An End User Perspective on the Telemac Suite in Coastal Application

Water Qualit

Morphological development of a small-scale beach nourishment in a non-tidal area

Combining hard and soft costal protection solutions can be an appropriate measure to enhance structure lifetime. This study aims to quantify the morphological evolution of the nourished stretch and adjacent coastlines. A small-scale beach nourishment has been performed in front of a rock revetment at site in Faxe Ladeplads in Zealand, Denmark. The overall objective is to learn more about the dynamics of small-scale nourishments in low energy environments. Monitoring techniques include repeated topographic (Trimble RTK-GPS, drone surveying) and bathymetric (single beam) measurements. To measure the hydrodynamic conditions two surface acceleration buoys deployed at -4 and -7 m water depth were used. Sediment volumes from nourishments of size 70,000 m3 and 20,000 m3 redistributed relatively quickly. The nourished material built up the cross-shore profile and a longshore bar in this area, and distributed sediments in the direction of the dominant littoral drift (SW). Results suggest that the morphological evolution of the nourishment is dependent on local hydrodynamic conditions and local geomorphology. These findings have implications for the main objectives of preventing wave overtopping onto an adjacent coastal road during extreme events and restoring a beach for recreation

Open-access portal with hindcast wave data for Skåne and Halland

Wave climate data for the Swedish provinces Skane and Halland, were hindcast using SWAN, a third-generation spectral wave model. The 40-year wave dataset, from 1979 to 2019, is made available through an open-access data portal (https://gis.sgi.se/vagmodell/). The wave data has a three-hour resolution and includes significant wave height, peak wave period, and wave direction. The wave model domain encompasses the Baltic Sea, Öresund, Kattegat, and Skagerrak. Along the coast of Skane and Halland, the spatial resolution of the computational nodes, from which data can be extracted in the portal, is 250 m. In the offshore areas, the resolution of the computational grid is coarser. The simulated significant wave height was validated against observations from 25 wave gauges, operating intermittently during the simulation period. The coefficient of determination, R2, for these comparisons ranged from 0.46 to 0.93 for the different stations. For 15 wave gauges, R2 values for the comparisons exceeded 0.80. The wave model will continuously be updated and developed

Nature-based shore protection against ship waves in intra-coastal fairways

Sjötrafik har alltid haft en stor betydelse för vårt samhälle genom att transportera gods och människor mellan och inom länder. Transporter till sjöss har stora fördelar associerat till relativt låga klimatutsläpp och transportkostnader. Tyvärr medför sjötrafik även en negativ påverkan på vår miljö. Den negativa påverkan kan till exempel bestå av utsläpp av luftföroreningar, tömning av ballastvatten eller utsläpp av olja. I farleder kan fartyg även inverka på de hydrodynamiska förhållandena genom att generera strömmar och vågor. Fartygsvågor kan resultera i skador på stränder och konstruktioner vid vattnet, öka grumlingen i vattnet, eller till och med innebära en fara för människor som vistas i eller på vattnet. Särskilt stor blir påverkan från fartygsvågor i farleder som naturligt inte utsätts för vindvågor. Det gäller farleder inomskärs, i vattendrag och i sjöar. Fartygsvågor kan här utgöra ett betydande tillskott till de totala vågkrafterna som påverkar stränderna. Om vågorna är tillräckligt stora och frekventa kan de orsaka erosion av stränderna. Denna effekt kan minskas genom att sänka fartygens hastighet, ändra fartygsrutter, begränsa storleken på fartygen eller förstärka stränderna med erosionsskydd. En farled där påverkan av fartygs- och båttrafik varit påtaglig under en lång tid är Furusundsleden i Stockholms skärgård. Furusundsleden är en viktig farled med reguljär trafik av passagerarfärjor till Åland, Finland och Estland. Därutöver trafikeras farleden även av skärgårdstrafik och kryssningsfartyg under sommarhalvåret. Fartygserosionen i Furusundsleden har varit ett uppmärksammat problem ända sedan 1980-talet. Hastigheterna har begränsats för större fartyg med effekten av erosionen avtagit längs farleden. För vissa sträckor har hastighetsbegränsningen dock inte varit en tillräcklig åtgärd för att förhindra erosionen. Därför har tidigare utredningar föreslagit någon form av erosionsskydd längs med dessa stränder. Traditionellt har erosionsskydd i farleder utgjorts av att stränderna har stabiliserats med sten eller betong. Denna metod har i många fall hindrat erosionen av stränderna, men på bekostnad av natur-, landskaps- och rekreationsvärden. De traditionella skydden kräver vanligen mer material och har en hög underhållskostnad. Därför börjar traditionella erosionsskydd alltmer ersättas av naturbaserade lösningar för att motverka erosion. Naturbaserade lösningar innebär att man tar hjälp eller inspireras av naturliga processer för att skapa erosionsskydd som bevarar eller tillskapar värden för naturen och människan. Eftersom naturbaserade lösningar är en relativt ny metodik finns det liten erfarenhet av hur de fungerar som erosionsskydd mot fartygsvågor. Denna avhandling syftar till att undersöka effektiviteten av naturbaserade lösningar som erosionsskydd i farleder och metoder för att beräkna fartygsvågor i farleder med varierande djupförhållanden. För att undersökan effektiviteten av naturbaserade lösningar anlades olika typer av naturbaserade lösningar på tre platser i Furusundsleden, som är belägen i Stockholms skärgård. Två av platserna utgjordes av eroderande moränjord, där en flera meter hög erosionsbrant uppstått. Den tredje platsen utgjordes av ett område där vassen nästintill försvunnit på grund av fartygsvågorna. Olika varianter av naturbaserade erosionsskydd testades. Experimenten visade att en variant där en stenrevel, som löpte parallellt med stranden, kombinerades med vegetation innanför var mest framgångsrik att hindra erosionen. Innanför stenreveln skapades förutsättningar för finare sediment att ackumulera och vegetation att växa. Utöver fältexperimenten med de naturbaserade erosionsskydden innefattar avhandlingen även en ny matematisk modell för att identifiera platser där fartygstrafik kan ge upphov till erosion längs en farled. Modellen är i första hand tänkt att fungera som ett stöd inför beslut om åtgärder i en farled. Det kan vara åtgärder som till exempel att begränsa hastigheten eller identifiera lokaler där behov av erosionsskydd behöver utredas ytterligare

Measurements and analysis of primary ship waves in the Stockholm Archipelago, Sweden

Primary ship waves generated by conventional marine vessels were investigated in the Furusund fairway located in the Stockholm archipelago, Sweden. Continuous water level measurements at two locations in the fairway were analyzed. In total, 466 such events were extracted during two months of measurements. The collected data were used to evaluate 13 existing predictive equations for drawdown height or squat. However, none of the equations were able to satisfactorily predict the drawdown height. Instead, a new equation for drawdown height and period was derived based on simplified descriptions of the main physical processes together with field measurements, employing multiple regression analysis to derive coefficients in the equation. The proposed equation for drawdown height performed better than the existing equations with an R2 value of 0.65, whereas the equation for the drawdown period was R2 = 0.64. The main conclusion from this study is that an empirical equation can satisfactorily predict primary ship waves for a large data set

Shoreline Change in the Kunduchi Beach Area, Tanzania

Coastal erosion is a global problem affecting almost every country in the world having a coastline. This problem is expected to accelerate in the future due to the global warming, which most likely will cause a sea level rise and increase the number of storm events around the globe. The effect from the erosion costs 700 million US dollars each year for the US alone and will increase in the future with the accelerating coastal erosion. The money used for minimizing the effects from the erosion, in a poor country like Tanzania, could instead be used to increase the living and health standards in the country. Kunduchi and the studied coastal stretch of 23 km are situated north of Dar es Salaam in Tanzania on the African east coast. In the 1980´s it was reported about severe erosion in the area. Erosion, resulting in a retreating shoreline, over hundreds of meters on several locations, and the collapse of the Africana Hotel. The setback of the beach has lead to that many of the hotel and house owners have applied different methods of shore protection. Resulting in the building of groins and seawalls, without any expertise, to protect their properties. The purpose of the study is to clarify and quantify the governing sediment transport processes in the area, quantify the historical shoreline movement, and propose suitable mitigation measures to reduce the impact of the erosion. In the present study the theory behind the beach dynamics in the area is studied along with general theories about sediment transport and shoreline formations. An extensive field visit was carried out during July and August 2007 with field measurements of beach profiles and sediment samples. A synoptical study was made of the coastal stretch, which led to an area description. Besides this, visits were made to different organisations and authorities with connection to the area and the current problem. Results from the analysis indicate that the governing transport process in the area is longshore transport. By a numerical analysis the main transport direction along the coast is determined to be north. Further, the shoreline change analysis shows accretion along the shoreline between 1953 and 1981, followed by severe erosion from 1981 until 2005. During 2005 to 2007 there has been accretion that almost has restored the shoreline position. Groins and seawalls have been used as the major mitigation measures in the past. The future recommendation is to utilize beach nourishment instead. Sand can probably be taken from the harbour basin in Dar es Salaam, which would both benefit the repeatedly dredged harbour as well as the Kunduchi beach area. Another recommendation for the future beach management in the area is to start a cooperation between the dwellers in the area, hotel owners, the municipality and the government. The shore protection law should be implemented, which states that no structure should be build within 60 m of the highest shoreline

Decision support tool to mitigate ship-induced erosion in non-uniform, sheltered coastal fairways

The negative impact of maritime traffic in terms of shore erosion in sheltered coastal fairways can be mitigated by sustainable fairway management. Mitigation measures include regulating the ship traffic in terms of speed, routes, or size of ships, but can also involve erosion protection along a fairway. For effective shoreline management of a fairway, it is essential to predict ship waves, to identify sites with potential erosion problems, and to investigate the effectiveness of different measures before implementing them. Several attempts have been made to develop site-specific criteria for managing ship waves. However, few available generic models consider primary waves generated by large ships in confined fairways. Therefore, a tool for supporting decisions in fairway management was developed. The decision support tool is based on simplified formulas for ship- and wind-wave prediction, combined in a framework that enables automatic, rapid assessments on large spatial and temporal scales. Moreover, the tool requires only readily available input data, such as data on AIS, bathymetry, shoreline geometry, wind, fairway centreline, and grain size. The output from the model includes ship and wind wave heights and potential erosion sites. The decision support tool was applied to the Furusund Fairway, Sweden, by simulating one year of ship traffic to validate its capability of identifying potential erosion sites. The simulation demonstrated that the tool was capable of identifying known erosion sites in the fairway. Additionally, scenarios with different speed regulation strategies for the Furusund Fairway were investigated using the decision support tool. Overall, it is concluded that the developed tool enables rapid assessment of ship waves, wind waves, and potential erosion over large areas in fairways

Predicting ship waves in sheltered waterways – An application of XBeach to the Stockholm Archipelago, Sweden

Predicting hydrodynamic forces from ship waves along a waterway is essential for managing a sustainable shoreline in fairways. In this context, a numerical model can be a useful tool for calculating ship waves in fairways with complex geometry. XBeach is a numerical model offering the potential to be a one-tool solution for simulating ship waves from the ship to the shore. However, XBeach has not been evaluated against field measurements of ship waves. Thus, the objective of this paper is (1) to compare XBeach against high-quality field measurements of ship waves and (2) to assess its general applicability to ship wave simulations through an extensive sensitivity analysis with regard to the main input parameters. Water level measurements from 42 passages of the M/S Baltic Princess in the Furusund navigational fairway in the Stockholm Archipelago were chosen to test and evaluate XBeach. The results showed that XBeach was able to generate and propagate the primary and secondary waves. Primary waves were reproduced well with a mean absolute error (MAE) of 3 cm for the drawdown height. The overall secondary wave field pattern was represented by XBeach; however, for the largest, single divergent wave comparison for height, period, and timing showed deviation from the observations. Overall, XBeach was found to be a robust model for ship wave applications, only requiring input data typically available. Sensitivity analysis for a generic hull, derived from the type of vessel studied and with the corresponding dimensions as the real hull, showed similar results enabling robust and reliable simulations without access to detailed technical drawings

The relation between longshore variations in grain size distribution and sediment transport processes

This study investigates the relationship between grain-size distributions and sediment transport processes at Ängelholm Beach in southwest Sweden. In total, 308 longshore and cross-shore distributed sediment samples are analysed with respect to median grain size and sorting. The longshore sediment transport is almost unidirectional from north to south. Its gradients cause erosion in the north and accretion in the south. The longshore transport sorts the sediment, leading to coarsening in eroding areas and deposition of finer sediment in accreting areas. In the eroding part of the beach, the aeolian transport is limited, and the median grain sizes on the beach are coarser than in the dunes. In the accreting part of the beach, where the dunes are prograding, sediment within the range of dune-building grain-sizes is mostly available at the beach. The results support that sediment supply of appropriate grain sizes is an important factor controlling the long-term dune evolution