Debris-flow volume quantile prediction from catchment morphometry

Abstract

Estimation of the volumes of potential future debris flows is a key factor in hazard assessment and mitigation. Worldwide, however, there are few catchments for which detailed volume-frequency information is available. We (1) reconstructed volume-frequency curves for 10 debris-flow catchments in Saline Valley, California (USA), from a large number of well-preserved, unmodified surficial flow deposits, and (2) assessed the correlations between lobe-volume quantiles and a set of morphometric catchment characteristics. We found statistically significant correlations between lobe-volume quantiles, including median and maximum, and catchment relief, length (planimetric distance from the fan apex to the most distant point along the watershed boundary), perimeter, and Melton ratio (relief divided by the square root of catchment area). These findings show that it may be possible to roughly estimate debris-flow lobe-volume quantiles from basic catchment characteristics that can be obtained from globally available elevation data. This may assist in design-volume estimation for debris-flow catchments where past flow volumes are otherwise unknown.

Regional debris‐flow and debris‐flood frequency–magnitude relationships

“…Locally, and in relatively homogenous geological, geomorphological and climatic locations, single watershed variable correlations with F–M pairs may be achieved (e.g. de Haas and Densmore, 2019), but this necessitates a statistically significant number of detailed studies.…”

Extreme Precipitation Across Adjacent Burned and Unburned Watersheds Reveals Impacts of Low Severity Wildfire on Debris‐Flow Processes

“…De Haas et al. (2019), in their study of unburned debris flow fans in Saline Valley, California, similarly found that debris‐flow volumes were best correlated with watershed morphometric parameters related to basin size (e.g., area, length, perimeter) rather than slope. In the burned portion of our study area, debris‐flow volume had a relatively strong, negative correlation with the Melton Ratio ( ρ = −0.74, p = 0.03), followed by a more modest positive correlation with basin area ( ρ = 0.64, p = 0.07).…”

“…The first four watershed characteristics ( A23 , F23 , S50 , RU ), which provide information about slope or the combination of steep slopes and drainage area, are similar to measures of terrain steepness that are often found to be related to debris‐flow likelihood (Cannon et al., 2010; Staley et al., 2017). The last five watershed characteristics ( A , R , L , P , MR ), which except for MR are generally related to watershed size, are more likely to be related to debris‐flow volume (Cannon et al., 2010; De Haas & Densmore, 2019; Gartner et al., 2014).…”

“…Past studies have developed empirical models that relate watershed morphometry, rainfall intensity‐duration, and soil burn severity with debris‐flow initiation (Staley et al., 2017). Similar models have been developed in unburned settings that relate watershed morphometry to debris‐flow volume (De Haas & Densmore, 2019) and the potential for debris flows versus floods (Wilford et al., 2004). These relationships are valuable for rapid hazard assessments and also provide insight into factors that are most important in determining debris‐flow initiation and magnitude.…”

“…In unburned, forested catchments in western Canada, Wilford et al., (2004) found watersheds with a Melton ratio (watershed relief divided by the square root of watershed area) of greater than 0.6 and a watershed length less than 2.7 km were prone to debris‐flow initiation. In 10 arid watersheds in California, USA, de Haas and Densmore (2019) reported watershed area, length, perimeter, and relief were positively related to debris‐flow volumes, while the Melton ratio was negatively related. Using data collected from postwildfire debris flows throughout the western USA, Staley et al., (2017) proposed an empirical model for predicting debris flow rainfall intensity‐duration thresholds.…”