Special Sessions
Sponsored by the Geomorphology Specialty Group
Association of American Geographers 102nd Annual Meeting
Chicago, Illinois, March 7-11.

Geomorphology Specialty Group Graduate Student Paper Competition I

Paper Session 2150
Wednesday, 3/8/06, from 8:00 AM - 9:40 PM

Sponsorship(s):

Geomorphology Specialty Group

Organizer(s):

Susan W.S. Millar - Syracuse University

Chair(s):

Susan W.S. Millar - Syracuse University

Introducer:

Susan W.S. Millar - Syracuse University

Abstract(s):

• 8:05 AM Author(s):
  *Inci Gunerlap - University of Illinois at Urbana-Champaign
  Bruce L. Rhodes - University of Illinois at Urbana-Champaign
  

  Abstract Title: The Spatial Relation between Planform Migration and Curvature of Meandering Rivers.

  
  

  Planform migration is a fundamental, yet incompletely understood, aspect of the dynamics of meandering rivers. Current theoretical models aimed at predicting planform migration relate the rates of meander migration to spatially extended curvature where weighting of the influence of curvature on migration rate decays exponentially over distance upstream. This theoretical relation, however, has not been rigorously evaluated empirically. Furthermore, although models based on exponential-weighting of curvature effects yield fairly realistic predictions of meander migration, such models are incapable of reproducing complex forms of bend development, such as double heading or compound looping. The objective of this study is to investigate empirically the spatial relation between planform migration and planform curvature along a meandering river containing compound loops. The study presents the development of a new methodology based on parametric cubic spline interpolation for a better characterization of planform and curvature of meandering rivers and for investigating in detail the relationship between spatially extended curvature and local rates of bend migration for a study reach along a highly sinuous section of the Embarras River in Illinois, which contains compound loops. Results indicate that the spatial structure of migration rate-curvature relation may be more complex than currently is assumed. The study provides a first step toward unraveling the spatial structure of planform evolution of meandering rivers with compound loops. This will allow evaluating empirically the validity of assumptions underlying theoretical models of meander migration and refine the predictive capabilities of these models.

  Keywords: curvature, meandering, parametric cubic spline fitting, planform migration, GIS

  
  
• 8:20 AM Author(s):
  *Zachary A. Mussleman - University of Kentucky
  

  Abstract Title: Nonlinearity and complexity illustrated within a coastal plain fluvial system

  
  

  Nonlinear and complex system behaviors have not been widely demonstrated in real-world earth surface processes and landforms. Nonlinear behavior in earth surface systems provides many possibilities for complex behavior not possible in linear systems. The goal of this paper is to illustrate complex nonlinear dynamics in a real earth surface system (the lower Trinity River basin). Within southeastern Texas, an opportunistic geomorphic experiment arose when the Trinity River was impounded. The dam represents a marked moment and place of a system perturbation. Geomorphological effects of the lower Trinity River tributaries were investigated through five different types of data: resurveys of bridge cross-sections, planform change as measured from aerial photographs, field mapping of indicators of geomorphic change, examination of alluvium, and analysis of published discharge and sediment load data. Within the lower Trinity River basin, the tributaries are reacting in a nonlinear and complex manor. Nonlinear behavior is illustrated through delayed or lagged responses, self-limiting processes, competitive interactions, and multiple modes of adjustment. Delayed or lagged responses are illustrated through sediment budgets for two tributaries. Evidence of self-limiting processes, as degradation and vertical accretion, has been observed at numerous locations. The competitive interaction between vegetation and erosion has possibly led to further accretion, and multiple modes of adjustment have occurred at stream cross-sections in response to varying flow conditions. Location and timing of these nonlinear system behaviors suggests the possibility that the systems perturbation was caused by the damming of the trunk stream.

  Keywords: suspended sediment, secondary flow, tidal river, fluvial,geomorphology, delta, California

  Keywords: Fluvial Geomorphology, river, sediment, system-nonlinear, Texas

  
  
• 8:35 AM Author(s):
  *Benjamin T Crosby - Massachusetts Institute of Technology
  Kelin X Whipple - Massachusetts Institute of Technology
  Mark W Schmeeckle - Arizona State University
  

  Abstract Title: Reevaluating the Transmission of Incision Signals Through River Networks

  
  

  During pulses of incision in river networks, the rate and form of channel response has important implications on the tectonic unloading of mountain ranges, the timing of sediment delivery to depositional basins and the resilience of ecological systems during surface rejuvenation. To study the rate and form of this transient response following incision, we combine field and remotely sensed observations from the Waipaoa River, New Zealand with numerical modeling of landscape evolution (CHILD). The Waipaoa River provides an ideal natural laboratory because the basin is currently responding to a large magnitude (50- 100m) pulse of incision initiated ~18,000 years ago. In the Waipaoa we identify ~236 knickpoints, which we define here as discrete convexities in the channel longitudinal profile separating adjusting regions of the basin from regions of relic, unadjusted topography. We find knickpoints consistently located in tributaries either just upstream of their mainstem confluence or at drainage areas around one square kilometer. The consistency of this knickpoint distribution suggests that their present position may not be a function of progressive upstream adjustment in the channel, but rather a consequence of a threshold drainage area where fluvial bedrock incision becomes inefficient. We test this hypothesis using a numerical landscape evolution model that employs recently developed sedimentflux dependent bedrock incision rules and discover knickpoints developing at tributary junctions and small drainage areas. This demonstrates that thresholds in bedrock incision processes lead to knickpoint stagnation and the development of the hanging tributaries frequently observed in rapidly incising fluvial systems.

  Keywords: sediment transport, channel morphology, drylands

  Keywords: fluvial geomorphology, erosion, bedrock incision, knickpoint, waterfall, modeling, thresholds, field methods, channel morphology

  
  
• 8:50 AM Author(s):
  *Jonathon Dinkin - Towson University
  

  Abstract Title: The Effects of Imperviousness on the Channel Morphology of Perennial Streams in the Piedmont Region of Central Maryland

  
  

  Impervious surfaces increase the variability of urban stream discharge by directing storm water runoff directly into streams. These hydrologic changes then affect channel morphology. In this study, I examined urban and rural stream channels in 26 watersheds in the piedmont region of central Maryland in order to determine differences in bankfull height, width, and area; median particle size; and the channel longitudinal slope. The effects of watershed area were controlled with a novel approach: sites were selected using GIS and the National Elevation Dataset to have matching watershed areas of exactly (±0.03%) 6 km2, 12 km2, or 18 km2. Percent impervious cover was calculated from Landsat 7 imagery; watersheds with >10% impervious cover were considered urban. Manning’s equation was used to calculate bankfull discharge. Results indicate that urban streams have a significantly greater cross-sectional area, wetted perimeter, and width than rural streams. This study confirms previous work that suggests that streams will erode their channels in response to urbanization. Channel stabilization or storm water management should be strongly considered during stream restoration or during new development.

  Keywords: impervious,urban,stream,morphology,watershed

  
  
• 9:05 AM Author(s):
  *Dale K Splinter - Oklahoma State University
  Daniel C Dauwalter - Oklahoma State University
  Richard A Martson - Kansas State University
  William L Fisher - Oklahoma State University
  

  Abstract Title: Ecoregion/Wateshed Charcteristics of Eastern Oklahoma Streams

  
  

  One hundred and forty-nine stream reaches were surveyed over three-years in eastern Oklahoma to better understand patterns between the characteristics of stream channels. We evaluated differences of the characteristics of stream channels at the ecoregion scale (Boston Mountains, Ozark Highlands, and Ouachita Mountains) and morphometry at the watershed scale. A co-variance test was performed that evaluated whether downstream trends in geomorphic variables were significantly different (p< 0.05) among ecoregions. At the watershed scale, significant differences exist in some combination of ordered basin and drainage density, relief, circularity ratio, and ruggedness number. This information is important for the future management application of stream channel morphology recently undertaken by the Oklahoma Department of Wildlife Conservation.

  Keywords: ecoregion, geomorphology, oklahoma