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Without Biology, Rivers are Just Landforms

Janine Castro, PhD
Columbia River Fish & Wildlife Conservation Office
US Fish & Wildlife Service
Portland, Oregon

Authors: Janine M. Castro1 and Colin R. Thorne2

1 U.S. Fish and Wildlife Service, Vancouver, Washington
2 School of Geography, University of Nottingham, Nottingham, UK

River restoration science has rested comfortably within the disciplines of geology, hydrology, and engineering since its inception. This is at least partially due to the work of Lane in the 1950s when he conceptualized a dynamic equilibrium between the amount of stream flow, the slope of the channel, and the amount and size of sediment – the stream balance equation. Even further back, circa 1890, the Manning’s equation, which still influences most stream restoration projects designed today, included the variables of slope and hydraulic radius, and the ever-confounding roughness coefficient – n. Biology, while completely absent in Lane’s stream balance equation, implicitly appears in the Manning’s equation buried in the roughness factor. Arguably, two of the most influential equations that have shaped contemporary river restoration design left out the power of biology. While water and sediment create fluvial landforms, biology builds habitat – and the primary driver of most river restoration projects is ecosystem recovery. To address this biological omission, the Stream Evolution Triangle (SET) explicitly includes biology as a co-equal stream morphology driver, along with geology and hydrology. Through the integration of geology, hydrology, and biology, the SET provides improved understanding of potential morphological “stream states” at the reach scale following both natural and anthropogenic disturbances. Hence, the SET assumes dynamic morphological evolution through time and recognizes variable rates of change for both spatial and temporal scales, along with numerous latent trajectories. Potential utility of the SET in stream restoration planning and design stems from improved understanding and explanation of stream planform evolution by explicitly including the role of biology, which provides insights into appropriate restoration strategies to counter adverse impacts from past disturbance, while building future resilience.