Calibration for sediment transport

[Derek Warren]

Hello Shae,

      Derek Warren here with Horrocks Engineers. We are running both Kineros and SWAT models for a sediment basin analysis. After doing so we discovered that the amount of sediment Yield is much less than what was surveyed for this existing basin which we will be using to calibrate our other basins. This being the case I turned to calibration. There is an article on your website that talkes about calibration and that for Kineros specifically you can calibrate for a sediment transport model by changing the factors of splash and COH or cohesion. I tried changing splash, but the change was pretty minimal. Changing COH was much more reactive, but in order to justify such a change I need to know how AGWA calculates it. I was wondering if you could tell me the units of COH or if unitless how it is calculated? Or if you have any other suggestions for calibration that would be welcome as well. Just let me know as soon as you can.

Thank you,

-Derek Warren

[Shea]

Hi Derek,

Unfortunately we're having some DNS issues so the links I'm posting are not working at this time, but they will come back online hopefully within the next day. 

COH is calculated using the soil erodibility factor in USLE (Kusle). In AGWA, Kusle is obtained from the kwfact field in the SSURGO chorizon table. It's units are (T^-1). The equation in AGWA to calculate COH from Kusle is

If clay <= 0.22 Then
    coh = 5.6 * Kusle / (188 - (468 * clay) + (907 * (clay ^ 2))) * 0.5
Else
    coh = 5.6 * Kusle / 130 * 0.5
End If
The 0.5 multiplier at the end of those equations I do not have documentation on. It's been there since the beginning of AGWA 20+ years ago.

For more on COH, keep reading. In KINEROS, COH is the cg term in equation 5 on the KINEROS website (https://www.tucson.ars.ag.gov/kineros) in the Erosion + Sediment Transport section of the documentation, although equation 5 refers to a channel and the output is volume per unit length of channel (L^2/T). For planes, A becomes h in equation 5 and the output is volume per unit length per unit width (L/T). For both channels and planes, equation 5 gives the rate of sediment production during a given time step at a specific spatial node. The sediment out from a channel or plane is the sediment discharge at the downstream end of the channel or plane (as opposed to the sediment production during a given time temp at a specific spatial node within the plane or channel). Sediment discharge = (water discharge) x (sediment concentration) x (particle density).

In the original KINEROS manual (http://www.tucson.ars.ag.gov/unit/Publications/PDFfiles/703.pdf, also linked to on the sidebar of the documentation section of the KINEROS website under "Download 1990 KINEROS Manual"), equation 5 from the website is equation (37) on page number 28, where cg is still the term of interest. Skipping ahead to page number 57, equation (47) calculates cg from Kusle. You should recognize equation (47) from the equation posted above. 

Shea

P.S. Until the DNS issues are resolved, I was able to use archive.org to get to the original KINEROS manual, but it looks like the Erosion + Sediment Transport section of the documentation on the KINEROS website is blank.

https://web.archive.org/web/20220221121350/https://www.tucson.ars.ag.gov/unit/Publications/PDFfiles/703.pdf