Geomorphology and dynamics of the estuary of the Negro river.

LONGO A.C.; PERILLO G.; MOREIRAS S.M

Santiago, Chile

Workshop; South America Water from Space Conference,; 2018

With the aim of developing a spatiotemporal analysis of the geomorphological dynamics of the Negro River estuary from the 30's to the present, this study is carried out as a part of the Ph.D. Thesis in Geology, Earth Sciences of the UNC. The Negro River, with a flow controlled by different dams operating on the waters of its two tributaries, the Neuquén and Limay Rivers, develops an estuary of the coastal plain. This type of estuary is characterized by a sedimentary load provided by the rivers that is relatively small when compared to the dynamic forces that redistribute the material (Piccolo and Perillo, 1997, 1999), based on the classification proposed by Perillo (1995). There are two sediment banks located on both sides of the Negro River discharge channel: the San Miguel Bank developed to the west and the La Hoya Bank to the east of the main channel (del Rio et al, 1991). The average amplitude of the tides at the mouth of the river is 3.35 m and 2.44 m in sicigia and quadrature, respectively (SHN, 1993). The influence of these tides can be detected in San Javier about 66 km from the coast. Firstly, the lower estuary system of the Negro River is digitalized and exposed from the point of view of sediment banks mobilization for the years 1935, 1936, 1974 and 1986 based on del Río et al (1991). Secondly, the same process is carried out on Cartografía de 1972 (Subsecretaría de Recursos Hídricos, provided by Prefectura Naval) and also on an aerial photography from 1957 (Puerto Belgrano Air Base of the Naval Hydrographic Service (SHN), provided by the INDEVI). Finally, a survey and cartographic analysis of the study area was carried out through Landsat 8 images and historical images of 1997, 2004 and 2015, available in Google Earth Pro. All this data was incorporated into GIS for the integration and the spatial analysis. The response of the estuary dynamics to the behavior of the upper and middle basins of the Negro River results from the anthropogenic modifications and the interaction of these with the influence of the open sea intrusion into the fluvial valley. There is a great contribution of coastal sediments from the erosion of the Río Negro coast and its transport by the drift towards the Buenos Aires coast. The route of the aforementioned banks is modified by the discharge of the river which exerts an impact purely hydrodynamic. There is a greater thrust for drift towards the northeast as a consequence of diminished flow by anthropic control and with this a decrease of the contribution of fluvial sediments. It is assumed, under these conditions, that the constitution of sediments banks is mostly due to coastal erosion. The sediment banks, Miguel and La Hoya, under a regime of exogenous processes, clearly expose the coexistence, and therefore the joint action of climatic, fluvial and anthropic factors.