Figure courtesy of David Jay.
Forcing of tides by non-astronomical processes: amplitude scaleogram of Columbia River flow fluctuations (m3 s-1) at The Dalles, Oregon, 1878-1996, as a function of date (x-axis) and log (base 2) of frequency in cycles yr-1 (y-axis), as derived using continuous wavelet transform (CWT) analysis (Jay and Flinchem, 1997). Note the prominent annual and (in some periods) six-monthly cycles, indicative of high flows in the spring and some winters. Most of the larger freshets in the record occurred before 1900. Anecdotal evidence suggests that the 1849-78 period was also very wet, with the two largest known spring freshets being in 1849 and 1894. The annual flow cycle (1 cycle yr-1) and all fluctuations with periods between 3 mo and 2 yr have been severely damped by flow regulation (dams) and to some extent by climate change. High frequency flow fluctuations (periods of 1-7 d) were naturally weak, but have been greatly enhanced by daily and weekly power-peaking cycles (upper right-hand corner). The Dalles has the longest gauging record on the west coast of the US. The fluctuations documented here exert a strong effect on Columbia River tides.
