The Influence of Climatic Variations on River Delta Hydrodynamics and Morphodynamics in the Parnaíba Delta, Brazil

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.