STUDY OF SEICHE IN LAKE BIWA-KO (IV) : OBSERVATION WITH A NEW PORTABLE LONG PERIOD WATER LEVEL GAUGE

A new portable long period water level gauge was designed in order to verify the results of numerical experiments with a computer about the seiche in Lake Biwa-ko, especially about the longitudinal oscillations. Using two water level gauges of this type, an observation was performed for a month in Otsu and Hikone at the same time. The observed periods of seiche agree well with the periods derived from the numerical experiments. The seiche with the period of about four hours is found for the first time in the north basin of Lake Biwa-ko from the frequency analysis of the records in Hikone. The observed amplitude ratio and the observed phase difference between those two observation sites agree with the experimental results about seiche of mode 1, mode 2 and mode 3. But the observed result of seiche of mode 4 disagrees with the experimental result.