Manly Lagoon Dredging Project - Manly Council - NSW Government

Manly Lagoon Dredging Project – Review of Environmental FactorsPrepared for Manly and Warringah Councils2010). The dredging works are also largely confined to within Manly Lagoon (aquatic habitat)and all land based activities will be occurring on cleared/highly modified land.Pest SpeciesThe proposed works have the potential to introduce and spread non-native marinevegetation in Manly Lagoon via translocation on silt curtains and dredging machinery(including excavators), which is identified in Schedule 6 of the Fisheries Management Act1994 as a key threatening process for native species. Of particular concern is the non-nativespecies Caulerpa (Caulerpa taxifolia), which is listed as a Class 1 noxious species in allNSW waters under the Fisheries Management Act 1994. Caulerpa taxifolia is a potentialthreat because it grows rapidly, and may out-compete and smother native flora such asseagrass. It also produces toxic substances that deter many herbivores from grazing upon it,reducing the potential for grazing to limit its extent and distribution. It can also survive out ofwater in moist conditions (e.g. silt curtains) for several days (I&I NSW, 2009).Endangered Ecological CommunitiesNo works / shore-based site presence will occur or be established along the south bank ofthe lagoon, where three of the five sections of EECs are located (Figure 5.10). Nodisturbance to bank vegetation due to the proposed works is anticipated in these areas, andthere is no significant foreseeable indirect impact on these areas of EEC.Nolan Reserve is the preferred location for the dewatering of dredge spoil and theestablishment of a contractor’s compound. Two sections of the Swamp Sclerophyll ForestEEC are located within Nolan Reserve and may potentially be indirectly impacted upon bythe shore-based activities.The proposed site compound (construction and dewatering zone) is indicated on the SitePlan in Appendix M. This location was selected from a range of proposed options, based onenvironmental and topographical considerations, and access to the Lagoon. Access pointsto the Lagoon for the dredging pipes may potentially require minimal clearing of vegetation;however adequate protection will be provided to preserve the EEC in the vicinity.Impacts on any EEC are considered unlikely, since no direct disturbance of any EEC will berequired by the works proposed due to the use of a floating barge platform during dredging,and the works proposed will be of a relatively short duration. The greatest risk to the EEC isconsidered to be physical damage from accidental vehicle strike during site establishment ordecommissioning, or from soil erosion in the event of uncontrolled discharge of water in thearea.The Seven Part Tests for the two EECs concluded that the proposal is not likely to result in asignificant impact on the local occurrence of Swamp Sclerophyll Forest on CoastalFloodplain or Swamp Oak Floodplain Forest (Warringah Council, 2010; Appendix N).2 July 2010 Cardno (NSW/ACT) Pty Ltd 77H:\Doc\2010\Reports.2010\Rep2580v4.doc