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Aquino da Silva, A.G.; Stattegger, K.; Schwarzer, K.; Vital, H., and Heise, B., 2015. The influence of climatic variations on river delta hydrodynamics and morphodynamics in the Parnaíba Delta, Brazil. In this work, we present a baseline study on the geo-environmental, morphodynamical, and hydrodynamical conditions of the Parnaíba River and its mouth, the Parnaíba River Delta (PRD). The outline of the PRD indicates that waves are the major forcing factor for delta development. Furthermore, the shape of the delta suggests that there is a considerable degree of asymmetry in its formation. The asymmetry is the result of coastal current influence on the reworking of the sediments that are discharged by the river. To investigate the hydrodynamic conditions of the area, field measurements were conducted on the river, offshore of the PRD, and on the tidal channels of the west part of the delta. At these locations, the currents, salinity, temperature, and tidal dynamics were measured. In addition, a time series of rainfall, river discharge, and suspended sediment concentration (SSC) were obtained from Brazilian governmental agencies. The interpretation of all of the data was used to determine how they interact to characterize the hydro- and morphodynamics of the PRD. Harmonic analysis was of high importance in the analysis of the time series, and it was employed to identify longer periods presenting similarities in terms of meteorological conditions. This allowed determination of the interconnection between rainfall, river discharge, and SSC with the occurrence and intensity of the El Niño-Southern Oscillation. The influence of river discharge, rainfall, and SSC on shoreline change was demonstrated through the analysis of decadal shoreline evolution using a series of LANDSAT images covering the period from 1981 to 2009. The analysis revealed that most changes occurred westward from the PR mouth. Changes in spit migration velocity were correlated to variations in riverine sediment yielded as a result of variations of river discharge and SSC. [ABSTRACT FROM AUTHOR]

The sedimentological character of material in transport and on the riverbed were investigated in order to record the sedimentary dynamicsin the lowermost Amazon. Suspended sediment concentration measurements show that net deposition occurs on the delta plain (between Obidosand the Xingu River), while downstream suspended sediment transport remains approximately constant. Lateral sediment input is compensatedby erosion in deeply incised channels keeping the region in a dynamic equilibrium. The surficial distribution of bedload sediments carried by the Amazon shows a corridor of sands (channel deposits) borderedby silty sediments at the margins. It consists chiefly of very fine sands, which become fine and medium-coarse sands laterally (Figure 6). The development of bedforms on the sand surface reflects strong bottom currents and sediment transport, as well as tidal effects. Nearshore sedimentary facies identified were interlaminated fine and coarsesilt, interlaminated silt and sand, faintly laminated mud, and mottled mud. [ABSTRACT FROM AUTHOR]

Economic development of the São Francisco River basin has increased by building seven river dams since the 1950s. Subsequently, strong coastal erosion reaching maximum rates of 98.6 m/year has been recorded at the river mouth, also leading to the destruction of a coastal village. This work combines discharge data with new sediment and hydro-acoustic records, collected in January 2009, to verify the impact of river damming on processes, controlling coastline evolution. Data analysis is focused on discharge evolution, morphology and sediment composition of subaqueous dunes as well as on the impact by tidal currents. Discharge has been strongly regulated since 1986, when the last river dam was implemented. Again, bedform morphology seems to be not affected neither by reduced river-discharge nor by reduced sediment supply. However, migration rates of these dunes, as calculated, are lower due to decreased discharge. At the same time, tidal impact is strengthened at the lowermost part of the river. From this we assume, that the replenishment of sediment at the coast near the river-mouth might be time-delayed, which could support coastal erosion. [ABSTRACT FROM AUTHOR]