Two-dimensional hydrodynamic models are increasingly common in riverine research and management. However, input data are not standardized among studies, and assessments of model performance are uncommon, which hinder interpretation of model results and comparisons among studies. Herein, we describe a framework for two-dimensional hydrodynamic model input data collection, model calibration and validation to evaluate model predictions. We present a logical process for the validation of depth and velocity that recognizes the inherent spatial uncertainty in the field measurements and modelling results. The hydrodynamic model we present as an example shows agreement between predicted and observed water surface elevation, area of inundation and spatial distributions of depth and velocity at calibration and independent validation discharges. If this model development and assessment framework was adopted by others, it would allow comparison between studies and provide a foundation for establishing model performance standards. Figure 6. Longitudinal water surface elevation plot comparing predicted (open circles) with observed (filled circles) values at T1 study site at a discharge of 58.1 m 3 s À1 (n = 719, RMSE = 0.0346).This was a discharge used for calibration K. A. WRIGHT ET AL.

Squalls are one of the main issues for the design of West Africa floating units mooring systems. At the present time and due to the lack of more relevant information and models, squalls are represented by on site time series of time varying wind speed and relative heading. The first FPSO units were designed on the basis of a reduced Squall database. Nowadays, the number of squall records has been significantly increased and a response based analysis can be carried out. The present paper is focused on the Gulf of Guinea environment. The area has been divided into two zones: North (Nigeria…) and South (Congo, Angola…). This approach enabled us to deal with 90 Squall events for North zone and 115 Squall events for South zone. Two different mooring systems, with quite different natural periods, have been investigated in order to cover the range of already installed spread moored FPSO’s. For every Squall of the database, time domain and modal simulations have been carried out in order to obtain the maximum values of the axial tension in mooring lines and of the offset of a standard spread moored unit. Then a statistical procedure is applied a) to estimate 100-year return period values for these parameters and b) to assess overall trends besides the differences between results from both zones and both mooring systems. A comparative study has also been carried out to relate the 100-year return period extrapolations with the values derived from classical design procedures in order to evaluate the potential design margins for extreme responses. Finally, areas needing further investigation are identified.

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