Clevedon Flood Hazard Mapping

This paper details the flood hazard mapping study of the Wairoa River and Taitaia Stream that Tonkin & Taylor carried out for Manukau City Council. The purpose of the study was to provide flood extents that can be used in the Clevedon Village Sustainable Development Plan, and be incorporated into a plan change to the Manukau Operative District Plan for Clevedon Village. The plan provides for the expansion of the existing Clevedon settlement onto the rural land outside the existing village core and between the Wairoa River and Taitaia Stream.

The hydrological modeling involved calibration and validation of a number of subcatchments for the 263 km2 Wairoa catchment (including Taitaia sub-catchment). Key hydrological features were the application of data from two flow gauges and five rainfall gauges and role of two large water supply dams.

The hydraulic modeling assessment was carried out using a dynamically coupled 1D/2D model of the Wairoa River and Taitaia Stream. We carried out calibration using historical records and carried out a sensitivity assessment of the flood extents to challenge various assumptions that were made in the modelling process.