STORMWATER 2010 National Conference of the Stormwater Industry Association Conference Proceedings CAPTURING THE STORM: GETTING STORMWATER OUT OF THE GUTTER Author/s: Mr Chris J Devitt, Director Technical Services, Orange City Council Mr Martin D Haege, Senior Environmental Engineer, Geolyse Pty Ltd Ms Kerry B Fragar, Environmental Monitoring Consultant, Geolyse Pty Ltd SUMMARY Historically engineers have managed stormwater with pits, pipe, channels and basins; or more recently, vegetated swales, bioretention systems and constructed wetlands. Stormwater is no longer an urban by- product to manage and dispose of safely. Created in relatively large and consistent volumes with even small rainfall events, urban stormwater should be viewed as a legitimate water source that, as part of an integrated system, can reduce demand on potable supplies or even supplement potable supplies. Orange City Council s Blackmans Swamp Creek Stormwater Harvesting Scheme signals a revolution in the way urban stormwater runoff is viewed and utilised by water authorities and the general public. The project is the first large scale stormwater harvesting scheme in Australia which intentionally harvests stormwater for addition to drinking water supplies. The scheme helps underpin the security of Orange s future water supplies, ultimately capable of providing up to 2,000 megalitres per year, approximately 35% of the City s current annual water requirements. Evolution of the harvesting scheme from conceptual design, approvals and construction through to operational reality involved a diverse range of disciplines and skill sets. The project involved engineers, environmental consultants, risk management and water quality specialists, community interest groups, construction teams and operational staff. Diversity of knowledge was required to overcome the lack of relevant guidelines and precedents for developing a groundbreaking scheme of this nature. This paper presents an overview of the harvesting scheme and results from its initial operational phase. It discusses the process involved in undertaking the project from conceptualisation through to operational reality and highlights the challenges faced throughout design, approval, construction and operational refinement. Operational data and experience has been applied to the design of a recently approved expansion of the scheme that will harvest water stormwater from the Ploughmans Creek system. This expansion will further reinforce stormwater as a key component of Orange s integrated water supply system. INTRODUCTION The city of Orange is located approximately 250 kilometres west of Sydney in the Central Tablelands of New South Wales. Challenges in operating a water supply system for the population of 38,000 are attributed to the city s location high in the catchment, the lack of any substantial river system and limited groundwater supplies. The city therefore relies on a network of creeks which traverse the area, requiring innovative water management. Dry conditions over several years and subsequent well below average runoff saw the City s water supply levels drop gradually from the start of 2002. While it was understood that normal rainfall patterns were likely to eventually return and the storage levels rise, the water supply situation at the time was seen as a significant concern. A water restriction regime commenced in January 2003 and restrictions reached Level 5 in May 2008. In August 2008 Council s two supply storages dropped to less than 25% capacity which meant that without significant inflows, the City had approximately one year of water supply remaining. With the real potential of restricted water access, the future growth and development of Orange was facing challenges. In response, Orange City Council is pursuing an integrated package of non-structural and structural programs to help secure the city s water needs. Council s non-structural measures aimed at reducing Orange s water demand include the introduction of water restrictions, a leak detection and pressure reduction program, a 1 STORMWATER 2010 National Conference of the Stormwater Industry Association Conference Proceedings rainwater tank subsidy, an exchange program for showerheads, the installation of water saving devices in all Council buildings, liaison with large water users and extensive community education. As a consequence of these initiatives, annual water usage in Orange has dropped from a high of 7,100 ML in 2002 to 3,782 ML in 2009/2010. Structural initiatives considered included reconnecting historical water supplies, groundwater, extraction from disused mines, connection with adjacent local water utilities, stormwater harvesting from upstream and downstream catchments and regional water security initiatives. Stormwater harvesting emerged as a viable option worthy of detailed investigation. The Blackmans Swamp Creek Stormwater Harvesting Scheme (BSCSHS) is a key component of an integrated package of water security initiatives which is being implemented by Orange City Council. SCHEME DEVELOPMENT Conceptual Design The scheme was first proposed in 2008 when various water supply options were being considered. This phase of the project involved dedication to brainstorming and the refinement of ideas amongst a team of engineering staff. Due to the urgency of this project and its unique nature, assessment of concepts was given high priority. Stormwater harvesting options included harvesting from rural catchments upstream of the city or from various sites downstream of the city. The Blackmans Swamp Creek scheme was seen as the preferred option because: The catchment generates large and regular flows even from small rainfall events, due to significant development existing in the catchment; The creek passes reasonably close to Suma Park Dam; and There was some existing infrastructure in place including utilisable access, adequate power supply and an existing pipeline. The very high level of treatment provided by Council s main water filtration plant, which treats water from Suma Park Dam, was also seen as an advantage for any scheme responsible for adding a new water source to the dam. Design of the scheme required a thorough understanding of the stormwater and creek system, including catchment characteristics, flow patterns, existing demands and stormwater quality. Extensive modelling was undertaken to determine creek flows and the scheme performance under various operating scenarios. The urban area of Orange lies within two local creek catchments, the largest of which is Blackmans Swamp Creek, which covers about 34 km² to its junction with Summer Hill Creek. Blackmans Swamp Creek rises in rural land south of the city and flows through the central business district, heading in a north-easterly direction, passing immediately west of Suma Park Dam, the City s main water supply dam, before joining with Summer Hill Creek a kilometre downstream of the dam. Approximately 70% of the city falls within this catchment (refer to Figure 1). The catchment area of Blackmans Swamp Creek upstream of the harvesting point is 30.5 km2. The stormwater harvesting scheme holding pond, which is on an unnamed tributary to Blackmans Swamp Creek, has a further catchment area of 2.5 km2 (refer to Figure 1). 2 STORMWATER 2010 National Conference of the Stormwater Industry Association Conference Proceedings Figure 1: Blackmans Swamp Creek catchment Modelling of the catchment indicated that the average annual runoff passing the stormwater harvesting location is approximately 9,480 ML/year and ranges from 2,400 to 25,000 ML/year. The volume of runoff generated from rainfall events is dependent on antecedent conditions. Modelling indicates that on average, 10 mm of rainfall across the Blackmans Swamp Creek catchment produces approximately 140 ML of runoff, but this can range from 70 ML to 200 ML depending on antecedent conditions and rainfall patterns. The harvesting scheme underwent several revisions during the approval process and in its current configuration is expected to harvest an average of 800 ML/year. This is about 15% of the city s current unrestricted demand. Additional stages will see the average harvest increase to around 2,000 ML/year. Approvals The scheme was defined as a stormwater management system under State Environmental Planning Policy (Infrastructure) 2007 that could be carried out by or on behalf of a public authority (Orange City Council) without consent on any land. Whilst development consent was not required to construct or operate the scheme, Council had an obligation under Part 5 of the Environmental Planning and Assessment Act, 1979 to consider the environmental impacts of the activity. A Review of Environmental Factors (REF, Geolyse, 2008) was prepared to assist in the determination process. The REF provided a comprehensive outline of the project and concluded that the construction and operation of the scheme was unlikely to result in a significant adverse environmental impact. It was acknowledged that removing water from the system must have a downstream impact and the challenge was to adaptively manage the scheme s use so that the significance is minimised and that the needs of downstream users and the aquatic environment are not compromised (Geolyse, 2008). The initial use of the scheme was linked to emergency conditions and harvesting will occur until the combined storage in Suma Park Dam and Spring Creek Dam exceeds 50%. Ministerial authorisation was required to allow 3 STORMWATER 2010 National Conference of the Stormwater