Scheme Update post Storm Babet Report

June 2024

The Midleton Flood Relief Scheme Update post Storm Babet Report and Appendix has been made publicly available; 

• Scheme Update post Storm Babet
• Scheme Update post Storm Babet Appendix

As part of the Midleton FRS project, Arup was asked by Cork County Council (CCC) to prepare a post event review report for the Storm Babet flood which severely impacted Midleton on the 18th of October 2023. A detailed report which described the impact of the event in the town was issued in December 2023. The report also compared the observed flood levels and extents with the hydraulic modelling of the existing scenario which was originally presented in the scheme hydraulics report. The reader is referred to the links below for access to the report. 

Storm Babet Flood Event Report

Storm Babet Flood Event Report Appendices

This report considers the impact of Storm Babet in the context of the design hydrology and the proposed scheme for Midleton. As Babet was an extreme event, it provides very useful data on the QH relationship at the Ballyedmond gauge for high flow events which in turn allows for the rating curve for the gauge to be reassessed. Any change to the rating curve will impact on the Amax series for the gauge and hence on the Qmed and design flows for the whole scheme, given that the Ballyedmond gauge was used as the Qmed 
pivotal site adjustment factor for the scheme HEPs. Any upwards revision in the design flows will impact on the scheme given that higher flows will entail high water levels etc.

The Scheme Update post Storm Babet Report details the work undertaken as part of the hydrology and proposed scheme update and should be read in conjunction with the various other reports produced to date as part of the project.

The scope of the Scheme Update post Storm Babet Report for the hydrology/ proposed scheme reassessment in light of Storm Babet is given as: 
Hydrology reassessment 

• Assess and update the rating curve of the Ballyedmond gauge and derive an updated Amax series;
• Derive a new Qmed and Qmed Pivotal site adjustment factor for the gauge;
• Review of the growth curve of the scheme;
• Update the design hydrology flows for the scheme area;
• Assessment of the likely magnitude of Storm Babet at the gauge by considering the findings of the hydraulic modelling and separate rainfall runoff modelling;
• Modelling of Storm Babet through Midleton using the existing scenario hydraulic model and make a brief comparison with the observed flood extents and flood depths during the event.

Proposed Flood Relief Scheme reassessment 

• Assessment of the design water levels with the scheme in place considering any change to the scheme hydrology arising from the work noted above.
• Update as necessary the proposed scheme in order to ensure that the target Standard of Protection (SoP)is maintained in light of any revision to the hydrology.
• Assessment of the performance of the updated scheme if a fluvial event with the magnitude of Storm Babet were to occur again.