Darling Bourke 2009, Rural Flood Study Darling River Floodplain

Brief description

Development of floodplains in the western rural areas of NSW is managed through Part 8 of the Water Act 1912. Part 8 was gazetted in 1984 and makes provisions concerning 'flood control works' that affect, or are likely to affect, flooding or floodplain functions. Part 8 was amended in 1999 to allow for more strategic control of flood control works through the preparation of rural Floodplain Management Plans (FMPs) and a more streamlined and resource efficient approval process. The amendments also required that rural FMPs be developed in accordance with the provisions and policies of the operative NSW Manual (currently, Floodplain Development Manual, NSW Government, 2005).

The manual supports the primary objective of the New South Wales Government's Flood Prone Land Policy to reduce the impact of flooding and flood liability on individual owners and occupiers of flood prone property, and to reduce private and public losses resulting from floods, utilising ecologically positive methods wherever possible. The formulation and implementation of FMPs is the cornerstone of the policy and the process for their preparation is described in the manual.

Administrative orders published in April 2007, inter alia, divided the responsibilities under Part 8 of the Water Act 1912 between the Department of Environment and Climate Change (preparing rural FMPs) and the Department of Water and Energy (implementing the plans through licensing and compliance functions).

On 1 July 2009, following a Reorganisation of Government Agencies, the licensing and compliance functions regarding Part 8 were transferred to the newly established Office of Water within the renamed Department of Environment, Climate Change and Water (DECCW). Please note that any reference in this document to the Department of Environment and Climate Change, and Department of Water and Energy, is to be construed as a reference to DECCW.

The development of a rural FMP progresses through three (3) key stages: Data Collection & Flood Study (FS) - in general, includes data collection for hydrology, hydraulic and environmental aspects; defines the nature and extent of flooding, including development of a computer-based hydraulic model of flood behaviour; Floodplain Risk Management Study (FRMS)- in general evaluates management options based on hydraulic modelling, analysis of the floodplain environment and social and economic considerations, to address existing and future floodplain risk management issues; and Floodplain Management Plan (FMP) - presents the recommended management measures for the floodplain, as determined in the Floodplain Risk Management Study, and includes an implementation program with priorities.

This current project, overseen by the Darling River Floodplain (Bogan River confluence to Louth) Floodplain Management Committee (the Committee) and prepared for DECCW, includes only the first of the above three elements of the Floodplain Management Plan process, and is structured as follows:

Stage 1: Data Compendium and Digital Terrain Model

All information and knowledge of the flood regime in the study area are included in a Compendium of Data (COD), as a permanent record, and for later use in Stage 2 of the FS.

A Digital Terrain Model was prepared for hydraulic modelling use in Stage 2 of the FS and the results presented on an appropriate Geographic Information System (GIS).

Stage 2: Calibrated Hydraulic Model and Final Flood Study Report

A calibrated computer based hydraulic model was developed to quantify the distribution of floodwaters during historical flood events and for later use in designing a floodway network (as part of the FRMS) in order to evaluate management options.

The Compendium of Data was completed in July 2008. This Report covers Stage 2: Calibrated Hydraulic Model and Final Flood Study Report.

The Commonwealth Government's Natural Disaster Mitigation Program (NDMP) and the New South Wales State Government through the NSW State Emergency Management Committee (SEMC) have jointly provided funding for the project.

Lineage

Maintenance and Update Frequency: asNeeded

Statement: Airborne Laser Survey In response to the topographical data requirements identified in the early stages of the Study, an Airborne Laser Survey (ALS) of the study area was commissioned in order to provide the data to develop a Digital Terrain Model (DTM) of the Darling River Floodplain. The survey area encompassed approximately 4,000 km2 and included Bourke Township and the village of Louth. ALS data was supplied: With a stated vertical accuracy +/- 0.15m @ 67% confidence; With a stated horizontal accuracy +/- 0.30m @ 67% confidence; Geo-referenced to GDA94, MGA Zone 55; and Elevations reduced to the Australian Height Datum (AHD). A Digital Terrain Model (DTM) was created from the ALS data. In addition, a Triangular Irregular Network (TIN) was constructed covering the Darling River, its tributaries and a river buffer area that extends 100m either side of each river bank, ensuring sufficient detail of the important features of the river bank were captured. The TIN has coverage of approximately 120 km2 and includes break lines that define the edges of features of importance for flood modelling, such as the top of levees or other channel works on the flood plain. At the same time, spatially geo-referenced aerial photographs (ortho-imagery) of the area were captured. A Digital Elevation Model (DEM) was created from the TIN as a means of verifying the coherence of the data in the TIN. Figure 4-1 presents the DEM of the study area. PLEASE NOTE: The above data has been altered from the content received by Geoscience Australia from NSW Office of Environment and Heritage on 23 October 2014. The following datasets have been altered or created: Point cloud has been classified (ground class 2 / non-ground class 1) DarlingBourke2009\z55\2009\Mass_Points\LAS\Classified\AHD\Tiles_1k_1k Classification was conducted using LAStools' lasground.exe with a 5m step DEMs have been created at 1m and 5m resolution DarlingBourke2009\z55\2009\DEM\GRID\ASCII_GRID\Tiles_1mx1m DarlingBourke2009\z55\2009\DEM\GRID\ESRI_GRID\Mosaic_01m\darbourke01m DarlingBourke2009\z55\2009\DEM\GRID\ASCII_GRID\Tiles_5mx5m DarlingBourke2009\z55\2009\DEM\GRID\ESRI_GRID\Mosaic_05m\darbourke05m DEM creation was conducted using LAStools' las2dem.exe The following datasets have not been altered: Imagery DarlingBourke2009\z55\2009\Imagery\ECW\Tiles_1k_1k Contains 0.36 metre resolution RGB imagery in ECW format Metadata DarlingBourke2009\z55\2009\metadata Contains: flood study report tile indices statement of intellectual property ownership DarlingBourke2009\z55\2009\metadata\Flood_Study_Geodatabase Contains files used for flood study analysis DarlingBourke2009\z55\2009\metadata\Flood_Study_Geodatabase\Darling River\drtin TIN representing ground surface DarlingBourke2009\z55\2009\metadata\Flood_Study_Geodatabase\Darling River\DarlingRiver.gdb The file geodatabase contains a hillshade, a raster and within the feature dataset entitled 'DRVector' there are 7 items: DRBreaklinesLines - 3D breaklines in a line feature class DRBreaklinesMultipatch - 3D breaklines in a multipatch format DRBreaklinesPolygon - 3D breaklines in a polygon feature class DRSamplePoints - the multipoints that the Terrain model and TIN are based on DRSamplePointsDiscrete - individual points, rather than multipoints, indicates the spread of the LiDAR sample points DRTerrain - terrain model StructuresPoints - point data over structures of interest

Notes

Purpose
The manual supports the primary objective of the New South Wales Government's Flood Prone Land Policy to reduce the impact of flooding and flood liability on individual owners and occupiers of flood prone property, and to reduce private and public losses resulting from floods, utilising ecologically positive methods wherever possible.