Height difference in 'surface last datum' and DTM

Kylian

Hi Support,

I'm currently working on a retention area where two flooding overlays are calculated. Here's a short description:

A base model allows water to flow through an inlet into the retention area, controlled by a static weir, until it reaches a certain height. The retention area is significantly lower than the upstream area (see picture 1 attached).

In the second run, an additional amount of water is added from an inlet. The "surface last datum" overlay from the first model is used as the initial water level in the second run (see picture 2 attached).

However, when I examine the results of the second overlay, it appears that almost every cell in the overlay has a small water column on it (between 10 and 70 mm), even in locations that are higher in elevation, and do not show water stress in the results of overlay 1.

Upon investigating the issue, I noticed that the "surface last datum" from the first overlay displayed slight differences compared to the DTM (Digital Terrain Model) at locations where water stress is not observed in overlay 1. This could possibly explain why cells show water, even when they don't actually have water on them.

I've attached some pictures that could help explain the above, attached in this discussion. In the first picture, the results from overlay 1 are shown, indicating that in the blue areas water stress is observed. in picture 2, the first timeframe of the second overlay is shown, where most cells show water collumns on them. In picture 3 & 4, the differences between the DTM and the "surface last datum" are shown, indicating differences in height eventhough no water is observed in the model results of overlay 1.

I'm trying to understand what possibly went wrong here, and maybe someone on the support team/forum has an idea to fix this issue.

Please let me know if you need any further information or clarification. Thank you for your support.

kind regards,

Kylian Postema