# Initial bottom differs from the geometry file

**URL:** <https://opentelemac.org/forum/t/initial-bottom-differs-from-the-geometry-file/7989>\
**Category:** TELEMAC-2D\
**Created:** [April 14, 2025, 10:20pm UTC](https://opentelemac.org/forum/t/initial-bottom-differs-from-the-geometry-file/7989 "2025-04-14T22:20:51Z")\
**Posts on this page:** 7\
**Page:** 1

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**Author:** ![user\_17764](https://opentelemac.org/forum/letter_avatar_proxy/v4/letter/u/e9c0ed/32.png) [@user\_17764](https://opentelemac.org/forum/u/user_17764)\
**Post date:** [April 14, 2025, 10:20pm UTC](https://opentelemac.org/forum/t/initial-bottom-differs-from-the-geometry-file/7989/1 "2025-04-14T22:20:51Z")

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Hello,

I created a mesh and ran a telemac 2D case (v8p3r0 on mac; files attached). It turned out that the initial bottom elevation in the result file (r2d.slf) differed from that of the geometry file (new\_bridge\_no\_dam\_2yr.slf). The elevation difference isn’t large, but I am confused because I thought they should be identical (see the picture).

I was wondering if anyone has experienced this before. What could have been the causes?

[name removed]

[t2d.cas](https://opentelemac.org/forum/uploads/short-url/tc93xsah855jmZ4gJ8Vpz8aQRSU.cas) (2.54 KB)  
[new\_bridge\_no\_dam\_saddle.cli](https://opentelemac.org/forum/uploads/short-url/pcb2FSUZ2AUqgLp7aI8Yk51xeNo.cli) (86.5 KB)  
[new\_bridge\_no\_dam\_2yr.slf](https://opentelemac.org/forum/uploads/short-url/qX27X1sMJdZUSMxZkZuRFe0RSC5.slf) (988 KB)

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<div class="post-metadata">

**Author:** ![user\_17764](https://opentelemac.org/forum/letter_avatar_proxy/v4/letter/u/e9c0ed/32.png) [@user\_17764](https://opentelemac.org/forum/u/user_17764)\
**Post date:** [April 14, 2025, 10:26pm UTC](https://opentelemac.org/forum/t/initial-bottom-differs-from-the-geometry-file/7989/2 "2025-04-14T22:26:52Z")

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Somehow the website did not let me upload the result file and the screenshot…

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<div class="post-metadata">

**Author:** ![user\_17764](https://opentelemac.org/forum/letter_avatar_proxy/v4/letter/u/e9c0ed/32.png) [@user\_17764](https://opentelemac.org/forum/u/user_17764)\
**Post date:** [April 15, 2025, 1:30am UTC](https://opentelemac.org/forum/t/initial-bottom-differs-from-the-geometry-file/7989/3 "2025-04-15T01:30:16Z")

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But the attachment should be able to generate a result file within minutes. Apologies for so many posts.

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**Author:** ![user\_18194](https://opentelemac.org/forum/letter_avatar_proxy/v4/letter/u/f9ae1b/32.png) [@user\_18194](https://opentelemac.org/forum/u/user_18194)\
**Post date:** [April 15, 2025, 5:36am UTC](https://opentelemac.org/forum/t/initial-bottom-differs-from-the-geometry-file/7989/4 "2025-04-15T05:36:48Z")

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This usually happens when you use the key “BOTTOM SMOTHING”.

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<div class="post-metadata">

**Author:** ![user\_17764](https://opentelemac.org/forum/letter_avatar_proxy/v4/letter/u/e9c0ed/32.png) [@user\_17764](https://opentelemac.org/forum/u/user_17764)\
**Post date:** [April 15, 2025, 4:25pm UTC](https://opentelemac.org/forum/t/initial-bottom-differs-from-the-geometry-file/7989/5 "2025-04-15T16:25:28Z")

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I see! Thanks!

Do you know if BOTTOM SMOOTHING also applies during the simulation (like every time step)?

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<div class="post-metadata">

**Author:** ![user\_18194](https://opentelemac.org/forum/letter_avatar_proxy/v4/letter/u/f9ae1b/32.png) [@user\_18194](https://opentelemac.org/forum/u/user_18194)\
**Post date:** [April 16, 2025, 7:29am UTC](https://opentelemac.org/forum/t/initial-bottom-differs-from-the-geometry-file/7989/6 "2025-04-16T07:29:02Z")

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I don’t really know.

But I suspect it’s some sort of an AMR according to a conditional check every few timesteps.

Please correct me if I’m wrong, I can look it up further.

From what I’ve tried, if your model doesn’t require a very sophisticated mesh resolution, like channel slopes or sudden drop on the depth there is no need for the mesh refinement.

Even if it needed, it’s better to try to refine the mesh first using stbtel and see if the results are convenient or severe hydrodynamic conditions requires this key active.

In this case of activating the keyword sensitivity analysis is even more critical, as the degree of refinement could change the results entirely.

Good luck with your study

[name removed]

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**Author:** ![user\_13673](https://opentelemac.org/forum/letter_avatar_proxy/v4/letter/u/e480ec/32.png) [@user\_13673](https://opentelemac.org/forum/u/user_13673)\
**Post date:** [April 16, 2025, 3:39pm UTC](https://opentelemac.org/forum/t/initial-bottom-differs-from-the-geometry-file/7989/7 "2025-04-16T15:39:59Z")

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Your answer is in the user manual. CONFRON is called once.