Wondzell, Steven M.; Swanson, Frederick J. 1996. Seasonal and storm dynamics of the hyporheic zone of a 4th-order mountain stream. I: Hydrologic processes. Journal of the North American Benthological Society. 15(1): 3-19.
The objective of this study was to quantify fluxes of ground water and advected channelwater through the shallow aquifer adjacent to a 4th-order mountain stream. A network of wells wasinstalled from 1989 to .1992. Water-table elevations were measured seasonally and during storms.These data were used to calibrate MODFLOW, a 2-dimensional groundwater flow model. The fluxesof water through the subsurface were estimated from the head distributions predicted by the modelfor 8 steady state model runs bracketing the observed range in baseflow conditions, and for 1 transientsimulation of a large storm. The overall pattern of subsurface flow changed little over the course ofthe year, even though the relative flux of advected channel water and ground water changed amongseasons and during storms. Apparently the longitudinal gradient of the main valley, the location ofthe stream, and the influence of secondary channels determined the pattern of subsurface flows.Subsurface fluxes through a gravel bar were dominated by advected channel water but fluxes throughthe floodplain were dominated by ground water. Flow rates were positively correlated to estimatedstream discharge during base-flow periods, but decreased slightly during storms because of precip-itation inputs to the aquifer. The mean residence time of water stored within the aquifer was ap-proximately 10 d for the gravel bar and 30 d for the floodplain during baseflow periods. Even thoughprecipitation during the simulated storm equaled 12% and 23% of the water stored in the gravel barand the floodplain, respectively, the mean residence time of water remained long.
Key words: hyporheic zone, advected channel water, ground water, groundwater flow models,streams, aquifer, water budget, flow path, geomorphology.