Cartographic Models To Characterize Changes In Fluvial Landscapes
Bock, Andrew 1
1 University of Colorado - Department of Geography
Because of their structure and function, riparian areas occupy a unique position in the landscape, as they are subject to change over time in response to geomorphic and hydrologic factors and are important pathways for flows of energy and matter. Riparian landscapes represent a shifting mosaic of vegetation and land cover patches of varying properties, maintained by stream dynamics with a high degree of patch heterogeneity in the longitudinal, lateral, and vertical directions. In the Western United States, the current structure of fluvial landscapes is influenced by complex interactions between both social and environmental factors. Anthropogenic manipulations of flow regimes have altered the riparian landscape by impacting processes of primary and secondary succession in increasingly disconnected floodplains. Anderson et al. (2008) suggests the spatial extent of the Fremont Cottonwood, Populus fremontii, a keystone species in riparian ecosystems in semiarid climates, will decline markedly in the future due to changes in flow regimes. Within Colorado, previous studies like Merritt and Cooper (2000) have noted significant changes in riparian zone vegetation and channel morphology when comparing regulated and unregulated reaches in the Green and Yampa Rivers.
Channel reconfiguration, or restoration, has become a common practice in the Western United States to re-create the physical and biological conditions from some ‘reference condition’ or re-establish levels necessary to maintain natural communities or hydrologic function. Channel and floodplain characteristics constitute the framework within which these conditions can exist. An understanding of historic processes, conditions, and rates of anthropogenic impacts is a prerequisite to successful restoration design (Kondolf, 1995).
One tool to quantify and evaluate historic spatio-temporal dynamics in landscape structure is cartographic modeling. Land cover information derived from chronosequenced aerial photographs, historical maps, and remotely sensed data can be processed by map algebra and cellular automata operations to analyze landscape changes. In addition to land cover and vegetation, stream channel geometry, meander rates and patterns, and creation of fluvial landforms must be considered in efforts to model riparian vegetation (Cooper, 2000). Cross-referencing change detection of vegetation and channel patterns with historical records of streamflow, climate, and land use patterns provides insight into the types and magnitude of cross-scale processes that influence fluvial landscapes, and provides a reference point for further management and planning.
Anderson, D.C., Cooper, D.J., Northcott, K., 2007, Dams, Floodplain Use, and Riparian Forest Conservation in the Semiarid Upper Colorado River Basin, USA: Environmental Management, v.40, p.453-475.
Kondolf, G.M., and M. Larson, 1995, Historical channel analysis and its application to riparian and aquatic habitat restoration: Aquatic Conservation v.5, p.109-206.
Merritt, D.M., Cooper, D.J., 2000, Riparian Vegetation and Channel Change in Response to River Regulation: A Comparitive Study of Regulated and Unregulated Streams in the Green River Basin, USA: Regulated Rivers: Research & Management, v. 16, p.543-564.