Honiara Flood Risk Management Study and Plan

The key purpose of the Honiara Flood Risk Management Study and Plan was to develop a strategic plan to better manage flood risks in the greater Honiara area, thereby building and strengthening the City’s resilience to catchment flooding. This is to be facilitated through the development of fit-for-purpose flood modelling for greater Honiara’s main river systems, with these primary applications: (i) to inform and enhance City land use planning; (ii) to inform and enhance emergency response planning, including the development of flash flood warning systems; and (iii) to assess the viability of potential flood mitigation options.  Within greater Honiara, the immediate areas of focus were the Mataniko River, the lower Lungga River floodplain, Burns Creek and the White River.

The Tropical Cyclone Ita, caused very heavy rain and severe flooding in and around Honiara on 3 April 2014. Flooding of the Mataniko River apparently destroyed 239 houses and claimed 21 lives. East of Honiara, the Lungga River flooded Henderson International Airport. The total economic damage attributed to this flood has been estimated by the World Bank at US$108 million, equivalent to 9.2% of GDP. Losses from this flood have compelled the Solomon Island government and the World Bank to complete missions to identify and survey flood peak levels, assess the flood damage and its wider impacts, consider means to improve resilience to flooding, and now to commission this Flood Risk Management Study & Plan for Honiara and its environs.

The seriousness of the impacts from flooding such as the April 2014 flood can largely be attributed to the exposure and vulnerability resulting from significant unregulated urbanization. More specifically, it can be attributed to the many at-risk dwellings located in low lying areas (such as Koa Hill) and the presence of low-resilience housing styles (traditional leaf houses), which were damaged to a greater extent than other dwelling types. However, the flood depths, flow velocities, and debris load were such that even block concrete houses were destroyed at Koa Hill. Limited community response to flood warnings (warnings not heeded) is thought to have contributed to the impact. Therefore, education to improve emergency preparedness is also important.

To help build the capacity of the Solomon Island Government to be resilient to future flood risk events, FCG New Zealand played a supporting role the development of the Honiara Flood Risk and Management Study and Plan as part of the World Bank supported Natural Disaster Risk Reduction Program.