Urban stormwater runoff is a critical source of degradation to stream ecosystems globally. Despite broad appreciation by stream ecologists of negative effects of stormwater runoff, stormwater management objectives still typically center on flood and pollution mitigation without an explicit focus on altered hydrology. Resulting management approaches are unlikely to protect the ecological structure and function of streams adequately. We present critical elements of stormwater management necessary for protecting stream ecosystems through 5 principles intended to be broadly applicable to all urban landscapes that drain to a receiving stream: 1) the ecosystems to be protected and a target ecological state should be explicitly identified; 2) the postdevelopment balance of evapotranspiration, stream flow, and infiltration should mimic the predevelopment balance, which typically requires keeping significant runoff volume from reaching the stream; 3) stormwater control measures (SCMs) should deliver flow regimes that mimic the predevelopment regime in quality and quantity; 4) SCMs should have capacity to store rain events for all storms that would not have produced widespread surface runoff in a predevelopment state, thereby avoiding increased frequency of disturbance to biota; and 5) SCMs should be applied to all impervious surfaces in the catchment of the target stream. These principles present a range of technical and social challenges. Existing infrastructural, institutional, or governance contexts often prevent application of the principles to the degree necessary to achieve effective protection or restoration, but significant potential exists for multiple co-benefits from SCM technologies (e.g., water supply and climate-change adaptation) that may remove barriers to implementation. Our set of ideal principles for stream protection is intended as a guide for innovators who seek to develop new approaches to stormwater management rather than accept seemingly insurmountable historical constraints, which guarantee future, ongoing degradation.

This study explores system interactions of stormwater management solutions using Sustainable Urban Drainage System (SuDS) and Green Infrastructure (GI) within the wider urban landscape. A series of interdependencies between urban components relating to stormwater management are identified. These include physical interdependency, geographical interdependency, cyber interdependency and logical interdependency, as defined by Peerenboom (2001). Stormwater management using SuDS/GI are viewed according to their Hydrological, Ecological and the Built Environment functions during events up to the design rain (non-flood condition) and during controlled exceedance and uncontrolled inundation (flood condition). The inclusion of SuDS/GI into the urban fabric is shown to modify urban functional and relational interdependencies under both these conditions. Within the context of the UK, there are fragmented responsibilities across planning scales created by SuDS/GI solutions which have not addressed the relational complexities that exist between agencies and competent authorities. The paper identifies the key barriers towards effective adoption of SuDS/GI within the context of the UK as physical barriers, perception/information barriers and organisational barriers.

A Blue-Green City aims to recreate a naturally-oriented water cycle while contributing to the amenity of the city by bringing water management and green infrastructure together. The Blue-Green approach is more than a stormwater management strategy aimed at improving water quality and providing flood risk benefits. It can also provide important ecosystem services and socio-cultural benefits when the urban system is in a non-flood, or green, condition. However, quantitative evaluation of benefits and the appraisal of the relative significance of each benefit in a given location are not well understood. The Blue-Green Cities Research Project aims to develop procedures for the robust evaluation of the multiple functionalities of Blue-Green infrastructure (BGI) components within flood risk management (FRM) strategies. The salient environmental challenge of FRM cuts across disciplinary boundaries, hence an interdisciplinary approach aims to avoid partial framing of the ongoing FRM debate. The Consortium will produce an urban flood model to simulate the movement of water and sediment through Blue-Green features. Individual and institutional agents will be incorporated into the model to illustrate how behavioural changes impact on flooding and vice versa. A methodological approach for evaluating the interaction of urban FRM components with the wider urban system will be developed and highlight where, when and to whom a range of benefits may accrue from BGI and other flood management interventions under non-flood and flood conditions. Recognition of the compound uncertainties involved in achieving multiple benefits at scale will be part of the robust method of uncertainty evaluation that will run throughout the project. The deliverables will be applied to the Demonstration Case Study, Newcastle, UK, in the final year of the project (2015). This paper will introduce the Blue-Green Cities Research Project and the novel, interdisciplinary framework that is adopted to investigate multiple benefits of FRM strategies.

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