HYPORHEIC EXCHANGE THROUGHOUT A STREAM NETWORK AND IMPLICATIONS FOR WATER QUALITY: STUDIES WITHIN THE LOOKOUT CREEK BASIN, OREGON

Studies of hyporheic exchange have typically been limited to single stream reaches, documenting the factors controlling exchange and the effects of exchange on nutrient cycling. Stream reaches, however, are hydrologically connected through the entire stream network and to adjacent uplands. At the network scale, the geomorphologic template controls the spatial distribution of head gradients that drive hyporheic and larger groundwater-surface water exchanges. It is within this larger context that we report the results of studies of hyporheic exchange and geomorphic controls on these exchanges in the 5th-order Lookout Creek basin in central Oregon. We have developed regression models of stream geomorphic profiles, solute transport models from stream tracer experiments in numerous reaches, and groundwater flow models for reaches of different stream order to characterize the evolution in the factors controlling hyporheic exchange from headwater channels to mainstem Lookout Creek. Our results suggest that bedform size, spacing, and frequency are important controls on stream water hyporheic retention, and are also likely to be important controls on locations of biogeochemical cycling.