Wind-Driven Waves Can Damage Shorelines
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Coastal Water Levels
Guidance for Flood Risk Analysis and Mapping Coastal Water Levels May 2016 Requirements for the Federal Emergency Management Agency (FEMA) Risk Mapping, Assessment, and Planning (Risk MAP) Program are specified separately by statute, regulation, or FEMA policy (primarily the Standards for Flood Risk Analysis and Mapping). This document provides guidance to support the requirements and recommends approaches for effective and efficient implementation. Alternate approaches that comply with all requirements are acceptable. For more information, please visit the FEMA Guidelines and Standards for Flood Risk Analysis and Mapping webpage (www.fema.gov/guidelines-and-standards-flood-risk-analysis-and- mapping). Copies of the Standards for Flood Risk Analysis and Mapping policy, related guidance, technical references, and other information about the guidelines and standards development process are all available here. You can also search directly by document title at www.fema.gov/library. Water Levels May 2016 Guidance Document 67 Page i Document History Affected Section or Date Description Subsection Initial version of new transformed guidance. The content was derived from the Guidelines and Specifications for Flood Hazard Mapping Partners, Procedure Memoranda, First Publication May 2016 and/or Operating Guidance documents. It has been reorganized and is being published separately from the standards. Water Levels May 2016 Guidance Document 67 Page ii Table of Contents 1.0 Topic Overview ................................................................................................................. -
Tsunami, Seiches, and Tides Key Ideas Seiches
Tsunami, Seiches, And Tides Key Ideas l The wavelengths of tsunami, seiches and tides are so great that they always behave as shallow-water waves. l Because wave speed is proportional to wavelength, these waves move rapidly through the water. l A seiche is a pendulum-like rocking of water in a basin. l Tsunami are caused by displacement of water by forces that cause earthquakes, by landslides, by eruptions or by asteroid impacts. l Tides are caused by the gravitational attraction of the sun and the moon, by inertia, and by basin resonance. 1 Seiches What are the characteristics of a seiche? Water rocking back and forth at a specific resonant frequency in a confined area is a seiche. Seiches are also called standing waves. The node is the position in a standing wave where water moves sideways, but does not rise or fall. 2 1 Seiches A seiche in Lake Geneva. The blue line represents the hypothetical whole wave of which the seiche is a part. 3 Tsunami and Seismic Sea Waves Tsunami are long-wavelength, shallow-water, progressive waves caused by the rapid displacement of ocean water. Tsunami generated by the vertical movement of earth along faults are seismic sea waves. What else can generate tsunami? llandslides licebergs falling from glaciers lvolcanic eruptions lother direct displacements of the water surface 4 2 Tsunami and Seismic Sea Waves A tsunami, which occurred in 1946, was generated by a rupture along a submerged fault. The tsunami traveled at speeds of 212 meters per second. 5 Tsunami Speed How can the speed of a tsunami be calculated? Remember, because tsunami have extremely long wavelengths, they always behave as shallow water waves. -
Numerical Calculation of Seiche Motions in Harbours of Arbitrary Shape
NUMERICAL CALCULATION OF SEICHE MOTIONS IN HARBOURS OF ARBITRARY SHAPE P. Gaillard Sogreah, Grenoble, France ABSTRACT A new method of calculation of wave diffraction around islands, off- shore structures, and of long wave oscillations within offshore or shore-connected harbours is presented. The method is a combination of the finite element technique with an analytical representation of the wave pattern in the far field. Examples of application are given, and results are compared with other theoretical and experimental investig- ations. INTRODUCTION The prediction of possible resonant response of harbours to long wave excitation may be an important factor at the design stage. Hydraulic scale models have the disadvantage of introducing some bias in the results due to wave reflection on the wave paddle and on the tank boundaries. Numerical methods on the other hand can avoid such spurious effects by an appropriate representation of the unbounded water medium outside the harbour. Various numerical methods exist for calculating the seiche motions in harbours of arbitrary shape and water depth configuration. Among these, the hybrid-element methods, as described by Berkhoff [l] , Bettess and Zienkiewicz [2] , Chen and Mei [3j , Sakai and Tsukioka [8] use a com- bination of the finite element technique with other methods for repre- senting the velocity potential within the harbour and in the offshore zone. This paper presents a new method based on the same general approach, with an analytical representation of the wave pattern in the far field. It differs from the former methods in several aspects stressed hereafter. We consider here two kinds of applications: a) the first is the study of wave diffraction by islands or bottom seated obstacles in the open sea and the study of wave oscil- lations within and around an offshore harbour. -
Estimation of Significant Wave Height Using Satellite Data
Research Journal of Applied Sciences, Engineering and Technology 4(24): 5332-5338, 2012 ISSN: 2040-7467 © Maxwell Scientific Organization, 2012 Submitted: March 18, 2012 Accepted: April 23, 2012 Published: December 15, 2012 Estimation of Significant Wave Height Using Satellite Data R.D. Sathiya and V. Vaithiyanathan School of Computing, SASTRA University, Thirumalaisamudram, India Abstract: Among the different ocean physical parameters applied in the hydrographic studies, sufficient work has not been noticed in the existing research. So it is planned to evaluate the wave height from the satellite sensors (OceanSAT 1, 2 data) without the influence of tide. The model was developed with the comparison of the actual data of maximum height of water level which we have collected for 24 h in beach. The same correlated with the derived data from the earlier satellite imagery. To get the result of the significant wave height, beach profile was alone taking into account the height of the ocean swell, the wave height was deduced from the tide chart. For defining the relationship between the wave height and the tides a large amount of good quality of data for a significant period is required. Radar scatterometers are also able to provide sea surface wind speed and the direction of accuracy. Aim of this study is to give the relationship between the height, tides and speed of the wind, such relationship can be useful in preparing a wave table, which will be of immense value for mariners. Therefore, the relationship between significant wave height and the radar backscattering cross section has been evaluated with back propagation neural network algorithm. -
Deep Ocean Wind Waves Ch
Deep Ocean Wind Waves Ch. 1 Waves, Tides and Shallow-Water Processes: J. Wright, A. Colling, & D. Park: Butterworth-Heinemann, Oxford UK, 1999, 2nd Edition, 227 pp. AdOc 4060/5060 Spring 2013 Types of Waves Classifiers •Disturbing force •Restoring force •Type of wave •Wavelength •Period •Frequency Waves transmit energy, not mass, across ocean surfaces. Wave behavior depends on a wave’s size and water depth. Wind waves: energy is transferred from wind to water. Waves can change direction by refraction and diffraction, can interfere with one another, & reflect from solid objects. Orbital waves are a type of progressive wave: i.e. waves of moving energy traveling in one direction along a surface, where particles of water move in closed circles as the wave passes. Free waves move independently of the generating force: wind waves. In forced waves the disturbing force is applied continuously: tides Parts of an ocean wave •Crest •Trough •Wave height (H) •Wavelength (L) •Wave speed (c) •Still water level •Orbital motion •Frequency f = 1/T •Period T=L/c Water molecules in the crest of the wave •Depth of wave base = move in the same direction as the wave, ½L, from still water but molecules in the trough move in the •Wave steepness =H/L opposite direction. 1 • If wave steepness > /7, the wave breaks Group Velocity against Phase Velocity = Cg<<Cp Factors Affecting Wind Wave Development •Waves originate in a “sea”area •A fully developed sea is the maximum height of waves produced by conditions of wind speed, duration, and fetch •Swell are waves -
Continuous Seiche in Bays and Harbors
Manuscript prepared for Ocean Sci. with version 2014/07/29 7.12 Copernicus papers of the LATEX class copernicus.cls. Date: 14 February 2016 Continuous seiche in bays and harbors J. Park1, J. MacMahan2, W. V. Sweet3, and K. Kotun1 1National Park Service, 950 N. Krome Ave, Homestead, FL, USA 2Naval Postgraduate School, 833 Dyer Rd., Monterey, CA 93943, USA 3NOAA, 1305 East West Hwy, Silver Spring, MD, USA Correspondence to: J. Park ([email protected]) Abstract. Seiches are often considered a transitory phenomenon wherein large amplitude water level oscillations are excited by a geophysical event, eventually dissipating some time after the event. However, continuous small–amplitude seiches have been recognized presenting a question as to the origin of continuous forcing. We examine 6 bays around the Pacific where continuous seiches 5 are evident, and based on spectral, modal and kinematic analysis suggest that tidally–forced shelf– resonances are a primary driver of continuous seiches. 1 Introduction It is long recognized that coastal water levels resonate. Resonances span the ocean as tides (Darwin, 1899) and bays as seiches (Airy, 1877; Chrystal, 1906). Bays and harbors offer refuge from the open 10 ocean by effectively decoupling wind waves and swell from an anchorage, although offshore waves are effective in driving resonant modes in the infragravity regime at periods of 30 s to 5 minutes (Okihiro and Guza, 1996; Thotagamuwage and Pattiaratchi, 2014), and at periods between 5 minutes and 2 hours bays and harbors can act as efficient amplifiers (Miles and Munk, 1961). Tides expressed on coasts are significantly altered by coastline and bathymetry, for example, 15 continental shelves modulate tidal amplitudes and dissipate tidal energy (Taylor, 1919) such that tidally–driven standing waves are a persistent feature on continental shelves (Webb, 1976; Clarke and Battisti, 1981). -
Swell and Wave Forecasting
Lecture 24 Part II Swell and Wave Forecasting 29 Swell and Wave Forecasting • Motivation • Terminology • Wave Formation • Wave Decay • Wave Refraction • Shoaling • Rouge Waves 30 Motivation • In Hawaii, surf is the number one weather-related killer. More lives are lost to surf-related accidents every year in Hawaii than another weather event. • Between 1993 to 1997, 238 ocean drownings occurred and 473 people were hospitalized for ocean-related spine injuries, with 77 directly caused by breaking waves. 31 Going for an Unintended Swim? Lulls: Between sets, lulls in the waves can draw inexperienced people to their deaths. 32 Motivation Surf is the number one weather-related killer in Hawaii. 33 Motivation - Marine Safety Surf's up! Heavy surf on the Columbia River bar tests a Coast Guard vessel approaching the mouth of the Columbia River. 34 Sharks Cove Oahu 35 Giant Waves Peggotty Beach, Massachusetts February 9, 1978 36 Categories of Waves at Sea Wave Type: Restoring Force: Capillary waves Surface Tension Wavelets Surface Tension & Gravity Chop Gravity Swell Gravity Tides Gravity and Earth’s rotation 37 Ocean Waves Terminology Wavelength - L - the horizontal distance from crest to crest. Wave height - the vertical distance from crest to trough. Wave period - the time between one crest and the next crest. Wave frequency - the number of crests passing by a certain point in a certain amount of time. Wave speed - the rate of movement of the wave form. C = L/T 38 Wave Spectra Wave spectra as a function of wave period 39 Open Ocean – Deep Water Waves • Orbits largest at sea sfc. -
TSUNAMI and SEICHE
TSUNAMI and SEICHE DEFINITIONS: Seiche – The action of a series of standing waves (sloshing action) of an enclosed body or partially enclosed body of water caused by earthquake shaking. Seiche action can affect harbors, bays, lakes, rivers, and canals. Tsunami – A sea wave of local or distant origin that results from large-scale displacements of the seafloor associated with large earthquakes, major submarine slides, or exploding volcanic islands. BACKGROUND INFORMATION: Tsunami The Pacific Coast of Washington is at risk from tsunamis. These destructive waves can be caused by coastal or submarine landslides or volcanism, but they are most commonly caused by large submarine earthquakes. Tsunamis are generated when these geologic events cause large, rapid movements in the sea floor that displace the water column above. That swift change creates a series of high-energy waves that radiate outward like pond ripples. Offshore tsunamis would strike the adjacent shorelines within minutes and also cross the ocean at speeds as great as 600 miles per hour to strike distant shores. In 1946, a tsunami was initiated by an earthquake in the Aleutian Islands of Alaska; in less than 5 hours, it reached Hawaii with waves as high as 55 feet and killed 173 people. Tsunami waves can continue for hours. The first wave can be followed by others a few minutes or a few hours later, and the later waves are commonly larger. The first wave to strike Crescent City, California, caused by the Alaska earthquake in Prince William Sound in 1964, was 9 feet above the tide level; the second, 29 minutes later, was 6 feet above tide, the third was about 11 feet above the tide level, and the fourth, most damaging wave was more than 16 feet above the tide level. -
Unit 4 Earthquake Effects
Unit 4 Earthquake Effects INTRODUCTION In the last unit, we looked at the causes and characteristics of earthquakes. Now let’s take a look at an earthquake’s effects on the natural and built environments. Knowing more about the effects of earthquakes helps us understand the mitigation steps that must be taken to protect a community from a seismic event. Unit 4 covers the following topics: • What are some effects of earthquakes on the natural and built environments? • What building characteristics are significant to seismic design? • How do buildings resist earthquake forces? • What secondary consequences of earthquakes must we be concerned with? WHAT ARE SOME EFFECTS OF EARTHQUAKES ON THE NATURAL ENVIRONMENT? In the last unit, we reviewed the different types of seismic waves that produce the violent ground shaking, or motion, associated with earthquakes. These wave vibrations produce several different effects on the natural environment that also can cause tremendous damage to the built environment (buildings, transportation lines and structures, communications lines, and utilities). Researching potential problems, known as site investigation, is a good first step in reducing damage to the built environment due to earthquakes. Page 4-2 Earthquake Effects Liquefaction Strong ground motion during an earthquake can cause water-saturated, unconsolidated soil to act more like a dense fluid than a solid; this process is called liquefaction. Liquefaction occurs when a material of solid consistency is transformed, with increased water pressure, in to a liquefied state. Water saturated, granular sediments such as silts, sands, and gravel that are free of clay particles are susceptible to liquefaction. Imagine what would happen to a building if the soil beneath it suddenly behaved like a liquid. -
Statistics of Extreme Waves in Coastal Waters: Large Scale Experiments and Advanced Numerical Simulations
fluids Article Statistics of Extreme Waves in Coastal Waters: Large Scale Experiments and Advanced Numerical Simulations Jie Zhang 1,2, Michel Benoit 1,2,* , Olivier Kimmoun 1,2, Amin Chabchoub 3,4 and Hung-Chu Hsu 5 1 École Centrale Marseille, 13013 Marseille, France; [email protected] (J.Z.); [email protected] (O.K.) 2 Aix Marseille Univ, CNRS, Centrale Marseille, IRPHE UMR 7342, 13013 Marseille, France 3 Centre for Wind, Waves and Water, School of Civil Engineering, The University of Sydney, Sydney, NSW 2006, Australia; [email protected] 4 Marine Studies Institute, The University of Sydney, Sydney, NSW 2006, Australia 5 Department of Marine Environment and Engineering, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan; [email protected] * Correspondence: [email protected] Received: 7 February 2019; Accepted: 20 May 2019; Published: 29 May 2019 Abstract: The formation mechanism of extreme waves in the coastal areas is still an open contemporary problem in fluid mechanics and ocean engineering. Previous studies have shown that the transition of water depth from a deeper to a shallower zone increases the occurrence probability of large waves. Indeed, more efforts are required to improve the understanding of extreme wave statistics variations in such conditions. To achieve this goal, large scale experiments of unidirectional irregular waves propagating over a variable bottom profile considering different transition water depths were performed. The validation of two highly nonlinear numerical models was performed for one representative case. The collected data were examined and interpreted by using spectral or bispectral analysis as well as statistical analysis. -
Surface Seiches in Flathead Lake
Hydrol. Earth Syst. Sci., 19, 2605–2615, 2015 www.hydrol-earth-syst-sci.net/19/2605/2015/ doi:10.5194/hess-19-2605-2015 © Author(s) 2015. CC Attribution 3.0 License. Surface seiches in Flathead Lake G. Kirillin1,2, M. S. Lorang2, T. C. Lippmann2,3, C. C. Gotschalk2, and S. Schimmelpfennig1 1Department of Ecohydrology, Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB), Berlin, Germany 2The University of Montana, Flathead Lake Biological Station, Polson, MT, USA 3University of New Hampshire, Dept. of Earth Sciences and Center for Coastal and Ocean Mapping, NH, USA Correspondence to: G. Kirilin ([email protected]) Received: 10 October 2014 – Published in Hydrol. Earth Syst. Sci. Discuss.: 10 December 2014 Revised: 14 April 2015 – Accepted: 11 May 2015 – Published: 3 June 2015 Abstract. Standing surface waves or seiches are inherent hy- namics. Seiches exist in any (semi) enclosed basin, where drodynamic features of enclosed water bodies. Their two- long surface waves reflecting at opposite shores interfere to dimensional structure is important for estimating flood risk, produce a standing wave. The longest possible seiche (the coastal erosion, and bottom sediment transport, and for un- first “fundamental” mode) has the wavelength λ that is twice derstanding shoreline habitats and lake ecology in general. the distance between the shores, L. The wavelengths of other In this work, we present analysis of two-dimensional seiche possible modes decrease by even fractions of the distance be- characteristics in Flathead Lake, Montana, USA, a large in- tween shores. Therefore, for the majority of possible modes, termountain lake known to have high seiche amplitudes. -
Random Wave Analysis
RANDOM WA VE ANALYSIS The goal of this handout is to consider statistical and probabilistic descriptions of random wave heights and periods. In design, random waves are often represented by a single characteristic wave height and wave period. Most often, the significant wave height is used to represent wave heights in a random sea. It is important to understand, however, that wave heights have some statistical variability about this representative value. Knowledge of the probability distribution of wave heights is therefore essential to fully describe the range of wave conditions expected, especially the extreme values that are most important for design. Short Term Statistics of Sea Waves: Short term statistics describe the probabilities of qccurrence of wave heights and periods that occur within one observation or measurement of ocean waves. Such an observation typically consists of a wave record over a short time period, ranging from a few minutes to perhaps 15 or 30 minutes. An example is shown below in Figure 1 for a 150 second wave record. @. ,; 3 <D@ Q) Q ® ®<V®®®@@@ (fJI@ .~ ; 2 "' "' ~" '- U)" 150 ~ -Il. Time.I (s) ;:::" -2 Figure 1. Example of short term wave record from a random sea (Goda, 2002) . ' Zero-Crossing Analysis The standard. method of determining the short-term statistics of a wave record is through the zero-crossing analysis. Either the so-called zero-upcrossing method or the zero downcrossing method may be used; the statistics should be the same for a sufficiently long record. Figure 1 shows the results from a zero-upcrossing analysis. In this case, the mean water level is first determined.