This dataset represents a stream network (centreline) of features both natural and artificial across NSW, classified using the Strahler Stream Order method, undertaken by the Department in 2013. This is a legacy, unmaintained and best endeavours dataset based upon a static (2012) copy of the now NSW Department of Customer Services (DCS) | Spatial Services: NSW Hydro Line. Today this updated, but unclassified network, forms part of the NSW Digital Topographic Database (DTDB) and NSW Foundation Data Framework administered by DCS.

Classification of the stream network was completed using the ‘RivEX’ tool (www.rivex.co.uk) in combination with ESRI ArcMap by the Departments Geospatial practitioners.

The dataset was initially broken down against 13 Catchment Management Authority (CMA) catchment boundaries (as at 2012), or smaller subsets to aid RivEx processing, which closely aligned to hydrological catchments. The edges of the subsets were checked to ensure hydro lines fell within the correct hydrological unit.

There were issues with the RivEx processing time if there were too many features processed at once. As a result, catchments were often further broken down into smaller hydrological sub-catchments if the dataset remained too large.

Catchments were processed (classified) in order of stream flow to ensure the order at the end of one catchment was used as the beginning of any it flowed into.

For Victorian and Queensland datasets – any stream that flowed into NSW waterways were extracted (by complete catchment) and processed in exactly the same way as the NSW hydro lines data. Queensland was processed first so the Strahler results could be incorporated in the northern catchments of NSW. Victorian streams were processed before the NSW Murray & Lower Murray Darling areas to ensure continuity of stream order application in NSW.

A summarised workflow is provided below:

• Input dataset: 2012 DCS NSW Hydro Line
• Break the input dataset into manageable catchments for processing
• Complete topology checks (ArcMap) on catchment subsets
• Undertake basic hydrological enforcement by flipping geometric line directions where required to align with stream flow / class order direction.
• Run Strahler processing (RivEX)
• Undertake visual quality assurance of results & manually resolve issues.
• Recombine catchments to assemble a statewide dataset
• Output dataset: Hydro Line (2012) Strahler Stream Order Classification NSW

Note: Victorian and Queensland data was also sought (best available) so accurate Strahler assessments at the State borders could be assessed.

• Please refer to the significant limitation of use for this dataset contained in this document.

Note: If you would like to ask a question, make any suggestions, or tell us how you are using this dataset, please visit the NSW Water Hub which has an online forum you can join.