Impacts to Hydrological Processes and Inland Water Environmental Quality
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Strategic Assessment for the Perth and Peel Regions 7 IMPACTS TO HYDROLOGICAL PROCESSES AND INLAND WATER ENVIRONMENTAL QUALITY 7.1 KEY FINDINGS • Water is managed through an extensive array of policies and processes. The State is committed to strategic reform of water legislation to provide a system that is flexible, progressive and capable of managing water today and into the future. • The most significant threat to water dependent environmental values within the Advice Area comes from a drying climate; new hydrological regimes are inevitable in some areas. • Increased recharge associated with land use changes may represent opportunity to balance falling groundwater levels resulting from reduced rainfall, however this hinges on strong allocation and licensing processes and the identification of alternative supplies built into land planning process. • The State will continue to incorporate the most up to date knowledge on water availability into allocation planning, including consideration of climate change and environment water requirements, to inform decision making in the face of likely increased demand. • In areas of limited groundwater availability, DoW will work with planning agencies and developers to address the shortfall and protect sensitive groundwater dependent ecosystems. This will be facilitated through the development of sub-regional water management strategies. Water constraints identified will form the platform for work to be undertaken through the Perth-Peel Regional Water Supply Strategy, which will be the strategic response for securing water sources for future development proposed. • Better Urban Water Management (WAPC 2008a) is a key tool for ensuring appropriate management of water dependent values through development of new urban, industrial and rural residential areas. The State is committed to ensuring this document is fit for purpose through a number of enhancements including a broadening of the scope. • Nutrients export risk are a critical issue in a number proposed urban and industrial areas in proximity of sensitive receptors such as the Ellen Brook and the Peel Harvey-Estuary. Specific commitments have been made to investigate appropriate mitigation options prior to rezoning of these areas. • Monitoring and reporting of water quality in the Peel-Harvey and Swan-Canning will be improved through measures including the development of estuarine health indicators and water quality criteria for all sub-catchments. • An extensive suite of management options, guided by Water Quality Improvement Plans, is proposed for the Swan-Canning and Peel Harvey catchments in order to manage nutrient issues © ECO LOGICAL AUSTRALIA PTY LTD 161 Strategic Assessment for the Perth and Peel Regions both from past practices and into the future and in the case of Peel Harvey will be overseen by a new Water Quality taskforce. • Acceptability of development within P1 and P2 areas in Gnangara and Jandakot underground water pollution control areas will be confirmed through a comprehensive assessment of land and water factors before proceeding with rezoning in order to protect drinking water supplies. 7.2 EPA OBJECTIVE The following EPA objectives for hydrological processes and inland waters environmental quality are applicable to this assessment: To maintain the hydrological regimes of groundwater and surface water so that existing and potential uses, including ecosystem maintenance, are protected. To maintain the quality of groundwater and surface water, sediment and biota so that the environmental values, both ecological and social, are protected. 7.3 ENVIRONMENTAL POLICY AND GUIDANCE Key policy and guidance relevant to this assessment with regard to hydrological processes and inland waters environmental quality include but are not limited to: • State Planning Policy 2.1 Peel-Harvey Coastal Plain Catchment (WAPC 2003b). • State Planning Policy 2.2 Gnangara Groundwater Protection (WAPC 2005). • State Planning Policy 2.3 Jandakot Groundwater Protection (WAPC 2003c). • State Planning Policy 2.6 State Coastal Planning Policy (WAPC 2013). • State Planning Policy 2.7 Public Drinking Water Source Policy (WAPC 2003d). • State Planning Policy 2.9 Water Resources (WAPC 2006a). • State Planning Policy 2.10 Swan Canning River System (WAPC 2006b). • Environmental Protection (Peel Inlet-Harvey Estuary) Policy (EPA 1992). • Guidance Statement No. 28: Protection of the Lake Clifton Catchment (EPA 1998). • Position Statement No. 4: Environmental Protection of Wetlands (EPA 2004). • Statewide policy No. 5: Environmental water provisions policy for Western Australia (Water and Rivers Commission 2000). • EPA Guidance Statement 33 Chapters B4 Wetlands and B5 Waterways of Environmental guidance for land planning and development (EPA 2008c). There are also various land use and water management strategies, water quality improvement plans, drainage and water management plans, allocation plans for surface water and groundwater resources and floodplain management strategies that are in operation across the Advice Area. © ECO LOGICAL AUSTRALIA PTY LTD 162 Strategic Assessment for the Perth and Peel Regions 7.4 EXISTING ENVIRONMENT 7.4.1 Key values The Advice Area supports a range of surface water and groundwater systems that have a high degree of interaction due to the nature of the landforms present. These systems include important groundwater aquifers, estuaries, wetlands, rivers, streams and their catchments. These systems are of value for their support of ecological processes, functions and assets as well many consumptive and non- consumptive uses, including: • public and private potable and non-potable water supply; • recreation and tourism; • fisheries (recreational and commercial); • cultural and heritage (Aboriginal and non-Aboriginal); • landscape and aesthetics; and • educational and scientific activities. The EPA has advised that key water assets for consideration in planning and evaluating the impacts of future development within the Advice Area are wetland and rivers systems, including the Swan Canning and Peel-Harvey estuaries, and groundwater resources (EPA 2015a). Groundwater Groundwater aquifers within the Advice Area are valued for a range of functions including: • Support of wetlands, caves and springs and their associated ecosystems, including subterranean fauna. • Support of groundwater dependent vegetation. • Drinking (potable) water supply from both the confined and unconfined aquifers. • Non-potable water supply for domestic use, industry, irrigated agriculture, open space irrigation, all mostly from the unconfined superficial aquifer, with some from the Leederville aquifer. • Its part in the integrated water cycle, including discharge to lakes, rivers, estuaries and the ocean. • Limiting saltwater intrusion from the ocean salt water wedge. Within the Swan Coastal Plain portion of the Advice Area, the superficial formations average approximately 50 m in thickness. Below the superficial formations there are a number of confined and semi-confined aquifers, the most extensive of which are the Leederville, which is highly variable but typically several hundred metres thick, and the Yarragadee, which can extend to a depth of greater than 1,000 m. To the north of Perth (between the ocean, the Swan River, Ellenbrook and Moore River, centred about 15 km north-east of Wanneroo), the Gnangara groundwater system provides the largest source of potable water in south-west WA. Studies carried out in preparation of the Draft Gnangara Sustainability © ECO LOGICAL AUSTRALIA PTY LTD 163 Strategic Assessment for the Perth and Peel Regions Strategy showed that abstraction and use of Gnangara groundwater is worth $300 million a year to the Western Australian economy or a total net present value of $6.7 billion. In this location, the superficial formations host an aquifer of around 45 m thickness. The Gnangara and Jandakot Mounds are the two major superficial aquifer systems within the Advice Area. The Gnangara Mound supports a wide range of groundwater dependent ecosystems. The Draft Gnangara Sustainability Strategy identified 45 significant wetlands supported by the Gnangara groundwater system. Those within the boundary of the Advice Area include: • aquatic habitats in the karstic cave system around Yanchep National Park; • permanent deeper surface waters (with good buffering capacity) in the northern linear chain wetlands of the Spearwood interdunal system (Loch McNess, Nowergup Lake, Yonderup Lake and Lake Goollelal); • tumulus springs (organic mound springs) in the Ellen Brook region; • surface waters in the Ellen Brook region of the eastern side of the Gnangara Mound (for instance, Twin Swamps) including the ephemeral clay-dominated swamps (such as Ellenbrook Nature Reserve); and • habitat complexes in the large shallow wetland systems on the Bassendean Dune system (Melaleuca Park and Lexia wetlands). The smaller Jandakot Mound occurs to the south of Perth (between the ocean and the Swan, Canning and Serpentine rivers) with an average aquifer thickness of 20 – 30 m. Jandakot Mound also supports important groundwater dependent ecosystems, including the Ramsar listed Thomsons and Forrestdale lakes. On both the Gnangara and Jandakot Mounds remnant Banksia woodlands with a shallow depth to groundwater table are known to be dependent on groundwater for part of their water needs. These groundwater mounds comprise the key shallow groundwater features of the Advice Area. They are recharged directly by rainfall infiltration and, apart from a few