Process-based ecological river restoration: visualizing three-dimensional connectivity and dynamic vectors to recover lost linkages. Ecology and Society 11(2): 5.

[1] We monitored summertime base flow water temperatures of hyporheic discharge to surface water in main, side, and spring channels located within the bank-full scour zone of the gravel-and cobble-bedded Umatilla River, Oregon, USA. Diel temperature cycles in hyporheic discharge were common, but spatially variable. Relative to the main channel's diel cycle, hyporheic discharge locations typically had similar daily mean temperatures, but smaller diel ranges (compressed by 2 to 6°C) and desynchronized phases (offset by 0 to 6 h). In spring channels (which received only hyporheic discharge), surface water diel cycles were also compressed (by 2 to 6°C) and desynchronized (by À4 to 6 h) relative to the main channel, creating diverse daytime and nighttime mosaics of surface water temperatures across main, side, and spring channels, despite only minor differences (<1°C) in daily mean temperatures among the channels. The river's hyporheic zone received and stored heat from the channel, yet hyporheic return flows carried heat back to the channel minutes to months after removal. Associated surface water temperature dynamics were therefore complex. Hyporheic discharge was not simply ''cooler'' or ''warmer'' than main channel water. Instead, instantaneous temperature differences between channel water and hyporheic discharge typically arose from diel temperature cycles in hyporheic discharge that were buffered and lagged relative to diel cycles in the main channel.

We develop and illustrate the concept of 'hydrologic spiralling' using a high-resolution (2 Â 2 m grid cell) simulation of hyporheic hydrology across a 1.7 km 2 section of the sand, gravel and cobble floodplain aquifer of the upper Umatilla River of northeastern Oregon, USA. We parameterized the model using a continuous map of surface water stage derived from LIDAR remote sensing data. Model results reveal the presence of complex spatial patterns of hyporheic exchange across spatial scales. We use simulation results to describe streams as a collection of hierarchically organized, individual flow paths that spiral across ecotones within streams and knit together stream ecosystems. Such a view underscores the importance of: (1) gross hyporheic exchange rates in rivers, (2) the differing ecological roles of short and long hyporheic flow paths, and (3) the downstream movement of water and solutes outside of the stream channel (e.g. in the alluvial aquifer). Hydrologic spirals underscore important limitations of empirical measures of biotic solute uptake from streams and provide a needed hydrologic framework for emerging research foci in stream ecology such as hydrologic connectivity, spatial and temporal variation in biogeochemical cycling rates and the role of stream geomorphology as a dominant control on stream ecosystem dynamics.