| Regional curves of hydraulic geometry are frequently constructed for physiographic provinces, regions that have similar geologic structure, climate, and geomorphic history. As a result, the factors controlling channel form are more alike than would be the case for streams across widespread geographic regions. However, geology can vary significantly within a physiographic province. The purpose of this study, therefore, was to determine if regional curves would be more precise predictors of hydraulic geometry if developed for geologically similar streams within a physiographic province. A total of 34 reaches on six ungauged mountain streams in the Ridge and Valley Physiographic Province of Pennsylvania were used to develop lithologically controlled regional curves for drainage area versus bankfull cross-sectional area, bankfull width, and bankfull mean depth.;The slope, y-intercept, and R2 value of the non-carbonate lithologically controlled regional curves were compared to three distinct regional curves of varying watershed size and physiography. These comparisons reveal that lithologically controlled regional curves for bankfull cross-sectional area are consistently statistically different than the other three curves. The factors that may influence differences in the regional curves include bedrock geology, geologic structure, physiography, channel gradient, watershed size, riparian vegetation, and land use. Comparison of R2 values shows regional curves derived from a larger sample size and including a majority of larger watersheds (>75 km2) produce less variance. An additional regional curve was derived by combing hydraulic geometry data from the lithologically controlled watersheds and non-carbonate watersheds initially investigated by Chaplin (2005). Higher R2 values indicate the combined curves developed with a larger sample size and dominated by larger watersheds produce less variance compared to the lithologically controlled curves. Future regional curve investigators should include ungauged watersheds, increase sample size, and more fully constrain the variables controlling natural channel dimensions to assess if more precise hydraulic geometry relationships can be developed within physiographic provinces. |
