Fourth in a series

“To think of any river as nothing but water is to ignore the greater part of it."

- Hal Borland

In the early 1970s, Robin Vannote presented a novel idea to a group of freshwater scientists who had gathered from across the country at the Stroud Water Research Center in rural Pennsylvania. His idea would evolve into the “River Continuum Concept”, which forever changed our understanding of streams and rivers. As you may have guessed, both from its name and my last post, the River Continuum Concept was based on the fact that a river flows, which might seem pretty obvious to you.

“In those days,” Vannote told me many years later, “most scientists studied a square meter of water to death.” But a stream is fundamentally different from a lake: it changes constantly as it moves downstream, and it can only be understood as a continuum. Bern Sweeney, then a young graduate student at the University of Pennsylvania, vividly remembers Vannote outlining his idea. “The scientists gathered in that room were just in awe. It was a major, major event.” Part of the reason was that, in hindsight, the concept was so simple that they couldn’t believe no one had thought of it before.

From those early insights, Vannote, other Stroud Center staff, and a few university colleagues developed the River Continuum Concept, which revolutionized stream research.

During the same period, noted geologist Luna Leopold was developing a formula for understanding a stream’s physical behavior. He saw that a river’s width, depth, velocity, and temperature change constantly as the water flows downstream. More importantly, he recognized that those changes are interrelated — and because a change in one factor affects all the others, a river’s pattern is predictable.

Drawing on these physical studies, Vannote and his colleagues added a critical element to the puzzle of how streams work. They argued that a river’s biological and chemical processes correspond to its physical attributes, and that the nature of biological communities changes just as the river itself does as it flows downstream. This means that the structure of a stream’s living communities is also predictable and that the communities adapt to the particular conditions of a stretch of stream.

The work of Vannote, Leopold, and others not only upended traditional scientific thinking; it also added a crucial new approach to water and watershed policy making. Underlying the economic, social, and political factors that had dictated almost all previous water policy, they demonstrated that a stream’s geological, geographic, physical, and biological dynamics must undergird the effective management of water resources. Big engineering solutions, such as massive dams and moving channels, would give way to understanding a stream’s ecology, and politics would henceforth have to take science into account.

A river is not a static body of water, and it is more than the sum of its parts. It is a single continuum that flows ceaselessly from its source to the sea. To understand what is happening at any point along the way, you must understand both what is happening upstream and what is entering it from the land through which it flows.