Contrasting Geomorphic Responses to Climatic, Anthropogenic, and Fluvial Change Across Modern to Millennial Time Scales, Clackamas River, Oregon PDF Download

Author: Peter J. Wampler
Publisher:
ISBN:
Category : Fluvial geomorphology
Languages : en
Pages : 796

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Geomorphic change along the lower Clackamas River is occurring at a millennial scale due to climate change; a decadal scale as a result River Mill Dam operation; and at an annual scale since 1996 due to a meander cutoff. Channel response to these three mechanisms is incision. Holocene strath terraces, inset into Pleistocene terraces, are broadly synchronous with other terraces in the Pacific Northwest, suggesting a regional aggradational event at the Pleistocene/Holocene boundary. A maximum incision rate of 4.3 mm/year occurs where the river emerges from the Western Cascade Mountains and decreases to 1.4 mm/year near the river mouth. Tectonic uplift, bedrock erodibility, rapid base-level change downstream, or a systematic decrease in Holocene sediment flux may be contributing to the extremely rapid incision rates observed. The River Island mining site experienced a meander cutoff during flooding in 1996, resulting in channel length reduction of 1,100 meters as the river began flowing through a series of gravel pits. Within two days of the peak flow, 3.5 hectares of land and 105,500 m3 of gravel were eroded from the river bank just above the cutoff location. Reach slope increased from 0.0022 to approximately 0.0035 in the cutoff reach. The knick point from the meander cutoff migrated 2,290 meters upstream between 1996 and 2003, resulting in increased bed load transport, incision of 1 to 2 meters, and rapid water table lowering. Ninety-six percent of the total migration distance occurred during the first winter following meander cutoff. Hydrologic changes below River Mill Dam, completed in 1911, are minimal but a set of dam-induced geomorphic changes, resulting from sediment trapping behind the dam, have occurred. Degradation for 3 km below the dam is reflected by regularly spaced bedrock pools with an average spacing of 250 m, or approximately 3.6 channel widths. Measurable downstream effects include: 1) surface grain-size increase; 2) side channel area reduction; 3) gravel bar erosion and bedrock exposure; 4) lowering of water surface elevations; and 5) channel narrowing. Between 1908 and 2000, water surface elevation dropped an average of 0.8 m for 17 km below the dam, presumably due to bed degradation.

Author:
Publisher:
ISBN:
Category : Dissertations, Academic
Languages : en
Pages : 780

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Author: Scott D. Ducar
Publisher:
ISBN:
Category : Alluvial streams
Languages : en
Pages : 183

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"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.

Author: Kurt D. Carpenter
Publisher: U.S. Department of the Interior, U.S. Geological Survey
ISBN:
Category :
Languages : en
Pages : 90

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This report presents results from a 2009–10 assessment of the lower half of the Molalla River. The report describes the geomorphic setting and processes governing the physical layout of the river channel and evaluates changes in river geometry over the past several decades using analyses of aerial imagery and other quantitative techniques. The peak-flow hydrology in the Molalla River has been characterized by a series of large floods during the 1960s and 1970s, a period of relatively small peak flows from 1975 to 1995, and a relative increase in severity of events in the past 15 years. Although incomplete, the gaging record for the early 20th century showed only modest high flows. The flood chronology since 1960 has affected the geomorphology of the river corridor, principally by increasing the active-channel width. The area affected by channel migration in the late 20th century, however, was reduced by the construction of revetments along the river corridor which acted to contain channel movement. The study area along the Molalla River was divided into six unique geomorphic reaches. The upper-most reach, designated GR6, is a narrow, bedrock-controlled reach with ample shade and large riffles. The next downstream reach, GR5, is also largely bedrock controlled but has a wider flood plain and active channel-migration zone. The longest geomorphic reach, GR4, has a wide channel-migration zone with many strategically placed revetments that work in concert with bounding bedrock to the northeast to suppress overall channel movement. In contrast, GR3 is a wide, active reach that responds more dramatically to flood and non-flood periods than the other geomorphic reaches. The anthropogenically confined GR2, adjacent the City of Canby, has relatively little historical channel movement and relatively few gravel bars. Finally, the farthest downstream reach, GR1, is an actively meandering reach that most closely resembles its pre-development state. Detailed analysis of aerial imagery from 1994, 2000, 2005, and 2009 showed that channel-migration activity and active-channel widths were greater in GR3 than in any other geomorphic reach and were related directly to the timing and magnitude of high flows. Similarly, the revegetation of exposed bars is significant in GR3 and elsewhere when large floods do not occur. A qualitative analysis of older aerial imagery dating back to 1936 showed that the recent channel-migration activity in GR3 is no greater than it was historically. Channel-migration activity in GR2, GR4, and GR5 was reduced relative to historical rates as a consequence of the construction of revetments and encroachment along the river corridor. Analyses of the longitudinal water-surface profile first suggested a possible accumulation of alluvium in GR3, but subsequent analysis of the shape of the longitudinal profile juxtaposed against bedrock outcrops in the river channel showed that the river is largely flowing over a shelf of bedrock and not filling with sediment. Water-quality, benthic algae, and benthic invertebrate conditions were examined during summer low-flow periods to determine the overall health of the river and to provide possible insights into the physical or chemical influences on diatom assemblages. A wetter than normal spring in 2010 resulted in higher-than-normal flows in July and August that may have delayed the algal growing season and limited the accrual of algal biomass in the river. Longitudinal changes in water quality, including downstream increases in water temperature and specific conductance, were observed in the Molalla River during August and September. Such patterns are typical of many rivers receiving inputs from anthropogenic sources in the flood plain, including agricultural and rural residential lands (Milk and Gribble Creek basins) as well as some urban runoff in the lower river. Nutrient concentrations in the Molalla River were generally low at most sampling sites but did increase at the Goods Bridge and Knights Bridge sites, presumably from a greater influence from anthropogenic sources that enter the river from tributaries, agricultural irrigation returns, or groundwater in the lower basin. Nitrate concentrations at Glen Avon and Knights Bridges exceeded their respective reference values for streams in the Cascade Range and Willamette Valley. Although the nitrate-nitrogen concentrations were somewhat elevated, phosphorus, in contrast, is relatively much less abundant in the Molalla River. N:P ratios for soluble, biologically available nitrogen and phosphorus were lower in the upper middle reaches (less than 5), but the absolute concentrations of orthophosphorus (0.010 milligrams per liter or less in July) suggest that attached periphytic algae in the river may be limited by phosphorus concentrations or some other factor, but probably not by nitrogen. The Molalla River has lower phosphorus concentrations than other rivers draining the Cascade Range because the phosphate-rich rocks of the Oregon High Cascades, prevalent in other drainages, are not present in the Molalla River basin, which is wholly contained within the Western Cascade Range geologic province. The 2010 algal growing season was delayed due to an unusually cold and wet spring, which produced streamflows 12–18 percent higher than normal in July and August and could have limited the accrual of periphyton biomass in the river. Nevertheless, a healthy biofilm of diatoms and other types of algae developed in the shallow riffle habitats during July, covering the entire stream channel in some areas. Generally, riffle habitats appeared healthy, with little sediment and low substrate embeddedness (that is, the degree of infilling of fine sediments around gravels and cobbles) was less than 5 percent at all sites except the Knights Bridge site, where embeddedness was about 10 to 25 percent higher. Algal biomass levels in July were moderate, ranging from 30 to 55 mg of chlorophyll-a per square meter, and the high densities of benthic macroinvertebrate grazers in the riffles suggests that the accumulation of algae (biomass levels) may have been limited by these herbivores. In August, however, a benthic bloom of filamentous green algae (Cladophora glomerata) increased algal biomass in the lower river, with nuisance levels at the Knights Bridge site. Higher nutrient concentrations (both nitrate and orthophosphate) combined with fewer invertebrate grazers (mostly snails) likely contributed to the higher biomass at this site. Long filaments of Cladophora also were observed in the area near the Canby drinking-water treatment plant, where in previous years, algae have clogged water intakes during periods of senescence when algae detach from the river bed and enter the intake. In 2010, algal biomass conditions were not as severe and the intakes were not affected. Distinct fluctuations in concentrations of dissolved oxygen and in pH levels from algal photosynthesis were observed at all sites sampled, with the largest diel changes and highest daily maximum values occurring at the two most downstream sites, particularly at Knights Bridge. Although some relatively high pH values were measured (as much as 8.4 units), none of the pH measurements exceeded State of Oregon water-quality standards, even in the afternoon hours on warm sunny days. Dissolved oxygen concentrations at Goods Bridge and Knights Bridge did not meet the 8 milligrams per liter criteria in the early morning hours, but compliance with the standards is only evaluated with 30-day average minimum values, which were not available. Relative to the salmon spawning criteria, for which the data collected during this study applies only to the Glen Avon Bridge site in September, water temperature, pH, and concentrations of dissolved oxygen all met the state standard in effect. Thirty-three species of algae were identified in the Molalla River, including fast growing small diatoms and very large stalked diatoms, filamentous green and blue-greens, and a few planktonic forms of green and blue-green algae that may have washed into the river from an upstream pond. The occurrence of high-biomass forming types of algae in the river, including filamentous greens such as Cladophora and large stalked diatoms such as Cymbella and Gomphoneis, could be a concern for fish populations because of the potential for smothering fish redds or by impacting benthic invertebrate populations that feed fish. Together, most of these algae (and overall algal biomass) are typical of generally high quality waters with little organic pollution, high concentrations of dissolved oxygen, and alkaline pH. The relatively high percentage of eutrophic taxa does, however, suggest some degree of nutrient enrichment in the river, despite the relatively low concentrations observed at most sites. Uptake of dissolved nutrients by algae, and inputs of additional nutrients, complicates interpretations regarding nutrient concentrations in the river, especially because samples were collected during summer growing season. Although the bulk of the diatom species generally were similar among at least the four upstream sampling sites, the multivariate ordination suggests a downstream trend in assemblage structure from the Glen Avon Bridge site to the Highway 213 Bridge. The next downstream site, at Goods Bridge, near the downstream end of the alluvial GR3 reach, however, plotted closer to the most upstream site at Glen Avon Bridge, which indicates a change in assemblage structure. The algal indicator species analysis showed a change in species composition at the Goods Bridge site, including decreases in eutrophic diatoms, increases in the relative abundance of oligotrophic diatoms, and an increase in diatoms sensitive to organic pollution that suggests an improvement in water quality conditions. Although this may be related to the enhanced water exchange into and out of the streambed in the alluvial reach, and such hyporheic activity could work to clean the river of organic compounds and nutrients, small decreases in water quality (lower concentration of dissolved oxygen, and higher conductance and nutrient concentrations) were observed between the Highway 213 and Goods Bridge sites. The multivariate analysis relating the diatom species composition data to the geomorphic and water-quality variables indicated that the presence of local gravel bars, bedrock, exposure to the sun (open canopy), and pH had a significant role in shaping the diatom assemblage structure. Although there was a high percentage of similarity among samples, many of these factors have the potential to affect diatoms and other algae through various interrelated mechanisms that relate to channel mobility and associated effects on light available for algal photosynthesis, for example, and other potential factors. Although only qualitatively addressed for this study, benthic macroinvertebrates, including mayflies, caddisflies, and stoneflies, were abundant in the Molalla River and indicate a high degree of secondary production in the riffles throughout the study reach. Snails, another voracious grazer of algae, also were relatively abundant at the Goods Bridge and Knights Bridge sites. Additionally, large numbers of the large caddisfly larvae Dicosmoecus were observed throughout most of the lower river in a range of depths and habitats. The large densities of these grazers, combined with the moderate level of algal biomass, suggest that invertebrate grazers could have limited the accrual of algae during summer 2010, an assertion that could be evaluated with further study. In northern California’s Eel River, high abundances of Dicosmoecus were detected in summers following winters that lacked bankfull flow, as was the case for the Molalla River in water year 2010. The lack of disturbance might explain the high abundance of these herbivores in the Molalla River. The information from this study can be used to adapt management strategies for the Molalla River and its flood plain. These strategies may assist in developing and maintaining a healthy river environment that includes high-quality water for aquatic life and human consumption.

Author: Sam J. VanLaningham
Publisher:
ISBN:
Category : Argon-argon dating
Languages : en
Pages : 396

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This research focuses on the development of new techniques to explore terrestrial-ocean climate linkages along the Pacific Northwest-northeast Pacific Ocean margin. This is done by investigating river response to climate change and by unraveling this history preserved in continental margin sediments. A significant component of this work centers on developing a 40Ar-39Ar incremental heating method to fingerprint bulk fluvial sediment entering this region. Results show reproducible ages from individual rivers accounting for the majority of sediment delivered offshore. A 40Ar-39Ar detrital mixture model is developed to examine the fidelity of these results and shows that the bulk ages measured from river mouth sediments can be accurate indicators of the average age of feldspars eroded from a given catchment area. The bulk sediment ages are combined with Nd isotopic analyses into a ternary mixing model to better understand the sources of terrigenous material delivered to offshore continental margin sites. Downcore Ar-Nd isotopic compositions can be described by three general river sediment sources proximal to the core site, the Umpqua, Rogue+Klamath, and Eel Rivers, from ~14 ka to Present. Results from the ternary model also suggest that differential contributions of eroded material plays the primary role in provenance changes seen at the core site, rather than sediment transport changes due to ocean circulation. This research culminates in a modeling effort to examine downcore provenance changes. We develop a model that balances basin-averaged 40Ar-39Ar ages (detrital mixtures) of the contributing fluvial basins and predicts the bulk sediment value at the core site. We find that the Upper Klamath Basin (which contained pluvial Lake Modoc during Marine Isotope Stage 2) is the most influential source area that can contribute to younger bulk sediment 40Ar-39Ar ages at the core site, relative to present day values. The Eel River is also shown to have a considerable influence on changes in margin sedimentation. Combinations of increases in the sediment fluxes out of these two basins can describe the 40Ar-39Ar provenance evolution observed at the core site over the 22-14 ka time period. Overall, this new 40Ar-39Ar isotopic technique, together with the Nd isotopic system and the use of detrital mixture modeling show tremendous promise as a multi-faceted strategy to assess erosion and provenance change through the continuous history preserved in fine-grained marine sedimentary records.

Author: Kurt D. Carpenter
Publisher: CreateSpace
ISBN: 9781500486426
Category : Technology & Engineering
Languages : en
Pages : 86

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This report presents results from a 2009–10 assessment of the lower half of the Molalla River. The report describes the geomorphic setting and processes governing the physical layout of the river channel and evaluates changes in river geometry over the past several decades using analyses of aerial imagery and other quantitative techniques.

Author: Jennifer Rose Wallick
Publisher:
ISBN:
Category : River channels
Languages : en
Pages : 344

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Book Description
Channel evolution and influences of changing floodplain characteristics, heterogenous bank materials, and altered flow regimes were examined along the Willamette River, a large alluvial river in northwestern Oregon. The Willamette River is composed of a series of geomorphically diverse reaches, which have each evolved uniquely in the century following Euro-American settlement. The river was divided into three large (30-50 km) alluvial reaches according to physiographic characteristics. The historically anastomosing and relatively steep McKenzie Reach (uppermost study reach), extends between the confluences of the McKenzie and Long Tom Rivers. The Willamette along the lower-gradient Santiam Reach (between the confluences of the Santiam and Yamhill Rivers is primarily contained within a single channel and has experienced lower rates of erosion than upper reaches. The Long Tom Reach (extending between the confluences of the Long Tom and Santiam Rivers), acts as a transition between the upper and lower Willamette, as it is here that the channel adopts a single-thread planform and becomes more stable. To assess the role of bank materials on bank-erosion rates, a method for detecting relative differences in erodibility between bank materials along large floodplains was developed. Coupling historic patterns of channel change with a simple model of bank erodibility enabled tracking of relative changes in bank erodibility among time intervals and bank materials. The analysis was applied to the McKenzie Reach for three time periods: 1850-1895, 1895-1932, and 1972-1995, and relative differences in bank erodibility were calculated for Holocene alluvium, partially cemented Pleistocene gravels, and revetments constructed in the 20th century. This simple model of bank erodibility reveals that, for all three periods, banks composed of Holocene alluvium were at least 2-5 times more erodible than banks composed of Pleistocene gravels. Revetment installed in the twentieth century was highly resistant to erosion and was at least 10 times less erodible than Pleistocene gravels. To examine larger-scale controls of geology, flooding, and human intervention on channel stability, rates and styles of historic channel change were determined for the McKenzie, Long Tom and Santiam Reaches and were linked with events or factors that may have triggered the observed patterns of channel change. Effects of anthropogenic activities on channel change were assessed by reviewing historic documents describing settlement patterns, riparian deforestation, channel improvements, and other actions. The role of flooding was assessed by compiling gauge records, anecdotal accounts of flooding, and by comparing stream-power distributions of large historic floods against smaller, post-dam floods with a 2-D flood model. Analyses of these larger-scale controls revealed that between 1850 and 1895, a period marked by the 3 largest floods of record, all reaches experienced numerous avulsions, increases in channel width, and decreases in centerline length. During the interval 1895-1932, a period with frequent, moderate-sized floods, migration rates increased by 50-300%, sinuosity increased and channel width decreased. The interval 1932-1995 was initially marked by rapid migration, but channel stabilization and dam building slowed erosion rates, causing the Long Tom and Santiam Reaches to display similar migration rates as those recorded for 1850-1895. Along the upper Willamette (McKenzie Reach), channel change during 1972 to 1995 was primarily limited to lateral migration along areas unrestricted by revetments and occurred at rates similar to 1850-1895 levels. Channel width decreased along all reaches during the 20th century. It is hypothesized that flooding may have been the primary factor responsible for the large-scale straightening and widening that occurred during 1850-1895. Actions taken to reduce streamside wood and side-channels along the McKenzie and Long Tom Reaches may have also contributed to widening. Along some areas of the floodplain, where the largely straightened and widened 1895 channel flowed through Holocene alluvium, the channel developed small bends that subsequently migrated rapidly downstream, and triggered rapid migration of adjacent bends. This concurrence of events and conditions suggests that accelerated erosion during the period 1895-1932 results from a combination of a "primed" planform, highly erodible bank materials, and a highly erosive flow regime with many moderate-sized floods. Migration rates 1895-1932 may have also increased as a result of land clearing and snag removal, as increasing numbers of settlers occupied floodplain lands in this interval. Anthropogenic activities have no clear effect on planform or erosion rates until the 193 D's, when widespread bank stabilization and dam construction resulted in diminished migration rates, fewer avulsions, and channel narrowing. By the late century, 30-45% of each reach was stabilized with revetments, while naturally resistant bank materials bordered an additional 13-30% of the channel length. Results indicate that revetments, naturally resistant bank materials, and flow regulation restrict migration and channel movement along the modern Willamette River. Efforts aiming to increase lateral migration on the Willamette River might consider removing revetment from bends bordered by Holocene alluvium along higher-gradient areas of the floodplain. However, such efforts may not create the suite of floodplain dynamics displayed by the historic Willamette, as much of the rapid migration, side channel maintenance and avulsions were related to flooding, channel change along adjacent bends, and large wood; all of which are largely absent from the modern floodplain.

Author: Adam L. Majeski
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages :

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Fluvial adjustment to base level change has its roots in the fundamental concepts of geomorphology. This thesis explores the rate of erosion and sedimentation on the Colorado and Dirty Devil rivers and North Wash Creek under the current base level changes related to the drawdown conditions of Lake Powell. Through cross section and long profile resurveys, the current state of each system is captured and added to the historic record of sedimentation in Lake Powell. All three systems are generally forming narrow and deep incised channels driven by the rapid rate of base level fall. Cross sections that deviate from this are due to site-specific factors, such as channel armoring, the presence of local base levels, or bedrock canyon width in relation to active channel width. In all systems, sediment is being transported through the establishing fluvial regime and is deposited at or below the new base level. This has caused rapid downstream progradation of each delta front. The volume of sediment accumulation and erosion and rates through time are calculated for each system. Deposit volume is proportional to each systems drainage basin area, as are the rates and magnitudes of deposition and erosion. The percentage of sediment eroded versus deposited shows an inverse relationship, with North Wash eroding the greatest percentage of its delta. Field observations and repeat photography on the distribution, orientation, and activity of lateral slumping and mud cracks identify that thick beds of fine-grained and cohesive silts and clays are necessary for these features to form. These features act to destabilize sediment and, in the case of bank failure, deliver it directly to the channel.

Author: Barbara K. Burkholder
Publisher:
ISBN:
Category : Bars (Geomorphology)
Languages : en
Pages : 358

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The hyporheic zone influences the thermal regime of rivers, buffering temperature by storing and releasing heat over a range of timescales. We examined the relationship between hyporheic exchange and temperature along a 24-km reach of the lower Clackamas River, a large gravel-bed river in northwestern Oregon (median discharge = 75.7 m3/s; minimum mean monthly discharge = 22.7 m3/s in August 2006). With a simple mixing model, we estimated how much hyporheic exchange cools the river during hot summer months. Hyporheic exchange was primarily identified by temperature anomalies, which are patches of water that demonstrate at least a 1° C temperature difference from the main channel. Forty hyporheic temperature anomalies were identified through field investigations and TIR (Thermal-Infrared-Radiometry) in summer 2006. The location of anomalies was associated with specific geomorphic features, primarily bar channels and bar heads that act as preferential pathways for hyporheic flow. Detailed field characterization and groundwater modeling on three Clackamas gravel bars indicate residence times of hyporheic water can vary from hours to weeks and months. This was largely determined by hydraulic conductivity, which is affected by how recently the gravel bar formed or was reworked. Upscaling of modeled discharges and hydrologic parameters from these bars to the other anomalies on the Clackamas network shows that hyporheic discharge from anomalies comprises a small fraction (“ 1 %) of mainstem discharge, resulting in small river cooling effects (0.012° C). However, the presence of cooler patches of water within rivers can act as thermal refugia for fish and other aquatic organisms, making the creation or enhancement of hyporheic exchange an attractive method in restoring the thermal regime of rivers.

Author: Jessica E. Halofsky
Publisher:
ISBN:
Category : Climatic changes
Languages : en
Pages : 0

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"A science-management adaptation partnership was developed among the Columbia River Gorge National Scenic Area, Mount Hood National Forest, and Willamette National Forest, and other organizations (hereafter referred to as CMWAP) to identify climate change issues relevant for resource management in central Oregon and southern Washington). This partnership assessed the vulnerability of natural resources to climate change and developed adaptation options that minimize negative impacts of climate change and facilitate transition of ecosystems and organizations to a warmer climate. The vulnerability assessment focused on water resources and infrastructure, fisheries, vegetation, wildlife, recreation, and ecosystem services. The vulnerability assessment shows that the effects of climate change on hydrology in the CMWAP assessment area will be significant, primarily because decreased snowpack and earlier snowmelt will shift the timing and magnitude of streamflow; peak flows will be higher, and summer low flows will be lower. Projected changes in climate and hydrology will affect aquatic and terrestrial ecosystems, especially as frequency of extreme climate events (drought, low snowpack) and ecological disturbances (flooding, wildfire) increase. Distribution and abundance of coldwater fish species are expected to decrease in response to higher water temperature, although effects will vary as a function of local habitat and competition with nonnative fish. Higher air temperature, through its influence on soil moisture, is expected to cause gradual changes in the distribution and abundance of plant species, with drought-tolerant species becoming more dominant. Increased frequency and extent of wildfire (and in some cases insects) will facilitate vegetation change, in some cases leading to altered structure and function of ecosystems, although the frequency and extent of disturbances are uncertain. Vegetation change will alter wildlife habitat, with both positive and negative effects depending on animal species and ecosystem. Animal species with a narrow range of preferred habitats (e.g., riparian systems, old forest) will be the most vulnerable to more disturbance and large-scale shifts in flora. The effects of climate change on recreation activities are difficult to project, although higher temperatures are expected to create more opportunities for warm-weather activities (e.g., hiking, camping, water-based recreation) and fewer opportunities for snow-based activities (e.g., skiing, snowmobiling). Recreationists modify their activities according to current conditions, but recreation management by federal agencies has generally not been so flexible. Of the ecosystem services considered in the assessment, (1) timber supply and carbon sequestration may be affected by lower productivity and higher frequency and extent of disturbances, (2) native pollinators may be affected by altered vegetation distribution and phenological mismatches between insects and plants, and (3) decreased salmon populations will reduce the availability of an important first food for tribes in the assessment area. CMWAP resource managers developed adaptation options in response to the vulnerabilities of each resource, including high-level strategies and on-the-ground tactics. Many adaptation options are intended to increase the resilience of aquatic and terrestrial ecosystems, or to reduce the effects of existing stressors (e.g., removal of nonnative species). In aquatic systems, a dominant theme is to restore the structure and function of streams to retain cold water for fish and other aquatic organisms. In forest systems, dominant themes of adaptation are to decrease stand density and increase structural and genetic diversity to confer resilience to drought. Many adaptation options can accomplish multiple outcomes; for example, restoring the hydrologic function of streams and wetlands will benefit coldwater fish species and riparian wildlife species as well as reduce impacts on infrastructure. Many existing management practices are already "climate smart" or require minor adjustment to make them so. Long-term monitoring is needed to detect climate change effects on natural resources and evaluate the effectiveness of adaptation options."