The move to unify the technological approach to flood management across Malaysia is important, as a fifth of the country’s population is estimated to be at risk from flooding. Large areas of the country repeatedly suffer from prolonged, significant floods; these cause widespread disruption for communities, business and critical infrastructure, often requiring many tens, or even hundreds, of thousands of people to be evacuated from affected areas. The impact of flooding has been made worse over the past decade by rapid urban growth and land use change, as these developments have modified the rivers’ flow regimes and flooding mechanisms.
Situated near the equator, Malaysia’s humid tropical climate brings an average of 2.5 metres of rainfall per year to the Peninsula, while in some parts of East Malaysia, on the island of Borneo, totals have been known to exceed 4 metres. What is more, the majority of the rain falls during the North East monsoon, typically between November and March, and has its biggest impact on the Peninsula’s east coast and East Malaysia. Meanwhile, the inter-monsoon period brings thunderstorms and flash flooding to the west coast, notably the capital city Kuala Lumpur. Here, the urban population of 8 million is densely packed, and the stormwater drainage channels often cannot cope with the rainfall intensities, so that the impacts can be huge.
Malaysia’s Department of Irrigation and Drainage has wholeheartedly embraced a modern ‘non-structural’ approach to flood management, with the development of its world-leading National Flood Forecasting and Warning System (NaFFWS). The system is the result of many decades of hard work installing a network of over 700 observation gauges across tricky terrain, including dense rainforest. Already successfully trialled in three catchments in Malaysia, the scheme has now been broadened to 11 more river basins in the north-west of the country, and 11 further catchments on the east coast, by local consultants in partnership with developers of the system’s core, HR Wallingford; before further extensions take it to the remaining part of peninsular and eastern Malaysia.
NaFFWS is based upon a three-stage process. First, engineers set up the system by gathering historical rainfall and flow data as well as creating models of the runoff, river channels and flood plains; Second, the data is combined with weather forecasts and on-the-ground measurements to predict water levels; finally, the system is set to run operationally and continuously, with forecasts and warnings automatically generated.
Typically, automatic simulations are carried out several times a day to forecast water levels and flows in the river channels, and to map the flood inundation process within the flood plains. Hydrological rainfall-runoff models represent the upper catchments, running in continuous simulation mode in order to keep their internal states updated and representative of current conditions. These feed the boundaries of 1D and 2D hydrodynamic models, which model the flows in the river channels, and simulate the movement of water in the flood plains.