# Tute M05 Calculate Afflux Arc

From Tuflow

# Introduction

In this page we compare the peak flood levels for the existing and developed case runs to calculate flood afflux. This requires the **3D analyst toolbox**. If you do not have this toolbox it will be necessary to calculate the results outside of ArcMap using the TUFLOW utilities. This process is outlined __ in the tutorial module.__

# Method

- Open ArcMap and ensure that you have a 3D analyst licence available (if you do not have a 3D analyst licence, the TUFLOW utilities can be used to create the difference raster see
__here__. - From the
**TUFLOW\Results\M05\2D\**folder, open both the**M05_5m_dev_001_hMax.asc**and**M05_5m_exg_001_hMax.asc**grids. These can simply be dragged and dropped into the layer control or they can be imported using the*Conversion >> To Raster >> ASCII to Raster*toolbox item. - Once these grids have been opened they can be coloured or interrogated using the standard ArcGIS methods. In the image below they have been shaded.
- To calculate the flood impacts we will subtract the existing case results from the developed case. To do the open the
**3D Analyst Tools>> Raster Math >> Minus**item from the toolboxes: - At the dialogue, subtract the existing (exg) results from the developed (dev) results to (i.e. impact = dev - exg). This will create a new raster difference grid that can be styled or coloured as desired.

# Conclusion

ArcMap has been used to calculate the flood afflux. Please return to __Module 5.__