In: III Simpósio Brasileiro de Oceanografia, 2008, São Paulo. Oceanografia e Mudanças Globais. São Paulo : Instituto Oceanográfico da USP, 2006, 545-558. 545 Numerical simulation of the hydrodynamic in the Curimataú estuary, RN Brazil Fernando Pinheiro Andutta 1 , Luiz Bruner de Miranda 1 , Belmiro Mendes de Castro 1 , Roberto Fioravanti Carelli Fontes 2 & Carlos Augusto Ramos e Silva 3 1. Oceanographic Institute, University of São Paulo, Cd. Universitária, Praça do Oceanográfico, 191, São Paulo, Brazil, CEP 05508-900. andutta@io.usp.br, miranda@io.usp.br, bmcastro@usp.br 2. São Vicente Campus, São Paulo State University, Pça Infante Dom Henrique s/n, São Vicente, SP, Brazil, CEP 11330-900. rcfontes@csv.unesp.br 3. Departamento de Oceanogafia e Liminologia da UFRN, Natal. CEP 59075-970, Brazil caugusto_99@yahoo.com Abstract The Curimataú River estuary is a shallow partially mixed (type 2) tropical estuary, located in the Rio Grande do Norte (RN) state, northeast Brazilian coast (lat. 06 o 18’S); the main system is composed by three rivers: Curimataú, Cunhaú and Guaratuba. The numerical model Delft3D-Flow was used to study hydrodynamic features of the estuary. The model predictions were evaluated using the Skill parameter based in the comparison of the theoretical solutions with observations of hourly values of tidal heights, currents and salinity at an anchor station located at the cell (M=279; N=323). The applied computational grid is curvilinear with around 6,000 horizontal wet points, including the inner shelf. Open boundary conditions was obtained from the analysis of 2.7 years of hourly tidal heights, recorded at Natal harbor, and the inner boundaries conditions were controlled by freshwater input into the three main rivers. Initial conditions of hydrographic properties were uniform in the previous simulations and, only the temperature was set to a constant value in whole simulation. The steady-state of the fields of velocity and thermohaline properties was reached after almost four weeks of simulation of the baroclinic mode. The best fit between the model and the observations was for the semidiurnal spring tide oscillation with a Skill=0.98; for the velocities and salinities simulations during this tidal condition the best mean Skills values were 0.82 and 0.94, respectively. Key words: Curimataú estuary, circulation, numerical model, validation. 1. INTRODUCTION The Curimataú river estuary (lat. 06 o 18’S) in the Rio Grande do Norte state (RN), in the northeastern tropical region, is a coastal plain tropical estuary oriented in a SW-NE direction (Fig. 1). The Curimataú river estuary is driven by semidiurnal mesotidal with ranges at the river mouth over 2 m during spring tides and the main river source is located in the Paraiba state (PA) with a drainage basin with an area of 3,589 km 2 , but only 830 km 2 of them within RN state. It is shallow (<10 m), being 500 m wide and deeper near the mouth ( 10 m) at high water, were alongshore barrier reefs are located (Fig. 1). Inshore the reefs, sedimentation and erosion due to the action of tidal currents are very intense and sand banks are exposed during low water. Almost 2 km up, the estuary widens out to 1,800 m at high water and is characterized by a central channel with a depth of 7 m. On the left and right margins wide shallow sand banks may be observed during the low tides and, near the confluence with the Cunhaú river, the main channel narrows to almost 300 m. Due to the erosion, transport and deposition processes linked to the evolution of coastal regions and adjacent beaches, a comprehensive study on the morphology of the estuarine environment, under the influence of the Curimataú river, was presented by Souza (2004) based on bathymetry, echo-sounding, sediment sampling, orbital and acoustic remote sensing imagery.