Bulked vs. Clearwater Discharge in AGWA with K2

[Michael Founds]

Hello,

I am running some pre and post-fire simulations of a watershed using K2 within AGWA to evaluate the relative increase in peak flows in a recently burned area. I was hoping to get some clarification of whether it might be necessary to account for increases in discharge due to the high post-fire sediment concentration in the water known as "bulking". 

Many of the rapid methods applied by WERT teams in California use a flow modifier method (Foltz et al., 2009) to develop post-fire multipliers based on relative contribution of soil burned at district severities. These modifiers are then multiplied by a "sediment bulking factor" that is proportional to the burn severity (Gusman, 2011). My question is whether a "bulking factor" could be applied to the peak discharges from a K2 model, or if this is unnecessary with how the parameters were applied for post-fire conditions using the burn severity tool. I was under the impression that the burn severity tool applied the post-fire parameters developed for burned conditions (Canfield et. al., 2005), so I thought it may be unnecessary to add an additional "bulking factor" to a process based model. However, I could not find a reference to this topic specific to K2 in any of the academic literature. If flow bulking is not accounted for, would it be reasonable to use the sediment transport estimates produced from K2 to create a sediment bulking factor for the peak discharge?

Thanks in advance for any input!

Michael

Canfield, H.E., D.C. Goodrich, and I.S. Burns. 2005. Selection of parameter values to model post-fire runoff and sediment transport at the watershed scale in southwestern forests. In: Proceedings, ASCE Watershed Management Conference, Williamsburg, VA, July 19-22, 2005. 

 

Foltz, R.B., P.R. Robichaud, and H.H. Rhee. 2009. A synthesis of post-fire road treatments for BAER teams: methods, treatment effectiveness, and decision making tools for rehabilitation. Gen. Tech. Rep. RMRS-GTR-228. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. Retrieved from https://www.fs.usda.gov/treesearch/pubs/32967.

Gusman, A.J. 2011. Sediment/debris bulking factors and post-fire hydrology for Ventura County.

WEST Consultants, Inc. San Diego, CA. May 2011. https://docplayer.net/26973239-Sediment-debrisbulking-

factors.html