Isochrone maps - are they widely available?

[WaterEngineer]

I need isochrone maps for a water contamination analysis. Does anyone know if these are widely available? A quick google search hasn't given me much, just information on what they are.

I could use the rational method to calculate the runoff instead, but I would rather the time-area method, for which I need the isochrone maps.

Ideally I would like to calculate the amount of runoff going into the river at different points along it.

 

[Studiot]

Would these be for the Sahara Desert?

I am, of course guessing from your time of posting and therefore your probable time zone, in the absence of better information.

 

[Bobbywhy]

From our EPA, this seems to deal with runoff calculations into rivers and lakes. I am not sure if this will be useful or not...

http://nepis.epa.gov/Exe/ZyNET.exe/...ackDesc=Results page&MaximumPages=5&ZyEntry=1