areas assessed and
flood hazard maps produced. Possible structural mitigation options were also modelled to
determine potential impacts on flood height.
Documentation was also produced on the model including the adaptation, validation procedures
and design events used.
Floodplain Management Guidelines
The Guidelines were defined in consultation with Samoan stakeholders to determine acceptable
design events based on potential damage categories and severity with respect to local vulnerability
(social and financial), land-use, infrastructure and available disaster relief action.
The objectives of the Guidelines are to:
 Assist the (PUMA) in its planning and development assessment as prescribed by the 2004
Planning and Urban Management Act Part III, Section 8 and Part IV.
 Promote awareness and provide information for developers on the requirements of the
development consents process for development proposed for floodplains.
 provide useful resource and advisory to responsible authority (PUMA) as provided for under
Section 46 of the 2004 PUM Act and, authorities enforcing building codes, building and
maintenance of public infrastructures, utilities, drainage systems and emergency agencies
to coordinate their relevant and ‘connected’ activities in various aspects of the floodplain to
reduce flood risks and associated flood costs.
Flood Risk Management Plan
The Action Plan includes proposed flood mitigation strategies and measures (structural/nonstructural) based on the flood hazard mapping carried out. The framework was developed in
partnership with Samoan stakeholders outlining future activities, priorities and institutional
requirements for effective flood risk management
The overall goal of the Action Plan is to reduce social, economic and environmental impacts of
floods on the people of Apia thereby facilitating the achievement of national development goals.
The objectives of the Plan are to:
 Identify and map the flood hazard within the lower Vaisigano River catchment
 Identify flood risk management options and indicate how these may be assessed in more
detail
 Strengthen a nationally coordinated flood forecasting and warning systems
 Support public outreach and educations activities to improve awareness of flood risk and
hazard and promote recommended preparedness actions communities can take to reduce
risks to themselves and to others
 Manage activities in floodplains in a manner compatible with multiple and competing uses,
including existing and proposed urban development within Apia.
 Strengthen capacity of the Ministry of Natural Resources and Environment, in particular
Water Resources Division, PUMA, Meteorology Division and DMO and other relevant
agencies to provide consistency in flood risk management
 Incorporate flood risk management in the national planning and budgetary processes
 Update the Action Plan regularly and employ adaptive management strategies in order to
take full advantage of scientific and technological advances, and to use the best available
floodplain management practices, principles and information
Economic analysis of flood risk reduction measures for the lower Vaisigano catchment area
The economic study assessed the priority structural and non-structural measures identified by
stakeholders during a consultation meeting held with SOPAC in March 2007. These include the
construction of floodwalls, the construction on a by-pass channel, improvement of the current flood
forecasting system and strengthened development control by requiring houses built in the
floodplain to have raised floors.
The study concludes that significant future savings can be achieved by investing in flood
management measures. Savings, in terms of avoided flood damages, can be realized through an
improved flood forecasting system accompanied by an improved flood warning system. The most
effective measure, in terms of reducing flood damages, according to the study is building new
homes located in the floodplain with raised flood heights. The study also considered the costs and
benefits of investing in large-scale flood management projects such as floodwalls along the banks
of the lower Vaisigano and the construction of a by-pass channel. However these measures were
found not to be economically feasible due to the high construction and maintenance costs involved.
Reports produced
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Lumbroso D., Titimaea, A., Penaia, A., and Bonte-Grapentin, M. (2006) Technical Report:
Capacity Building in Flood Risk Management. ER 0069a
Lumbroso D., Titimaea, A., Penaia, A., and Bonte-Grapentin, M. (2006) Training Report:
Capacity Building in Flood Risk Management.. ER0069b
Pelesikoti, N, Bonte-Grapentin, M; Biukoto, L. (2007) Samoa Flood Management Action Plan
2007-2012. Draft for consideration of GoS
Pelesikoti, N, Bonte-Grapentin, M; Biukoto, L. (2007) Samoa Floodplain Management: A
Guideline for Planning and Development Assessment. Draft for consideration of GoS
Woodruff, A. Economic Analysis of Flood Risk Reduction Measures for the Lower Vaisigano
Catchment Area. Draft for consideration of GoS