Performance assessment of the database downscaled ocean waves (DOW) on Santa Catarina coast, South Brazil

ABSTRACT: This work presents a validation of wave parameters from the new sixty years Downscaled Ocean Waves (DOW) reanalysis database. This study compares quantiles of the Gumbel distribution of Hs (significant wave height) and Tp (peak period) from simulated data with an 11 months' time series obtained from a buoy moored seaward on the Santa Catarina coast. Analysis by means of Gumbel distribution quantiles allows more weight to be given to the highest values of the time series, which are especially important in design projects. The statistical parameters used to verify the fit between the measured and the modeled data included: RMSE, BIAS, Scatter Index and Pearson Correlation Coefficient. Mean direction (9m) validation was conducted qualitatively. The database showed good fit of the mean conditions, especially Hs which was well Reproduced by the wave model. Underestimation of Tp, related mainly to the low spatial and temporal resolution of wind data used to generate waves, highlights this general modeling problem. Based on calculated statistical parameters, DOW data were considered comparable to the values obtained by measurements; however, such data must be cautiously used for extreme events analysis and in areas of bimodal sea conditions, where major deficiencies in the database were observed.The authors are also thankful to the Brazilian government through the Ministério do Meio Ambiente (MMA) and the Agência Brasileira de Cooperação (ABC) for the financial support of this research (within the project Transference of Methodologies and Tools to Support the Brazilian Coastal Management)

Comparison between optical and acoustical estimation of suspended sediment concentration: Field study from a muddy coast

The aim of this study is to evaluate the ability of a 1.5 MHz Pulse-coherent Acoustic Doppler Profiler (PCADP) to measure suspended sediment concentration (SSC) in a muddy environment where SSC varies over several orders of magnitude. Two seasonal deployments were conducted south of the Atchafalaya-Vermilion Bay system along the Louisiana coast, USA. During a low discharge period of the Atchafalaya River, acoustical estimates of SSC were in good agreement with OBSs deployed. The second deployment was conducted during a high discharge period of the Atchafalaya River. The passage of a cold front across the coast resulted in a rapid advection of the river plume to the study area. High sensitivity of the OBS to fine-grained suspended sediments led to high values from the OBS readings. On the other hand, the PCADP barely sensed the transportation of fine-grained sediments and significantly responded to the combined wave and current shear stress close to sea bed. To reduce the influence of temporal variation of grain size distribution, acoustical backscatter measurements were calibrated over a time span of a few hours. The resulting SSC estimates from the time-adaptive calibration of the PCADPs were in good agreement with data from OBS sensors. © 2013 Elsevier Ltd