This paper investigated the characteristics of time series of the salinity(chloineion) at Shinjiko Lake, wich is under construction of refreshing water, for the surrounding area has been caused many drought damage by the intrusion of saltywater from Nakaumi Lake since 1922.
This refreshing water was planned to use for newly reclaimed land and the existing farmland.
The salinity has been mesaured once or twice by month since 1972 to 1981, and their variations and correlations with related hydrological observations such as rain, streamflow and sea level were examined. Moreover the probability of nonexceedance of the salinity for paddy field was examined.
Correlogram and spectrum of streamflow showed the periodicity of 3～6 months than that of 1 year, and the effect of markov chain. The salinity had little periodicity, while the variation as markov chain was shown.
The most effectual factor to the salinity is the sea level of Japan Sea, which rises up in Summar(this season has many dearth of water), and falls down in winter(this season has much water with much snow). And from winter to summer, the salinity decreased, on the contrary from spring to fall it mostly increased, for the annual tidal range of mean monthly level is 0.4 meters but tidal range in a day is only 0.2 meters in this area.
The probability of nonexceedance of the salinity showed that the water could not be used even for rice paddy field in this condition. Because this sample even at the upper lawyer(1 meter depth) and near the entrance of Hi River showed that the probability of that use was about 20% in irrigation period.