Getting started with flood modelling

08-15-2019 02:12 PM
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We're starting a project to map various flood inundation scenarios in a dozen plus locations. I'm an old hand with GIS tools in and out of the Esri ecosystem but brand new to the world of ArcHydro. I've read through the documents here. Much of the terminology is foreign to me and I don't know what applies to this project and what I can safely ignore learning about (at first). How would you recommend proceeding? What tools do I need to look at first?

I've installed the ArcHydro tools for ArcMap 10.7 and Pro 2.4, have access to 3D and Spatial Analyst, and ArcInfo level licensing.

Input data available:

  • Bare earth 1m raster elevation models built from Lidar. Waterbodies are flattened but not perfect (some edges push up, have higher elevation from the waterbody centers)
  • Vector stream lines and waterbodies that approximate but do not match the DEM surface closely enough to use as-is (e.g. not suitable for flattening)
  • Area of interest polygons (communities and neighbourhoods potentially at risk). The polys are aribitrary rectangles and don't match any topographical features.
  • Table of flood water elevations/depths scenarios to model (3 to 5 flood levels per community, so up to 75 scenarios total)

I anticipate needing to:

  • generate shoreline vector polygons
    • We would prefer not to have to digitize all of them from ortho photos. Is there some auto or semi-auto method of snapping/rubber sheeting the exsiting coarser vectors to the DEM, perhaps using centroids to identify water areas, create polys from the flattish elev, then Reshape Geometry for the parts that need cleaning?
  • re-flatten elevation from new shoreline data
    • This seems straightforward: use the Level DEM hydro tool, but requires the above 1st.
  • generate raster elevation surfaces for each depth level, for each project area
    • Is it a simple "conditional (if DEM < new-Z) then (new-Z) else (DEM)" or is there a more sophisticated tool in ArcHydro to use?
    • Remove areas from previous that wouldn't be part of the inundation area (e.g. sinks that happen to be lower elevation than new-Z but aren't connected to that waterbody)
  • For the cartography near the end, do people prefer using rasters for the various inundations or is it better to take the time to convert to polygons, smooth/generalize and all that?
  • And finally where should the gravity center of the project be: Pro or ArcMap (or both)?

Thanks in advance for your thoughts and time.

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