Case Studies

Catchment 9 & 16 Drainage Planning and Design

Discipline

Integrated Water Planning

Client

City of Greater Dandenong

Start Date:

January 2018

Completion Date:

2019

Project Overview & Outcome

Overview

The City of Greater Dandenong engaged Engeny to undertake flood mapping and the detailed design of mitigation works.

Outcome

Engeny’s work improved Council’s ability to manage flooding with a targeted approach to implementing structural mitigation works. The review and request of survey data provided confidence on the accuracy of Council’s existing drainage system and it’s performance with the existing conditions modelling highlighting the flooding hotspots.

Structural mitigation works were targeted to resolve these flooding issues with the flood reduction benefits quantified with modelling. Feasibility assessments, which included extensive communication with Council, informed the selection of preferred structural mitigation works and ensured key construction constraints and the potential social, economic and environmental impacts were considered.

Project Details

The Problem

This work advanced Council’s ability to manage flooding across the selected catchments draining into Mile Creek through Engeny’s work.

The Response

This work has included:

Feasibility assessments including undertaking site visits, Dial Before You Dig enquiries, review of feature level survey data, identification of construction constraints, required authority approvals, etc.
Preparation of preliminary design drainage layout plans and cost estimates including the approval of drainage connections to Melbourne Water’s Mile Creek and works within VicRoads or VicTrack owned reserves.
Ultimately the preparation of detailed design plans.

The Details

Enhancement of Council’s digital GIS data including the review and request of survey data and drainage plans to build a robust database which significantly improves Council’s understanding of the existing drainage system.
Development of new hydrologic and hydraulic models covering the selected catchments within the municipality, including Council and Melbourne Water drainage assets, to define floodplain behaviour. These models were created using RORB and TUFLOW, Melbourne Water’s preferred modelling software in line with the Australian Rainfall and Runoff 2019 hydrological approaches.
Analysis of modelling outputs including the interrogation of peak flows, velocities, flood safety hazard categories, etc, for both the 10% AEP and 1% AEP storm events. This analysis established the existing flood risk affecting specific hotspots within the catchment.
Assessment of structural mitigation works which could be implemented to address flood risk. The resultant flood risk reduction was quantified by considering the changes to the number of properties and dwellings affected in addition to the flood safety criteria within roads.
Preparation of flood mapping deliverables and associated documentation to assist Council to manage flooding within the selected catchments and also provide the justification / basis behind the proposed mitigation works by summarising the flood mitigation benefits which would be achieved.

The Result

Following on from the flood mapping and mitigation study, Engeny has progressed the proposed structural works to preliminary designs. The project is currently in progress however detailed designs plans will ultimately be developed which will inform Council’s capital works program for several years to come.

Project Relevance

Flood modelling utilising RORB, TUFLOW and HEC-RAS (all created by Engeny).
Verification of models to historical flood data supplied by residents at community meetings.
Stockyard Creek and Bennison Creek (waterways) and Foster drainage system modelling and assessment.
Identification of existing system constraints.
Drainage system performance reporting including identifying the level of service currently provided and areas of shortfall.
Assessment of structural flood mitigation options.
Concept design of flood mitigation works.
Cost estimates and qualitative assessments of benefits

Project Innovation

The low to medium density residential areas in the township of Foster contain properties that are directly connected to the pipe drainage system and those with downpipes connected to the back of kerb. The relatively small size of the township enabled Engeny to adopt an innovative approach to flood modelling using ‘virtual pits’ to represent back of kerb connections for those properties not directly connected to the pipe drainage system. This approach meant that pit inlet capacity could be modelled more accurately within residential areas which was considered to be particularly important given the nature of flooding reported by residents.

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