Use of Stormwater as an Alternative Supply Source

Changing climate, increasing demand for potable water supplies and increased community interest for sustainable use of fresh water sources have resulted in a new focus on water use and sourcing. New sources are being sought, in conjunction with water demand minimisation strategies, to decrease the pressure on existing urban water resources. At the same time, the management of stormwater is being re-examined with the focus changing from the traditional practice of rapid disposal of stormwater (to reduce the risks of flooding) to utilisation of stormwater as an alternative water supply source. The focus of this thesis is the use of stormwater as an alternative supply source in urban areas at a cluster (or neighbourhood) scale. A decision making framework was developed to assist the adoption of a holistic approach to determining the most appropriate stormwater use scheme option. It was developed as an integrated planning tool to be used in the initial stages of investigating water sourcing and stormwater management ideas. Due to the time constraints of this project, the focus of the decision making framework was on the technical components (with associated issues) and financial costs. Since additional issues such as environmental, social and economic issues, are crucial to ensure a balanced view is taken in the decision making process, they are included in the process through additional information sources. Development of the decision making framework considered the following steps: • Development of stormwater use scheme options based on the technical components and associated issues of collection, storage, treatment, distribution and end use; • Development of screening tools to screen out infeasible or clearly inferior stormwater use scheme options; • Development of steps in the decision making framework; and • Demonstration of the decision making framework through the use of a case study. The decision making framework consists of eleven steps. The initial six steps of the decision making framework relates to collection and end use issues and are based around matching stormwater runoff to demand and matching stormwater quality to required quality. Steps 7 to 9 of the decision making framework consist of examining and determining feasible storage, treatment and distribution options. Step 10 of the decision making framework focuses on the integration of the feasible technical options identified in the previous steps, in order to develop stormwater use scheme options. The final step of the decision making framework is to determine costs of the stormwater use scheme options and compare the scheme options on the basis of cost, reliability of supply, quantity of stormwater utilised and end use demands met. The decision making framework was demonstrated as an easy and practical tool for determining the most appropriate stormwater use scheme through the use of a case study. An existing urban area was chosen as the case study due to the potential for the greater impact in terms of minimising potable water use for non-potable end uses. Feasible collection, storage, distribution, treatment and end use options were determined and integrated into 19 stormwater use schemes. Comparison of all the stormwater use scheme options, as well as the base case with no stormwater use, determined four options as being superior in terms of financial costs, reliability, quantity of stormwater used and end uses met. The decision making framework was developed based on existing constraints (such as the lack of guidelines directly examining stormwater use) and knowledge, while being flexible enough to include future scientific and practical knowledge, as it becomes available. Recommendations for future development of the decision making framework include expanding this decision making framework to identify the optimum scales of stormwater use schemes. Additionally, an effective yet simple to use costing tool needs to be developed so that all environmental, social and economic costs are determined and actual benefits of stormwater use schemes can be determined