Stopbanks Renewal Prioritisation A risk based approach for planning asset renewals

The Waikato Regional Council owns and manages more than 620 km of flood control stopbanks. The stopbanks provide flood protection for approximately 120,000 hectares of farmland and several urban settlements and towns. The asset management plans provide for condition and performance assessment of the stopbanks, based on annual visual inspections, regular surveys, monitoring during floods and regular reviews of the hydrology and hydraulics of the flood protection systems.

The service levels of the stopbanks are defined by their ability to withstand a specific design flood event without overtopping. Stopbanks heights are determined on the basis of the design flood level with an additional freeboard allowing for uncertainties in flood estimations and stopbank settlement. Maintaining the stopbanks at their design crest level requires regular surveys of crest levels, comparing these to design flood levels and topping up of stopbanks to required levels. In preparation for the Long Term Plan (LTP), a full review of stopbanks heights was carried in 2013 which found that approximately 90 km of stopbanks have lost the freeboard height through settlement and significant renewal works are required.

To ensure that budgets are spent to reduce risks to Council within the shortest timeframes, a risk based prioritisation process was developed to establish the LTP renewal works programme. The process has been applied utilising all the asset monitoring information and formed the basis for planning, and renewal works programme decision making during the last LTP.

This paper provides an outline of the process followed and examples of the resulting programme options to assist Council decisions making and adoption through the LTP.