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I need to do a neighborhood scale drainage analysis. The analysis needs to accurately show the drainage area to each storm drain inlet. Using GRASS on QGIS 2.12.1 on OS X, I have been able to delineate basic watersheds. However, the DEM file does not appear to be precise enough to pick up curb/gutters, which significantly impact drainage patterns (the flow direction just runs over the curbs in many cases), nor does the analysis account for subsurface drainage networks, which collect drainage from one location and deliver it to another.

Is there a way to 'fine tune' the DEM to add curbs and/or a way to model a storm drain network in QGIS (on Mac)?

  • If you have the curb data in vector format convert to raster, reclassify to 0 (no curb) [average curb height] (curb). Add this to your dem, assuming the dem has a small cell size to accommodate the curb area relatively well. This should get you curb boundaries to control the flow. You could do sometime similar for drains, subtract by a large number to create a sink. That may introduce another challenge though. – user92055 Apr 2 '17 at 1:31
  • Thanks. This generally worked. I started with a 'road edges' layer, added a buffer of 2 and assigned a height of 0.75 feet to each object. The buffer made the lines thicker when I rasterized it. Instead of adding the curb height, I subtracted the gutter depth from the DEM using raster calculator, which seemed to produce the most predictable results. – Chris M Apr 4 '17 at 16:37

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