Summary - City of Gosnells

Wetlands Field Survey 826.2 Geomorphic classification of wetlands in the MKSEA areaThe wetlands of the MKSEA were classified in this survey according to the geomorphic system of Semeniuk(1987), in which the hydroperiod and geomorphic features of wetlands were the sole determinants of wetlandclass (regardless of wetland biota or the factors that maintain the wetland conditions). Most of the existinggeomorphic classifications and mapping of the wetlands of the MKSEA in DEC (2008a) were confirmed inthe current field survey. From the additional fine-scale data that were collected in the current survey(Appendix D) there were, however, some wetlands (Table 6.2) that may require changes to the currentgeomorphic classification. If any changes were to be made to the geomorphic classification of wetlands inthe MKSEA relative to DEC (2008a), these changes would not affect the wetland management categories ofthese wetlands. The wetlands involved will require detailed survey of the topography and an appropriatelydesignedground and surface water monitoring program in order to compile the data necessary for proposingchanges to the SCP Wetlands Dataset. Given the expert resources of wetland specialists to design such adetailed study, a range of pragmatic objectives that could contribute to the remediation of the hydrologicalregime and better management of the biodiversity of the area, apart from a scientifically accurateclassification of the wetlands, could be met by such a study. Some of these objectives could include acharacterisation of the processes that have been important in the development of the wetland (and thus adetermination of the baseline hydrological regime of these wetlands, prior to the widespread alteration of thecatchment) an assessment of the effects of the local drainage scheme on these wetlands and a determinationof the environmental water requirements of the biota of the wetlands. In the interim, the recommendations ofthe current survey may be useful as a preliminary guide to inform the more sustainable management of thesewetlands and the biodiversity that many of them support.The conclusions reached about the geomorphic classification of wetlands in the MKSEA are listed below.a. Palusplains that are mapped in DEC (2008b) where no change in geomorphic classification isrecommended from the current surveyMost of the study sites surveyed in the MKSEA (Sites 1, 2, 4, 7, 8, 9, 10, 11, 12, 13, 17, 18, 19, 20, 26,28, 30, 31 and 32) were located on gently sloping to gently undulating plains that were underlain byshallow aquitards and were waterlogged in the early spring of 2007 and 2008 (Table 6.2). These areaswere all mapped as palusplains in DEC (2008b) and were confirmed as palusplains in the current fieldsurvey.Sites 1, 2 and 4 are located adjacent to Yule Brook and were floodplains before the brook was excavatedin response to the greater volume of surface flow that was initiated by clearing in the catchment area andthe need to increase the conveyance of this storm water (and water drained from superficial aquifers bydrains) via Yule Brook towards the Canning River. These floodplain areas should be restored.b. Palusplains that are mapped in DEC (2008b) where a change of classification to floodplain may beconsideredA few of the study sites surveyed in the MKSEA (Sites 3, 5, 6, 14, 16 and 21) were located on gentlyundulating plains (that occasionally included a few very small basins or channels). All of these areaswere shallowly inundated in early spring of 2007 and 2008. These areas were all mapped as palusplainsin DEC (2008b) but were considered to be floodplains on the data obtained in the current field survey.Sites 3, 5 and 21 are located adjacent to Yule Brook and were probably inundated for longer and, attimes, experienced higher standing water levels that at present. The vegetation of these floodplain areasshould be regenerated as part of a comprehensive plan to restore Yule Brook as a living stream. Sites 6,14 and 16 are located at the base of sand dunes and the wetlands there are probably partly maintained byseepage from the base of these dunes. These wetlands are currently drained by excavated channels thatexport water downslope to Yule Brook via Lot 106 Wanaping Rd or via Brentwood Rd and a drain inthe University of Western Australia Allison Baird Flora Reserve.These wetlands require protection by the reservation of an appropriate buffer zone upslope from them inthe dunes that should be revegetated and kept free of all development and infrastructure. The stormwaterfrom any developments upslope from these wetlands should be infiltrated at source to maintain seepageTauss, C. and Weston, A.S. (2010). The flora, vegetation and wetlands of the Maddington-Kenwick Strategic Employment Area.A survey of the rural lands in the vicinity of the Greater Brixton Street Wetlands. Report to the City of Gosnells, W.A. Version 18.04.10