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Empirical Wave Run-Up Formula for Wave, Storm Surge and Berm Width

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Empirical Wave Run-Up Formula for Wave, Storm Surge and Berm Width Coastal Engineering 115 (2016) 67–78 Contents lists available at ScienceDirect Coastal Engineering journal homepage: www.elsevier.com/locate/coastaleng Empirical wave run-up formula for wave, storm surge and berm width Hyoungsu Park ⁎,DanielT.Cox School of Civil and Construction Engineering, Oregon State University, Corvallis, OR 97331-2302, USA article info abstract Article history: An empirical model to predict wave run-up on beaches considering storm wave and surge conditions and berm Received 18 April 2015 widths (dry beach) has been derived through a synthetic data set generated from a one-dimensional Boussinesq Received in revised form 6 October 2015 wave model. The new run-up equation is expressed as a function of a new Iribarren number composed of three Accepted 23 October 2015 regions: the foreshore, the berm or dry beach width, and the dune. The dissipative effect of the berm is included Available online 30 December 2015 as a reduction factor expressed as a function of the berm width normalized by the offshore wavelength. The equa- Keywords: tion is relatively simple but is shown to be applicable for a fairly wide variety of berm widths and storm wave Wave run-up conditions associated with extreme events such as hurricanes, and it is shown to be an improvement over Iribarren number existing empirical run-up models that do not consider the berm width explicitly. In addition, the new parameter- Boussinesq model ization of the Iribarren number considering the three regions and the berm width reduction factor are shown to Hurricane improve other empirical models. Dune © 2015 Elsevier B.V. All rights reserved. Berm 1. Introduction and is widely utilized for wave run-up on beaches and coastal structures and for tsunami inundation. The Iribarren number is Many cases of inundation and coastal flooding occur during ex- treme events such as hurricanes when the maximum wave run-up tanβ ξ ¼ pffiffiffiffiffiffiffiffiffi ð1Þ exceeds the dune crest. Therefore, the severity of hurricanes can be H=L grossly determined by the relation among the wave and surge con- ditions and the beach morphology (Sallenger, 2000). Although where β is the angle of the characteristic slope, H is the characteristic existing time-dependent numerical models provide accurate, deter- wave height, and L is the characteristic wavelength. For consistency, ministic estimates of wave run-up for given boundary conditions, it is we use the nomenclature “Iribarren number” rather than “surf-similar- fi nevertheless necessary to develop simpli ed expressions for wave ity parameter” because the parameter is also used for coastal structures run-up that can be used, for example, in probabilistic models for a and tsunamis without surf zones, and we follow the conventional nota- range of surge and wave forcing and morphological conditions. The tion of ξ. fi complex nature of wave run-up on realistic cross-shore pro les pro- For beaches, β is often taken as the angle of the foreshore slope around fi hibits analytical solutions, so simpli ed run-up formulas rely on empir- the still water shoreline, although other values have been used such as fi ical approaches based on eld observations (e.g., Holman, 1986) and the slope at the breakpoint or the mean slope over the active portion of fi laboratory experiments (e.g., Mase, 1989). Few eld observations the surf zone. For coastal structures, β is generally less ambiguous since exist, however, of run-up during extreme storm events (e.g., Senechal rubble mound revetments and breakwater are typically built with a con- et al., 2011), so it is necessary to consider the suitability of these empir- stant slope, usually much steeper than sand beaches. The characteristic ical equations for extreme events. wave height is typically the deep water wave height, H0, the wave height Generally, wave run-up is characterized by the Iribarren number, at breaking Hb, or, in the case of coastal structures, the incident wave which is also known as the surf-similarity parameter (Battjes, 1974), height at the toe of the structure, Hi. Similarly, the characteristic wave- 2 length can be the deep water wavelength L0 = gT /2π, the wavelength at breaking Lb estimated using linear wave theory and the local water depth at breaking, or the wavelength estimated at the toe of a coastal structure. There are a variety of wave conditions to consider such as reg- ular waves from laboratory studies, irregular waves, and transient waves ⁎ Corresponding author. Tel.: +1 541 602 8618; fax: +1 541 737 3052. E-mail addresses: [email protected] (H. Park), [email protected] such as tsunamis. For regular wave studies, H and T are not ambiguous. (D.T. Cox). For the case of irregular waves, H is generally characterized by the http://dx.doi.org/10.1016/j.coastaleng.2015.10.006 0378-3839/© 2015 Elsevier B.V. All rights reserved. 68 H. Park, D.T. Cox / Coastal Engineering 115 (2016) 67–78 significant wave height Hs,andT is generally characterized by the peak structure and, and the subscript m denotes that the wavelength is com- period Tp, although other characterizations are possible such as H1/10 or puted using the mean period. This work was later extended by De Waal themeanwaveperiodTm. For transient wave studies such as for tsunamis and Van der Meer (1992) and VanderMeer (1998) to provide a general modeled as solitary waves, H is generally the maximum positive displace- wave run-up model on dikes to account for the design of the berm, ment at a given depth, and T is defined as the duration over which the roughness effects of the dike, and wave direction through a combination positive displacement exceeds a certain value, for example. of reduction factors and is given as Since Hunt (1959), empirical run-up models have been expressed as a function of the Iribarren number, % R2 ¼ : γ γ γ ξ ð Þ 1 6 1 2 3 p 8 Hs R ¼ Kξ ð2Þ H where the subscript p denotes that Iribarren number is defined using γ where R is the maximum run-up defined as the vertical projection the peak period Tp. The reduction factor is a dimensionless number above the still water level, and K is an empirical constant. less than 1.0, determined experimentally to account for effects of the γ Holman (1986) used field observations of wave run-up at Duck, NC, berm geometry, 1, surface roughness such as natural grass or rock, γ γ to develop an empirical run-up model on natural beaches using a simi- 2, and wave direction, 3. This run-up model has an empirical maxi- γ γ lar form as Eq. (2) and is given by mum limit of R2%/Hs =3.2 2 3. Eqs. (7) and (8) have been widely adopted for the design of coastal structures, and examples of their application are summarized in coastal R2% ¼ : ξ þ : ð Þ 0 83 f 0 2 3 H0 engineering manuals (e.g., Pullen et al., 2007; USACE, 2003). Similar to run-up models for beaches, some empirical models use slightly different where the run-up is the value exceeded by 2% of the run-up events, R2%, forms of the Iribarren number, particularly when defining the slope be- normalized by the significant wave height in deep water. The Iribarren cause some revetments and dikes may be composed of multiple slopes number is defined using the angle of the foreshore slope βf,significant or may include relatively short, flat berms. The need to account for the wave height in deep water, and the wavelength in deep water using profile shape was recognized by Saville (1958), and models generally the peak wave period: employ an ‘equivalent slope’ as summarized by Mase et al. (2013). Although tsunamis can occur on vastly different scales compared to tanβ ξ ¼ qffiffiffiffiffiffiffiffiffiffiffif ð Þ wind waves on beaches and coastal structures, the Iribarren number has f 4 H0 been found to be a suitable parameter for tsunami run-up studies. For L 0 example, Kobayashi and Karjadi (1994) combined numerical model re- sults with laboratory experiments to develop an empirical formula to Mase (1989) developed a similar run-up equation based on irregular predict the run-up height normalized by the incident solitary wave am- waves generated in a laboratory on a plane slopes and is written as plitude (A0) as a function of Iribarren number, given as R2% ¼ : ξ0:71 ð Þ 1 86 f 5 R 0:395 H0 ¼ 2:955ξ ð9Þ A0 where Eq. (4) was used to define the Iribarren number in a similar man- ner as Holman (1986), and the foreshore slope was the same as the where the Iribarren number is defined using a characteristic period for slope for the incident waves prior to breaking and ranged from 1/30 the solitary wave defined as the duration over which the free surface ex- to 1/5. ceeds 0.05A0. Kobayashi and Karjadi (1994) show that Eq. (9) is applica- Using data sets from US East and West Coast beaches, Stockdon et al. ble for 0.125 b ξ b 1.757 and that changing the definition of the (2006) developed an empirical wave run-up model (hereinafter re- characteristic period based on exceedance of either 0.01A0 or 0.1A0 ferred to as the “Stockdon model” for brevity) using an Iribarren-like changes the predicted run-up on the order of 10%. form given as The application of Iribarren number for tsunami run-up was analyt- ically studied by Madsen and Fuhrman (2008), and it highlighted hi 0:5 ¼ : : β ðÞ0:5 þ : : β 2 þ : that run-up solutions for the canonical run-up depend on Iribarren R2% 1 1035 tan f H0L0 0 5 H0L0 0 563 tan f 0 0004 number for the non-breaking regular wave.
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