Marmion Marine Park management Plan - Department of ...

Actions1. Maintain liaison between the Water Authority, EPA, City of Wanneroo and CALMto minimise detrimental environmental effects of outfalls.2. Ensure that further monitoring and evaluation of nutrient input is undertaken toquantify the ecological effects of the nutrient discharge from the Beenyup TreatmentPlant, and to enable a prediction to be made of the likely levels of nutrients that willdischarge in groundwater (see 26.9 Drainage and Discharge).3. Co-ordinate monitoring and research programs being undertaken by State agencies,CSIRO and tertiary institutions.15.0 COASTAL PROCESSESComplex interactions between wind, waves, hydrology and geology are always occurring in coastalprocesses that continuously shape the coastline.Swell-induced onshore transport occurs in a complex zone of swell wave interference behind theMarmion reefs. This has led to major movement of sediment from the reefs to the mainland coast toform Lal Bank, Whitford Plain and the transgressive dunes that overlay the mainland ridge. Atpresent, minor onshore transport is evident as a thin plume of sand moving across the seagrasscovered bank.In the surf zone, swell-induced longshore transport moves sand towards the zone of onshore transportbehind the Marmion Reefs. This has minimised longshore sediment losses from within the Park areaand has been dominant in maintaining the triangular shape of Whitford Plain. Local wave-inducedlongshore transport in the surf zone moves sediment northward in summer, especially along the shorebetween Sorrento and Mullaloo Point, and along the rocky coast immediately north of Mullaloo. Incontrast, during winter, transport is southwards especially between Ocean Reef and Hillarys where thecoast erodes each winter. Owing to the dominance of the summer wind-wave regime, there is a netmovement of sediment northwards. This has led to modification of the swell-controlled shape of theWhitford Plain.Wind transport which blows sand inland on coasts exposed to south-west and westerly winds is also anongoing coastal process. With the exception of the 'Little Desert' north of Mullaloo there is, at28