Inundation Mapping

[Baxter E. Vieux]

>Phew! The more I think of it, the more complex it becomes. Obviously,
>any rise in water levels downstream is not just dependent on the two
>factors mentioned above, but also on the capacity of upstream areas
>to take flooding. I suppose you could even model that in grass, but 
>you would need a *lot* of processing power!


This is why you need a real distributed hydrology model. The inundation
is, as you say, the result of many factors. Digital rainfall raining
on digital soils, topography, landuse, channel characteristics are easily
handled if the distributed hydrology model utilizes maps of these
parameters (which r.water.fea does). The output hydrographs and flow
depth maps can be transformed into inundation maps with a little effort
if one has the stage-discharge rating curve at selected  points on the
main stem of the river, an accurate flood plain DEM, and a suitable
method for extrapolating depth at a particular point in time at particular
point in the river to the flood plain. The latter problem of extending
this surface to cover the flood plain  cannot done by the usual GIS 
operations since algorithms, such as r.neighbors, do not respect the
hydraulic aspects of water moving downstream in a flood plain. If you
apply such a routine you typically get a very "un-hydraulic" surface!

Baxter Vieux
Associate Professor
Environmental Modeling and GIS Lab
School of Civil Engineering and Environmental Science
University of Oklahoma
Norman, Oklahoma 73019 USA
Home Page: http://chief.ecn.uoknor.edu/