Tony Dolphin

The offshore breakwater scheme at Sea Palling, England: sand transport generated by tidal currents

The interaction between the alongshore, progressive wave tidal currents and the tidal tombolos existing in the lee of the shore parallel breakwaters at Sea Palling, Norfolk, UK, was examined. The TELEMAC2D and ARTEMIS hydrodynamic models were used to simulate tidal flows and waves conditions through the system, determining bed shear stresses and resultant sand transport during a spring-neap-spring cycle. Fieldwork measurements were used to validate the model results and propose values for the relative magnitude of sand transport occurring during calm, low-amplitude wave conditions. These occur as a background to much higher energy, at-shore wave events, the time series analyses of which, have previously been used to evaluate the regional sediment budget.

Use of GPS and X-Band Radar to track tidal currents around the shore parallel breakwaters at Sea Palling, Norfolk, UK

ABSTRACT Phillips, R., Vincent, C.E., Bell, P.S., Dolphin, T., and Bacon, J., 2013. Use of GPS and X-Band Radar to track tidal currents around the shore parallel breakwaters at Sea Palling, Norfolk, UK Sea Palling on the East coast of the UK has a series of 9 shore parallel rock breakwaters. The numerical model TELEMAC2D has been used to simulate tidal currents around the system to assess the tidal contribution to sediment budgets and transport pathways. Numerical simulations are particularly useful for identifying the important processes involved in a complex system such as these breakwaters and understanding how the breakwaters might effect the local coastal region. Models are classically evaluated using a number of measurement stations to calibrate and then check it is giving realistic results. It is important to assess both the spatial and temporal performance of a model, but this is difficult with a model having tens of thousands of nodes, based on only a few discrete locations. This paper presents a method using Lagrangian data to assess confidence that can be applied to model performance. Measurements were made by deploying drogues tracked by X-band radar or GPS receivers throughout the breakwater system during calm “no wave” and “no wind” conditions to ensure that only tidal effects were measured. Modelled deployments were made at coincident times and locations for comparison and model performance statistics were calculated. Evidence of a number of features predicted by the model were found, giving confidence to its performance. Radar drogues are cheap to make and data capture onshore reduces the risk of data loss. GPS drogues can be used in a wider spatial area, however their onboard data storage requires drogue retrieval for data download.

Velocity of RFID Tagged Gravel in a Non-uniform Longshore Transport System

ABSTRACT Dolphin, T.; Lee, J.; Phillips, R.; Taylor, C.J.L., and Dyer, K., 2016. Velocity of RFID tagged gravel in a nonuniform longshore transport system. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 363–367. Coconut Creek (Florida), ISSN 0749-0208. Radio-frequency Identification (RFID) tags were embedded into 940 native beach gravel particles and deployed at source on Benhole Beach (Somerset, UK) to develop an understanding of gravel transport along a frontage that is likely to be subjected to construction activity associated with the proposed development of the Hinkley Point C power station. The study lasted for three years, the longest of its kind to be published, and maintained high detection rates (78% on completion) typical of RFID experiments. Tracer distribution through time highlighted non-uniformity in the longshore transport system and that a single average or centroid velocity is meaningless, as it cannot account for alongshore variability – instead methods that can account for alongshore variability in the transport system were needed. Spatial patterns in the density of detected tracer revealed transport pathways. Alongshore variation in tracer velocity was linked to changes in the geomorphology: (i) tracer velocity was slowest over beaches, owing to increased surface roughness, burial and deposition at high elevations; (ii) velocity rose/fell with changes in coastline orientation and wave obliquity; and (iii) the highest velocities were found in areas of exposed smooth rock platform; however small ridges (up to 40 cm) in the rock platform and angular blocks derived from cliff and platform erosion led to significant reductions.

MEASURED AND PREDICTED SUSPENDED SAND TRANSPORT ON A SANDY SHOREFACE

This paper describes on site field measurements of sand transport with two different types of instruments at 13 m water depth at a location 2 km off the coast of Noordwijk aan Zee, The Netherlands. The measurements are compared with results from four practical model combinations using different predictors for the combined current and wave-related shear stress, the reference concentration and the wave boundary layer thickness. Measurements are also compared with results from the Bailard suspended load sand transport model. Best overall predictions of the measured suspended transport rates are made with the Bailard model. Read More: http://ascelibrary.org/doi/abs/10.1061/40855%28214%2986