Logging Impacts of the 1970 ’ s vs . the 1990 ’ s in the Caspar Creek Watershed 1

The Caspar Creek watershed study provides resource professionals with information regarding the impacts of timber operations conducted under varying forest practices on sensitive aquatic habitats. In the South Fork watershed, roads were constructed near watercourse channels in the 1960’s, and the watershed was selectively logged using tractors during the early 1970’s. Subwatersheds in the North Fork were clearcut from 1985 to 1991 using predominantly cable yarding and roads located high on ridges. Numerous landslides were documented after road construction and logging in the South Fork owing to inadequate road, skid trail, and landing design, placement, and construction. In contrast, the size and number of landslides after timber operations in the North Fork to date have been similar in logged and unlogged units. Considerably more hillslope erosion and sediment yield have also been documented after logging operations in the South Fork, when compared to the North Fork. An analysis of the storm events associated with documented landslides showed that high 3-day or 10-day precipitation totals in combination with moderately high 1-day amounts have been more important than very high 1-day totals alone in triggering debris sliding at Caspar Creek. Storm sequences meeting the criteria required for causing documented landslides were found to have occurred in all phases of the 36-year study, with the greatest number occurring in water year 1998. Numerous large landslides associated with the road system in the South Fork occurred in early 1998, indicating that “legacy” roads continue to be significant sources of sediment decades after they were constructed. The impacts of harvesting and road construction in a secondgrowth redwood/Douglas-fir forest have been studied for 36 years in the Caspar Creek watershed. This allows us to compare the impacts from the first phase of the project, completed before the implementation of the modern Forest Practice Rules in California, with those associated with considerably improved forestry practices. Specifically, in the South Fork, roads were constructed in 1967, and the entire basin was selectively harvested from 1971 to 1973, before the enactment of the Z’Berg Nejedly Forest Practice Act of 1973. Approximately 6.8 km (4.2 mi) of road were built low on the slopes in the watershed, much of it adjacent to the South Fork channel, and tractors were used to skid logs to low-slope landings. Some of the skid trails were built in small stream channels. In contrast, 47.8 percent of the North Fork, within 10 nested subwatersheds, was clearcut from 1985 to 1992 using 11.4 km (7.1 mi) of existing roads and 8.4 km (5.2 mi) of new roads located high on the ridges (Preface, fig. 2, these proceedings). The steeper slopes were cable yarded. This long-term instream monitoring study provides resource professionals in California with information regarding the impacts of timber operations with varying forest practices on sensitive aquatic habitats. In this paper, we present a discussion of the geology and geomorphology present in the Caspar Creek drainage, as well as a summary of the major erosional sources which have followed logging in the gaged portions of each tributary. Additionally, we compare and contrast rainfall and runoff events that occurred during both phases of the study. A summary of the sediment yields documented during the life of the study is presented, and changes in sediment generation attributable to improved forest practices are discussed. Finally, recommendations are offered to forest managers regarding the applicability of Caspar Creek results to other California watersheds. Geology and Geomorphology Physiography The North Fork of Caspar Creek above its weir drains a watershed of 473 ha (1,169 ac), in northern California, whereas the area above the South Fork weir is approximately 424 ha (1,047 ac). These small watersheds, located inland from the central Mendocino County coast, are about 11 km (7 mi) southeast of Fort Bragg. The low point of each experimental watershed is at its weir, 85 m (275 ft) for the North Fork and 50 m (160 ft) for the South Fork, with the high points 310 m (1,020 ft) and 320 m (1,057 ft), respectively.