Saturday, November 14, 2015

Forest Board Manual Update for Landslides

The Forest Practices Board met on Tuesday, November 10, 2015 (fpb_mtgpacket). One part of the meeting was to consider adopting an update to the Forest Board Manual Section 16 Guidelines for Evaluating Potentially Unstable Slopes and Landforms. The Manual is not a hard fast rule but the fact that it is official guidance suggests that deviating from the guidance may be challenged. Hence, timber industry wants to minimize specific language in the Manual while safety and conservation minded folks would like a stronger worded guidance to ensure forest practices that may impact potentially unstable slopes gets a thorough assessment. The conservation part of the guidance is that a significant motive of forest practice rules is to protect fish habitat. Landslide frequency and magnitude can have a harmful impact on fish habitat.  

The Board approved the new Manual Section 16. However, they indicated they wanted some areas reviewed that had been raised during public comment including comments by geologists. It is my understanding that the intent is to have DNR staff and technical experts review the issues over the next few months.

I did submit some comments regarding deep-seated landslides. One comment slightly modified to better fit this post is presented below:

Rule identified landforms (WAC 222-16-050) identifies 5 categories of unstable slopes A through E. With the exception of toe areas of deep-seated landslides (category B) and groundwater recharge to glacial deep-seated landslides (category C), deep-seated landslides will fall under the catch all category (category E).

Within Part 6 of the Manual, deep-seated landslides are only assessed in Part 6.1. Glacial deep-seated landslides are placed in another category, Part 6.2.  Part 6.2 references back to Part 6.1 so that glacial deep-seated landslides are evaluated in both Part 6.1 and Part 6.2.  

Part 6.2 should apply to all deep-seated landslides. Part 6.2 includes recommendations that should be applicable to all deep-seated landslides not just glacial deep-seated landslides. It is important that all deep-seated landslides be included in the evaluation procedures in Section 6.2.

It appears that the intent is to not include all deep-seated landslides in Section 6.2. The Board should ask if that is the intent and, if so, what is the justification of excluding deep-seated landslides from this level of review. Deep-seated non glacial landslides are very common and wide spread and are found in both non glaciated and glaciated areas throughout Washington State. Some of these landslides are potentially very dangerous and not considering the potential impacts from proposed forest practices would be a failure of the Board Manual.  

Presented below is an example of a deep-seated non glacial landslide location where a forest practice was proposed on Sumas Mountain in Whatcom County, the North Zender timber sale (#91633). This proposed timber harvest is clearly located on a deep-seated landslide per LiDAR imagery presented below as well as previous geologic mapping and expansion of the slide and further runout poses significant risk. 


The proposed Board Manual would have the landslide assessed under Part 6.1 but not under Part 6.2. The criteria and assessment of Part 6.2 would not apply to this obvious deep-seated landslide simply because it is not a glacial deep-seated landslide. There no reasonable basis that Part 6.2 should not apply to this landslide or similar deep-seated landslides.

4 comments:

Geoffrey Middaugh said...

Seems reasonable. Question: In your picture of the Sumas slide areas: Are the exceptions for the toe and the aquifer recharge areas applied to these slides (outside the red lines), and are they excluded due to those exceptions? If so, does applying 6.2 mean that no disturbance could occur on the slide area.

Dan McShane said...

In the case of the Sumas Mountain example, only 6.1 would apply. All 6.1 does is provide guidance on determining a relative age of the landslide: Is it active, dormant, or relict. How the landslide is assessed beyond that the Manual is silent. If 6.2 is applied a more rigorous investigation would be done including the groundwater. The harvest may still go forward, but some more review would be done before that decision is made. In the case of this Sumas Mountain landslide, the evaluation was limited to the trees being straight and no surface indications within the harvest area of recent movement. The underlying geology was never discussed nor was any mechanism of sliding presented.

Wendy Harris said...

Thanks for following and weighing in on the landslide/harvest issue. On a different subject, I saw that the afternoon agenda included discussion on non point source pollution. Is there an attempt to ensure that forest practices comply with the CWA and what other changes are being recommended?

Dan McShane said...

Whole different topic Wendy and not before the Forest Practice Board at this time.