N. W. H. Allsop

Bio: N. W. H. Allsop is an academic researcher from HR Wallingford. The author has contributed to research in topics: Armour & Shallow water equations. The author has an hindex of 9, co-authored 28 publications receiving 618 citations.

Influence of parapets and recurves on wave overtopping and wave loading of complex vertical walls

Abstract: Increasing sea water levels and storminess has intensified the need for structural measures to reduce wave overtopping without significantly raising the height of the wall. The use of recurves, wave return walls, and parapets on vertical walls has been shown capable of significantly reducing wave overtopping, but may increase wave loading. Many parapet and recurve solutions have been used in practice, but no general guidance on their design are yet available. In this paper a significant amount of data have been gathered together under the EC CLASH project (EU project no. EVK3-CT-2001-00058) and studied more systematically for the first time. This paper discusses problems with systematic approaches to both overtopping and wave loading. It concludes with a simple reduction factor for wave overtopping depending on geometrical dimensions of the parapets and some guidance on wave loading for these cases.

EurOtop, European Overtopping Manual - Wave overtopping of sea defences and related structures: Assessment manual

Abstract: The manual has been intended to assist engineers who are already aware of the general principles and methods of coastal engineering. The manual uses methods and data from research studies around Europe and overseas so readers are expected to be familiar with wave and response parameters and the use of empirical equations for prediction. Users may be concerned with existing defences, or considering possible rehabilitation or new-build.

Sea-level rise induced amplification of coastal protection design heights

Abstract: Coastal protection design heights typically consider the superimposed effects of tides, surges, waves, and relative sea-level rise (SLR), neglecting non-linear feedbacks between these forcing factors. Here, we use hydrodynamic modelling and multivariate statistics to show that shallow coastal areas are extremely sensitive to changing non-linear interactions between individual components caused by SLR. As sea-level increases, the depth-limitation of waves relaxes, resulting in waves with larger periods, greater amplitudes, and higher run-up; moreover, depth and frictional changes affect tide, surge, and wave characteristics, altering the relative importance of other risk factors. Consequently, sea-level driven changes in wave characteristics, and to a lesser extent, tides, amplify the resulting design heights by an average of 48–56%, relative to design changes caused by SLR alone. Since many of the world’s most vulnerable coastlines are impacted by depth-limited waves, our results suggest that the overall influence of SLR may be greatly underestimated in many regions.

Coastal flooding: impacts of coupled wave-surge-tide models

Abstract: Wind waves and elevated water levels together can cause flooding in low-lying coastal areas, where the water level may be a combination of mean sea level, tides and surges generated by storm events. In areas with a wide continental shelf a travelling external surge may combine with the locally generated surge and waves and there can be significant interaction between the propagation of the tide and surge. Wave height at the coast is controlled largely by water depth. So the effect of tides and surges on waves must also be considered, while waves contribute to the total water level by means of wave setup through radiation stress. These processes are well understood and accurately predicted by models, assuming good bathymetry and wind forcing is available. Other interactions between surges and waves include the processes of surface wind-stress and bottom friction as well as depth and current refraction of waves by surge water levels and currents, and some of the details of these processes are still not well understood. The recent coastal flooding in Myanmar (May 2008) in the Irrawaddy River Delta is an example of the severity of such events, with a surge of over 3 m exacerbated by heavy precipitation. Here, we review the existing capability for combined modelling of tides, surges and waves, their interactions and the development of coupled models.