Water Resources Collections and Archives

Livestock grazing in the western United States has lead to riparian ecosystem and stream channel degradation. Establishing fenced-off exclosures is a common management strategy that aims to passively restore these areas, however, relatively few studies have assessed the evolution of exclosed reaches over time. We evaluated temporal trends in channel form and riparian vegetation along a 4.2 km reach of Long Creek (drainage area of 180 km2), a tributary to Sycan Marsh in western Lake County, Oregon. The Nature Conservancy implemented reduced livestock grazing along this reach in 1996 and complete exclosure in 1999. Based on previous studies that documented vegetation establishment and subsequent sediment accumulation on channel banks, we hypothesized that the channel would have narrowed and vegetation would have re-established after eleven years of cattle exclosure.   In October 2011, we surveyed seven previously-established cross sections and compared channel geometry in 2011 to surveys conducted since 1990. We also took photos at these locations and compared them to historical images. We found no consistent trend in channel morphology, but two cross sections demonstrated narrowing, one of which was likely driven by reduced flow velocity from a downstream beaver dam. Vegetation had successfully established along the streambanks, but in addition to the riparian species, upland lodgepole pines were also abundant along the channel and on the floodplain.  Our results suggest that beavers should be encouraged so their dams will increase overbank flow and discourage the invasion of upland plant species. We also propose improvements in monitoring methods to ensure repeatability of cross-sections over an extended monitoring period.