ABSTRACT
The state of Victoria in Australia has experienced a number of large-scale and intense flood-events in the last 5 years. An assessment has been undertaken of the structures impacted by these flood events.
The objective was to better understand the impact of the floods on bridge and culvert assets and to enable VicRoads, the state road authority of Victoria, to proactively manage these events in the future. VicRoads Technical Services undertook a project to develop a risk-based approach for the identification and assessment of bridges which are at-risk of damage or loss of serviceability as a consequence of major flooding events. Once the risk is understood, appropriate action can be taken to ensure the ongoing safety, stability and serviceability of VicRoads’ bridges over water.
A comprehensive literature review was undertaken to understand the topic and to review current practices and systems to identify, record and manage structures prone to flooding. Heron and Bowe (2010) discuss a screening and hydraulic vulnerability rating system developed by O’Connor Sutton Cronin Consulting Engineers on behalf of Iarnrod Eireann (IE) which manages over 300 bridges in Ireland. Lloyd, Webby & Millais (2009) discuss a system developed by the NZTA and the process involved in conducting an assessment of structures in New Zealand susceptible to flood damage. The Federal Highway Administration (2012) provide the technical standard for knowledge and practice in the design, evaluation and inspection of bridges for scour in the United States. The United Kingdom Highways Agency (2006) provides a methodology for assessing the potential for a bridge to suffer from scour damage.
In considering the practices, systems and methodologies an impact evaluation criteria was developed in combination with the experience of VicRoads Bridge Engineers and case studies of flooded VicRoads structures. The requirements of historical and current bridge design codes have not been factored into the impact evaluation criteria. The following Structure Scour Characteristic (SSC) Factor was developed which gives an indication of the potential for the structure to be affected by scour during flooding. () SSC = WA + WB + WG + HA + FF + PP + AP + DF https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/eq143.tif"/>
where WA = waterway area; WB = waterway bed material; WG = longitudinal grade of the waterway; HA = horizontal alignment, FF = freeboard between the high water flood level and the soffit of the superstructure; PP = pile protection of the pier columns and piles; AP = abutment batter protection; and DF = depth to foundation.
A case study was completed with the aim of achieving a better understanding of flood impacts on bridges and to validate the weighting adopted in the SSC Factor and the risk appraisal spreadsheet that was developed based on this. While only small scale the results validated the methodology with close correlation to known events. Future work needs to be undertaken to broaden the trial and ensure the methodology can be adopted across the state.
