The USGS emergency assessment debris model, established by Gartner, Cannon, and Santi in 2014, draws upon a specific subset of data encompassing 92 sediment deposition volumes resulting from debris flows occurring in the two years following a fire event.
This USGS emergency assessment debris model has demonstrated its efficacy in continuously simulating debris yield within a two-year window for relatively modest watersheds, covering areas smaller than 30 km².
Among a multitude of models derived from multiple linear regression analyses, the most robust one provides forecasts for sediment volumes originating from debris flows during the specified post-fire period. These predictions are encapsulated in the following equation:
|
\begin{aligned}
& \ln V=4.22+0.39 \times \sqrt{i 15}+0.36 \times \ln \text { Bmh }+0.13 \times \sqrt{R} \\\\
& V=\text { Volume of Sediment }\left(\mathrm{m}^3\right) \\
& i 15=\text { Peak 15-minute Rainfall Intensity }(\mathrm{mm} / \mathrm{h}) \\
& \text {Bmh }=\text { Watershed Burned at moderate and high severity }\left(\mathrm{km}^2\right) \\
& R=\text { Relief }(\mathrm{m})=\mathrm{h}_2-\mathrm{h}_1 \\
& \quad h_2=\text { Highest Elevation in the Watershed }(\mathrm{m}) \\
& \quad h_1=\text { Lowest Elevation in the Watershed }(\mathrm{m})
\end{aligned}
|
Required Parameters
Parameters that are required to utilize this method within HEC-HMS include the maximum 15-minute precipitation [inches or millimeters], watershed relief [feet or meters], and watershed area burned at moderate and high severity [mi² or km²] .
A Note on Parameter Estimation
The Flow Rate Threshold parameter was introduced as an independent variable to segment storm events for continuous simulation. It establishes the lower boundary for direct runoff flow rate, marking the commencement of a debris flow event when the direct runoff exceeds this threshold. Conversely, the event concludes when the direct runoff drops below the specified threshold. This parameter assumes particular significance in the calibration process, especially for continuous simulations.
