Wave data recording program Abbot Point Region For the years 1977 to 1996 Conservation data report No. W06.2 ISSN 0158-7757 RE ? Wave data recording program - Abbot Point Region for the years 1977 to 1996 1 May 1997 y ISSN 0158 - 7757 y RE Wave data recording program Abbot Point Region For the years 1977 to 1996 Abstract This report summarises the primary analyses of wave the Department of Environment. Direct enquiries to the data recorded using a Datawell non-directional Manager, Education and Information Unit, PO Box waverider buoy in water depths of approximately 155 BRISBANE ALBERT STREET QLD 4002. 12 metres, at offshore locations near Abbot Point in northern Queensland. Data were from 7 May 1977 to RE??? May 1997 9 August 1979 and from 8 November 1982 to Recycled paper saves energy and resources 31 October 1996. The data were divided into seasonal groupings for analysis. No estimations of wave Contents direction data have been provided. 1 Introduction 2 Recording equipment This report has been prepared by the Coastal 2.1 Waverider system Management Branch, Division of Conservation, 2.2 Wave pole system Department of Environment on behalf of the Beach 2.3 Station configuration Protection Authority. 2.4 Laboratory calibration checks 3 Wave recording and analysis procedures Wave data recording program 4 Data losses Abbot Point Region 1977–1996 5 Wave climate 5.1 Methodology Disclaimer 6 Data presentation While data in this report were collected, processed and 7 References compiled with reasonable care, the accuracy and 8 Other reports in this series reliability of this information is not guaranteed in any way by the Beach Protection Authority. Neither the Appendices Queensland Government nor the Authority accepts Appendix 1. Details of wave recorder liability for any decision or actions taken on the basis installation. of this report. Appendix 2. Major meteorological events. Appendix 3. Tropical cyclones of the east Copyright coast of Queensland. Queensland Government 1997 Copyright protects this publication. Except for purposes permitted by the Copyright Act, storage, transmission or reproduction of all or any part by any means is prohibited without prior written permission of Wave data recording program - Abbot Point Region for the years 1977 to 1996 2 May 1997 y ISSN 0158 - 7757 y RE Tables The Beach Protection Authority, as part of its long term data collection program, has maintained a network of Table 1. Wave statistics; wave period (Tp)/wave wave recording stations along the Queensland coast since height (Hsig) occurrences—all data, all 1968. This report summarises the primary analyses of directions, measured in days. wave data collected at the Abbot Point station. It also Table 2. Wave statistics; wave period (Tp)/wave provides brief details of the recording equipment, the height (Hsig) occurrences—summer methods of handling raw data and the type of analyses data, all directions, measured in days. employed. Table 3. Wave statistics; wave period (Tp)/wave height (Hsig) occurrences—winter data, all directions, measured in days. 2 Recording equipment Table 4. Wave statistics; wave period (Tp)/wave The Beach Protection Authority’s wave recording height (Hsig) occurrences—all data, all program utilises either of two systems to measure wave directions, measured in percentage data; the waverider buoy or the wave pole system. occurrences. Table 5. Wave statistics; wave period (Tp)/wave 2.1 Waverider system height (Hsig) occurrences—summer The waverider system manufactured by Datawell bv of data, all directions, measured in the Netherlands utilises a waverider buoy to measure percentage occurrences. the sea surface fluctuations at an offshore location. Table 6. Wave statistics; wave period (Tp)/wave Both directional and non-directional buoys are height (Hsig) occurrences—winter data, presently in operation with the Authority. all directions, measured in percentage occurrences. Both the directional and non-directional waverider buoys measure vertical acceleration by means of an Figures accelerometer, mounted on a gravity stabilised platform suspended in a fluid filled plastic sphere Figure 1. Locality plan. located at the bottom of the buoy. The vertical Figure 2. Percentage (of time) exceedance of wave accelerations are then twice integrated to give vertical heights (Hsig) for all wave periods (Tp). displacement. Figure 3. Histogram percentage (of time) occurrence of wave heights (Hsig) for The directional buoy also measures acceleration in the all wave periods (Tp). horizontal plane using two additional accelerometers Figure 4. Histogram percentage (of time) fixed at perpendicular axes. After conversion of these occurrence of wave periods (Tp) for accelerations to horizontal displacements, the direction all wave heights (Hsig). of the buoy movement is derived by a transformation Figure 5. Wave parameter relationships. to north-south and east-west using a bearing from the Figure 6. Daily wave recordings. on-board fluxgate compass. Figure 7. Whole recording period wave heights (Hsig). The vertical buoy displacement, representing the Figure 8. Cyclone tracks. instantaneous water level, and directional data (if present) are then transmitted to the recording station as 1 Introduction a frequency modulated high frequency radio signal. Wave data recording program - Abbot Point Region for the years 1977 to 1996 3 May 1997 y ISSN 0158 - 7757 y RE and, along with the paper charts, transferred to the 2.2 Wave pole system Brisbane office for processing. The wave pole system, manufactured by the On 11 November 1993, the Abbot Point wave Queensland Government Hydraulics Laboratory, recording station was re-established with a non- consists of a single perforated metal pipe surrounding directional waverider buoy and the recording system an inner metal pipe, which acts as a coaxial upgraded to a personal computer (PC) based system transmission line to the water, with an enclosed circuit utilising the Datawell DIWAR waverider receiver/ board housing containing an electronic oscillator digitiser. The water level data, digitised at 0.39 second mounted on the top. This system is mounted vertically intervals (2.56Hz), is recorded in bursts of 4096 points on a suitable offshore structure. (approximately 26 minutes) and recorded on the hard disk of the PC. Relative wave height measurements are taken based on the principle that a sharp change in the electrical The proprietary software running on the PC controls impedance of the wave pole occurs at the fluctuating the timing of data recording and processes the data in water surface and the period of oscillation is linearly ‘near real time’ to provide a set of standard sea-state proportional to the length of the wave pole that is not parameters and spectra that may be accessed remotely immersed in water. via the public telephone network. Recorded data and analysis results are downloaded daily to a central Water surface elevations are recorded at the wave pole computer system in Brisbane for checking, further and are transferred via radio modem to a remote data processing and archiving. recording computer. Further information on the operation of the waverider 2.3 Station configuration buoy and the recording systems can be obtained from In the original configuration of the Abbot Point station, the sources listed in section 7 of this report. for the period 7 May 1977 to 9 August 1979, the installation comprised a waverider 6000 series non- 2.4 Laboratory calibration checks directional buoy and a recording station consisting of a Waverider buoys used by the Authority are calibrated WAREP Mark II waverider receiver coupled to an before deployment and also after recovery. Normally, a ANMA analogue recorder. The WAREP receiver buoy is calibrated once every twelve months. controlled the timing of data recording and provided a Calibration is performed at the Queensland paper chart of the water level recordings and relayed Government Hydraulics Laboratory using a buoy an analogue signal to the ANMA analogue recorder. calibrator (ferris wheel) to simulate sinusoidal waves with amplitudes of either 2m or 2.8m depending on Between 8 November 1982 and 10 November 1993, whether a 0.7m or 0.9m buoy is involved. The the recording station was upgraded to a WAREP Mark calibrator is electrically controlled and the frequency II waverider receiver and a DIMA digitiser/ recorder. may be varied from 0.016–0.25Hz. It is usual to check The WAREP receiver controlled the timing of data three frequencies during a calibration. The following recording and provided a paper chart of the water level characteristics of the buoy are also checked during the signal. Wave data were recorded by the DIMA unit in calibration procedure: 20 minute bursts and digitised at 0.5 second intervals • compass (directional buoy), (2.0Hz). The data were recorded on digital cassettes Wave data recording program - Abbot Point Region for the years 1977 to 1996 4 May 1997 y ISSN 0158 - 7757 y RE • phase and amplitude response, The zero upcrossing analysis is equivalent in both • accelerometer platform stability, systems. • platform tilt, • battery capacity, Wave parameters resulting from this processing • power output. include the following: No adjustment to the recorded wave data in this report, S(f) Energy density spectrum, due to the laboratory calibration results, is done in any Hsig Significant wave height (time way. domain), the average of the highest one third of the waves in 3 Wave recording and analysis the record, Hmax The highest individual wave in procedures From 7 May 1977 to 9 August 1979, wave data were the record, recorded twice daily, each of 20 minutes duration, with Hrms The root mean square of the the timing of recordings set at 0300, and 1500 hours wave heights in the record (time Australian Eastern Standard Time (AEST). domain), Tsig Significant wave period (time Over the period 8 November 1982 to 10 November domain), the average period of 1993, wave data were recorded four times per day at the highest one third of waves in 0300, 0900, 1500 and 2100 hours (AEST).