Groundwater's Fingerprint in Stream Network Branching Angles

Abstract

Branching river networks are prominent features of the Earth's surface, but the mechanisms that create branching river networks patterns remain elusive. Recent studies have suggested that climate, tectonics, and lithology may control both longitudinal profiles of channel incision and the planform geometry of stream networks. Here we show, by analyzing almost 1 million river junctions and over 4.2 million groundwater wells across the contiguous United States, that stream network branching angles vary systematically with the degree to which streams lose water to, or gain water from, nearby groundwater aquifers. Streams whose surfaces lie above nearby groundwater levels, and thus are likely to be losing flow to underlying aquifers, tend to have narrower branching angles than streams that lie below nearby groundwater levels, and thus are likely to gain flow from groundwater. This systematic relationship persists across several stream orders, and across a wide range in channel gradients.