Lower Waikato main channel flood protection performance review

Report: TR 2022/46

Authors: Anderson Aimusu

A performance review has been undertaken for flood protection assets on the Lower Waikato River main channel. The assessment scope is outlined in the project management plan. The scope covers collation and review of previous literature and models, updating the models with most recent hydrology, cross-section and stopbank survey data, and incorporating specific flood assets within the system to improve model outputs and flood protection stopbanks performance.

The stopbank performance is a measure of the vulnerability of a stopbank to overtopping under a design event. The assessment process involves comparing actual crest levels of a stopbank against the corresponding design flood level to establish a performance grade for a 100 m length of the stopbank. Performance grades define the percentage of freeboard left compared to design freeboard, which informs the need and timing for stopbank upgrades.

The review also involves modelling future climate change hydrology and design flood profiles to inform stakeholders of the potential increase in flood risks resulting from future climate. In addition, it informs the Council of the potential loss in flood protection service level to assist in management decisions to build community resilience against future flooding.