Water drop trace?

[JoshuaDamron]

Greetings,
  An engineer in my department inquired how effectively ArcGIS could model a drainage basin.  I am not extensively familiar with modeling drainage in ArcGIS so I am hoping someone can guide this question for me:

Are there extensions or add-ons available for ArcGIS that will enable a model to be performed where an analyst can place a drop of water on a digital elevation model or TIN surface and trace the downhill route that drop will take both overland and through the City's underground storm drainage pipe network all the way to a creek then to its final river destination?

Is this a realistic expectation for ArcGIS or would I be better off looking into industry specific software (for example those offered by Autodesk)?

Any thoughts are appreciated.

[MarkBoucher · Accepted solution]

Joshua,

To do the trace you need a flow direction grid. If you have that, the Arc Hydro tool bar has a trace tool that draws a graphic line (not feature) along the flow path. You need Spatial Analyst (SA) for this. The graphic lines can be converted to features using a function in the Draw toolbar pull down menu and possibly some other tool.

To get the flow direction grid, you have to process the a DEM. Arc Hydro or the geoprocessing and SA hydrology tools can be used for this. You may need to Recondition the DEM (Arc Hydro term for when you "burn in streams" to eliminate bridges that "block" the stream in the DEM.) You may also need to "build walls" where the DEM watershed boundary is not well define by the DEM (very flat areas and/or low-res DEM). You will need to fill in the "sinks" so that every internal cell of the DEM has a cell next to it that is lower than it that will allow the proper determination of the flow direction along the surface and the flow path will not stop mid watershed.

To burn streams and build walls simply using SA, you have to create polylines for the streams and walls, convert each of them to rasters and then subtract the stream raster from the DEM and add the wall raster to the DEM. I suggest using a large number for the stream raster value (1000) and a small number for the wall raster value (100), this way when you build a wall after burning the streams, any stream that have to go through walls will not be "blocked" when you do the fill sinks function. The stream and wall values don't have to mimic reality. You are looking to get the flow direction right, not the elevation. If you want the right elevation, go back to the DEM.

One tip is that you only need to burn stream when the DEM ill defines or miss defines a main flow path that you know for certain exists. You can burn streams where underground storm drains exist. You can burn streams through bridges or culverts on creeks. You don't have to burn streams where the DEM defines them well. If you burn streams where the DEM defines them well, your stream polyline could end up poorly representing the stream.

Likely more than you asked for.... Hope this helps.

[JoshuaDamron]

Likely more than you asked for.... Hope this helps.

Actually this was exactly what I was hoping for.  Thank you for taking the time to clearly outline the steps involved.  Your post gives me an idea of what level of commitment I'm making if I tell my engineer "of course ArcGIS can do that!" 

I'm certain that any product used for a certain level of drainage analysis requires a high degree of fine tuning and ArcHydro is in this same ball park.  My City has a very high resolution TIN/DEM which generated 1' contours, this is really nice because the DEM shows all of the curb lines and the crowns of most streets.  I can see that if we go in the direction of using ArcHydro for drainage analysis this data will save a lot of time. 

Its unfortunate that a line, not a feature line is generated with a trace.  I'm connecting a few dots and for storm inlet structures and pipes, I'm assuming you build the pipe into a sink with parallel walls on each side, ending the walls at the inlets/outlets to let the water in/out and creating what ArcHydro sees as a channel for the water? 

Is it possible for ArcHydro to bring pipe size, slope, friction coefficients into an analysis to model capacity constraints?  If I calculated how much water a storm inlet (or series of inlets) were to capture for say a 100 year storm, could ArcHydro analyze if the downstream pipe network can handle it? Or is this beyond the scope of ArcHydro at this time in its development? 

Thank you again for the thorough description of what ArcHydro can do for me.

[MarkBoucher]

Is it possible for ArcHydro to bring pipe size, slope, friction coefficients into an analysis to model capacity constraints?  If I calculated how much water a storm inlet (or series of inlets) were to capture for say a 100 year storm, could ArcHydro analyze if the downstream pipe network can handle it? Or is this beyond the scope of ArcHydro at this time in its development?.

Arc Hydro does not do pipe or channel capacity calculations. It's main purpose is to delineate watersheds and gather geographic measurements of watersheds for further calculations elsewhere. The Arc Hydro/SA/HEC-GeoHMS tools can be further used to collect agregated information such as infiltration rates supplied via other data sets. These can then be brought into other software packages to do analysis. HEC-GeoRAS can help build in a HEC-RAS model that is used for channel capacity including culverts and bridges (though I don't think GeoRAS will extract bridge/culvert date from ArcMap.)

There may be some third party software that works with the software above to perform hyrdaulic capacity calcs inside ArcMap, but I don't know of any specifically.

  I'm connecting a few dots and for storm  inlet structures and pipes, I'm assuming you build the pipe into a sink  with parallel walls on each side, ending the walls at the inlets/outlets  to let the water in/out and creating what ArcHydro sees as a channel  for the water? 

I don't normally bound the pipes with walls. This is just too much detail for my use. If you want to try this you need to take into consideration that the DEM grid does not parallel the curb lines. Because of this, the distance your walls are from the pipe polyline will be important. It will likely be further from the curb line than you want. Also, if your DEM is as fine grained as you say, processing times will be multiplied. Mine are 10'x10' and large watersheds take time to process. See the link below my signature for tips on avoiding errors and saving computation time in Arc Hydro.

The inlet catchment deliniation would likely be better done with a TIN or something.

[JoshuaDamron]

Mark,
  Thank you for another descriptive reply.  It is very helpful to have a sense of ArcHydros intended uses & functionality, it sounds like at this time ArcHydro is designed towards developing watersheds in general, and less towards analyzing flow characteristics.  I checked out the Army Corps of Engineers website and I may have to read up on the software they have made available.  Thank you for pointing me in that direction.  I did find a post in the ArcGIS blog (http://blogs.esri.com/esri/arcgis/2013/08/26/urban-hydrology-modeling-using-gis/) about urban hydrology modeling, so I see that (as you have mentioned) ArcHydro does have some ability to model urban hydrology as it interacts with pipe networks. 

A big focus for me is managing the impacts of land use on Public Works pipe infrastructure, I may have to do more poking around to find the right tool set but I can see that ArcHydro offers tools that can act as a step in the process of getting to where I need to go. 

I had earlier checked out your problem solving forum post, it is great to see the ArcHydro community build its own troubleshooting guide.

Thank you again for passing on your knowledge of ArcHydro, you have been very helpful.

All the best,
Joshua