2016-07-18 General Committee Meeting - Item 3 - Attachment 1 - Flood Management Plan

7.3 Flood Studies Survey                                          7.3.2		 Bathymetric Survey




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Flood studies will generally be informed by a flood model         Bathymetric survey is information relating to river and lake




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of the area under investigation. Flood models are typically       bed surfaces. Bathymetric survey is typically undertaken




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computer based simulations of the terrain and other               below normal water surface levels. Detailed bathymetric
landform features combined with algorithms to translate           survey was been collected for the lower reaches of the
rainfall into runoff and flooding conditions. To create           Noosa River in 201017. This survey was collected using a
an accurate flood model of a location requires survey             combination of depth sonar readings and GPS tracking
information of the terrain and any significant features           to map the bed surface of the river. Sandy coastal river
which may influence the flow of flood waters. There are           estuaries like the Noosa River are dynamic systems that are
typically three types of survey data required for flood           continuously changing due to freshwater flows and tidal
models. These being: ground survey; bathymetric survey            currents. This survey offers a snap shot in time of the river
and waterway crossings survey.                                    bed during ambient (non flood) flow conditions.

7.3.1         Ground survey                                       Standard ALS survey techniques do not capture terrain
                                                                  surfaces below water levels although specialised equipment
Ground survey data for flood models was traditionally             and processes continue to be developed in this field. In
collected as a series of cross sections surveyed across semi-     2013 a pilot study was conducted on the Sunshine Coast
regular intervals along a waterway and capturing ground           as a collaboration between the Queensland Government,
levels which extend across the flood plain. The collection        CRC for Spatial Information (CRCSI) and the Department
of cross section survey over large areas is labour intensive      of Climate Change and Energy Efficiency (DCCEE). The
and returns a relatively limited portrayal of the terrain.        aim of the pilot study was to provide useful evidence to
More contemporary survey methods utilise aerial laser             inform future data gathering by considering the methods
scanning (ALS) also referred to as LiDAR. ALS survey              and technology available and the relationship between
is undertaken from a specialised aircraft and sensor              the accuracy of the bathymetry and our confidence in the
equipment and provides a detailed record of surface levels        modelling outputs. The pilot study found that the current
capable of capturing dozens of readings per square metre          technology of bathymetric LIDAR was not recommended
across entire catchment areas. ALS data sets are extensive        for streams, estuaries and lakes but may be an efficient
and offer a detailed assessment of visible surfaces capable       method for near-shore coastal areas.
of generating an accurate representation of the terrain and
other features from potentially billions of surface point         The collection of additional bathymetric survey of the
records.                                                          Noosa River is recommended to supplement existing
                                                                  survey of the River’s bed profile to help monitor and
ALS data sets for a location are generated periodically by        understand changes over time and potential impacts.
government agencies and private suppliers. A 2016 series of
ALS data has been captured for Noosa and post processing
of this data is underway.




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     Lower Noosa River Hydrographic Survey Definium Survey 2010




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