9526669 Wondzell The objective of this study is to quantify the flux of water through the hyporheic zone of a mountain stream network from a small heawater stream (first-order), through intermediate sized streams (third-order and fifth-order), and along the mainstem (sixth-order) of the McKenzie River basin, Oregon. Comparisons will be made among the sizes of the selected stream reaches, and between constrained and unconstrained stream reaches of each stream size to identify the geomorphic and hydrologic factors regulating the exchange of surface and ground water along the logitudinal profile of a mountain stream network. The exchange flow of sstream water and the discharge of ground water through the hyporheic zone will be estimated at each site under the range of stream discharges observed for each season of the year. Well networks will be instaled on the valley floor at each study site to characterize the flow net. The locations of each well will be mapped and the elevation of the well head and the ground level at each well will be surveyed. Water-table elevations will be measured monthly from the well network and from stage plates located in the active stream channell at each study site. Saturated hydraulic conductivities (k) will be calculated from falling-head slug tests and continuous tracer injections. These data will be used to calibrate the numerical flow model, MODFLOW, to predict the head observed within the network of wells at each study site. The head distribution predicted from the calibrated model will be used to estimate subsurface fluxes.
