**5. Conclusions**

64 Hydrodynamics – Natural Water Bodies

Fig. 14. Biochemical Oxygen Demand simulations over time

Fig. 15. Dissolved Oxygen simulations over time

The solution obtained for the two-dimensional Saint-Venant and A-D-R equations using an Eulerian-Lagrangian method has great versatility, obtaining consistent and satisfactory results for different types of flow and open channel conditions. The considered scheme provides numerical stability that avoids numerical oscillations of the obtained solutions and also allows significant larger time steps (Δt). The combination with the Eulerian solution for diffusive terms is always guaranteed satisfying the C-F-L condition.

About the hydrodynamics study of Coatzacoalcos river, it was determined that the river behaviour is influenced by several factors, being the most important the hydrological aspect, which varies depending on the time of the year. Because of this, it was observed that dry season presents an important tide penetration towards the mainland of the river, while for rain season when the river flow increase, the penetration is less significant and the water mainly flows downstream to the mouth in the Gulf of Mexico.

On the other hand, the pollutants transport is dominated strongly by the hydrodynamics, and the difference for the two simulated seasons was observed. This simulation shows higher concentrations and also a more significant dispersion in dry season, because the tide penetration occurs intermittently upstream and downstream in the area near to the river mouth. While for rain season there is no significant contaminant dispersion, with a local effect of the simulated discharges.

Thus, a solution algorithm has been proposed to the study open channel hydrodynamics, which together with the A-D-R equation solution allows the study of transport,

**4** 

*Brazil* 

**Challenges and Solutions for** 

**in Rivers in the Amazon Basin** 

*Program in Ecological Sciences of Tropical Biodiversity* 

**Hydrodynamic and Water Quality** 

Alan Cavalcanti da Cunha1, Daímio Chaves Brito1,

*2Universidade de Brasilia. Laboratory of Energy and Environment 3Environmental Analysis and Geoprocessing Laboratory CENA* 

Antonio C. Brasil Junior2, Luis Aramis dos Reis Pinheiro2, Helenilza Ferreira Albuquerque Cunha1, Eldo Santos1 and Alex V. Krusche3 *1Federal University of Amapá - Environmental Science Department and Graduated* 

This research is part of a multidisciplinary research initiative in marine microbiology whose goal is to investigate microbial ecology and marine biogeochemistry in the Amazon River plume. Aspects related to Amazon River fluvial sources impacts on the global carbon cycle of the tropical Atlantic Ocean are investigated within the ROCA project (River-Ocean Continuum of the Amazon). This project is intended to provide an updated and integrated overview of the physical, chemical and biological properties of the continuous Amazon River system, starting at *Óbidos*, located 800 km from the mouth of the river, and interacting to the discharge influence region at the Atlantic Ocean (Amazon River plume). This geographic focal region includes the coast of the State of *Amapá* and the north of *Marajó*

The ROCA project is focused on the connection between the terrestrial Amazon River and the ocean plume. This plume extends for hundreds of kilometres from the river delta towards the open sea. This connection is vital for the understanding of the regional and global impacts of natural and anthropogenic changes, as well as possible responses to climate change (Richey et al. 1986; Richey et al. 1990; Brito, 2010). Different phenomena of interest are typically linked to the quantity and quality of river water (flows of carbon and nutrient dynamics) and the dynamics of sediments. All of them are strongly influenced by substances transport characteristics and water bodies physical properties and physical properties in the water bodies, constrained by spatial distribution of water flow (influenced by bottom topography and coastline of river mouth archipelago) and the unsteady interaction with tides and ocean currents. These very complex phenomena at the Amazon

Based on this framework, river and ocean plume hydrodinamics are fundamental components in the complex interactions between physical and biotic aspects of river-ocean

**1. Introduction** 

archipelago in Northeast Brazilian Amazon.

mouth are still not fully understood.

transformation and reaction of pollutants, being the basis of the water quality model proposed.
