Fwd: Reservoir sediment density
Jim Almendinger
Your question below is good -- I should give a bit more explanation:
The number I gave for reservoir sediment bulk density (0.5 g/mL = 0.5
ton/m3) refers to the mass (i.e., dry weight) of the sediment per unit
volume of wet sediment. For example, a 1 mL cube of wet sediment may
weigh 1.28 g (i.e., the wet bulk density is 1.28 g/mL). Of this,
about 0.5 g is sediment, and the remainder (0.78 g) is water.
The number 0.5 g/mL is not constant -- it may range from 0.15 g/mL at
the sediment/water interface where the sediment is very "soupy", and
it can increase to over 0.7 g/mL deeper in the sediment, as it becomes
more compacted due to the weight of the overlying sediment.
These units -- "dry" mass per wet volume -- is likely what most SWAT
modelers would want. SWAT calculates sediment as a mass -- and they
mean "dry" mass here. If you have a reservoir and you know the
sediment volume from in-filling -- it is almost certainly a "wet"
volume.
If you'd like a reference, you may cite the following paper, which
gives a total mass of sediment being delivered by the Mississippi
River each year to Lake Pepin during the 1990s as 876,000 tons,
filling in a volume of 1,600,000 m3. Dividing the two gives a bulk
density of 0.55 ton/m3, or 0.55 g/mL. This bulk density is the
average from 10 lake-sediment cores, with 35-40 subsamples analyzed in
each core. Lake Pepin receives very silty sediment from Minnesota's
agricultural lands; I suspect it is similar to many reservoir
sediments. (So maybe I should've used 0.55 g/mL -- but it is
variable, and if you need a simple number to use, 0.5 g/mL should be
OK, as long as you just need an estimate.)
Engstrom, D.R., Almendinger, J.E. and Wolin, J.A. 2009. Historical
changes in sediment and phosphorus loading to the upper Mississippi
River: mass-balance reconstructions from the sediments of Lake Pepin.
Journal of Paleolimnology. DOI 10.1007/s10933-008-9292-5 (volume and
page numbers await printed copies -- this reference is for the
electronic pre-print that was released).
Cheers,
-- Jim
Begin forwarded message:
> From: Rocky <rocky...@gmail.com>
> Date: April 28, 2009 11:07:31 AM CDT
> To: Jim Almendinger <din...@smm.org>
> Subject: Re: Change in units from my data of reservoir
>
> Dear Dr. Almendinger,
>
> I am also interested in this point, as there is a very large reservoir
> in my study area. Thank you for your idea. Here I have a question
> about the density of sediment (0.5 ton/m3), which is a good reference
> value for me. I am wondering if 0.5 ton/m3 = 500kg/m3 seems lower
> than the water density (1 ton/m3 = 1000 kg/m3). But sediment may be a
> little denser than water. Am I right? I am looking forward to hearing
> from you. Thank you for your attention.
>
> Sincerely,
> Rocky
>
>
> On Apr 27, 11:17 pm, Jim Almendinger <din...@smm.org> wrote:
>> A fair number to use for the bulk density of fine-grained (silty to
>> clayey) reservoir sediment is about 0.5 g/mL, which equals 0.5 metric
>> tons per cubic meter. Sandy deltaic sediments can be appreciably
>> more
>> dense; sediment that has been subaerially exposed, dried, and
>> compacted can also be denser.
>> If you've got an estimate of trapped sediment volume in your
>> reservoir
>> (sediment thickness * area), then:
>> -- convert it to mass
>> -- divide by the age of the reservoir, to get an average mass /
>> year
>> of trapped sediment
>> -- compare this to your sed_in minus sed_out for the reservoir,
>> over a
>> number of years of model run, to see if the model is trapping about
>> the right amount of sediment. It can vary widely from year to year,
>> so be sure to average as many years as you think are necessary.
>>
>> I hope this is what you were really asking about...
>> Good luck,
>> -- Jim
>>
>> On Apr 27, 2009, at 4:26 AM, Modelling wrote:
>>
>>
>>
>>> Dear users
>>
>>> I have a reservoir. In my output data rsv.dbf I have sed_in and
>>> sed_out (ton) and in Output.std (ton/ha) I need those values in
>>> volume, I mean, I have data in Mm^3 I need to compare if its true,
>>> but
>>> I dont know how to do the conversion. Please if any body knows.
>>
>>> thank you in advance.
>>
>> Dr. James E. Almendinger, Senior Scientist
>> St. Croix Watershed Research Station
>> Science Museum of Minnesota
>> 16910 152nd St. N
>> Marine on St. Croix, MN 55047
>> tel: 651-433-5953 X 19
>> fax: 651-433-5924
>> email: din...@smm.org
>> web:www.smm.org/SCWRS/
>
>
> --
> BEGIN-ANTISPAM-VOTING-LINKS
> ------------------------------------------------------
>
> Teach CanIt if this mail (ID 5940210) is spam:
> Spam: https://canit.smm.org/canit/b.php?i=5940210&m=0b808b2e5b63&t=20090428&c=s
> Not spam: https://canit.smm.org/canit/b.php?i=5940210&m=0b808b2e5b63&t=20090428&c=n
> Forget vote: https://canit.smm.org/canit/b.php?i=5940210&m=0b808b2e5b63&t=20090428&c=f
> ------------------------------------------------------
> END-ANTISPAM-VOTING-LINKS
>
Dr. James E. Almendinger, Senior Scientist
St. Croix Watershed Research Station
Science Museum of Minnesota
16910 152nd St. N
Marine on St. Croix, MN 55047
tel: 651-433-5953 X 19
fax: 651-433-5924
email: din...@smm.org
web: www.smm.org/SCWRS/
