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Seattle, WA 98104
giscenter@kingcounty.gov

+ 47.59909 N
- 122.33136 W

+ 47°  35' 56.72"
- 122° 19' 52.90"

 

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

Description | Contacts | Attribute Information | Constraints

Data layer thumbnail image

Description

Layer name: LSR_F_ALPINEFANMORELIKELYDF
Subject category: enviro
Title: Landslide Hazards along River Corridors - Alpine fans more likely subject to debris flows
Feature Count: 269
Feature Type: Polygon
Abstract: 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.
Purpose: 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.
Status: Complete
Updated: None planned
Time period of content: (single date,as YYYYMMDD):: 20160620
Time period of content: (date range, as YYYYMMDD):: -
Spatial reference: WA State Plane North
FGDC Documentation: Classic or FAQ
Open Data Availability: Yes
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,
Lineage: Not available
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).

Contacts

Maintained by:
King County King County Dept of Natural Resources and Parks, Water and Lands Resource Division
Primary: Ken Rauscher, GIS Analyst, 206-477-4414
(How to e-mail a County contact)
Secondary: KCGIS Center; giscenter@kingcounty.gov. This mailbox is monitored during business hours.

Attribute Information

ItemDescriptionDomain
_Mapby_Author of mapped shapes
KC_DNRP
_MapDate_Date Author completed mapping
2016-06
_MapMethod_Method used to identify more or less likely subject to debris flows
Relative Relief Ratio
_Likelihood_Describes whether more or less likely subject to debris flows
More likely
_TypeofFan_Description of fan
Alpine fan
_LiDARSourc_Source LiDAR imagery and date imagery data sent to Author
KC GIS 2016-06


Constraints

Access: Access Constraint: Data is not available on GIS Data Portal, it may be available via a custom data request

Use: Use Constraint: King County data are made available with the understanding that they shall be used exclusively by the obtainer or his/her authorized agents. Digital products may not be reproduced or redistributed in any form or by any means without the express written authorization of King County.