Download or read book The Signal of Modern to Holocene Drivers of Complex Channel Response of a Small Alluvial Stream written by Scott D. Ducar and published by . This book was released on 2020 with total page 183 pages. Available in PDF, EPUB and Kindle. Book excerpt: "Small alluvial streams (~100km2 drainage area) are important for water resources and aquatic habitat. Small streams throughout the Western United States are impacted by anthropogenic land-use including urban development, mining, logging, beaver trapping, grazing, and farming. Land-use change can trigger a complex series of channel response (such as stream channel incision or channel migration) that vary spatially and temporally in the watershed. However, streams also respond to other external forcings, such as tectonically or climatically-driven changes in discharge or base-level, which make disentangling the drivers of channel response complicated. Therefore, it is important to place modern channel changes into a longer geomorphic context to fully understand the complex response initiated by land-use. In order to understand how changes in land-use may drive spatially variable channel response, we examine a representative small alluvial stream, Lower Dry Creek (LDC), a tributary to the Boise River in Idaho. LDC marks the transition from the rugged and largely undeveloped upland Dry Creek Experimental Watershed to the lower gradient, agricultural, and residential section of the watershed. LDC has a complex history of placer mining, beaver trapping, grazing, and farming since the 1850s. Recent (post-1997) growth in the region converted LDC's expansive floodplain from agricultural land to housing developments. Most of the recent development and historic and current farmland are on the broad, low gradient Hidden Springs Terrace. We use remote sensing, hydraulic modeling, grain size analysis, and field observations to quantify how the distinct reaches of LDC are changing over human time scales; we use Quaternary dating methods and geomorphic mapping to examine how LDC has changed over centennial to millennial time scales. Optically Stimulated Luminescence (OSL) dates of fluvial sediments in an upper reach indicate incision in LDC after 4.79 ± 1.05 ka. Around 0.79 to 0.67 ka, LDC deposited a large packet of sheetfloods and cross-bedded sands, which correlate to a period of more fire activity and alluvial fan deposition in the region. After approximately 0.67 ka the reach incised 2.4 m. In the late 1800s, placer mining in the upper reach of LDC shifted the channel behavior from incision to lateral adjustment. We measured an average of 0.6 m/yr of meander migration from 1938 to 2019. Migration rate increased threefold after 1992 (which corresponds temporally with a large rain-on-snow flood event in 1997), but slowed after 2011."--Boise State University ScholarWorks.