Poster Abstracts
2006 Binghamton Geomorphology Symposium
Oct 20-22, 2006, Columbia, South Carolina
(presented in alphabetical order, index to be added later)
Geomorphological History and Analysis of an Urbanizing Karst Catchment. Stacey Armstrong*, Robert T. Pavlowsky and Marc Owen, Department of Geography, Missouri State University, Springfield, MO, U.S.A. *E-mail: stacey01@missouristate.edu
The Ward Branch Watershed (28 km²) on the southern edge of Springfield, Missouri in Greene County has experienced rapid urbanization over the past few years. During this period one of its tributaries (2.14km²) has encountered severe erosion and flooding causing concern for local property owners. Evidence for both stability and disturbance presently exists in the channel system. This study examines the influence of land use and related drainage network changes on stream morphology and stability in an urbanized Ozark tributary. Historical analysis is based on a government land ordinance survey in 1838 and historical aerial photography for 1936, 1953, 1975, 1982, 1990, 1996 and 2005. Field methods included using a total station, GIS and differential GPS to collect a detailed longitudinal profile, cross-sectional profiles, pebble counts and fluvial disturbance indicators. In addition, interviews with local residents are used to provide personal accounts of geomorphic changes. Preliminary results indicate that the upper portion of the catchment has been de-coupled from the middle and lower reaches by artificial means. Channel head-cutting in the middle reach is releasing sediment and destabilizing the channel. However, bedrock control limits the response of the lower reaches except where sedimentation is occurring at the confluence with the Ward Branch. Results will help to develop environmental planning and stormwater management strategies with the goal to reduce geomorphic instability and maintain a stable channel in a changing landscape.
Geomorphological Effects of an Extreme Flood Event on an Urbanized River System, Toronto, August 19th 2005. Peter Ashmore* and John McDonald, Department of Geography, University of Western Ontario, London, Ontario, Canada. *E-mail: pashmore@uwo.ca
Highland Creek is a highly urbanized (85% or the basin area) stream system in east Toronto with a drainage area of approximately 102 km 2 (see Ashmore et al. poster). The river is deeply incised into glacial deposits and many reaches have thin or no alluvial cover. Since urbanization in the 1970s the stream-flow regime shows very large increases in flood flows, especially of the annual instantaneous maximum discharge, and this is probably a major cause of ongoing erosion problems along the already-energetic stream system. On August 19th, 2005 Toronto experienced an extremely intense rainstorm with totals and short-term intensities well in excess of 100 year recurrence intervals. The centre of the storm tracked across the upper part of the Highland Creek basin. Short-term peak rainfall intensity was close to 200mm/hr. There was no operational stream gauge on the stream system at that time but a previously-calibrated runoff model for the basin indicates that peak flow in the east branch (drainage area 40 km 2) was of the order of 500 m3 s-1 and the flood wave passed through the system in only 4-5 hours. This peak flow is comparable with the extreme (99th percentile) instantaneous flows for all regions of the United States (O’Connor and Costa, 2004). Peak total and specific stream power were of the order of 50,000 W m-1 and 1000 Wm-2 in some reaches. Complete assessment of the geomorphic effects on the channel system are only just beginning, based on recently-available pre- and post-storm, large-scale aerial photography. Many reaches show considerable widening, channel migration and in one case a large meander cut off. Infrastructure damage included collapse of armour-stone bank protection and loss of a long section of sanitary sewer on the valley floor. Channel reconstruction and restoration is already underway in one severely-affected reach. Analysis of the geomorphic response to this event will allow better understanding of the dynamics of semi-alluvial, till-bed channels and potential improvements in erosion mitigation and channel restoration design in this type of channel in urbanizing basins.
Urbanization Effects on Stream-flow and Channel Morphology in Toronto: the Case of Highland Creek. Peter Ashmore1,*, John McDonald1, Leif Burge2, Joe Desloges3 and Mariane Ferencevic1, 1 Department of Geography, University of Western Ontario, London, Ontario, Canada, 2Department of Geography, University of Toronto, Toronto, Ontario, Canada (now at Okanagan College, Kelowna, B.C.), 3 Department of Geography, University of Toronto, Toronto, Ontario, Canada. *E-mail: pashmore@uwo.ca
Many small drainage basins in the Toronto region have undergone rapid urbanization over the past 30-40 years. Stream-flow regimes have shown some dramatic changes in some, but not all cases. Compared to the non-urban catchments, the highly urbanized basins show upward trends in maximum annual daily mean flows but much more obvious increases in instantaneous maximum flows. Highland Creek in Scarborough (east Toronto) shows the largest changes increases` in annual maximum instantaneous discharge. Like many of the streams in the region, Highland Creek originates in a low-relief upland and then becomes more incised and confined further downstream as it approaches the Lake Ontario shoreline. The steep valley sides are cut into glacial deposits and alluvial deposition is very limited within the valleys – many channels have only a thin (or no) alluvial cover (typically coarse gravel) overlying Quaternary deposits. Stream power is very low in the headwaters and peaks in the downstream reaches where gradients are steeper. The headwaters are entirely artificial grass or concrete-lined drainage channels for light industrial areas. The natural reaches further downstream have suffered from chronic erosion problems following local channelization and increases in maximum flood flows, beginning with rapid urbanization in the 1960s and 1970s. Substantial infrastructure is at risk. Channel widening and bend cutoff have occurred in many places in response to large increases in peak stream power and channel incision may have accelerated but channel engineering has mitigated this response. Currently, channel gradients in some reaches are up to 4 times steeper than predicted from regime equations for gravel-bed rivers and widths are lower than predicted. With sufficient sediment supply braiding is possible in some reaches. Local erosion mitigation has been partially successful but major problems persist, requiring research on the morpho-dynamics of these semi-alluvial, incising streams and analysis of the historical changes in channel morphology.
Step-Pool Water Chemistry along the East Fork of Dallas Creek, Mount Sneffels Wilderness Area, CO: A Preliminary Assessment. Mark W. Barker1, 2, *, Netra Regmi11,3, J. L. Kincaid1,4, Elke Sauter1,5, Technological University of Costa Rica, San Jose, Costa Rica; and John R. Giardino1,2,3,4, Robin L. Autenrieth2,6. 1High Alpine Research Program, Texas A&M, 2Water Management and Hydrological Sciences Program, Texas A&M, 3Department of Geology & Geophysics, Texas A&M, 4Department of Geography, Texas A&M, 5Technological University of Costa Rica, San Jose, Costa Rica, 6Department of Civil Engineering, Texas A&M University, College Station, Texas, U.S.A.. *E-mail: mwbarker0@lycos.com
Mountain streams have been studied from various points of view ranging from geomorphic description and process (e.g., step pool formation and occurrence) to ecological habitat. However, no study has attempted to examine the relationship between step pools and water chemistry. We have focused on the water chemistry in both steps and pools in the upper reaches of the East Fork of Dallas Creeks in the Mount Sneffels Wilderness Are to understand the relationship step pools and their water chemistry play in habitat ecology of a stream. The East Fork of Dallas Creek, primarily a snowmelt fed stream, flows from a group of three lakes that are situated in a series of compound cirques on the southwestern slopes of Mount Sneffels (4, 313 m). The stream, consisting of countless step-pools, flows from an elevation of 3,566 m at the upper Blue Lake through near pristine forest in the upper elevations. Along its route the stream flows through recreational and agricultural areas merging with the Uncompahgre River at 2,470 m. Step-pool water chemistry relationships combined with habitat characteristics act as a guide for measuring stream health in the wilderness area. Quantitative differences in temperature, pH, dissolved oxygen (DO), conductivity and total dissolved salts (TDS) of step-pools were examined in three predetermined zones of East Fork Dallas Creek. In addition, the use of components from the USGS National Water Quality Assessment Program, Geomorphic River Styles and the Rosgen schemes provided a geological and ecological backdrop as to clues in identifying step-pool chemistry, habitat requirements and potential anthrogeomorphic inputs. Preliminary analysis suggests that there are minimum differences in pH, conductivity, TDS and temperature between steps and the pools. DO appears to be higher in steps than in pools. There does appear to be changes in the parameters along the course of the stream. Morphologically the East Fork of Dallas Creek ranges from A2 to A3 in the upper and middle reaches to B2 to B3 in the lower reaches.
Human and Natural Impacts on Landscape Aggradation in the Maya Lowlands. Timothy Beach1, * and Sheryl Luzzadder-Beach2, 1Georgetown University, Washington, D.C., U.S.A., 2George Mason University, Fairfax, VA, U.S.A.. *E-mail: beacht@georgetown.edu
This poster begins to differentiate the major drivers and chronology of erosion and aggradation in the tropical, karst landscapes of the Maya Lowlands. We use water, soils, radiocarbon, and archaeological data to determine the quantity, timing, and causes of aggradation along a cross-section of the Maya Lowlands from the karst uplands into the coastal plain of Belize. Water sources in the uplands have low quantities of dissolved ions but water in the coastal plain has high amounts of dissolved ions and is nearly saturated in sulfate. Geomorphic findings come from many excavations across a gradient from upland valleys, sinks, and fans into the coastal plain wetlands. We found this landscape was c. 120 cm lower and mantled by what is now a distinct paleosol in the early to middle Maya Preclassic (3200 BP to 2300 BP). From the Late Preclassic (2300–1700 BP) to Classic Periods (1700-1000 BP), the landscape aggraded by an average of 120 cm from four main sources: river flooding, accelerated erosion, ancient Maya landscape manipulation, and gypsum precipitation from a rise in a water table nearly saturated in calcium and sulfate ions. Accelerated soil erosion was the main driver of the sedimentation on upland valleys and fans, but water table rise, probably driven by sea-level rise, was the main driver on the wetlands of the coastal plain because the aggraded sediments here are dominantly composed of gypsum derived from the groundwater. This latter mechanism represents a rarer driver of aggradation and a large scale environmental change that occurred during periods of intensive Maya land use and climatic instability.
Railroad Beds and Coho Salmon Habitat in Oregon: Lateral Structural Disconnection in the River Landscape. Paul Blanton, Department of Geography, University of Oregon, Eugene, OR, U.S.A. E-mail: pblanton@uoregon.edu
Where possible, railroad builders in the Pacific Northwest followed riverbanks. While railroads and other transportation structures are often included in lists of land uses affecting river landscapes, they are not the focus of process-based study linking land use, impacts, and habitat form and function. My contention is that railroad beds in river floodplains disrupt the creation and maintenance of viable side-channel habitat needed to support endangered Coho salmon populations. I used GIS to analyze the spatial relationship between the location of railroad lines and Coho salmon habitat (present and historical) in the state of Oregon. 46% of total stream segment length of present Coho habitat is within 50’ of a railroad line. 72% of historic Coho habitat that is no longer functional is within 50’ of a railroad line. These preliminary results suggest the importance of further investigation of railroad lines and floodplain habitat dynamics. I suggest a multiple scale framework for subsequent research to explore the impacts of railroad beds on hydrologic, geomorphic, and ecological processes in the river landscape. This framework involves lumping linear floodplain structures as similar landscape elements, emphasizes process-based landscape-oriented approaches, and identifies key variables and processes at different scales. Linear floodplain structures such as railroad beds, roads, dikes, and levees all cause lateral disconnection of the river from its floodplain and the rest of the river landscape. This disconnection results in disruption of flows of water, sediment, and biota which leads to habitat degradation. Floodplain land use dynamics should be included along with understanding of geomorphic process in the landscape to assist in addressing critical management issues such as flow alteration of dams, wetland protection and mitigation, and identification of key areas for river habitat protection and rehabilitation.
Repeat Photography: Before and After – Reconstruction of the Rio Vista Dam on the San Marcos River. Michelle Bussemey, Department of Geography, Texas State University, San Marcos, TX, U.S.A. E-mail: misha@txstate.edu
The use of repeat photography as a field method is a practical and simple interpretive tool to show changes in the physical landscape. The significance of comparing photographs is vital to understanding the temporal change of not only the physical landscape, but also change in the cultural landscape and human impact on a place. The relevancy of repeat photography as a technique in field research is addressed by the growing concerns of urban land-use, changes in the global climate, and the effects of man-made structures on geomorphic and fluvial systems. The employment of these techniques helps analyze the impact of the changes and structural improvements made to the Rio Vista Dam in San Marcos, Texas during the spring of 2006. The severe changes in the surrounding landscape and fluvial processes of the San Marcos River are examined by comparing nine sets of photographs. The spatial and temporal difficulties encountered while performing the field method are compounded by the drastic change in the riparian landscape, river channel, and increase in human use. The enormous rise in the amount of users to the area is causing congestion in the river, muddiness of the waters, and trash to accumulate in the river and on the shore. Alterations of the river by impoundments, diversions, urbanization, recreational developments, and overcrowding can be considered the main causes of habitat degradation (McCoig, Cradit, & Fox 1986). The effects the newly constructed dam will have on the endangered gambusia and Texas wild rice could be catastrophic if the amount of users to the area continues to increase. Without proper supervision and restraints, the delicate San Marcos River system will reflect the impact of overuse and overcrowding.
Aerial Photographic Analysis of Channel Change and Riparian Vegetation Growth in Canyon de Chelly National Monument, Arizona, 1935-2004. Daniel Cadol* and Sara Rathburn, Department of Geosciences, Colorado State University, Fort Collins, CO, U.S.A. *E-mail: cadol@cnr.colostate.edu
Aerial photographs over the past 70 years show that the establishment and expansion of invasive tamarisk (Tamarix ssp.) and Russian olive (Elaeagnus angustifolia) has coincided with channel narrowing and incision. Photo sets from 1934, 1964, 1975, 1981, 1989, and 2004 were used to track changes in vegetation and channel morphology through time. In 1934, scattered riparian vegetation, including cottonwood (Populus ssp.) and willow (Salix ssp.), covered <1% of the canyon bottom. By 1975 vegetation had expanded somewhat in the lower reaches, and the channel narrowed in the upper reaches. During the 1980s vegetation coverage expanded rapidly into areas that had recently been active channel. In 2004 80% of the channel was single threaded, with an average width of 6.5m, and most was lined with a riparian vegetation belt which covered 30% of the canyon bottom. The remaining 20% of the canyon, primarily in the lowermost reaches, remained a wide wash, lined with stands of woody vegetation. Over the full study period, it was found that vegetation growth and channel narrowing occurred at a nearly one-to-one ratio. However, over shorter time periods local vegetation had minimal effect on channel change. Earlier time periods saw channel narrowing in excess of vegetation growth, and often in the absence of vegetation growth. Later time periods saw vegetation growth in excess of channel narrowing, often in the absence of channel narrowing. Channel changes occurred earliest in the upper reaches and later in lower reaches. Changes were observed simultaneously in both main branches of the canyon. However a review of channel change studies throughout the southern Colorado Plateau failed to show a consistent regional pattern of change from 1935-2004. The evidence implicates internal thresholds as the initiator of channel change, with the important caveat that vegetation introduction has altered the magnitude and pattern of channel changes.
Multivariate Analysis of Mining Effects on Alpine Fluvial Forms and Processes near Silverton, Colorado, USA. Mindy M. Conyers, Department of Geography, Texas State University, San Marcos, TX, U.S.A. E-mail: mc1062@txstate.edu
Recent research in the field of geomorphology has focused on the numerous ways in which human activities can alter the surface of the Earth. Of particular interest to some geomorphologists are the impacts to a river system caused by mining operations. Effects of mining include sediment load alteration, alterations in the spatial distribution of near-channel processes, riparian vegetation adjustments, and many others. In mountain watersheds, mining can be particularly influential in changing fluvial systems due to relatively small channels and rapid adjustment rates. However, assessing the impact of near-channel mining effects on in-channel fluvial forms and processes can be difficult because these effects often exhibit colinearity with other variables such as controls on hydraulic geometry, differences in geology, and land use variability.
This study focuses on the effects of long-term mining on the spatial distribution of major fluvial forms and processes in the Upper Animas River watershed near Silverton, Colorado. This area has long been affected by extensive mining of precious metals, leaving mine tailings available for input into the Animas, Cement, and Mineral Creek stream systems. Although nearly all of the mining has ceased, the long-term effects of the tailings and hydrologic shifts can still control various fluvial forms in the long term.
To describe this control, multivariate statistical analysis can be combined with spatial associations (lags) to predict sampled stream cross-sectional forms and processes from natural and anthropogenic near-channel boundary conditions. Residual analysis allows the dominant effects of the downstream hydraulic geometry and geology to be separated, both statistically and spatially, from effects such as anthropogenic mining activities. Research into the controls on the Upper Animas fluvial system will lead to a more thorough understanding of the impacts humans have on the Earth’s surface.
The conflict between societal needs and the desire to restore ecosystems is particularly evident in large river ecosystems where management has and will continue to focus on the utility of large river channels and floodplains for agriculture, navigation, and flood control. Many large rivers have been engineered to create narrow, deep channels from what historically were often shallow, complex, shifting, multi-channeled rivers resulting in the elimination of critical habitats for native biota and impairment of fluvial geomorphic and ecologically significant processes such as sediment and nutrient retention and floodplain inundation. Despite the recognition of the damages these structures inflict upon large river ecosystems, many are simply too valued by society to remove. The challenge facing large river managers today is to find successful alternatives that will restore geomorphological and ecological processes and forms in the presence of persistent human impacts such as hardened channel boundaries, levees and extensive floodplain agriculture. One promising restoration alternative that has recently emerged is the restoration of secondary channels that cut across the agricultural floodplains of large rivers. This approach may essentially permit the restoration of small side-segments of more “natural” river environment while avoiding the need to remove engineering control of the main channel or take large areas of floodplain out of agricultural use. These secondary channels have tremendous potential to increase the diversity of hydraulic habitats, provide critical habitat for endangered native species, functioning as nutrient retention and processing “hot spots” that may reduce the overall solute load in the system, and increase lateral connectivity. This poster explores the potential that secondary-channels represent as a potential mechanism for achieving the elusive and difficult compromise between ecosystem integrity and continued human use of large rivers.
Geomorphic and Archaeological evidence of Deforestation for a Roman-era Ship-building Industry, Rough Cilicia, Turkey. Martin Doyle1,*, Nick Rauh2 and Hulya Caner3, 1Department of Geography, University of North Carolina, Chapel Hill, NC, U.S.A., 2Department of Classics, Purdue University, West Lafayette, IN, U.S.A., 3Istanbul Polytechnic University, Istanbul, Turkey. *E-mail: mwdoyle@email.unc.edu
The goal of this project was to identify what combination of forces precipitated urban development in the ancient Mediterranean world, whether the remnants of such forces are identifiable in the archaeological record, and whether the geomorphic effects of such settlement changes have a lasting impact on the contemporary landscape. Specifically, we sought to document whether the natural resource of timber (cedrus libani) was the primary stimulus for urban and regional development as induced by the expansion of the distant Roman Empire.
This study was part of the Rough Cilicia Survey Project, which is an ongoing archaeological investigation of a 60 km coastal strip in southern Turkey. For this portion of the survey, we examined long-term hillslope erosion rates that were commensurate with a suspected era of deforestation driven by a shipbuilding industry in the periphery of the Roman Empire. A combination of geologic field data, numerical modeling of landscape processes, dendrochronology, and palynology was used to quantify the area impacted by deforestation and the timing of such impacts. A commensurate archaeological study utilized regional field surveys to investigate spatial settlement patterns of peripheral societies undergoing urban development.
The results suggest that erosion associated with deforestation 2000 years ago left a measurable impact on the landscape, and one that has left a legacy landuse change on the landscape. This impact was governed by a combination of topography and the unique ecology of the Cedar of Lebanon (cedrus libani), the removal of which caused a cascading effect on the landscape, which was essentially a coupled human/environment threshold. The land use conversion persisted for the past two millennia, as once the landscape was developed, it was possible to introduce other forms of landuse that precluded the potential recovery of the landscape to pre-disturbance conditions.
Effects of Flood Management Practices on Channel Morphology in the San Marcos River, Texas. Frank Engel* and Joanna Curran, Department of Geography, Texas State University, San Marcos, TX, U.S.A. *E-mail: being@txstate.edu
Effects from human management are ever present in today’s river systems. Decisions made to reduce flooding, allocate water, or create hydropower have significant impacts in fluvial geomorphology. Texas rivers are no exception. This study considers the effects of flood control structures on channel morphology as well as sediment transport in the San Marcos River, Texas. The primary objective of this study is to determine if the flood control structures are playing a role in the evolution of a sediment wedge forming at the confluence of the San Marcos River and a tributary, Sessoms Creek. Results show that since the flood control structures were completed, only two flood events could have produced any significant transport of material from the wedge. Observations downstream of the wedge show areas moderate to extensive mass wasting of the channel banks all along the length of the Upper San Marcos River. Our analysis shows significant aggradation, and widening downstream throughout the study reach. Based on the known history of the sediment wedge and observed impacts in the study reach, it is most likely that the flood control structures are primarily responsible for the creation of the wedge as well as the downstream channel bed aggradation and reach widening.
Erosion of Hydraulic Mining Sediment and Channel Change: Sacramento Valley, California. Subhajit Ghoshal1,*, L. Allan James1, Michael B. Singer2 and Rolf E. Aalto3, 1Geography Dept., University South Carolina, Columbia SC, U,S,A,, 2Institute for Computational Earth Systems Science, UC Santa Barbara, Santa Barbara, CA U.S.A., 3Department of Earth and Space Sciences, University of Washington, Seattle, WA, U.S.A. *E-mail: subhajitghoshal@gmail.com
Hydraulic gold mining in Sierra Nevada of California (1853-1884) displaced great volumes of sediment from upland placer gravels. This sediment was formerly believed to have been entirely trapped upstream of foothills dams or to have passed completely through the Sacramento Valley to the Delta. This study tests the hypothesis that large deposits of historical sediment remain in the bed, banks and terraces of piedmont rivers downstream of foothill dams where floods remobilize and redeposit them. This could represent a substantial proportion of the modern sediment loads in the system.
This study presents preliminary findings from field reconnaissance in the summer of 2006 and on-going remote sensing analyses. A planimetric and volumetric study is being conducted to document the spatial and temporal variation of channel enlargement and lateral migration and associated magnitudes of erosion. This includes a time-series analysis between time periods of historical maps, aerial photographs, 1999 LIDAR data and DEM derivatives, and DOQs, to estimate channel change and erosion rates of the historical sediment along the lower Yuba, Bear, and Feather Rivers. Furthermore, LIDAR data, hand-core data, and ground-penetrating radar (GPR) survey data are being studied to estimate volumes of the historical sediment eroded from selected floodplain sites along the lower Feather and Yuba Rivers. Finally, sediment compositions of the sand-sized fraction are being studied to facilitate identification of hydraulic mining sediment and to evaluate the degree to which deposits are diluted with sediment from other sources.
Sediment budget approach to evaluate urban-related instability in an Ozark Stream. Mark A.Gossard*, Robert T. Pavlowsky and Marc R. Owen. Missouri State University and Ozarks Environmental and Water Resources Institute, Springfield, MO, U.S.A. *E-mail: Gossard927@missouristate.edu
Sediment load variations can cause channel instability in gravel bed rivers. Accelerated gravel sediment inputs due to land use-related disturbances have been shown to cause channel and bank instability in Ozarks streams. Ward Branch is a heavily urbanized watershed in Springfield, Missouri for which restoration measures are planned. This study aims to use a sediment budget approach to understand the sources and transport patterns of bed load in a particularly unstable 300 meter long “disturbance” reach along Ward Branch where bank erosion and channel incision is releasing excess gravel to the stream. Urbanization has increased the 2-year flood peak by more than three times the pre-settlement condition. Channel form and erosion/deposition were monitored over a 12 month period. The methods used in this study are (i) repeated cross-section and longitudinal surveys of the channel, (ii) scour chains and bank erosion pins, (iii) pebble counts and sieving of both the bank and bed materials, and (iv) painted tracers to monitor bedload movement. Rainfall records and flood peaks are also being monitored. Results of the tracer experiments showed that during three bankfull floods and one larger event, the D25 moved 25 meters, D40 moved 15 meters, D50 moved 20 meters, 84 moved 16 meters, 90 moved 12 meters, and the D95 moved 7 meters on average with an overall recovery rate of 34%. Results from this study will be used to plan bed and bank stabilization measures and understand channel storage and mobility dynamics of Ward Branch.
Culverts and CRUD (Coarse Riparian Urban Debris): The Importance of Anthropogenic Objects in an Urban Stream. Judith L. Grable, Department of Physics, Astronomy, and Geosciences, Valdosta State University, Valdosta, GA, U.S.A Email: jlgrable@valdosta.edu
Field observations and measurements of Second Creek, a small (8.8 km long) urban stream located in Knoxville, Tennessee, USA, revealed an increase in particle size due to the addition of particles of anthropogenic origin. The addition and removal of such particles may occur at any time, without regard for storms or seasons. This type of perturbation, and others, such as the effects of adjacent construction activities and the armoring of portions of the stream channel, create an urban disturbance regime of varying spatial and temporal scales. Geomorphic adjustment to such disturbances are hindered in Second Creek by the effective decoupling of many stream reaches. Water and suspended sediment pass through the system, but bedload transport has been interrupted by the presence of many culverts along the length of the stream.
Downstream hydrologic changes following impoundment of the West Branch Delaware River, New York, U.S.A Jorene L Hamilton, Department of Geological Sciences, Binghamton University, Binghamton, NY, U.S.A. E-mail: jhamilt1@binghamton.edu
The Cannonsville Dam and Reservoir are located on the West Branch Delaware River in the Catskill region of New York; about 193 kilometers northwest of New York City. The primary purpose of the dam is to create a reservoir that supplies New York City with potable water. Pursuant to this, there have been several water quality studies focusing on the West Branch Delaware River, however limited attention has been paid to the downstream hydrologic effects of the Cannonsville Dam.
The study area includes three USGS gauging stations, including a critical gauge that is located downstream of the dam but upstream of any confluences. Using the Indicators of Hydrologic Alteration (IHA) Version 7, pre- and post-impoundment gauging records were analyzed for changes in mean annual flow, base flow, and mean annual minimum and maximum single and multiple day discharges. The IHA results indicate that impoundment has significantly decreased the mean annual discharge and mean annual maximum flows of the West Branch Delaware River. The effects of the dam on the base flow and mean annual single and multiple day minimum discharges, however, vary with distance downstream of the dam. Less than 2.25 kilometers downstream of the dam, base flow and minimum flows decreased, whereas farther downstream flows tended to increase. Analysis of upstream gauging data indicates that changes in flow regime of the West Branch Delaware River have been relatively minor, suggesting that changes downstream of the dam are, in fact, related to impoundment.
Contribution of Land Use Dynamics in Causation of Mass Movements in Surroundings of Kothmale Reservoir of Sri Lanka. H.M. Jayani Rupi Herath, Department of Geography, University of Sri Jayewardenepura, Sri Lanka. E-mail: Jayani_herath@yahoo.co.uk
Kothmale Reservoir was built under the Accelerated Mahaweli Development Program, with the aim of several imperative aspirations. After the construction, surroundings were declared as reserve areas with minimal human interference. Although it was done after evacuating the inhabitants of the area, subsequent generations of these families were regaining occupation of this subtle and sensitive landscape. Occupation of these marginal lands and the construction of a massive reservoir in the hill country caused an increase in incidence of mass movements in the Upper Mahaweli Catchment which also includes this reservoir.
The objective of this study was to evaluate the Mass Movements in the surrounding of the Kothmale Reservoir and its contributory factors in relation to Land Use alterations due to human interference. The study used aerial remote sensing data and field observations during the analysis. Remote sensing data of 1972 and 1999 were analysed using MFWORKS software.
There were 21 sites of mass movements and according to Wyoming Landslide Classification there were 2 translational slides, 1 rock fall and 18 soil creeps. When considering the causative factors, there were 14 sites of reservoir induced and 4 sites of rain induced Mass Movements while there was one site with both rain and the reservoir induced features. One site of mass movement was due to a natural fracture and the other one was initiated due to human interferences. Only 5 sites out of 21, the land use type had been a static between 1972 and 1999. In all the other 16 sites, there had been some sort of transformation of Land Use due to human interference. Of the sites where there was no change of land use, the most important characteristic was that their close proximity to the reservoir. This shows the importance of human induced land use dynamics in initiation and contribution to the Mass Movements in the Kothmale Reservoir surroundings.
Impact of In-Channel Geomorphic Structures on Surface-Subsurface Exchange of Water and Heat in Streams. E.T. Hester1, * and M.W. Doyle2, 1Curriculum in Ecology, 2Department of Geography, University of North Carolina, Chapel Hill, NC, U.S.A. *E-mail: ethester@email.unc.edu
In-channel geomorphic structures such as debris dams and steps are common in undisturbed streams, are often installed as part of stream restoration projects, and can significantly enhance exchange of water across the streambed. Surface-subsurface exchange is also an important cooling mechanism in summer for streams suffering elevated temperatures due to climate change or loss of riparian shade. However, the effects of many basic geomorphic structure characteristics (e.g., size and type) and hydro-geologic boundary conditions on water and heat exchange are poorly known but critical to understanding the impact of channel morphology on stream community and ecosystem ecology dynamics. We combine surface and groundwater numerical hydraulic and heat flow models with field hydraulic and temperature measurements using a three-dimensional sensor network to quantify these relationships and their implications for stream functioning and restoration design. Results show that while water exchange with the subsurface generally increases linearly with geomorphic structure height, the residence time and size of the induced subsurface flow cell respond nonlinearly. Such hydrologic aspects of exchange also respond nonlinearly various hydrologic and geologic controls, such as depth to bedrock, groundwater recharge, and channel slope. Finally, thermal effects, such as the degree of heat exchange via hydrodynamic mixing and heat conduction within the induced subsurface flow cell, and the corresponding temperature moderation of water as it returns to the surface, also appear to respond nonlinearly to basic descriptive parameters of in-channel geomorphic structures. These nonlinear trends have significant implications for understanding natural stream function as well as optimizing stream restoration design to maximize functions such as reactive time in the subsurface or reduction of maximum summer temperatures.
Mapping River-Channel Structures: Methodology, Issues, and Applications. Michael L. Hughes1,2, *, Patricia F. McDowell1 and W. Andrew Marcus1, 1Department of Geography, University of Oregon, Eugene, OR, U.S.A., 2Presently at E. Voinovich Center for Leadership and Public Affairs at Ohio University, Athens, OH U.S.A. *E-mail: hughesm@ohio.edu
One of the most obvious ways humans affect fluvial systems is the placement of structures along river channels. While the hydrogeomorphic impacts of dams on large river systems have received much attention, the singular and cumulative impacts other channel structures, such as levees, road embankments, revetments, and groins have received comparatively little attention and scholarly literature on this topic has been scarce. A fundamental step in understanding how channel structures affect fluvial systems is to map, date, and describe structure locations; however, this task presents a number of unique challenges that must be met in order to investigate cause-and-effect in relation to human structural impacts in fluvial systems. The focus of this paper is to present a functional methodology for acquiring channel-structure data and processing them to produce a map with attributes that are useful for spatial analysis. This methodology includes a blend of GPS and instrumental survey techniques, query of agency database records, interviews with key agency personnel and landowners, and on-screen aerial interpretation and digitizing techniques in a GIS. Access to river locations with channel structures for data acquisition, limitations in agency database records, deterioration of historically significant channel structures in the field, and photo-interpretational ambiguity can present difficulties in mapping and dating channel structures and therefore should be anticipated in any study aimed at understanding human structural impacts. An example of a channel-structure map along 120 kilometers of the Umatilla River, northeastern Oregon, illustrates both the ubiquity and diversity of channel structures in a laterally mobile gravel-bed channel system, as well as the spatial variability of channel processes that triggered their construction. This map and its attributes were designed to support testing of the hypothesis that structures placed between flood events of comparable magnitude exert a significant control on channel processes operating during sequential flood events.
Bed slope and bank resistance as drivers for channel adjustment in an Arizona stream impacted by invasive plant species. Kristin Jaeger* and Ellen Wohl, Department of Geosciences, Colorado State University, Fort Collins, CO, U.S.A. *E-mail: kljaeger@warnercnr.colostate.edu
Much like other streams in the American southwest, the stream channels in Canyon de Chelly National Monument in northeastern Arizona have experienced cycles of incision and aggradation throughout the late Quaternary. The most recent episode of incision coincided with the widespread expansion of exotic tamarisk and Russian olive. It is unclear, however, whether channel incision is occurring in response to plant establishment or in response to other mechanisms. To address this issue, unit stream power, channel geometry, bed slope, bank resistance, riparian vegetation, and channel entrenchment (here defined as total difference between channel and top of lowest bank) were measured along approximately 16 km of channel. These data were used to assess correlations among potential control variables and channel geometry. Two alternate scenarios could occur with respect to the assumption that local bank resistance is the primary control on channel entrenchment. One scenario is that the channel geometry correlates with the presence of higher bank resistance caused by geotechnical and vegetative factors. Under this scenario, narrow, entrenched cross sections will have greater slope and more resistant banks as a result of greater silt or clay content or higher root density. An alternative second scenario is that there is no correlation between variations in bed slope and channel entrenchment, and bank resistance. This scenario reflects ongoing complex response throughout the drainage network rather than local controls. Preliminary findings indicate that variations in channel slope exist, with locally steep stream sections associated with narrow channel geometry and resistant banks composed of cohesive clay units. These findings suggest that channel slope and bank resistance are major drivers for channel geometry.
Hydrogeomorphic controls and anthropogenic influences on light availability in rivers. Jason P. Julian*, J. Adam Riggsbee and Martin W. Doyle. Department of Geography, University of North Carolina, Chapel Hill, NC, U.S.A. *E-mail: jjulian@unc.edu
Light is vital to the dynamics of aquatic ecosystems. It drives photosynthesis and photochemical reactions, affects thermal structure, and influences aquatic biota. Light availability in rivers is dictated by topography, riparian vegetation, channel geometry, optical water quality, and hydrology. The human role in changing these hydrogeomorphic controls has altered riverine light environments through channel incision, deforestation, channelization, urbanization, and dam construction. Here we assess and quantify the effect of anthropogenic influences on light availability in three rivers: Deep River, NC; Baraboo River, WI; and Big Spring Creek, WI. We used a series of four photosynthetically active radiation (PAR) sensors to measure i) above-canopy PAR, ii) PAR above water surface, iii) PAR below water surface, and iv) benthic PAR (i.e., on stream bed). These measurements were used to develop empirical light attenuation coefficients, which were then used in combination with measurements of optical water quality and shading to develop a Benthic Light Availability Model (BLAM). Channel surveys and flow records were used with BLAM to quantify how riverine light availability varies through space and time, and how it is affected by anthropogenic disturbances. Finally, we demonstrate the implications of light availability on two processes governing riverine biogeochemistry: primary productivity and photochemical processing of dissolved organic matter.
Alluvial-bedrock channel boundary forcing and human built forcing agents in the Guadalupe River. Amanda Keen-Zebert and Joanna Curran, Department of Geography, Texas State University, San Marcos, TX, U.S.A. E-mail: keen-zebert@txstate.edu
Channel boundary forcing is a process that interrupts the longitudinal processes operating in streams. A channel boundary forcing agent, whether natural or anthropogenic in origin, exerts a local control that either eclipses or punctuates trends at a more generalized spatial scale. In mixed boundary rivers, where both bedrock and alluvial reaches alternate downstream, the impact of channel boundary forcing is potentially great. The Guadalupe River is a shallowly incised bedrock channel that is variably alluviated. Road crossings and small run of the river dams in the Guadalupe River obstruct flow and cause deposition upstream and scour downstream thereby forcing boundary type to be alluvial upstream and bedrock downstream. The downstream distance of the forcing effect of roads ranges from 0.94 kilometers to 2.02 kilometers from the road crossing. The longitudinal extent of the forcing effect of dams ranges from 0.56 to 2.04 kilometers. The extent of forcing effect is greater where forcing agents are closely spaced and the forcing effect is compounded. Forcing agents may also originate from non-anthropogenic processes. For example, logjams and groups of large individual boulders locally disrupt flow and the transport of sediment downstream. This research explores the concept of channel boundary forcing and its applications in mixed alluvial bedrock streams and compares anthropogenic and non-anthropogenic forcing agents.
Spatially Heterogeneous Bank Sedimentology and Geomorphic Response of a Semi-Alluvial Urban River: Highland Creek, Southern Ontario, Canada. M.Toni Largo1, *, Joseph R. Desloges1 and Leif M. Burge2, 1Department of Geography and Program in Planning, University of Toronto, Toronto, ON, Canada, 2Okanagan College, Kelowna, B.C., Canada. *E-mail: largot@geog.utoronto.ca
This study provides an analysis of bank sedimentology and floodplain stratigraphy of Highland Creek in order to determine the influence of a rapidly altered (urbanized) flow regime on the Holocene valley system. Highland Creek (Ad = 100 km2) is typical of many rivers in this region which are entrenched and characterized by channel banks composed of alluvial and glacial materials. The mixed alluvial character of the sediments strongly influences the rate and extent of channel erosion to the altered flow regime. In response to 50% and almost 300% increases to mean annual flow and maximum instantaneous flow, respectively, the channel has steepened, widened and coarsened especially downstream of confluences. Lateral erosion of the channel margin has exceeded as much as 60 m in the last 30 years alone consuming floodplain materials as old as 5000 years B.P. The lateral instability has greatly exceeded vertical entrenchment which we estimate to be less than 1.0 m since urbanization was complete in the early 1970’s. This is in part due to the highly resistant nature of lodgement till which makes up a significant portion of the lower channel boundary. The style of floodplain response to the much higher flow regime can be grouped into three categories. 1) In upper semi-alluvial reaches bank heights have increased primarily due to bed degradation exposing more of the till whereas the overlying alluvial sediment thickness decreased due to floodplain stripping. 2) In middle mixed-alluvial reaches bank heights have increased due to bed degradation and overbank deposition while 3) in sandy alluvial reaches near the outlet bank heights have increased primarily due to overbank deposition. Channel cutoffs, avulsions and widening have dominated the upper reaches whereas widening dominates the lower reaches. Overall, we estimate that the turnover of floodplain materials has accelerated by at least 2 orders of magnitude compared to more “average” rates of Holocene floodplain development in this region.
The first documented discovery of gold in the U.S. occurred in 1799 in Cabarrus County, North Carolina, leading to the nation’s first gold rush between about 1830 and 1860. The use of mercury amalgamation to recover fine gold particles led to the release of unprecedented amounts of mercury to the environment. Although mercury is the most common contaminant of aquatic ecosystems worldwide (e.g., responsible for 80% of all fish consumption advisories in the U.S.), its sources, pathways and toxicity-controlling processes are complex and relatively poorly understood when compared to other metals like, for example, lead.
Although North Carolina led the nation in gold production until 1848, and produced more gold than any other state in the southern Piedmont gold belt, few studies of mercury contamination associated with this mining exist. The purpose of this study is to determine the magnitude and explain the distribution of mercury contamination in floodplain sediments more than 100 years after large-scale gold mining ceased in the region. This paper presents preliminary data suggesting that floodplain sediments are highly contaminated downstream from the Gold Hill mining district, one of the most intensively mined areas in the North Carolina gold belt. Maximum background Hg concentrations in 25 samples collected from source area soils is about 0.1 ppm. Over 500 samples collected from exploratory floodplain cores show that about half are contaminated above 0.1 ppm and 25% had more than 5 times the maximum background concentration. Cores in overbank deposits display well-defined peaks in mercury concentrations and suggest that about 100-180 cm of sediment has accumulated on these floodplains during the past 150 years.
Varied Mining Impacts in Four Gulf Coastal Plain Rivers. Joann Mossa*, Jim Rasmussen and David Coley, Department of Geography, University of Florida, Gainesville, FL, U.S.A. *E-mail: mossa@geog.ufl.edu
Alluvial rivers and their floodplains are experiencing increasing pressures as sources of gravel and sand used in construction. Mining activities result in direct alterations to fluvial systems, as well as a number of indirect changes associated with increasing the vulnerability of the landscape, especially its propensity to change during flood events. Four case studies with different types of mining impacts on fluvial systems are described. One is the Bouie River in Mississippi, where historical in-stream mining of the channel bed and margins has directly altered the form of the channel. Some portions of the channel are several times wider than others such that the channel resembles a chain of lakes. In some places, mined reaches are more that ten times wider and deeper than average depths in other reaches. Two, Thompson Creek in Mississippi has indirect changes associated with floodplain mining, where channel position has altered in multiple locations by avulsing into mining pits. Three, the Leaf River shows changes just upstream of the confluence with the mined Bouie River. It shows reduced stage elevations, decreased mean bed elevations, and increased planform instability, likely due to headcutting associated with expanding pits in its mined tributary. Four, the Escambia River in Florida shows reduced stage elevations, increased bed elevations, and increased width-depth ratios, largely in connection with mining on its tributary Big Escambia Creek. The differing channel bed responses in these latter two systems appear due to the different mining practices. Findings suggest that the effects of mining are varied and that those concerned with potential environmental and economic impacts of mining need to look beyond the mined reach to adjoining streams, including larger ones.
Determining the Effect of Best Management Practices on Channel Substrate. Ryan P. Murphy1 and Enrique Gomezdelcampo2, *, 1Hull & Associates, Inc., Toledo, OH, U.S.A., 2Department of Geology and Center for Environmental Programs, Bowling Green State University, Bowling Green, OH, U.S.A. * E-mail: egomezd@bgsu.edu
The Sandusky River watershed, located in northwest Ohio, has been influenced by agriculture since the late 1800s. In 2003, the Ohio Environmental Protection Agency (OEPA) identified various tributaries and reaches of the Sandusky River as failing to meet biological water quality standards mainly due to siltation. To assess the effectiveness of best management practices (BMP), channel cutoffs were used as they represent unique archives of substrates that existed in the previous channel. In this study, a channel cutoff of the Sandusky River in Crawford County, Ohio near the city of Bucyrus was identified using recent digital aerial photography. Historical aerial photographs and USGS peak discharge data suggest the channel was likely abandoned between 1957 and 1964. Twelve sediment cores between two and three meters in depth were collected with a vibracore. Grainsize analyses of the channel cutoff substrates located within the core were completed and the percent gravel, sand, silt, and clay were determined. These data were
compared to assess the extent of change in channel cutoff and current channel substrates. Results from this study show a fining trend from a mean grainsize of -1.52Ф (gravel) in the channel cutoff substrates to -0.92Ф (sand) in the current channel substrates. To explain this fining a series of hypotheses is examined, including sediment storage, trends in population and crop cultivation, existence of BMPs, and sediment transport during floods. Evidence from this study strongly suggests that a shift from the cultivation of low cover crops (hay and oats) to high cover crops (corn and soy bean) has increased the delivery of fine grain sediments into streams, minimizing the effectiveness of BMPs in Crawford County.
Unintended large-scale effects of human shoreline stabilization on coastline evolution. A. Brad Murray*, Jordan M. Slott and Andrew D. Ashton, Division of Earth and Ocean Sciences, Nicholas School of the Environment and Earth Sciences; Center for Nonlinear and Complex Systems, Duke University, Durham, NC, U.S.A. *E-mail: abmurray@duke.edu
Experiments with a recently developed model of large-scale coastline evolution (Ashton et al., Nature, 2001) indicate that moderate shifts in storm patterns, one possible outcome of global warming, may accelerate the rate at which shorelines erode or accrete (Slott et al., GRL, 2006). However, such analyses assume mobile sandy shorelines and are not applicable to present shorelines where human shoreline stabilization practices, such as beach nourishment (i.e. placing sand on an eroding beach), have increasingly fixed the location of the shorelines adjacent to coastal communities. Scientists and coastal engineers have typically only considered the site-specific consequences of shoreline stabilization; here we explore the large-scale (10’s kms) and long-term (decades to centuries) effects using a numerical model of alongshore sediment transport.
We conducted pairs of numerical experiments on a cuspate-cape shoreline and varied the wave-climate forcing across each pair, each representing different storminess scenarios. For each experiment-pair we ran a control experiment with no shoreline stabilization and a second where a beach nourishment project stabilized a cape tip. By comparing the results of these two parallel runs, we isolate the tendency of the shoreline to migrate landward or seaward along the domain due solely to beach nourishment.
The effects of localized stabilization were not limited to areas adjacent to the nourished area, in the direction of net sediment transport, as may be expected. Long-range interactions cause significant shoreline changes at locations several tens of kilometers away from the nourishment project, in each direction. The magnitude of these effects rivaled the erosion we expect from sea-level rise alone over the coming century.
Downstream tributary responses to the damming of the Trinity River, southeastern Texas. Zachary A. Musselman, Department of Earth Sciences, Eastern Kentucky University, Richmond, KY, U.S.A. Email: Zachary.Musselman@eku.edu
The role humans play in causing change within fluvial systems may be dramatic. Anthropogenic influences on a river will vary both spatially and temporally depending on the magnitude and frequency of the impacting event. Impounding a river is one possible anthropogenic impact on fluvial systems. While impacts of dams will vary with local geological, ecological, hydrological, climatological and land use/management conditions, dams offer an optimal opportunity to investigate the role of human impacts on a fluvial system. Within southeastern Texas, an opportunistic geomorphic experiment arose when the Trinity River was impounded. The Livingston Dam represents a marked moment and place of the human role in changing a fluvial system. Impoundments and dams influence downstream ecology, hydrology, and geomorphology by altering discharge and sediment dynamics. These downstream effects, by extension, influence stream ecology, riparian land use and water resources and through coupling processes, affect tributaries of the impounded trunk stream. While the downstream impacts of dams have been discussed widely in the literature, very little attention has been given toward the tributaries downstream of a dam. The purpose of this study is to describe and explain tributary changes within the lower Trinity River basin, Texas, downstream of Livingston Dam. On the Trinity River, flow has been minimally affected, while the sediment regime has been altered for nearly 60km below the impoundment. Geomorphological effects of eight lower Trinity River tributaries within this affected reach were investigated through five different types of data: analysis of published discharge and sediment load data, examination of alluvium, planform change as measured from aerial photographs, resurveys of bridge cross-sections, and field mapping of indicators of geomorphic change. Results suggest that the dam may have minimal impact on the downstream tributaries. Over-riding system factors may provide greater control on geomorphological changes in the lower Trinity system.
Classifying Headwater Catchments in the Little River Watershed, TN. Charles J. Phillips* and Carol P. Harden, Department of Geography, University of Tennessee, Knoxville, TN, U.S.A. *E-mail: cphill11@utk.edu
Headwater catchments are dynamic environments where the stream system and the surrounding land surface are closely connected. Recently, Lafrenz (UT Geography) developed a process-oriented watershed classification that coupled Geographic Information Systems (GIS) with field observations to classify headwater catchments in the Great Smoky Mountains National Park (GSMNP). The objective of the research presented here is to extend and further test the Lafrenz classification by applying it in a nearby watershed with a greater variety of land use, geology, and topography. I chose the Little River Watershed (611 km2) for this study because it contains a portion of the relatively pristine GSMNP, which was part of the Lafrenz study area, but also extends into the agricultural, residential, commercial, and urban lands of the Valley and Ridge.
This classification scheme is a two step process. The first step of this process was conducted in a GIS using a 10m digital elevation model to delineate the headwater catchments. Once the headwater catchments are delineated, the percentage of land use, geology, circularity, mean elevation, mean slope, and resultant aspect were calculated and used to group catchments. Results of this “top-down” classification are shown in this poster. The second step of this classification, which will be completed in the coming months, will use bankfull width, bankfull depth, median particle size, stored sediment, velocity, pH, and temperature metrics of headwater streams to group the headwater catchments from the “bottom-up.” Finally, the two methods will be compared to see how well the GIS classification represents field observations. A classification of this type will allow governments and organizations to effectively use their resources to improve conditions within a watershed.
River channel responses to changes in some controlling factors : Barlad River, Romania. Maria R Rădoane* and Nicolae Rădoane, Department of Geography, University of Suceava, Romania. *E-mail: radoane@usv.ro
Almost all the alluvial rivers, either with gravel or with sand bed, have undergone important changes in the last decades. The anthropic modifications stand out as dominant control factors of the river beds in almost all the regions of Europe. Strictly connected with this common tendency, our work will assess the behaviour of a river bed deepened in fine materials and which were rectified and embanked. The river bed of Barlad river (247 km long and with a drainage basin area of 7395 km2) was examined from the point of view of the geometry of the cross-sections, of the plane geometry and of the type of deposits from the perimeter of the river channel. The data basis obtained represented the foundation of the following problems: (i) the modification of shape of the longitudinal profile through sediments storing from the drainage system; (ii) the shape of the cross-section and the tendencies of change under the influence of the human interventions; (iii) the role of the channel deposits in the control of the channel morphology. The main conclusion of the work is that new river bed of the Barlad river, intensely rectified and embanked after 1974 – 1985 presents all the premises to develop to the initial meander shape of its trajectory. In this case, the geomorphological memory of the river (proved by the existence of some generations of meanders, among which some of the type “goose neck”) influences in a special way the establishment of this tendency.
Recovery of Stream Health after Cattle Exclusion Investigator. Sheila C. Ranganath, Biological Systems Engineering, Virginia Tech, Blacksburg, VA, U.S.A. E-mail:
shrangan@vt.edu
Many streams in Virginia are experiencing severe bank degradation, habitat destruction, and poor water quality due to cattle access. Unrestricted stream access results in frequent defecation in and near the water, and trampling of the streambanks and riparian vegetation. This causes impairments to the stream due to sediment deposition, decreased dissolved oxygen levels and increased nutrient inputs. Platts (1982) concluded that direct cattle access to streams had the largest impact on degraded stream and riparian environments when compared to other non-point source pollution sources. Approximately 85% of riparian livestock studies concluded that cattle have a negative impact on overall stream health (Belsky et al., 1999). The USDA-Natural Resources Conservation Service (USDA-NRCS) has made a notable effort to keep cattle out of streams. One of the Agency’s programs focused on limiting cattle access to streams is the Conservation Reserve Enhancement Program (CREP). The goal of CREP is to reduce the incidence of runoff, sediment, and nutrients from agricultural production into streams through cattle exclusion and the implementation of pollution-filtering vegetation. This is accomplished through the installation of streambank fencing, riparian buffers, filter strips, wetland areas, trees, and grasses to improve and protect water quality (USDA, 2005). The USDA-NRCS has made one of the largest contributions to stream restoration among federal and state conservation agencies. The CREP program is prevalent in Virginia; however, its
effectiveness in enhancing stream health has not been monitored extensively, and no attempt has been made to evaluate how long the recovery process takes. The main goal of this project is monitor the success of the CREP program and to evaluate the time required for significant aquatic and geomorphic stream improvements to occur.
Oxbow lakes as indicators of channel change, Leaf River, Mississippi, USA. Jim Rasmussen* and Joann Mossa, Department of Geography, University of Florida, Gainesville, FL, U.S.A. *E-mail: jrasmus1@yahoo.com.
Over the past 40 years the Leaf River in southeastern Mississippi has been subjected to both flood plain and in-channel gravel mining. Our study assesses the impacts of this activity on the channel geomorphology of a 12-kilometer reach of stream. We utilize field survey data from the river and four of its oxbow lakes to measure changes in channel geometry and bed elevation over the past century. Our research found that the Leaf River has a higher width to depth ratio than the older channels that are represented in the oxbow lakes. This trend toward wider and shallower channels occurs gradually until about 50 years ago. Since that time the width depth ratio has changed only slightly while the channel has undergone as much as three meters of degradation. This information suggests the channel geomorphology of the Leaf River was already in flux before local gravel mining prompted recent channel degradation. It also calls into question the use of a simple cause and effect approach to understanding human impacts and geomorphic change and reminds us that the landforms we study are a result of the byplay between a suite of natural and human processes.
Biogeochemical Consequences of Suspended Sediments in River Ecosystems during Floods. J. Adam Riggsbee1,*, Jason P. Julian2, Martin W. Doyle2 and Robert G.Wetzel1, 1Department of Environmental Sciences and Engineering, University of North Carolina, Chapel Hill, NC, U.S.A., 2Department of Geography, University of North Carolina, Chapel Hill, NC, U.S.A. *E-mail: ariggsbee@restorationsystems.com
Development activities in watersheds have increased fine sediment loading, flood frequency, and magnitude. Such changes also impact river biogeochemical processes across a range of flow conditions. To determine the effects of high suspended sediment loads on river biogeochemistry, we used a longitudinal water sampling network during a dam removal event on the Deep River, North Carolina. Suspended sediment concentrations following dam removal reached a maximum of ~325 mg L-1, which were near sediment concentrations carried during natural bankfull flood events. Concentrations of dissolved organic carbon (DOC), total nitrogen (TN), total dissolved nitrogen (TDN), dissolved inorganic nitrogen (DIN), dissolved organic nitrogen (DON), total phosphorus (TP), soluble reactive phosphorus (SRP), and total dissolved iron (Fed) were measured at one location upstream and three locations downstream of the reservoir. We coupled these concentration data with discharge measurements at each of the monitoring stations to generate water and biogeochemical budgets, as well as quantify the transport and attenuation of sediment and solute loads in a channel network.
In separate laboratory experiments, suspended sediment solutions of similar concentrations (~325 mg L-1) were exposed to simulated solar radiation, equivalent to one clear, summer day at the study site (36o N). We found that sediment suspensions in the presence of simulated solar radiation were significant sources of C (1.43 + 0.66 mg C L-1 d-1) and DON (0.02 + 0.04 mg N L-1 d-1), but not DIN or SRP. Finally, the introduction of sediments lowered river water Fed concentrations immediately (~ 24%) and progressively (~40-90%) in both light and dark treatments. Research presented here was designed to test laboratory based results in a simulated flood event – dam removal.
A technical note regarding the use of impervious surfaces as a proxy for urban impacts on hydrologic systems. Martin C. Roberge* and Angela Carlisle, Department of Geography and Environmental Planning, Towson University, Towson, MD, U.S.A.
*E-mail: mroberge@towson.edu
Human impact research has long used Total Impervious surface Area (TIA) as a proxy for the impact of urbanization on rivers. Impervious surfaces such as asphalt and concrete have a distinct radiometric signature in remotely sensed imagery. These materials limit infiltration and contribute to direct runoff, physically linking TIA to hydrologic processes. Population density and other indicators of urban development do not have such advantages for hydrologic research. TIA is limited as a proxy because five or more competing methods produce different estimates of TIA, hampering direct comparison of research results.
This study compared three common methods for estimating TIA: 1) ‘Planimetric’ estimates require ‘edge-of-pavement’ and ‘building footprint’ data frequently created for municipal governments from aerial photography; 2) ‘Landsat’ estimates are measured from supervised classification of Landsat imagery; 3) ‘LU/LC’ estimates are taken from landcover maps by multiplying the area of a land cover class by published impervious surface ratios.
This study compares the three methods on a random sample of fifty urban, suburban, and rural sites in the Baltimore Metropolitan region. Our results reinforce previous findings that estimates of TIA are not comparable between methods. Despite correlation among the three methods, planimetric methods produce significantly lower estimates of TIA, especially in urban settings. Landsat methods may be the most reliable, due to a lower variance around the mean of the three methods, but they appear to systematically underestimate TIA in rural sites averaging under 25 percent TIA. This systematic bias results in a ‘gap,’ with the Landsat methods placing twelve times as many sites under 1 percent TIA as the other methods, and half as many sites between 1 and 25 percent TIA. This gap produces an artificial separation between urban and rural sites that may be responsible for certain ‘threshold’ effects observed in some previous research.
Infiltration rates of precipitation in soil and its affect in alpine tundra. Carol F. Sawyer, Department of Geography, Texas State University, San Marcos, TX, U.S.A. E-mail: sawyer@txstate.edu
Given the extreme climate and fragile establishment of alpine tundra, areas above or near the treeline are especially vulnerable following disturbance (human or natural) or changes in the fluvial environment. To become initially established, vegetation in alpine regions needs certain conditions to succeed. Infiltration rates of soil affect the amount of surface runoff and subsequent stream flow of an area, in addition to influencing the vegetation of an area. Infiltration rates of soil on or near logging or utility- access roads are different than in the surrounding tundra. These roads, usually unpaved, then serve as conduits of debris flows or surface runoff. These roads change the topography of an area, encourage access to previously remote areas, and influence the drainage system. Additionally, areas compacted by humans (either on foot or vehicle) can change the distribution of vegetation, either from either death of vegetation or by preventing vegetation establishment at a site. Near Glacier National Park, Montana, dirt roads cross relict solifluction treads and risers. Comparison of infiltration rates between soil near unpaved roads and the tundra can show the possible impact of the roads. Future concerns include changes in infiltration from roads constructed for access to wildland fires.
Use of gold mining-related mercury in geochemical profiles to investigate timing and rates of historical floodplain sedimentation in the North Carolina Piedmont. Gwenda J. Schlomer1, * and Robert T. Pavlowsky1, and Scott A. Lecce2, 1Department of Geography, Geology, and Planning, Missouri State University, Springfield, MO, U.S.A., 2Department of Geography, East Carolina University, Greenville, NC, U.S.A. *E-mail: Gwenda528@missouristate.edu
The environmental history of a watershed can be preserved in vertically-accreted floodplain deposits, offering the potential to reconstruct major disturbances to a fluvial system. Human settlement and land clearing tend to increase sedimentation rates on valley floors, particularly during forest to agriculture conversion. Mining pollution tracers may be useful to study and date historical floodplain units. The upper Dutch Buffalo River watershed in the North Carolina Piedmont was first introduced to gold mining from the Gold Hill mining district located near the headwaters. Gold was first mined in the district in the early 1800’s and peaked between 1830 and 1860. Ore processing involved mercury (Hg) amalgamation to refine gold ores resulting in the release of Hg contaminated sediments that now act as geochemical tracers to date overbank floodplain units. This study investigates the spatial patterns of mining-related geochemical profiles in alluvial deposits to establish timing and rate of sedimentation. Sediment cores were collected in summer 2006 along three cross-valley floodplain transects located in the upper, middle and lower reaches of the watershed and analyzed for 34 elements and other physical properties including organic matter, pH, grain size distribution, and color. Preliminary results indicate that Hg is a useful tool to interpret patterns of floodplain sedimentation. Peak Hg concentrations in sediment cores range from 15 ppm near the Gold Hill District (approximately 150 times natural background) to 6 ppm in the lower reaches. Average sedimentation rates since the beginning of the mining period range from 0.5 cm/yr near Gold Hill to 1 cm/yr in the lower watershed. Mining related trace elements associated with episodes of copper and zinc mining may be used to further refine sedimentation rates. Future research will attempt to determine if there is geochemical and/or mineralogical differentiation between younger historical units and older pre-settlement alluvial deposits.
Morphological changes attributed to gravel mining along the Colorado River, Texas. Cody M. Simmang, Texas State University, San Marcos, TX, U.S.A. E-mail: CS1414@txstate.edu
There are countless bridges, buildings, parking lots, miles of highway, and numerous other structures throughout the United States. All of these structures require aggregate in their construction. Regions such as Austin, Texas have expanded at an exceptionally rapid rate, and demand for abundant sources of nearby gravels is being partially accommodated by floodplain mines along the Colorado River. While there is no doubt that gravel is necessary for the development, growth, and improvement of infrastructure, an assessment of how the excavation process and subsequent evolution of the site over time affects its surroundings, particularly the river system, should be addressed.
Many breaches into floodplain gravel mines are observed along the Colorado River. Streambed incision, bank erosion, channel widening, and channel straightening (through meander cutoffs) are documented results of gravel mining in fluvial environments. Incision affects both upstream and downstream reaches, resulting in damage to structures, and can cost millions of dollars to repair. A loss of riparian vegetation is commonly observed, which can increase runoff into the river. An increase in turbidity and changes in average grain size also affect aquatic life.
An analysis of sediment transported through these areas provides data necessary to describe past morphological changes and predict future changes brought on by floodplain gravel mining. An evaluation of differences in sediment supply as a result of gravel mining is accomplished with the aid of topographic maps and aerial photographs to identify the location and evolution of gravel mines. Sediment traps placed upstream and downstream of these sites allow for measurement of differences in quantity and grain size distribution of sediment going into and coming out of each study area. Recent channel cross sections will be compared to older measurements to evaluate change. Differences in sediment supply will depend on several factors such as depth of the gravel pit compared to river depth and increased runoff from the loss of riparian vegetation.
Relative importance of flow regime vs. geomorphic structure on organic matter retention: shifting drivers with altered hydrology. M. J. Small1, *, M. W. Doyle1 and D. M. Thompson2, 1Department of Geography, University of North Carolina at Chapel Hill, NC, U.S.A., 2Department of Physics, Astronomy, and Geophysics, Connecticut College, New London, CT, U.S.A. *E-mail: mjsmall@email.unc.edu
This study examines the interactions between altered hydrology, geomorphology, and organic matter (OM) stores and fluxes at various spatio-temporal scales. Using a river with regular flood releases from an upstream dam, we examined the dynamics of retention and transport of OM in response to changing hydraulic regime. To complement this field study, we also used a flume to examine the role of turbulence and discharge ramping on OM mobilization.
Field studies showed that at low flood frequencies, hydrology was the main driver of OM storage, but at greater frequencies (> 10 per year), channel structure gained importance in OM storage. A simple model derived from the data showed that geomorphic complexity may decrease sensitivity to increased flooding frequency.
Through the flume study, we found that turbulence and discharge ramping controlled OM mobilization at smaller scales. Results indicate that the frequency of flooding may be much more important than the actual maximum discharge, as OM in the flume was mobilized in pulses during ramping and after boulder-overtopping, but did not necessarily increase monotonically with increasing discharge. Thus, the size of geomorphic structures relative to the depth of flow and the frequency of floods was found to be important, supporting the observations made from the field studies.
The field and flume studies suggest that with increased frequency of flooding, channel structure and complexity become more important in OM retention. This makes the ecological resource of OM increasingly patchy, which may change invertebrate density and diversity via OM availability. Control of the food web may switch from hydrologically-driven to geomorphically-driven with increasing flood frequency. The effect of increased flood frequency may be less severe in systems with structural complexity, suggesting that restoration or enhancing channel complexity in regulated streams may be critical to off-setting some of the impacts of flow manipulation.
Views of the Rivers: Visualizing Temporal Detail in Multi-Decadal Records of Regulated and Non-Regulated Streamflows. Erik R. Strandhagen*, W. Andrew Marcus and James E. Meacham, Department of Geography, University of Oregon, Eugene, OR, U.S.A. *E-mail: ers_carto@yahoo.com
This research applies a novel raster-based approach to plot hydrographs using dual timescale axes that enhance visualization of inter- and intra-annual streamflow. The raster-based method is applied to the Yellowstone and Snake Rivers at two U.S. Geological Survey (USGS) streamflow stations with over 32,000 continuous records each. The long-term streamflow discharge patterns are plotted as two dimensional and three-dimensional raster hydrographs to support different perceptual visualization tasks. The raster hydrograph improves the ability to identify, compare, and contrast inter- and intra-annual streamflow fluctuations of regulated and natural rivers. The raster hydrograph contributes to developing an improved understanding of the magnitude, frequency, and timing of peak and low streamflow in the rivers, thus enhancing collaborative management of surface water resources. Guidelines are introduced in for plotting time-series data to improve graphical communication of the range and frequency of variations in flow. The research products provide useful visualization tools for communicating information that aids policymaking, management, and education concerning streamflow.
The Effects of Human Impacts on Alluvial Channels in Italy. Nicola Surian1,*, Luisa Pellegrini2, Massimo Rinaldi3, Chiara Audisio4, Giuseppe Barbero2, Giulia Doretti4, Gabriele Duci2, Franca Maraga4, Cristina Simoncini4, Liliana Teruggi3, Ornella Turitto4, Pier Luigi Vercesi2, 1Dipartimento di Geografia, University of Padova, Italy, 2Dipartimento di Scienze della Terra, University of Pavia, Italy, 3Dipartimento di Ingegneria Civile, University of Firenze, Italy, 4 C.N.R. – I.R.P.I., Torino, Italy. *E-mail: nicola.surian@unipd.it
Most Italian rivers have experienced considerable channel adjustments, in particular in the last decades. Two main types of adjustments have been recognized, channel incision and narrowing. Incision is commonly on the order of 3-4 m, but in some cases even more than 10 m, whereas narrowing is commonly more than 50 %, in some rivers up to 85-90 %. In several rivers incision and narrowing have led to changes in channel pattern, from braided to wandering or single-thread.
The causes of such channel adjustments are represented by various types of human impacts. Land use changes (e.g. reforestation), sediment mining, dams and channelization have induced, and in many cases still induce, channel instability through modification of flow regime, channel boundary conditions and, in particular, sediment supply to river channels.
Channel changes in Italian rivers have been analysed in several studies since the 1970s but, as recently shown by Surian and Rinaldi (2003), there is still a need for more research about this issue. The poster reports the results of an on going national project which aims to improve the present knowledge of channel adjustments, and in particular of the most recent ones (i.e. those of the last 10-20 years). Other goals of the project are (a) a better understanding of the relationship between the different human interventions and channel adjustments and (b) an analysis of practical implications of channel adjustments in terms of planning, maintenance and restoration of alluvial channels.
Fluvial Geomorphology and Urbanization in Phoenix, Maricopa County, Arizona:
A Natural Laboratory for Studying Human Alteration of Dryland Fluvial Systems.
Nathan A. Toké* and J Ramón Arrowsmith, School of Earth and Space Exploration, Arizona State University, Tempe, AZ, U.S.A. *E-mail: nathan.toke@asu.edu
Maricopa County is characterized by low relief basins with intervening bedrock mountain ranges. Fluvial processes, driven by low frequency but high intensity rainfall events convey runoff and sediment from adjacent uplands and urbanized desert piedmonts to tributaries of the lower Colorado River. Since the 1950’s, the population of metropolitan Phoenix has increased tenfold. Now, approximately 3.5 million people live within 1500 square kilometers of developed land. With so much growth, the fluvial system has been severely altered. Urbanization and attempts to control flooding have led to 1) an increase in impermeable landcover, 2) straightening and channelization of piedmont distributaries and washes, 3) alteration or removal of riparian vegetation, 4) diversion of runoff and sediment into localized retention basins, and 5) damming of the previously non-ephemeral Salt, Verde, and Gila Rivers of the lower Colorado River system. The ongoing urbanization surrounding greater Phoenix represents a special opportunity to explore the responses of dryland fluvial processes to these types of changes. Phoenix’s continued growth provides opportunities to set up monitoring experiments to study fluvial responses during the initiation of new urban developments. Additionally, existing urban catchments are monitored by the Maricopa County flood control district; therefore precipitation and hydrograph data mining in conjunction with historical land use mapping and drainage basin delineation should reveal valuable information about the urban fluvial system. Geomorphic mapping and stratigraphic analyses of urban sediments provides data to compare with geomorphic investigations of undeveloped piedmonts. Through these analyses and substituting space for time we will be able to better understand 1) how urbanization transforms drainage basin architecture, 2) how sediment moves through the urban landscape, 3) how urbanization patterns control the transportation of chemicals through the landscape, and 4) how fluvial changes influence and feedback between biological and social parts of urban ecosystems.
The Effects of Inundation and Geomorphology on Floodplain Vegetation in a Regulated River. Sally S. Whisler1,*, Melanie J. Small2 and Martin W. Doyle2, 1Carolina Environmental Program, University of North Carolina, Chapel Hill, NC, U.S.A., 2Department of Geography, University of North Carolina, Chapel Hill, NC, U.S.A. *E-mail: whisler@email.unc.edu
In their classic paper on geomorphology and ecology of floodplains, Osterkamp and Hupp described the distribution of vegetation species with respect to floodplain morphology, hydrology, and other geomorphic variables. Importantly, their understanding was based on natural flow (i.e., no flow regulation) and natural channels. However, rivers of the world are increasingly regulated and disturbed by landscape scale changes, making it critical to understanding whether the Osterkamp and Hupp theory should be re-considered for regulated rivers.
This study examines the effects of frequent inundation on the distribution of vegetation species on a floodplain. Using a dam-regulated reach of river, we developed surveys to model the frequency and duration of inundation at multiple transects along the reach with distinct channel and floodplain morphologies. At these same transects, we established riparian vegetation plots to examine species richness with distances from the channel. The ongoing analysis is quantifying correlations between the location of vegetation and hydro-geomorphic variables, specifically focusing on the relationship between water at low and high flow, topographic slope, and the presence/absence of species, based on a HEC-RAS model of inundation and the ordination of the vegetation species. These conclusions will be tested for the application of the geomorphic levels described by Osterkamp and Hupp on regulated rivers.
Preliminary results indicate a reduction in the number of species with slope rather than with increased frequency of inundation, perhaps suggesting a stronger control of species richness by topographic features (i.e., geomorphology) than by inundation. The implications of this study may be linked to the effects of increased flooding from climate change and regulation of flow on bank vegetation and the broader ecological health of the river ecosystem, and the applicability of classic geomorphic-ecological concepts to human-altered landscapes and ecosystems.