Channel change and bed-material transport in the Umpqua River basin, Oregon

Abstract

The Umpqua River drains 12,103 km 2 of western Oregon, heading in the Cascade Range and draining portions of the Klamath Mountains and Coast Range before entering the Pacific Ocean. Above the head of tide, the Umpqua River, along with its major tributaries, the North and South Umpqua Rivers, flows on a mixed bedrock and alluvium bed, alternating between bedrock rapids and intermittent, shallow gravel bars composed of gravel to cobble-sized clasts. These bars have been a source of commercial aggregate since the mid-twentieth century. Below the head of tide, the Umpqua River contains large bars composed of mud and sand. Motivated by ongoing permitting and aquatic habitat concerns related to instream gravel mining on the fluvial reaches, this study evaluated spatial and temporal trends in channel change and bedmaterial transport for 350 km of river channel along the Umpqua, North Umpqua, and South Umpqua Rivers. The assessment produced (1) detailed mapping of the active channel, using aerial photographs and repeat surveys and (2) a quantitative estimation of bed-material flux that drew upon detailed measurements of particle size and lithology, equations of transport capacity, and a sediment yield analysis. Bed-material transport capacity estimates at 45 sites throughout the South Umpqua and mainstem Umpqua Rivers for the period 1951-2008 result in wide-ranging transport capacity estimates, reflecting the difficulty of applying equations of bed-material transport to a supply-limited river. Median transport capacity values calculated from surface-based equations of bedload transport for each of the study reaches provide indications of maximum possible transport rates and range from 8,000 to 27,000 metric tons/yr for the South Umpqua River and 20,000 to 82,000 metric tons/yr for the mainstem Umpqua River upstream of the head of tide; the North Umpqua River probably contributes little bed material. A plausible range of average annual transport rates for the South and mainstem Umpqua Rivers, based on bedload transport capacity estimates for bars with reasonable values for reference shear stress, is between 500 and 20,000 metric tons/yr. An empirical bed-material yield analysis predicts 20,000-50,000 metric tons/yr on the South Umpqua River and mainstem Umpqua River through the Coast Range, decreasing to approximately 30,000 metric tons/yr at the head of tide. Surveys of individual mining sites in the South Umpqua River indicate minimum local bed-material flux rates that are typically less than 10,000 metric tons/yr but that range up to 30,600 metric tons/yr in high-flow years. On the basis of all of these analyses, actual bedload flux in most years is probably less than 25,000 metric tons/yr in the South Umpqua River and Umpqua Rivers, with the North Umpqua River probably contributing negligible amounts. For comparison, the estimated annual volume of commercial gravel extraction from the South Umpqua River between 2001 and 2004 ranged from 610 to 36,570 metric tons, indicating that historical instream gravel extraction m...

Geologic and physiographic controls on bed-material yield, transport, and channel morphology for alluvial and bedrock rivers, western Oregon

“…The valley reaches (Table 1) were defi ned by the studies of Wallick et al (2010Wallick et al ( , 2011 and Jones et al (2011Jones et al ( , 2012aJones et al ( , 2012bJones et al ( , 2012c and include the contiguous portions of the 17 rivers in which the channel beds are composed of, or are locally fl anked by, substantial accumulations of modern alluvium. All of these reaches have gradi-ents less than 0.005 and would be considered transport or response reaches in the Montgomery and Buffi ngton (1997) categorization.…”

“…3; Table 1; Tables DR1 and DR2 [see footnote 1]). Additionally, we mapped the geomorphic fl oodplain for each reach, defi ned as the lateral extent of Holocene-era fl uvial processes , on the basis of available geology, soils, and topography and reconnaissance fi eld inspection, as described in Wallick et al (2011) for the Umpqua River. From this mapping, we evaluated 2005-2009 channel centerline migration rates relative to the fl oodplain centerline for the intervening period in the manner of O'Connor et al (2003b).…”

“…Note: Recruitment and extraction values are summarized fromWallick et al (2010Wallick et al ( , 2011 andJones et al (2011Jones et al ( , 2012bJones et al ( , 2012c. *For some reaches, the number of reporting sites varied during the assessed period of record.…”

Using repeat lidar to estimate sediment transport in a steep stream

“…To compare these results with our estimates of bed material transport in Tahoma Creek, we must estimate what percentage of the delta deposition documented in Alder Lake consists of coarse material. In the absence of any sediment samples of these delta deposits, we assume this could reasonably range from 20% to 40% [ Pratt‐Sitaula et al , ; Wallick et al , ]. These relatively high values reflect the steep nature of the contributing streams, in which coarse material transported as bed load is likely to constitute a large percentage of the total load, and the fact that the finest fraction of sediments may be transported beyond the surveyed extents of the delta.…”

Landscape influence on the local distribution of western pond turtles

“…The geology underlying the South Umpqua River in the Klamath Mountains and Western Cascades provinces generates much more extreme river flows because it lacks extensive groundwater storage (Wallick et al. ). The Umpqua River's peak flows are most influenced by winter storm events (Wallick et al.…”