The Influence of Current on the Height of Wind Wave Run-Up: A comparison of experimental results with the Czech National Standard

Abstract

One of the basic questions related to the safety of dikes and river levees is the size of the freeboard. One of the important parameters for freeboard design is the height of waves and wave run-up on levee slopes. Routine and standardised calculations of wave run-up deal with the freeboards of dams where wind waves originate on the still water of the reservoir. In the case of running water in streams (thereinafter only "currents") the effect of wave and current interaction on wave run-up is usually not taken into account due to the lack of reliable knowledge regarding the phenomenon. In the Czech Republic this question is topical in the case of large rivers such as the Elbe, the Vltava and the Morava. Within the framework of the projects Hydralab III and NAZV QI 92A139, hydraulic research and further analysis focused on wave run-up as a result of the combination of current and wind wave parameters were performed. The laboratory research was carried out in a hydraulic flume with a wavemaker on the right bank and a levee with a slope of 1:3 installed on the left bank opposite the wavemaker. Waves were generated both perpendicular and oblique to the levee axis; the angle of oblique wave attack varied within the range of ± 30°. The aim of this paper is to compare the results of the mentioned research with recommendations mentioned in the Czech National Standard CSN 75 0255 Calculation of wave effects on water structures and to quantify the effect of current on the wave run-up height. Jednou ze základních otázek spojených s bezpečností hráze je návrh převýšení její koruny nad maximální hladinou vzdouvané vody. Důležitým parametrem ovlivňujícím návrh převýšení je výška vln vybíhajících po svahu hráze. Běžné postupy výpočtu výšky výběhu vlny na svah jsou realizovány za předpokladu, že vlny vznikají na stojatých vodách. Vliv proudění se obvykle vzhledem k nízké úrovni znalostí tohoto jevu na tekoucích vodách zanedbává. V podmínkách České Republiky je otázka vlivu proudění na výšku výběhu relevantní zejména na velkých tocích jako Labe, Vltava nebo Morava. V rámci projektů Hydralab III a NAZV QI 92A139 byl uskutečněn hydraulický výzkum a analýza dat se speciálním zaměřením na výšku výběhu větrových vln při započtení vlivu proudění. Výzkum byl realizován na modelu hráze se sklonem svahu 1 : 3, který byl umístěn ve zkušební nádrži osazené vlnoproduktorem vedeným rovnoběžně s modelem hráze. Vlny zde byly generovány jednak kolmo vzhledem k podélné ose hráze, jednak šikmo v rozsahu úhlů ± 30°. Výsledky výzkumu byly porovnány s doporučeními uvedenými v České státní normě ČSN 75 0255 Výpočet účinků vln na stavby na vodních nádržích a zdržích.KLÍČOVÁ SLOVA: ochranná hráz, hrázka, větrová vlna, výška vlny, výběh vlny, proudění, návrh převýšení.

Wave Run-Ups and Overtopping Affected by Oblique Wave Approaches and Currents

“…The effect of different factors on wave run-up heights and wave overtopping discharges may be expressed by correction factors γ included in the formula originally suggested by Hunt (1959) and then improved by EurOtop (2018). As shown in Riha and Spano (2012), the correction factor for the angle of wave approach γ β can be supplemented by a combined factor for the angle of the wave approach and flow velocity γ βv . The advantage of this approach is that it reflects whether the waves are generated against or along the direction of the flow.…”

Comparative Assessment of Different Modelling Schemes and Their Applicability to Inland Small Reservoirs: A Central Europe Case Study

“…Based on the current knowledge and research results in the field of wave mechanics and the stabilization of dams [8,22], the wave run-up of with 2% exceedance probability R 2% was selected to verify the overtopping of the dam crest.…”

“…The important decision during the design process consists in the formulation of the protection degree-setting up of the design wave height and design wind speed. Dams and embankments should be protected from the effects of waves of 1% exceedance probability according to the mentioned STN; however, 2% probability of run-up height exceedance is currently recommended for practical use, as a result of expert observations and discussions [22]. The remaining shoreline of the reservoir should be protected from the effects of characteristic wave with 13% probability of exceedance due to possible high expenses spent on stabilization measures [16,17].…”

Spectral analysis of oscillatory wind wave parameters in fetch-limited deep-water conditions at a small reservoir and their prediction: Case Study of the Hulín Reservoir in the Czech Republic

“…When certain conditions are met, it can be assumed that the relationships between wave parameters can still be sufficiently plausibly described by linear wave propagation theory. In the last decade in the Czech Republic, numerous types of research have been performed on closed reservoirs, and draft protective measures have been applied to banks (Kotaška, 2019;Pelikán and Marková, 2013;Pelikán and Šlezingr, 2015;Pelikán and Koutný, 2016;Říha and Špano, 2012;Špano, 2019;Špano and Duchan, 2021;Špano et al 2022).…”