| Summary: | 碩士 === 中華科技大學 === 土木防災與管理碩士班 === 107 === In this paper the Mann-Kendall (M-K) trend test of observed flow and detection and inference of significant trend have been executed based on significance level of 5% (α=5％) and the observed flow and suspended sediment transport (from 1950~2017) at Lanyang Bridge Station, Chiayuang Bridge Station, Ximen Bridge Station, and Niu-Dou Station of Lanyang River Basin.
As for the observed monthly average discharge affected by the seasonality, in this paper the PW (Pre-Whitening) and TFPW (Trend-Free Pre-Whitening) technologies are used to remove the correlation of observed discharge, and then the trend test is executed based on MK-PW and MK-TFPW methods. The results are simultaneously compared with the result of trend test of SK method proposed by Hirsch et al (1982).
The result reveals that, except for the annual maximum daily discharge of Ximen Bridge Station showing no significant trend, the annual discharge M-K test, MK-PW and MK- TFPW of monthly average discharge, and SK trend test of annual runoff, annual mean daily discharge, annual minimum daily discharge, wet season runoff, and dry season runoff all show significant declining trend. The annual observed discharges of other stations all show no significant trend. This result indicates the daily depletion trend of discharge at Ilan River Ximen Bridge Station.
As for the SK trend test results of monthly average discharges in all stations of Lanyang River Basin, it shows the significant rising trend of monthly average discharge over the years. Except for the monthly average discharge of Ximen Bridge Station, other stations show no significant trend.
In this paper the observation of variation of suspended sediment transport before and after 1999 (the year of 921 Earthquake) reveals that, under same amount of discharge, the earthquake effect has no significant impact on the suspended sediment transport in the research area, so it did not result in the variation of suspended sediment transport in the river way.
The M-K trend test results of suspended sediment transport at all stations in Lanyang River Basin reveal that the dry season sediment transport and annual maximum daily sediment transport of Lanyang Bridge Station and the minimum daily sediment transport of Niu-Dou Station are showing significant rising trend, while the dry season sediment transport of Ximen Bridge Station is showing significant declining trend. The trend test results of sediment transport of all other stations are showing no significant trend.
Keywords: Mann-Kendall trend analysis, hydrological time series, hypothesis test, significant trend
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