Nichols, Charles R.

Roggen, Elena van

Weymer, Bradley

English

University of New Orleans

University of New Orleans ScholarWorks@UNO Ocean Waves Workshop Feb 28th, 9:45 AM - 10:00 AM Session 1 Paper - Beach Profile Changes at Freshwater Beach in Queensland, Australia Elena van Roggen Marine Information Resources Corporation Bradley Weymer Marine Information Resources Corporation and Texas A&M University Charles R. Nichols Marine Information Resources Corporation, rnichols@mirc-us.com Follow this and additional works at: https://scholarworks.uno.edu/oceanwaves Roggen, Elena van; Weymer, Bradley; and Nichols, Charles R., "Session 1 Paper - Beach Profile Changes at Freshwater Beach in Queensland, Australia" (2013). Ocean Waves Workshop. 4. https://scholarworks.uno.edu/oceanwaves/2013/Session1/4 This Event is brought to you for free and open access by ScholarWorks@UNO. It has been accepted for inclusion in Ocean Waves Workshop by an authorized administrator of ScholarWorks@UNO. For more information, please contact scholarworks@uno.edu. Ocean Waves Workshop (http://www.oceanwavesworkshop.uno.edu) Proceedings (2013) / 10  Beach Profile Changes at Freshwater Beach in Queensland, Australia Elena van Roggen1) and C. Reid Nichols 1) 1) Marine Information Resources Corporation  *Corresponding author: evanroggen@mirc-us.com  Abstract—Environmental factors such as waves, temperature, and beach gradients are very important for amphibious planning.  At the Shoalwater Bay Training Area in Queensland, Australia, beach profiles changes measured from nautical charts, and surveys in 2009 and 2012 are considered to have been caused by severe storms and in particular the relationship between wave height and wave period.  Future work to look at changes in wave steepness in association with erosion and accretion would support the management of Freshwater Beach. 1. Introduction During 2009 and 2012, the Remote Sensing Division of the Naval Research Laboratory conducted several multidisciplinary and integrated coastal studies at Freshwater Beach in Queensland, Australia to assess the utility of hyperspectral imagery to retrieve shallow water bathymetry and estimate trafficability parameters [1]. While oceanographic and geotechnical data were collected to support the exploitation of hyperspectral imagery, they also provided information on the manner in which wave and current action deposited and reworked sediments along beaches facing the Coral Sea. Data and information collected from these remote sensing studies have the secondary benefit of characterizing beach profile changes that were measured using GPS survey equipment.  These beach changes are considered to be in response to wave energy experienced during storms occurring between remote sensing experiments.   Understanding the effects of wave and storm surge action on beach profiling will help not only predict gradients on unfamiliar beaches, but also predict changes to known beach profiles where military training takes place. Both predictions are essential for the planning of surf zone breaching by amphibious vehicles including air cushion vehicles (or hovercraft), as well as for the safety of those attempting to traverse the dune system from the foreshore. Over-water performance for hovercraft is also greatly impacted by wave height and period while slope and “step-up” have to be considered for surf zone breaching and overland movement. The Queensland coast is often subject to multiple tropical cyclones per year, and has seen a number of severe cyclones in the past seven years. Tropical cyclone Yasi in 2011, one of the strongest cyclones in recent history, had wind speeds of up to 285km/h and a 5m tidal surge [3]. Tropical cyclone Ului in 2010 had wind speeds up to 215km/h and a storm surge of 2.45m. Tropical cyclones and Coral Sea low pressure systems, all of which produce gale-force winds along the Queensland coast, have an almost 50% chance of being followed by another storm event within 60 days [5]. The frequency of such events fluctuates annually and is influenced by the Southern Oscillation.  Cyclone effects are amplified in the region of the study area for two reasons. First, the Swain reefs at the southern tip of the Great Barrier Reef lie about 100km off the coast of Freshwater Beach, creating the Capricorn Channel (Fig. 1). This channel funnels winds and currents into a northwest/southeast direction along the coast, the direction with the longest fetch [5]. Secondly, the average cyclone path travels from east to west just north of the study area (Fig. 2). The clockwise rotation of tropical cyclones causes areas just south of their paths to be hit with the highest wind speeds when approaching the coast. Thus, the southern Queensland coast receives some of the worst cyclone effects.   Figure 1. Location of the Capricorn Channel in relation to the study site.  Figure 2. Path of tropical cyclone Yasi [3]. A series of recent floods also impacted the Queensland coast, beginning in December 2010, with a high concentration of moderate to major floods in the Rockhampton area. The Fitzroy river, whose watershed includes the study area, reached one of its highest depths ever recorded of 9.20m in early January 2011 [6]. Such  Ocean Waves Workshop (http://scholarworks.uno.edu/oceanwaves/) Proceedings (2013) / 11  severe flood events may have contributed to the observed beach profile changes at Freshwater Beach in the form of sediment accretion. 3.   Methods Beach profiles prior to 2009 were calculated from nautical charts, while kinematic GPS was used to measure beach profiles during 2009.  The most recent surveys during 2012 involved the use of kinematic GPS, Total Stations (electronic distance meter and theodolite) and ground-based LiDAR. The combined use of these instruments made it possible to accurately gather large amounts of survey measurements quickly. Kinematic GPS data were also used to provide beach profiles. Water levels were obtained from a GPS buoy and traditional tide predictions.  Data from this buoy were essential to tide-synchronize imagery and to de-tide multi-beam echosounder data from very shallow water surveys. Wave measurements were obtained from wave buoys managed by the Queensland Government Department of Environment and Heritage Protection at various locations surrounding the study site. These Datawell 0.9m diameter GPS Waverider buoys include lengths of rubber in their moorings to allow for stretching up to three times its length [2]. Wave heights and periods are recorded, in addition to wave direction and sea surface temperature [2]. Significant wave height, maximum wave height, period and zero crossing period, direction, and temperature are collected as averages every 26.6 minutes. Fig. 3 shows a diagram of the Waverider buoy components.  Buoys were deployed offshore of MacKay, Hay Point, Emu Park, and Gladstone – locations both north and south of the study site (Fig. 4), with a maximum distance around 215km. Table 1 provides station  data for each buoy, including installation date and water depth.   Wave buoy data from the eight most recent storm events impacting the study area can be compared to beach profiles. These events included tropical cyclones Jim, Larry, and Wati from 2006, Hamish from 2009, Ului from 2010, Anthony and Yasi from 2011, and Oswald from 2013. As an example, plots of significant wave height, period, direction, and sea surface temperature during the storm events for Mackay are included in Fig. 5.  The average wave direction of all buoys during storm events is approximately 100° from true north. This is comparable to the angle of the Queensland coast in the study site's region, and also comparable to the angle of the Capricorn Channel from true north. This further proves the power of the channel to direct winds, and therefore waves, toward the study area parallel to the coast.  The maximum wave height for all buoy locations and storm events occurred at McKay with a height of 9.44m during tropical cyclone Ului. Ului also had some of the highest average wave heights between the four buoy locations.         Figure 3. Datawell 0.9m GPS Waverider buoy [2]  Figure 4. Locations of wave buoys in relation to the study site   Table 1. Wave buoys surrounding the study site [2].  Latitude Longitude Start Date Depth Mackay 21° 02.375'S 149° 32.750'E 20/9/75 28 Hay Point 21° 16.276'S 149° 18.572'E 3/2/93 10 Emu Park 23° 18.380'S 151° 04.380'E 24/7/96 18 Gladstone 23° 53.670'S 151° 30.220'E 23/7/09 13  Beach profiles derived from data collection along with historical chart data at Freshwater Beach are displayed in Fig. 6. Erosion since 2006 is visible, and may be attributed to recent storm wave action. Ocean Waves Workshop (http://www.oceanwavesworkshop.uno.edu) Proceedings (2013) / 12  Figure 5. Wave buoy records at Mackay during recent storm events [7]. Accessible data included (a) significant wave height (b) dominant or peak wave period (c) wave direction (d) and sea surface temperature.  Figure 6. Northern Freshwater Beach profile. [4]  4.    Results and Conclusions The average difference between beach profiles (Fig. 6) is -6.016m. By observation, this erosion is linked to episodic extreme weather events that have been associated with large waves, such as those associated with the storm events previously mentioned. This, along with impacts from currents, flooding events, and other natural processes may explain the changes in Freshwater Beach's profile over the past seven years.  While large waves are typically thought of as being responsible for beach erosion, the relationship between wave height and wave period is also significant. Longer period waves tend to result in less erosion than the shorter period waves.   Wave steepness, a parameter used to describe the ratio of a wave's height to its length, may also be used to understand beach erosion. When the steepness is greater than approximately 0.025, the waves are considered erosional, while those less than 0.025, are considered accretional [8]. The calculation of wave steepness requires not only wave height, but also wavelength - a parameter not included in public data provided by the Queensland wave monitoring program.    A more accurate estimation of the effects of extreme wave actions on beach profiles is difficult without having access to long-term wave observations, currents, and water level records.  At a minimum, the computation of wave steepness should be standard for wave buoy measurements and recording, and should be easily accessible to the public as a complement to basic wave records. This additional information would be useful to compare with beach profile changes and is an important factor to help prevent capsizing by boaters. Shoreline retreat leads to greater landward encroachment of waves and flooding by the Coral Sea. Future analyses should systematically compare wave buoy data with beach profiles in order to determine the rate of the beach’s recovery from these episodic weather events. Such studies would provide insight into shoreline morphology beneficial for land use planning, development, tactical planning, and numerous other applications.  References [1] Bachmann, C. M.,  R.A. Fusina, M.J. Montes, R-R Li, C. Gross, C.R. Nichols,  J.C. Fry, C. Parrish, J. Sellars, S. White, C. Jones, and K. Lee, 2012. Talisman-Saber 2009 Remote Sensing Experiment, NRL Memorandum Report NRL/MR/7230—9404, Washington, D.C.: Naval Research Laboratory.  [2] Wave Recording at Mackay. Available online. URL: http://www.ehp.qld.gov.au/coastal/monitoring/waves/site.php?siteid=11. Accessed on December 6, 2012. [3] Tropical Cyclone Yasi February 2011. Available online. URL: http://www.ehp.qld.gov.au/management/pdf/tc_yasi_feb_2011.pdf. Accessed on December 6, 2012.  [4] Weymer, Bradley A., Elena van Roggen, Chris Houser, and Rick Giardino. 2012. Alongshore variability in beach planform and foredune height of an embayed beach: Shoalwater Bay, Queensland, Australia. American Geophysical Union Fall Meeting, San Francisco, California. [5] Queensland Government, Environmental Protection Agency, 2004. Mackay Coast Study Report, chapter 10: Waves. Available online, URL: http://www.ehp.qld.gov.au/register/p01549aj.pdf. Accessed on January 25, 2013. [6] Australian Government Bureau of Meteorology, 2011. Flood Warning System for the Fitzroy River . Available online, URL: http://www.bom.gov.au/qld/flood/brochures/fitzroy/fitzroy.pdf. Accessed on February 7, 2012 [7] Coastal Impacts Unit: Department of Science, Information Technology, Innovation and the Arts. Deagon, Queensland Australia [8] The Jersey Shoreline, 2010. Rethinking Storm-Related Beach Erosion. Available online, URL: -15-55152535-1000 -500 0 500Elevation (m) Distance from HAT (m) All Elevations in Reference to LAT (8.167m) All Distances in Reference to HAT (13.307m) Historical Chart DataTHEMAS'12 ProfileResidual(a) (b) (c) (d)  Ocean Waves Workshop (http://scholarworks.uno.edu/oceanwaves/) Proceedings (2013) / 13  http://www.njseagrant.org/jersey-shoreline/vol26_no4/articles/rethinking-beach-erosion.html. Accessed on February 26, 2013.                                                                 

Session 1 Paper - Beach Profile Changes at Freshwater Beach in Queensland, Australia

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Session 1 Paper - Beach Profile Changes at Freshwater Beach in Queensland, Australia

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