Environmental Design Parameter Determination, Numerical Calculation Of Overtopping Flow And Wave Conditions For Tolerable Overtopping Seadikes

Storm surge is one of the most important disasters affecting coastal areas ofChina. For the fact that the cities, whose economy is relatively developed in China,usually concentrate in the coastal region, much focus has been put on the subject ofpreventing storm surge disasters. Sea dikes, as a major part of coastal structures toprevent storm surge, is the most effective and direct engineering measures. It needs totake account into many factors to determine the environmental design parameter. Thatincludes the uncertainty of environmental conditions, engineering investment, failurerisk and so on, among which the joint design standard of a variety of environmentalconditions has attracted researchers’ attention widely. In determining the elevation ofseawalls, the traditional approach donot allow overtopping event, whereas,overtopping cannot be avoided due to the economic reason and the uncertaintiesassociated with the prediction of environmental conditions. Therefore it is necessaryto consider the allowable overtopping rate and to check the stability of the crest andinner slope affected by overtopping flow. Since the overtopping flow with the sameovertopping rate could act on crest and inner slope of seadikes in a different way, it isa necessary to study the maximum overtopping event and overtopping flow for thedesign of the crest and inner slope of seadikes.This paper studies the design standard of environmental conditions for slopedseadikes with a tolerable overtopping rate, and investigates the overtopping flow andthe wave conditions of the water area behind the seadikes by numerical models. Theaim of this paper is to provide references for the design of crest elevation and innerslope of seadikes. The main wok of this paper is as following:Considering the observational material is limited in some engineering projectarea, numerical models are used to hindcast the multi-dimensional long-term extremestatistical series dominated by wind, wave and water level, respectively. Thehindcasted results are verified by the data from observation stations adjacent theproject site. The models uses in this paper are RAMS for wind, POM, and SWAN, among which, noticing the possible stability issues in diffraction of SWAN, a steadywave model, which is robust in wave diffraction and do not include wind effect, isused in the wave field calculation in offshore.By introducing the location parameter, the maximum entropy distribution withfour parameters can fit the data more flexibly and describe the nonlinear waves withno apriority. The maximum entropy distribution model is used to estimate oceanenvironmental conditions, such as wind, wave and water level. Then a threedimensional nested logic distribution model is established, with maximum entropydistribution as the marginal distribution. This model can take account into the fact thatthe dominant factor and secondary factors may obey different marginal distributionsto some extent.For a multidimensional joint distribution model, there are numerouscombinations corresponding to some joint return period, hence a constraint conditionis needed. This paper uses overtopping rate as the constraint condition to calculate thejoint return value of environmental conditions and crest elevation with four methods.The results are analyzed to compare the effect of the three kinds of series and fourmethods on the crest elevation determination. Besides, the maximum singleovertopping volume is calculate to check the dangerous situation caused by peakwave overtopping volume, and an attempt is tried to determine the joint return valueof environmental conditions and crest elevation with maximum single overtoppingvolume as the constraint condition.For the hydrologic design parameter of crest and inner slope, a numerical wavetank is established to analyze overtopping flow on crest and inner slope. The modelutilizes CIP method for advection equation and THINC method for free surfacecapture, which are efficient in dealing with problems with large deformation of freesurface and multi free surfaces. Some published experiments are employed to verifythe numerical wave tank, including dam break problems, regular wave and solitarywave passing through submerged obstacles, and the overtopping flow on the crest andsecondary wave behind seadikes. This numerical wave tank is utilized to analyze theovertopping flow velocity field on the crest and inner slope. Two types of profiles areinvestigated from the aspect of velocity field and erosion analysis based on differenterosion index, and the comparisons of two profiles are given in the end.For the seadikes with the function of protecting water areas behind it, there is ademand to estimate wave conditions disturbed by wave overtopping. In this paper, the transmitted wave by overtopping is considered as a kind of transmitted energy, as atransmission factor added in the numerical wave propagation model based on energybalance. This model can take all factors into consideration including diffraction,reflection, refraction and overtopping transmission to estimate the wave height behindthe seadikes. Calculations are carried out to study the feasibility of constructing AiHua port in Qingdao with a comparison between two port layouts in design. Waveheights inside the port for different environmental design conditions are simulated,and two kinds of parameters are calculated to evaluate the wave conditions for the twolayouts to provide references for decision makers.