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Land use change and watershed response in Greater Vancouver mountain stream systems Shepherd, Jennifer Lise

Abstract

This research investigated human induced land use patterns, land cover change and hydrologic response in mountain watersheds. The hypothesis was that the spatial pattern of land use patches in a watershed influences runoff generating mechanisms, and thus affects peak flows and stream ecosystems. The goal was to increase the understanding of the influence of landscape pattern on environmental process, and thus provide a scientific basis for the design of urban development that maintains the structure and function of biological communities along a stream system. The study was a first attempt to apply the methods of landscape pattern analysis from landscape ecology to hydrology and stream response. Previous analyses in hydrology have not explicitly considered the spatial arrangement of land use/cover patterns in the watershed. Although statistical relationships between landscape pattern and stream discharge were not achieved because of limitations of the hydrological modelling, this study laid the groundwork for the realization of this goal. The geographic information system (GIS) software Maplnfo, and a hydrologic model based on the Rational Method, were used to investigate the relationships between land use patterns and their effect on the hydrology of four steep mountain stream systems in the Greater Vancouver region of British Columbia. Accepted land use/ cover categories and landscape metrics were used to quantify and characterise landscape change, across time (1946-1995) and between watersheds. Composite runoff coefficients ( Q were calculated for each land use, and a five-year peak stream discharge (Q) that took the changing landscape into consideration was modelled. Stream pattern, total impervious surface (TLA), and road networks were assessed as part of the description of the landscape. This thesis considered relationships between: discharge and percent land use area; discharge and total imperviouss area; discharge and landscape pattern; and percent land use area and landscape pattern. It was found that calculated discharge, percent impervious, and developed area increased across all watersheds across all time periods. The number of road crossings on the creek mainstem and total road length in the watersheds increased with percentage of developed area in the watersheds, and there was a linear relationship between C coefficient and the length of roads in the watershed. Development emerged in discrete patches, generally in the more accessible and flatter regions of the basin. Patch shape metrics followed an increasing trend with development levels between zero and twenty percent. However, between twenty and fifty percent developed the metrics scattered and did not have an apparent trend. This was likely due to a shift in the landscape matrix from forest cover to development. Increased development was associated with fragmentation of the landscape because more land use/cover categories were present in the watershed. This created a situation where average patch size decreased, patch diversity and density increased, and the watersheds had a fragmented appearance. Developed patches generally had a more complex shape than forest patches. The likelihood of finding a forest patch adjacent to a developed patch decreased as development increased.

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