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Suspended Solids
2

Suspended Solids

Suspended Solids

(OP)
Does the added weight of silt carried in a river increase the density of the water in a significant fashion?  

I'm looking at a coffer dam design and the engineer from another office has used 62.43 for the density.  I usually use 62.4 (62.42 is the greatest density for 4 degC), and I was wondering if this extra .01 pcf would account for silt in the flow.  The amount of silt load is fairly heavy (Red River (North)).

The precision isn't an issue, I just want to get a bit of a handle on the increased density for better understanding.

Thanks, Dik

RE: Suspended Solids

Most sediment transport equations I've seen neglect the density changes of water due to suspended solids.  Unless it's honest to god mud, I doubt it would be significant enough to change the density of the fluid.

I'd bet you're just looking at a typeo, unless the water's brackish, which does change the density.   

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com

RE: Suspended Solids

(OP)
Thanks, beej... it's not a typo, because it's repeated.  I don't think it's significant, but just want to confirm this.  I can get a container fill it and weigh it... and compare this with tapwater... but, I didn't want to do this...

Dik

RE: Suspended Solids

I have a chart that shows a maximum of 62.43 at 4C. Reference CRC handbook or the following also:
http://www.engineeringtoolbox.com/water-density-specific-weight-d_595.html


assuming a dry unit weight of 100 pcf for the silt, you would need just 0.08% silt per cubic foot of water to increase the weight to 62.43. However, I have not seen the density of water ever changed from 62.4 for a hydraulic or structural analysis. I would be more inclined to assume some deposition of silt at the base of the cofferdam rather than assuming any change to the density of water.

RE: Suspended Solids

(OP)
Thanks... my reference had 62.42... happy for the correction and explains his use of the number.

Dik

RE: Suspended Solids

The more important thing in my mind, is if your coffer dam holds up under 62.42 water and fails under 62.43 water, you need to redesign your coffer dam.  

/grin

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com

RE: Suspended Solids

62.4 has always been good enough for me.

RE: Suspended Solids

(OP)
beej:
I agree; I try not to design anything that tight...

Hokie:
same here...

thanks, gentlemen

Dik

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