Marine Natural Values Study Summary - Parks Victoria

Physical Parameters and ProcessesThe geology of Port Phillip HeadsMarine National Park is dunecalcarenite (limestone) with somesections covered with sand, thoughPopes Eye has an artificial structureof basalt blocks. The park has a widevariety of exposure. Outside the Headsthe southern coasts of Point Lonsdaleand Point Nepean are exposed tosouth-westerly weather and swells ofBass Strait. They receive ocean wavesaveraging about 1.7 metres, whichbreak on the outer reef flats and arriveon the beach with reduced energyand wave height.Between the Heads is a narrow, deep(100 metres) stretch of water that isvery turbulent due to swell, waves,tides and weather. Tidal currentsthrough the Heads dominate watercirculation in southern Port Phillip Bayand can be as fast as 2.5m/s.The park beaches on the inside coastof the Heads receive low wave energyand are dynamic with natural accretionand attrition of sand, covering anduncovering the reefs and otherhabitats.Further inside the bay, Popes Eye andPortsea Hole have moderate exposureto waves and currents.Point Nepean, looking across the Heads to Point Lonsdale,Port Phillip Heads Marine National Park. Photo by SteffanHowe, Parks Victoria.The islands of Mud Islands createa sheltered lagoon, however strongtidal currents and storm eventscontinually alter the shape of MudIslands and the Great Sands. SwanBay is a large shallow shelteredlagoon, with a constricted connectionto Port Phillip Bay by natural andartificial channels either sideof Swan Island.The park has an unequal semidiurnaltidal pattern, with flooding andebbing having both a higherand lower event per day.Tides vary in the different sectionsof the park, from 1.2 metres springand 0.6 metres neap tides in PointLonsdale and Point Nepean, to 0.7metres spring and 0.1 metres neaptides in Portsea Hole and Mud Islands.Tidal currents diminish before theyreach Swan Bay, with a tidal amplitude