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Landslide Hazards along River Corridors - Alpine fans more likely subject to debris flows

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Summary

Suitable for general reference and analyses.

Identifies only depositional fans that are located in alpine areas and are more likely subject to debris flows along the river corridor within the study limits in King County.

Description

Depositional fans are formed when sediment moving down a steep channel is deposited where the channel gradient abruptly decreases, for example where a steep valley-wall tributary reaches the valley floor.

Sediment can be carried down such a steep channel in flow-type landslides (debris flows, debris floods) or as sediment can be carried by streamflow.

Fans are subject to a range of hazards depending which of the preceding processes are active.

Debris flows are a style of landslide movement that entail landslide debris moving in a fluid state down a channel, often travelling a long distance from the point of origin.

This layer represents fans that are located in alpine areas and are more likely subject to debris flows.

Layer information

Layer Name	lsr_f_alpinefanmorelikelydf_area
Subject Category	Environment
Title	Landslide Hazards along River Corridors - Alpine fans more likely subject to debris flows
Feature Count	269
Feature Type	Polygon
Next Update	None planned
Spatial reference	EPSG:2926
Control ID	2560
Place Keywords	Pacific NW, King County, WA, Washington State
Theme Keywords	Enviro, Pacific NW, King County WA, Washington State, Landslide, Slide, Mass Movement, Landslide Hazard Mapping, Debris Slides, Shallow Landslides, Shallow Landsliding, Debris Sliding
Supplemental Information	Research in British Columbia has identified a simple landscape metric that identifies alpine drainage basins that are more likely to produce debris flows (Wilford et al. 2009). This metric is variously known as the Relative Relief Ratio (used here) or the Melton Ratio (see figure below). The ratio increases with the elevation range of the basin and decreases with the square root of the basin area. The ratio will therefore be greatest for small basins that span a large elevation change. Research in British Columbia has shown that basins with a Relative Relief Ratio of 0.6 or more are more likely to produce debris flows, and that fans with a Relative Relief Ratio less than 0.6 are more likely to produce debris floods or normal fluvial flooding (Wilford et al. 2009).

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Attribute information

OBJECTID From Esri	Description Internal feature number. Domain Sequential unique whole numbers that are automatically generated.
Mapby From King County	Description Author of mapped shapes Domain KC_DNRP
MapDate From King County	Description Date Author completed mapping Domain 2016-06
MapMethod From King County	Description Method used to identify more or less likely subject to debris flows Domain Relative Relief Ratio
Likelihood From King County	Description Describes whether more or less likely subject to debris flows Domain More likely
TypeofFan From King County	Description Description of fan Domain Alpine fan
LiDARSourc From King County	Description Source LiDAR imagery and date imagery data sent to Author Domain KC GIS 2016-06
Shape From Esri	Description Feature geometry. Domain Coordinates defining the features.
Shape.area No Source Noted	Description Not Found Domain Not Found
Shape.len No Source Noted	Description Not Found Domain Not Found

Contact information

Maintained by	DNRP - Water and Land Resources
Primary	Harkeerat Kang Harkeerat.Kang@kingcounty.gov

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