Unincorporated King County to be Remapped using Lidar

According to this KOMO News piece, King County unveiled Monday, May 5th an initiative to re-map unincorporated county land over the next two years partially to help identify potential landslide areas.

King County will dedicate $800,000 to take advantage of much improved technology to remap the county using latest lidar equipment.

The last survey done in 1980 doesn’t have the resolution or clarity that is now available – though it famously aided identification of the previously unknown Seattle Fault.

Lidar takes advantage of reflected laser light – using sophisticated algorithms to discard ‘false’ reflections from trees and vegetation. Thus the ground is laid bare of that vegetation and elevation maps – accurate to about half a centimeter – can be mapped by an survey airplane for a 1 kilometer wide swath. (If needed, better resolutions can be achieved by flying at lower elevations and mapping a narrower swath.)

The new mapping will:

• reveal new areas of slide risks
• Possibly clear areas previously thought to be at risk
• predict the potential type of slide
• suggest likely paths and areas covered by a debris field

Any new or existing risk areas will get noted on property owners titles, notifying potential buyers of the current status/risk. And such notifications can be unclear and create issues for current land owners – but make entire sense for buyers. See this LA Times story for some of the issues when new fault line maps there recently constrained existing and proposed development on previously unknown faults.

The current King County slide risk map can be viewed at:

http://your.kingcounty.gov/dnrp/library/water-and-land/flooding/local-hazard-mitigation-plan-update/landslide-hazard-map.pdf.