Characterizing Cyclic Water‐Level Fluctuations in Irrigation Canals

A technique is demonstrated for characterizing water‐level fluctuations in irrigation canals using amplitude spectral estimates obtained with a fast Fourier transform. The technique, which is often used to analyze mechanical vibrations and electrical signals, is used with hourly water‐stage data to calculate dominant frequencies, amplitudes, and peaking times of water‐level fluctuations in eight irrigation canals in Utah and Washington. The results of this analysis indicate that water‐level fluctuations dominated by a daily cycle are statistically significant and that the time of peak water level occurred between 4 and 10 a.m. in all the canals studied. Amplitudes of water‐level fluctuations in six of the eight canals that were unlined and unregulated are found to depend on canal (reach) length. Low frequency fluctuations with periods ranging from three to 10 days existed in the canals, but are statistically significant only in the spring and fall. Observations are presented about the causes and possible measures for controlling water level fluctuations in the study canals.