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Scientific Investigations Report 2011–5041

Channel Change and Bed-Material Transport in the Umpqua River Basin, Oregon

The Umpqua River

The Umpqua River drains 12,103 km2 of western Oregon, heading in the Cascade Range and Klamath Mountains before traversing the Coast Range and entering the Pacific Ocean through Winchester Bay at Reedsport (fig. 1). The Umpqua River begins 179 km from its mouth at the confluence of the North and South Umpqua Rivers near the city of Roseburg. The main tributaries of the main stem Umpqua River and their drainage areas are the Smith River (961 km2), Elk Creek (756 km2), and the Calapooya Creek (637 km2) (figs. 1 and 3).

The North Umpqua River drains 3,520 km2, with headwaters in the High Cascades. Major tributaries and their drainage areas include the Little River (533 km2) and Steamboat Creek (425 km2), both located upstream of the study area. The upper North Umpqua River is noteworthy for its scenery and native fish populations, with approximately 55 km of the channel between Soda Springs Powerhouse and Rock Creek designated as a Wild and Scenic River. The South Umpqua River drains the northern Klamath Mountains and part of the Western Cascades. At its confluence with the North Umpqua River, the South Umpqua River has a drainage area of 4,665 km2. The main tributaries in the study area and their drainage areas are Lookingglass Creek (417 km2), Myrtle Creek (308 km2), Cow Creek (1,292 km2), and Jackson Creek (490 km2) (figs. 1 and 3).

The Umpqua River basin contains two federally designated wilderness areas, the Boulder Creek Wilderness in the North Umpqua River subbasin, and the Rogue–Umpqua Divide Wilderness in the South Umpqua River subbasin.

Geography and Geology

The drainage basin is flanked to the north by the Siuslaw and Willamette River basins, to the east by the Deschutes and Klamath River drainages, and to the south by the Rogue and Coquille River basins. The basin has its headwaters in the Cascade Range, is bounded on the south by the Klamath Mountains, and transects the Coast Range before entering the Pacific Ocean (fig. 1).

The Umpqua River basin can be divided into five distinctive geomorphic provinces (fig. 1), each of which has a unique physiography. The North Umpqua River originates in the predominantly low-relief High Cascades province, where highly permeable Pliocene and Quaternary lava flows result in low rates of surface-water runoff and sediment transport (Jefferson and others, 2010).

Downstream of the High Cascades province, the North Umpqua River drains parts of the steeply dissected Western Cascades province, where the South Umpqua River has its headwaters. The weathered Tertiary volcanic rocks of the Western Cascades support higher rates of runoff and erosion than the High Cascades terrain, and mass wasting processes are a dominant mechanism of hillslope sediment production (Stillwater Sciences, 2000).

Downstream of the Western Cascades province, the South Umpqua River enters the Klamath Mountains province near Tiller at FPKM 281. The rugged terrain of the Klamath Mountains is underlain by a Cretaceous and Jurassic accretionary complex composed of weakly to intensely metamorphosed sedimentary, volcanic, and intrusive igneous rocks, primarily of Early Cretaceous and Jurassic age (Ramp, 1972; Wells and others, 2001). The Klamath Mountains are the source of several gravel-rich rivers in southern Oregon and northern California, including the Chetco and Smith Rivers (Wallick and others, 2010; MFG, Inc. and others, 2006).

The South Umpqua River leaves the Klamath Mountains and enters the Paleocene and Eocene marine volcanic sedimentary rocks of the Coast Range province at about FPKM 200. Similarly, the North Umpqua River leaves the Western Cascades at NUFPKM 45 and enters the Coast Range province. Both rivers first flow through the predominantly volcanic rocks of the Siletz River Volcanics before entering the soft sandstones and siltstones of the Umpqua Group near their confluence at FPKM 170 (Wells and others, 2001). From there, the Umpqua River meanders northwestward for about 20 km through Coles and Garden Valleys before bisecting the higher portion of the Coast Range within a narrow valley trending northwest for 145 km. For this stretch, the river follows large meanders primarily incised into soft marine sediment of the Tyee and Elkton Formations (Ramp, 1972). Approximately 16 km from its mouth, the lower Umpqua River exits the Coast Range and flows through a coastal plain to the Pacific Ocean.

The main stem Umpqua River is locally flanked by flood‑plain and terrace deposits within its entrenched meandering course through the Coast Range (Personius, 1993; Personius and others, 2003), reflecting episodes of river aggradation in conjunction with overall incision of the river during the Quaternary period. The youngest terrace, forming a surface 2–15 m above river level, is apparently associated with a period of enhanced gravel transport and channel aggradation about 10,000 years before present (Personius, 1993; Personius and others, 2003), although this surface is locally capped by younger deposits and probably was inundated by a large flood in December 1964. This episode of aggradation broadly correlates with aggradation of several Cascade Range rivers draining into the Willamette River valley (O’Connor and others, 2001; Wampler, 2004). Even higher surfaces are locally preserved, including some reaching 200 m above the present river level. One such surface at FPKM 70 is 41 m above present river level and has a thermoluminescence age of 116 ± 20 thousand years ago (ka) (Personius, 1993; Personius and others, 2003), indicating a long-term valley incision rate of 0.3 to 0.4 mm/yr.

The lower Umpqua River valley, particularly along the lowermost 40 km, has been strongly affected by the 130 m of sea-level rise after the culmination of the last maximum glacial period 18,000 years ago. Along the Oregon coast, rising sea levels have flooded river valleys incised during low stands of sea level, creating estuaries now extending inland from the coast. This is the case for the Umpqua River, as well as for the Smith River, which joins the Umpqua River at FPKM 14 and is tidally affected for its lower 40 km (Personius, 1993). With the onset of sea-level rise, and especially during the last 2,000 years of relatively stable sea level, these estuarine reaches have been filling with fluvial sediment (Komar, 1997, p. 30–32), but for rivers such as the Umpqua and Smith Rivers, the low gradient (fig. 3) and far upstream propagation of tidal influence indicates that the sediment supply has not matched Holocene sea-level rise and that these rivers have not yet attained a graded profile to the coast. Because of the low gradients in the downstream reaches of the Umpqua and Smith Rivers, coarse bed material probably is not transported through these reaches to the Pacific Ocean.

Hydrology

Information on basin hydrology derives from USGS streamflow-measurement records in the basin extending discontinuously back to 1905. Many of these data are available from the USGS (U.S. Geological Survey, 2010b), with some synthesis provided by Jones and Stearns (1930). The mean annual flow of the Umpqua River near Elkton at FPKM 84.7 for 1955–2004 is 210 m3/s, which closely corresponds to the combined mean flows for the North Umpqua River at Winchester (NUFPKM 2.5; 106 m3/s), and the South Umpqua River near Brockway (FPKM 195.3, 78 m3/s) for the same period (fig. 4, table 1). Despite a contributing area 25 percent smaller than the South Umpqua River, the North Umpqua River supplies more than 50 percent of the water at Elkton (compared to 37 percent provided by the South Umpqua River), primarily because of a greater area of high-elevation terrain subject to orographically enhanced precipitation (fig. 1, table 1). This high terrain, associated with Quaternary volcanic rocks of the High Cascades province, also explains the much lower intra-annual flow variability of the North Umpqua River, where the mean January flow is only 6.7 times that of August. By contrast, the mean January flow for the South Umpqua River is 57 times greater than the mean August flow. The young volcanic uplands of the North Umpqua River headwaters have poorly integrated surface drainage networks and host large-volume groundwater systems, resulting in attenuated surface runoff and large spring complexes that maintain relatively high and steady summer flows. By contrast, the more dissected and older rocks of the Western Cascades and Klamath Mountains terrains underlying much of the South Umpqua River headwaters generate flows that more quickly respond to episodes of precipitation and drought (Jones and Stearns, 1930).

Peak flows in the Umpqua River basin typically derive from winter frontal systems, with the largest flows resulting from regional rain-on-snow events. The peak of record for the South Umpqua, North Umpqua, and main stem Umpqua Rivers was in late December 1964, when 7,505 m3/s was reported for the main stem near Elkton, and 4,250 and 3,540 m3/s were reported for the North Umpqua River at Winchester and South Umpqua River near Brockway, respectively (table 1). The December 1964 flood probably was the largest since the rain-on-snow flood of 1861. The 2-year recurrence-interval flow is about 1,256 m3/s for the North Umpqua River near Winchester, 1,292 m3/s for the South Umpqua River at Brockway, and 2,660 m3/s for the main stem Umpqua River at Elkton (table 1).

At least two smaller episodes of widespread flooding have occurred in recent decades. From November 1996 through January 1997, a series of storms caused extensive regional flooding, resulting in three distinct periods of high flows in the Umpqua River basin (fig. 4). Most stream gages in the South Umpqua River basin, as well as the Elkton gage on the Umpqua River, had their highest flows during December 4–9, 1996, but the largest flows for the North Umpqua gages were about 2 weeks earlier on November 18, 1996 (table 1; Risley, 2004). Heavy rains in late December 1996 led to a third period of high flows during January 1–2, 1997. These high flows triggered numerous landslides, but the discharges for this flood were lower than for the November and December 1996 floods (Risley, 2004). The peak discharges for the November–December 1996 floods ranged from 5- to 10-year recurrence-interval flows at most sites, except for the Tiller gage on the South Umpqua River, where discharge was approximately similar to the 30-year recurrence interval event (table 1, fig. 5). A flood peaking on December 31, 2005, and continuing into early January 2006, was similar in magnitude to peak flows from the winter of 1996–97 (table 1).

Since the early 1950s, flow has been regulated by Pacific Power hydroelectric projects on the North Umpqua River, which include eight developments in the upper basin (fig. 1). These dams only minimally affect peak flows because they have limited storage, and much of their contributing area lies in the groundwater-dominated High Cascades terrain (Stillwater Sciences, 1998). For example, within the bypass reaches of these hydroelectric dams, the 1.5-year recurrence interval flood has been reduced by 15–30 percent, but larger floods (greater than 5-year recurrence interval) are unchanged (Stillwater Sciences, 1998).

In the South Umpqua River basin, Galesville Reservoir was constructed in the upper Cow Creek basin in 1985 to reduce flooding along the lower reaches of Cow Creek. Although Galesville Reservoir almost certainly has a pronounced effect on peak flows on Cow Creek, peak flows farther downstream on the South Umpqua River near Brockway did not show a marked decline following dam construction (fig. 5). It is unlikely that either Galesville Reservoir or the North Umpqua hydroelectric dams strongly influence peak flows as far downstream as the USGS gage near Elkton on the Umpqua River because they control only a small portion of the total drainage-area runoff at this gage (fig. 3).

Because channel morphology and bed-material transport is strongly affected by flood magnitude, streamflow records at 11 USGS streamflow-gaging stations in the Umpqua River basin were examined to evaluate temporal trends in peak flows (table 2). Although more than 70 streamflow and crest stage stations have historically been operated in the basin, only 11 had records extending at least 25 years with minimal flow regulation (defined here as basins where less than 10 percent of the contributing area is regulated by dams or bypass canals). With the exception of the Umpqua River near Elkton, most records begin in the 1940s or 1950s. For most of these sites, peak flows had a decreasing trend during the period of analysis. On the basis of a two-tailed nonparametric Kendall’s tau test with a 5-percent level of significance (p <0.025 and p >0.975) the trend was statistically significant for 4 of the 11 sites, including West Fork of Cow Creek near Glendale, Lookingglass Creek at Brockway, North Umpqua River at Winchester, and Calapooya River near Oakland (table 2). The South Umpqua River near Brockway site had a p value of 0.03, which was nearly significant (table 2). This decreasing trend in peak flow mainly is due to long-term climate cycles. Most of these gaging stations began operating during the cool, wet period along the Oregon coast from 1946 to 1976; however, since 1976 the climate has been warmer and drier, although some shorter periods of cool/wet years have occurred since 1976 (Oregon Climate Service, written commun., 1999). The Umpqua River gaging station near Elkton has the longest flood record (104 years), resulting in this record spanning multiple dry (including the 1920s and 1930s) and wet cycles and thereby having no significant overall trend.

Description of Study Area

The study area encompasses the downstream semi‑alluvial sections of the North Umpqua and South Umpqua Rivers and the entire main stem Umpqua River (fig. 1, table 3). For both the North and South Umpqua Rivers, the semi-alluvial sections begin where the rivers exit the mountainous headwaters, widen, and flow on a mixed bed of bedrock and alluvium flanked by variable widths of flood plain and terraces. For the North Umpqua River, this transition to a dominantly alluvial character approximately corresponds with the confluence of the Little River at NUFPKM 44.8 (flood‑plain kilometers for the North Umpqua River are measured with respect to the confluence with the South Umpqua River). Downstream of the Little River confluence, the North Umpqua River generally is 60–85 m wide and flows on a bed of sandstone and basalt, locally mantled by thin accumulations of sand and gravel. The average gradient from the Little River confluence to the confluence with the South Umpqua River is 0.00177 (table 3). In this reach, the North Umpqua River is flanked by a valley bottom typically less than 0.8 km wide formed of recent flood-plain deposits and small terrace remnants.

For the South Umpqua River, the confluence of Jackson Creek at FPKM 280.9 near Tiller approximately marks the transition from a confined mountain stream to a mixed alluvial and bedrock channel locally flanked by active gravel bars, flood-plain surfaces, and terraces. Between the junction of Jackson and Cow Creeks, the South Umpqua River flows generally westward with an average gradient of 0.00249 (table 3) and a width typically less than 45 m. In this reach, the valley alternates between confined canyon reaches and sections as wide as 1.6 km. Wider sections contain channel flanking gravel bars, flood plains, tributary fans, and terrace deposits. With the confluence of Cow Creek at FPKM 230.9, the drainage area of the South Umpqua River increases by about one-third and the channel widens to 60–120 m (fig. 3) as the river flows generally northward on an alternating bed of bedrock and alluvium for 76 km to the junction with the North Umpqua River. Within this reach, the average gradient is 0.001 as the South Umpqua River winds through canyons alternating with valleys as wide as 3.5 km, and is locally flanked by gravel bars, flood plains, and terraces. The channel widens, and the number of gravel bars decreases for the 19 km of the main stem Umpqua River downstream of the confluence of the North Umpqua and South Umpqua Rivers. From FPKM 152 to about FPKM 40, the river flows within deep and narrow meanders incised through the Coast Range, with narrow flanking flood plains and terraces almost everywhere less than 0.8 km wide. The channel in this reach typically is 85–170 m wide and consists of long pools separated by bedrock rapids; the average gradient between FPKM 152 and the head of tide at FPKM 40 is 0.00073 (table 3). From FPKM 40 to the mouth, the Umpqua River progressively widens and is flanked by low flood plains, tidal marshes, and sand bars, especially downstream of the mouth of the Smith River at FPKM 14.

The overall physical setting, as well as the distribution of in-stream gravel-mining permits (Jo Ann Miles and Robert Lobdell, Oregon Department of State Lands, written commun., 2008), lends itself to delineation of valley reaches to help organize sediment-related issues, analyses, and findings (fig. 1, table 3). These reaches are, from downstream to upstream:

  1. Tidal reach (fig. 6), between FPKM 0 and approximately 40, distinguished by tidal influence, low gradients, expansive sediment deposits, and historical sand and gravel removal for navigation and commercial aggregate;
  2. Coast Range reach (fig. 7), between approximately FPKM 40 and 152, characterized by a confined valley with bedrock channel and few gravel deposits;
  3. Garden Valley reach (fig. 8) of broad valleys, between where the Umpqua River enters the Coast Range at FPKM 152 and the confluence of the South Umpqua and North Umpqua Rivers at approximately FPKM 169, a relatively short reach with several historically mined gravel bars;
  4. Roseburg reach (fig. 9) of the South Umpqua River, between the confluence with the North Umpqua River (FPKM 169) and the Cow Creek confluence at FPKM 231, where there are abundant gravel bars and several recently active in-stream gravel mining operations;
  5. Days Creek reach of the South Umpqua River (fig. 10), between the Cow Creek confluence at approximately FPKM 231 and 275, which constitutes the uppermost semi-alluvial reach of the South Umpqua River; and
  6. North Umpqua reach of the North Umpqua River (fig. 11) between NUFPKM 0 and the Little River confluence at NUFPKM 45, a reach locally flanked by alluvial deposits but with no recent in-stream gravel mining.

Historical Descriptions of the Umpqua River

We reviewed several Umpqua River basin historical documents (many also summarized by Beckham [1986], Winterbotham [1994], and Markers [2000]) for observations and accounts pertinent to channel conditions. The most useful of these are reports of early exploration and navigation surveys documenting channel characteristics at first European-American settlement. Accounts of historical land-use activities are also relevant to understanding historical and present channel conditions. Abundant archival photographs, at the Douglas County Historical Society and elsewhere, locally document channel conditions as far back as circa 1900. A primary conclusion from inspection of these historical sources is that gravel was scarce in many reaches of the Umpqua River. This is particularly evident for the Coast Range reach of the main stem Umpqua River. For example, David Douglas, a botanist (and county namesake) accompanying an expedition of the Hudson’s Bay Company, describes his October 16, 1826, evening activities at their camp near the present location of Elkton (Douglas, 1914, p. 223; FPKM 72.1; Coast Range reach):

I employed myself chopping wood, kindling the fire, and forming the encampment; and after, in the twilight, bathed in the river: course north-west; bed sandstone; ninety yards broad; not deep, but full of holes and deep chinks worn out by the water.

Similarly John Work, employed by the Hudson’s Bay Company, describes following the main stem Umpqua River between Elkton and Scottsburg (FPKM 40) in his journal entry for June 8, 1834 (Scott, 1923): “No stones worth mentioning all the way: the river runs on a bed of soft slatey rock.” Two weeks later, on June 17, John Work was camping along the Umpqua River just downstream of the Calapooya Creek confluence (FPKM 156; Garden Valley reach) where he reported:

The Umquah here is about 150 yards wide & runs over a rocky bottom of soft slatey rock & is not very deep. A horse can ford it at present.

The most extensive early survey was by U.S. Army Engineers lieutenant R.S. Williamson in 1870 while investigating navigation possibilities. His report (U.S. House of Representatives, 1871) described the several bedrock rapids between Scottsburg and Roseburg and provided a general characterization of the river:

The average width of the river, when bankfull, appeared to be about 200 feet; but at its extreme low-water stage the water is divided at many places into half a dozen or more streams, varying in width from two to thirty feet, and separated from each other by walls of rock sometimes five or six feet in height. In passing through some of these narrow place[s] the velocity of the current was 400 feet per minute. At each of these rapids between the channel and the shore there is a bench of sandstone, generally flat, varying from two to five feet in height above the low-water mark, and averaging about seventy-five feet in width. During ordinary stages of the river this is covered with water. The river contains no sand-bars, its bottom being coarse gravel, on solid bed-rock; consequently any improvements which may be made to the river are likely to be permanent.

A subsequent survey in 1910 encompassing most of the Roseburg, Garden Valley, and Coast Range reaches by the Junior Engineer F.E. Leefe of the U.S. Engineer Office (U.S. House of Representatives, 1911) reiterates Williamson’s findings:

In the stretch of river under examination between Roseburg and Scottsburg, a distance of 86 miles, the low water fall is about 465 feet. Throughout this distance the river at low water is a succession of rocky rapids with pools of quiet water between, of varying lengths and depths. The river flows over a rocky sandstone bottom much of the way, with many dangerous reefs and projections. With such a fall, averaging nearly 5½ per mile, the current is strong over the rapids at all stages.

Although sand and gravel accumulations are barely mentioned in many of these accounts of the South Umpqua and main stem Umpqua Rivers, except for noting their scarcity, some historical photographs show bars flanking the channel (fig. 12). We have found fewer early descriptions of the Days Creek reach of the South Umpqua River at the time of first exploration, but it too was apparently locally flowing on bedrock, at least near its downstream end, because in-channel potholes near the Cow Creek confluence were targets for gold miners in the 1850s (Beckham, 1986, p. 93).

Although no detailed surveys were conducted for the North Umpqua River, reports by the Wilkes Expedition on their 1841 overland trip between the Willamette Valley and San Francisco Bay (including geologist James Dwight Dana) state that the North Umpqua River ran on bedrock where they crossed it near the present location of Winchester (North Umpqua RM 7; Dana, 1849, p. 662). Similarly, Markers (2000, p. 133) noted:

The North Umpqua River has been pronounced, by experts in the driving of streams, to be the best driving stream in Oregon or Washington. It is singularly free from shifting sand bars and gravel shoals….

The character of the Tidal reach was distinctly different; drifting sand and gravel bars caused persistent navigation problems between the mouth and the head of tide at Scottsburg (FPKM 40), leading to multiple bathymetric surveys beginning in the late 18th century (summarized by Beckham, 1986, p. 149–152). These issues ultimately resulted in construction of the jetties and substantial and ongoing dredging of the lower channel. Shallow gravel bars near Brandy Bar (FPKM 27.5) also caused navigation hazards; this area ultimately became the reach of primary 20th and 21st century sand and gravel mining by Umpqua River Navigation Company and its successors.

Land-Use and Landscape Disturbance in the Umpqua River Basin

Although fur traders and early explorers entered the mouth of the Umpqua River basin in the late 18th century, European-American settlement of the basin did not fully commence until the mid-19th century following the passage of the Donation Land Act in 1850 and subsequent Federal programs (Beckham, 1986). The earliest immigrants to the basin claimed the fertile bottomlands and broad prairies of the central Umpqua River basin leaving more marginal ground, including rugged forest lands and flood-prone tributary valleys to later arrivals. These early settlement patterns are still evident today, as most of the basin’s population lives in the wide valley bottoms in the incorporated areas of Roseburg, Winston, and nearby towns (Geyer, 2003b, 2003c, 2003d). The upper parts of the North Umpqua and South Umpqua River basins primarily are federally held forest lands, but the lower parts of these drainage basins mostly are privately owned, and the basins are managed for forestry and agriculture (Geyer, 2003a, 2003b, 2003c, 2003d). Nearly 70 percent of lands in the main stem Umpqua River basin (downstream of the confluence of North Umpqua and South Umpqua Rivers) are managed primarily for forestry, with the balance being for agriculture, residential, industrial, or other land uses (Oregon State University, 2010).

Descriptions of historical land-use and landscape disturbance that have potentially affected channel and bed‑material conditions are summarized by Beckham (1986), although watershed studies and other sources provide supplementary information. In the Umpqua River basin, the disturbances that are most likely to influence channel conditions and bed-material transport include navigational dredging, placer mining, in-stream gravel mining, impoundments for hydropower and flood control, and forestry and other land-use practices (table 4).

Placer Mining

Gold mining in the Umpqua River basin began in 1852 on the South Umpqua River near Riddle and in lower Cow Creek (Beckham, 1986, p. 225–226). The widespread placer mining on the South Umpqua River and its tributaries Olalla Creek (a tributary of Lookinglass Creek), Myrtle, Cow, and Coffee Creeks (Diller, 1914; Ramp, 1972) probably had the most significant effects on in-stream gravel conditions (figs. 9 and 10). All these drainages enter the South Umpqua River within the Roseburg and Days Creek reaches. Placer mining in the late 19th and early 20th centuries involved extensive excavation of alluvial terraces flanking the present watercourses, in places aided by elaborate hydraulic works (fig. 13). Beckham (1986, p. 93) noted the impact of these activities on the stream channels:

Mining generated terrible problems for the Indians. The cascade of debris down the creeks and rivers had calamitous impact on the fish runs: mining destroyed the spawning grounds by washing away the gravels and coating the river bottom with mud.

Such effects, as well as possible large inputs of gravel to South Umpqua tributaries, may still have implications for the present-day sediment conditions in the Umpqua River system.

Umpqua River Gravel Mining

Gravel bars in the Umpqua River basin have provided a local source of aggregate used in local road building and construction projects since the early 1900s. Although records describing mining practices, quantities, and locations prior to 2001 are scarce, anecdotal accounts from landowners and limited information on gravel mining permits (Oregon Department of State Lands, written commun., 2008) indicate that at least 17 sites along the South Umpqua and main stem Umpqua Rivers either had active permits for gravel removal or documented mining in recent decades.

Longtime residents and gravel operators report that the 1970s was a period of particularly high extraction rates, during which time gravel bars were mined with a dragline and scraped of all available sediment until bedrock was reached (Kelly Guido, Umpqua Sand and Gravel, oral commun., 2008). By the mid-1980s, mined volumes had decreased; in recent decades, most bars owned by the main gravel operators have been mined only 2 to 3 times each (Mike Flewling, Knife River Corporation, oral commun., 2008; Joy Smith, Umpqua Sand and Gravel, oral commun., 2008). Gravel mining regulations have changed substantially since the 1970s, and now near-channel gravel typically is harvested by bar skimming, whereby scrapers or other heavy equipment are used to remove only the surface of the bar, typically to an elevation close to the low-flow water level. No permits for in-stream gravel extraction have been issued since 2004, the last year in which mining occurred upstream of the Tidal reach. In the intervening years, two main operators continue to seek approval for future mining at six sites (figs. 1 and 9) on the South Umpqua River:

  • Umpqua Sand and Gravel Bar, FPKM 171.4, operated by Umpqua Sand and Gravel
  • Shady Bar, FPKM 186.2, operated by Knife River Corporation
  • Little Valley Bar, FPKM 189.7, operated by Knife River Corporation
  • Weigle Bar, FPKM 211, operated by Knife River Corporation
  • Gazley East Bar, FPKM 232, operated by Knife River Corporation
  • Days Creek Bar, FPKM 249.9, operated by Knife River Corporation

Extraction volumes for 2001–04 provided by the Umpqua Sand and Gravel and Knife River Corporation show that mining in 2001, 2003, and 2004 removed volumes at individual sites ranging from 610 to 21,500 metric tons (based on volumes provided in bar surveys and a bulk density of 2.1 metric tons/m3). In 2001 and 2003, 9,260 and 610 metric tons of gravel were removed from Umpqua Sand and Gravel Bar, respectively, and in 2004, a combined total of 36,570 metric tons was extracted from Days Creek, Weigle, and Umpqua Sand and Gravel bars. Other sites also may have been mined during this period, but no records were available.

Dams

Mill dams and other small obstructions served various needs of early settlers, and later, larger dams have provided for hydropower and flood control. Of these early dams near Kellogg (FPKM 105.4; Coast Range reach), Roseburg (FPKM 182; Roseburg reach), and Winchester (NUFPKM 10.2; North Umpqua reach), only the Winchester Dam, a 3-m-high concrete structure on the lower North Umpqua River, remains. Anecdotal accounts indicate that some gravel passes over Winchester Dam, although most bed-material sediment is likely trapped in its shallow upstream reservoir, which has aggraded approximately 2 m since dam construction in 1904 (Timothy Brady, City of Roseburg Water Plant Superintendent, oral commun., November 15, 2010).

Pacific Power’s North Umpqua Hydroelectric Project was constructed during 1952–55 and now traps bedload from the upstream 32 percent of the North Umpqua River basin. However, a 2002 amendment to the 2001 Federal Energy Regulatory Commission (FERC) re-licensing settlement for PacifiCorps’ hydroelectric project in the North Umpqua Basin calls for a gravel augmentation plan to increase the amount of spawning habitat downstream of Soda Springs Dam (fig. 1, PacifiCorp, 2002). The augmentation plan included a one-time experimental pulse of 2,300 m3 of spawning size gravel, equivalent to the long-term average annual bedload input to this reach, or approximately 3,680 metric tons (based on a bulk density of 1.6 metric tons/m3 as provided by Stillwater Sciences, written commun., 2010), which was added to the river in August of 2004 (Stillwater Science, 2006). Additionally, 56 m3 (approximately 90 metric tons) will be distributed seven times during the course of the new FERC license (PacifiCorp, 2002). Sediment studies conducted as part of relicensing these facilities and to monitor the gravel augmentation are summarized later in the section “Previous Water and Sediment Studies in the Umpqua River Basin.” Galesville Reservoir on Cow Creek began filling in 1985, and since then has trapped all bed material from the upper 192.4 km2 of Cow Creek, encompassing 5.9 percent of the South Umpqua River basin at the Cow Creek confluence.

Forest Management and Fire

Because they potentially influence large portions of the basin, watershed-scale disturbances, including forest fires, development and logging, and related activities can affect channel morphology and bed-material conditions throughout the Umpqua River basin. Timber harvest and associated road building can increase peak flows (Wemple and others, 1996; Jones and Grant, 1996, 2001; Bowling and others, 2000) and the frequency of landslides (Kelsey and others, 1995), resulting in sedimentation along lower reaches of affected basins (Madej, 1995). Douglas County, whose boundaries closely follow that of the Umpqua River basin, was second in the nation in timber harvest from Federal lands between 1949 and 1970 (Beckham, 1986, p. 174).

Peak timber production was during the 1950s–1960s, when annual timber harvest from National Forest Lands in Douglas County ranged from 149.6 to 637.6 million board feet (Beckham, 1986, p. 174). Log production from public lands decreased substantially after 1988 when management emphasis shifted from timber production to habitat protection. For comparison, log production in 1988 was 397 million board feet, but annual average harvest 1991–2000 was 29 million board feet, which diminished to 6.7 million board feet during 2001–03 (as calculated from data provided by U.S. Forest Service, 2006). Although detailed records describing historical logging practices, road building, and associated landscape changes are lacking for the Umpqua River basin, it is possible that intensive timber harvest peaked in the 1950s–1960s, but remained elevated through the 1980s, likely affecting bed‑material influx to the Umpqua River and its major tributaries.

Linking historical patterns of forest fire with changes to channel character is difficult due to sparse records connecting fire extent and severity to subsequent changes in channel condition. Historically, Native Americans used annual, late-summer fires to clear brush and ensure open areas for hunting and berry gathering along valley bottoms (Beckham, 1986). By the early 1900s, however, Federal fire‑suppression programs became more aggressive (Beckham, 1986; Geyer, 2003a–d). In recent decades, fires have burned increasingly larger areas of the basin, including fires in 1987 (31 km2 burned area), 1996 (73 km2), and 2002 (341.8 km2) (as determined from U.S. Forest Service [2010] mapping data). Most of the fires in 2002, including the Boulder Fire (193 km2), were in the South Umpqua River basin, where 6 percent of the total drainage basin area was burned (as determined by the U.S. Forest Service [2010]). Possible long‑term effects of these fires include increased runoff and erosion associated with canopy removal (U.S. Forest Service, 2003).

Navigation Improvements and Commercial Dredging

Historical navigation improvements were focused in the Tidal reach, which has been the only section of river with extensive commercial boat traffic, but upstream reaches also had many rapids modified in the early 1870s in an attempt to promote navigation from the Pacific Ocean to Roseburg (Markers, 2000). Likewise, some bedrock rapids were modified in the late 19th century on the South Umpqua and North Umpqua Rivers to facilitate log drives (Beckham, 1986).

By 1900, the emphasis on improving navigation on the Umpqua River shifted to the river’s mouth, and between the 1920s and 1940s, the USACE, together with local entities, constructed major jetties to ensure a stable entrance to the lower river channel (Beckham, 1986). Beginning in 1927, the Corps of Engineers also began deepening the channel between the river’s mouth and Reedsport, and constructed a boat turning basin in Winchester Bay in 1945 (Beckham, 1986, p. 153). Navigational dredging by the Corps of Engineers has continued, with annual removal volumes from 1991 to 2008 averaging 157,070 m3 (fig. 14; Judy Linton, U.S. Army Corps of Engineers, written commun., 2008).

Commercial dredging of the Umpqua River estuary for sand and gravel aggregate began in 1918 and has been focused primarily in the area near Brandy Bar, between FPKM 25.9 and 30.6, where Umpqua River Navigation Company and its successor Knife River Corporation operated between 1949 and 2002 (Lidstone and Associates, written commun., 2008). The amount of bed-material sediment removed by commercial dredging during this period ranged from 22,070 to 339,250 m3/yr, averaging 136,380 m3/yr (fig. 14; as determined from records provided by Lidstone and Associates, written commun., 2008; CH2M Hill, 1971).

Previous Water and Sediment Studies in the Umpqua River Basin

Previous reports from hydrology and sediment transport studies for the Umpqua River basin were reviewed for this study. Although many studies are peripherally related (such as turbidity and other water-quality studies), two previous studies are directly relevant to gravel transport and channel morphology in the study area: (1) the basinwide analysis of sediment transport by Curtiss (1975) and (2) the sediment transport analyses by Stillwater Sciences (2000) in support of the FERC relicensing of the Pacific Power hydroelectric facilities on the North Umpqua River.

The Curtiss (1975) report expands on an earlier USGS report by Onions (1969) by providing estimates of annual suspended-sediment discharge for 11 sites in the Umpqua River basin based on as many as 18 years of suspended‑sediment measurements between 1956 and 1973. Although there were no measurements of bedload in this study, Curtiss (1975) calculated total sediment loads (bedload plus suspended load) on the basis of measurements at Flynn Creek (a Coast Range stream in the Alsea River basin), where bedload constituted 3 percent of the mean annual suspended‑sediment yield. This ratio was applied for the sites in the Umpqua River basin, except for Cow Creek, where field observations implied that bedload composed 5 percent of the total load. Although no known bedload measurements for the Umpqua River system substantiate these values, bedload transport rates typically scale with suspended load, and the analysis by Curtiss (1975) probably provides a reasonable guide to the relative contributions of bed material to the Umpqua River system. For the calculated mean annual total sediment discharge of 1.54 × 106 metric tons/yr of the South Umpqua River at Brockway, the Curtiss (1975) analysis indicates that 0.28 × 106 metric tons/yr enters through Lookingglass Creek, 0.34 × 106 metric tons/yr joins at Cow Creek, and 0.28 × 106 metric tons/yr comes from the upper basin upstream of the Tiller gaging station.

These values suggest that more than 80 percent of the sediment entering the South Umpqua River is derived from tributaries downstream of Tiller. At the Elkton streamflow‑gaging station on the main stem Umpqua River, where 3.18 × 106 metric tons/yr of sediment passes each year, 23 percent is from the North Umpqua River at Winchester (0.72 × 106 metric tons/yr), 49 percent from the South Umpqua River at Brockway (1.54 × 106 metric tons/yr), 5 percent from the Calapooya Creek (0.17 × 106 metric tons/yr), with the balance likely from the lower South Umpqua River and unmeasured tributaries entering the main stem Umpqua River between the confluence of the North Umpqua and South Umpqua Rivers and the Elkton streamflow-gaging station. These results indicate that the South Umpqua River supplies a greater amount of sediment to the Umpqua River than is contributed by the North Umpqua River.

In terms of bed-material transport, if the 3 and 5 percent ratios are correct, the Curtiss (1975) measurements indicate an annual bedload transport rate of 8,400 metric tons at Tiller, near the upstream end of the Days Creek reach at FPKM 273; 46,000 metric tons at the Brockway streamflow measurement site on the South Umpqua River within the Roseburg reach near FPKM 195.3; and 160,000 metric tons at the Elkton measurement site on the main stem Umpqua River in the Coast Range reach at FPKM 72.1. Considered similarly, Cow Creek, the North Umpqua River, Lookingglass Creek, and Calapooya Creek contributed 17,000, 22,000, 8,400, and 5,100 metric tons/yr, respectively, to the South and main stem Umpqua Rivers. Considering the relative propensity of the Klamath Mountains terrain to produce gravel compared to the other geologic provinces, as well as the dams on the North Umpqua River (which would reduce bed-material fluxes substantially in comparison with suspended loads), the Curtiss (1975) estimates probably exceed actual values for the North Umpqua River and Umpqua River at Elkton sites.

Stillwater Sciences (2000) prepared sediment budgets for the North Umpqua River to assess the role of Pacific Power’s North Umpqua River hydroelectric project on North Umpqua River sediment conditions. Their analysis incorporated a reanalysis of the suspended load data summarized by Curtiss (1975), analysis of reservoir sedimentation data, estimates of geomorphic process rates, and landslide inventory information. They concluded that the dams on the North Umpqua River trap all bedload from the upper 32 percent of the North Umpqua River basin but that the effect of this bed-material sediment reduction on downstream reaches is more than compensated by enhanced sediment production from 20th century land-use practices—primarily forest practices—and the effects of the 1964 flood. Specifically, Stillwater Sciences (2000) postulated that downstream of Steamboat Creek (a tributary entering the North Umpqua River approximately 30 km upstream of the study area), the effects of land use doubled the average annual bedload flux to 16,330 metric tons/yr, from a “reference condition” (pre-1950, minimal land-use effects) value of less than 8,160 metric tons/yr, despite total bed-material blockage since 1952 at Soda Springs Dam (about 60 km upstream of the study area). Although these conclusions for the North Umpqua River remain unverified, enhanced bed-material contributions to the Umpqua River system from increased sediment yield in managed lands may be an important basinwide factor.

Stillwater Sciences also monitored the August 2004 experimental gravel augmentation, which entailed a release of 3,680 metric tons of spawning size gravel at two sites near Soda Springs Dam (Stillwater Sciences, 2006). Reconnaissance-level monitoring following the augmentation determined that (1) the experiment demonstrated where natural deposition would occur within this confined section of river and (2) a 2-year recurrence-interval flow in December 2004 was sufficient to mobilize all of the augmentation gravel; however, a 5-year recurrence-interval flood in December 2005 redistributed the spawning gravels along the channel margins. Overall, the August 2004 gravel augmentation experiment increased the total area of suitable spawning habitat between Soda Springs Dam and Boulder Creek (Stillwater Sciences, 2006).

First posted September 29, 2011

For additional information contact:
Utah Water Science Center Director,
U.S. Geological Survey, 2329 West Orton Circle
West Valley City, UT
84119-2047
http://ut.water.usgs.gov

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