Natural Streams and the Legacy of Water-Powered Mills

TLDR

Gravel‑bedded streams are widely assumed to naturally form meandering channels with fine‑grained floodplains, a model that drives a multibillion‑dollar restoration industry. Mapping and dating of mid‑Atlantic stream deposits, together with historical records, show that pre‑European settlement streams were small anabranching channels in vegetated wetlands with little sediment but high organic carbon, and that mill‑dam sedimentation buried these wetlands, making most floodplains fill terraces rather than natural meandering channels.

Abstract

Gravel-bedded streams are thought to have a characteristic meandering form bordered by a self-formed, fine-grained floodplain. This ideal guides a multibillion-dollar stream restoration industry. We have mapped and dated many of the deposits along mid-Atlantic streams that formed the basis for this widely accepted model. These data, as well as historical maps and records, show instead that before European settlement, the streams were small anabranching channels within extensive vegetated wetlands that accumulated little sediment but stored substantial organic carbon. Subsequently, 1 to 5 meters of slackwater sedimentation, behind tens of thousands of 17th- to 19th-century milldams, buried the presettlement wetlands with fine sediment. These findings show that most floodplains along mid-Atlantic streams are actually fill terraces, and historically incised channels are not natural archetypes for meandering streams.