Douglas Shire Council commissioned Trinity Engineering and Consulting Pty Ltd (TEC) to review the drainage networks in Ribbon Avenue and adjacent streets.

The drainage assessment was required to identify drainage upgrade options available and provide a recommendation to improve the stormwater immunity to the residential properties.

The commission extends only to concept development phase and this report provides Council with information on the options available for further discussion with Councillors and residents before proceeding to detailed design phase.

This report presents the design rationale, constraints and extent identified in the Concept Design Phase.



Council subsequently extended the scope of the commission to consider a risk assessment phase andΒ develop further options that address capacity and operational risks for the stormwater drainage system.

Douglas Shire Council commissioned a review of the drainage networks in Ribbon Avenue and adjacent streets following significant flooding in early 2017.


This report provides the findings of the concept development phase including options considered to address the flooding risks.

The current stormwater drainage system for Ribbon Avenue is limited to an underground system only as there is no formalised overland flow path.


The system capacity was assessed as being less than the capacity required to convey runoff from a rainfall event with a

1-year average recurrence interval, (1-year ARI or Q1).

This indicates that there is a very high risk of localised flooding each year.

The absence of any reliefΒ flow paths means the consequences are significant on properties in the local area.


Nine options were assessed to a concept design level to determine the increased level of service able to be provided for each option as well as the shortcomings of each option.