Landslide Hazards along River Corridors - Lowland fans

Description

Layer name: LSR_F_LOWLANDFANS
Subject category: enviro
Title: Landslide Hazards along River Corridors - Lowland fans
Feature Count: 372
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.
Purpose: Suitable for general reference and analyses. Identifies only depositional fans in Puget Lowland areas 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: No simple metric was identified in the literature that could be used to screen lowland basins and identify those most likely to be inundated by such debris flows. A review of sites with known recent debris flows or debris floods in the Puget Lowland areas of King County suggests that they share some characteristics in common: (1) all of the recent incidents reviewed entailed discharge from ravines with steep side slopes, typically > 60 percent slopes; (2) all discharged onto well-defined, preexisting fans, and these flows were often initiated by a sudden release of water, and in a number of recent cases this has been the result of failure of an upstream beaver dam; (3) where the channel gradient above the fan was steep, in excess of a 15 percent slope, the discharge was in the form of a debris flow; and (4) where the channel gradient was less than a 15 percent slope, the discharge took the form of a debris flood. These observations are based on a small number of recent incidents, which is not enough to develop robust screening criteria. Based on the characteristics above, DNRP geologists used LiDAR imagery and closely spaced contour lines to map depositional fans in the Puget Lowland areas.

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

Constraints

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