## 1 Introduction
### Current Understanding and Evaluation of SuDS  
The use of SuDS in reducing runoff emerged in the UK in the late 1980s. By 1992, the \"Scope for Control of Urban Runoff\" [5] guidelines were published, providing guidance on a range of technical interventions to control runoff. Further guidance documents were published in 2000 [6], which formalised the term sustainable drainage systems. Since 2000, there have been a number of SuDS regulatory and policy documents published, including DEFRA's \"Non-statutory technical standards for sustainable drainage systems\" [7]. In some countries, such as Scotland, SuDS have been mandatory in most new developments since 2003 [8]. SuDS are designed to meet specific performance criteria relating to (i) hydraulics, (ii) water quality, (iii) amenity and (iv) biodiversity [9]. SuDS components are generally volume based and designed to manage the interaction between the drainage system and the built environment to facilitate the management of exceedance flows [9]. Additionally, SuDS can provide treatment of the surface water runoff, thereby improving water quality, and in so doing can significantly contribute to the amenity of an area, delivering added value and improving wellbeing. Papers modelling the impacts of SuDS on runoff are becoming more common (e.g., [10; 11]) but there are few studies that actively monitor the performance of deployed SuDS. SuDS monitoring is often qualitative and constrained by a lack of budget. [PERSON] [12] found that SuDS monitoring and evaluation in Scotland is achieved on an \"informal, ad-hoc basis and not at regular intervals as recommend by The SuDS Manual\" [12]. When monitoring and evaluation is undertaken, it is often descriptive: ranging from an annual site visit to take photographs, to fairly basic, routine maintenance [12]. There are fewer studies still that quantitatively measure the performance of SuDS, particularly in urban areas and/or retrofit scenarios, due to the challenges in designing and implementing these studies [13; 14; 15]. Without monitoring and evaluation, it is unknown whether the SuDS systems are under or over performing. A database of case studies of blue-green infrastructure (BGI), a term which is often used interchangeably with SuDS, was compiled by [PERSON] and [PERSON] [16] to highlight the processes that supported their implementation, such as governance and stakeholder relationships, rather than the physical components of the BGI. The case studies included public awareness campaigns, such as The Netherlands \"Live with Water\" and a case study of retrofit SuDS in Augustenberg in Malmo, Sweden (with similar drivers to the project reported in this paper). The neighbourhood of Augustenberg experienced periods of socio-economic decline, and frequently suffered from floods caused by overflowing drainage systems [16]. SuDS, including retention ponds and green roofs, were installed in this collaborative project involving the city council, a social housing company and the local residents. This scheme resulted in a significant reduction in rainwater runoff and improved the visual amenity of the area. [PERSON] and [PERSON] [16] identified a number of lessons from these case studies relating to championship: raising awareness within organisations, amongst stakeholders and with the wider public; collaborative working; developing a sound evidence base; and monitoring and evaluation. They found that, in many cases, establishing or adopting BGI was a result of the enthusiasm and commitment of one individual, one organisation or a particular stakeholder partnership i.e., a \"champion\". They noted the importance of engaging residents in the development and implementation of BGI projects to reduce the likelihood of objections and conflicts [16]. The lack of \"appropriate monitoring\" and evaluation of SuDS projects is routinely cited as a barrier to their implementation [13; 17].