Wave transformation across a rock platform, Belinho, Portugal

Much is known about wave attenuation across sandy nearshore environments or coral reef platforms. Limited field work has aimed to measure and assess attenuation across rock platforms. We designed and implemented a field experiment at Belinho, Portugal, to address this need. Field work was conducted in June, 2006, over a sequence of five tidal cycles. We deployed a shore-normal array of seven KPSI pressure transducers, installed 0.15 m above the bed and spaced between 10 and 15 m apart, to measure surface water levels. When all instruments were submerged by the rising tide, they were sampled at 20Hz.. The instrument array spanned the inter-tidal platform composed of schist. The surface, about 70 m wide, is irregular and cut by many shore perpendicular channels. To assess the attenuation and transformation of waves across this surface as a result of shoaling and breaking, we derived spectral estimates of wave height and period through each high tide series. Wave heights at the outermost PT ranged between about 0. 4 to 0.9 m. At the innermost PT, corresponding values were 0.5 to 1.14 m. Wave periods averaged about 10 s through the study. Our results showed that a breaking criterion of 0.42 + c fit our data.