The Application of Simulating WAves Nearshore Model for Wave Height Simulation at Bangkhuntien Shoreline

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1 America Joural of Evirometal Scieces 6 (3): , 2010 ISSN X 2010 Sciece Publicatios The Applicatio of Simulatig WAves Nearshore Model for Wave Height Simulatio at Bagkhutie Shorelie 1 Prasertsak Ekphisutsutor, 1 Prugcha Wogwises, 2 Chaiyuth Chiarasri, 3 Suphat Vogvisessomjai ad 4 Jiag Zhu 1 The Joit Graduate School of Eergy ad Eviromet, 2 Departmet of Civil Egieerig Kig Mogkut s Uiversity of Techology Thoburi, Bagkok, 10140, Thailad 3 Team Cosultig Egieerig ad Maagemet Co., Ltd., 151 TEAM Buildig, Nua Cha Road, Bueg Kum, Bagkok 10230, Thailad 4 Istitue of Atmospheric Physics, Chiese Academic of Scieces, Beijig, PR Chia Abstract: Problem statemet: I this study, the sigificat wave height at the Upper Gulf of Thailad ad the chage of wave height at Bagkhutie shorelie were simulated by usig the Simulatig WAves Nearshore Model (SWAN) versio Approach: The simulated sigificat wave height by the SWAN model at Petchburi buoy statio ad Ko Srichag buoy statio were compared with the observed sigificat wave height at these statios for the model verificatio. The sigificat wave height by the SWAN model at Bagkhutie shorelie from were simulated. Results: The simulated results show that the maximum sigificat wave height at Bagkhutie shorelie was i a rage of m while the average maximum sigificat wave height was 1.47 m. The average sigificat wave height were i a rage of m while the average sigificat wave height of 21 years simulated data at Bagkhutie shorelie was 0.35 m. Coclusio: The fidigs of this study could be useful for the erosive calculatio, shorelie protectio ad coastal zoe maagemet activities. Key words: Sigificat wave height, SWAN, the Upper Gulf of Thailad, Bagkhutie shorelie INTRODUCTION The Bagkhutie district is a district of the Bagkok Muicipality uder the authority of the Goveror of Bagkok, Thailad. Bagkhutie shorelie is the oly muddy shorelie i the Bagkhutie. This shorelie is located i the Upper Gulf of Thailad. There are four river mouths i the Upper Gulf of Thailad: The Mae Klog, the Tha Chi, the Chao Phraya ad the Bag Pakog which are illustrated i Fig. 1. This shorelie is a part of a muddy coastlie with magrove forests. The legth of this shorelie is about 5 km (Ekphisutsutor et al., 2010; Kamphuis, 1999). I the past, this coastlie was a real iter-tidal area with plety of magrove bushes beig subject to floodig ad allowig the delta to maitai a dyamic equilibrium. Its coastlie could, at times, be eroded but was built up agai, depedig o the sedimet load ad the goverig hydraulic coditios (Horikawa ad Hattori, 1987; Kamphuis, 1999). The Bagkhutie coastal zoe was degraded ad loss of the lad occurred due to the erosive forces of the sea. The sedimet supply decreased from the river ad the attackig of wave ad curret seem to be the major factors causig the shorelie erosio i this area (Kamphuis, 1999; Jackso, 1999). Therefore, i this study the wave characteristics i this area from ca be simulated by SWAN cycle III versio model (Booij et al., 2004) ad will be used for the erosio study, shorelie protectio ad coastal zoe maagemet (Jackso, 1999; Saleh et al., 2010). Correspodig Author: Prasertsak Ekphisutsutor, The Joit Graduate School of Eergy ad Eviromet, Kig Mogkut s Uiversity of Techology Thoburi, Bagkok, 10140, Thailad 299

2 Fig. 1: Map of Thailad ad the locatio of Bagkhutie shorelie MATERIALS AND METHODS The sigificat wave height at the Upper Gulf of Thailad ad Bagkhutie shorelie must be properly uderstood by ivestigatig the wave forces o the shorelie. Kowledge of the waves geerated by wid ad the sedimet trasported by wave height is very useful i shorelie erosio study i this area. The wave characteristics i this area from were simulated by SWAN cycle III versio model (Hargreaves ad Aa, 2001; Hasselma et al., 1973; Booij et al., 2004; Waawog et al., 2010; 2011). Model descriptio: The SWAN model was developed by Delft Uiversity of Techology (Hargreaves ad Aa, 2001; Hasselma et al., 1973; Booij et al., 2004; Waawog et al., 2010; 2011) ad is free for the public domai. It is used by may govermet authorities, research istitutes ad cosultat worldwide. The feedback has widely idicated the reliability of the SWAN i several experimets ad field cases. It is widely used for earshore wave forecasts aroud the world. Based o the wave actio balace equatio with sources ad siks, the shallow water wave model SWAN (acroym for Simulatig WAves Nearshore) is a extesio of the deep water third-geeratio wave models. It icorporates the state-of-the-art formulatios for the deep water processes of wave geeratio, dissipatio ad quadruplet wave-wave iteractios from the WAM (WAve Model) model (Guther et al., 1992; 300 Hargreaves ad Aa, 2001; Kome et al., 1996). I shallow water, these processes have bee supplemeted with the formulatios for dissipatio due to bottom frictio, triad wave-wave iteractios ad depthiduced breakig. The SWAN is fully spectral (i all directios ad frequecies) ad computes the evolutio of wid waves i coastal regios with shallow water ad ambiet curret. Wid-geerated waves have irregular wave heights ad periods, caused by the irregular ature of wid. The sea surface elevatio, i oe poit as a fuctio of time, ca be described as: i i i (1) i η (t) = a cos( σ t + α ) Whe: η = The sea surface elevatio α I = The amplitude of the i th = Wave compoet σ I = The relative radia or circular frequecy of the i th = Wave compoet i the presece of the ambiet curret (equal to the absolute radia frequecy ω = Whe o ambiet curret is preseted) σ i = The radom phase of the i th = Wave compoet. This is called the radomphase model The total eergy desity at a frequecy f is distributed over the directios θ i E(θ), it follows that: 2π E(f ) = E(f, θ)dθ (2) 0

3 Based o the eergy desity spectrum, the itegral wave parameters ca be obtaied. These parameters ca be expressed i terms of th momet of the eergy desity spectrum: Am. J. Eviro. Sci., 6 (3): , 2010 m f E(f )df = (3) 0 The total eergy of a wave system is the sum of its kietic eergy ad its potetial eergy. The kietic eergy is the part of total eergy. The kietic eergy per uit legth of wave crest for a liear wave ca be foud from: E k = ρ gh L (4) The potetial eergy per uit legth of wave crest for a liear wave is give by: E p = ρ gh L (5) Fig. 2: The bathymetry map of the Upper Gulf of Thailad Study domai: The study domai was covered from E i logitude ad N i latitude with resolutio of km as show i Fig. 2. The study area covered the Bagkhutie shorelie. Accordig to the Airy theory, the total wave eergy i oe wave legth per uit crest width is give by: 2 ρgh L E = EP + Ek = (6) 8 Total average wave eergy per uit surface area, termed the specific eergy or eergy desity, is give by: 2 E ρgh E = = (7) L 8 Where: H = The sigificat wave height ρ = The specific gravity of sea water g = Gravity acceleratio I this study SWAN cycle III versio 40.51, supported by Rijkswaterstaat (as part of the Miistry of Trasport, Public Works ad Water Maagemet, the Netherlads was used. The SWAN model (Hasselma et al., 1973; 1985; 1988) was used to solve the wave variace spectrum or eergy desity, wave eergy over frequecies ad propagatio directios. Data collectio: The bathymetry data (1: 240,000) at the Upper Gulf of Thailad were take from the Hydrological Departmet of the Royal Thai Navy, wid data (10 m height) obtaied from the Thai Meteorological Departmet (TMD) was collected i every 3 hours at Pilot statio ad the observed sigificat wave height at Petchburi buoy ad Ko Srichag buoy (as show i Fig. 2) were take from the Geo-Iformatics ad Space Techology Developmet Agecy (Public Orgaizatio) (GISTDA). Figure 3 shows the wid rose diagram (Pilot statio) durig These wid data were used to geerate the sigificat wave height. The wid field was uiformed alog the shorelie with speeds that were observed at the Pilot statio. Geerally, the wave fields respoded very well with the wid patter. Model performace: The simulated performace is evaluated usig a goodess of fit measures, amely the Correlatio Coefficiet (CC): CC = Where: 301 i= 1 ( Ho ) ( Ho ) ( Hm ) ( Hm i i ) ( Ho ) ( Ho ) ( m ) ( m i H H i ) i= 1 i= (8)

4 H = The sigificat wave height, the subscripts o ad m = Represet the observed ad model simulated values respectively Model verificatio: The SWAN model has bee verified with the buoy observatioal data (the sigificat wave heights) i 1996 ad 1998 at Petchburi ad Ko Srichag statios respectively. Fig. 4a shows the calibratio result at Petchburi i Figure 4b shows the calibratio result at Ko Srichag i Figure 5a shows the verificatio result at Petchburi i Figure 5b shows the verificatio result at Ko Srichag i The solid red lie represets the simulated result ad the dashed blue lie represets the observed sigificat wave height. Figure 6a shows the correlatio betwee the observed sigificat wave heights ad the simulated sigificat wave heights from the model at Petchburi statio i Figure 6b shows the correlatio betwee the observed sigificat wave heights at Ko Srichag statio ad the simulated sigificat wave heights from the model i The Correlatio Coefficiet (CC) at Petchburi ad Ko Srichag statios were 0.72 ad 0.82 respectively. Figure 7a shows the correlatio betwee the observed sigificat wave heights at Petchburi statio ad the simulated sigificat wave heights from the model i1996. Figure 7b shows the correlatio betwee the observed sigificat wave heights ad the simulated sigificat wave heights at Ko Srichag statio from the model i The Correlatio Coefficiet (CC) at Petchburi ad Ko Srichag statios i 1998 showed the same value of The compariso of the observed sigificat wave height at the buoy statios ad the simulated sigificat wave heights preseted that the simulatio correspoded with the observatio. Fig. 3: Wid rose diagram at Pilot statio 302

5 Fig. 4: Calibratio results at Petchburi ad Ko Srichag statios i 1996 Fig. 6: Correlatio betwee the observed sigificat wave heights ad the simulated sigificat wave height i 1996 Petchburi statio Ko Srichag statio Fig. 5: Verificatio results at Petchburi ad Ko Srichag statios i 1998 Petchburi statio Ko Srichag statio Model simulatio: The SWAN model simulated the sigificat wave height from (the data were ot collected i 1982 ad 1983) at the Upper Gulf of Thailad. Sigificat wave height at Bagkhutie shorelie i the Upper Gulf of Thailad: The applicatio of a two-dimesioal model based o the SWAN model to predict the sigificat wave height at the Upper Gulf of Thailad has bee described. The predicted result was i a good agreemet with the observed sigificat wave height. 303

6 Fig. 7: Correlatio betwee the observed sigificat wave heights ad the simulated sigificat wave height i 1998 Petchburi statio Ko Srichag statio RESULTS SWAN model showed that the model ca be used to simulate the sigificat wave height at Bagkhutie shorelie i the Upper Gulf of Thailad. Figure 8 shows the observed wid fields ad the of the Chagig Seaso, the wid blew from South simulated sigificat wave height at 21:00 UTC, o 15th to North ad the average wid speed was about December 1998 (NE Mosoo). Figure 8a shows the m sec 1 ad Fig. 9b shows the sigificat wave ifluece of the Northeast mosoo, the wid blew from height of about 0.8 m, far away from the shorelie. Northeast to Southwest ad the average wid speed was There was a icrease i wave height at the shorelie about m sec 1 ad Fig. 8b shows the sigificat accordig to the accumulated wid eergy from the wave height of approximately 0.2 m, ear the sea shore deep sea. The size of the sigificat wave height was ad there was icreasig wave height far away from the illustrated by a cotour lie while ad the vector with sea shore accordig to the accumulated wid eergy. arrows represeted the sigificat wave directio. 304 Fig. 8: The simulated sigificat wave height at the surface elevatio shows the observed wid data ad the simulated sigificat wave height at sea surface, from the model o 15th December 1998 at 21:00 UTC (NE Mosoo) The size of the sigificat wave height was show by a cotour lie ad the vector with arrows represets the sigificat wave directio. Figure 9 shows the observed wid fields ad the simulated sigificat wave height at 21:00 UTC, o 1st March 1998 (Chagig Seaso). Figure 9a presets the ifluece

7 Fig. 9: The simulated sigificat wave height at the surface elevatio shows the observed wid data ad the simulated sigificat wave height at sea surface, from the model o 1st March 1998 at 21:00 UTC (Chagig Seaso) Fig. 10: The simulated sigificat wave height at the surface elevatio shows the observed wid data ad the simulated sigificat wave height at sea surface, from the model o 15th September 1998 at 21:00 UTC (SW Mosoo) Figure 10 shows the observed wid fields ad the simulated sigificat wave height at 21:00 UTC, o 15th September 1998 (SW Mosoo). Figure 10a preseted the ifluece of Southwest mosoo, the wid blew from South to North ad the average wid speed was about 8.24 m sec 1. Figure 10b expressed the sigificat wave height of approximately 0.4 m from the shorelie. DISCUSSION There was icreasig wave height o the seashore accordig to the accumulated wid eergy 305 from the deep sea far away from the shorelie ad there was icreasig to a wave height o the seashore, accordig to the accumulated wid eergy from the deep sea. The size of the sigificat wave height was represeted by a cotour lie ad the vector with arrows represeted the sigificat wave directio. The applicatio of a two dimesioal model based o the SWAN predicted the sigificat wave height at Bagkhutie shorelie by usig the 3 h wid speed at Pilot statio. The sigificat wave height at Bagkhutie shorelie has bee described ad show i Fig. 11.

8 Fig. 11: Sigificat wave height (m) at Bagkhutie shorelie Table 1: The summary of wave characteristics at Bagkhutie shorelie from Latitude ' Logitude ' Latitude Logitude Latitude ' Logitude ' Maximum Average Average Maximum Average Average Maximum Average Average Year sigificat sigificat sigificat sigificat sigificat sigificat sigificat sigificat sigificat (TS) wave height (HS) wave height (HS) wave period (TS) wave height (HS) wave height (HS) wave period (TS) wave Height (HS) wave Height (HS) wave period (m) (m) (sec) (m) (m) (sec) (m) (m) (sec) Average

9 CONCLUSION Bagkhutie shorelie was degraded ad loss of the lad occurred. The attackig wave is oe of the major factors of the shorelie erosio, especially at Bagkhutie shorelie. The SWAN model ca be used to simulate the hourly sigificat wave height at the Upper Gulf of Thailad ad Bagkhutie shorelie. The simulated results showed that the maximum sigificat wave height at Bagkhutie shorelie were i a rage of m. The average sigificat wave height were i a rage of m while the average sigificat wave height of the 21 years simulated data at Bagkhutie shorelie was 0.35 m as show i Table 1. Recommedatio: The wave height is oe of the major factors of the Bagkhutie shorelie erosio. The relatio of wave ad erosio should be studied. The mechaisms of the erosio ad other factors will be cosidered for Bagkhutie shorelie ad other shorelies which have the erosio problems. The shorelie erosio must be simulated uder the erosio parameters. The predictio of the shorelie erosio, suitable solves ad suitable protectios will be cosidered i the future. ACKNOWLEDGMENT This study was supported by the Joit Graduate School of Eergy ad Eviromet, Kig Mogkut s Uiversity of Techology Thoburi. Special thaks are offered to the Hydrological Departmet of the Royal Thai Navy, the Royal Thai Survey Departmet (RTSD). The authors are grateful to Faculty of Civil Egieerig ad Geoscieces Delft Uiversity of Techology for kigly providig the SWAN model. Fially, the authors are greatly idebted to Mr. Michael Willig for helpful commets o Eglish grammar ad usage. REFERENCES Booij, N., I.J.G. Haagsma, L.H. Holthuijse, A.T.M.M. Kiefteburg ad R.C. Ris et al., SWAN cycle III Versio Users maual. Delft Uiversity of Techology. Ekphisutsutor, P., P. Wogwises, C. Chiarasri, U. W. Humpries ad S. Vogvisessomjai, Numerical modelig of erosio for muddy coast at Bagkhutie shorelie. Thailad. J. Eviro. Sci. Eg., 2: Guther, H., S. Hasselma ad P.A.E.M. Jasse, The WAM model cycle 4 (revised versio), Rechezetrum. Hargreaves, J.C. ad J. D. Aa, Commets o Improvemet of the Short Fetch Behavior i the Wave Ocea Model (WAM). J. Atmos. Oceaic Tech., 18: Hasselma, H., T. P. Barett, E. Bouws, H. Carlso ad D.E. Cartwright et al., Measuremets of wid-wave growth ad swell decay durig the Joit North Sea Wave Project (JONSWAP). Dtsch. Hydrogr. Z. Suppl., 12, pp: 95. Hasselma, S., K. Hasselma, E. Bauer, P.A.E.M. Jasse ad G.J. Kome et al., The WAM model-a third geeratio ocea wave predictio model. J. Phys. Ocea., 18: Hasselma, S., K. Hasselma, J.H. Alleder ad T.P. Barett, Computatios ad parameterizatios of the oliear eergy trasfer i a gravity-wave spectrum, Part II: Parameterizatios of the oliear eergy trasfer for applicatio i wave models. J. Phys. Ocea., 15: Horikawa, K. ad M. Hattori, The earshore eviromet research ceter project. America Society of Civil Egieers. Jackso, N.L., Evaluatio of criteria for predictig erosio ad accretio o a estuarie sad beach. J. Estuaries Coast., 22: Kamphuis, J.W., Itroductio to Coastal Egieerig ad Maagemet. 1st Ed., World Scietific Publishig Compay, Sigapore, ISBN: 10: , pp: 472. Kome, G., L. Cavaleri, M. Doela, K. Hasselma ad S. Hasselma et al., Dyamics ad Modelig of Ocea Waves. 1st Ed., Cambridge Uiversity Press, Cambridge, UK., ISBN: 10: , pp: 556. Saleh, E., J. Beliku, T. Aug ad A. Sigh, Wave Characteristics i Sabah Waters. Am. J. Eviro. Sci., 6: Waawog, W., U.W. Humphries, P. Wogwises, S. Vogvisessomjai ad W. Lueagaram, umerical aalysis of wave ad hydrodyamic models for eergy balace ad primitive equatios. J. Math. Stat. Sci., 2: Waawog, W., U.W. Humphries, P. Wogwises ad S. Vogvisessomjai, Three steps of oe-way ested grid for eergy balace equatios by wave model. J. Comp. Math. Sci., 5: