Geomorphic-hydrologic-vegetation relationships in the Gwynns Falls Watershed
Mason Throneburg
Analysis of random plots of vegetation collected along the riparian corridor of the Gwynns Falls watershed shows a clustering of wet and dry species that is more pronounced in the lower watershed than elsewhere. It is hypothesized that urban changes to the landscape resulting in hydrologic and geomorphologic alterations could result in habitat changes reflected in plant distributions. For example, increased peak discharges and decreased sediment loads caused by the greater imperviousness of urban areas could result in channel incision, reducing the frequency of flood events and lowering the water table. This could favor species adapted to drier habitats. This study explores this hypothesis by examining detailed vegetation plots within the context of the hydrology and geomorphology of the adjacent stream channel.
  During the summer of 2003, 3 of the 73 10 x 10 meter plots randomly selected and sampled adjacent to the streams of the watershed in 1997 were chosen for further study. These 10 x 100 meter plots were sampled along both sides of the stream along with detailed observations of stream morphology. Sites are evaluated for adaptation to wet environments by assigning numeric values to the United States Fish and Wildlife Service wetland indicator categories and averaged to produce a site wetness index. Stream geomorphology is currently being studied by direct observation, field surveys, comparisons of topographic maps spanning nearly a century, USGS stream flow records, and stream survey information associated with bridge construction. These data are being used to reconstruct the historical stream as a reference for understanding how urbanization may have influenced stream morphology and behavior, as well as the associated riparian vegetative community.
Keywords: Geomorphic, hydrologic, vegetation, Gwynns Falls Watershed

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