Modelling dune erosion, overwash and inundation of barrier islands

Physical model experiments are performed at Deltares to investigate the morphological response of barrier islands on extreme storm events. The experiments included dune erosion, overwash and inundation regimes. Extensive measurement techniques made detailed comparison with numerical models possible. This paper describes the comparison between the physical model results and the numerical morphodynamic model XBeach. It appeared that XBeach simulates the main characteristics in hydro- and morphodynamics at profiles with shallow foreshores, which are characteristic for barrier islands, well. However, the absolute results of especially the overwash experiments still do not agree with the measurements. It is expected that several generic issues regarding small-scale physical model experiments are of influence here. Nevertheless, calibration of the XBeach model seems to be necessary for shallow profiles. Especially the calibration of the wave characteristics on the shallow foreshore, related to the morphodynamics is far from trivial.Hydraulic EngineeringCivil Engineering and Geoscience

Ingleses - Brazil: Solutions to urban problems due to coastal morphology

Master project report. This report describes the research done by the authors to the erosion and dune migration problems in the town Ingleses. Ingleses is located in the north of Ilha Santa Catarina in Brazil. This report describes a follow-up research on the research in 2007 of project group CF71 from Delft University of Technology. The beach erosion in the embayed beach threatens the buildings at the southern stretch of the beach. Furthermore, a large dune field, Moçambique Dune, is migrating towards the north and encroaches houses in the southern part of Ingleses. The aim off this report is to give better insight in the problem and present a solution. Research has been done to investigate the migration speed of the dune and the erosion rate of the beach. This is done by a photo analysis. Aerial photographs from several years and a Geographical Information System are used for this purpose. The average migration speed since 1938 of Moçambique Dune is a little more than three meters per year. In the southern part of Ingleses, the beach erodes one to two meters per year since 1960. The zero-solution is also a part of this research. Using the migration speed of the dune, the damage is quantified in case no measures are taken. Also the damage at the coast is quantified with the use of the erosion rates. Especially the damage at the coast will be significant. This zero-solution is a reference situation for the solution presented in this report and gives insight in the scale of the problems. A maximum loss of 1,5 million euro’s per year is expected in case no actions are taken. The solution presented in this report is a beach nourishment. For the nourishment, sand will be used from Moçambique Dune. This way, two problems are solved at the same time. For the design fill a beach width of 38 meter will be constructed. Also an advanced fill is calculated for a design lifetime of 10 years. The design fill is calculated with the erosion rates calculated with the photo analysis. The fill sand from the dune is coarser then the sand from the native beach. For this reason the beach will be steeper after the nourishment. In the report the construction method for the nourishment is also considered. Two construction methods are elaborated, the use of trucks and the use of pumps and pipelines. For both methods an estimation is made for the construction time and the construction costs. Both construction methods are compared in a Multi Criteria Analysis (MCA). In this comparison the pipelines turned out to be the better method. However, this method is more expensive. The zero-solution and the nourishment are also compared in a MCA. In this comparison the nourishment turned out to be the better solution. The nourishment is also the cheaper solution. Another aim of this project is the improvement of the numerical model made in 2007. Some scenarios are modelled in this research. The first scenario is the situation from 1938 when the sand from Moçambique Dune was an input of the system. Other scenarios are investigated to analyze the bypass at the northern headland. Finally, the scenario with the designed nourishment is modelled. The numerical model appeared to still be extremely sensitive to several parameters that still are not well-known like the wave characteristics and sediment bypass. Further extensive research to these parameters is necessary in order to obtain a reliable model. During this research a lot of additional data about the coastal system around Ingleses is collected and analyzed. Assumptions are verified and a better insight in several important parameters is given. It is concluded that a nourishment is a suitable and feasible solution for the erosion problems. The sand from the Moçambique Dune can be used for this nourishment which is a suitable solution for the encroachment problems as well.Hydraulic EngineeringCivil Engineering and Geoscience

Exploring marine and aeolian controls on coastal foredune growth using a coupled numerical model

Coastal landscape change represents aggregated sediment transport gradients from spatially and temporally variable marine and aeolian forces. Numerous tools exist that independently simulate subaqueous and subaerial coastal profile change in response to these physical forces on a range of time scales. In this capacity, coastal foredunes have been treated primarily as wind-driven features. However, there are several marine controls on coastal foredune growth, such as sediment supply and moisture effects on aeolian processes. To improve understanding of interactions across the land-sea interface, here the development of the new Windsurf-coupled numerical modeling framework is presented. Windsurf couples standalone subaqueous and subaerial coastal change models to simulate the co-evolution of the coastal zone in response to both marine and aeolian processes. Windsurf is applied to a progradational, dissipative coastal system inWashington, USA, demonstrating the ability of the model framework to simulate sediment exchanges between the nearshore, beach, and dune for a one-year period. Windsurf simulations generally reproduce observed cycles of seasonal beach progradation and retreat, as well as dune growth, with reasonable skill. Exploratory model simulations are used to further explore the implications of environmental forcing variability on annual-scale coastal profile evolution. The findings of this work support the hypothesis that there are both direct and indirect oceanographic and meteorological controls on coastal foredune progradation, with this new modeling tool providing a new means of exploring complex morphodynamic feedback mechanisms.Coastal Engineerin

A comprehensive sediment budget for the Mississippi Barrier Islands

In order to conceive any realistic plan for post-Katrina island restoration, it is necessary to understand the physical processes that move sand along the littoral drift zone off the coast of Mississippi. This littoral zone influences the character of the Mississippi barrier islands as they exist in an ever changing cycle. To help in this understanding, a sediment transport model was conducted to establish a current sediment budget for the islands. This study evaluated the existing regional sediment transport magnitudes and directions for the Mississippi and Alabama barrier islands fronting Mississippi Sound including daily conditions and hurricanes. A method was developed to incorporate all relevant hurricanes from 1917 to 2010 in the analysis. For the long term average net longshore transport along the southern shorelines of the barriers (i.e. exposed to the Gulf of Mexico), the contribution of year averaged conditions and hurricanes are of similar order of magnitude, although the mean annual percentage occurrence of hurricanes is no more than about 3%. Along the northern shores (Mississippi Sound side) the transport is considerably smaller and the contributions of cold fronts and hurricanes to the sediment transports are more or less equal. For the year-averaged conditions (excluding hurricanes) a westward directed net transport is found. The net effect of the historic hurricanes is also westward in direction. However, for individual hurricanes (e.g. Camille and Katrina) the net transport along Ship Island can be directed eastward due to the dominance of ebb flows after the eye of the hurricane had passed.Hydraulic EngineeringCivil Engineering and Geoscience