Yeppoon Main Beach: Monitoring and analysis for the period 2001 - 2004

The Yeppoon Main Beach is one of the most prominent beaches along the Capricorn Coast. A 90 year history of human activities on this beach has significantly changed the

beach from well-established natural dune system to a beach with a rubble-mound seawall that has cut off the beach from dunal buffer and sand storage. The recent reconstruction of a seawall and development of an esplanade started in December 2000 and was completed in February 2003. The goal was to achieve a safe attractive beach and modernise the recreation area along the beach.

The current study analysed beach changes after reconstruction of the existing rubble mound seawall. The presented analyses cover observed changes to the beach since October 2001 when the new seawall was almost completed. They are based on regular beach profiles measurement and application of a numerical model MEPBAY, based on the crenulate shaped bay theory.

The analysis of the last eight years of wave data (since 1996) indicate the moderate wave conditions with the very stable predominant waves direction of about 84° azimuth. Maximum recorded wave height, Hmax, was up to 3.9m, recorded in winter 2004 having wave peak periods in the order of 5-6 seconds. Maximum average annual significant wave height, Hm0, was about 2.5m.

The beach conditions have been without significant trends in progressing erosion or accretion for the period after the seawall reconstruction. The fluctuations of the shoreline are periodical. The most exposed parts of the beach to the wave action are its central and northern parts. The last year total accumulation of sand along the beach was in the order of 1900m3 with minor erosion in its central part. Average accumulation of sand for the previous two years was 700m3.

Without engineering intervention it is not expected there will be any sufficient natural accumulation of sand in front of the seawall in this region to reduce wave reflection and to increase wave energy absorption by the natural sandy beach.

Because littoral drift is very low in the region of the Y eppoon Main Beach, the crossshore sediment transport plays a much more important role in reshaping of the beach. Thus the crenulate shaped bay theory may find applicability to the analysis of beach restoration. MEPBA Y model was used for this analysis. The recorded shoreline was used to verify the local wave direction and the best agreement was obtained for nearshore wave direction in the order of 90° azimuth and the angle between the control

line and wave crests in the order of 38°.

The program MEPBA Y allowed analysis of several positions of artificial headlands to obtain optimal improvement of the beach considering its stability and protection of the seawall.

Least costly option, worth considering, would be a short, of the order of 40m, extension of the rocks on the beach in front of the bluff. It may improve beach conditions in the northern part of the beach and consequently positively influence on the stability of the whole beach.