Dan Piggott. Hydraulic Modeller at

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1 Hints for building healthy models Reducing the likelihood of problems and Solving any that do occur

2 Introduction Dan Piggott Hydraulic Modeller at Edenvale Young Associates

3 Topics Focus on TUFLOW, but will discuss ISIS in context of linked models Steps for building a healthy model To attempt to avoid problems before they happen Diagnosing problems that do occur Some tips for fixing problems once you ve diagnosed them

4 Healthy Models

5 Good Foundations Terrain is the basis of a TUFLOW model Check the LIDAR Holes in the LIDAR an obvious problem Can be fixed with a simple Z shape patch

6 Good Foundations LIDAR Z shape patches Avoid selecting null value z points

7 When Filtering Goes Wrong Poorly filtered LIDAR can cause instabilities and negatively affect results Section of the TUFLOW manual

8 When Filtering Goes More Wrong On rare occasions LIDAR may be very badly filtered This may need sending back for re-filtering!

9 Filtered Out Features Filtering may also remove important features, e.g. embankments

10 Filtered Out Features These can be replaced with Z Shapes

11 Filtered Out Features Z shape merging and ignoring points

12 Filtered Out Features This could pick up low points

13 Filtered Out Features Z shape is given NO MERGE in Shape_Options

14 Likely to Offend Small channels that intersect bank boundaries can create problems

15 Likely to Offend If the channel is not important then remove it with a Z shape -99,999 points tell TUFLOW to ignore elevations between that point and next vertices either side

16 Likely to Offend If it is important then consider how to better represent Side spill from ISIS Modelling in 1D Could add a spill from ISIS

17 Ditches Representing ditches Z shape lines can be used, but not always accurate For example, what if the ditch is much more narrow compared to the cell size?

18 Ditches Flow constriction cells could be applied to the ditch Though if the ditch is important may be better to model in 1D or set up a second domain with smaller grid sizes

19 Multiple Domains Flow across 2D-2D link boundaries is often problematic

20 Multiple Domains So try and avoid it as much as possible! Minimise the amount of flood water crossing the boundary Deep water is more problematic

21 Use a Z shape layer to ensure cells along the link in both domains are using the same elevations Set Shape_width to greater than 0, but less than 1.5 times the smaller cell size Multiple Domains

22 River Boundaries Positioning boundaries Take care when placing river boundaries Steep terrain close to boundaries can form small, unstable ponds of water Widening the ISIS channel can help remove instabilities that may be occurring alongside it

24 Parallel Channels Parallel rivers not uncommon for these to become unstable!

25 Parallel Channels TUFLOW cells coded out and side spills added to ISIS

26 Time Steps Time steps and Courant numbers Not considered best practice to simply reduce time step for an unstable model If time steps too large though, results may be unstable and meaningless Limiting factor is Courant stability criterion

27 Time Steps 2D domains, Courant number generally needs to be less than 10 and typically around 5 Cr = t 2gH x General rule of thumb aim for timestep between half and a quarter of the grid size

28 Time Steps If terrain is steep and/or flow is supercritical, may be necessary to reduce timestep Mass errors can indicate too large a timestep As of TUFLOW build AA, Map Output Data Types == Cr can be used to output t Courant number

29 ISIS Channel Widths Instabilities can arise if ISIS cross section widths are less than the TUFLOW cell size Keep this in mind when trimming

30 ISIS Channel Widths Extend the cross section to at least one cell width Although two can be better

31 Replacing HX with SX Large areas of flat water on the flood plain can cause instabilities.

32 Replacing HX with SX Replacing these HX connections with SX ones can significantly improve the model here

33 Replacing HX with SX New spill units need to be added to ISIS Two for each river unit (one for each bank) Add HT boundaries so these can be linked to TUFLOW Very time consuming use HX where possible!

34 Replacing HX with SX Before After

35 Good Housekeeping Modelling logs Excellent for keeping track of changes to a model Enables others to see what work has been done

36 Good Housekeeping File naming conventions Establishing a good system can greatly help you and others to understand the model Cuts down on clutter and confusion

37 Good Housekeeping Our convention: RiverName_v01-A_f100 Applies to.ief and.tcf files New MapInfo layers given version number to match version of model run

38 Good Housekeeping We ve found organising files into a logical folder system is a great help Relative path names mean model can be easily moved

39 Diagnosing Problems

40 Diagnostic Files Check the log files (.tlf and/or.zzd) This one failed in TUFLOW

41 Diagnostic Files It s a good way to know where to start looking! This one failed in ISIS

42 Point me to it Message layers Imported from the TUFLOW log folder

43 Diagnosing Faults ISIS plot long section animate stage and flow to check for problems Cross-check with.zzd file

44 Diagnosing Faults SMS results Can be used to check for: Unexpected elevations (ground and water) Mass errors Flow paths

45 Diagnosing Faults Water level lines Useful for mapping outputs, but also for checking water levels in SMS Can help identify areas where there are problems

46 Fixing Model Problems

47 If the.zzd File Reports a Problem The problem is most likely in ISIS (check the long section plot) Sometimes a problem in TUFLOW though (that translates back to the ISIS model)

48 Some common ISIS problems Culverts add hats or enable the automatic hat option! Surcharging bridge units replace with orifice or enable switch ISIS channel widths too low ISIS reach length very small, or very different from TUFLOW Areas of flat water on the floodplain

49 If the.tlf File Reports a Problem The problem is most likely in TUFLOW (check the message layer) Causes will vary for each individual model Some common problems though include

50 Terrain! As mentioned earlier, good terrain is important for a healthy model Check the message layer in MapInfo (or other GIS) Overlay this on your LIDAR (with boundaries and nodes visible) ibl

51 Materials! Sudden changes in materials, usually from rough to smooth, along the flow path can cause problems Import your message layer over your materials layer Use a material patch to help Rough Smooth Patch (with rough material applied) Rough

52 Summary

53 Summary Reviewing and modifying terrain Multiple domains Boundary placement Appropriate time steps Channel widths Good housekeeping Diagnosing faults Some tips for fixing problems

54 ISIS-TUFLOW Healthy Models & Debugging Dan Piggott Edenvale Young

Boundaries of 1D 2D modelling. Suzanne Callaway Senior Hydraulic Modeller

Boundaries of 1D 2D modelling. Suzanne Callaway Senior Hydraulic Modeller Boundaries of 1D 2D modelling Suzanne Callaway Senior Hydraulic Modeller Introduction Why is it important to define 1D 2D boundaries carefully? Defining boundaries between 1D and 2D models (Flood Modeller