Summary - City of Gosnells

Wetlands Field Survey 816.1 Identification and delineation of wetlands in the MKSEAThe identification and delineation of wetlands relies on the characterisation of the hydrology, hydric soilsand vegetation (Hill et al., 1996; Tiner,1999) and a general guide for this is provided in DEC (2007). Inaccordance with these principles, investigations were conducted to distinguish between putative wetland andupland zones in the MKSEA. A limited field survey of the hydrology and shallow stratigraphy of thevegetated wetlands of the MKSEA that are mapped in DEC (2008a) was undertaken in addition to thedetailed flora and vegetation study reported above. Obligate and facultative wetland flora plants at eachstudy site in the survey area and elsewhere were noted during the flora and vegetation survey (Appendix D).In the current survey, the uplands of the MKSEA were found to be either naturally elevated landforms ormore low-lying areas where the land surface had been elevated above the high watertable of the surroundingterrain by the importation of sand (or other fill materials). The natural upland areas of the MKSEA were alldeep Bassendean Sands. The boundaries between the natural uplands of the area and the wetlands (that wereall underlain by muddy sediments of the Guildford Formation or shallow sand over muddy sediments) weresubtle in some areas and difficult to map. The locations of these boundaries are provisionally indicated(Figure 11). However, they will require detailed topographic survey and further study of hydrology andstratigraphy to map at a finer scale prior to a final determination of development and buffer zones. Therewere two main locations of boundaries of this type in the MKSEA.• In Precinct 2 of MKSEA there was an irregular boundary between the Pinjarra Plain wetlands and theBassendean Dune uplands that extended obliquely from Tonkin Highway (just south of Brentwood Rd) toVictoria Rd. This was a sensitive boundary in terms of the very high natural conservation values that arelocated in several areas along this boundary and the wetland processes that still operate along the areaswhere native vegetation has been cleared.• In Precinct 1 the boundary above continued along the contact between the Pinjarra Plain wetlands and theBassendean Dunes and divided this precinct into an upland zone in the north east and a wetland zone inthe south-west.The artificially raised areas throughout the MKSEA were mapped, very approximately, from aerialphotographs, as non-wetlands. This mapping was also not a definitive assessment and there was notsufficient access to many properties to verify the location of many areas of fill. This mapping does, however,provide an indication of the scale and pattern of the (largely unregulated) filling of the local wetlands.There was ample evidence of hydric soils, high water tables and surface and groundwater dependantvegetation indicative of wetland conditions in most of the sample sites representative of the MKSEA in thecurrent survey (Table 6.2). The native vegetation of most of the MKSEA had predominantly obligatewetland species in the areas of shallow sand over Guildford Formation and in areas of clayey sands andsandy clays. Most of the areas mapped as wetlands in the SCP Wetland Dataset (DEC, 2008a) wereconfirmed as wetlands in the current survey (Figure 11). There was also an additional wetland area identifiedin the current survey that had not been mapped previously as wetland area in DEC (2008a).The boundaries between the extensive palusplains and the Bassendean Dune uplands that were mapped in thecurrent survey (Figure 11) differ somewhat from the boundary mapped in the SCP Wetland Dataset (Figures9 and 10). There was also an additional wetland area identified in the current survey that had not beenmapped previously as wetland area in DEC (2008a). To provide the evidence necessary to support amodification of the wetland boundary in the SCP Wetland Dataset (i.e. to more accurately delineate thewetlands in this area prior to any planning decisions), a fine scale hydrogeological study to describe thestratigraphy and the hydrology of the wetlands along the interface of the wetlands and the Bassendean Dunesis recommended. It is likely that Muchea Limestone aquifers in the MKSEA are closely connected towetlands in BFS 387. The occurrences of Muchea Limestone in the MKSEA (and the catchment areas of theaquifers associated with these occurrences) require further investigation and detailed mapping to understandhow these wetlands are maintained and how they interact with the Greater Brixton Street Wetlands.Subsequently, measures can be taken to protect catchment areas, conserve and restore wetlands in theMKSEA and link them via vegetated corridors to bushlands reserved in the Greater Brixton Street Wetlands.Tauss, 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