The connections between rivers and their watersheds over multiple scales.

摘要

This research explores the interactions between a watershed and its river by examining how watersheds influence river discharge at a variety of spatial scales. Discharge in a river channel grows as drainage basin area increases following the general equation: Q = kAc, where Q is river discharge, k is a measure of river base flow, A is upstream drainage area, and c is the scaling power dependency. Land use is a critical variable in the examination of river discharge, with discharge having significant geologic and ecologic influences on fluvial systems. Discharge is assumed to scale linearly or nearly linearly with drainage area (c∼1), but in spite of its widespread application the relationship has not been explicitly tested with respect to urbanization. Here we show that in small, urban settings the scaling is nonlinear for peak flows. These higher discharges in urban rivers have the potential to increase erosion, degrade aquatic habitats, and significantly alter channel forms. From historic aerial photographs, a majority of the measured widths (67 of 85) were statistically wider in 1999 than in 1947 on the urban Little Lehigh Creek, while the widths from rural Sacony Creek are more evenly distributed among those that widened, narrowed, and those that were statistically unchanged. This research also investigates the nature of the scaling relationship between discharge and drainage area across a wider geographic area by examining five large, undammed main-stem rivers (John Day, Salmon, Wabash, Greenbrier, and Yellowstone) and one river with extensive dams, the Colorado River. The John Day, Salmon, Wabash, Greenbrier rivers scale at values of ∼0.8, and variables including slope, elevation, and evapotranspiration may account for the decrease in c values from 1. The Yellowstone watershed's c value of ∼0.5 decreases over time, possibly through climatic factors, while the c value Colorado River has been influenced by dams. The results from this small set of rivers have implications for the ability to model landscape evolution through river erosion.