GEOTECHNOLOGY APPLIED TO THE MORPHOLOGICAL ANALYSIS OF ARACATIMIRIM RIVER ESTUARY (TORRÕES - CE)

Estuaries are unstable coastal environments of transitional character between the continent and the ocean that plays an important role in fauna reproduction. In general, these types of coastal features have suffered several environmental impacts due to inadequate forms of use and occupation, which result in significant modifications in the morphology of river mouths. This work aims to apply geotechnologies to study the morphological changes at the mouth of Aracatimirim River, Ceará, Brazil, contributing with useful information on the monitoring and environmental management of tropical coastal estuaries. The methodology was divided into three stages: recognition of the study area; field activity and data processing and integration. The Aracatimirim River estuary underwent major changes between 1985 and 2013, where it was possible to identify five evolutionary phases into this period. Previously, built by bar, it evolved to an estuary of coastal plain, accompanied by the progression of Torrões beach and agglutination of "barriers spits" to the continent. It is the main navigable river of the area of Itarema municipality. After the development of this work, it was possible to conclude that the forms of use and occupation in the surroundings of the Aracaratimirim River estuary had a wide growth in the last years, which reflects clearly in the estuary morphology, currently classified as an estuary of coastal plain. The morphological changes within the estuary interfere on not only the environmental conditions, but also in the economy and social conditions of the local community.

Effects of mud supply on large-scale estuary morphology and development over centuries to millennia

Alluvial river estuaries consist largely of sand but are typically flanked by mudflats and salt marshes. The analogy with meandering rivers that are kept narrower than braided rivers by cohesive floodplain formation raises the question of how large-scale estuarine morphology and the late Holocene development of estuaries are affected by cohesive sediment. In this study we combine sand and mud transport processes and study their interaction effects on morphologically modelled estuaries on centennial to millennial timescales. The numerical modelling package Delft3D was applied in 2-DH starting from an idealised convergent estuary. The mixed sediment was modelled with an active layer and storage module with fluxes predicted by the Partheniades–Krone relations for mud and Engelund–Hansen for sand. The model was subjected to a range of idealised boundary conditions of tidal range, river discharge, waves and mud input. The model results show that mud is predominantly stored in mudflats on the side of the estuary. Marine mud supply only influences the mouth of the estuary, whereas fluvial mud is distributed along the whole estuary. Coastal waves stir up mud and remove the tendency to form muddy coastlines and the formation of mudflats in the downstream part of the estuary. Widening continues in estuaries with only sand, while mud supply leads to a narrower constant width and reduced channel and bar dynamics. This self-confinement eventually leads to a dynamic equilibrium in which lateral channel migration and mudflat expansion are balanced on average. However, for higher mud concentrations, higher discharge and low tidal amplitude, the estuary narrows and fills to become a tidal delta.

Effects of mud supply on large-scale estuary morphology and development over centuries to millennia

Alluvial river estuaries consist largely of sand but are typically flanked by mud flats and salt marshes. The analogy with meandering rivers, that are kept narrower than braided rivers by cohesive floodplain formation, raises the question how large-scale estuarine morphology and late Holocene development of estuaries are affected by cohesive sediment. In this study we combine sand and mud transport processes and study their interaction effects on morphologically modelled estuaires on centennial to millennial time-scales. The numerical modelling package Delft3D was applied in 2DH starting from an idealised convergent estuary. The mixed sediment was modelled with an active layer and storage module with fluxes predicted by the Partheniades-Krone relations for mud, and Engelund-Hansen for sand. The model was subjected to a range of idealised boundary conditions of tidal range, river discharge, waves and mud input. The model results show that mud is predominantly stored in mudflats on the side of the estuary. Marine mud supply only influences the mouth of the estuary whereas fluvial mud is distributed along the whole estuary. Coastal waves stir up mud and remove the tendency to form muddy coastlines and the formation of mudflats in the downstream part of the estuary. Widening continues in estuaries with only sand while mud supply leads to a narrower constant width and reduced channel and bar dynamics. This self-confinement eventually leads to a dynamic equilibrium where lateral channel migration and mud flat expansion are on average balanced. However, for higher mud concentrations, higher discharge and low tidal amplitude the estuary narrows and fills to become a tidal delta.