The Minerva Debris Flow Model

Intense and persistent rainfall infiltrates bedrock and surficial material, increasing pore water pressure, which can result in slope failure. Debris flows are generated when such a landslide intersects a flowing body of water, or when saturated bed sediments are mobilized and begin flowing downstream. Debris flows can be very destructive, frequently damaging buildings and roads constructed on debris flow fans.

For this study we define a “debris flow” model, intended as a conceptual abstraction of a watershed described by the properties and the terms that a geoscientist may use to determine which creek is more likely to generate debris flows. With debris flow, we refer to the class from the updated Varnes classification (Hungr et al., 2014). Table 1 summarizes the properties used to define the debris flow model, drawn from the scientific literature (Bovis and Jakob, 1999; Friele, 2012; Goudie, 2014; Holm et al., 2016; Howes and Kenk, 1997; Hungr et al., 2014; Jackson, 2019; Jackson et al., 2014; Segoni et al., 2018; Strahler, 1957; Wilford et al., 2004)

Instance Property-Value-Frequency Model Definition Source Comments
has surficial form -Fan(s)-always  (Harvey A. 2013, Alluvial Fan, in Goudie A. (Eds) Encyclopedia of Geomorphology, Routledge, London and New York, p 1202) Fans are where debris flows deposit.
has surficial form -Terrace(s)-usually  (Bridge J. S., 2013, Alluvium in Goudie A. (Eds) Encyclopedia of Geomorphology, Routledge, London and New York, p 516-521) Terraces are formed by downcutting and lateral erosion of alluvial sediments by streams. Debris flows can generate terraces (Bridge 2013), hence, terraces can be indicator of debris flow activity. 
has surficial form -Hummock(s)-always Howes and Kenk 1997 Hummocky topography may be indicator of landslide debris (Howes and Kenk, 1997)
has water -River/Stream-always Hungr et al 2014 Debris flows occur periodically on established paths, usually gullies and first- or second- order streams (Hungr et al., 2014)
has rainfall -Extreme Rainfall-always Segoni 2018, Friele 2012 Debris flows are triggered by intense rainfall (Segoni et al., 2018).  Rainfall threshold for this study are derived from Friele (2012).
has rainfall -Severe Rainfall-usually Segoni 2018, Friele 2012 Debris flows are triggered by intense rainfall (Segoni et al., 2018).  Rainfall threshold for this study are derived from Friele (2012).
has rainfall -Moderate Rainfall-sometimes Segoni 2018, Friele 2012 Debris flows are triggered by intense rainfall (Segoni et al., 2018).  Rainfall threshold for this study are derived from Friele (2012).
has rainfall -Mild Rainfall-rarely Segoni 2018, Friele 2012 Debris flows are triggered by intense rainfall (Segoni et al., 2018).  Rainfall threshold for this study are derived from Friele (2012).
has geomorph process -ErosionalProcess-always Bovis and Jakob 1999 Streams with active erosional processes are more likely to experience debris flows than streams with less active erosional processes (Bovis and Jakob, 1999).
has geomorph process -MassMovement-always Guzzetti et al 2012 Landslides are more likely to occur on slopes or valleys that have experienced landslides before (Guzzetti et al., 2012)
has been logged within years -5-10 years-always Jackson 2019 Literature Review Landslides are extremely likely by 5 to 10 years after tree harvesting. Most of tree roots have died, and new trees are too small to provide anchoring effect with their roots on the slope (Jackson 2019)
has been logged within years -10-20 years-usually Jackson 2019 Literature Review Landslides are likely by 10 to 20 years after tree harvesting as new trees are starting to provide anchoring effect with their roots on the slope (Jackson 2019)
has been logged within years -0-5 years-usually Jackson 2019 Literature Review Landslides are likely by 0 to 5 years after tree harvesting as the trees are dead but some roots are still providing anchoring effect on the slope (Jackson 2019)
has fire within years -0-2 years-always Jackson 2019 Literature Review Debris flows are very likely for 2 years after a wildfire. Water cannot infiltrate, runoff and erosion increase as the soil becomes water repellent and loses cohesion because of the fire heat (Jackson 2019).
has fire within years -3-5 years-usually Jackson 2019 Literature Review Debris flows are likely between 3 to 5 years after a wildfire. The water-repellent soil horizon degrades but the roots of dead trees are starting to rot and they do not support the slope with their anchoring effect anymore (Jackson 2019).
has fire within years -5-10 years-always Jackson 2019 Literature Review Debris flows are very likely between 5 to 10 years after a wildfire. Roots of dead trees decay, and they are not supporting the soil anymore as for the case of tree harvesting logging (Jackson 2019).
has fire within years -10-20 years-usually Jackson 2019 Literature Review Debris flows are likely between 10 to 20 years after a wildfire. The roots have lost anchoring effect and the new trees are still too small to support the slope (Jakson 2019).
has transport line -Road Resource-always Jackson 2019 Literature Review Logging roads are the greatest aggravating factor for landslide activity as compared to undisturbed slopes (Jackson 2019)
has transport line -Road Resource Demographic-always Jackson 2019 Literature Review Logging roads are the greatest aggravating factor for landslide activity as compared to undisturbed slopes (Jackson 2019).
has transport line -Road Unclassified Or Unknown-always Jackson 2019 Literature Review The ‘Road Unclassified Or Unknown’ in this area of BC are mostly old inactive logging roads. This assessment has been done by visual evaluation of the data. Logging roads are the greatest aggravating factor for landslide activity as compared to undisturbed slopes (Jackson 2019).
has bed rock -volcanic igneous rock-always Bovis and Jakob 1999 Quaternary volcanic rocks in BC have usually weak geotechnical properties. Basin underlain by these weak rocks are likely to experience frequent and large debris flow events (Bovis and Jakob 1999).
has fire within years ->20 years-sometimes Jackson 2019 Literature Review After 20 year since a wildfire, trees have regrown and the wildfire effects on slope stability have diminished (Jackson 2019)
has surficial material -Colluvium-Usually Bovis and Jakob 1999 Debris flows are common is areas with easily erodible material.
has surficial material -Morainal Material (Till)-Always Bovis and Jakob 1999 Debris flows are common is areas with easily erodible material.
has stream order -1-Always Hungr et al 2014 Debris flows occur periodically on established paths, usually gullies and first- or second- order streams (Hungr et al., 2014)
has stream order -2-Always Hungr et al 2014 Debris flows occur periodically on established paths, usually gullies and first- or second- order streams (Hungr et al., 2014)
has stream order -3-rarely Hungr et al 2014 Debris flows occur periodically on established paths, usually gullies and first- or second- order streams (Hungr et al., 2014)
has stream order -4-rarely Hungr et al 2014 Debris flows occur periodically on established paths, usually gullies and first- or second- order streams (Hungr et al., 2014)
has stream order -5-rarely Hungr et al 2014 Debris flows occur periodically on established paths, usually gullies and first- or second- order streams (Hungr et al., 2014)
has been logged within years ->20 years-sometimes Jackson 2019 Literature Review By 20 year since logging, trees have regrown and the roots are anchoring the soil again (Jackson 2019)
has geomorph process -Debris Flow-must_be Wilford et al., 2004, Bovis and Jakob 1999, Holm 2016 Melton ratio (number that takes into account relief and area of a watershed) and watershed length allows discrimination of debris flow, debris flood, and flood prone fans (Jackson 2019).
has landslide type-debrsi flow-Always Hungr et al 2014 Debris flows occur periodically on established path. Determining the frequency of event is a non-trivial task, but the fact that someone mapped a debris flow in a specific channel, indicates the channel as prone to debris flows events.
has landslide type-Fall -usually Bovis and Jakob 1999 Any landslide types may accumulate debris in a channel that can be then mobilized into a debris flow
has landslide type-Flow-usually Bovis and Jakob 1999 Any landslide types may accumulate debris in a channel that can be then mobilized into a debris flow
has landslide type-Slide-usually Bovis and Jakob 1999 Any landslide types may accumulate debris in a channel that can be then mobilized into a debris flow
has landslide type-Spread-usually Bovis and Jakob 1999 Any landslide types may accumulate debris in a channel that can be then mobilized into a debris flow
has landslide type-Topple-usually Bovis and Jakob 1999 Any landslide types may accumulate debris in a channel that can be then mobilized into a debris flow
has landslide type-Slope deformation-usually Bovis and Jakob 1999 Any landslide types may accumulate debris in a channel that can be then mobilized into a debris flow
has slope -Very steep-always Hungr et al 2014 Debris flows occur periodically on established paths, usually gullies and first- or second- order streams (Hungr et al., 2014)
has slope -Steep-always Hungr et al 2014 Debris flows occur periodically on established paths, usually gullies and first- or second- order streams (Hungr et al., 2014)
has slope -moderately steep-usually Hungr et al 2014 Debris flows occur periodically on established paths, usually gullies and first- or second- order streams (Hungr et al., 2014)
has slope -moderate-usually Hungr et al 2014 Debris flows occur periodically on established paths, usually gullies and first- or second- order streams (Hungr et al., 2014)
has slope -gentle-rarely Hungr et al 2014 Debris flows occur periodically on established paths, usually gullies and first- or second- order streams (Hungr et al., 2014)
has slope -plain-never Hungr et al 2014 Debris flows occur periodically on established paths, usually gullies and first- or second- order streams (Hungr et al., 2014)
has surficial form -cliff-always Howes and Kenk 1997 Cliffs indicate steep terrains where sediments may be mobilized as debris flows.
has surficial form -cones-always Howes and Kenk 1997 Cones store sediments that may be re-mobilized into debris flow.
has water -permafrost-always Hungr et al 2014 Permafrost degradation can destabilize sediments
has texture -blocks-always Howes and Kenk 1997 The presence of blocks can be indicator of landslide processes
has texture -rubble-always Howes and Kenk 1997 The presence of rubble is an indicator of landsldies processes.

Table 1 The debris flow Minerva Intelligence model. Model name, property, property value, information source and rationale are shown in the table

References

Bovis, M. and Jakob, M.: The role of debris supply conditions in predicting debris flow activity, Earth Surf. Process. Landforms, 24(July), 1039–1054, doi:10.1002/(SICI)1096-9837(199910)24, 1999.

Friele, P. A.: Volcanic Landslide Risk Management, Lillooet River Valley, BC: Start of north and south FSRs to Meager Confluence, Meager Creek and Upper Lillooet River., 2012.

Goudie, A.: Alphabetical Glossary of Geomorphology, Int. Assoc. Geomorphol., (July), 84, 2014.

Holm, K., Jakob, M., Scordo, E., Strouth, A., Wang, R. and Adhikari, R.: Identification , Prioritization , and Risk Reduction : Steep Creek Fans Crossed by Highways in Alberta, GeoVancouver – 69th Can. Geotech. Conf., CD-Rom, 2016.

Howes, D. E. and Kenk, E.: Terrain Classification System for British Columbia., 1997.

Hungr, O., Leroueil, S. and Picarelli, L.: The Varnes classification of landslide types, an update, Landslides, 11(2), 167–194, doi:10.1007/s10346-013-0436-y, 2014.

Jackson, L. E.: Recommendation for adding logging, logging road, wildfire, and morphometric parameters to the soil slide model., 2019.

Jackson, L. E., Blais-Stevens, A., Hermanns, R. L. and Jermyn, C. E.: Late glacial and holocene sedimentation and investigation of fjord tsunami potential in lower howe sound, british columbia, Eng. Geol. Soc. Territ. – Vol. 4 Mar. Coast. Process., 59–62, doi:10.1007/978-3-319-08660-6_12, 2014.

Segoni, S., Tofani, V., Rosi, A., Catani, F. and Casagli, N.: Combination of Rainfall Thresholds and Susceptibility Maps for Dynamic Landslide Hazard Assessment at Regional Scale, Front. Earth Sci., 6(June), doi:10.3389/feart.2018.00085, 2018.

Strahler, A. N.: Quantitative Analysis of Watershed Geomorphology, Transactions of the American Geophysical Union., Trans. Am. Geophys. Union, 38(6), 913–920, 1957.

Wilford, D. J., Sakals, M. E., Innes, J. L., Sidle, R. C. and Bergerud, W. A.: Recognition of debris flow, debris flood and flood hazard through watershed morphometrics, Landslides, 1(1), 61–66, doi:10.1007/s10346-003-0002-0, 2004.