Swash Processes and Dune Erosion: Emphasis on Vessel-Generated Waves

Abstract

In navigable waterways, owing to the relatively short fetches for wind wave generation, the free waves generated by moving vessels often produce the dominant wave action with respect to erosion of the shore. In response to the fairly recent introduction of high-speed ferries, combined with a planned expansion within the passenger- and car-carrying ship market, the need to model and predict coastline changes as a result of exposure to vessel-generated waves has become a topic of increased research. Although several studies have been and continue to be conducted, the research on the impact of these types of waves on the shore is still in its early stages.



In response, this study was initiated with the objective to generate state-of-the-art technical guidance and modeling tools for quantifying cross-shore profile changes near and above the shoreline caused by vessel-generated waves. To fulfill the objective, the behavior of vessel-generated waves along the coast and their effect with regards to beach and dune erosion were investigated.



Several independent, but inter-related studies were conducted for this thesis. One study presents a method to generate a set of practical tools, in the form of graphs. The graphs can be used to provide recommended maximum vessel speeds that will cause lower run-up than already naturally occurring by wind-generated waves.



Based on observations of experimental vessel-generated wave trains, a characteristic wave height distribution, consisting of increasing and subsequently decreasing wave heights, was noted. On mild but reflective beaches significant interaction between subsequent waves in the swash zone was also observed. A numerical model, based on the ?ballistics theory? was modified and shown to reproduce the swash hydrodynamics well if interaction was accounted for. An analytical sediment transport model for the swash zone was also employed and calibrated to field data.



Lastly, analytical models to predict dune erosion were developed, calibrated, and validated. The models describe erosion on a wave-by-wave basis, and are thought to be useful to estimate the impact from vessel-generated wave trains where the events are episodic and of relatively short duration. The total erosion is a function of the sediment properties, intensity, and frequency of the swash, where the frequency can be determined with knowledge of regularly scheduled vessel passages. In addition to erosion from the direct impact of waves, models to predict dune recession by mass failure were developed. The models are based on elementary engineering statics and soil mechanics. The models developed and/or calibrated for this study are believed to be applicable to both vessel- and wind-generated waves.

Abstract (Swedish)

Popular Abstract in Swedish

Fartygsgenererade vågor ofta orsakar större kustförändringar jämfört med vindvågor utmed stränder där stryklängden är begränsad. Med bakgrund av att fartygstrafiken, särskilt från höghastighetsfärjor, och dess potentiella miljöeffekter har forskning inom detta område ökat. Fast att ett antal studier har och fortsätter undangöras, forskning om fartygsgenererade vågor och dess påverkan på stränder är fortfaranderelativt nytt inom forskning.



Denna studie syftar på att utveckla effektiva verktyg för att beräkna effekten av fartygsgenererade vågor vid kustområden. För att fullgöra detta mål har fartygsgenererade vågor och dess påverkan på dynor och stränder undersökts.



Ett antal ensamstående men relaterade studier har gjorts för detta arbete. Med avseende på uppspolningshöjder (ej kustförändringar) har en metod framtagits för att ge rekommendationer för den optimala hastigheten ett fartyg kan köra utan att orsaka högre uppspolningshöjder än de som vindvågor ger.



Analys av uppmätta fartygsgenererade vågor nära stränder visade att vågpaket kan beskrivas av ett antal vågor med ökande och därefter minskande våghöjder. I ett laboratorie experiment var interaktion mellan följande vågor högt, särskilt på milt lutande men reflekterande stränder. En numerisk modell framtogs och gav bra resultat med avseende på hydrodynamiken på stranden om interaktion inkluderades. En analytisk modell för att beskriva sediment transport i vågskvalpsområdet implementerades och kalibrerades under denna studie.



Analytiska modeller framtogs för att beräkna erosion av dynor utsatta för vågor och självtyngd. Modellerna validerades med data från laboratorie experiment.

• author: Erikson, Li
• supervisor: Hans Hanson
• opponent: Professor Kriebel, David, US Naval Academy, USA
• organization: Division of Water Resources Engineering
• publishing date: 2005
• type: Thesis
• publication status: published
• subject: Water Engineering
• keywords: marklära, kartografi, klimatologi, Civil engineering, hydraulic engineering, geomorfologi, Fysisk geografi, climatology, cartography, pedology, geomorphology, Naturvetenskap, Physical geography, Natural science, swash, erosion, vessel-generated waves, dunes, offshore technology, soil mechanics, Väg- och vattenbyggnadsteknik
• in: Coastal Engineering, Marine Geology, Computers and Geosciences
• pages: 200 pages
• defense location: lecture hall V:A, Department of Water Resources Engineering, John Ericssonsväg 1, Lund Institute of Technology
• defense date: 2005-06-14 10:00:00
• ISSN: 1101-9824
• language: English
• LU publication?: yes
• id: e0cea96d-e912-436d-af2a-a04d2ef8f1bd (old id 545121)
• date added to LUP: 2016-04-01 15:44:18
• date last changed: 2019-05-21 11:21:32