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Purpose of the Report: 

To review and update flood hydrology estimates for the Waikanae and Otaki Rivers using recent data and modelling approaches. 

Geographic Area Covered: 

The report covers the Waikanae and Otaki River catchments located in the Kāpiti Coast District, New Zealand. 

Summary of the Report: 

This report presents a review of flood hydrology for the Waikanae and Otaki Rivers, prepared by Horizons Regional Council. It aims to update flood estimates using recent hydrological data and modelling techniques. The study evaluates historical flood records, rainfall data, and catchment characteristics to refine estimates of peak flows for various annual exceedance probabilities (AEPs). The report discusses the limitations of previous models and incorporates updated rainfall-runoff modelling using HEC-HMS and other tools. Calibration was performed using observed flood events, and sensitivity analyses were conducted to assess the impact of different parameters. The updated flood estimates are intended to support floodplain management, infrastructure planning, and risk mitigation strategies. The report concludes that the revised hydrological estimates provide a more accurate representation of flood risks in the Waikanae and Otaki catchments and recommends further data collection and model refinement to improve future assessments.