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Overland Flow Paths generated using catchment threshold of 0.2Ha within the WDC Drainage District. Generated July 2021 |
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Overland Flow Paths generated using catchment threshold of 0.2Ha within the WDC Drainage District. Generated July 2021 |
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Morphum Environmental |
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5000 |
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<DIV STYLE="text-align:Left;"><DIV><DIV><P STYLE="text-align:Justify;"><SPAN>Overland flow paths were derived from a flow accumulation surface that was extracted from a hydrologically corrected DEM. Flow paths were defined using a flow accumulation threshold of 500 cells, i.e. to qualify for inclusion in the flow path network, a minimum catchment area of 2,000 m2 was required (500 cells x 4 m2 each). OLFPs were delineated iteratively, with additional burn lines created with each iteration to correct flow paths that spill out of their channels and follow an incorrect trajectory. This is often caused by manmade structures such as bridges but also natural features such as dense vegetation incorrectly included within the DEM (as opposed to the surface model or DSM). </SPAN><SPAN>Additionally, significant stormwater pipes were utilised as these pipes are unlikely to reach capacity and have a significant role in the </SPAN><SPAN>conveyance of water</SPAN><SPAN>. </SPAN><SPAN>Several iterations using this approach were conducted until a fair representation of the flow paths was obtained. Flow paths were first converted to vector polylines</SPAN><SPAN>. </SPAN><SPAN> The resulting feature class can be visualized by symbolizing on the catchment area</SPAN><SPAN>.</SPAN></P><P STYLE="text-align:Justify;"><SPAN>Disclaimer</SPAN></P><P STYLE="text-align:Justify;"><SPAN><SPAN>This overland flow path layer provides a high-level understanding of routes where surface stormwater may flow during rainfall events. </SPAN></SPAN></P><P><SPAN><SPAN>It is subject to the following limitations:</SPAN></SPAN></P><OL STYLE="margin:0 0 0 0;padding:0 0 0 0;"><LI><P STYLE="text-align:Justify;"><SPAN><SPAN>The layer uses a surface generated by LiDAR only and does not account for the stormwater reticulation network or for any surface obstructions such as buildings or fences.</SPAN></SPAN></P></LI><LI><P STYLE="text-align:Justify;"><SPAN><SPAN>The layer is subject to limitations in the LiDAR data. These include lower precision under dense foliage and lack of LiDAR data in some rural areas in the District.</SPAN></SPAN></P></LI><LI><P STYLE="text-align:Justify;"><SPAN><SPAN>The layer is generated through a GIS algorithm which divides terrain into a grid of squares. Water is modelled to flow from each grid square to the lowest adjacent grid square. This method means that fine features such as kerbs may not be accurately represented.</SPAN></SPAN></P></LI><LI><P STYLE="text-align:Justify;"><SPAN><SPAN>The layer does not include any assessment of depth, width, or rate, of flows.</SPAN></SPAN></P></LI><LI><P STYLE="text-align:Justify;"><SPAN><SPAN>In some locations, change to landform since LiDAR was generated will have altered overland flow paths from those displayed on the layer.</SPAN></SPAN></P></LI></OL><P STYLE="text-align:Justify;"><SPAN>These limitations mean that overland flow paths represented on the layer should not be considered definitive and are subject to further investigation. Likewise, flow paths that exist in reality, may not be represented on this layer.</SPAN></P></DIV></DIV></DIV> |
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<DIV STYLE="text-align:Left;"><DIV><DIV><UL STYLE="margin:0 0 0 0;padding:0 0 0 0;"><LI><P STYLE="text-align:Justify;margin:0 0 8 0;"><SPAN><SPAN>OLFPs represent a synthetic flow path network and do not necessarily indicate where water will flow under specific storm events or represent specific flow rates. </SPAN></SPAN></P></LI><LI><P STYLE="text-align:Justify;margin:0 0 8 0;"><SPAN><SPAN>Delineated flow paths have one-dimensional geometry, i.e. they represent the centreline of potential surface flow routes and do not provide information on flow width, depth or velocity. </SPAN></SPAN></P></LI><LI><P STYLE="text-align:Justify;margin:0 0 8 0;"><SPAN><SPAN>OLFPs are derived from a bare-ground DEM and therefore do not account for the effects of buildings or other built structures such as fences which may deflect surface flows. Ground truthing of delineated flow paths should be undertaken in areas of particular concern to inform decision-making.</SPAN></SPAN></P></LI><LI><P STYLE="text-align:Justify;margin:0 0 8 0;"><SPAN><SPAN>The current OLFP network is the result of extensive modification of the DEM. However, further burning-in of the spill points of smaller depressions is likely to modify the route of some of the lower order flow paths within the depression footprints. </SPAN></SPAN></P><P STYLE="text-align:Justify;margin:0 0 8 0;"><SPAN>The OLFP datasets are produced under the assumption that all pipes are blocked and that all but the largest culverts on major channels are also blocked. This is a conservative assumption but provides the basis for planning for resilience during large events.</SPAN></P></LI></UL></DIV></DIV></DIV> |
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| title:
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Overland Flowpaths 2021 |
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| tags:
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["OLFPs","Morphum Environmental"] |
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en-US |
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150000000 |
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