Won’t logging cause landslides?
Many other geologists do not agree with SJW’s certified engineering geologist (or the State’s geologists) that harvesting on unstable areas and active landslides will pose “no significant risk of accelerating or exacerbating land movement or sliding. There are a number of large and small, active landslides in the plan area, some as close as 600’ downslope of people’s homes. Logging is proposed on these slides. Who should determine the level of risk to the upslope homeowners?? What is “significant risk”? The NTMP clearly acknowledges that the plan is proposed along the San Andreas Fault zone which is already geologically unstable without additional human intervention. Some of these slides probably occurred, in part, as a result of the previous clear-cutting and other ‘legacy’ land use activities in the area. The area is also in a zone of high rainfall which can add to the already vulnerable site conditions. For instance, pg 12, Mitigation Point G7-7: “This is a secondary deep-seated tra
The bulk of the logging zone is located along the notoriously active San Andreas Fault Zone. According to the NTMP, on-the-ground conditions consist of extremely unstable slopes, steep “inner gorge” areas along seven tributaries, and numerous active landslides, including a 6+ acre slide below the Chemeketa Park neighborhood. The plan notes large channel bank failure, watercourse flow already constricted by slide movement undercutting stream banks, recent bank failure in other locations, and notes that ‘future movement’ of some slides is very likely even during moderate storms. Logging will be allowed on most of the slide areas, and tractor operations are also proposed on unstable areas and steep, highly erodable slopes with a gradient over 50%. Skid trails often concentrate run-off leading to increased erosion and sometimes landsliding. Removal of canopy can reduce rainfall interception and increase runoff on landslides and steep slopes as well.
