Awanui River Catchment Flood Risk Assessment

Awanui River Catchment located in Northland covers 45,500 hectares of land with a total stream network of 192 kilometres. To obtain high confidence in modelling results best practice methods were required in this study. The key components of this study are survey of sufficient river cross-sections, use of LiDAR data to generate DTM for 2D model input, sufficient raingauges and flow gauges, model calibration using 1D and 2-D combination and flood hazard mapping. The hydrological component of the model was represented by 195 sub-catchments in MIKE11 while hydraulic component was undertaken using MIKE FLOOD involving MIKE11 and MIKE21.

Extensive model calibration was undertaken using major flood event recorded at five raingauges and five stream gauges. Various ARI rainfalls were derived from HIRDS model based on NIWA rainfall records. HIRDS rainfalls were generated at five locations within the catchment to account for aerial distribution of rainfall.

Flooding of the Kaitaia Township and its suburbs due to spills from Awanui and Tarawhataroa Rivers has been identified as a significant hazard. The current model has identified the problems and possible mitigation options. The model will form a building block and will be used by NRC to undertake remedial options to manage flood risk.