Pisit,
I agree with others that conducting any phenomenological project such as flood
forecasting will require DEMs but it also requires a lot more data for such
things as precipitation, demographics, geology, slope, soils, etc. to do a good
job.
For a small area such as a city, 10-m DEMs is good but 1-m or sub-meter DEMs
would be better and multiple DEM datasets, some acquired during a flood would be
even better. (If you are doing a project for a government agency, consider
flying the area with LIDAR or IFSAR.)
Point data for buildings in the floodplain are needed. These data should have
the following attribute data: cost to replace building, number of residents,
mobility of residents (older people would have a higher death count), number,
types, and value of animals (data for cows versus cats for example would be
needed), time of year (to assess the impact on crops), number and types of
vehicles owned by each property owner, type of building (wood vs brick etc),
buildings with basements, etc.
Polygon data for geology, soil types, and other physical properties of the earth
such as parking lots, which do not absorb water. The geology and soil data will
help you decide which areas will and won't allow water to runoff, where streams
will occur, etc. Polygon data should also include stream areas.
Line data for streams (should also be polygons to constrain the amount of water
runoff), roads and streets (for evacuation and emergency vehicle routing),
electrical utilities, water and sewer networks (to remove water from the area
and to map areas to be searched for casualties).
Now with point/line/polygon data in your GIS you can do flood modeling
(forecasting) with data about expected amount of rainfall in a certain period of
time assuming that the system is not too chaotic.
With point-in-polygon analysis techniques you should be able to show which
buildings will be damaged by a specific level of flooding. A simple calculation
should tell you the cost of the damage to those buildings if your data are
suffciently detailed enough. And if the cows are in the field, you should be
able to calculate the loss of livestock.
With polygon-polygon techniques you should be able to delineate soils/rock type
zones that increase and reduce the impact of continuous and serial rainfall in
an area. (Chances are that back-to-back storms will cause more than damage than
one single, large storm.)
What GIS along with meteorology, geology, soils science etc. gives you is an
opportunity to quantify phenomena, visualize the impact zone, and calculate
losses.
Hope that the ideas off the top of my head help.
David
"Nattis, Randy" wrote:
> Pisit,
>
> Using GIS to map flood plains (which data is already out there), you must
> understand the climo (precip) of the region of concern, past histories. GIS
> is very useful in modeling flood prone areas. High resolution DEM (10 m)
> might help. You would have to formulate a scheme for amount of precip into
> the area (up stream, etc), current levels of rivers and streams. I could go
> on, but depending on what you need, either a quick and dirty forecast or an
> actually study of the entire area, based on soil moisture, snow cover (time
> of year and location dependant), tributaries, flood plain, etc.
>
> I hope I could help some more, but I'm a bit busy. If you need, please
> get a hold of me at some point next week and I may be able to help some more
>
> Take care and good luck,
>
> Randy B. Nattis
>
> GIS SPECIALIST / METEOROLOGIST
>
> Tetra Tech EMI
> 101 Marietta Street
> Suite 2400
> Atlanta, GA 30303
> 404-225-5530
>
> Nattisr@ttemi.com
>
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