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Is it possible to conduct a flood model analysis with QGIS using a DEM? Need to simulate rising water levels on a 250k map.

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Check out InaSAFE plugin for QGIS It can handle different risk assessments - flood models being one of them. – underdark Feb 1 '13 at 7:47

If it were me, I'd be looking to

and the guys who developed it

This plugin however is only used to view analysis output, and you need input data (in 2dm mesh files and .dat format) from a model (like TUFLOW).

From the crayfish website:

Crayfish Viewer can be used to view results from hydraulic modelling packages and other software that write SMS .2dm mesh files and .dat (binary) data files. These modelling packages include TUFLOW and ISIS 2D.

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to respectfully contrast @underdark's answer and InaSAFE, I suspect you are going to want to produce results related to time and so will need to include Mannings n as a parameter in the model. – Willy Feb 1 '13 at 7:58

Depending on your needs, this method might be of use.

I have not tested this in QGIS, but it should be possible.

basically you use cost of distance to set the "cost" (as height) of the water flow. This way you get connected polygons of same hight. Thus this method represent rising water levels well, but not necessarily storm floods and the like.

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