calculating vertical distance to water

I would like to calculate the minimum vertical distance to nearest
water for a series of archaeological sites. I have the site list,
elevation data and a hydrology net, but can't seem to figure out
how to make the actual calculation...

I'd appreciate any suggestions... Thanks, bjr

---------------------------------------------------------------------
Bret James Ruby Voice: (812) 855-9544
Glenn A. Black Laboratory of Archaeology Fax: (812) 855-1864
9th and Fess Streets Bitnet: bruby@indiana
Bloomington, IN 47405 Internet: bruby@indiana.edu
---------------------------------------------------------------------

     Here at Rutgers we are working on a GRASS site analysis program
for querying information about the nearest targets from the
given sites, including horizontal and vertical distances from a site
to its nearest target, the ratio of the two, etc. This module will be
useful for determining nearest source of water to archaeological sites
and their vertical and horizontal distances.
     We are interested in what data layer format (raster, site, or
whatever) you and other potential users would like to use as input/output
in such a program.

---
Jianping Xu (jianp@ocean.rutgers.edu), Scott Madry (madry@ocean.rutgers.edu)
Cook College Remote Sensing Center
Rutgers University
New Brunswick, NJ 08903-0231