Manning's n?

[Niguse Abebe]

Hi! 

I'm simulating riparian vegetation in reach mode using Manning’s n, but increasing n unexpectedly leads to higher Qw and Qs, with reversed erosion/deposition. It seems n doesn’t capture vegetation effects well. Any suggestions on better ways to represent vegetation in the channel?  

[N. S.]

Hi Niguse, 

I've found something similar in the past. I don't have a solution or reason for this, but my work around has been to: 

1. calculate Manning's n and leave as is: I do not calibrate with it or adjust thereafter, and

2. adjust the m value spatially for where your slower water/ riparian vegetation will be. 

Good luck,

Neeltje Slingerland

On Wed, Aug 27, 2025, 7:53 a.m. Niguse Abebe <nigus...@gmail.com> wrote:

Hi! 

I'm simulating riparian vegetation in reach mode using Manning’s n, but increasing n unexpectedly leads to higher Qw and Qs, with reversed erosion/deposition. It seems n doesn’t capture vegetation effects well. Any suggestions on better ways to represent vegetation in the channel?  

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[Tom Coulthard]

Hi both,

N will change the hydraulics - you get deeper flows and slower velocities. But sometimes this can result in more erosion as it causes the water to deflect or concentrate more on areas where there are smaller n values. You have to change manning by quite a bit to have an impact as well. 

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From: caesar-...@googlegroups.com <caesar-...@googlegroups.com> on behalf of N. S. <n.slin...@gmail.com>
Sent: Thursday, August 28, 2025 11:53:25 AM
To: caesar-...@googlegroups.com <caesar-...@googlegroups.com>
Subject: Re: Manning's n?

 

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