Evidence suggests that hyporheic exchange is significant in large streams of the Willamette Basin.
Hyporheic exchange can affect both the quantity and chemistry of water in streams and adjacent aquifers. For example, hyporheic exchange can cause a significant underestimate of stream discharge if a considerable volume of water is flowing within the channel deposits at the point of a streamflow measurement. In addition, because hyporheic exchange involves not only water, but also associated chemicals dissolved in the water, constituents, such as nutrients and pesticides, may undergo important biogeochemical transformations within the hyporheic zone. First, injections of rhodamine WT dye in nine streams yielded graphs of dye concentration versus time with long recession times characteristic of active hyporheic exchange. Second, in the Willamette and Santiam Rivers, detailed measurements of water discharge revealed areas where streamflow losses and gains could not be accounted for by tributary inflows or diversions.