The Tualatin and Newaukum Rivers and Johnson Creek were the only streams in Oregon and Washington found to fit these criteria. In addition, a nonurbanized basin was needed as a reference to compare to urbanizing basins. The requirements for the reference basin were that it be in western Oregon or Washington, have no large city or metropolitan suburban area, have flow records of at least 50 years and have minimal disruption of the natural flow by diversion or impoundment. The Luckiamute River, gaged near Suver, was chosen as a nonurbanized reference basin. It meets the above criteria and is part of the lower Willamette basin, as are the other two Oregon streams.
Peak flow is the highest flow of a period.
An increase in Q p may indicate an increased flashiness of a stream. Because Q p depends in part on the size of the drainage basin, it cannot be easily compared from stream to stream. Two main flow variables were used in this study, Q p and Q v . For the Luckiamute and Newaukum Rivers and Johnson Creek, the published instantaneous Q p for each event was used as the peak value. However, for the Tualatin basin, only one instantaneous peak per year was published, no matter how many peak events occurred.