Heijs J, Wilkinson D, Couriel E
Water Sci Technol. 2002;46(6-7):35-46.
The people who live in North Shore City (New Zealand) consider the beaches as their greatest asset. Following public outcry on frequent beach pollution caused by wet weather sewer overflows, Project CARE commenced in 1998 to plan the improvements to the city's separated wastewater and stormwater systems to protect the streams and beaches, particularly from a public health perspective. The investigation included building hydrological and hydraulic models to represent the wastewater and stormwater systems and a receiving waters model to simulate the impacts on the beaches. These models were later used to explore options for improvement. It was found that North Shore City has a very leaky wastewater system that is under capacity. The resulting wet weather overflows (12 per year on average) are the most important contributor to the problem although stormwater pollution alone is big enough to cause problems (at a smaller magnitude). A cost optimisation model (iterative process using performance/cost relationships) was then used to assist in identifying the optimal set of improvement works (storage, repair and increased capacity, wastewater treatment plant) to meet different performance targets and to cater for growth up to the year 2050. Cost Benefit analyses, looking at improvements in system performance and water quality, show diminishing returns for performance levels better than 2 overflows per year. The total costs that meet this target are estimated at almost NZ$300M (US$135M).
居住在新西兰北岸市的人们将海滩视为他们最宝贵的资产。在公众对潮湿天气导致下水道溢流造成的频繁海滩污染提出强烈抗议后，1998年启动了CARE项目，以规划改善该市的分流式废水和雨水系统，从而保护溪流和海滩，特别是从公共卫生角度出发。调查包括建立水文和水力模型来模拟废水和雨水系统，以及建立受纳水体模型来模拟对海滩的影响。这些模型后来被用于探索改进方案。结果发现，北岸市的废水系统漏洞百出且处理能力不足。由此导致的潮湿天气溢流（平均每年12次）是该问题的最重要成因，尽管仅雨水污染就足以引发问题（规模较小）。随后使用了成本优化模型（利用性能/成本关系的迭代过程）来协助确定最佳的改进工程组合（储存、修复和增加容量、污水处理厂），以满足不同的性能目标并适应到2050年的增长需求。成本效益分析着眼于系统性能和水质的改善，结果表明，每年溢流次数少于2次的性能水平的回报递减。达到这一目标的总成本估计近3亿新西兰元（1.35亿美元）。
