Latest Contributions by DeanDjokic

You should not have to do anything after running Arc Hydro install .msi (assuming it successfully installed).  The Arc Hydro add-in should just "appear" next time you open Pro and so should the Arc Hydro Pro toolbox.  If it does not, try to uninstall it (using Windows Add/Remove Programs) and then installing it again.  Make sure that all instances of ArcGIS Pro are closed before you do uninstall/install.  You will need admin rights for installing. ... View more

Steve, Depending on the quality of your DEM and streams, this could be an "easy" exercise.  If your DEM and the flow direction match the placement and elevation of your streams, then you can directly use the HAND (Height Above Nearest Drainage) approach.  You will need the following rasters (I suggest that you use .tif format for your rasters): DEM (i'll call it DEM.tif).  Should be in correct horizontal/vertical units - e.g. meters. Flow direction raster derived from the DEM (FDR.tif) that "flows" into your streams. Stream raster (STR.tif).  This can have value of 1 where stream cells are and nodata elsewhere.  The elevation of the streams (thalweg) should be reflected in the DEM. The steps are then (these are all core Spatial Analyst functions - you do not need Arc Hydro): Use "Flow Distance" (Hydrology toolset) to calculate the HAND (HAND.tif) surface (that is the "output raster".  Specify inputs stream raster (STR), surface raster (DEM) and flow direction raster (FDR). Keep all other parameters at their default values. Once you have the HAND surface, to get the depth and extent of flooding for a specific depth (D) in the same vertical units as the DEM, use the simple conditional statement (use CON SA function from “Conditional” toolset) and specify: HAND.tif as your conditional raster. Expression as: Value is less than or equal to 3 (D is your flooding depth – in your case it is 3). 3 as your true raster (D is your flooding depth – in your case it is 3). Leave false raster entry empty (meaning all values outside of your flood extent will be nodata). Specify output raster (I like to put name of the depth in the output name – e.g. fe3m.tif – for flood extent of 3m, but it can be anything). That’s it.  In the output raster, where you have values, area is flooded and where it is nodata, it is “dry”.  If you want to calculate depth of flooding for each cell, just use the MINUS function and use fe3m.tif and HAND.tif as inputs (in that order). Hope this works for you. ... View more

Thanks for the problem elaboration. As always, there are many ways to do it, but I think the easiest would be to use "Drainage Area Characterization" Arc Hydro tool (in Terrain Morphology -> Drainage Boundary Processing toolset). This tool "slices" through each drainage area from its bottom up and calculates elevation-area-volume (EAV) curves and stores that in the resulting EAV table. So your workflow is then to calculate for each drainage area the water volume coming in based on the P-E-I (precip, evaporation, infiltration), from that volume look up the depth from EAV table and add that to the minimal elevation in each drainage area. That gives you the "water surface elevation" (WSE) in each drainage area after being "filled" with water. Calculate WSE-DEM and where positive you have "flood" (ignore the rest). Convert that into a polygon and that is your result. ... View more

When using HAND method for "flooding", the "Input Flood Depth" is the depth above stream centerline that you want to "flood" with.  What that specific value is, is up to you.  For example, if you use the "max depth of the creek", that is the equivalent of the "bankfull" and most of the resulting flood polygon should be contained within the channel.  Anything higher should start spilling into the overbanks and you should get "flooding". So where do you get that number?  Depends on what you are doing.  It can come from the observations (e.g. high water mark or a stage from a gage) or through flow modeling and rating curve to convert flow to depth.  If you are doing the rating curve approach, make sure that the rating curve is based on the same resolution data you used to derive HAND with (or is adjusted accordingly). And remember that inherent assumption in HAND flood modeling approach is that your water surface is uniform (constant) and parallel to the bottom of the channel.  For each channel segment.  So if you expect that the depth will change (significantly) as you go downstream, you should partition the overall stream into multiple segments that have uniform (but variable from segment to segment) depth and then use "Define HAND-based Flood Depth and Extent from Table" tool to get the floodplain.  More work but might give you better results. If you stream segment is short, then first follow the approach you have presented (single reach), see if you like the results, and if not, then use the "table" approach.  Note that you will have to reprocess the input data and partition the streams and get their catchments before you can use the "table" approach. Hope this helps. ... View more