June 24th 1999
June 24, 1999 Mendocino Redwood Co. responds to concerns Submitted by Nancy Budge, Mendocino Redwood Co. Concern has been raised over the potential impact of the J-Road Timber Harvest Plan (THP) on slope stability and sediment delivery to the Albion River. Much of the concern arises from the presence of deep-seated translational landslides and shallow debris slides within the harvest area. The Mendocino Redwood Company (MRC) asked Tim Best, the consulting geologist on the harvest plan, to briefly clarify findings related to these concerns. The following is a summary of his comments: "Two of landslides on the J-Road Plan are ancient, deep-seated translational landslides, each encompassing about 5 acres. The other landslides are shallow debris slides, and are substantially smaller. The two types slides are different in their origin, potential for failure, and volume of sediment likely to be delivered to the Albion River. A deep-seated translational landslide is one in which the failure extends well below the ground surface and into bedrock. They tend to be well vegetated and often support dense stands of timber. Movement typically occurs in small increments, triggered by very large storm events or by earthquakes. Because of their low rate of movement, most researchers do not consider such landslides to be significant sources of sediment to the stream particularly in comparison to the more common shallower debris slides. The two deep-seated landslides on the J-Road plan support a dense stand of 80+ year old second growth timber that are mostly undisturbed by slide movement. There is no evidence of open ground cracks or fresh scarps to suggest recent movement of the slide. The two slides are considered to be dormant or have very low levels of activity. Any future movement is likely to be small and occur very infrequently. Anytime trees are harvested there is a concern that during a rainstorm the likelihood of the harvested slope eroding, or becoming saturated and then destabilized, will increase. These potential problems are unlikely to affect sediment delivery from the two deep-seated landslides on the J-Road plan for several reasons. First, the proposed harvest is relatively light (less than 40% of the trees will be removed and no harvesting within 100 feet of the Albion River) and will probably have little impact on the stability of the slide mass. Landslide studies conducted in other watersheds have not documented significant increases in deep-seated slide movement with selection harvests. The straight stumps and subdued slide topography strongly suggests that neither one of the two slides were impacted by the previous clear-cut harvest in early 1900's. Second, because of the nature of these ancient slides, any increase in movement would likely be small and not result in significant sediment delivery. Any impact from the harvest would likely be negligible in comparison to the effects of large storms and would be short lived, diminishing significantly as the vegetation becomes re-established. Shallow debris slides, on the other hand, are rapid moving shallow features that usually incorporate only the overlying surficial mantle of loose soil and weathered bedrock. Because these failures are more active and more numerous than deep-seated failures, they are responsible for a greater percentage of the sediment delivered to streams. An old 1950's road cut across one of the deep-seated landslides in the J-Road Plan. Typical of that time, this "legacy" road was poorly constructed by sidecasting thick loose spoils onto the steep slopes below the road. As a result several shallow debris slides have occurred along the outside edge of this old road. Erosion and instability from these old, poorly designed roads is often a leading source of management related erosion. This road is not proposed to be used in timber operations but is proposed to be decommissioned to mitigate the ongoing erosion problems. By decommissioning this road and correcting existing erosion problems elsewhere along the other roads, sediment input to the Albion River may be reduced below current conditions." Mendocino Redwood Company is aware of how previous harvesting activities have left potential problems for the watersheds. Because of this, the company is identifying, prioritizing, and mitigating the causes of degradation of aquatic habitat. The company consults with engineering geologists to identify specific problems and develop remedial measures to minimize impact of current activities and rehabilitate eroding forest "legacy" roads. Mendocino Beacon article, dated June 3, 1999