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test, Kendall's rank correlation test and the Anderson's correlogram test for
randomness and trend identification. The annual sediment load data from
1950 to 1990 and the monthly sediment load data from 1950 to 1969 were
used. The periodicity was analysed by harmonic analysis and the stochastic
component was modelled by autoregressive model. The analysis of the results
indicated that the annual sediment load series is trend-free at 5% significance
level and the monthly means and standard deviations of sediment load have
periodicity. The month-to-month correlation structure was found nonstationary.
Using the AR(1) model for the dependent stochastic component, 100 years of
monthly sediment data were generated, and the observed and generated data
matched well.
Jassby et al. (2003) developed a time series model of the Secchi depth for
Lake Tahoe, USA
incorporating a mechanistic understanding of interannual
variability. The Secchi depth was found occasionally over 40 m for Lake
Tahoe, but the mean annual Secchi depth has declined by about 10 m since
1967, prompting a large-scale restoration programme. The year-to-year
variability was found to be extremely high, obscuring restoration actions and
compliance with water quality standards. The model focussed on the Secchi
depth during summer, when the lake is least transparent and most heavily
used. Interannual variability for the summer season was driven largely by
precipitation differences. The model offers a tool for determining the
compliance with water quality standards when precipitation anomalies may
persist for years. It was also demonstrated by means of an ex-post forecast
that the increasing Secchi depths during 1999-2001 are simply climate-driven
and do not represent a recovery of the lake. The long-term trend for summer
is attributed to the accumulation of allochthonous mineral suspension.
Panda et al. (2011) examined trends in sediment load of the tropical
(Peninsular) river basins of India and explored influence of climatic and
human forcing mechanisms on the land-ocean fluvial systems. Sediment time
series of different timescale during the period 1986-87 to 2005-06 from 133
gauging stations was analyzed. Results indicated dramatic reductions in
sediment load in the tropical river basins, which is beyond the fold of assignable
natural variability. Around 88 and 62% of the total 133 gauging stations
showed a decline in sediment loads in the monsoon and non-monsoon seasons,
respectively. The significant downward trends outnumbered the corresponding
upward trends in high proportions for both the seasons. Striking spatial
coherence was observed among the significant trends, suggesting the presence
of the cross-correlation among the sediment records. The regional trends,
which account the spatial correlation, also indicated a widespread nature of
sediment declines. The rainfall, characterized by the non-significant decreasing
trends and frequent drought years, was found to be the primary controller of
sediment loads for most of the river basins. It was concluded that a little
change in rainfall towards the deficit side leads to a significant reduction in
the sediment load. Among the tropical rivers, the maximum reduction in
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