Abstract

Geometry, sediment, and woody-vegetation data were collected from bottomland geomorphic surfaces at valley sections along three gaged perennial streams of northern Virginia. The basins of the streams differ widely in topography and physiography; mean discharges vary from 0.196 to 323 m3 per sec. Prevalent surfaces identified were the depositional bar, the active-channel shelf, the flood plain, and terraces. The stages corresponding to active-channel–shelf levels were equivalent to flow durations of 5% to 13%. Stages corresponding to flood-plain levels were equivalent to discharges with 1.4- to 2.0-yr recurrence intervals. The discharge data and statistical tests of geomorphic-surface, sediment, and vegetative data suggest that the various alluvial features are formed and maintained by hydraulically controlled sorting processes.

Analysis of woody-plant and geomorphic data shows that each surface supports characteristic species, some of which are nearly unique to a surface. Tests of sediment type with species distribution showed lower correlation than that of geomorphic surface with species. It is inferred that plant distributions largely are controlled by flow frequency and intensity, and that plants may help to identify geomorphic levels and potential for flood damage.

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