Sediment flux and geomorphic change drive flood risk in the Philippines

Issued: Tue, 27 Aug 2019 10:31:00 BST

Dr Richard Williams, alongside Dr CP David at the University of the Philippines (Diliman), is leading a project investigating flood risk management in the Philippines. The project is funded by a £679k grant from the Natural Environment Research Council (UK) and the Department of Science & Technology’s Philippine Council for Industry, Energy, and Emerging Technology Research and Development (DOST-PCIEERD), and a £37k capacity building grant from the Scottish Funding Council.

In the Philippines, rivers are particularly dynamic; risks arising from sedimentation and erosion need to be assessed and incorporated into flood risk management in geomorphologically active settings. This research project aims to:

  • develop a national-scale catchment characteristics database, and associated river geometry relations, to assess the susceptibility of different catchments to morphological change impacts on flood hazard
  • assess flood hazards arising from morphological change associated with variations in sediment supply and the influence of lateral constraints on channel morphological adjustment.

River morphology results from sediment transport and sedimentation, which are both a consequence of water flow. Episodic variation in natural (e.g. typhoons, earthquakes, volcanoes) and anthropogenic (e.g. gravel mining, river bank protection) sediment supply drives changes in riverbed levels. These changes determine channel capacity and flow routing, and thus associated flood risk to people and property. The same factors determine variations in lateral bank erosion rates; elevated rates result in the loss of developed floodplain and the failure of critical infrastructure such as road bridges. Despite the significance of variation in riverbed levels and channel position for flood risk, geomorphological processes are commonly overlooked in flood risk mapping.

To date, the research team have installed hydrometric monitoring equipment in two research catchments in the island of Luzon, and undertaken an airborne LiDAR survey. The team are also analysing satellite imagery using Google Earth Engine to quantify channel change at a national scale.