How to investigate increasing water levels in waterways

This article is a stub.

When using the Water Overlay, water should generally be in balance. Extraordinary events such as breaches or excessive rainfall may cause an excess of water to be added to (and possibly remain in) the model. But in general, and especially in stationary calculations, you would expect the amount of water flowing into the model to roughly balance the amount of water being removed from the water as well.

How to check whether water levels rise

You may be able to see visually on the overlay where potential issues exist, but by placing a measurement in the waterway you will be able to see more accurately whether the water level rises excessively over time.

How to check whether water flows properly through a waterway:

1. Ensure the Water Overlay has a surface last value result type.
2. Open the measuring tool.
3. Create a point measurement, in the location where you suspect the water level rises.
4. Set the primary overlay to surface last value.
5. Set the measurement graph display mode to "fit to graph".
6. You now see the water level in that location in the waterway, across all timeframes of the simulation.

See if the resulting line is relatively flat, which would indicate that water remains more or less balanced. It's natural for the water level to be influences by temporary factors, so the water level going up and down during the simulation is fine. However, if the overal trent is for the water to keep rising, there may be an issue.

What can you look for when a flow issue occurs

Because water can flow in and out of any location through a number of routes and have varying origins, it can be quite challenging to find the root cause of the increase of the water (if there even is a single cause). However, a number of avenues of investigation are relevant.

Is there any excessive input?

• Check whether the configurated rainfall is the amount that you expect. You can do so at the weather event step in the configuration wizard, where the total amount of rainfall during the calculation is listed.
• Check whether there are any inlets or other constructions introducing water to the model at an unexpected rate. Check constructions near the location of the issue first.
• Check whether there are hydrological features in the project area, such as inundation areas or breaches, introducing an excessive amount of water to the model.

Is the location a bottleneck?

• Check whether the terrain in the location with the issue acts as a bottleneck or a valley due to height. Use the surface elevation result type of the Water Overlay, or the general heightmap overlay and see how the terrain is structured.
• Check whether there are hydraulic structures or hydrological features missing from the project area which should be there. For those that do exist, check whether they are correctly configured to remove water from the area, or from the model entirely..
• Check wherer there are any other flow issues in or around the area. They can have causes of their own, but may cause water to be retained leading to increasing water levels.

Is there an edge of the calculation model nearby?

• Check what the current grid cell size is, and check whether the issue occurs near the edge of the project area. Note that the outer two cells of the project area are not part of the calculation.
• Check whether the location of the issue is inside the designated 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 level areas only, check whether the location of the issue is covered by a water level area. If it is set to specified areas only, check whether the location of the issue is covered by a limit area.
• Check whether the issue takes place near the the edge of the calculation area. The closer to the edge a calculation takes place, the more chance there is of unintended edge effects.