Hans Hanson

MODERN FUNCTIONAL DESIGN OF GROIN SYSTEMS

A special reflecting wall 12 m long and 2.1 m high was built off the beach at Reggio Calabria, and 30 wave gauges were assembled before the wall and were connected to an electronic station on land. It was possible to observe the reflection of wind waves generated by a very stable wind over a fetch of 10 Km. The experiment aimed to verify the general closed solution for the wave group mechanics (Boccotti, 1988, 1989), for the special case of the wave reflection.Significant features on Wadden Sea wave climate are evaluated in respect of the state of the art. Main emphasis was laid on an analysis of the governing boundary conditions of local wave climate in island sheltered Wadden Sea areas with extensions being sufficient for local wind wave growth. Explanatory for significant wave heights a reliable parametrization of local wave climate has been evaluated by using generally available data of water level and wind measurements.

Coastal Evolution Modeling at Multiple Scales in Regional Sediment Management Applications

Abstract : A numerical model called GenCade is introduced that simulates shoreline change relative to regional morphologic constraints upon which these processes take place. The evolution of multiple interacting coastal projects and morphologic features and pathways, such as those associated with inlets and adjacent beaches can also be simulated. GenCade calculates longshore sediment transport rates induced by waves and tidal currents, shoreline change, tidal inlet shoal and bar volume evolution, natural bypassing, and the fate of coastal restoration and stabilization projects. It is intended for project- and regional-scale applications, engineering decision support, and long-term morphology response to physical and anthropogenic forcing. Capabilities of the model are illustrated by an application to the south shore of Long Island, NY. The Long Island application has multiple coastal structures and features that are maintained to varying degrees of frequency. Cumulative response of the beaches from a variety of coastal projects leads to complexity in regional coastal management. GenCade is presented as a tool to unify management of local projects at regional scales.

A New Approach to Represent Tidal Currents and Bathymetric Features in the One-Line Model Concept

The GENESIS model has been widely used for predictions of long-term shoreline evolution along wave-dominated open-coast beaches. However, to be applied in the vicinity of coastal inlets new capabilities needed to be implemented. This paper describes two new capabilities recently implemented in the model. The first is the extension of the model to calculate the longshore sediment transport rate by means of a generalized version of the Bagnold formula (1963) which makes it possible to describe longshore transport and shoreline change originating from multiple sources of a longshore current, such as wind and tide. The second is provision for inclusion of a pre-specified offshore contour to allow dominant local or regional bathymetric features to be represented in the wave transformation. Illustrative examples indicate promising results for these major enhancements of the model. INTRODUCTION Significant offset between upand down-drift beaches are typically found adjacent to inlet jetties where a dominant direction of longshore sediment transport exists. Down-drift beaches are often suffering from chronic erosion and in need of remedial measures. Several remediation measures have been proposed and implemented for reducing erosion and increasing the longevity of material placed in such hot spots. These include lengthening the down-drift jetty, placement of an external spur 1) Department of Water Resources Engineering, Lund University, Box 118, Lund, Sweden S-221 00. Email: Hans.H~.nson@,tvd.lth.se. 2) U.S. Army Engineer Research and Development Center, Coastal and Hydraulics Laboratory, 3909 Halls Ferry Rd., Vicksburg, MS 39180.

Modeling regional sediment transport and barrier elongation at Long Island coast, United States

A new numerical model of regional sediment transport and barrier elongation, supplied by sediment coming from longshore sediment transport (LST), was developed. The spit growth and barrier elongation model was based on the model proposed by Kraus (1999). The LST rate used as input for the spit growth and barrier elongation model was simulated by the one-line model of shoreline change (Hanson, 1987) combined with the inlet reservoir model (Kraus, 2000; Larson et al., 2006). The model was applied to field data from the south coast of Long Island, United States. The simulation results were compared with measurements of the annual net LST rate and the barrier elongation. Overall, the model simulations were in good agreement with the measured data.

Sheet flow and suspension under wave groups in a large wave flume (SISTEX99)

Detailed measurements of sediment concentrations in the sheet flow layer and in the suspension layer for flat bed conditions under prototype wave groups are presented. These measurements are part of experiments on near-bed sand transport processes, carried out in the Large Wave Flume in Hannover, Germany (SISTEX99). The results show that concentrations in the sheet flow layer are highly coherent with the instantaneous near-bed velocity. In the suspension layer, however, concentrations respond much slower to changes in near-bed velocity: at some distance from the bed concentrations increase and decrease on the time scale of the wave group, with a time delay relative to the peak wave within the wave group.