Using the CON statement to calculate reservoir extent for a given dam height

Question

I have a DEM and the dam site.  Many years ago the Virtual Campus course on Spatial Analyst had an exercise to calculate the reservoir extent for a given dam height.  The Map Algebra script had a portion that input the dam height and a portion that included a CON statement.

Does anyone remember this

Victor Gillespie

VictorGillespie · Answer

Hi Matt, I will try yours.  However, I received the original script from Timothy at ESRI on the Spatial Analyst thread.

FYI

Re: Using the CON statement to calculate reservoir extent for a given dam height

Yes, that Virtual Campus Course is still available - Learning ArcGIS Spatial Analyst

The Con statement you are looking for is something like this:

Con([BasinRaster] AND ([ElevationRaster] <= [HeightValue]), [HeightValue]) 
This Con statement translates as "If the cell is inside the basin and its elevation is less than or equal to [HeightValue], then return a value of [HeightValue]; else return NoData."

VictorGillespie · Answer

Hi Matt, Thanks for this.  I will try it later this month & I will let you know.

Regards

VictorI have a DEM and the dam site.  Many years ago the Virtual Campus course on Spatial Analyst had an exercise to calculate the reservoir extent for a given dam height.  The Map Algebra script had a portion that input the dam height and a portion that included a CON statement.

Does anyone remember this

Victor Gillespie

MattMead · Answer

I've never seen that, but I think the statement in RasterCalculator would be:

NewDEM=SetNull(TerrainDEM > DamElevation,TerrainDEM)

I'm not at a computer that has GIS on it, but that should set everything above your dam crest elevation(or whatever elevation you use for the "DamElevation" in that statement) to Null and leave you with just a raster showing everything that would be "inside" your reservoir.  This will still show any instances that are true outside of your dam area ex downstream of the dam crest would also remain unchanged.