VGrace Mitchell

A technical decision-making framework: stormwater as an alternative supply source

Stormwater harvesting is a relatively new concept which has developed using traditional stormwater management practices as well as water resourcing and holistic water management concepts. While stormwater harvesting systems have been designed and constructed in the past, the planning and design processes have not followed an integrated approach. This paper addresses this issue and describes a decision-making framework (DMF) that determines the most appropriate stormwater harvesting scheme option based primarily on technical feasibility and financial costs with a focus on neighbourhood-scale development. A case study of an existing urban area in the suburb of Sunshine in Melbourne, Australia, was conducted to demonstrate the DMF. Comparison of all stormwater harvesting scheme options determined that while one scheme option was the most effective option in terms of cost, reliability, quantity of stormwater used and end uses met, several other options could also be examined further for detailed analysis.

Microbial challenge-testing of treatment processes for quantifying stormwater recycling risks and management

Pathogenic microorganisms have been identified as the main human health risks associated with the reuse of treated urban stormwater (runoff from paved and unpaved urban areas). As part of the Smart Water initiative (Victorian Government, Australia), a collaborative evaluation of three existing integrated stormwater recycling systems, and the risks involved in non-potable reuse of treated urban stormwater is being undertaken. Three stormwater recycling systems were selected at urban locations to provide a range of barriers including biofiltration, storage tanks, UV disinfection, a constructed wetland, and retention ponds. Recycled water from each of the systems is used for open space irrigation. In order to adequately undertake exposure assessments, it was necessary to quantify the efficacy of key barriers in each exposure pathway. Given that none of the selected treatment systems had previously been evaluated for their treatment efficiency, experimental work was carried out comprising dry and wet weather monitoring of each system (for a period of 12 months), as well as challenging the barriers with model microbes (for viruses, bacteria and parasitic protozoa) to provide input data for use in Quantitative Microbial Risk Assessment.

Designing for Sustainable Water and Nutrient Outcomes in Urban Developments in Melbourne

Abstract What is the best way to manage water and nutrients when providing water services for urban developments in Melbourne? Melbourne, as with most other major cities in Australia, is facing stresses on its water supply and degradation of receiving water bodies due to stormwater and wastewater discharges. Urban developments need to address these concerns, however there is still much debate regarding which service provision combinations are preferable. This paper seeks to clarify urban water servicing design principles for conservation of water supplies and prevention of eutrophication. Two developments have been studied: (i) Kalkallo, a representative greenfield site, and (ii) Box Hill, a representative multi-storey brownfield site. Various water and sewerage servicing options, with varying levels of end use management, have been assessed by undertaking water and contaminant balances. Results have demonstrated a self-sufficient residential supply without connection to water mains sacrifices reliability. Reclaimed water stores require significantly less land than stormwater stores placed under the same demand, however stormwater stores more effectively reduce eutrophication risks in Port Philip Bay, the bay Melbourne surrounds. On-site reclaimed water systems are ideally suited to apartment towers because of minimal storage size requirements. End use efficiency should always be a priority for conserving water

Examining the Technical Feasibility of Using Stormwater as an Alternative Supply Source within an Existing Urban Area - a Case Study

Abstract Due to pressure on urban water supplies, stormwater has increasingly been considered as a resource. This view provides opportunities to use stormwater within urban areas. However, there is still limited understanding of how a stormwater use scheme can be implemented, particularly in existing urban areas. A decision making framework to investigate the viability of potential stormwater use scheme options was developed. This framework examines the feasibility of stormwater use in urban areas at a cluster or neighbourhood scale. This paper describes how the decision making framework was adapted to a case study in the suburb of Sunshine in Melbourne, Victoria, and demonstrates how this framework can be applied to a residential urban area. Comparison of all stormwater use scheme options determined that, while one scheme option was the most effective option in terms of cost, reliability, quantity of stormwater used and end uses met, several other options could also be examined further for detailed analysis. As the decision making framework is developed further, additional issues such as environmental, social and economic could be examined.

The effect of rainwater tank design on sediment re- suspension and subsequent outlet water quality

Abstract This paper reports the results of laboratory experiments investigating the effect of rainwater tank design on re-suspension of accumulated sediment and the resultant water quality. Twenty-eight different configurations that represented different tank designs in combination with various water levels and quantities of stored sediment were investigated. Re-suspension of sediment was observed during all experiments regardless of the position of the top inlet (whether side or centrally positioned), position of the bottom outlet (50,100,200, 400 and 600 mm above the base of the tank), the shape of the tank base (flat or conical), the initial water level in the tank (empty, quarter full or half full), the sediment thickness (10 or 20 mm), the particle size (two particle size ranges) or inflow rate (0.5 or 1.0 L/s). The re-suspended sediment contaminated the out-flowing water, and the greatest impact (worst outcome for water quality) was observed for a centrally located top inlet and an outlet located 50 mm above the tank base. The least contamination of the out-flowing water was observed when the inlet was positioned on the side of the tank. To reduce the potential for contamination of the out-flowing water, it is recommended that rainwater tanks preferably have a side inlet and a conical base, that the sediment thickness in the tank be maintained at low levels by regularly cleaning the tank, and that the tank water be not used during or immediately following rainfall events.