Esperance area acid sulfate soil hazard mapping

This project created a regional scale (1:100 000) acid sulfate soil (ASS) hazard map for the Lake Warden and Esperance town areas, using a combination of existing soil-landscape mapping information and elevation data, supported by field observations and laboratory data from 18 soil cores and 29 additional borelogs with descriptive information useful for identifying ASS and potential ASS materials. All data gathered during this project used common standards and protocols developed in Australia for identifying and mapping ASS materials. The project extends the mapping for acid sulfate soil in the region, complementing existing maps compiled for other parts of the state. This map should be used in conjunction with protocols developed by the Department of Environment and Conservation for the management of acid sulfate soil materials. The resulting hazard map classifies the landscape according to the probability of intercepting ASS materials within the top 6m of regolith. A three-class rating is used: ‘high probability of occurrence’, ‘low probability of occurrence, ‘very low probability of occurrence’, commonly used on regional-scale ASS hazard maps in Australia. This scale of mapping is only suitable to signal the need for further assessment prior to land development involving excavation and/or drainage. Management decisions and actions will require individual site investigations. The recent (Quaternary) geomorphology of the Esperance area where ASS materials may be found was a near-shore shallow marine and lacustrine/estuarine sedimentary environment. This was followed by a period of sea regression and deposition of aeolian (wind-blown) sands over these deposits. Thus, ASS materials have a high probability of occurrence in current low-lying areas, swamps and lakes. These landscapes cover about 8,140 ha of reserves, agricultural and rural-residential land around Esperance township. ASS materials may also be found under sand sheets and dunes that blanket lakes and swamps. In these situations, ASS materials are only likely to be intercepted in the swales (depressions) of dunes and under very shallow sand sheets, and so they are rated as having a low probability of occurrence. These landscapes cover about 2,170 ha of land, mostly on the southern (town) side of the lake system, extending east of Bandy Creek to near the wastewater treatment plant and tip. Much of this area is residential, light industrial, rural residential and unallocated Crown land. The soil-landscape map units that correspond to these geomorphological environments are the Gore 1, 2 and 3 subsystems and low-lying parts of the Tooregullup 5 subsystem. All other areas around Esperance, including headlands, larger dunes and sand sheets west of town, and all land north of the coastal plain that the lakes system occupies, is considered very low probability of occurrence. This study and existing protocols on identifying and managing ASS materials provides land planners and developers in Esperance with guidelines to manage potential issues relating to acid generation caused by dewatering or excavation