# A new tool to characterise the socio-environmental dimensions of urban rivers: Urban river socio-environmental index

Laurent Lespez, Marie-Anne Germaine, Frédéric Gob, Evelyne Tales, Nathalie Thommeret, Lucile de Milleville, Virginie Archaimbault, Manon Letourneur

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## ► To cite this version:

Laurent Lespez, Marie-Anne Germaine, Frédéric Gob, Evelyne Tales, Nathalie Thommeret, et al.. A new tool to characterise the socio-environmental dimensions of urban rivers: Urban river socio-environmental index. Landscape and Urban Planning, 2025, 122 (1), pp.105388. 10.1016/j.landurbplan.2025.105388. hal-05023312v2

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Submitted on 3 May 2025

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Research Paper

# A new tool to characterise the socio-environmental dimensions of urban rivers: Urban river socio-environmental index

Laurent Lespez<sup>a,*</sup>, Marie-Anne Germaine<sup>b</sup>, Frédéric Gob<sup>c</sup>, Evelyne Tales<sup>d</sup>, Nathalie Thommeret<sup>a</sup>, Lucile de Milleville<sup>a,e</sup>, Virginie Archaimbault<sup>d</sup>, Manon Letourneur<sup>c</sup>

## HIGHLIGHTS

* Urban streams, often neglected and highly artificialized, are crucial for urban ecosystem balance and can enhance the connection between cities, residents, and nature.

* We developed the URBS index, a socio-environmental quality assessment tool for small urban rivers, integrating both hydro-ecological and social dimensions.

* The URBS approach reveals a great longitudinal diversity of urban streams, which argues for a combination of the watershed and territorial approaches to management and restoration strategies.

* This approach identifies reaches that are ideal for reconnecting residents with urban streams and enhancing environmental education.

## GRAPHICAL ABSTRACT

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## ARTICLE INFO

**Keywords:**

Environmental evaluation

Socio-ecosystem

Social connectivity

Urban River

Indicators

River restoration

## ABSTRACT

Numerous studies have highlighted the dramatic hydro-geomorphological and ecological alterations that are the hydrological consequences of urban sprawl. However, most studies did not include the social dimensions. We propose an innovative interdisciplinary approach that combines biophysical and social issues using an example in the Paris urban area. We developed an Urban River Socio-environmental index (URBS) as a practical tool to assess the socio-environmental quality of the stream environment and social connectivity. The URBS is a multi-criteria index composed of four indicators calculated at the reach scale: hydro-geomorphology, macro-invertebrates, riparian vegetation, and social connectivity. We used the index to assess the organisation of several reaches along the stream and to provide a detailed functional socio-environmental typology. To exemplify the discussion, we used the URBS to assess the current situation of the Morbras River. Our results highlight the marked longitudinal diversity of urban streams and call for a combination of watershed and territorial

<footnote><sup>a</sup> Université Paris-Est Créteil Val-de-Marne, Laboratoire de géographie physique (LGP) CNRS UMR 8591, 2 rue Henri Dunant, 94320 Thiais, France</footnote>

<footnote><sup>b</sup> Université Paris Nanterre, UMR LAVUE CNRS 7218, équipe Mosaïques, 200, avenue de la République 92001 Nanterre Cedex France</footnote>

<footnote><sup>c</sup> Université Paris 1 Panthéon-Sorbonne, Laboratoire de géographie physique (LGP) CNRS UMR 8591, 2 rue Henri Dunant, 94320 Thiais, France</footnote>

<footnote><sup>d</sup> Université Paris-Saclay, INRAE, UR HYCAR, 1 rue Pierre-Gilles de Gennes, CS 10030, 92761 Antony Cedex, France</footnote>

<footnote><sup>e</sup> Université Paris-Cité, Laboratoire PRODIG CNRS UMR 8586, 8 rue Albert Einstein 75013 Paris, France</footnote>

<footnote>* Corresponding author at: Laboratoire de Géographie Physique (LGP) CNRS, Univ. Paris-Est Créteil, 2 rue Henri Dunant, 94320 Thiais, France.
E-mail addresses: laurent.lespez@u-pec.fr, laurent.lespez@cnrs.fr (L. Lespez).</footnote>
approaches to management and/or restoration. This approach makes it possible to account for the diversity of territories thereby avoiding a form of landscape standardisation or 'blandscaping'.

# 1. Introduction

Studies of urban riverscapes have focused on major waterways because they are valued for their waterfronts and landmarks (Macdonald, 2017) and the green and blue infrastructure they provide (Perini & Sabbion, 2016). In contrast, urban streams (<10 m wide and therefore wadeable) have remained on the back burner in urban projects (Gray, 2016; Ranta et al., 2021), even though they often represent the largest part of the hydrographic network in megalopolises and are crucial environmental infrastructures for future urban development to better meet the demand for more nature in cities. This is partly because urbanisation has profoundly altered urban streams: human-made rivers, which are often converted into canals or even covered over, no longer support biodiversity and have even become completely invisible. Such conversions involve three main issues: an increase in impervious surfaces, the installation of drainage systems for stormwater runoff, and the channeling of streams and bank protection (embankments) for flood mitigation. Taken together, these factors have a significant impact on hydrology. In particular, increasing the flashiness component of the hydrological regime (Booth et al., 2016; Fletcher et al., 2024; Oudin et al., 2018) has a cascade of consequences, including the incision and widening of channels, modification of the composition of the bed substrate (Ashmore et al., 2023; Chin, 2006; Dawson & Ashmore, 2025; Hawley et al., 2022; Russell et al., 2020), degradation of water quality, and alteration of the composition, structure and richness of aquatic communities (Allan & Allan, 1995; Palmer et al., 1994; Roy et al., 2016; Walsh et al., 2005). As the issue of nature and environmental risk management in cities has become central to urban development, there has been a considerable boom in ecological river restoration projects in European metropolitan areas, stimulated by the Water Framework Directive (Gray, 2016; Ranta et al., 2021).

In general, River restoration covers a wide variety of management activities designed to enhance river processes and forms to improve hydrological, geomorphic, and/or ecological processes (Cottet et al., 2021; Lespez et al., 2015; Wohl et al., 2005, 2015). However, biodiversity conservation is difficult to reconcile with human use of the biophysical environment (Bonthoux & Chollet, 2024). Given that human pressure is significant and constant in urban environments, we hypothesise that one way to promote biodiversity conservation and restoration is to limit disturbance to the ecosystem and encourage local people to care for and respect nature. This hypothesis is consistent with the idea that ecological restoration should not only restore ecological systems, their composition and functionality but also renew and restore the relationship between humans and nature (Higgs, 2012; Dicks, 2021). The challenge is therefore to identify and publicize opportunities for human-nature encounters that strengthen the local community's sense of attachment to nature. Urban streams are one of the last remaining natural spaces in the city, offering places for recreation as well as other ways of relating to nature (resourcing and contemplation, among others). Despite their reduced dimensions and the impairment of their biophysical functioning, they still represent privileged spaces for reclaiming nature in cities and improving the quality of life of the inhabitants of the world's main densely populated cities (Everard & Moggridge, 2012; Lespez et al., 2022; Zingraff-Hamed et al., 2017, 2021). The need for more socio-environmental research on urban streams in the temperate western world is therefore becoming increasingly urgent (Francis, 2014; Hanna et al., 2018; Lespez et al., 2022; Murphy et al., 2022), while numerous recent studies of major rivers (Alvarado-Arias et al., 2023; Andersen Cirera, 2022; Che et al., 2012; Chen et al., 2017; Kondolf & Pinto, 2017) underline the important role of social connectivity.

Restoring urban streams is an opportunity to reconnect residents with their everyday environment, on the condition that projects are rethought to better integrate the ecological and social components of the hydrosystem. It is thus crucial to find a way to develop relational thinking approaches that focus on interdependencies rather than relying on independent diagnoses to improve our understanding of socio-ecosystems (Eyster et al., 2022). Assessing the relationship between a river and its environmental qualities and people thus requires the development of hybrid methods (Boelens et al., 2023; Lespez & Dufour, 2021; Wantzen, 2024). Pioneering approaches have been developed to meet these expectations. Multi-criteria tools have been proposed to assess fluvial environment improvement in urban flood mitigation projects, for example, the urban river restoration index URRIx (Vérol et al., 2019) or to assess ecosystem services provided by urban streams, for example the UsAs tool for urban assessment (Ranta et al., 2021), but they remain limited in some ways. For instance, social and ecological dimensions are missing in URRIx which focuses exclusively on effective measurements of flood control in urban contexts. Conversely, the UsAs tool is multifaceted, but is based on a detailed description of 87 indicators meaning it is not straightforward to use. Finally, none of the tools developed to date assess the possibility of encounters between residents and their environment while at the same time accounting for the ecological diversity of urban watercourses.

To fill this gap approaches are required that explicitly integrate natural and social diagnoses of urban streams using the same analytical scale, in order to incorporate their materiality and ecological potential in the dialogue. Furthermore, it is necessary to address the longitudinal diversity of the entire watercourse of urban streams, by developing both a continuous riverscape approach (Torgersen et al., 2022) and indicators that are suited to their specific severely degraded environments. In response to these challenges, we developed a new multi-criteria approach based on the precise characterisation of the materiality, formalised by the URBS (URBan river Socio-environmental) index. The multi-compartment methodology is designed to measure both the quality of the ecosystem and its potential for relationships with local communities. We expect that by providing a global vision of urban streams, the innovative proposed approach will help to prioritise management and restoration actions with an environmental and social perspective.

# 2. Study area

Problems with urban streams are common in the Paris metropolitan area. Indeed, streams of order 1 to 2 in Strahler's classification account for 72.4 % of the 4 850 km of rivers that cross the Paris region and in 2019, only 8 % of these small rivers were classified as having good ecological status. To illustrate our methodological approach, we chose the Morbras stream, an emblematic urban stream. The Morbras is a tributary of the Marne River in the eastern part of Paris conurbation (Fig. 1A). It is 17.7 km long and its catchment area covers 51 km² (Fig. 1B). The average gradient of the river is 0.5 % and the average width is slightly more than 6 m. According to the classification of the European Water framework directive, it is a highly modified waterbody. The hydrological regime of the Morbras is of the rainfall evaporation type characteristic of a degraded oceanic climate (annual rainfall between 650 mm and 721 mm). High water usually occurs in winter, and low water mainly occurs at the end of the summer, although storm events occur regularly during the summer. The mean annual discharge of the Morbras is 0.33 m³/s. Maximum discharge in the period 2000–2024 was 10.8 m³/s (recorded in June 2018), and corresponds to a flood with a return period of about 20 years, while the minimum
recorded discharge was 0.01 m³/s. This urban stream is a medium energy river, with a specific power ranging from 10 W/m² upstream to 34 W/m² in the lower part of the basin (i.e. Morbras Park) (de Milleville et al., 2023a).

The Morbras basin is more than 43 % urbanised and, the rate of urbanisation in the catchment almost tripled between 1949 and 2017. The Morbras flows not only through towns with different urban densities but also different forms and generations of urbanisation. Upstream, it flows over the Brie plateau at a gentle slope (0.3 %), around 110 m above sea level and crosses the Ferrière regional forest. The river has been straightened and widened as it flows through the forest. Today it looks more like a forest drain than a real small stream at the head of a catchment area. In the middle sections, its course passes through its first urban area (Roissy-en-Brie) mainly comprised of residential housing estates and multi-family buildings and a small forest patch, and a rain-water retention basin built in 1986 to limit flooding (Etang du Coq). Downstream, the longitudinal slope rises sharply to 1 % then gradually stabilises at around 0.7 %. The Morbras flows on through reaches containing small patches of forest, an agricultural area and a golf course, before entering the Morbras departmental recreational park (0.2 km²). It then flows between residential housing estates in the town of Sucy-en-Brie. Along the last reach, it is buried then channeled until it reaches the river Marne at 32 m elevation.

### 3. Methods: socio-environments of urban streams and their structural and material dimensions

River ecology is generally characterised by hydrological functioning, the physical dimension of the channel, i.e. hydrogeomorphology, which determines the habitats available to living species, riparian vegetation and the quality of aquatic fauna and flora hosted by the watercourse and its banks (Roy et al., 2016; Walsh et al., 2005). We decided to evaluate three standard criteria for the analysis of the ecological functioning of streams: hydro-geomorphological functioning, aquatic biodiversity and

riparian vegetation. We selected these three criteria because they are complementary and are very often used in the analysis of the environmental quality of urban streams. This choice also corresponds to an objective of parsimony because a tool needs to be easy to use.

Hydrogeomorphology, which results from variations in the flow regime and in the river channel shapes aquatic habitats that are potentially suitable for flora and fauna (Statzner & Higler, 1986). Hydrogeomorphology also reflects the intensity of changes associated with urbanisation and the effects of hydropeaking (Booth et al., 2016). Among the many potential indicators of aquatic biodiversity (Ranta et al., 2021), we chose aquatic macroinvertebrates because they are present even in severely degraded conditions like those found in urban streams. They are also used in standard surveys of European waterbodies (WFD 2001) meaning these data are generally available. Macro-invertebrates are good indicators of the quality of the aquatic environment and, as such, they are widely used to assess the effects of urbanisation on watercourses (Gál et al., 2019; Medupin, 2020; Paz et al., 2022). In such contexts, macroinvertebrate communities integrate degradation of water quality and hence enable a diagnosis of the quality of the watercourse (Bylak et al., 2022), which also explains why we did not choose to use water quality as a criterion. In addition, the physico-chemical status of all the urban streams of Paris conurbation is monitored continuously. Monitoring consists in measuring four main indicators: oxygen balance (dissolved oxygen, biological oxygen demand and dissolved organic carbon), temperature, acidification measured by pH and its variation, and nutrient contents (phosphorus, phosphate, nitrate, ammonium) thus making it possible to determine the physico-chemical quality of the river water, from very good to poor. Despite efforts to treat waste and rainwater and the general trend towards improving water quality, the quality of all the streams that cross the Paris conurbation including the Morbras, is poor (AESN, 2022). This means that water quality cannot differentiate sufficiently between urban streams and/or between different reaches within the same hydrographic network (Lespez & Germaine, 2024).

<figure><img src="image_5.png" /><figcaption>**Fig. 1.** The Morbras river basin. A. Location in the Paris conurbation. B. Interpreted aerial photograph showing land use and the hydrographic network and location of the places cited in the text. Sources: IGN BD TOPO®, IGN aerial photograph 2017–2018 (5–20 cm).</figcaption></figure>
Riparian vegetation is often present at the interface between the city, i.e. built-up areas and the aquatic environment, and hosts biodiversity. The riparian vegetation used to characterise the land-water interface is usually well managed by landowners in urban areas, but it is not rare for spontaneous vegetation to grow in private areas that have no economic or residential use, an exceptional situation in high-density urban areas, particularly in large European cities. The neglected banks of certain small urban rivers are particularly prone to this spontaneous vegetation. Finally, we chose one social dimension criterion: hydrosocial connectivity. We chose to adapt the concept of social connectivity in order to conduct a socio-environmental diagnosis that is easy to generalise and capable of assessing the potential for encounters between riverside populations and aquatic and riparian environments. In fact, we believe it is the best way to diagnose connections that the organisation of urban materiality allows or prevents between the city and aquatic and riparian environments (Kondolf & Pinto, 2017).

The interdisciplinary methodology used was designed to compare

the socio-environmental potential of river reaches either within a river system or between different river systems. This requires field investigations at a high spatial resolution to incorporate the longitudinal distribution of habitats, flora and fauna and their relationship with the surrounding urban landscapes in all their diversity. This approach also requires a combination of field diagnoses and photointerpretation to produce an exhaustive map of the variety of dimensions surveyed. The small size of the watershed of urban streams allowed us to use a high spatial resolution with high frequency measurements for the continuous characterisation of the channel, the banks, and the floodplain directly in the field (Fig. 2). The data were collected over a relatively short and hydrologically stable period, following a 20-year return flood in 2018.

### 3.1. Hydro-geomorphology

To measure the extent of alterations linked to changes in hydrological regimes and the direct consequences of channel and bank

<figure><img src="image_6.png" /><figcaption>**Fig. 2.** The multidimensional methodology of the URBS project.</figcaption></figure>
engineering which characterise urban streams, we calculated five indicators based on the hydro-geomorphological evaluation implemented in France (Gob et al., 2014, 2025) (Table 1). This dataset is part of the set described in detail in de Milleville et al., 2023a. The field data were acquired at different scales: the whole water course, along which embankments, cross-cutting obstacles, and riffler and pool sequences were recorded; cross-sections located on every riffler were surveyed, bankfull width and depth were measured, and the dominant sediment particle size was noted. Additional cross-sections were surveyed in reaches where the rifflers were spaced too far apart. A total of 370 cross-sections were considered along the 17.7 km of the course between autumn 2018 and end of 2021. The five indicators used to evaluate hydro-geomorphology were calculated for each of these cross-sections from the direct measurements taken at the cross-section concerned (e.g. substrate characteristics) or from other measurements at a larger scale corresponding to either a reach including the 10 upstream cross-sections (e.g. channel geometry) or a reach 15 or 50 times the bankfull width of the cross-section concerned (e.g. bedform characteristics and channel sinuosity, respectively) (Table 1).

The first indicator concerns longitudinal continuity, i.e. the presence of anthropogenic cross barriers that interrupt sediment transport and biological movements. The number of obstacles more than 1 m in height on a reach including the 10 upstream cross-sections were counted. The ideal situation corresponds to a reach with none such obstacles. The second indicator evaluates lateral connectivity by considering the combination of the rate of embankment and the sinuosity of a given reach. The best situation corresponds to less than 1 % of embankment of the riverbanks with any type of bank protection to prevent bank erosion

<table><caption>**Table 1**
Indicators and metrics calculated for the Index of Hydro-Geomorphology (IHG).</caption><thead><tr><th>Indicator</th><th>Metrics</th><th>Range</th><th>Score Max</th></tr></thead><tbody><tr><td>Longitudinal Continuity (mh_contlon)</td><td>The number of obstacles &gt; 1 m high found in the reach of the 10 upstream cross-sections</td><td>From very bad = 0 (2 obs. &lt; 1 m or 1 obs. &gt; 1 m) to very good = 1 (0 obstacle)</td><td>1</td></tr><tr><td>Lateral constraints (mh_contlat)</td><td>The embankment rate (ER) calculated for both banks in the reach of the 10 upstream cross-sections<br>The sinuosity index (SI) was calculated on 50 x Bankfull width centered on the cross-section</td><td>From very bad = 0 (ER &gt; 20%) to very good (ER ≤ 1 %)<br>From very bad = 0 (SI &lt; 1.05) to very good (SI &gt; 1.5)</td><td>1</td></tr><tr><td>Geometry (mh_geometry)</td><td>Bankfull width deviation (σw): standardised residuals in relation to the CARHYCE regional model, calculated from the average width of the 10 upstream profiles.<br>Bankfull depth deviation (σd): standardised residuals in relation to the CARHYCE regional model, calculated from the average depth of the 10 upstream profiles.</td><td>From very bad = 0 (σw &gt; 1.25) to very good (σw &lt; 0.75)<br>From very bad = 0 (σd &gt; 1.25) to very good (σd &lt; 0.75)</td><td>1</td></tr><tr><td>Substrate (mh_subst)</td><td>Bedload diversity of mobile particles. Silt (L), sand (S), gravel/pebbles (G), boulders (B) and bedrock (BR).</td><td>From very bad = 0 (only bedrock or blocks) to very good (presence of gravels and no visible bedrock)</td><td>1</td></tr><tr><td>Bed forms (mh_forme)</td><td>Number of rifflers (Rn° in a reach of 15 x Bankfull width upstream of the cross-section</td><td>From very bad = 0 (Rn°=0) to very good (Rn°≥3)</td><td>1</td></tr><tr><td>IHG</td><td></td><td></td><td>Σ/5</td></tr></tbody></table>

(retaining walls made of stone, concrete or wood, gabions, paving, embankments made of various materials, etc.), the situation is rated very bad when more than 20 % of the banks are protected. The sinuosity is included because in these small lowland rivers, straight channels are usually the result of manmade reshaping. Old maps of the area dating from the 18th and 19th centuries show river reaches with a succession of very well-formed meander bends. The lowest score was therefore given to reaches with a sinuosity index (SI) &lt; 1.05 and the best score to very sinuous reaches (SI &gt; 1.5). The third indicator concerns the geometry of the bed to emphasize a potential incision and or widening of the bed. Average bankfull width and depth calculated based on the 10 cross-sections measured upstream of a given riffler were compared with the regional models of downstream hydraulic geometry that provide reference situations from river reaches with only a small number of anthropogenic constraints (de Milleville et al., 2023a; Gob et al., 2014, 2025). The geometry indicator was considered as very bad if the deviation from the models was higher than 1.25 and very good if it was lower than 0.75. The fourth indicator concerns the size category of the sediment particle in a given riffler. The size of the particles was estimated visually and classified in 5 classes (silt, sand, gravel/pebble, boulder and bedrock). We consider the situation to be favourable when a potentially mobile gravel load is present. Its presence is not only important for biocenosis but also because this indicates that the bed load has not been totally evacuated by the changing hydraulic conditions. We consider the situation to be very good when gravels are present on the bed and there is no bedrock. At the opposite end of the scale, we consider the situation to be very bad if no gravel is present, only bedrock or boulders. Finally, the fifth indicator concerns the bedforms; more specifically rifflers whose absence could indicate a limited supply of coarse sediment, as is often the case in urban areas (Booth et al., 2016; de Milleville et al., 2023b; Jugie et al., 2018; Vietz et al., 2016; Colosimo, Wilcock, 2007). The occurrence of riffler/pool sequences is indeed expected in a lowland catchment such as the Morbras. On the same river, de Milleville et al. (2023a) showed that the number of pool/riffle sequences was considerably lower in reaches that were significantly altered by urbanisation, i. e. having undergone bed incision and widening, a high rate of embankment, and the quasi-disappearance of bedload. According to Leopold et al. (1964) the theoretical spacing between pool and riffler ranges between 5 and 7 times the bankfull width. Reaches in the Morbras were thus considered to be very good if there were more than three rifflers and very bad if there was no riffler. The Hydro-geomorphological index (IHG) is the mean of the five metrics standardised to 0–1.

## 3.2. Macroinvertebrates

To assess the effects of urbanisation on stream macroinvertebrates, it is important to analyse their condition not only in terms of structure but also from a functional perspective (Gál et al., 2019; Sterling et al., 2016). The challenge is to define an index for naturally poor environments like those found in urban multi-stressor contexts (Serra et al., 2019; White & Walsh, 2020). Some metrics proved to be particularly relevant to assess these conditions. The proportion of tolerant taxa, such as Chironomids or Oligochaeta, increases with urbanisation (Burcher & Benfield, 2006; Canobbio et al., 2013). Conversely, sensitive insect taxa, notably Ephemeroptera and Trichoptera, are adversely affected in highly urbanised contexts (Violin, 2011). Functional traits of benthic macro-invertebrates are also affected by urbanisation (Paz et al., 2022). The benthic macroinvertebrate communities in the Morbras, have already been the subject of a standard study using the I2M2 index protocol for a report on the status of this watercourse (de Milleville et al., 2021). However, this type of approach is not suitable if the objective is to establish a precise diagnosis of the watercourse. Indeed, in such urban environments where the substrate distribution is simplified, the spatial distribution of the communities is modified, which implies modifying the spatial resolution of the sample collection. A sampling protocol was therefore designed specifically for this study. It represents a compromise
between a reasonable sampling effort and a sufficient spatial resolution. Five stations were chosen randomly located along the watercourse, at an average of 3 km intervals, depending on public access to the stream. Stations were also located on each of the five different types of hydro-geomorphological reaches identified during a previous analysis (de Milleville et al., 2023a). Overall, the locations of the stations also account for the presence of local features (ponds, discharge from wastewater treatment plants, tributaries). The most upstream station is intentionally far from the source to avoid an intermittent watercourse sector. The sampling protocol was based on the literature (Baruch et al., 2018; Olson et al., 2016; Violin, 2011) which recommended the collection of five samples per station: two located on riffles, two located on riverbank habitats (woody or plant supports, or fine mineral supports) and one on the most representative support at the station concerned. This sampling protocol was applied during a snapshot campaign conducted in May 2020 after the flow had been stable for a minimum of 15 days. Previous experiments on the Morbras (de Milleville et al., 2021) have shown that this sampling period satisfactorily captures the status of macroinvertebrate communities.

Several metrics that are commonly used in community analysis and environmental quality assessment were calculated (Table 2). According to Barbour (1999), a biological metric is a biotic characteristic that changes predictably with increasing anthropogenic influence on the environment. Structure metrics quantitatively characterise the richness, diversity, and evenness of benthic communities. Compositional metrics correspond to the taxa identity of the community, such as the abundance or richness of a given group. Functional metrics reflect the processes that generate biodiversity and affect composition and structure, for example, reproduction, feeding mode, and more generally the biological traits of the taxa. Among all the metrics tested, we selected five that had a proven ecological meaning and that allowed us to distinguish between the five stations sampled on the Morbras. Taxonomic richness reflects local habitat heterogeneity: the more complex the habitat, the richer the community. Community stability, a result of environmental stability, is represented by evenness, which reflects the balance of a community. We selected the percentage of Ephemeroptera and Trichoptera taxa as a measure of community sensitivity because in an urban context, these two insect groups are adversely affected because they are the most sensitive taxa in the community (Cuffney et al., 2010; Baruch et al., 2018). In contrast, the GOLD metric (Gastropoda, Oligochaeta and Diptera abundances ratio) is a measure of the most tolerant component of the community and reflects the tolerance of the community to organic contamination and eutrophication. Indeed, Oligochaeta, Diptera (particularly Chironomids) and Gastropods respond positively to urbanisation (Utz et al., 2009) and the Oligochaeta ratio increases with habitat degradation in urban streams (Canobbio et al., 2013). Finally,

<table><caption>**Table 2**
Indicators and metrics calculated for the Index of Macroinvertebrates (IMI).</caption><thead><tr><th>Indicator</th><th>Metrics</th><th>Range</th><th>Max Score</th></tr></thead><tbody><tr><td>Diversity (Mi_S)</td><td>Taxa richness (number of taxa identified per station)</td><td>From very bad = 0 (x &lt; 21) to very good = 1 (x &gt; 28)</td><td>1</td></tr><tr><td>Stability (Mi_J)</td><td>Evenness (Pielou's index)</td><td>From very bad = 0 (x &lt; 0.05) to very good = 1 (x &gt; 0.59)</td><td>1</td></tr><tr><td>Sensitivity (Mi_ET_Tax)</td><td>% Ephemeroptera &amp; Trichoptera taxa</td><td>From very bad = 0 (x &lt; 2) to very good = 1 (x &gt; 18)</td><td>1</td></tr><tr><td>Tolerance (Mi_1GOLD)</td><td>% of individuals of Gastropoda, Oligochaeta, Diptera (expressed as 1-GOLD)</td><td>From very bad = 0 (x &lt; 0.37) to very good = 1 (x &gt; 0.8)</td><td>1</td></tr><tr><td>Functional trait (Mi_1ovo)</td><td>Reproductive strategy</td><td>From very bad = 0 (x &lt; 20) to very good = 1 (x &gt; 80)</td><td>1</td></tr><tr><td>IMI</td><td></td><td></td><td>Σ/5</td></tr></tbody></table>

we selected the ovoviviparity trait as a functional metric of benthic communities. In a context characterised by overall habitat degradation, frequent disturbances and environmental instability, taxa with this trait are favoured by using strategies of “parental care” that maximise survival of the young. These five metrics were transformed such that decreasing values indicate increasing stress. The Index of Macro-Invertebrates (IMI) is the mean of the five metrics standardised to 0–1.

### 3.3. Riparian vegetation

Riparian vegetation plays a key role in the quality of aquatic and riparian environments and the quality of landscapes in urban areas. We created a simple and robust analysis grid based on protocols defined by the national database CARHYCE (Gob et al., 2014, 2025), modified to include some recommendations concerning the diagnosis of linear riparian vegetation (Balligand et al., 2018; Dajoux et al., 2020).

The Riparian Vegetation Index is based on the measurement of 11 metrics calculated on homogeneous reaches identified in the field and mapped using GIS in several field campaigns conducted in spring 2021. These metrics were calculated on the right and left banks of the 61 homogeneous reaches identified in the field. The final score is the average of the metrics calculated on the two banks (Table 3). This includes the riparian vegetation cover, which is defined as the width of the vegetation strip and its continuity. The diversity of the riparian vegetation was estimated from the number of tree species, with a maximum score corresponding to 8 according to the reference standards used (Balligand et al., 2018). In addition, the vertical stratification of the vegetation was determined based on the references used in France: trees (>7 m), shrubs (0.7–7 m), herbaceous layers. The more diverse the vegetation cover, the higher the score. Vegetation dynamics reflects the stability of trees and shrubs, considered as an indicator of the state of the forest cover, and of the cover dynamics between 1933 and 2020, which corresponds to the period of urban expansion in the study catchment. Three metrics were used to evaluate the vitality of the riparian forest and its capacity to host biodiversity. The presence of dead wood is a good indicator of the presence of microhabitats (Dajoux et al., 2020). Renewal was assessed by the presence of shrub and tree seedlings, while the spontaneity of the stands was used to distinguish planted areas from areas characterised by

<table><caption>**Table 3**
Indicators and metrics calculated for the Index of Riparian Vegetation (IRV).</caption><thead><tr><th>Indicator</th><th>Metrics</th><th>Score</th><th>Score Max</th></tr></thead><tbody><tr><td rowspan="2">Spatial extent (mv_empris2)</td><td>Continuity</td><td>From absent = 0 to continuous = 0.5</td><td rowspan="2">1</td></tr><tr><td>Thickness</td><td>From absent = 0 to large (x &gt; 25 m) = 0.5</td></tr><tr><td rowspan="2">Diversity (mv_divers2)</td><td>Species diversity of trees</td><td>From bad = 0 (1 species) to very good (x &gt; 8 species) = 0.5</td><td rowspan="2">1</td></tr><tr><td>Vertical stratification (canopy, subcanopy, understory layers)</td><td>From bad = 0 (1 layer) to very good (3 layers) = 0.5</td></tr><tr><td rowspan="2">Dynamic (mv_dynam2)</td><td>Stability of the tree</td><td>From bad = 0 to good (3 layers) = 0.5</td><td rowspan="2">1</td></tr><tr><td>Change in the rate of forest cover 1933–1920</td><td>Negative = 0 and Positive = 0.5</td></tr><tr><td rowspan="2">Vitality (mv_vital2)</td><td>Dead wood</td><td>Absence = 0 and Presence = 0.333</td><td rowspan="2">1</td></tr><tr><td>Renewal</td><td>Absence = 0 and Presence = 0.333</td></tr><tr><td rowspan="2">Native plants (mv_Indige2)</td><td>Spontaneity</td><td>From Planted = 0.16 to Spontaneous = 0.333</td><td rowspan="2">1</td></tr><tr><td>Invasive species</td><td>Absence = 0 and Presence = 0.666</td></tr><tr><td rowspan="2">IRV</td><td>Exotic plants</td><td>Absence = 0 and Presence = 0.333</td><td rowspan="2">Σ/5</td></tr><tr><td></td><td></td></tr></tbody></table>
spontaneous vegetation. Finally, the presence of exotic and invasive plants that affect the ecological quality of riparian vegetation was considered. Along the Morbras River, Japanese knotweed (Fallopia japonica), Tree of heaven (Ailanthus altissimala), Himalayan balsam (Impatiens glandulifera), black locust (Robinia pseudoacacia), ash-leafed maple (Acer negundo) and cherry laurel (Prunus laurocerasus) have a high regional presence in the invasive alien plant suite (Wegnez, 2022). Non-invasive exotic species are particularly common along small urban streams because they are often chosen by residents as ornamental plants for their gardens and also by managers of public green spaces. They do not have the invasive character of the former and therefore cause less damage to the environment and to native species. Nevertheless, they have no relationship with the environment in which they are planted and consequently contribute to its modification. The Index of Riparian Vegetation (IRV) is the mean of the 5 metrics standardised to 0–1.

### 3.4. Hydrosocial connectivity

While most social approaches focus on discourses, we chose to consider the description of the spatial configuration of places and the materiality of landscapes because it determines the potential relationship between the inhabitants and users and the streams. Indeed, determining physical or visual accessibility is a prerequisite for understanding the quality of the relationship that residents are able to establish (or not) with the river. In fact, the materiality of landscapes both influences and reveals the relationships between societies and rivers (Berque, 1994). The characterisation of landscape-river organisation also provides knowledge about the care taken of the river and its relational potential (Chen et al., 2017; Tronto, 2020) and reflects both recent and long-standing individual (riparian owners, even users) and collective (associations, communities, river syndicates) development strategies and spontaneous dynamics. The analysis was based on adapting the concept of social connectivity to urban streams (Germaine & Temple-Boyer, 2022). The criteria were determined through numerous field observations, which enabled us to understand the practices of the river and its surroundings, as well as through exploratory interviews with managers (3), elected representatives (3) and residents (12) and two focus groups organised with different local actors concerned by small urban rivers. First, we identified 52 homogeneous reaches by examining maps, by using GIS, and in several field campaigns conducted from March to June 2021. To measure the potential relationship of the inhabitants with the river, 11 metrics (most of which were assessed on both banks) were determined in the field based on visual assessment (Table 4). The final score is the average of the metrics calculated on both banks. To get closer to the spaces experienced by the residents and users, the compartments we analysed were not limited to the channel itself. The metrics were then aggregated to produce five synthetic indicators.

The openness of the watercourse differentiates open and buried segments. Accessibility is the second criterion, as it defines the possibilities of opportunities for recreational, aesthetic and educational activities. It reflects any physical and visual connections between the city and the river. We distinguish between the physical and visual dimension of the river on the one hand, and those of the water on the other. The aim is to judge if it is possible to reach (and even touch) the banks and the water, or if they are even visible. Accessibility depends on the absence of obstacles such as walls, or fences, but also on the topography and the height and slope of the banks and finally on the height and density of the riparian vegetation. It also depends on the land tenure status of the riparian land. Access is not guaranteed simply because the owner is the public domain, and vice versa, but is key information for identifying development potential. We also observed the strip of land bordering the watercourses: primarily unsurfaced longitudinal footpaths or cycle paths, or paved paths. We also noted recreational and/or urban facilities (children's playgrounds, etc.) and any equipment (benches, picnic tables) installed near the river, as well as educational facilities aimed at

<table><caption>**Table 4**
Indicators and metrics calculated for the Index of Hydro-Social Connectivity (ICS).</caption><thead><tr><th>Indicator</th><th>Metrics</th><th>Range</th><th>Score Max</th></tr></thead><tbody><tr><td>Openness (Mc_open)</td><td>Covered river (0) or open-air river (1)</td><td>From very bad = 0 to very good = 1</td><td>1</td></tr><tr><td>Accessibility (Mc_acceberg)</td><td>Access to the banks (none = 0; possible = 0.17; easy = 0.33); Access to the water (none = 0; possible = 0.17; easy = 0.33); Land status (private = 0; public = 0.33)</td><td>From very bad = 0 (x &lt; 0.4) to very good (x &gt; 0.6)</td><td>1</td></tr><tr><td>Visibility (Mc</td><td>Bank visibility (none = 0; possible = 0.25; easy = 0.5); Water visibility (none = 0; possible = 0.25; easy = 0.5)</td><td>From very bad = 0 (x &lt; 0.5) to very good (x &gt; 0.75)</td><td>1</td></tr><tr><td>Amenities (Mc_equip)</td><td>Mobility options (pedestrian/ bike paths); Recreational amenities (number of benches, picnic tables, etc.); Educational tools (number of signs)</td><td>From very bad = 0 (x &lt; 0.5) to very good (x &gt; 0.75)</td><td>1</td></tr><tr><td>Attractiveness (Mc_attract)</td><td>Surrounding land use (industrial/commercial = 0; residential = 0.15; open spaces = 0.33); Shape of the area allowing access to the river (linear = 0; strip = 0.17; larger area = 0.33); Reputation (local use only = 0; regional use = 0.33)</td><td>From very bad = 0 (x &lt; 0.5) to very good (x &gt; 0.75)</td><td>1</td></tr><tr><td>ICS</td><td></td><td></td><td>Σ/5</td></tr></tbody></table>

raising awareness among passers-by (constructed or part of the natural heritage). These different public amenities attract attention to the riverfront to a greater or lesser extent. Finally, we evaluated the attractiveness of each reach. This indicator is based on the surrounding land-use patterns, including the immediate environment in which the river is located, by identifying the kinds of spaces it crosses (residential built-up area, agricultural land, etc.). The configuration of the reach was also considered to qualify the right-of-way through the area which the river is located. The shape of the accessible space around the river is either non-existent (buried or privatized) or corresponds to a strip of land parallel to the river of varying width, or lastly, to a larger space (like a park). The aim is to assess any potentially public space close to the river banks. Finally, the attractiveness of the reach is evaluated by deeming it unattractive or reserved for private use, whether it is only valued by the local riverside population or is more widely known (e.g. includes parking lots, whether or not it is served by public transport).

### 3.5. URBS index and classification of the reaches

Due to the specific nature of each diagnostic domain, field measurements were taken, and metric calculations were performed in different spatial reference frames. However, to provide a diagnosis that allows comparisons, we decided to use only one spatial grid. To this end, we calculated the values of the metrics and specific indices for the 370 cross-sections of the hydro-geomorphological diagnosis, as it represents the most accurate spatial grid. In the case of macroinvertebrates, as the five sampling stations corresponded to the five previously defined types of hydro-geomorphological reaches, the metrics were assigned to all cross-sections of the same hydro-geomorphological type. To standardize specific indices to build the synthetic index, we chose a method of scoring inspired by the assessment of hydro-geomorphology quality of Italian rivers (Rinaldi et al., 2013). Each specific index has a maximum value equal to 1. Because the final objective is to provide an overview of the main socio-environmental issues of urban streams, we formulated a synthetic index combining the four specific indices to globally assess the socio-environmental quality of urban rivers:
$$URBS = \frac{\sum IHG, IMI, IRV, ICS}{4}$$

This index should not be considered as a standard index because it is not based on adjustments to a statistical model: only its trend is meaningful, the higher the score, the better the socio-environmental status of the stream. To analyse and discuss our results, we performed a multivariate analysis to extract a typology of reaches with the same socio-environmental profile; i.e., we conducted a Principal Component Analysis (PCA, Pearson correlation) on the 370 cross sections and the 20 indicators calculated resulting from the four specific indices. The coordinates of each point obtained from the PCA were then used to perform hierarchical agglomerative clustering (HAC, Centering; Euclidean distance for dissimilarity and Ward's method of aggregation) to produce a coarse typology of the different reaches of the Morbras river.

# 4. Results

## 4.1. Specific indices (Fig. 3)

### 4.1.1. Hydro-geomorphology

The hydro-geomorphology of the Morbras can be considered of medium to good quality. Indeed 83 % of the cross sections studied had a hydro-geomorphological score (IHG) > 0.4, of which 39 % can be considered as good to very good (>0.6). The cross sections with the highest scores are located outside the built-up areas, in Morbras park at Sucy-en-Brie, in the agricultural areas downstream of La Queue-en-Brie and in Berchères wood. Only a few of the cross sections (7 %) were judged to be bad or very bad. The worst reaches are limited to the most upstream part of the river, in La Ferrière forest. There, the channel is over-calibrated, highly segmented by weirs, with very few bedforms and no gravel load, and only the lateral constraints are limited in number.

Surprisingly, in most of the reaches, the amount of embankment is rather limited, especially in the middle upper part of the course. The stream is therefore often able to erode its banks. In fact, the only continuous bank protection is in the heart of urbanised area of the Pontault-Combault crossing, Sucy-en-Brie and at the confluence with the Marne. Conversely, the values for longitudinal continuity are generally low. The situation is in fact quite binary, the river is either very fragmented as is the case of some reaches in the built-up areas of Roissy-en-Brie and Pontault-Combault, or contains very few obstacles, as is the case in most of the agricultural areas. The geometry of the river channel is also rather contrasted. On one hand, the width and a depth of some rural and urban reaches are similar to regional models: the geometry scores given to Morbras park, the upper reach of Pontault-Combault or the Berchère wood are good or very good. On the other hand, the channel is deeper and wider in some reaches. The form indicator shows that there are fewer rifline and pool sequences in the upstream half of the Morbras watercourse than farther downstream, where these sequences are more frequent. This pattern closely resembles that of the substrate indicator. Gravel loads are indeed present in the downstream reaches, whereas in the upper part of the river course, bedrock is visible in many of the cross-sections studied even though the local geology suggests that the riverbed should be composed of gravely material (pieces of flint, limestone chips, sandstone, etc.) provided by the surrounding substratum.

Hence, no clear pattern emerged from the distribution of the scores, rather significant heterogeneity, as most of the indicators in some reaches had good to very good scores (e.g. Morbras park), while others had very poor scores (e.g. La Ferrière forest). What is more, contrary to what might be expected, the hydro-geomorphological quality of the Morbras did not deteriorate downstream, i.e there was no obvious cumulative effect of urbanisation. However, the hydro-geomorphological quality of the more rural reaches was found to be generally better than that of the urbanised ones. Nonetheless, some urban reaches still had a rather high

score, for instance, the central reach in Roissy-en-Brie, where the river channel underwent ecological restoration in the 1990s (de Milleville et al., 2023a).

### 4.1.2. Macroinvertebrates

Regarding the macroinvertebrate community, we identified three different zones along the Morbras. In the downstream part of the Morbras from La Queue-en-Brie to Sucy-en-Brie, the ecological quality was found to be rather good with a fairly rich community, hosting the most sensitive taxa of the Morbras, while the highest evenness was recorded at these stations, suggesting that the community is well balanced with no taxa dominating. These observations reflect a low level of habitat alteration, with a sufficient number of refuge areas to ensure good distribution of organisms and hence satisfactory ecological functioning. In contrast, in the intermediate part of the Morbras (from Pontault-Combault to La Queue-en-Brie), invertebrate communities were found to be of mediocre to poor quality. Both the structure and composition of the benthic communities were altered as a result of habitat and physico-chemical degradation. Taxonomic richness was low, as was the ratio of sensitive taxa. We observed very strong dominance of highly tolerant taxa notably GOLD, reflecting a marked imbalance in the community and consequently degraded functioning. The recorded taxa reflected strong general habitat degradation along with high rates of organic pollution. The value of the ovoviviparity trait suggests the frequency of disturbances is high. The intermediate reach of the Morbras crosses a denser urban area, which may be more prone to sudden hydrological variations during rainfall events or more exposed to accidental discharges of wastewater. Finally, the Roissy-en-Brie section can be classified as a zone of medium quality. Relatively few taxa were identified but those that were present were well distributed and included sensitive taxa. These communities thus signal acceptable physico-chemical quality, with probably not too limited habitat diversity.

### 4.1.3. Riparian vegetation

The extent of riparian vegetation contrasts sharply in two different types of area. Wooded areas with continuous or slightly discontinuous riparian vegetation are present throughout the catchment and have a very good IRV rating. On the other hand, stretches with poor quality riparian vegetation correspond to urban stretches characterised by private gardens or open public spaces, for example downstream of Pontault-Combault and Roissy-en-Brie. The diversity of the vegetation is thus not a very discriminating factor. However, it is seldom bad, since even in deforested areas, the Morbras floodplain is free of monospecies plantations. The riparian vegetation is characterised by the frequent presence of three layers, whether planted (gardens and parks) or spontaneous, and the species diversity of the tree and shrub layers is in most cases moderate, with 5-7 tree species, which corresponds to the median of the results per reach. The worst reaches are planted urban sections with low species diversity, as is the case along the open sections in Roissy-en-Brie. The dynamics underline the contrast between the upstream and the downstream reaches of the Morbras. In fact, the upstream values are good, reflecting an increase in vegetation in the last century and generally stable stands. This corresponds to forest areas that are largely managed or crossings in towns containing recent plantations, like Pontault-Combault, where the urban project or rainwater management has enabled the establishment of patches of stable vegetation. The worst reaches are those located downstream from Pontault-Combault and correspond to urban sections characterised by private ownership where the tree cover is stable or declining, or to poorly managed areas where the tree cover suffers from the effects of storms and actions by the inhabitants (the agricultural part of the Champlain depression, Morbras park). The vitality of the vegetation underlines the contrast between very high quality areas, like Ferrière regional forest, Berchères wood and the wooded areas of the Champlain depression, and urban areas like Pontault-Combault and the Grand Val in Sucy-en-Brie, where the vegetation is completely controlled by the landowners or by the
managers of the public spaces, who planted scattered trees and shrubs in open lawns. The presence of exotic and invasive plants is a very discriminating indicator. The most favourable areas are located in the Champlain depression, and in Berchère wood, i.e., in areas with spontaneous vegetation and no invasive plants, and in areas with planted vegetation, but planted with native and generally well adapted plants. Areas dominated by exotics (bamboo, locust, willow) like Morbras park, or the private gardens of the Grand Val district of Sucy-en-Brie (conifers and exotic flowering plants) locally suffer from the presence of invasive species (Japanese knotweed and negundo maple).

To sum up, the riparian vegetation index is dominated by two main indicators, the spatial extent of the tree cover and the presence of invasive and exotic species. Not surprisingly, very good overall quality characterises forested areas, while good quality corresponds to areas with continuous or slightly discontinuous riparian vegetation, characterised by a good spontaneous renewal of the mainly native trees. Poor quality corresponds to the urban reaches, which are also characterised by a very sparse tree cover.

### 4.1.4. Social connectivity

The stream is open to the air over almost its entire course (97 %), except for part of the urban crossing in Sucy-en-Brie. In all, 38 % of the banks of the Morbras are accessible, both the right and left banks, but it is nevertheless possible to access at least one of the two banks of more than half of the Morbras stream thanks to the crossings. There are significant contrasts between the municipalities that are crossed. In the downstream part, the river is partly covered, completely inaccessible in Noiseau, while access is reduced to Morbras park in Sucy-en-Brie due to dense residential development along the river. In Ormesson-sur-Marne, the golf course and the castle form two vast linear inaccessible areas.

The proportion of accessible banks then increases progressively upstream, from 21 % at Ormesson-sur-Marne to 65 % at Roissy-en-Brie. Good access is enabled by several parks or public properties including Morbras park, the "du Coq" lake, which straddles Pontault-Combault and Roissy-en-Brie, the "Parc des Sources" in Roissy-en-Brie, and Ferrières regional forest upstream. The walkways along the banks of the Morbras, which vary in width and in development, should be added to the above list. Indeed, in the Roissy-en-Brie area, the banks of the Morbras are practically all publicly owned: the housing estates included a grassy strip a few dozen metres in width that allows people to walk along the river through several green spaces. The banks of small urban rivers can be used for non-motorised transportation. As such, they are part of the soft mobility network and can also be part of an urban green network. Finally, the river may form part of a larger accessible space such as a park. In this case, longer lasting, more relaxing activities are possible, such as picnics, games (soccer or other), contemplation, photography, or simply resting.

More generally, several types of reaches can be distinguished, corresponding to increasing levels of social connectivity. The river reaches between the residential sectors remain inaccessible and invisible, only private uses are possible there. Other inaccessible reaches exist in private non-residential spaces such as agricultural land or private estates. However, the land status of the riparian plots does not determine access to the watercourse, since half of the public riparian plots are nevertheless inaccessible whereas some private plots are equipped for collective use. In the end, despite the fact the river is not a public domain, it is basically accessible, and, apart from a few areas, can be used by both local residents and visitors. In other cases, the reach is located within a large public space, but is nevertheless physically inaccessible, for instance, downstream of Ormesson Castle park. The lack of maintenance of this space and the multiplicity of branch channels renders access to it complex.

### 4.1.5. Relationships between specific indices

PCA performed on the 20 different indicators estimated for the 370 cross-sections enabled us to structure our observations (Fig. 4). The first

factorial plane represents almost 50 % of the information. According to the first axis, the Index of Social Connectivity (ICS) is opposed to the three other sub-indices. This confirms, on the one hand, that the different elements that make up the specific hydro-ecological indices tend to converge and, on the other hand, that the value of social connectivity is poorly correlated with hydro-ecological parameters. The situation is different for the Index of Riparian Vegetation (IVR) that characterises the banks and the floodplain, since vitality, diversity and extent are located on the same part of the first factorial plane, close to the other synthetic hydro-ecological indices (IHG, IMI). However, the Indigeneity and Dynamics indicators are located at the opposite part of the factorial plane corresponding to watercourses of poor ecological quality. This situation reveals the influence of private gardens, where invasive and exotic species are most numerous, and the vegetation is delimited. The hydro-geomorphological indicators of continuity (mh_contlon and mh_contlat) are located in an intermediate position between the other hydro-ecological indicators and those of social connectivity. This suggests that some of the reaches the most favourable to people are also less artificialised by transverse or lateral barriers, at the expense of the ecological quality of the bed. Thus, the pattern of data on this factorial plane underscores the difficulty of articulating good social connectivity for local people with good ecological quality.

## 4.2. URBS score and classification of the reaches

### 4.2.1. URBS scores and classification of Morbras reaches

The scores of the synthetic URBS index range from 0.3 to 0.8 as an indicator of probable diversity of configurations (Fig. 5). URBS appears to be characterised by longitudinal organisation in homogeneous reaches. The organisation of these homogeneous reaches does not follow the upstream-downstream gradient, which in this case, is also a gradient of increasing urbanisation (Fig. 6). Reaches with low URBS scores are interspersed with reaches with higher URBS scores. The HAC, performed on factorial coordinates of the 370 cross sections, resulted in five classes, each comprising between 30 and 98 observations that are also characterised by their longitudinal organisation in homogeneous reaches (Fig. 7). This reveals the clear socio-environmental organisation of the Morbras because the classifications are also consistent with their URBS index values.

### 4.2.2. Reaches with the lowest URBS values and low ecological quality (Figs. 7–9)

Groups 1 and 2 correspond to reaches with altered geomorphology and barely diversified riparian vegetation suffering from the presence of exotic and invasive species. As a result of the alteration of environmental conditions (geomorphology and riparian vegetation), the ecological status is very disrupted, but less so in group 2 where the community appears to be more balanced despite the alterations. Both physical and visual accessibility are quite good and the potential for social valorization is also quite good, largely because these are urban areas where public land has been left open along the river to allow people to walk and discover the waterway.

### 4.2.3. Reaches with moderate URBS values and low socio-environmental quality (Figs. 7, 8, 10)

Group 3 comprises reaches of medium hydro-geomorphological quality, particularly due to their fairly good lateral and longitudinal continuity, and of reaches of medium social connectivity, with medium accessibility and attractiveness. These reaches are located in loose peri-urban spaces with forest vegetation and good spontaneity, despite a straight, often rectified, channel and a medium size substrate. Group 4 comprises stretches characterised by relatively good geomorphology (form and geometry) and quite good aquatic ecological quality, despite the fact the vegetation is not very spontaneous and despite the expansion of invasive species. Social connectivity is very poor because these stretches are private, difficult to access (Ormesson
<figure><img src="image_7.png" /><figcaption>Fig. 3. Maps showing the specific indices.</figcaption></figure>
<figure><img src="image_8.png" /><figcaption>**Fig. 4.** Correlation circle of the PCA performed on the 20 estimated indicators (in red) for the 370 cross sections. Specific indices (lines in blue) are represented as additional variables. The colour used for the label refers to the colour used for each domain in Fig. 3: hydrogeomorphology (blue), macro-invertebrates (light green), riparian vegetation (green), social connectivity (orange). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

golf course, Ormesson castle park and the Champlain depression).

### 4.2.4. Reaches with balanced profiles and good socio-ecological quality
(Figs. 7, 8, 11)

The reaches in group 5 are the most balanced, with accessible semi-wooded areas and high-quality hydro-ecological dynamics. But the quality of the riparian vegetation suffers from a lack of dynamic development and an average number of exotic and invasive plants. In

fact, this is characteristic of the way public parks have long been conceived as green spaces, alternating open spaces (lawns) with more enclosed areas and using non-native plants for landscape design as is the case in the Morbras park in Sucy-en-Brie. Nevertheless, the reaches in group 5 have good ecological and social development potential.

## 5. Discussion

### 5.1. Uncovering the high diversity of urban stream socio-environments

The study of Morbras river showed that urban streams are more complex objects than is often thought. The study demonstrated the great variability in socio-environmental conditions for a river that is only about twenty kilometres long and located in a major European conurbation, where environmental conditions are generally considered to be poor. Furthermore, the ecological quality of the environment is not simply distributed along a gradient of urbanisation. In fact, the opposite is true along the Morbras, since the environments with the best socio-environmental quality are located in the downstream part of the watershed and within (Morbras park) or close to dense urban areas (Champlain depression). This situation should be emphasised, both because it contradicts the oversimplification of river quality in urban areas, and because it offers opportunities for improving, managing or restoring aquatic environments in densely built-up areas where they are accessible to the population.

The identification of reaches of very low socio-environmental quality (Group 1 and 2) underlines the important roles of urban growth and hydraulic control in the transformation of river systems. This is the legacy of both multiple and repeated developments, particularly in cities. To date, all long-term environmental studies of the trajectory of socio-ecosystems in Europe have demonstrated the co-evolution of the city and the river in Paris (Barles, 2015) and their impact on the Parisian waterscapes since the early Middle Ages, sometimes far from the city (Benoit et al., 2005; Guillerme, 1983). Consequently, the current state of small watercourses is partly the result of a historical process during which they were transformed to supply the city with energy, plant and food resources before becoming involved in the urbanisation process, as shown by the few case studies available for the Paris metropolitan area (de Milleville et al., 2023b; Jugie et al., 2018). This explains both the channelisation and the artificialisation of the riverbanks, especially in

<figure><img src="image_9.png" /><figcaption>**Fig. 5.** Box plot showing the URBS indexes of each group of reaches.</figcaption></figure>
<figure><img src="image_10.png" /><figcaption>Fig. 6. URBS Score along the Morbras stream.</figcaption></figure>

<figure><img src="image_11.png" /><figcaption>Fig. 7. Map of the classified reaches.</figcaption></figure>

the urban crossings, where the reaches with the lowest socio-environmental quality are located. But this long evolution is also responsible for the alteration of the aquatic habitats and the long-standing deterioration of riparian vegetation, which suffers from both urban expansion and the introduction of exotic plants by private individuals or public space managers along the accessible reaches of the river.

It should also be noted that some of these reaches are already the result of former restoration projects. This is the case of the Roissy-en-Brie crossing, which is the first urban unit crossed by the Morbras upstream of the basin. These reaches correspond to developments built between 1970 and 1990, in which the urban project incorporated the river as a structuring element in built-up areas. This type of reach is also visible in the crossing of recently built areas in Pontault-Combault. There, public space is available, but the current configuration of the river, which was the result of an initial restoration of the rectified channels (de Milleville et al., 2023a), focused on landscape aspects, amenities for local people and the hydraulic capacity of the channels. These choices were accompanied by the production of insufficiently diversified flow forms and facies, and rather poor discontinuous riparian vegetation consisting only of small willows, which today limits the ecological potential of these restored reaches.

The identification of reaches of average socio-environmental quality (Groups 3 and 4) is to be expected where urban pressures are slightly reduced. However, it is important to bear in mind that the changes are of different kinds and that the restoration of better environmental quality

requires different kinds of action. Therefore, by working on hydrogeomorphology, in particular by improving the substrate and the alternation of riffles and pools, Group 3 can be significantly improved. Reaches in Group 4 present a different set of challenges. Although their ecological quality can already be improved by focusing on the natural regeneration of the vegetation and by limiting invasive species, their social connectivity is a particular challenge. Their social potential should be enhanced by the creation of public paths across private land, particularly in large private areas such as the golf course or the private park of the Château d'Ormesson. This is less common in France than elsewhere, as public footpaths across private land are rare and remain a complicated problem to solve.

Finally, the identification of reaches of high socio-environmental quality (Group 5) is particularly stimulating. In fact, along the Morbras in the Morbras park at Sucy-en-Brie, certain reaches have undeniable hydro-geomorphologic qualities, in particular the maintenance of lateral channel freedom and a variety of flow facies, and hence ecological potential. Located in the heart of urban areas, they are a window on what remains of the spontaneous natural dynamics of the stream. Visible and accessible, the channels and banks offer an opportunity to reconnect the local population with nature and could become a showcase of the good socio-environmental quality of small urban rivers in the Paris conurbation. Identifying these spaces would allow us to design restoration projects that include a social dimension, and to offer activities that connect the local population with their river. It is the ability to reveal this relational potential that makes URBS a useful tool
<figure><img src="image_12.png" /><figcaption>**Fig. 8.** Photographs illustrating the different socio-environmental quality groups identified along the Morbras river. A. The Morbras flowing through the Grand-Val district of Sucy-en-Brie (group 1). B. The Morbras flowing through Roissy-en-Brie, a previously restored section (group 2). C. The Morbras downstream of Roissy-en-Brie (group 3). D. The Morbras in the Champlain basin at La Queue-en-Brie (group 4). E. The Morbras in the Parc départemental du Morbras – Ormesson-sur-Marne and Sucy-en-Brie (group 5).</figcaption></figure>

for the characterisation of rivers. The realization of this potential depends on the appropriation of these spaces by their managers and on their ability to make them exemplary spaces for reconnecting people with their environment and for promoting an ecological vision of rivers in the city among local populations, who are often not aware of the capacity of urban rivers to form true ecosystems. In fact, urban pressure and quality of life issues, especially in residential areas where single-family homes alternate with apartment blocks, have long encouraged reflection on the recreational use of these publicly accessible natural spaces. Without excluding them, we believe there is potential here for a more ecological and undoubtedly more ambitious project.

All these observations suggest the need to avoid over-generalised approaches to the functioning of urban streams, as they inevitably lead to the simplification of the relationship between biophysical

environments and urban sprawl. This is maybe quite different in areas where urbanisation is much more recent, rapid and standardised, as is the case in certain North American and Australian cities (e.g. Kermode et al., 2021; Russell, 2021). Our approach emphasises the need for the construction of ecological restoration projects, that move away from a generic approach that would not do justice to local specificities. It also aims to promote approaches that combine biophysical and social diagnostics even before undertaking surveys with local inhabitants to fully understand the weight of materiality in the organisation of practices and the formation of representations. The proposed approach also has an educational value for managers, as it emphasises the fact that the socio-environmental quality of an urban watercourse depends on a variety of factors, including the way in which urban watercourses traverse the urban space.
<figure><img src="image_13.png" /><figcaption>Fig. 9. Radar graph of the reaches with lowest values of URBS and low ecological quality.</figcaption></figure>

<figure><img src="image_14.png" /><figcaption>Fig. 10. Radar graph of the reaches with moderate URBS values and low socio-environmental quality.</figcaption></figure>

<figure><img src="image_15.png" /><figcaption>Fig. 11. Radar graphs of the reaches with balanced profiles and good socio-ecological quality.</figcaption></figure>

## 5.2. The potential of integrated materiality-based diagnoses of urban streams

As we have shown, evaluating social and environmental data is neither simple nor straightforward. As Cortelezzi et al. (2019) point out, most studies of urban ecosystems do not include social descriptors as concrete variables. For example, Vérol et al. (2019) propose a supportive tool to assess fluvial environment improvement in urban flood projects. Their tool is a multi-criteria formulation based on watershed characteristics, the three dimensions of river connectivity, characterisation of riparian conditions (riparian vegetation and urban development), and hydraulic risk reduction. The tool allows quantification of the effects of design alternatives to help decision making but does not include any naturalist data about river biodiversity and does not consider the potential relationship between local people and the watercourse. Thus, the URBS approach is innovative because it combines two types of approaches that are usually used separately: social connectivity approaches (e.g. Che et al., 2012; Kondolf & Pinto, 2017; Hermida et al., 2019; Germaine & Temple-Boyer, 2022) and ecological river assessment. In addition, the management of a river system in all its diversity requires data to be acquired throughout the river system. Creating a toolbox cannot simply be the juxtaposition of expert opinions based on indicators proposing scores derived from different spatial references. A prerequisite for the comparison of knowledge between different fields of expertise is the establishment of a common spatial reference frame.
URBS makes it possible to combine ecological and social connectivity studies in a single methodology that can provide comprehensive and comparable information along the entire river network. The URBS approach will facilitate regular and homogeneous production of information pertaining to the various components to be compared in the context of a holistic approach. The URBS methodology accounts for the intrinsic quality of the biophysical environment and the physical capacity of the local population to encounter the biophysical environment of their daily lives. In urban contexts, where environmental quality is so compromised, it is not an approach to quantify the pressure or define specific standards or thresholds. Rather, it is a comparative approach within the socio-ecological system that is relatively easy to understand because it is based on indicators common to river management/restoration and urban organisation data that can be understood by most people.

The assessment of the natural characteristics of urban environments according to the principles of ecosystem services has become more common in recent years. These approaches involve attributing values to the various services provided by biophysical environments to populations (e.g., Hanna et al., 2018; Cortinovis et al., 2021). However, in practice, implementing an exhaustive quantitative approach is challenging (Vollmer et al., 2016; Murphy et al., 2022). Consequently, there has been a paucity of studies that have applied a comprehensive approach to the ecosystem services provided by urban rivers (Vérol et al., 2019). Such studies require the application of reductive methodologies both for the collection of data and the selection of indicators. As a result, it is difficult to develop a method that can be applied across diverse natural and socio-economic settings. In this context, the approach proposed by Ranta et al. (2021), which includes cultural services (UsAs) is the only work we found that tries to integrate the social dimensions in an environmental diagnosis of urban streams. But the UsAs index requires many indicators to be defined (e.g. 28 for urban biodiversity, 25 for cultural services) which are often calculated on a much larger scale than the river and its environment. It strives to be a comprehensive tool; however, with 87 indicators grouped in 17 services and functions, it requires a large quantity of information from different fields of knowledge. This complexity contradicts the principle of parsimony and renders generalisation difficult. Furthermore, the various indicators are obtained at different spatial scales, sometimes larger than the valley floor or the catchment area. This makes it very difficult, if not impossible, to distinguish between the different situations that can be observed along an urban stream, whereas the URBS approach has demonstrated its effectiveness in understanding the spatial organisation of the socio-environmental qualities of a small urban watercourse. As such, the URBS synthetic index is a first step in thinking about a combination of indicators that can cross disciplinary boundaries. It can be used to prioritise issues for managers by defining the specific challenges confronting each section. We consider it to be an effective tool for informing and ultimately building operational decision support tools to design ecological restoration projects that account not only for the ecological dimension but also for local social acceptability in consultation with end users. The results we obtained respect both the coherence of this small-scale river system and its great longitudinal variability, thereby underlining the need for small-scale studies.

## 5.3. The benefits of the materiality approach for the management of urban streams

### 5.3.1. Methodological difficulties of materiality approaches

Although the materiality approach is purported to be more objectively grounded than constructivist perspectives based on population and management stakeholder representations, it nonetheless involves a series of methodological challenges. It is clear that the choice of approach always involves a degree of selective decision-making. In accordance with the methodology proposed by Vérol et al. (2019), identical weights were assigned to each domain in order to calculate the

URBS. We acknowledge that this decision is arbitrary, and it should also be noted that the question of the weighting of the domains requires further consideration and is hence open to criticism. At this stage, the choice we have made corresponds to the objective of diagnosing the ecology of urban waterways as accurately as possible and comparing it with social connectivity, with the aim of managing riverscapes on a territorial basis.

The second point is that defining the URBS index required a significant methodological effort because we wanted to develop a detailed spatial approach to the socio-environmental quality of urban streams. This necessitated standardisation of methods, notably of the spatial resolution. The most difficult task was merging biological sampling with other collected data. In a way, this observation shows that it is always difficult to compare data on living organisms, which require extensive field surveys through inventories, with data used for social connectivity. The approach based on abiotic and urban structures makes it possible to define the material setting and to understand its specificities and its potential to improve the relationship between local people and their environment. A collective effort is required to determine the most appropriate scale to adopt to define the analytical framework required for a common diagnosis. In this case, we chose to use the finest grid resulting from the hydro-geomorphological diagnosis; other choices would have been possible, but none would have allowed a finer spatial resolution. We are well aware that the choice we made requires a substantial amount of data to be collected both remotely and in the field, but we believe this was the only possible way to effectively test the methodology we wanted to use.

### 5.3.2. Considerations for better rehabilitation of urban streams

* From recognising longitudinal diversity...

Of course, the management of urban streams, like other waterways, must be based on a longitudinal approach to the river system and in each catchment area. However, the URBS approach highlights the great longitudinal diversity of watercourses that are progressively swallowed up by the urban area. This suggests adding a territorial approach to their management or restoration. Taking this dimension into account avoids the standardisation of technical expertise favoured by the proliferation of restoration projects, which leaves little room for local specificities and could lead to the development of standardised projects specific to each epoch, with its dominant methods and concepts. The aforementioned restored sections of the Morbras in Roissy-en-Brie in the 1970s and 1990s are a very good example of this type of approach, where landscape amenities and the hydraulic capacity of the channel largely dominated the restoration project, to the detriment of the ecological quality of the environments created. The URBS approach must therefore encourage consideration of a sense of place in order to promote place-based ecological projects. For example, the potential and problems of restoration appear to be very different for degraded reaches of Groups 1 and 2, and it is undoubtedly advisable to develop specific projects for these different areas. The proposed typology also makes it possible to identify sections of particular interest because they are relatively well preserved from an ecological point of view (Groups 4 and 5). Even if the channel is oversized, the diversity of forms and vegetation remains interesting. These reaches in a better ecological condition are the ones that should be preserved as a priority. They can also serve as a local reference for new restoration projects.

* ... to overcome the dichotomy between social and natural objectives...

As it takes place in highly urbanised contexts, the rehabilitation of small urban rivers cannot be done without truly incorporating the social dimension. Urban streams are often disregarded due to their invisibility. A detailed and systematic description of the physical forms of the
watercourse and its surroundings makes it possible to understand the potential practical relationships that the inhabitants could forge with it. Thus, this study of the Morbras shows that, despite their status as non-state-owned watercourses, it is important to consider small urban rivers as a mosaic of private and public river banks, with a significant number of accessible and/or visible reaches. The ecological rehabilitation of small rivers therefore involves the modification of public spaces or even the creation of new public pathways, meaning it is essential to include the assessment of accessibility to the watercourse. Finally, we need to go beyond the dichotomy of social objectives on the one hand and natural objectives on the other: the latter should not be considered in opposition to each other, but rather in relation to each other. Diagnoses in the context of regulatory studies are very often thematic. The urban river is divided into different dimensions (hydrology, hydrogeomorphology, water quality, aquatic and riparian environment, social dimension). This explains why experts' knowledge of the river is often incomplete and fragmented. This can lead to problems in interpreting changes or pressures and hence in finding a sustainable solution. Due to the environmental heterogeneity and urbanisation gradients that characterise urban streams, we must design appropriate solutions to improve/restore ecological status and not be satisfied with ready-made solutions that supposedly fit all situations. We must also avoid a form of standardisation of the riverscapes or 'blandscaping' (Connop & Nash, 2018), which favours the scenic aspect at the expense of the ecological functionality of the restored environment.

* ... and produce recommendations for river managers

In conclusion, the establishment of URBS makes it possible to make recommendations to managers. For the Morbras, we propose a management strategy that includes three types of recommendations:

* Prioritise restoration actions in the most degraded reaches, by intervening in the compartments with the lowest scores (Groups 1 and 2).

* Decide which type of action to prioritise in medium quality sectors. For example, for Group 3, where it is necessary to improve the hydrogeomorphology and in particular the substrate and pool-riffle sequences through hydrogeomorphic restoration. In Group 4, it is necessary to improve accessibility, for example, by creating public paths on private land, in order to promote the relationship between the local population and the river, and hence recognition of its ecological potential.

* Preserve the reaches that appear functional from any point of view and develop them as a section to support environmental education (Group 5). Indeed, the reaches with the best socio-environmental scores seem to be particularly suitable for the transition from recreational activities to an introduction to ordinary ecology. However, we are also aware that the encounter between the public and the biophysical environment is not easy to manage and regulate. The problem of the number of visitors and their management needs to be addressed to preserve the socio-environmental balance highlighted. Raising public awareness of ecological issues is therefore a challenge for public landowners, who have to organise the way the public will be received and design the modalities right from the conception of the management or restoration project. It is a question of educating people about the natural rhythms of the river, the transport of its sediments, the habitats that are available, and the plants and animals which continue to thrive there despite the many pressures resulting from urbanisation.

## 6. Conclusion: promoting a shared ecological culture

Urban streams suffer from a lack of recognition. In addition to their modest dimensions, they have undergone extensive artificialisation which often leads residents to equate them with canals or even sewers.

Connecting urban populations to such streams therefore first requires making them more visible. This is all the more important because urban streams are an essential natural heritage, often forgotten, but crucial for the balance of urban ecosystems, and they offer the opportunity to improve the relationship between the city and its inhabitants, nature, and the aquatic environment. Research has shown that these watercourses offer opportunities to 'reclaim urban nature'. To account not only for the ecological dynamics, but also for the urban context in which they are located, we have developed an original multifactorial approach based on the production of a synthetic index of the socio-environmental quality of small urban rivers. The URBS index and typology are based on parameters that are easy to determine and are already widely used in ecological approaches to rivers. Thus, it is possible to combine a hydroecological and a social diagnosis based on objectively measurable material dimensions.

The URBS-type approach is based mainly on field observations and mapping and corresponds to a naturalistic and social field approach. It identifies different types of socio-environmental contexts and should be the starting point for socio-environmental management/restoration of watercourses. This dimension is crucial because it corresponds to the need to address socio-environmental issues not using remote expert approaches based on generic parameters, but localised approaches that fully integrate the territory crossed by the river (Boelens et al., 2016). Thus, as ecological restoration projects proliferate in cities, it is vital to promote a holistic approach that also restores the relationships between the populations and these particular watercourses (Dicks, 2021; Higgs, 2012; Hikuroa et al., 2021). It is crucial to help riverine communities take greater ownership of the challenges involved in river restoration. This means developing cognitive skills to promote a river culture beyond a small circle of experts. This is important because research shows that inhabitants' aesthetic evaluation is not necessarily related to the biological quality of the environment (Alvarado-Arias et al., 2023). For example, riparian resident's perceptions of riparian vegetation based on aesthetic values are unfortunately sometimes far removed from the biological value of the environment, as shown by Arsénio et al. (2020). To achieve this objective, it is thus necessary to disseminate and share the results of research with river managers and with the public through targeted actions. Therefore, based on our precise diagnosis and on our first recommendations targeting managers, we will propose innovative solutions that account for both the socio-cultural dimensions and the diversity of values of water and wetlands, in order to promote a river culture (Wantzen et al., 2016) applied to urban streams.

## CRediT authorship contribution statement

**Laurent Lespez:** Writing – review & editing, Writing – original draft, Validation, Supervision, Project administration, Methodology, Investigation, Formal analysis, Conceptualization. **Marie-Anne Germaine:** Writing – review & editing, Writing – original draft, Validation, Supervision, Methodology, Investigation, Formal analysis, Conceptualization. **Frédéric Gob:** Writing – review & editing, Writing – original draft, Validation, Supervision, Methodology, Investigation, Formal analysis, Conceptualization. **Evelyne Tales:** Writing – review & editing, Writing – original draft, Validation, Supervision, Methodology, Investigation, Formal analysis, Conceptualization. **Nathalie Thommeret:** Validation, Methodology, Investigation, Formal analysis, Data curation, Conceptualization. **Lucile de Milleville:** Investigation, Formal analysis. **Virginie Archaimbault:** Writing – review & editing, Writing – original draft, Validation, Methodology, Investigation, Formal analysis, Data curation, Conceptualization. **Manon Letourneur:** Methodology, Investigation.

## Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
## Acknowledgments

This work was supported by the Piren-Seine axis 3 of phase 8 of the PIREN-Seine (https://www.piren-seine.fr/) and more particularly in the block devoted to the ‘Trajectory of peri-urban rivers’. The authors of this article are grateful to the “Syndicat Mixte pour l’Aménagement du Morbras” and “the Metropole du Grand Paris” and the “Val-de-Marne departmental council” for their interest and collaboration in this study.

## Data availability

Data will be made available on request.

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