SAMOA FLOOD MANAGEMENT ACTION PLAN 2007-2012 - Pacific ...

3. Flood mitigation measures3.1. IntroductionThere is a wide range of possible measures for managing floods. These cover suchitems as structural measures which generally involve some type of construction (forexample, flood defence embankments and walls) and non-structural measures suchas flood warning, land use planning, development control and building control.This chapter details the various floodplain mitigation measures considered, inparticular for the lower Vaisigano River catchment including their advantages andpotential disadvantages. The actions required to investigate the various mitigationmeasures in more detail are also outlined.Structural measures considered include:o Flood walls and embankments.o Upstream flood storage.o The use of a by-pass channel.o Increasing the channel conveyance.o Improving the channel maintenance.o Pumping.o Flood proofing of new and existing buildings and other assets.Non-structural measures considered include:o Development control, which includes the avoidance of developments onfloodplains or the protection of new developments.o Flood forecasting and warning.o Floodplain zoning, to link land use with the flooding function of different parts ofthe floodplain.o Flood insurance.o Raising the awareness of flood risk and preparedness of individuals andorganisations to respond to a flood emergency. This includes the floodplainpopulation, floodplain managers and the emergency services.o Land use change.A preliminary assessment of a number of these measures has been made for theVaisigano River catchment using the results of the HEC-HMS hydrological model anda one dimensional HEC-RAS hydraulic model.Mainly due to a lack of data, the various measures have been described in isolation.However, a fundamental principle of effective flood management is that managementmeasures should not be considered in isolation. Rather, they need to be consideredcollectively on a integrated risk management basis in order to provide the bestcombination of measures for managing flood risk on floodplains taking account of thefollowing:o Their interactions.o Their suitability and effectiveness.o Economic effectiveness.o Social impacts.o Environmental impacts.A hydrological and a one dimensional hydraulic model of the Vaisigano River hasFlood management Action Plan 2007 16