Management of near‐channel ground water and surface water to maintain stream health and flood plain ecological function requires hydrogeologists to refocus their conceptual models of water exchange between the aquifer and stream. The high hydraulic conductivity fluvial plain directs ground water flow down‐plain where it exchanges with the stream channel creating gaining, losing, flow‐through, and parallel‐flow reaches. The resulting complex flow system requires consideration when profiles representing ground water flowpaths are constructed. In addition to interaction at the scale of the fluvial plain, exchange of ground water and surface water within and immediately adjacent to the stream channel creates hyporheic zones. The physical and bio‐geochemical extent of these zones depends on the head distribution and ground water flow directions, stream hydraulics, and channel bed conditions, and magnitudes and distributions of hydrogeologic parameters. Simulated conceptualizations of flow dynamics caused by slight increases in hydraulic potentials at the surface water‐stream bed interface indicate stream‐ground water mixing could occur to a depth of 1.7 m below the channel. Rescaling of traditional hydrogeologic approaches to include the fluvial plain and channel scale will result in opportunities to expand hydrogeologic research and participate in interdisciplinary research teams attempting to decipher and manage fluvial systems.

[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.

Human use of pharmaceuticals results in the excretion and disposal of compounds that become part of municipal and domestic waste streams. On-site waste water disposal and leaking city sewer systems can provide avenues for the migration of effluent to the underlying aquifers. This research assessed the occurrence and persistence of 22 target pharmaceuticals in septic tank effluent and two shallow, coarse-grained aquifers in western Montana. Twelve compounds (acetaminophen, caffeine, codeine, carbamazepine, cotinine, erythromycin-18, nicotine, paraxanthine, ranitidine, sulfamethoxazole, trimethoprim, and warfarin) were detected in a high school septic tank effluent. Three of the 12 compounds, carbamazepine, sulfamethoxazole, and nicotine, were detected in the underlying sand and gravel aquifer after effluent percolation through a 2.0-m thick sand vadose zone. Sampling of a second sand, gravel, and cobble dominated unconfined aquifer, partially overlain by septic systems and a city sewer system, revealed the presence of caffeine, carbamazepine, cotinine, nicotine, and trimethoprim. The presence of carbamazepine and sulfamethoxazole in these aquifers appears to correlate with local usage based on a reported monthly prescription volume. This work highlights the need for expanding geochemical investigations of sewage waste impacted ground water systems to include sampling for selected pharmaceuticals.

Measurements of groundwater–stream water interactions are increasingly recognized as important to understanding the ecology of fishes and other organisms in stream and riparian ecosystems. However, standard measurement techniques are often feasible only at small spatial scales, in areas with easy access, or in systems with relatively fine substrata. We developed simple new techniques for installing minipiezometers and obtaining estimates of vertical hydraulic gradient, hydraulic conductivity, and specific discharge in gravel and cobble streambeds that allowed for large numbers of measurements to be obtained in remote locations. Our approach yielded values comparable to those obtained through more traditional methods. Consequently, these techniques may provide a labor cost‐efficient way for detecting groundwater−stream water interaction patterns that are critical labor‐attributes of stream and riparian systems at multiple scales.