[pp.71-80]

A Study on Water Temperature Variations in the Middle Reach of the Shinano River

Guangwei HUANG and Nobuyuki TAMAI （Niigata University / Kanazawa University）

Abstract:
In this study, the characteristics of water temperature variations in the middle reach of the Shinano River are investigated. It is found that the daily maximum, daily mean and daily minimum air temperatures are good indicators of the daily maximum, daily mean and daily minimum water temperatures at the yearly scale. But the relationships between air and water temperatures depart from linearity at seasonal or shorter time scale. It is also shown that the 7-day moving averages of daily maximum water temperatures are linearly correlated with the 7-day moving averages of daily mean water depths at the seasonal scale. Besides, the characteristics of water temperature at the Ojiya site, which is about 17 km upstream of the Nagaoka station and the possible impact upon the water temperature at the Nagaoka are discussed in view of the operation of the Ojiya hydropower plant. Additionally, the issue of temperature sampling frequency is explored. It is revealed that one sampling per day in the morning may be able to capture the overall variation pattern of water temperature.

Key Word:
Shinano River, water temperature, diurnal variation, time scale, correlation

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