Tributary impacts, hydrological connectivity and distribution of sediment sinks along the middle-lower Amazon River
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By integrating hydro-geomorphic data collected from the field with remote sensing data, this dissertation investigates the roles of the tributaries and vast floodplain on suspended sediment distribution patterns in the Amazon River system. To assess the tributary impacts, I focused on the Solimões and Negro Rivers, and found the significant seasonal variations in surface water mixing and distribution patterns; however inter-annual variations between flooded (2009) and drought years (2005) were not notable. It is also observed that the anabranching channel patterns were observed to prevent fast mixing of different water types. Channel-floodplain hydro-sedimentary interactions were investigated over water-saturated floodplain in the lower Amazon by mapping geomorphic mosaic, and characterizing the seasonal flooding and storage patterns. Hydrological connectivity processes over floodplain varied significantly between geomorphic units, which were not correlated with their distance from the river, implying that application of the traditional “flood pulse” model is not applicable in the Amazon. The channel-floodplain connectivity also resulted in failure of the rating curve around Obidos due to the seasonal water storage in floodplain. Using a series of ADCP data, both the threshold of hydrological connectivity and geomorphic factors influencing the rating curve were assessed, and then the rating curve at Obidos was revised. Floodplain suspended sediment storage along the lower Amazon in between Manacapuru and Obidos was estimated as 79 million tons annually. However sedimentation rates which are determined by the connectivity processes and geomorphologic characteristics of floodplain significantly varied between different reaches, showing downstream increase in the magnitude of sediment sinks. This indicates a nonlinear geomorphic evolution of the Amazon floodplain at least since the Holocene through the river’s longitudinal profile. Through sequences of interrelated chapters, I arrived to the conclusion that the influences of the tributaries and channel-floodplain interactions on the Amazon River system’s suspended sediment distribution are significant and their patterns are more complex than expected. The major factor contributing to this complexity is the geomorphologic styles of the river, which are related both to the long-term evolution processes and to the current anabranching channel dynamics. These geomorphologic styles along the Amazon River are different reach-by-reach due to the varying interactive processes with regional tectonics, hydroclimatology and human activities.