Abstract
This paper presents a well-controlled laboratory experimental study to evaluate wave attenuation by artificial emergent plants (Phragmites australis) under different wave conditions and plant stem densities. Results showed substantial wave damping under investigated regular and irregular wave conditions and also the different rates of wave height and within canopy wave-induced flows as they travelled through the vegetated field under all tested conditions. The wave height decreased by 6%–25% at the insertion of the vegetation field and towards the downstream at a mean of 0.2 cm and 0.32 cm for regular and irregular waves respectively. The significant wave height along the vegetation field ranged from 0.89–1.76 cm and 0.8–1.28 cm with time mean height of 1.38 cm and 1.11 cm respectively for regular and irregular waves. This patterns as affected by plant density and also location from the leading edge of vegetation is investigated in the study. The wave energy attenuated by plant induced friction was predicted in terms of energy dissipation factor (fe) by Nielsen’s (1992) empirical model. Shear stress as a driving force of particle resuspension and the implication of the wave attenuation on near shore protection from erosion and sedimentation was discussed. The results and findings in this study will advance our understanding of wave attenuation by an emergent vegetation of Phragmites australis, in water system engineering like near shore and bank protection and restoration projects and also be employed for management purposes to reduce resuspension and erosion in shallow lakes.
Highlights
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Bottom characteristics are usually a main factor in determining wave dissipation, wetlands ecosystem is important as its effect on hydrodynamics is at the bottom but throughout the water column (Augustin et al 2009)
The greater part of wave height attenuated over the vegetation field mostly occurred along the first few meters of the vegetation field which was observed for both regular and irregular waves runs. This was similar to the findings observed by previous researchers (Kobayashi et al 1993; Mendez, Losada 2004; Augustin et al 2009)
Summary
IThnahtseronbdieutPaKerlchnoestoryaiawoerbgxonoemtmreeidtmnaess:stpiiwvlcaoueaeyvlsxeytedrpaaulfltooitssesre,nidmviuneaaf,tnwo2ioara,gn4teeo,,r6mva-qseetyurnrsiattn1tepii0mctu0reroepmytnooeegsrlaiegunsreeestne,notreairvne(negTdgdueNlitcktaeThetiri)onse,nseu,asorppsee2aahnn0nnos-r1iadcoe1he/noar)a.onnrandbnBdneibcali,eatccrrnrtoeookegsngriupoiedlarnaniort)tiimnewocoanastvihrysoean,dlvdlioiraierwranegedcgrlctauarlkoldyeaes-erstm(.oTwrTeNaatNvtaieTob,Tnosihslpuierssnaoomrdjuesectrrrtwcseeshaasoene. rrfdoecbaaircdbdooinrpersistent toxic organic compound has resulted in soil tional substrates are needed (Rylott et al 2011). The ecosystem, the interaction between water waves and aquatic vegetation need to be quantified. Bottom characteristics are usually a main factor in determining wave dissipation, wetlands ecosystem is important as its effect on hydrodynamics is at the bottom but throughout the water column (Augustin et al 2009). One important aspect is the attenuation of wave energy by aquatic vegetation (Suzuki et al 2011). Augustin et al (2009) used linear wave theory to laboratory experiments to quantify bulk drag force exerted by vegetation. Modeling studies were performed to investigate wave-vegetation interactions (Dalrymple et al 1984; Asano et al 1992; Mendez et al 1999; Mendez and Losada 2004; Mullarney, Henderson 2010). The above mentioned studies have reported changing rate of wave attenuation regarding the vegetation type and the study environment. Knutson et al (1982) in an early study reported a decrease in wave energy in salt marsh vegetation up to 26%. Mork (1996) conducted experiments on hyperborea kelp beds in the coast of Norway that showed attenuation of more than 60% of wave height. Tschirky et al (2000) in Lake Ontario recorded a 40%
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