FMA Challenge 1 (1D-2D linked): Difference between revisions
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Peak flood depths and water levels were exported to ESRII ASCII grids, and the flood extent was created by contouring the grid into a single region. Flows are outputted in .csv format and directly loaded into Excel. Profiles were created using the post processing utility TUFLOW_to_GIS and outputted into a .csv file.
The typical challenges experienced in situations similar to this usually relate to:<br>
*The use of contour data to create the DEM; and
*The model boundary/terrain data does not extend beyond the flooded area.
The presented solutions to these challenges are as follows:
==Using Contour Data to Create the DEM==
Contour data, without additional point elevations and/or 3D breaklines, is difficult to triangulate or interpolate to create an accurate DEM. The consequence of solely using contours is the resulting DEM can have a terraced or stair-step surface that contains flat sections where the contours form a U shape.
For example, the image below shows a part of the DEM. The red lines are the 2ft contours provided. Where the contours form a U shape, the triangulation or interpolation method typically forms flat (horizontal) areas inside the U as labeled “Flat” in the image. Between the Flats, Steps occur representing the drop in elevation to the next contour level.
[[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.
[[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.
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