Modeling Dissolved Oxygen Levels In the Navarrete-Cañuelas Sub-Basin Of the Matanza-Riachuelo River Watershed Provincia de Buenos Aires, Argentina

Abstract

Containing a sizable section of Argentine capital Buenos Aires, the Matanza-Riachuelo river’s 2,240 km2 drainage basin currently houses ~8 million people, many of which live in un-urbanized slums without potable drinking water or sanitation services. The river receives an estimated 82,000 m3 of untreated industrial waste daily, in addition to domestic wastes and agricultural runoff, and significant portions are found to be anoxic, especially during low-flow conditions. Attempting to contribute tangibly to Argentine federal-municipal watershed authority ACUMAR’s work remediating the river and improving quality of life of the basin’s inhabitants, this project aims to model current dissolved oxygen levels along tributary streams found in the Matanza-Riachuelo’s headwaters, and the sensitivity of the model to particular parameters. Specifically, this thesis focuses on the Navarrete-Cañuelas sub-basin of the watershed. Methods include developing and codifying a generalized model for dissolved oxygen in rivers and streams based on existing model STREADO, a large body of water quality research synthesized in Thomann & Mueller’s 1987 Principles of Surface Water Quality Modeling and Control, and ACUMAR publications. The resulting model was tested against “STREADO”, then calibrated for the Navarrete-Cañuelas streams using data from ACUMAR’s BDH-CMR database. In calibrating the model, a novel set of geospatial data was created. Simulations were then run to determine the Navarrete-Cañuelas sub-basin’s dissolved oxygen and biological oxygen demand profiles under mean and low-flow conditions, and the model’s sensitivity to variability in inputs (particularly sediment oxygen demand and non-point source pollution) were considered. The resulting calibrated model was found lacking for low-flow conditions, but shed light on modeling considerations for a stream such as the Navarrete-Cañuelas, which features shallow waters highly sensitive to changes in stream depth and influent wastes, allowing for recommendations to be developed regarding model refinements. Finally, the plausibility of design recommendations for changes in industrial discharge limits and the introduction of bioswales as interventions for rising non-point-source pollution along the river were briefly discussed, in response to simulations varying point-source and non-point-source pollution inputs respectively. These simulations find that interventions such as bioswales could be effective in addressing non-point-pollution in the headwaters of the Matanza-Riachuelo, simultaneously creating new public green space for residents in the area.