Geomorphology of Urban and Suburban Riparian Zones

The geomorphic pattern of riparian zones in urban and suburban watersheds is affected by several prominent trends that vary in their expression depending on the age of development and the dominant management regime: (1) truncation of headwater portions of the drainage network and replacement by storm drains; (2) incision and widening of channels in response to altered storm hydrographs and sediment supply; (3) fragmentation or longitudinal segmentation of the riparian corridor by frequent bridges, culverts, and road embankments or other kinds of artificial fill acting as either barriers or conduits; (4) introduction of detention ponds designed for temporary storage of storm runoff and associated constituents. The resulting mosaic of landforms includes a combination of natural features and elements of the built environment, but an understanding of its hydrologic, geomorphic and biogeochemical behavior requires that we treat it as an integrated system. The availability of high-resolution topographic data derived from airborne LiDAR allows us to capture the morphology of the entire drainage network and to describe and quantify longitudinal trends influencing propagation of flood waves and transient patterns of storage associated with floodplain inundation. Trends in the hydraulic geometry of stream channels and in the longitudinal sequencing of fluvial landforms may be compared among suburban watersheds developed during different time periods in order to assess the impact of management regime on geomorphic expression and on hydrologic and hydraulic function. The time-transgressive pattern of urban development in the Gwynns Falls watershed, the primary study site of the Baltimore Ecosystem Study, together with extensive recent development in adjacent Howard County, Maryland, offers a test case well suited for comparative analysis of drainage networks, channels and floodplains.