Understanding geomechanical and hydraulic vulnerabilities in dam-stopbank systems

Abstract

Floods are New Zealand’s most frequent and damaging natural events. Stopbanks and dams provide the primary means of physical protection for many communities and are, therefore, critical for protecting life, property, and other infrastructure. Embankments within catchments are often constructed from similar local materials. The geotechnical properties of these materials are often poorly characterised, understood and/or documented. Uncertainties in the performance of embankments are compounded due to the practice at the time of design and construction, as most embankments were constructed between ~1880 and 1980. In this study an experimental programme will be undertaken to improve the understanding of how geomechanical and hydraulic parameters influence failure modes. By understanding the relative influence of certain geotechnical and hydraulic parameters, such as relative flow-embankment orientation, defect orientation, and soil collapsibility, a generic vulnerability assessment framework will be developed. While the NZSOLD Dam Safety Guidelines provide performance criteria for dams, there is currently no equivalent for stopbanks. This can lead to differences in levels of resilience provided by dams and stopbanks which may not be proportional to the relative importance of the structures. To this end, the potential consequences of failure of individual embankments within larger systems will be examined. Findings from this will inform a broader method for assessing the vulnerability and consequences of other dam-stopbank systems. This project aims: (1) A deeper understanding of the importance of individual embankment elements, (2) a framework to identify “weak links” in stopbank-dam embankment networks, and (3) tools to prioritise maintenance, and investment in embankment systems. Ultimately, this project aims to move flood risk management towards a broader system wide view to improve resilience and safety in downstream communities.