Sponsored by the Geomorphology Specialty Group
Association of American Geographers 102nd Annual Meeting
Chicago, Illinois, March 7-11.
Sediment Transport in Fluvial Systems II
Paper Session 2519
Tuesday, 3/8/06, from 3:00 PM - 4:40 PM
Geomorphology Specialty Group
Michael Slattery - Texas Christian University
Michael Slattery - Texas Christian University
3:00 PM Author(s):
Scott Lecee - East Carolina University
Erica Kotecki - East Carolina University
Abstract Title: The 1999 Flood of the Century: Extraordinary Hydro-meteorological Event or Human-induced Catastrophe?
The recent flooding associated with Hurricane Katrina has renewed interest in the role that humans play in exacerbating flooding. Discussions in the popular media and some of the scientific literature following large floods frequently imply that the severity of these events was strongly related to human modifications of natural processes. Similar questions arose in 1999 surrounding flooding in the aftermath of Hurricane Floyd in eastern North Carolina. The “flood of the century” was reported in some circles as not a natural disaster, but rather a “human catastrophe” exacerbated by changes in the watershed associated with urbanization and channelization. The purpose of this paper is to assess the degree with which the rainfall and flooding associated with Hurricane Floyd should be viewed as either an extraordinary natural event or as one intensified by human activities. This question is approached using that rationale that if human activities had a significant impact on the severity of the 1999 event, then this impact should be exhibited in other measures of watershed hydrology. We examine the magnitude-frequency characteristics of precipitation and streamflow in eastern North Carolina, and relate trends in streamflow to precipitation and the level of urban development.
Keywords: floods, human impacts, Hurricane Floyd, North Carolina
- 3:20 PM Author(s):
*John M. Faustini - Oregon State University
Peter Leinenbach - USEPA, Region 10
Philip R. Kaufmann - USEPA, Western Ecology Division
Abstract Title: Assessing Sediment Sources and Impacts in Wadeable Streams in the John Day Basin, Oregon
Excess fine sediment in streams degrades spawning habitat, reduces growth and survival of juvenile fish, and has been linked to decreased diversity of both stream invertebrates and fish. Many human land uses and land cover modifications (e.g., logging, grazing, roads) tend to increase erosion, leading to an increase in fine sediment supplied to streams. We evaluated potential human impacts on streambed substrate by relating stream habitat survey data from a randomized survey design (n=72) and supplemental sampling (n=21) to human disturbance in the riparian zone and upstream catchment and to variations in sediment supply estimated with a GIS-based erosion model. We assess potential excess fine sediments using an index of excess fine sediments that accounts for dominant natural controls on particle size. Our erosion model combines the Revised Universal Soil Loss Equation with a delivery ratio approach to estimate spatially explicit potential sediment delivery to streams from surface soil erosion. We find that excess fine sediments are positively associated with several measures of human disturbance, but that streams draining areas underlain by erodible rocks or sediments are much more likely to have excess fine sediments than streams draining catchments underlain by resistant rocks. Preliminary erosion modeling results show that land cover changes associated with logging, fires, and forest roads strongly influence predicted soil erosion rates. However, in some portions of the basin, processes not included in the current model (e.g., mass wasting) may be the dominant source of sediment delivered to streams.
Keywords: fine sediments, stream habitat, human disturbance, erosion modeling, gis
- 3:40 PM Author(s):
*Michael C. Slattery - Texas Christian University
John Walden - University of St. Andrews
Jonathan D. Phillips - University of Kentucky
Abstract Title: Environmental Magnetic Analysis of Sediment Samples From the Lower Trinity River, Texas, USA
This paper presents the results of an environmental magnetic study of potential source materials to the sediment system of the lower Trinity River system, Texas, USA. Environmental magnetic analysis was performed on a total of 138 individual samples representing examples of potential source materials, including surface soils, drainage ditches, channel banks, exposed channel bedforms, and a small number of bedrock exposures. The purpose was to characterise the degree of variability of these potential sources to the Trinity system and, on the basis of the results obtained, to evaluate the potential for using environmental magnetic analysis to establish sediment-source linkages within the system and its sub-catchments. The results demonstrate considerable variability in the magnetic properties of the various source samples analysed. Some sub-catchments do appear to show distinct magnetic properties and, as a result, it may well be possible to identify their potential contribution to sediment supplied to the main river system immediately downstream.
Keywords: Magnetic analysis; sediment source; fingerprinting; Trinity River
- 4:00 PM Author(s):
*Mark Alan Fonstad, Assistant Professor - Texas State University, San Marcos
Abstract Title: Spatial Maps of River Hydrodynamics Produced by the Unification of Remote Sensing and Cellular Automata Modeling
Traditional fluvial characterization has used a reach-based sampling and surveying approach to analyze both the geomorphological and hydrodynamical environments. Recent innovations such as watershed-wide remote sensing of stream environments and realistic hydrodynamical simulations of flow have greatly extended the traditional monitoring and modeling techniques, and the possibility exists to couple these two approaches in order to map the geographical distribution of channel hydraulics and geomorphology. This should allow high-quality maps of hydrodynamics and potential sediment transport regimes to be produced for long stretches of rivers at low cost, even using existing historical data. As an example of this coupling, a cellular automaton flow model can be reformulated to solve for stream variables that would traditionally be used as calibration parameters by combining the automata iterations with the results of river remote sensing. Two specific assumptions underlie this approach. First, an imaged river water surface elevation approximates a gradually-varied, steady flow surface, and second, that discharge is transferred to neighboring areas based proportionately on the water slope. These simple and reasonable assumptions allow the cellular automata to extract spatial distributions of Manning’s n, depth-averaged velocity, shear stress, and stream power. The resulting grid-based array of remotely-sensed habitat and hydrodynamic variables can be classified using traditional supervised classification and/or object-based classification to yield high-quality habitat suitability maps. Also, the layers of spatial data can be correlated and regressed against one another in the search for predictive rules, or used to test existing rules such as regression equations predicting Manning’s n.
Keywords: geomorphology, modeling, remote sensing, cellular automata
- 4:20 PM Author(s):
*Allan James - University of South Carolina
Darrell Glen Watson - University of South Carolina
Abstract Title: LIDAR Map Data for Delineating Channel Headwater Networks but Not for Sediment Budgets
Airborne LIDAR data can generate topographic maps at far greater spatial and vertical resolutions than are commonly available. This paper evaluates accuracies of topographic maps and morphometry derived from LIDAR data for two gully systems under thick forest canopy in the upper Piedmont of South Carolina. Comparisons with field surveys indicate that LIDAR data detect gullies with.
Keywords: fluvial geomorphology LIDAR mapping gully morphology remote sensing
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.