# Calculating Runoff / Streams using DEM in ArcGIS

I am just curious about the workflow that many of you use for runoff/stream analysis using a DEM and create a "water network" from the results in ArcGIS 10.1? I know the average rainfall for different seasons throughout the year, but that's really all I have to work with for my area.

I mainly want to investigate where water will "end up" given a fairly large rain event. I am guessing you would use ArcHydro for this? Is there a different software suite or suite of tools that you would recommend for this?

Thanks!

Yes, I would use ArcHydro. I found a document on this page (updated link thanks to @Polygeo) a while ago, that outlines some possible workflows (from the ArcHydro Team). There have been some changes compared to ArcMap 10.0 so for me it was quite useful.

If you want to calculate streamflow from rainfall/precipitation events, a hydrological model is needed. HEC-HMS is a good & not that complicated model. You can use HEC-GeoHMS (addon for ArcGIS) to generate most of the inputs for HEC-HMS. A very good tutorial for both HEC-HMS & HEC-GeoHMS can be found here

You should look into the Soil Water Assessment Tool (SWAT) for this type of analysis. It really depends on the soil types in your area along with temperature and topography. There are simpler ways to approximate your runoff (USLE method or the rational method), however it would be better if you could get more information.

http://swat.tamu.edu/

Good luck!

Tools in the TauDEM toolbox (http://hydrology.usu.edu/taudem/taudem5/index.html) can be used for (parts of) such an analysis. A basic analysis may invlove the following steps:

• creating a DEM without/with few sinks
• finding steepest path from any cell in the DEM
• for each cell, finding how many contributing cells there are
• setting a cut-off for defing what (in terms of contributing cells) a stream is
• if needed, change "stream pixels" to vector lines
• if needed, find the contributing area to each stream at an interesting point (e.g. crossing of a road, railway line, ...)

The TauDEM tools are available for ArcGIS 9.3.1 and 10. Although I don't think 10.1 is mentioned on the web-page, I run it under ArcGIS 10.1. Pay attention to the installation instructions!

The HEC-HMS modeling system (mentioned by samphilips) gives you more advanced tools than this, but requires non-GIS work. The software can be found here: http://www.hec.usace.army.mil/software/hec-hms/.

I was told by a fellow GIS professional with extensive watershed analysis experience in the Pacific Northwest that ArcHydro was developed more from an engineering stand point and not so much of a natural resources stand point. I have never been able to find any documentation about this however. Anyone else? This was back when v1.1 from the U. Of Texas was the module in use so perhaps that was the case but the tools may have morphed over time/ versions?