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I want to create a raster surface representing the flood level in a creek based on output from a 1D hydraulic model.

I receive a 3D profile of the water surface in a creek line as a 3D Polyline (AutoCad format) from our hydraulic modelers. Each vertex of the polyline represents the coordinates and level of the water surface based on cross-sections used in the modelling.

I want to import the string into QGIS and generate a water surface as a raster for analysis - for example depths, extents, comparison of flood level to building floor levels, etc).

Basically I want to extend a surface horizontally and perpendicular from the string until it intersects a nominated raster surface (existing ground), along the length of the string. I would assume that the elevation varies linearly between each vertex of the polyline (which would be accurate enough for my work).

Is there a way to generate this surface in QGIS? I would appreciate any guidance.

Thanks

PS I have edited this question to hopefully make it clearer.

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    I'm afraid I don't understand what your input data looks like. Maybe others have the same problem since nobody has turned up with an answer yet. – underdark Oct 22 '13 at 17:55
  • I agree could you please be more specific about the input data? You mention various data types, dimensionality, and file formats. Please also consider rephrasing and editing your question for clarity, as you reference the word "string" in different contexts throughout it and the current phrasing is ambiguous. – Baskinomics Oct 22 '13 at 22:28
  • I understand the question, yet can't answer with a solution. As a step forward - here goes my attempt at explaining. Waterways tend to variate in width, depth, etc.. especially when you have lake surfaces in between. Data he has available is basically line data, built from calculated estimates of the water levels (points, connected with a polyline to create a 'surfaceline', or 'string' as the OP described. To visualize in top view which areas are covered in water, he needs to be able to intersect a water surface with a terrain model. – Tim Couwelier May 7 '14 at 12:58
  • So basically what he needs is to build a 'surface' for the waterline (aka stretch out the line to a surface), convert that into a raster, and compare the DEM with the water surface. Where the DEM is higher, there's no water on the surface, where the DEM is lower then the water level, flooding will occur. Comparison of the two gives an idea of the surface where water will be located, and based on how detailed you can make the comparison, ideally you could create a raster where the value respresents a flood depth. – Tim Couwelier May 7 '14 at 13:01

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