FLOOD INVESTIGATION & RISK ASSESSMENT
overview

Flood Investigation and Risk Assessment is a core business for Water Technology. With flood specialists in our Melbourne, Brisbane and regional offices having completed investigations in all parts of Australia, we provide an unparalleled depth of experience in this field. We provide a full range of flood investigation and risk assessment services for government and private clients at regional, township and site specific scales.

Key skills that distinguish our team include developing and extracting flood intelligence from flood investigations, data analysis and preparation of maps, community awareness brochures, property specific flood charts and total flood warning systems for emergency management.

Flood emergency response situations in Incident Control Centres (ICCs), with a knowledge of the information required and level of detail to facilitate the most efficient and effective emergency response. With members of the floodplains team leaders in the industry, Water Technology has delivered a large number of flood studies and flood risk management plans in the past 12 years in areas across Australia. We focus on delivering key flood projects in short timeframes, delivering on promises and meeting our client’s needs. Water Technology has delivered a number of studies recently that have progressed from flood mapping to having secured funding for flood mitigation design and construct in record time.

Capabilities
  • Expert hydrological/hydraulic analysis
  • Complex 1D, 2D, 3D and rain-on-grid hydraulic modelling
  • Flood mapping, risk assessment and community consultation
  • Floodplain risk management plans and flood warning systems
  • Expert witness services
  • Flood mitigation concept and functional design and construction advice
  • Flood related development application assessments and planning referrals
  • Environmental flow assessment and eco-hydraulics
  • Environmental watering infrastructure design
Client:
Gawler River Floodplain Management Authority
location:
Gawler, SA

Gawler Floodplain Assessment and Mapping Study

Image: Flooded Gawler River at Angle Vale

This project involved developing and modelling flood mitigation strategies to deal with the high risk of flooding of the townships of Two Wells, Virginia and Gawler and the high value horticultural areas of Northern Adelaide.

Flood mitigation strategies were developed through a combined technical and community reference group process, which stepped people through the technical and social issues that also needed to be addressed by the mitigation strategies.

Services provided:

  • Floodplain Behaviour and Assessment
  • Hydrology Review
  • Hydraulic Modelling and Validation
  • Flood Risk Mapping
  • Community Engagement

Water Technology working with Australian Water Environments.

Report: Gawler River Floodplain Mapping Report

Pilbara
Client:
Fortescue Metals Group
location:
Pilbara, WA

Fortescue Metals Group – Flood Modelling Support

Fortescue Metal Group own and operate four iron ore mines in the Pilbara, Western Australia. The region has an arid subtropical climate with highly variable rainfall that is seasonally impacted by monsoonal activity and tropical cyclones (Bureau of Meteorology; WA Govt). Understanding, and mitigating against, the impacts of flooding in this region is critical for Fortescue’s operations and infrastructure.

Water Technology completed flood modelling support for Fortescue’s mining operations in the Pilbara, Western Australia. The project involved Water Technology staff working within Fortescue’s Perth offices in a secondment style arrangement. Fortescue’s mining operations include large open pits and raised haul roads that are significantly impacted by the creeks flowing from the Chichester Ranges into the Fortescue Marsh. Tasks included developing detailed flood models to quantify and mitigate the impacts of flooding on infrastructure and to minimise changes to the overall hydrological regime.

Quantify and mitigate the impacts of flooding

The flood modelling support included large scale TUFLOW rain-on-grid hydraulic models along with smaller, more detailed models for the design of culvert and floodway structures. Water Technology staff were able to improve Fortescue’s flood modelling techniques and processes to increase the efficiency and reliability of future flood impact assessments. The scope of work also including reviewing and applying Pilbara hydrology techniques developed specifically for the region.

Key Services Provided:

  • Catchment Hydrology – Review, modelling and analysis
  • Rain-on-grid Hydraulic Modelling with TUFLOW
  • Flood impact assessment
  • Flood Risk Mapping
  • Waterway and Flood Infrastructure Modelling and Assessment
Client:
Department of Planning – WA
location:
Jigalong, WA

Jigalong is an remote community in the Pilbara. It is approximately 165 km east of Newman, in the Shire of East Pilbara. Jigalong is within the Nyiyaparli native title claim area. Jigalong Creek is immediately to the west of the community and a tributary of Jigalong Creek is immediately to the east.  The land adjoining the creeks is of high cultural significance.

Flood Risk Assessment

The Western Australia Department of Planning commissioned Water Technology to undertake a flood risk assessment of the Jigalong community. Water Technology completed the Flood Risk Assessment and Floodplain Management Strategy for the Jigalong Community, near Newman in the Pilbara.  This work was undertaken to provide information to the Department of Planning on the risk of flooding and associated hazards to property and infrastructure at Jigalong, and possible mitigation measures and development constraints.

Hydrologic and hydraulic modelling assessments.

A comprehensive hydrologic and hydraulic modelling assessment was undertaken which provided estimates of flood flows, levels, extents, depths, and hazard, and formed the basis for floodplain and design flood mapping.  The modelling revealed that Jigalong community is vulnerable to frequent, low hazard nuisance stormwater flooding, and less frequent but more severe flooding from Jigalong Creek and the tributary to the east of the community.  A floodplain management strategy was developed with the object of minimising flood risk and damage, including possible flood mitigation measures.

The scope of work required for this assessment involved a site survey and the development of a Digital Elevation Model (DEM), hydrological and hydraulic modelling, floodplain mapping, community consultation and the development of a floodplain development strategy including mitigation options assessment and develop-able land assessment.

The Jigalong Flood Risk Assessment was undertaken to provide the Department of Planning with flood mapping and information on flood behaviour to guide land use planning, emergency management and assessment of building and development in flood-prone areas for the Jigalong community.

Key Services Provided:

  • Catchment Hydrology – modelling and analysis
  • Hydraulic Modelling
  • Design Flood Mapping
  • Floodplain Management Strategy
  • Flood Risk Assessment
  • Stormwater Drainage Improvements and Recommendations

Related news.

Creating a Stormwater Management Plan for Curtin University
Client:
Curtin University
location:
Victoria Park, Bentley, Western Australia

Curtin University is Western Australia’s largest university. The main campus in Victoria Park, Bentley, supports a large student and staff population with a wide range of facilities and open space (approximately 117 hectares in size), including water bodies. Understanding the existing flood risk and assessing the impacts of proposed future development on the campus is important for planning and development decisions.

Stormwater Management Plan

Water Technology was commissioned by Curtin University to undertake a stormwater management plan of the entire Curtin University site in Victoria Park. Previous work had only considered small sections of the site’s catchment in isolation. The purpose of this project was to analyse the impacts of stormwater flooding for the entire site under existing conditions so that problem areas could be identified, and to assess the impacts of any future development. A detailed TUFLOW rain-on-grid hydraulic model was developed using LiDAR, feature survey and design drawings along with pit and pipe data from a collection of sources.

Complex hydraulics that included ephemeral lakes and numerous infiltration basins

The hydraulics of the site are significantly complex, including ephemeral lakes and numerous infiltration basins. As such, there was a need to work closely with the client to gain an in-depth understanding of the various features in the process of developing a model that was appropriate and reflective of the site.

This stormwater management plan study produced a significantly detailed TUFLOW hydraulic model, which is a valuable tool in identifying the flood risk on the Curtin University site for both existing conditions and future developed conditions. The work included the use of the model to simulate flood behaviour through the proposed ‘living stream’ network. The results from the modelling were used to assess potential impacts on the hydrological regime of the ‘living stream; system, and provided a range of recommended management measures to manage or mitigate any impacts.

Key Services Provided:

  • Site inspections
  • Hydrological modelling
  • Hydraulic modelling using TUFLOW with rain-on-grid
  • Detailed stormwater drainage network analysis
  • Flood impact and risk assessment
  • Scenario analysis and recommendations
  • Stormwater Management Plan
Yampi Sound access Road - Flood Vulnerability Assessment
Client:
JJL for the Department of Defence
location:
Derby, WA

Flood Vulnerability Assessment for Yampi Sound Road Crossing

The Yampi Sound Training Area, north of Derby WA, is a remote facility with significant access difficulties, unique environmental constraints and extremely high natural heritage value. Improving access, via a sealed road, was an identified need to aid better use of the facility. As the region is susceptible to extremes of weather, and has large floodplain areas, a flood vulnerability assessment was required.

For approximately 60km, Kimbolton Road crosses black soils, claypan and alluvial material traversing floodplains and river crossings, which becomes impassable in the wet season.

Pritchard Francis were engaged by JLL as lead consultant, with Water Technology as sub consultants, to carry out a Feasibility study of constructing 70km of sealed road along the Kimbolton Road track from Gibb River Road, approximately 40km from Derby, Western Australia, to Department of Defence training grounds in West Kimberley.

The project team carried out a feasibility study for the road construction, including the preliminary design of road pavement, river crossing options, possible track realignment, coordination of the geotechnical scope and for the road construction, borrow pit location investigations and fill material requirements.

Flood Vulnerability Assessment

Water Technology completed flood modelling of the entire floodplain to assess the vulnerability of the road to catchment and storm tide flooding and to assist in the design of river and creek crossings. Coastal tide and storm surge analysis was also completed to locate sections of the road subject to inundation from coastal conditions.  To assess the impacts of tidal inundation, both astronomical and storm tide were investigated to produce tide levels for different scenarios. These levels were compared to the surveyed road level to locate areas that are vulnerable to tidal inundation and to recommend locations for floodways or bridges.

Yampi-Sound-Inundation Yampi-Sound-Roadway-Inundation
Client:
Malley CMA / Murray Darling Basin Committee
location:
Murray River, VIC

The Living Murray Initiative and associated Environmental Works and Measures Program were established to improve the health of the River Murray system through recovery of water and effective distribution to the environment.

Water Technology has been involved in a number of eco-hydraulic projects through these initiatives to develop and assess water management options for improved environmental watering.

Water Technology undertook hydrodynamic modelling to assess proposed works and measures to significantly enhance the existing watering regime of the wetland systems around Lindsay, Mulcra and the Wallpolla Islands. This involved comparing flood extents based on historical, current and proposed infrastructure management. Prior to the development of environmental watering infrastructure, Water Technology undertook advection-dispersion model, investigated rates of mixing and turn-over times in the upper reaches of the system.

Client:
North Central CMA / Murray Darling Basin Committee
location:
Gunbower Forest, VIC / NSW

As part of Victoria’s Murray Darling Basin Plan Sustainable Diversion Limit Offset Works and Measure’s Program, the North Central Catchment Management Authority co-ordinated investigations to deliver environmental water to the Ramsar listed Gunbower Forest in an efficient and sustainable manner.

The objective of these investigations was to assess hydrological, ecological and structural feasibility of a range of water management options to deliver water to the Gunbower Forest.

Water Technology developed a number of 1D-2D hydraulic models of the system to evaluate the potential water management options and improve knowledge of the floodplain system, and worked closely with the CMA and ecologists to develop concepts of infrastructure and watering requirements for various target sites.

Client:
Ipswich City Council
location:
Thagoona, QLD

The Thagoona area has been subject to extensive flooding in the past; most notably the recent events of November 2008 and January 2011 and to a lesser extent in November 1999, May 1996 and December/January 1991/92. Extensive flooding also occurred in 1974 however much less development and infrastructure existed in the area at the time. The November 2008 event is the largest event since 1974 and caused the most flood damage in the history of occupation of the area with widespread overland flow through residential and agricultural lots, inundating houses, sheds and vehicles and causing scour damage on many roads and driveways.

The purpose of this study was to increase the resilience to flooding of the community within the catchment through identifying subcatchments, drainage and flooding behaviour, flood risk issues, potential impacts of future development, resilience opportunities, mitigation options and development of a flood risk management strategy.

Hydrological modelling was undertaken using WBNM and hydraulic modelling through TUFLOW. The WBNM model incorporates 137 subcatchments (2785 ha) and was initially calibrated to the Rational Method. The hydraulic model extent was reduced as much as possible to ensure reasonable runtimes with the 3m grid size while still encompassing the key areas of interest without downstream boundary effects. LiDAR data was used to make the 3m DEM of the hydraulic model area (5km x 4km, 2 million cells). Recent survey was used to capture road crest lines and swale centrelines to overlay the DEM. The hydraulic model includes over 100 culverts, bridges and two sections of trunk drainage within the more recently developed areas of Thagoona. The SMS software package was used to create animations of the flood progression.

Client:
Western Downs Regional Council
location:
Western Downs, QLD

Water Technology have stormwater and riverine flood studies for six towns in the Western Downs Regional Council (WDRC) area using MikeFLOOD to assist with the revision of their planning scheme following recent council amalgamations. Water Technology has also provided expert advice to WDRC with respect to inclusion of the modelling results in the scheme. Stormwater and riverine flooding studies have been undertaken for Chinchilla, Miles, Wandoan, Tara and Jandowae. In addition, for Dalby we have undertaken a stormwater study and assessing the effect of recent development on flooding through modification of the existing riverine flood model (developed by others). The riverine flood study identified areas at risk of inundation and their impact on current and future development. The stormwater analysis defined and mapped stormwater corridors, and defined trunk drainage infrastructure needed for development.

Interesting challenges that were faced during the project include: determining representative observed rainfall and runoff data, regionalisation of flood frequency analyses, regionalisation of model parameters, application of areal reduction factors to rainfall estimates on large catchments, stormwater flow path identification in (very) flat terrain and identification and documentation of structures (e.g. illegal bunds).

Client:
East Gippsland CMA
location:
Snowy River, NSW

This study was prepared for the East Gippsland CMA in June 2011 and involved a detailed hydraulic assessment of the impacts of the Snowy River Rehabilitation Project on the river and floodplain. The study incorporated an iterative hydraulic and geomorphic approach to assessing the implications of the river rehabilitation and also to assess risks associated with potential avulsion sites. A two-dimensional hydraulic model was developed to spatially resolve the effects of changes in vegetation communities along the floodplain and riparian zones on flood levels across the study area. The assessment also considered the effect of in-channel bars under a range of flow conditions, with the results indicating a high level of correlation between increased flood level and channel bar formation. Sensitivity testing of the hydraulic model also revealed that the inclusion of bed scour in the model is a critical assumption, as if the bed does not scour through the system during flood events, water levels and overbank flows are expected to be dramatically raised in a number of reaches, with follow-on effects downstream.

Client:
NORTH EAST CATCHMENT MANAGEMENT AUTHORITY (VICTORIA)
location:
CENTRAL VICTORIA

The Ovens River floodplain is one of the many within the Murray-Darling Basin that has been subject to anthropogenic changes, negatively impacting on the condition of floodplain and wetland environmental assets. The lower Ovens River and its floodplain wetlands are in much better condition than many other rivers in the basin due to the absence of major water storages and extractions from the upper catchment, with less impact on the magnitude, frequency and duration of flooding. However it still has a number of issues to manage; namely vegetation clearance, pest species, the operation of the Murray River and backwatering from Lake Mulwala, and the construction of levees, channel banks and roads, some of which have disconnected wetlands from the river.

The Lower Ovens Connectivity Study was a landmark project which integrated complex floodplain hydraulics, catchment hydrology, advanced spatial analysis, ecological assessments and environmental outcomes. Detailed 1D/2D hydrodynamic models were used to understand the flood behaviour across the floodplain at a range of different magnitude flow events. Extensive condition assessments of the significant ecological assets within the floodplain were also conducted. The study identified and mapped over 380 potential barriers to flow and produced a number of highly valuable datasets which relate areas such as wetland connectivity, frequency of wetland inundation and ecological condition that could serve as a benchmark for floodplain managers across the Murray-Darling Basin. The knowledge gained from the study was incorporated into a geodatabase that linked flood behaviour to connectivity and ecological assets within the floodplain.

The study concluded that much of the lower Ovens floodplain is in excellent condition and that there are few barriers which significantly reduce wetland connectivity, with 90% of the wetlands found to be inundated on average at least every two years. The approach developed in this study could easily be applied to other river systems across the country to improve understanding of the ecological condition and connectivity of floodplains and improve management of key environmental assets. The study has developed a number of tools that will significantly expand the North East CMA’s capacity to engage key stakeholders in identifying options for improving the management of unregulated flows to key environmental assets through the design and management of environmental infrastructure.

Client:
Queensland GovernmenT Department of Natural Resources and Mines (DNRM)
location:
GREATER REGIONAL QUEENSLAND

Widespread flooding occurred over large areas of Queensland in December 2010 and January 2011. On the 17th January 2011 a Commission of Inquiry into the Queensland Floods of 2010/2011 was established (termed the Queensland Flood Commission of Inquiry (QFCI)). The QFCI released its final report on 16 March 2012. The report made 177 recommendations across a broad range of issues including floodplain management, land use planning, building regulations, insurance, mines, emergency management and dam management. The QFCI was the catalysts for the Queensland Flood Mapping Project (FMP). Phase 3 of the FMP was transitioned to the Department of Natural Resources and Mines (DNRM), Queensland.

Water Technology was commissioned by the DNRM to carry out flood hazard mapping for a total of 12 rural towns located throughout Queensland in two distinct stages. The towns assessed as part of the study included Condamine, Flinton, Dulacca, Goomburra, Isisford, Jandowae, Karara, Kolijo, Nebo, Woorabinda, Gogango and Goomburra Upper, and included seven Local Government Areas throughout Queensland including the Western Downs Regional Council, Southern Downs Regional Council, Mackay Regional Council, Rockhampton Regional Council, Woorabinda Aboriginal Shire Council, Longreach Regional Council and Isaac Regional Council.

The project included the preparation of two dimensional flood models for each of the 12 regional towns located throughout greater Queensland. The hydraulic models were validated to historical flood information provided by the DNRM which included flood levels, flood extent as well as anecdotal flood records available for each of the towns. Once validated, the hydraulic models were used to assess flood risks for a range of design flood events ranging in magnitude from the 2% AEP to 0.2% AEP events. Additionally, the models were also used to prepare a range of gauge increment maps to aid in emergency and disaster management functions. Extensive GIS mapping including flood animations were prepared to fully inform the outcomes from the flood risk assessments for each of the towns.

Water Technology was able to successfully deliver all 13 township flood risk assessments (comprising 48 separate TUFLOW models), including reporting, 170 GIS maps, and flood animations within a period of four weeks from commissioning. Water Technology was the only consultant to complete their studies on time and received great feedback from DNRM on the quality of the work and the manner in which it was undertaken.

The flood information generated from this project is provided to each of the Local Government Agencies throughout Queensland and will also ultimately be uploaded to the Queensland Governments Flood Portal FloodCheck, which is an interactive web portal to provide a centralised database and repository of flood related information for use by Local Government and other associated agencies.

Client:
North Central Catchment Management Authority
Hepburn Shire Council
location:
CRESWICK, VIC

Creswick experienced significant flooding in late 2010 and early 2011 experiencing several large events in a short period. This had a devastating impact on the community.

Water Technology was commissioned to undertake a detailed flood study for Creswick to assist in providing the community with a greater level of protection from future flooding. The study involved detailed hydrological and hydraulic modelling of Creswick Creek, flood mapping, quantification and assessment of flood damages, and development and assessment of potential flood mitigation options.

A rainfall-runoff model was developed in RORB, which incorporated Creswick Creek, several tributaries and two upstream storages (Cosgrave Reservoir and St Georges Lake). A coupled 1D/2D hydraulic model was developed using MIKE FLOOD, to assess the extent of inundation, depths and water levels. Both models were developed using industry best practices and were rigorously calibrated and verified against historical flood events.

The hydraulic model was also used to test the effectiveness of a number of potential mitigation options, including deepening/widening of the creek, additional culverts and various levee alignments. A key element attributed to the success of this study was the active engagement of the community. This was developed over the course of the study and included community information sessions, questionnaires, media releases and meetings with the Technical Working Group and community based Steering Committee. The community concerns regarding levee heights were listened to and a level of protection was adopted to protect against the January 2011 flood level but which maintained the aesthetics of the township.

The final plan recommended a number of structural and non-structural options (warning systems, increased awareness and amended planning scheme overlays). As a result of extensive consultation, it was clear that the recommendations for Creswick had strong community support. Economic analysis indicated that the proposed mitigation option would reduce the cost of flood damages by up to 75%, with a benefit cost ratio of 0.8 (not including associated non-monetary costs).

The Creswick study has been held up as the example for all flood investigations to follow in Victoria. It led to an acceptable flood mitigation plan being developed and implemented in record time, and has dramatically reduced the flood risk for the Creswick community.

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