Morphological Modelling of a Nourishment at the Brouwersdam Beach
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Morphological modelling of a nourishment at the Brouwersdam beach R.A. Schrijvershof, BSc. This report is produced as part of the project KPP B&O Kust 1220040-000 © Deltares, 2015, B Title Morphological modelling of a nourishment at the Brouwersdam beach Client Project Pages Universiteit Utrecht 1220040-000 45 Rijkswaterstaat Zee en Delta Keywords Brouwersdam, morphology, nourishment, UNIBEST-CL+ Summary In the scope of an internship project for the Earth Surface and Water (ESW) master’s programme of Utrecht University a modelling study is performed with the UNIBEST-CL+ coastline model. The study aims at modelling different configurations for the planned nourishment, and it this way, establish a configuration that maximizes the ‘life-expectancy’ of the nourishment. Four different shapes in planform geometry and the effect of varying grain sizes of the used sediment are modelled. Results show that an UNIBEST coastline model is capable of reproducing the observed trends and magnitudes of coastline change if a modified Van Rijn (2004) sediment transport formula is used and a scaling factor of 1.5 in time is applied. The simulations with the nourishments show that different nourishment shapes cause different erosion rates and that if the coastline is positioned further from the original coastline, retreat will increase. The varying grain size diameter simulations shows that an increase in median diameter of sediment (D50) of 25 μm will decrease the retreat rate of the coastline with ~7 m and the decrease in surface area with 5000 m2 after 10 years. Version Date Author Initials Review Initials Approval Initials 1 27 March Reinier R.A. Dirk-Jan Walstra D.R. 2015 Schrijvershof Marian Lazar M. 2 10 April Reinier R.A. Dirk-Jan Walstra D.R. Claire van C. 2015 Schrijvershof Oeveren State final Morphological modelling of a nourishment at the Brouwersdam beach 10 April 2015, final Contents 1 Introduction 3 1.1 Background 3 1.2 Organisation 3 1.3 Aim of the present report 3 1.4 Definitions 4 1.5 Outline 4 2 Problem analysis 5 2.1 Project location 5 2.2 History of the Grevelingen estuary 5 2.3 Morphological developments 7 2.3.1 The ebb delta 7 2.3.2 The beach 11 2.4 Beach nourishment 14 2.5 Research questions 15 3 Data and modelling 16 3.1 Wave modelling with Delft3D-WAVE 16 3.1.1 Offshore wave climate 16 3.1.2 Bathymetry 17 3.1.3 Computational grids 17 3.2 Morphological modelling with UNIBEST-CL+ 20 3.2.1 Longshore Transport (LT) module 20 3.2.2 CoastLine (CL) module 21 3.2.3 Nourishment configurations 23 4 Results 25 4.1 Wave climates 25 4.2 Hindcast simulations 27 4.3 Forecast simulations 29 4.3.1 Without nourishment 29 4.3.2 Nourishment simulations 30 5 Discussion 34 6 Conclusions 36 6.1 Conclusions 36 6.2 Recommendations 36 References 37 Appendices 38 Morphological modelling of a nourishment at the Brouwersdam beach 1 of 45 10 April 2015, final List of figures Figure 2.1: Location of the Brouwersdam beach (c), in the Netherlands (a), at the border of the provinces Zuid-Holland and Zeeland (b) (sources: www.d-maps.com, Google Earth, Rijkswaterstaat vaklodingen) ........................................................ 6 Figure 2.2: Tidal currents in the ebb tidal delta of the Grevelingen estuary in 1964 (a) and in 2010 (b). E = ebb-dominant flow, F = flood-dominant flow, W = Wave- dominated (Nipius, 1998; from de Jongste et al., 2013) ...................................... 7 Figure 2.3: Bathymetry of the Grevelingen ebb delta for the period 1964 – 2010 ................... 10 Figure 2.4: Momentarily coastline position through time .......................................................... 13 Figure 2.5: For the period 1990 – 2014: (a) rates of coastline development along measuring lines in Figure 2.4; (b) change of beach surface area; (c) visualization of the calculation of beach volume; and (d-f) total beach volumes with varying boundaries. (source: JARKUS)........................................................................... 14 Figure 3.1: Delft3D-WAVE computational grids: (a) the coarse ‘zeeland’ grid (blue) with the nested medium ‘Brouwersdam’ grid (red), (b) the ‘Brouwersdam’ grid with the nested high resolution ‘Noordzeestrand’ grid (green). ....................................... 19 Figure 3.2: UNIBEST coastline model of 2005 (a) and 2014 (b) .............................................. 22 Figure 3.3: Nourishment types (Google Earth) ......................................................................... 23 Figure 4.1: Wave simulation results modelled on the 2004-2006 bathymetry (left) and the 2004-2010 bahtymetry (right) for offshore wave scenario 84 (a and b), scenario 42 (c and d), and scenario 78 (e and f) .............................................................. 26 Figure 4.2: Overview of JARKUS transect locations ................................................................ 27 Figure 4.3: Observed and simulated coastline development for the period 2005 – 2014 with different sediment transport formulae ................................................................. 28 Figure 4.4: Observed and simulated coastline development for the period 2005 – 2014 with the modified Van Rijn (2004) sediment transport formula .................................. 29 Figure 4.5: Coastline change in the period 2014 – 2023 .......................................................... 30 Figure 4.6: Coastline development for different nourishment types ......................................... 31 Figure 4.7: Nourishment surface area development for different nourishment types .............. 31 Figure 4.8: Decrease in surface area for different grain sizes ................................................. 32 Figure 4.9: Effect of grainsize on (a) coastline retreat and....................................................... 33 Figure 5.1: Development in surface area for nourishment ....................................................... 35 List of tables Table 3.1: Classification of offshore wave conditions (after Huisman and Luijendijk, 2009) ... 17 Table 3.2: Sediment transport settings for Van Rijn (2004) ..................................................... 21 Table 3.3: Simulation runs with settings ................................................................................... 24 Table 4.1: Nourishment development statistics ........................................................................ 30 Table 4.2: Fit functions of Figure 4.9 ........................................................................................ 33 2 of 45 Morphological modelling of a nourishment at the Brouwersdam beach 10 April 2015, final 1 Introduction 1.1 Background The Rijkswaterstaat Coastal Maintenance programme 2012 – 2015 (Dutch: Programma Kustlijnzorg 2012 – 2015) has included a beach nourishment at the south-western side of the Brouwersdam beach. The beach at this location is not included in the, in 1990, established basic coastline (BKL; BasisKustlijn) due to the presence of the dam at this location. Therefore, maintenance of the beach is usually not carried out by Rijkswaterstaat. However, extensive lobbying of stakeholders and a financial contribution of € 250,000 from the concerned provinces and municipalities has enabled the option for a single-time nourishment. This nourishment will consist of a volume of 500.000 m3. A volume of 400.000 m3 became available after shifts in the nourishment programme at the Schouwen-Duiveland (Zeeland) coast, in the context of the PINK (Pilot Innovatief Nederlands Kustbeheer) programme. This nourishment will enable the opportunity for stakeholders to benefit for a longer period of time from the beach and it is therefore important to investigate if there are any feasible measures that will increase the ‘life-expectancy’ of the nourishment. This report describes the study that is concerned with the morphological modelling of the nourishment with the UNIBEST-CL+ coastal modelling package. Previous work discussing the morphological developments of the beach at the Brouwersdam is Lazar (2007) and Wang (2010). Morphological modelling of the beach at the Brouwersdam has been executed before by Witteveen+Bos (2012) and Huibregtse (2013). Witteveen+Bos (2012) made an assessment on the expected morphological developments of the Grevelingen outer delta (including the beach) as response to the construction of a second tidal inlet system in the northern part of the Brouwersdam. Huibregtse (2013) focussed on modelling the expected morphological developments of the beach without any mitigation measures to be taken. This work was carried out with the UNIBEST-CL+ model and therefore the present research continues on the work of Huibregtse (2013). 1.2 Organisation The present report is produced as final product of an internship for the Earth Surface and Water (ESW) Masters programme of the Department of Physical Geography, at the Faculty of Geosciences, Utrecht University. The internship was carried out at Deltares, Delft. Here, the daily supervision was done by ir. D.R. Walstra and ir. B. Huisman was involved as expert in the UNIBEST modelling package. Supervision from Utrecht University was done by prof. dr. B.G. Ruessink. Furthermore, ir. M. Lazar. was involved in the project from Rijkswaterstaat Zee en Delta. 1.3 Aim of the present report The present study is concerned with the morphological modelling of several (feasible) configurations that can be implemented for the planned nourishment at the Brouwersdam beach. The report elaborates on the problem and quantifies the observed erosional patterns. The methods