Thursday, March 22, 2018

Comparing Lidar of Different Years at Dynamic Landscapes

The Washington State DNR has recently uploaded more lidar coverage ( Some of the recent uploads are of lidar that was flown in the early 2000s such as Jefferson County, but there is also some 2017 high resolution lidar that has been a bit of distraction to geomorphologist.

With multiple year available on the portal, there is also the opportunity to do comparisons at sites that have undergone change. Alluvial fans can be a good place to see significant changes.

Canyon Lakes Creek alluvial fan has been going through significant recent changes. The fan is in part controlled by the meanders of the Middle Fork Nooksack River as well as human infrastructure.       

2006 lidar

The change in flow on the fan has eroded into an old elevated terrace.

2013 lidar

The results have been significant property damage as the creek erodes new channels and flows and floods into areas not previously near the creek.    

Racehorse Creek is another creek that has been going through some big changes. A large landslide in the watershed in 2009 has greatly increased the sediment inputs to the stream. On the creeks lower reaches that has lead to the channel being filled and flooding and new overflow channels forming.

2006 lidar

2013 lidar, note the channel has been entirely filled 

The slide in Racehorse Creek has had some consequences to the few folks on the lower reaches of Racehorse Creek. One home has been abandoned due to the nearly winter long constant flooding.

The lumpy ground west of the lower reach of Racehorse Creek is a very large landslide deposit that dwarfs the event that took place in Racehorse Creek. The slide extended across the Nooksack River Valley. The age of this slide is not currently known.
Racehorse Slide

A comparison between 2006 and 2017 lidar shows the 2009 slide before and after. 

2006 lidar

2017 lidar
The slides are on dip slope of a sandstone unit within the Chuckanut Formation.

The 2009 slide is readily visible from the Nooksack Valley south of Kendal and appears as a sharp edged block missing from the the slope. The lidar suggests that the slip was off the same bed of the formation.

No comments: