Renewing Urban Streams with Recycled Water for Streamflow Augmentation: Hydrologic, Water Quality, and Ecosystem Services Management

As demands for freshwater withdrawals continue to escalate in water-stressed regions, negative consequences of alterations to natural systems will become ever more severe. Habitat restoration projects may mitigate some of these challenges, but new strategies will be needed to maintain or enhance ecosystem health while simultaneously meeting human needs. Recycled water is a reliable water source that can be used both directly and indirectly to renew degraded urban stream ecosystems. In this review, aspects of hydrology, water quality, and ecosystem services in relation to water reuse for urban stream renewal are evaluated to identify research needs and design considerations for new systems. Use of recycled water for streamflow augmentation in urban areas remains largely unexplored scientifically, despite its potential widespread applications among water and wastewater utilities. To move this innovative concept toward implementation, experimental studies in stream microcosms are needed to examine ecological response to coupled modification of both hydrology and water quality. Appropriate methods for selecting potential sites for urban stream renewal should be identified, along with ecological and economic metrics for evaluating success. Examples of projects in California, Japan, Israel, and Spain are used to identify different management scenarios. However, design criteria from both successful and unsuccessful case studies require additional review and synthesis to develop robust guidelines for recycled water use in urban stream renewal. Motivations for past stream renewal projects include regulatory requirements for water quality improvement and endangered species protection, although these motivations alone may not be enough to facilitate widespread adoption of reusing wastewater for ecosystem enhancement. Consequently, future project designs should include more detailed ecosystem service valuations to describe broader societal benefits and attract the attention of government agencies and private organizations that ultimately make the choice between environmental perturbation or enhancement.