Revision as of 09:31, 17 December 2014 view source Mitch3007 (talk \| contribs) Bureaucrats, Administrators 1,585 edits →2D Grid Resolution ← Older edit		Revision as of 09:31, 17 December 2014 view source Mitch3007 (talk \| contribs) Bureaucrats, Administrators 1,585 edits →2D Grid Resolution Newer edit →
Line 59: A 15ft (~4.5m) 2D grid resolution is extensively used for urban modelling, and in this case provides a good trade-off between resolution and run time. 15ft cells are small enough that flow paths down roads are adequately represented (provided the DEM accurately represents the roads as discussed above). To test the effect of different resolutions, simulations were made using grid resolutions of 5, 10, 15, 20 and 40 ft (Noted that only the 10 and 15ft are presented in this ~~tutorial~~example). Upon examination of the results, the flood extents varied by unexpected amounts between different resolutions. For example, the 10ft grid scenario (provided as part of the ftp download) produces a more extensive flood extent, even though the profile down the 1D channel is almost identical to the 15ft case. The extended flooding is the result of very shallow flow (less than 0.01ft deep) over large flat (horizontal) areas caused by the use of contours to create the DEM as discussed above. Due to the slightly coarser resolution the 15ft grid does not let water on to some of these flats, and they remain dry. Should an accurate DEM be made available for this Challenge, the flood extents are likely to be very different and much more consistent between different grid resolutions! This does raise one issue indirectly of flood mapping in urban areas where the flood depths are very shallow, or if using direct rainfall modelling. In these instances, mapping of urban areas may specify that flooding must be of a minimum depth to be mapped. For example, where the flooding is less than say, 0.05m, it is not mapped.

FMA Challenge 1 (1D-2D linked): Difference between revisions