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Purpose of the Report: 

To develop and calibrate a hydrological model for the Waiohine River catchment and produce design flood hydrographs. 

Geographic Area Covered: 

The report covers the Waiohine River catchment in the Greater Wellington Region, including the Mangatarere River and Kaipaitangata Stream. 

Summary of the Report: 

This report presents the development and calibration of a hydrological model for the Waiohine River catchment, including the Mangatarere River and Kaipaitangata Stream. The model was created using Hydstra software and calibrated against measured flow records. Design flood hydrographs were produced for several locations within the catchment. Rainfall data was sourced from five gauges and spatially distributed using Theissen Polygons. Areal reduction factors were applied to convert point rainfall estimates to catchment averages. Temporal patterns were derived from measured rainfall data and used in a Monte Carlo simulation approach. The model was calibrated by adjusting baseflow, routing, and loss parameters to match observed events. Design flood results were generated for various annual exceedance probabilities (AEPs), including 1:20, 1:50, 1:100, and probable maximum precipitation (PMP). The report includes detailed tables and figures showing rainfall depths, spatial distribution, and hydrograph outputs. The findings support flood risk assessment and planning in the Waiohine River catchment.