Need app for calculating watershed area upstream of a point

Discussion created by huffmanp on Sep 6, 2011
Latest reply on Sep 9, 2011 by huffmanp
I have this request from a non-ArcGIS user: "Is there an "app" for easily calculating watershed area upstream from a point on a stream?  I'm still using the 1964 river mile index.  You'd think we could make a **** of a cool visual and interactive river mile index."  Since this user is my supervisor and he's been talking about it for a while, I probably should give this request a bit of consideration.

I'm trying to figure out an efficient approach to this request. Does something like this exist? That would be most efficient. Or will I have to roll my own? 

Assets I have are a 10 meter DEM of the whole basin, and routed hydrography (I've been trying to get these guys using the Washington State SSHIAP hydro as a river mile index for quite a while. Is the NHD more appropriate now?).

Tools I have are ArcDesktop 9.3.1 and 10 with extensions, and ArcGIS Server 9.3.1. .NET.

Abilities I have include considerable spatial analyst experience with hydro modeling, some success with Model Builder, some python scripting,  some use of map mashups and Java Script API, and laughable ability with VB and Map Objects.

I suppose I should go the steps to derive an accumulation grid from the DEM. Then wouldn't each cell in the accumulation grid contain a count of all the cells that drain to the cell, so an ArcMap user could click on the grid with the i tool and get that value, multiply by the grid's cell area and that's your drainage area?  But then how do I streamline that for the user, and particularly how to I deliver that to the non-ArcMap user?

I suppose I could also convert the routed hydro to a grid and overlay the accumulation grid and see if I could get a grid that would give a ArcMap user both stream measure and accumulation information in one i click.