Geomorphic influences on habitat formation, distribution, and development and the classification of upland coastal Oregon streams Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/xp68kk50p

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  • A framework is presented for a more causal explanation and ordering of stream characteristics than traditional means have used. Patterns of stream habitat distribution are related to particular characteristics of the geomorphology of watersheds. Variability in stream characteristics can be explained by the spatial distribution of properties of the watershed and by identifying stages in the development of stream habitat. This has implications for the classification of streams in a geomorphic context, emphasizing the concepts of capacity and genesis. Within the context of a hierarchical watershed classification, stream segment is considered the most useful classification level for understanding habitat distribution and dynamics. Basins in basalt and sandstone geologic formations in the Oregon Coast Range were investigated for stream habitat distribution. In streams flowing through sandstone, repetitive patterns of large-scale valley segments are identified in headwaters to large rivers. Segment boundaries are identified by changes in valley morphology. Alternating patterns of wide valleys and constricted valleys are common in some landtype associations. The formation of these segments is influenced by bedrock stratigraphy and large-scale geomorphic processes such as slump-slides. Valley dimensions are quantified by nondimensional indices of valley width / channel width and the stream gradient index. Pool distribution was intensively analysed in 2.8 kilometers of a fourth order stream that flows through basalt bedrock. The mainstem was stratified by tributary junctions, each of which was further divided into 3 equal zones. Distributional patterns were analyzed by pool spacing, linear nearest neighbor, and by composition of zones. Pool spacing does not conform to the expected normal distribution with a median spacing at 5-7 channel widths. Pool spacing is strongly skewed towards shorter spacings and has a median spacing at 2-3 channel widths. Pools of similar size and type occur locally, which indicates that different areas of the stream have different conditions for habitat formation and development. Habitat distribution and composition is related to valley morphology, hillslope processes, location in relation to tributary junctions, and time since disturbance. Debris torrents are the dominant processes influencing the stream, these supplying sediment and instream structure of wood and boulders, as well as influencing channel slope. A balance between disturbance and recovery exists in unmanaged as well as perturbed watersheds. Effective management of watersheds must maintain the geomorphic integrity of the valley and stream. Classification of the stream and habitat in a geomorphic context enhances explanation and the understanding of the interaction between watershed form and process and characteristics of the stream. Stream habitat formation, distribution, and dynamics are better understood in the context of geomorphic concepts such as sediment storage and dynamics.
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