Phillips, Scott W.,
U.S. Geological Survey,
208 Carroll Bldg.,
8600 LaSalle Rd.,
Towson, MD 21286
Chesapeake Bay, the Nations's largest estuary, has been affected adversely by both population growth and natural processes, such as large floods, during the past several centuries. High nutrient and associated sediment loads have decreased water clarity, in turn reducing populations of submerged aquatic vegetation, one of the most important components of the ecosystem because they provide critical habitat for shellfish and finfish and food for waterfowl. Resource managers are attempting to reduce the amount of nutrients and sediments that enter the Chesapeake Bay (Fig. 1).
The USGS, through the Ecosystem Program (Home Page: http://chesapeake.usgs.gov/), will collect and interpret earth science information to hutrient and sediment reductions. The project will be a 5-year effort withelp determine the effectiveness, and response of the ecosystem, to the n the goal of providing information on nutrient and sediment conditions and trends, watershed response times, and increased understanding of factors affecting nutrient and sediment dynamics, retention time, and response of selected living resources. Sediment and nutrient investigations began in FY 1996, as a collaborative effort involving most Divisions of the Geological Survey, the WRD National Research Program, the WRD Districts of Maryland-Delaware-District of Columbia, Pennsylvania, and Virginia, and several major Universities within the Bay Region. Scientists representing most of these agencies met in FY 1996 to help develop a workplan for this investigation. The present report is devoted to the approaches deemed necessary to accomplish the general objective through the identification and/or interpretation of: 1) significant sources of sediment (erosion and channel degradation); 2) the processes that entrain and transport sediment; 3) the processes, locations, amounts, and rates of significant sediment deposition; and 4) the retention times and remobilization of stored sediment. All four sub-objectives will be investigated at various spatial scales and at three time scales, namely from 1985 to the present, the last 50 years, and the past several centuries.
Study approaches to the three principle sediment sources, outlined above, are: (1) Compilation and analysis of retrospective data set on overland erosion, drawn from the Smithsonian Environmental Research Center, the University of Maryland, and others. This effort will focus on small monitored watersheds located in physiographic regions or subregions identified as substantial source areas from gaging station sediment records. Whenever possible, these sites will be nested within increasingly larger watersheds where companion studies of channel and floodplain sediment aggradation and degradation have been or will be conducted as part of the present program. (2) Compilation and analysis of a retrospective data set on low-order channel incision occurring within the Bay watershed. Most of this information will come from studies conducted at Johns Hopkins University and the Universities of Maryland and Delaware. (3) Channel-stability monitoring along selected reaches of rivers to determine the long- and short-term trends in channel and flood-plain erosion or degradation. The alluvial areas of streams near the Bay and typically within the Coastal Plain (Fig. 1) are largely aggradational and represent significant sediment traps. However, rivers within the Piedmont and Great Valley (Fig. 1) function as both sediment sinks through flood-plain accretion and as sources through channel and bank erosion; at these sites most of our field efforts will involve the quantification of erosion of storage areas. Methodologies will include channel migration determination from aerial photography, analysis of current and historic cross sections, and dendrogeomorphic analysis of bank retreat. These techniques will permit quantitative estimates of current and recent sediment remobilization through degradation and channel migration and aid in estimation of retention time.
Additional field and lab work will include mapping of the surficial deposits and determining the geomorphic form of channels, flood plains, and valleys in both plan and cross-sectional views, using aerial photography, existing maps, cross sections, and stratigraphic information. Critical reaches will be resurveyed in detail. Sediment budgets will be integrated with estuarine deposition information from offshore river and bay sediment cores.
Hupp, Cliff R., U.S. Geological Survey, Water Resources Division, National Research Program, Reston, VA: Currently serves as Project Chief of the Vegetation and Hydrogeomorphology Project in the Branch of Research, Eastern Region. Experience and research during 19 years with USGS includes plant ecological and tree-ring analyses of mass wasting, floods, forested wetlands, and the riparian zone. Currently the Project is concentrating on the sediment and nutrient trapping function of forested wetlands and multi-disciplinary investigations of mountain watershed hydrology and ecology.Workshop Proceedings