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Channel evolution models (CEMs) are used to structure the interpretation of observed channel morphology to support long-term restoration of these systems. However, channels reflect the variety of their watersheds' climatological, ecological and physiographic contexts, and so no single CEM can be truly 'global'. Unrecognised differences between the assumptions and the reality of evolutionary trajectories of particular streams can subsequently lead to restoration actions that neither fully achieve their intended objectives nor successfully self-maintain even limited improvements. Despite the daunting variety of biophysical settings, however, urbanisation imposes distinctive, homogenising influences on virtually all watercourses, suggesting that even a relatively small set of evolutionary pathways can embrace much of the diversity of critical watershed drivers on urban channels. CEMs describing single-thread channel response to incision are most common in the published literature, but not every urban disturbance yields this classic sequence, initiated by excess transport capacity followed by incision, bank erosion, widening and ultimately a lowered re-equilibrated channel. A comprehensive urban CEM must also include responses under less common (but locally ubiquitous) conditions, such as excess sediment relative to transport capacity (the 'inverse' of the classic CEM), imposed constraints on vertical and/or lateral adjustment, and multi-thread channels or those influenced by instream or riparian vegetation. An urban CEM also requires a hierarchical framework that acknowledges fundamental differences in the process drivers within any given watershed, because a single observation of channel form can rarely pinpoint the context or evolutionary trajectory of every stream. We present a geomorphic framework for diagnosing and predicting the evolution of urban streams, potentially guiding the selection of restoration targets that are achievable within an urban context and sustainable without ongoing maintenance.

This introduction to the special section of Area 'Geography, Urban Geomorphology and Sustainability' provides an overview of the key landscapes and common themes in urban geomorphology (centred upon urban rivers, karst landscapes and the weathering of buildings) within the six papers comprising the special section. First, urban geomorphology is defined geographically confined to areas of concentrated urbanisation, where the natural environment is anthropogenically modified and where natural processes modify anthropogenic structures. A novel approach to sustainable urban geomorphology is developed through the case studies comprising the special section. These clearly illustrate key contemporary issues within the field and a long-term perspective, considering future as well as historic human—environment associations and modifications.

Sarajevo, the capital of Bosnia and Herzegovina, is located in a karst geomorphological environment. The topographical setting strongly influences the urban geographical distribution and urban development, as well as the sustainability policies implemented in the city. The incorporation of an environmental agenda and the focus on sustainable development have characterised urban planning in cities in Central and Eastern Europe that are transitioning from socialist to capitalist economic systems. Environmental policies in Sarajevo are defined within the Sarajevo Canton Development Strategy developed under the supervision of international experts at the end of the three-and-a-half years of siege in December 1995, and this is expected to last until 2015. This paper argues that, despite the consensus achieved for developing Sarajevo through strategies aligned with European regulations for sustainability, the built environment of the city has moved in an increasingly unsustainable direction as a result of the need to deal with vulnerable groups in the population and the international policies that tend to promote a neoliberal urban development. The first section of analysis focuses on Sarajevo's existing particular geomorphological constraints on the development of a secure and sustainable built environment. The second section examines the increase in the geomorphological risks of new construction developed after the conflict in relation to the post-war and post-socialist urban processes.

Expanding cities worldwide are gradually absorbing peripheral greenfield streams that often require some level of improvement to fulfil their role as central public spaces in the urban landscape. Restoration is often impossible due to physical constraints imposed by urban development coupled with fundamental biophysical modification from previous land use. However, it is possible to provide social amenity and improve stream ecosystem condition through the process of naturalisation – an implicitly social undertaking reliant on the well-informed participation of stakeholders. Urbanising greenfield sites present a special case of naturalisation that does not include a local community as it is absent in advance of development. The authors present a case study where they were involved as advising scientists in a stream naturalisation project in Melbourne, Australia. In the case study, the lack of this founder community in the consultation process coupled with limited integration between other stakeholders resulted in naturalisation goals unlikely to result in improved in-stream ecosystem condition. The final design adopted some features that extended beyond baseline regulatory standards for drainage schemes in new developments, but with insufficient provision for catchment-scale treatment of stormwater runoff, which has been recognised as a primary source of urban stream degradation. This study expands the concept of naturalisation – originally developed in the context of rural stream management – to include urbanising greenfield catchments where advocacy groups and urban planning officials from local government hold chief responsibility to represent the values and attitudes of the founder community in the consultation process.

This paper describes a GIS-based land-use diversity measure for residential neighbourhoods – the land-use diversity index (or LDI) model – as a possible urban sustainability criterion. The term 'land-use diversity' is proposed as representative of many physical attributes of neighbourhood form opposite to typical sprawl patterns. A diverse neighbourhood is one with a mixture of compatible land uses and housing types, containing an array of amenities in reasonable proximity to where people live. The prototype version of the LDI model incorporates 34 input variables, structured around four sub-indices. Its range of expected values are explored through four case study applications. Theoretically, index values can vary between 0 and 1, where 1 represents a condition of greater 'land-use diversity'. The two traditional urban neighbourhoods fared well (index values ranging between 0.627 and 0.726) because they have a greater range of land uses and neighbourhood amenities, a better integration of housing types and are more concentrated. These two neighbourhoods meet many of the 'exuberant diversity' criteria described by Jacobs. The two suburban neighbourhoods scored lower index values (between 0.250 and 0.363), indicating variables different to those for traditional urban forms. The LDI model differs from existing sprawl measures fundamentally, as it attempts to measure sprawl at a finer resolution (i.e. at the neighbourhood scale). It is anticipated the LDI model will assist with planning new, and reconfiguring old, neighbourhoods as they strive to meet smart growth criteria now being considered by many cities.

The Oxford Transport Strategy (OTS) implemented in the Oxford city centre in June 1999 had an environmental impact associated with reduced car traffic and improved air quality, particularly of SO2 and CO. The effect on reductions in atmospheric pollutants and improved air quality is examined in this paper. By examining records of change associated with specific traffic records and mean annual measures of pollutants, including NO2, NOx, SO2, CO, O3 and PM10, it is possible to relate trends over 15 years (between 1997 and 2012) and evaluate the impacts on buildings. Specifically, this study reveals that soiling was reduced following the OTS and that building decay features stabilised. This occurred when there were reduced levels of traffic on some streets and improved air quality (at Oxford Centre, High Street and generally at St Ebbes) in the Oxford city centre. Reduced concentrations of all measured pollutants (except O3 at the urban background site; with the least reductions in NO2 and PM10 and greatest reductions in NOx, SO2 and CO) indicate a cleaner urban atmosphere since the OTS. Since O3 was the only traffic pollutant that slightly increased in the post-OTS atmosphere, its impact on building stone merits more research.

This paper explores the potential application of the Urban River Survey (URS) method for assessment of the hydromorphological condition of a heavily modified waterbody pre- and post-implementation of mitigation measures. The findings of a case study are used to demonstrate the utilisation of URS for monitoring hydromorphological response to restoration and assessing hydromorphological quality, particularly in relation to ecological potential and the European Water Framework Directive (2000/60/EC).