Modelling Accuracy Uncertainties Impact Mapping: Difference between revisions

*The potential cumulative impact of multiple changes in the floodplain. For example, flood behaviour changes associated with a single development in isolation may be negligible, dozens of neighbouring developments over decades may however cause a significant change in flood behaviour relative to the pre-developed catchment state.<br>

 

=I am running existing and developed case and see differences away from the model changes. Why?=

Any geometry changes between models, no matter how small, will affect results, sometimes to a greater degree than that occurring in the area of change. For example, a few millimetres increase in water level can determine whether or not overtopping of an embankment occurs, and this can consequently cause even larger impacts on the downstream side of the embankment. Furthermore, these changes can be compounded by subsequent changes in timestepping when using the adaptive timestepping option (the default in TUFLOW HPC), especially at fringes of the flood extent, where cells are constantly wetting and drying. Modellers and reviewers should be judicious and pragmatic when assessing which impacts are real and which are numerical noise.<br>

* Use depth varying manning's n (lower manning's n for shallow water depths), specifically for direct rainfall models.

* Set appropriate <font color="blue"><tt>Map Cutoff Depth </tt></font> for the modelling task. e.g. direct rainfall models might have higher values to avoid undesirable noise on the wet/dry interface.<br>

 

=Why seemingly identical models can produce non-identical results?=