Prediction skill of nearshore profile evolution models

Abstract

[1] The hindcast prediction skill of a beach profile evolution model has been evaluated using bathymetric observations obtained at Duck, North Carolina. The model included coupling and feedback between evolving bathymetry, wave-averaged hydrodynamics, and parameterized cross-shore sediment transport. Statistically optimum predictions were obtained by tuning free model parameters using rigorous inverse methods. When compared to persistence predictions (i.e., substitution of the initial, observed profile at all prediction times), significant prediction skill was found for prediction periods longer than 3 days and shorter than 17 days. The average skill (defined as 1 minus the ratio of prediction to persistence error variances) for a typical 5-day prediction was 0.4, and the maximum skill was 0.8. In contrast to several previously published comparisons with field data, the present approach yielded significant predictive skill during conditions dominated by onshore sediment transport. To make significant predictions, it was necessary to vary model parameters values, which showed a dependence on wave conditions at the seaward boundary of the model domain. Finally, interpretation of the estimated parameter values and prediction skills suggests that (1) errors in existing hydrodynamic models contributed significantly to profile prediction error; (2) a transport model using only second-order statistics of hydrodynamics was as accurate as (and sometimes more accurate than) a typically used energetics model; (3) existing sediment transport models contained significant errors in the formulations describing downslope and bed load transport; and (4) when driving models with observed flow fields, sampling limitations contribute to profile prediction error.

Medium-term dynamics of a middle Adriatic barred beach

“…In fact, though some results on sandbar migration along the Tyrrhenian Sea were recently illustrated (e.g., Parlagreco et al, 2011), the bar dynamics of typical Adriatic sandy beaches have not been already investigated. Further, the correct understanding of the bar migration is important when dealing with beach management and tourism.…”

“…It is worth noting that the observed daily migration rate, i.e., that related to short-term events, of submerged bars in sandy beaches varies in the range (1-50) m day −1 , while the yearly rate, i.e., that related to medium-term events, is in the range (0.1-0.35) m day −1 (van Enckevort and Ruessink, 2003). Such values depend on the storm characteristics, but also on the basin type, hence migration rates in the ocean are generally different from those observed in the sea (see also Parlagreco et al, 2011). Further, the separation between the morphological effects induced by long-term and short-term events is difficult, especially in semi-enclosed basins like the Adriatic Sea, which is characterized by an extremely variable climate, with significantly large deviations of the wave characteristics from the mean values, even during a storm.…”

“…While numerical simulations well reproduced the offshore migration during severe conditions, some difficulties arose when reproducing the onshore bar motion during mild wave conditions (Gallagher et al, 1998;Plant et al, 2004), suggesting that not all processes involved in the bar migration were clearly understood and correctly simulated, e.g., lowerfrequency waves. Further, Ruessink et al (1998), who analyzed the cross-shore sediment transport and morphological changes occurring in the nearshore area of Terschelling (the Netherlands), stated that the role of the infragravity waves has not been completely understood.…”

Recurrent neural network modeling of nearshore sandbar behavior

“…Existing knowledge is incomplete and, accordingly, process models struggle to reproduce natural bar behavior on timescales of a few days to weeks (Plant, Holland, & Puleo, 2004;Van Rijn et al, 2003) and have uncertain skill on longer scales (Roelvink, Meijer, Houwman, Bakker, & Spanhoff, 1995;Van Rijn et al, 2003). While most models are, to some extent, capable of predicting the rather rapid offshore sandbar migration under breaking waves (1-20 m day −1 ), they fail to reproduce the subsequent recovery of a beach profile (e.g., onshore bar migration, <1-5 m day −1 ) under relatively quiescent wave conditions, possibly because of missing relevant processes.…”

Space-Time Resolved Experiments for Water Waves

“…Our space-time measurement allows to experimentally measure the joint space-time power spectrum iments. Indeed, it has been observed numerically [33] and experimentally [34,35] …”