Grant, Gordon E.; Crozier, Michael J.; Swanson, Frederick J. 1984. An approach to evaluating off-site effects of timber harvest activities on channel morphology. In: O'Loughlin, C. L.; Pearce, A. J., eds. Symposium on the effects of forest land use on erosion and slope stability: proceedings; 1984 May 7-11; Honolulu, HI. Honolulu, HI: University of Hawaii, Environment and Policy Institute: 177-186.
The downstream effect of forest practices has proved difficult to evaluate for a number of reasons. Differences in rock type, hydrology, topography, soils and disturbance history may all produce highly variable responses among drainage basins. In particular, the management history of a basin is often complex, with logging and road construction taking place over prolonged periods in different parts of the basin, which makes comparisons between basins with different histories uncertain. In addition, similar processes can give rise to different end results, depending on the type of terrain. Conversely, a particular form of channel response can often be attributed to multiple causative factors. All of these circumstances make it difficult to evaluate the causes and importance of downstream effects.
A study was undertaken to determine whether off-site effects of timber harvest activities were an important factor in producing channel changes among fourth and fifth order streams in the western Cascade Range of Oregon. In this paper, we suggest a theoretical framework mechanisms might influence stream channel morphology. We also present an air photo interpretation technique for measuring stream channel response to disturbance, and report preliminary results from the analysis of a large storm event.