Sponsored by the Geomorphology Specialty Group
Association of American Geographers 102nd Annual Meeting
Chicago, Illinois, March 7-11.
Human Imapcts in Geomorpholgy
Paper Session 4517
Friday, 3/10/06, from 4:00 PM - 5:40 PM
Geomorphology Specialty Group
William H. Renwick - Miami University
William H. Renwick - Miami University
4:00 PM Author(s):
*Dan Royall - UNC-Greensboro
Deborah Shoffner - UNC-Greensboro
Anita Henderson - UNC-Greensboro
Abstract Title: Hydraulic Biotope Composition in Urban and Rural Piedmont Streams
Reports citing inconsistent or weak correlations between traditional physical indicators of stream health and biotic assemblages suggest the need for improvements in physical data collection and assessment. Hypothesizing that better information on bedform-scale hydraulic factors might be useful in this regard, we examined the hydraulic-unit/biotope compositions of four stream reaches, two urban and two rural, near the city of Greensboro in the North Carolina Piedmont. Information on woody debris occurrence and size was also collected. Based on areal coverage of hydraulic-unit classes as defined in the River Styles framework (Brierley and Fryirs, 2005) and other related research, the hydraulic biotope diversities of all reaches appear comparable. However, there are important compositional differences between the rural and urban reaches. Pools are most common in the urban reaches, runs are more prominent in the rural reaches, and glides, which are often transitional between higher and lower energy environments, are a substantial component of all reaches. Woody debris was often responsible for the creation of slackwater units. Most hydraulic unit classes are best differentiated on the bases of ‘roughness’ Reynolds number and shear velocity. With a few exceptions, the diversity of aquatic macroinvertebrate groups in these reaches appears to be poorly correlated with hydraulic-biotope diversity alone. We interpret this result to confirm the importance of using multiple physical and chemical criteria for assessing stream habitat quality. Better information regarding changes in hydraulic biotope composition and structure with stage is needed and might improve correlations between these physical habitat variables and aquatic biodiversity.
Keywords: stream, hydraulic biotope, aquatic biodiversity, North Carolina
- 4:20 PM Author(s):
*Martin Roberge - Towson University
Abstract Title: Timing and response of stream morphology to urbanization
Current stream restoration practice relies upon models that predict eventual urban stream channel stability. However, these models may not fit the conditions found in most urban watersheds. A number of these models were derived from Simon (1989), who describes the response of a channel over time to a single channel disturbance. Wolman’s (1967) model of sediment flux in an urbanizing channel refers to a small watershed that is disturbed suddenly and completely during construction and then adjusts to a new, steady set of watershed conditions. Observations from watersheds in the Baltimore Metropolitan region do not appear to fit the initial conditions or predictions of these models. Population peaked in the 1950’s in many East Coast urban centers, allowing more than 50 years for streams to reach a new equilibrium, yet severe bank erosion is still common in these watersheds. Baltimore’s outlying urban, suburban, and rural watersheds saw continuous development between the 18th and 21st centuries, so streams have no steady condition with which they may ‘equilibriate’. Many measures of hydrologic variability are well explained by variations in percent impervious land cover, but geomorphic variables, such as bankfull width, slope, or pool-riffle distance have much weaker relationships. Measures of ‘development date’ do not appear to strengthen these geomorphic relationships during first analysis. More work will be necessary to empirically derive the relationship between development, hydrologic change, and subsequent geomorphic change. Future stream restoration work may become more effective by focusing efforts on controlling suspended sediment rather than achieving ‘channel stability’.
Keywords: Fluvial Geomorphology; urbanization; stream restorationS
- 4:40 PM Author(s):
*Anne Chin - Texas A&M University
Herve Piegay - CNRS
Kenneth J. Gregory - University of Southampton
Stanley V. Gregory - Oregon State University
Melinda D. Daniels - University of Cennecticut
Michael A. Urban - University of Missouri
Wendy Bigler - Southern Illinois University Carbondale
Anya Butt - Central College
Judith L. Grable - Valdosta State University
Ellen E. Wohl - Colorado State University
Abstract Title: Perceptions of wood in rivers and challenges for stream restoration
This study develops from a survey undertaken in 10 countries to assess how people perceive of wood in rivers (Piegay et al., 2005). Questionnaires given to students 20-25 years of age showed that most respondents hold the traditional and rather negative views of wood in rivers (as unaesthetic, dangerous, and needing improvement), except in forested areas of Oregon, Germany, and Sweden. In the U.S., contrasting results from Texas and Oregon prompted a further investigation into whether one or the other view may be represented across the country, and whether perceptions may vary regionally. Surveys administered to students in six additional states (Colorado, Connecticut, Georgia, Illinois, Iowa, and Missouri) indicated that most students across the U.S. hold the traditional views of wood in rivers. Except in Oregon, students viewed channels with wood to be less aesthetically pleasing and needing more improvement. Analysis of the reasons given for improvement needs suggests that Oregon students are more concerned with improving channels without wood for fauna habitat, whereas respondents elsewhere focused on the need for cleaning woodrich rivers for flood risk management. These results pose challenges for restoring channels with wood for ecological benefits. They also underscore the importance of public education across the country to increase awareness of the ecological function of wood in rivers, in addition to advancing scientific knowledge.
Keywords: fluvial geomorphology, river channels, woody debris, river management, stream restoration
- 5:00 PM Author(s):
*James A Hyatt, Dr. - Eastern Connecticut State University
Andrew H Ivester, Dr. - University of West Georgia
Tim Chowns, Dr. - University of West Georgia
Abstract Title: Sedimentary Records of Human-Induced Landscape Change Associated with Massive Soil Erosion in Georgia
Providence Canyon State Park (PCSP), located 7 km from Lumpkin GA, is testament to the extreme to which human-induced soil erosion can alter landscapes. These canyons, some >60 m deep, formed following European settlement in the late 1700’s and introduced large quantities of alluvium downvalley. We report on 7 new vibra cores (< 4.5 m long) recovered along a narrow valley transect (#1) and a broad valley transect (#2) near the juncture of canyon headlands and Turner Creek, a small braided stream draining PCSP. These cores penetrate alluvium into pre-existing Cretaceous sediments. They contain evidence of pre-canyon pedogenesis, valley-floor incision, subsequent and rapid alluvial aggradation, and lateral valley-side encroachment. Sharp erosive contacts between pre-canyon clayey-sands and > 4m of post-canyon alluvium are marked by coarse sand, iron stones, broken iron-pan fragments, organic detritus and large (10 cm diameter) kaolin balls. Exploratory AMS 14-C dates of root fragments within kaolin balls immediately above the Cretaceous-alluvium contact at transect #1 contain modern post-bomb carbon (i.e. younger than 1960). Although we anticipated modern and likely non-finite 14-C dates at this site, the presence of post 1960 carbon immediately above Cretaceous sediment indicates extensive erosion and redeposition of alluvium. This underscores the difficulty in establishing recent sedimentary chronologies in tightly confined valleys. We await additional 14-C dates from transect #2 cores in preparation for new work designed to test whether optically stimulated luminescence (OSL) can successfully constrain our interpretations of human-induced landscape change.
Keywords: geomorphology-sediments, georgia-river, erosion, sedimentation, vibracore
- 5:20 PM Author(s):
*William H. Renwick - Miami University
Zac D. Anderek - Miami University
Abstract Title: Reservoir sedimentation in Ohio: Evidence of long-term trends in erosion and sediment delivery.
We have compiled recent reservoir sedimentation rates for 68 reservoirs in Ohio. The database includes a wide range of drainage areas and environmental conditions. The time periods represented span most of the 20th century, but data are more concentrated for the period since mid-century. Sedimentation rates showed no clear correlation with watershed land-use or topographic variables. However, clear differences in sedimentation patterns are evident between the more agricultural and low-relief northwestern part of Ohio and the more forested and hilly southeast. The effect of drainage area on sedimentation rates is stronger in the northwest than in the southeast, and greater in the early to mid-20th century than more recently. This is consistent with greater agricultural erosion in the northwest, and more efficient sediment delivery in the southeast. These patterns also suggest a declining influence of agricultural sediment on overall sedimentation rates, presumably as a result of increasing adoption of soil conservation practices. In the southeast there is a weak indication of increasing sedimentation downstream. If such a trend were confirmed it would indicate that streams are remobilizing sediment through bed and bank erosion, moving formerly deposited sediment downstream through the drainage system. Taken together, these trends indicate that land use alone is not a useful predictor of sediment yield, and sediment delivery is less significant than erosion rates in determining the downstream impacts of human activity on reservoir sedimentation.
Keywords: Sedimentation, reservoirs, erosion, sediment delivery
Session Description: This series of three special paper sessions are co-sponsored by the Coastal and Marine Geography (CoMa) and Geomorphology specialty groups. The research presented in the paper sessions cover a broad spectrum of spatial and temporal scales within aeolian geomorphology.