How to investigate odd behavior near model edges

When using the Water Overlay, water should, for the most part, be able to flow naturally. However, as with any model, at some point the Water Overlay has an edge, leading to partially unexpected behavior collectively known as edge effects.

How to check whether there are edge effects

• First check whether the issue you are seeing occurs at the edge of the calculation area. You can do so at the weather event step in the configuration wizard, where you can check the configuration for the calculation area. If it is set to Water Areas only, check whether the location of the issue is at the border of a Water Area. If it is set to specified areas only, check whether the location of the issue is at the edge of a Limit Area.
• An easy way to get a sense of whether the issue you are seeing is an edge effect, is to increase or decrease the size of the calculation area. Ideally, if your dataset is sufficient, the odd behavior should reoccur at the new edge of the calculation area, provided that circumstances are mostly comparable.

How to resolve an edge effect

Main article: Edge effects (Water Overlay)

• If possible, expand the calculation area so that a natural barrier falls entirely within the project area. Then add boundary conditions, such as Inlets, to precisely control the in- and outflow of water into the relevant area.
• If no natural border is available, you can opt to expand the calculation area, so that the edges are further away from the area of interest. The further the edges are removed from the relevant area, the less impactful their effects will be. Do make sure that any added area is also covered by data sets similar to the data sets you have already used for your relevant area. Otherwise you may encounter issues such as waterways suddenly being empty halfway between the relevant area and the edge of the calculation area.