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This surface depression layer highlights areas within the urban areas of WDC which may be prone to surface flooding as a result of overland flow and poor drainage. |
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This surface depression layer highlights areas within the urban areas of WDC which may be prone to surface flooding as a result of overland flow and poor drainage. |
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Morphum Environmental, July 2021 |
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5000 |
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[] |
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<DIV STYLE="text-align:Left;"><DIV><DIV><P STYLE="margin:0 0 11 0;"><SPAN><SPAN>Surface depressions are defined as areas on the DEM that are surrounded by cells of higher elevation and which could therefore potentially fill if their outlets were blocked. The extent to which depressions are formed on the DEM surface therefore depends on the degree to which the DEM has been corrected. </SPAN></SPAN></P><P STYLE="margin:0 0 11 0;"><SPAN>To map surface depressions for this project, </SPAN><SPAN>the supplied OLFP network was analysed to identify areas where surface pooling of water may result in localised flooding</SPAN><SPAN>. </SPAN></P><P STYLE="margin:0 0 11 0;"><SPAN>Many surface depressions are either artefacts of the DEM or so shallow as to be of little interest from a flood hazard perspective. In order to refine the depressions dataset to those of potential interest from a management perspective, all cells of less than 50 mm depth were therefore removed, and the remaining areas were required to meet all the following criteria to qualify as a depression:</SPAN></P><UL STYLE="margin:0 0 0 0;padding:0 0 0 0;"><LI><P STYLE="margin:0 0 11 0;"><SPAN><SPAN>Surface area > 100 m2 </SPAN></SPAN></P></LI><LI><P STYLE="margin:0 0 11 0;"><SPAN><SPAN>Maximum depth > 0.20 m </SPAN></SPAN></P></LI><LI><P STYLE="margin:0 0 11 0;"><SPAN><SPAN>Volume > 20 m3</SPAN></SPAN></P></LI></UL><P STYLE="margin:0 0 11 0;"><SPAN><SPAN>Surface depressions matching the above criteria have been converted into polygon features and attributed with the following fields</SPAN></SPAN></P><UL STYLE="margin:0 0 0 0;padding:0 0 0 0;"><LI><P STYLE="margin:0 0 11 0;"><SPAN><SPAN>SURFACE_ARA: Area (m2) of surface depression</SPAN></SPAN></P></LI><LI><P STYLE="margin:0 0 11 0;"><SPAN><SPAN>VOLUME: Estimated volume of the surface depression (m3)</SPAN></SPAN></P></LI><LI><P STYLE="margin:0 0 11 0;"><SPAN><SPAN>MIN_DEPTH: Minimum estimated depression depth within the surface depression</SPAN></SPAN></P></LI><LI><P STYLE="margin:0 0 11 0;"><SPAN><SPAN>MAX_DEPTH: Maximum estimated depression depth within the surface depression</SPAN></SPAN></P></LI></UL><P><SPAN /></P></DIV></DIV></DIV> |
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<DIV STYLE="text-align:Left;"><DIV><DIV><P STYLE="font-weight:bold;margin:0 0 11 0;"><SPAN><SPAN>Use Limitations</SPAN></SPAN></P><UL STYLE="margin:0 0 0 0;padding:0 0 0 0;"><LI><P STYLE="margin:0 0 11 0;"><SPAN><SPAN>Depression footprints define the areal extent of depressions when they are at maximum capacity, and assume a source of flow exists to fill them. However, depressions will not necessarily fill to the point of overflowing during rainfall events and therefore these storages represent a ‘worst case’ scenario. </SPAN></SPAN></P></LI><LI><P STYLE="margin:0 0 11 0;"><SPAN><SPAN>The OLFP and depressions datasets are produced under the assumption that the majority of pipes are blocked except for significant pipes, culverts and major channels. This is a conservative assumption but provides the basis for planning for resilience during large events.</SPAN></SPAN></P></LI></UL><UL STYLE="margin:0 0 0 0;padding:0 0 0 0;"><LI><P STYLE="font-weight:bold;margin:0 0 11 0;"><SPAN>OLFPs and depressions 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</SPAN><SPAN>-</SPAN><SPAN>truthing of extracted depressions should always be undertaken in areas of particular concern to inform decision-making.</SPAN></P></LI></UL><P><SPAN /></P></DIV></DIV></DIV> |
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| title:
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OLFP Surface Depressions |
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| tags:
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["Surface Depressions","OLFPs","Morphum Environmental"] |
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en-US |
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150000000 |
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