FMA Challenge 1 (1D-2D linked): Difference between revisions
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[[File:Contour Data FMA Challenge 1.jpg|600px]]
When the 2D flow patterns are observed, as per the velocity arrows in the image below, the water appears to be “cascading” down the roads. Along the flat areas the velocities are low, and where the elevations suddenly drop to the next flat section the velocities are high, thereby creating the cascading effect.<br>
[[File:Cascades.jpg|600px]]
The 2D flow patterns reflect the terraced or stepped nature of the DEM, which is not a realistic representation of the road topography. Some interpolation methods such as IDW (Inverse Distance Weighting) can provide a smoother DEM, but may not preserve the contours, and where the U shapes are pronounced they will still have a strongly terraced effect.
The resulting 2D depths and water levels are also unrealistic as can be seen in the image below. The blue shades are the depths and the blue lines the water level contours every 0.5ft. Where the steps occur in the DEM, the water level contours are closely spaced, and along the flats they are wide apart. The depths vary significantly along the road when they should be reasonably uniform.<br>
[[File:Contour Data.jpg|600px]]
For 2D modeling, especially in flat urban areas, contours should not be used to create the DEM. If the contours were generated from a DEM, then the original DEM should be used or the original terrain data should be provided and the DEM recreated from this data. If contours are used, additional point data and/or 3D breaklines along the low and high points need to be provided to prevent the terraced effect from occurring.
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