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Accurate rainfall modeling is crucial to understand the way water is intercepted, infiltrates and flows through surfaces and rivers. In particular, it is paramount for the study of the influence of rainfall spatio-temporal distribution on basin hydrologic response and the structure of floods. Current weather radar products allow capturing the variability of rainfall extremes mainly at 1 km spatial resolution. In France, radar measurements are performed at a 5-minute time step, while gauge-based reanalysis are computed at hourly resolutions. During short-duration high-intensity precipitations, pluvial floods (PF, or flash floods) can occur outside the hydrographic network in runoff-prone areas, leading to various types of damages such as soil erosion, mud and debris flows, landslides, vegetation uprooting or sediment load deposits. Contrary to fluvial floods, PF are highly correlated to local rainfall. Depending on generic susceptibility linked to topography, soil texture and land use, specific precipitation patterns can trigger intense overland flow. Hence, after extreme weather events, precise reports on PF locations provide key information for rainfall reanalysis and downscaling at fine spatial resolution.This work focuses on two extreme Mediterranean events (more than 300 mm of rainfall in 24 hours) that took place in the South of France between 2018 and 2020. Time series of hourly rainfall intensities from Comephore radar reanalysis data at 1 km resolution (Météo-France) are confronted to (i) maps of PF that occurred during the events and (ii) generic susceptibility maps to surface runoff. For (i), runoff-related impact maps of the events are produced using the remote sensing-based FuSVIPR algorithm (Cerbelaud et al., 2023) based on Sentinel-2 temporal change images and Pléiades satellite or airborne post event acquisitions. For (ii), the IRIP© method (Dehotin and Breil, 2011; Cerbelaud et al., 2022) is used to generate PF susceptibility maps. The model is run with the RGE Alti® 5 m DEM, the OSO French land cover dataset, and soil type susceptibility characteristics derived from both climatological information and the ESDAC database.We primarily show that areas with higher IRIP levels are more likely to be impacted by PFs, and even more so where short-term precipitation was heavier. Additionally, rainfall intensities are negatively correlated with IRIP susceptibility scores in PF impacted areas. This corroborates that somewhat higher rainfall intensities are required for flash floods to occur in less susceptible areas. Similarly, comparatively smaller rainfall amounts can trigger PFs in locations where susceptibility is high. Then, the Comephore products are downscaled at 50 m resolution on both events using the SAMPO stochastic simulator (Leblois and Creutin, 2013). Among multiple scenarios, optimal ones are chosen based on the assumption that the negative correlation with the IRIP susceptibility levels in the affected areas should be equally or even more present in the downscaled rainfall time series. This study hence suggests an original way of selecting disaggregated extreme rainfall scenarios that are consistent with the observed consequences of intense runoff on the land surface using various tools such as a stochastic simulator, a hydrological risk mapping method and earth observation data.

Due to global change, cities of the future will have to deal with more intense runoff and longer drought sequences, in addition to a growing urban and peri-urban population. French Mediterranean cities, such as Toulon, are already densely urbanised and exposed to the effects of global warming. The adaptation of their infrastructures is problematic. Cities with high development potential, such as Dakar, offer the opportunity to imagine other solutions for the management of water resources and its extremes in the context of global change. In particular, it is a question of managing the flows of water and substances linked to intense runoff events according to an ecohydrological logic that makes it possible to reduce environmental risks and increase social and economic benefits. To do this, we use a hydrologically-based geomatics model (IRIP) that produces predictive maps of areas of generation, transfer and accumulation of intense runoff and associated nutrients. This allows us to target effective intervention areas to reduce risks and increase water resources, for example by simulating land use change in appropriate locations and at the same time stimulating specific biological processes. The fundamental principle of ecohydrology is to balance energy flows with biological metabolic flows at the sub-catchment scale. The mapping of intense runoff processes is a first step illustrated in this article for the cities of Toulon and Dakar. This first step is part of the Dakar'2030 project, which aims to rethink urban development and adapt it to climate change.

Along with fluvial floods (FFs), surface water floods (SWFs) caused by extreme overland flow are one of the main flood hazards occurring after heavy rainfall. Using physics-based distributed hydrological models, surface runoff can be simulated from precipitation inputs to investigate regions prone to soil erosion, mudflows or landslides. Geomatics approaches have also been developed to map susceptibility towards intense surface runoff without explicit hydrological modeling or event-based rainfall forcing. However, in order for these methods to be applicable for prevention purposes, they need to be comprehensively evaluated using proxy data of runoff-related impacts following a given event. Here, the IRIP geomatics mapping model, or “Indicator of Intense Pluvial Runoff”, is faced with rainfall radar measurements and damage maps derived from satellite imagery and supervised classification algorithms. Six watersheds in the Aude and Alpes-Maritimes departments in the South of France are investigated over more than 2000 km2 of rural areas during two flash-flood events. The results of this study show that the greater the IRIP susceptibility scores, the more SWFs are detected by the remote sensing-based detection algorithm. Proportions of damaged plots become even larger when considering areas which experienced heavier precipitations. A negative relationship between the mean IRIP accumulation scores and the intensity of rainfall is found among damaged plots, confirming that SWFs preferably occur over potentially riskier areas where rainfall is lower. Land use and soil hydraulic conductivity are identified as the most relevant indicators for IRIP to define production areas responsible for downslope deteriorations. Multivariate logistic regression is also used to determine the relative weights of upstream and local topography, uphill production areas and rainfall intensity for explaining SWF occurrence. This work overall confirms the relevance of IRIP methodology while suggesting improvements to its core framework to implement better prevention strategies against SWF-related hazards.

International audience; Description and validation of a new simple, inexpensive iso-pressure device for quantitative measurements of gas emissions in river (the SNIFFER for "Sampler of Natural InFluxes of Foul Emissions from River sediment"). The Sniffer was validated, during two field campaigns, a first in winter (18/12/13 to 20/02/14) and a second in spring (16/04/14 to 14/05/14) on a stream receiving some organic matter from a combined sewer overflow. The measured CH4 emissions are of the order of 0.50 L/(m2.day). This production is far from negligible and commits us to reconsider the contribution of water systems in total greenhouse gas emissions.; Description et validation d’un nouveau dispositif iso-pression simple, peu couteux de mesures quantitatives des émissions de gaz en rivière (le SNIFFER pour "Sampler of Natural INFluxes of Foul Emissions from River sediment"), validé, lors de deux campagnes de terrain, une première hivernale (18/12/13 au 20/02/14) et une seconde printanière (16/04/14 au 14/05/14) sur un cours d’eau soumis à des apports de matière organique d’un déversoir d’orage. Les émissions mesurées sont de l’ordre de 0,50 L/(m2.J) de CH4. Cette production est loin d’être négligeable et nous engage à reconsidérer la contribution des hydrosystèmes fluviaux dans les émissions totales de gaz à effet de serre.

International audience; Faecal indicator bacteria (FIB) and bacterial pathogens from combined sewer overflow (CSO) in peri-urban streams represent a major public health concern worldwide. In this study, the relationships between the hydrological regime and the loads and persistence of CSO-borne bacterial contaminants among benthic sediments of a small peri-urban stream were explored. Combined sewer overflow events and their impact on benthic sediment layers at a short distance from a CSO were monitored. Concentrations of Escherichia coli (EC) and intestinal enterococci (IE) and of two bacterial pathogens, Pseudomonas aeruginosa (PA) and Aeromonas caviae (AC), were assessed. Relations with hydraulic, hydromorphic and physicochemical factors were analysed. PA cells in benthic sediments increased exponentially with time (0.15 log PA per day), as long as the river discharge remained below the sediment transport. Cycles of erosive floods and low-flow periods were found to play a critical role in PA settling and growth among benthic riverbed sediments. These hydrological and hydraulic shear forces did not correlate with changing IE, EC, and AC concentrations in the benthic sediments. Their dynamics were rather related to changing physicochemical conditions (total N, phosphate, and organic carbon). AC population size decreases most rapidly with a mean rate of 0.04 log per day according to the duration of the low-flow period, indicating a poor tropism of AC for river systems. River sediments were found significant biotopes for PA outdoor development. These analyses demonstrate the significance of PA and AC as long- and short-term indicators, respectively, of a river microbiological quality.

The effect of vegetation on the volumes of water that infiltrates into the soil has been extensively studied, but not the redistribution that occurs radially from trees. This is especially important in arid and semi-arid areas where water volumes are scarce and water resources management must be more scrupulous. In the present study, the influence of native vegetation (huizache trees) on the redistribution of infiltration in a semi-arid zone in the central Mexican plateau was analyzed. Single ring infiltration tests were carried out with a radial distribution in 2 trees: 4 located inside the crown of the tree and 4 outside it, in 4 different axes, giving a total of 32 tests per tree. Likewise, particle size distribution and soil texture analysis were carried out in 4 orthogonal directions and dry bulk density and initial water content tests at each sampling point were performed. The results showed a zone of influence located between r / 2 and r of the tree canopy, where the infiltration is much greater compared to the other points. Based on these results, the methodology for a third tree was redesigned, in order to characterize various infiltration areas. So that 3 zones were established within the tree: near, intermediate and far, taking 2 tests in each zone, in orthogonal direction, and taking a test in each zone of 4 additional axes, a total of 36 tests. The results of the infiltration tests with this methodology showed similar results to the other two trees: low infiltration rates close to the tree trunk, high infiltration rates in the area between r / 2 and r of the canopy and again low rates of infiltration in the area outside the crown. Additionally, the particle size distribution analyzes showed the presence of 4 types of soil: loam, sandy-loam, clay-loam and silt-loam soil. On the other hand, the initial water content and dry bulk density do not seem to affect the infiltration process to a greater extent and they vary indiscriminately. The above suggests that the area between r / 2 and r is the one that captures the highest infiltration volumes, it may be due to the shadow effect produced by the treetops, although the soil texture has an influence on the infiltration rates, it does not influence the form of radial redistribution of tree infiltration.

Riparian vegetation along the rivers is one of the ways that allows restoration of surface water quality, stabilizing the banks, reducing erosion risks and offering habitat to flora and fauna. The modification of these ecosystems affects sediment transport and deposition in rivers. Sediments retained in a reservoir suggest an impact on the dynamics of the erosion processes and on the equilibrium of riparian ecosystems. If this tendency continues, it will not only affect the generation of electricity, but it will also impact ecosystems, either due to the excess of sediments or to lack of them. This paper analyzes the dynamics of the riparian ecosystems, upstream and downstream of “El Caracol”, a hydroelectric dam located in Guerrero, Mexico, based on Landsat TM and ETM + images corresponding to early spring (March-April) for the period of 1984-2010. The analysis was established by mapping the dynamics of the NDVI as an indicator of the areas affected by the migration of the vegetation and the erosion of the margins. The results show a decrease in NDVI in the study period. While degraded areas have a negative NDVI trend, there are areas within the same reservoir, where the index increases, indicating an increase in sediment deposition being an important factor in explaining vegetation migration.

The term flooding is often associated with a stream overflow or a marine flood, runoff-floods is rarely considered, and today suffers from a lack of knowledge and control of the phenomenon. This paper, presents a geographic information system iRIP@ – Flooding by Intense Pluvial Runoff (French acronym), which is a new tool to mapping flooding by runoff as a tool for decision-making by mapping runoff flooding in Gareat El Taref catchment (Northeast Algeria), with identifying the area of production, transfer and accumulation of flood.Us results, we have cards represent the potential of a territory to generate the various hydraulic dynamics of runoff: the runoff production card, the runoff transfer, the runoff accumulation card, the runoff-flooding card.A visual simulation on the flood risk card indicates that the areas with an important runoff flood risk are the communes of Khenchela Oum El Bouaghi Ain El Beida and F’kirina. Moreover, the roads that join Khenchela with Ain El Beida and with Oum El Bouaghi.Khenchela city is exposed to a great risk of flooding by runoff, the solution proposed by the authorities and that summarizes by the construction of a canal is not sufficient, because on the one hand the north of the city remains exposed to this risk. On the other hand, a large area of runoff production is located between the canal and the city.It is probably operating to encourage farmers to introduce certain agricultural practices that are part of a sustainable management of flood risk by runoff.

Este artículo contiene 3 figuras, 2 tablas., Nitrogen uptake (N-uptake) within the hyporheic zone provides key ecological services, such as nutrient removal, of stream ecosystems. We hypothesize that the hydraulic conductivity (Kf) of the hyporheic sediments governs nutrient uptake rates through effects on the: i) surface and subsurface flow (i.e. hyporheic flow); and ii) hyporheic N-uptake. Here, we worked at two hierarchical spatial scales (reach- and hyporheic-scale) to disentangle the role of Kf on N-uptake. At the reach scale, we performed co-injected N-NH4+ and Cl– additions in six reaches with contrasting reach Kf (10−1 – 10−5 m/s) and simultaneously determined a) in-stream N-uptake (hyporheic+benthic N-uptake), and b) hyporheic flow, N-uptake, and c) microbial abundance at the hyporheic scale. Results suggest that Kf determines the contribution of the hyporheic zone to hydrological exchange, but that its role varies between scales to determine in-stream N-uptake. At the reach scale, Kf variability seems to determine the extent at which the hyporheic zone contribute to hyporheic flow; and thus, to N-uptake velocity. At the hyporheic scale, Kf seems to indirectly determine hyporheic N-uptake through the proportion of surface water that enters the hyporheic zone (i.e. relative connectivity) and the abundance of the microbial community. These results suggest an interplay between Kf at both scales and the spatial heterogeneity, which will ultimately drive in-stream N-uptake at reach-scale. In this sense, we found that Kf can be considered as a unifying variable for stream biogeochemical processes and as an important variable to derive the contribution of hyporheic zone to in-stream nutrient removal capacity.

The IRIP method, for Indicator of intense pluvial runoff, in French, is a geomatics method which allows mapping the susceptibility of territory to surface runoff and that provides three maps of susceptibility to the generation, transfer and accumulation of runoff. It is based on the combination of binary maps that represent the impact of a given factor (favourable or not favourable) to runoff. These factors are summed up to provide susceptibility maps to runoff with levels ranging from 0 to 5. To be used for risk prevention, the quality and limitations of the produced maps must be assessed. However, runoff data are very scarce and not available everywhere in a territory. Proxy data of impacts related to runoff can provide information useful for the evaluation of the IRIP maps. However, both information cannot be compared directly and a specific methodology to compare susceptibility maps and proxy data must be proposed. This paper presents such a method that accounts for the hazard level, the vulnerability of the study area and possible mitigation actions taken to reduce the risk. The evaluation method is assessed using runoff-related impacts on railways as proxy data to compare with the maps. The evaluation is made on a 80 km railway line in Normandy (North of France), where a comprehensive database of runoff-related impacts on the railway has been gathered over the whole 20th century. The results show that the evaluation method is robust and relevant. The comparison with runoff-related impacts on the railway also shows that the susceptibility maps produced by the IRIP model provide relevant information related to runoff and that they can be used to design risk management strategies, as illustrated in the railway context.

International audience; The Cd, Cr, Cu, Ni, and Pb concentrations in the sediments of Lake Mariout were measured and estimated by statistical approaches using the contamination factor (CF), pollution load index (PLI), geo-accumulation index (I-geo), Nemerow index (I-in), ecological hazard index, and potential ecological hazard index (RI). The aim of the present work was to assess the current situation of Lake Mariout compared with other Egyptian lakes regarding heavy metal pollution in the sediment and to identify the putative sources. The measured concentration levels of heavy metals in Lake Mariout sediments were higher than the geochemical background reference condition by a factor of two to three, except for sediment sampled near the Umoum drain, where metal concentrations were close to the geochemical background reference condition. The PLI ranged from moderately to heavily polluted classes. The I-geo ranged from uncontaminated to moderately contaminated classes, where the RI indicates a low hazard. The comparison of Lake Mariout with other lakes indicates that all heavy metal concentrations except for Cd in Lake Mariout were higher than the average concentrations in Edku Lake. However, the average concentrations of Cd and Ni in Burullus Lake were higher than those found in the current study. For Manzala Lake, the Cd, Cu, and Pb concentrations were higher than the measured concentrations in Lake Mariout. The environmental hazard assessments of heavy metal concentrations in the Lake Mariout sediment determined the prevalence of possible anthropogenic pollution sources near the East and West Wastewater Treatment Plants and the El-Max pumping station.

International audience; Surface runoff is the hydrological process at the origin of phenomena such as soil erosion, floods out of rivers, mudflows, debris flows and can generate major damage. This paper presents a method to create maps of surface runoff susceptibility. The method, called IRIP (Indicator of Intense Pluvial Runoff, French acronym), uses a combination of landscape factors to create three maps representing the susceptibility (1) to generate, (2) to transfer, and (3) to accumulate surface runoff. The method input data are the topography, the land use and the soil type. The method aims to be simple to implement and robust for any type of study area, with no requirement for calibration or specific input format. In a second part, the paper focuses on the evaluation of the surface runoff susceptibility maps. The method is applied in the Lézarde catchment (210 km², northern France) and the susceptibility maps are evaluated by comparison with two risk regulatory zonings of surface runoff and soil erosion, and two databases of surface runoff impacts on roads and railways. Comparison tests are performed using a standard verification method for dichotomous forecasting along with five verification indicators: accuracy, bias, success ratio, probability of detection, and false alarm ratio. The evaluation shows that the susceptibility map of surface runoff accumulation is able to identify the concentrated surface runoff flows and that the susceptibility map of transfer is able to identify areas that are susceptible to soil erosion. Concerning the ability of the IRIP method to detect sections of the transportation network susceptible to be impacted by surface runoff, the evaluation tests show promising probabilities of detection (73-90%) but also high false alarm ratios (77-92%). However, a qualitative analysis of the local configuration of the infrastructure shows that taking into account the transportation network vulnerability can explain numerous false alarms. This paper shows that the IRIP method can be a valuable tool to facilitate field analysis and perform surface runoff zonings and opens interesting prospects for the use of the IRIP method in a context of risk management.

International audience; In urbanized areas, small streams can be greatly damaged by urban inflows and combined sewer overflows. These polluted inputs can be several times higher than the natural stream flow over short time periods. Sound knowledge of the spatial distribution of the discharged pollutants in sediments is therefore crucial for designing monitoring strategies and suitable remediation operations. This field study combines geomorphic characterization, hydraulic conductivity measurement and pollutant assays in sediments of a small suburban river. The study site was divided up into geomorphic units: riffles, pools and runs. The last two were grouped into one class named "pool-runs" owing to their closely similar open channel flow hydraulics. Benthic and hyporheic sediments were sampled at 2 m intervals. Conventional particulate pollutants (Cr, Pb, N-org, P-tot& C-org) were assayed in samples. The main result was: pollutants were not randomly distributed in the stream sediments, but their location showed clear concentration differences by geomorphic units, with preferential accumulation in the hyporheic zones of riffle units and a lesser one in the hyporheic zones of pools. A decrease in hydraulic conductivity was significantly correlated with an increase in pollutant concentration. This occurred mainly at the transition between riffles and pool units. The down-welling water fluxes in the sediment calculated using Darcy's formula reflect this slowdown. Our findings highlight the need to take into account the geomorphological and hydrological functioning of a stream to accurately locate the biogeochemical hotspots to be treated and thereby develop more relevant monitoring and remediation methodologies.

Surface runoff is one of the hydrological processes involved in floods, pollution transfer, soil erosion and mudslide. Many models allow the simulation and the mapping of surface runoff and erosion hazards. Field observations of this hydrological process are not common although they are crucial to evaluate surface runoff models and to investigate or assess different kinds of hazards linked to this process. In this study, a simple field monitoring network is implemented to assess the relevance of a surface runoff susceptibility mapping method. The network is based on spatially distributed observations (nine different locations in the catchment) of soil water content and rainfall events. These data are analyzed to determine if surface runoff occurs. Two surface runoff mechanisms are considered: surface runoff by saturation of the soil surface horizon and surface runoff by infiltration excess (also called hortonian runoff). The monitoring strategy includes continuous records of soil surface water content and rainfall with a 5 min time step. Soil infiltration capacity time series are calculated using field soil water content and in situ measurements of soil hydraulic conductivity. Comparison of soil infiltration capacity and rainfall intensity time series allows detecting the occurrence of surface runoff by infiltration-excess. Comparison of surface soil water content with saturated water content values allows detecting the occurrence of surface runoff by saturation of the soil surface horizon. Automatic records were complemented with direct field observations of surface runoff in the experimental catchment after each significant rainfall event. The presented observation method allows the identification of fast and short-lived surface runoff processes at a small spatial and temporal resolution in natural conditions. The results also highlight the relationship between surface runoff and factors usually integrated in surface runoff mapping such as topography, rainfall parameters, soil or land cover. This study opens interesting prospects for the use of spatially distributed measurement for surface runoff detection, spatially distributed hydrological models implementation and validation at a reasonable cost. (C) 2015 Elsevier B.V. All rights reserved.

International audience; This editorial provides a summary of scientific advances and new research avenues presented at the 2017 EcoHydrology conference held in Lyon (France) at the end of 2015.; Cet édito propose une synthèse des avancées scientifiques et des nouvelles voies de recherche présentées à la conférence EcoHydrologie 2017, qui s'est tenue à Lyon ( France) à la fin 2015.

Our aim was to provide guidelines for restoring and enhancing the self-purification capacity of Mediterranean urban creeks (no summer flow), in particular their resilience to pollution induced by discharges of combined sewer overflows (CSO).

Resume Les inondations par ruissellement sont peu prises en compte dans la gestion des territoires, et en particulier par la nouvelle competence GEMAPI. Or, le ruissellement intense peut contribuer de maniere significative a des inondations en versant et a la hausse des debits d’eau lors des episodes d’inondation et au transfert des polluants stockes dans les sols des versants. Dans cet article, l'auteur propose d'evaluer le potentiel d'interception du ruissellement par les zones humides de tete de bassin versant (TBV), qu'elles soient fonctionnelles ou potentielles.

International audience; Railways are critical infrastructures for the transportation of people and goods and network failures must be controlled in order to maintain safety and to limit economic losses. The railway network is exposed to natural hazards and particularly to intense pluvial runoff. Due to the complexity of the phenomenon, management of risks induced by pluvial runoff raises technical and scientific issues. An innovative method for runoff susceptibility mapping, called IRIP for "Indicator of Intense Pluvial Runoff", has been created and adapted to the railway context. The objective of this paper is to evaluate the relevance of the mapping method and to provide application advice. The mapping method is evaluated by comparison with the results of a hydraulic diagnosis, on a 20 km railway line, using quantitative and qualitative comparisons. On the basis of contingency tables, probabilities of detection (POD, railway sections exposed and detected by IRIP) and false alarm ratios (FAR, railway sections detected by IRIP whereas they are not exposed) are computed. POD range from 94 to 100% and FAR range from 20 to 26%. Then spatial information provided by the maps is compared with field observations and recommendations. It is shown that the mapping method can bring substantial contribution to risk identification and that the IRIP method can allow pushing forward the current risk reduction methods. Thus, the surface runoff maps open up new opportunities to manage surface runoff, such as targeting mitigation actions at the origin of the hazard in partnership with the other territory stakeholders.

International audience; Rivers are often challenged by fecal contaminations. The barrier effect of sediments against fecal bacteria was investigated through the use of a microbial source tracking (MST) toolbox, and by Next Generation Sequencing (NGS) of V5-V6 16S rRNA gene (rrs) sequences. Non-metric multi-dimensional scaling analysis of V5-V6 16S rRNA gene sequences differentiated bacteriomes according to their compartment of origin i.e., surface water against benthic and hyporheic sediments. Classification of these reads showed the most prevalent operating taxonomic units (OTU) to be allocated to Flavobacterium and Aquabacterium. Relative numbers of Gaiella, Haliangium, and Thermoleophilum OTU matched the observed differentiation of bacteriomes according to river compartments. OTU patterns were found impacted by combined sewer overflows (CSO) through an observed increase in diversity from the sewer to the hyporheic sediments. These changes appeared driven by direct transfers of bacterial contaminants from wastewaters but also by organic inputs favoring previously undetectable bacterial groups among sediments. These NGS datasets appeared more sensitive at tracking community changes than MST markers. The human-specific MST marker HF183 was strictly detected among CSO-impacted surface waters and not river bed sediments. The ruminant-specific DNA marker was more broadly distributed but intense bovine pollution was required to detect transfers from surface water to benthic and hyporheic sediments. Some OTU showed distribution patterns in line with these MST datasets such as those allocated to the Aeromonas, Acinetobacter, and Pseudomonas. Fecal indicators (Escherichia coli and total thermotolerant coliforms) were detected all over the river course but their concentrations were not correlated with MST ones. Overall, MST and NGS datasets suggested a poor colonization of river sediments by bovine and sewer bacterial contaminants. No environmental outbreak of these bacterial contaminants was detected.

National audience; Choisir, affiner et évaluer une stratégie de gestion des inondations implique d’avoir défini explicitement des objectifs. Cela suppose aussi que les effets puissent être évalués a priori, si possible de manière quantitative, pour comparer et affiner des solutions. Cette communication donne quelques clefs de compréhension sur l’efficacité d’ouvrages de gestion des inondations, au sens hydrologique (réduction des surfaces inondées). Nous rappelons quelques recommandations relatives à la définition de l’ « efficacité » d’actions de gestion de l’aléa inondation, qu’elles relèvent de l’ingénierie classique ou écologique, et formulons des mises en garde contre des mauvaises interprétations de résultats (généralisation abusive, affirmations tronquée…). Enfin, nous évoquons les problèmes méthodologiques rendant complexe l’évaluation de l’effet de plusieurs petits ouvrages, puis de modifications du lit majeur. Ces quelques éléments de réflexion seront repris de manière plus détaillée dans le chapitre « Crues et inondations » de l’ouvrage ASTEE « Ingénierie écologique appliquée aux milieux aquatiques : pour qui ? pour quels bénéfices ? » à paraître en 2017.

FloodRisk, 3rd European Conference on Flood Risk Management, Lyon, FRA, 17-/10/2016 - 21/10/2016; International audience; Indicator of Intense Pluvial Runoff (French Acronym) - is a method to map the susceptibility of territories to surface runoff generation, transfer and accumulation. The method is based on a geomatic combination of landscape factors extracted from topography, land use and soil type. This study is part of the method evaluation process and suggests using information from post-event surveys of surface runoff events to evaluate the agreement between the IRIP maps and the field observations. Surface runoff susceptibility maps are produced at five meters resolution for three impact areas on railways with different infrastructure and environment configurations. First, information categories are extracted from the post-event surveys, and then the IRIP maps are analyzed to see if and how the information categories are retrieved. This study shows that the IRIP maps fit the impact description. The areas susceptible to surface runoff transfer fit the gullies locations and the areas susceptible to surface runoff accumulation fit the sediment deposit traces. The comparison also highlights that the IRIP maps can give further information on the event spatial dynamics. Given the simplicity and the robustness of the mapping method, IRIP can be a tool to perform surface runoff post-event surveys and to improve the surface runoff hazard assessment.

La conservation de la biodiversité est actuellement un enjeu majeur qui s’insère progressivement dans les politiques publiques d’aménagement d’un territoire de gestion administrative, ceci dans le but de maitriser l’impact de l’activité humaine sur son environnement naturel. Les infrastructures de transport terrestre créent des ruptures sur les écosystèmes et paysages. Le projet exploratoire RHIZU (Ruissellement Intense et Zones HUmides) a pour objet d’évaluer les conditions de coexistence entre infrastructures linéaires de transport et écosystèmes de type zones humides. L’hypothèse majeure qui est traitée dans cet article repose sur une gestion repensée des eaux de ruissellement au voisinage d’une infrastructure linéaire de transport terrestre. Une reconsidération de cette gestion par le concepteur puis l’exploitant voire par d’autres acteurs des territoires ciblés permettrait de développer ou restaurer des zones humides. Outre l’impact positif induit sur la biodiversité, le maillage paysager de ces habitats souvent dégradés et en régression serait renforcé en particulier dans les paysages à forte composante anthropique traversés par les infrastructures de transport terrestre en concevant ces dernières comme parties intégrées du maillage des zones humides. L’article rappelle les conditions d’existence, les types et rôles des zones humides. Il présente ensuite les facteurs de réussite de cette approche qui doit (1) tenir compte des modalités de gestion des eaux de ruissellement par le concepteur et l’exploitant et (2) bénéficier de méthodologies spatialisées opérationnelles permettant de détecter et évaluer des contextes favorables au sein des paysages sur les plans hydrologique et écologique. Une illustration de ces aspects est présentée sur un tronçon de la ligne LGV Méditerranée traité à l’aide d’un outil géomatique en cours de développement à l’IRSTEA et à la SNCF. Les métriques déployées doivent être approfondies pour parvenir à un outil d’aide à la décision faisant face à la diversité des situations de gestion du ruissellement sur les axes de transport. Néanmoins, cette première étude de faisabilité présente de réelles perspectives de s’appuyer localement sur des services écologiques rendus par les zones humides. À partir de cette nouvelle approche qui combine les enjeux de sécurité hydraulique et les enjeux zones humides à partir de nouveaux cribles comme l’analyse du ruissellement proposée ici, la production des linéaires de transport pourrait être satisfaite tout en contribuant à plus large échelle aux continuités écologiques. The conservation of biodiversity is currently a major problem which is gradually inserted into the development of public policy of administrative territory, with the aim of controlling the impact of human activity on the natural environment. Land transport infrastructure creates disruptions to ecosystems and landscapes. The exploratory project RIZHU (intense runoff and wetlands), is to assess the conditions of coexistence of land transport infrastructure with that of the wetlands. The hypothesis is that a redesigned management of runoff water in the vicinity of the linear land transport infrastructure may help to restore a wetland mesh which conditions their interconnection. The feasibility of this hypothesis is tested and discussed in this article in order to bring the designer and the developer to consider this opportunity. The article recalls the conditions of existence, types and roles of wetlands. It then introduces the approach of the success factors which are: (1) convince the designer and the operator of the appropriateness of a redesigned management of storm water and (2) to benefit from operational space methods for the detection and evaluation of favorable hydrological and ecological contexts within landscapes. An illustration of these aspects is presented in a section of the TGV Méditerranée processed using a GIS tool under development at Irstea and SNCF. The tested indicators still need to be improved to achieve a tool able to assist the decision facing the variety of storm water management situations on the land transport system. Nevertheless, this initial feasibility study presents real opportunities as it combines the issues of water security and continuity of the ecological corridor of wetlands.

International audience; To contribute to solving the dilemma of the conflicting needs of water managers and ecologists, we are proposing an approach for the use and development of existing biomonitoring tools. For running waters, a harmonization system allows to use a set of various biotic indices. Functional traits are regarded as a basis for assessing ecological functioning. They take into account the dynamics of water exchanges between surface water and groundwater. In lakes, the oligochaete index IOBL describes the metabolic potential of deep-water sediments. Coupled with percent pollution-sensitive oligochaete species, it allows to defi ne a typology of lake sediments. The presented tools are integrated through a conceptual framework, including research management and technology transfer procedures.

International audience; When involved late in flood mitigation projects, biologists can suggest only minor changes. Conception should be multidisciplinary from the start. Riverscapes appear an excellent support to exchange information and share common conceptual views. Biologists thus summarize their expertise and local analyses, including a description of the potential biodiversity and processes. We built a riverscape typology for Polish mountain rivers and used it as a support to discuss compromises and adaptations for dry dams and river training. Translating the technical solutions into shift of types guide the choices. Serving a purpose, the typology is case-dependant and could be revised during a project. Riverscapes could also potentially be useful in multidisciplinary research.

Le site Othu de Grezieu-la-Varenne (Rhone) a ete concu pour suivre l’impact d’un deversoir d’orage sur un ruisseau periurbain. Il est compose de trois stations instrumentees (en amont, en aval et sur un deversoir d’orage), equipees d’un pluviometre, de debitmetres (riviere, deversoir et reseaux d’assainissement), de capteurs (conductivite, pH, turbidite) et d’echantillonneurs. Apres une presentation du site et de sa localisation, nous decrivons l’instrumentation et notre demarche entreprise pour maitriser la qualite des donnees de terrain. Des procedures et fiches de terrain formalisent cette demarche qualite. Des exemples sont donnes et les limites du systeme actuel sont precisees en fin de l’article.

International audience; Combined Sewer Overflows (CSO) in small pen-urban streams and rivers are potentially toxic for their biocenosis. Improving the management of CSO discharges requires better knowledge of their dynamics and toxicity. In view to characterizing this toxicity, we sampled the different compartments (benthic and hyporheic zone) of a pen-urban stream located near the city of Lyon in France. The samples were taken at different distances from a CSO and at three period characteristic of different hydrological conditions. Their toxic effects were assessed by bioassays on the dissolved fraction (D. magna, V. fished and B. calyciflorus bioassays) and on the particle fraction (V. fished and H. incongruens bioassays). The results highlighted significant toxicity of the particulate fraction for the benthic and hyporheic samples, in particular downstream of the CSO, but with high spatio-temporal variability. This variability can first be attributed to the variability of CSO discharge sampling as a function of season and rainfall, and the dynamics of polluted particles (trapping of transported particles in infiltration zones, mobilization during floods). These parameters play a fundamental role in the distribution of pollutants according to the geomorphology of stream facies. Regarding dissolved pollutants, the chemical exchanges taking place at the "water-sediment" interface trigger the transfer of pollutants from one phase to another, after which the dispersion of these pollutants is governed by hydraulic flows. Finally, critical zones and periods are identified for the pen-urban river toxicity studied: benthic sediments under mean flow downstream: hyporheic sediments after a storm event downstream, close to the CSO. Recommendations are made on the basis of the knowledge obtained to optimize the management of these discharges.

The Jucar River Basin (Spain) harbours endemic aquatic species that are declining or going extinct at an alarming rate. After evaluating several possible stressors, flow modification is identified as the factor critically threatening one endemic cyprinid fish species Chondrostoma arrigonis. Physical habitat for this species is compared for river reaches with different flow modification histories to understand local extinctions across this species' historical range. Time-series of physical habitat, generated using PHABSIM, indicate a dramatic reduction in habitat area with flow modification. Our findings indicate that efforts to regulate and stabilize flows in the Jucar River Basin may cause the rapid extinction of the remaining populations. Copyright © 2007 John Wiley & Sons, Ltd.

International audience; Railways can modify flow paths and have an impact on runoff transfer within catchments. The French railway network includes various structures designed to collect and safely route water flows from upstream of the railway infrastructures towards an outlet. Runoff is a risk for railway infrastructures and is source of many incidents impacting both the civil infrastructure but also all the secondary services required for the railway functioning. These risks occur due to dysfunction of hydraulic structures, which may have been inappropriately designed or for which the environment may have evolved due to land cover change. Erosion of the railway basement, flooding and mudslides are the most frequent consequences of a poorly functioning drainage network. Their impacts on rail operations can be: speed limitations, interruption of the traffic, and even derailments in the worst cases. Irstea developed a methodology for the runoff risk mapping called IRIP (Flooding by Intense Pluvial Runoff) which provides a vision at the catchment scale, of the surface runoff and its potential dynamics from the production areas down to the downstream areas of accumulation. Based on this methodology, the engineering department at SNCF, in collaboration with Irstea, is developing an operational tool, which aims to improve the diagnosis and the management of runoff risk on the French railway network. An assessment of the method is presented, based on a data base collecting historical incidents relating to runoff.; Les voies ferrées sont des éléments structurant des bassins versants qui modifient les chemins de l'eau. Le réseau ferré national est équipé de dispositifs hydrauliques de collecte et d'acheminement des écoulements depuis l'amontde l'infrastructure jusqu'à un exutoire. Le ruissellement est à l'origine de nombreux incidents sur les infrastructures ferroviaires; autant sur les ouvrages linéaires que sur les aménagements connexes nécessaires à l'exploitation ferroviaire. Ces incidents peuvent trouver leur origine dans l'absence ou le mauvais fonctionnement des dispositifs hydrauliques dont le bassin versant a pu être mal apprécié ou a évolué en raison de modifications de l'occupation des sols. L'érosion de l'assise des voies de chemin de fer, leur submersion par les eaux ou la création d'obstacles par les coulées de boues sont les principaux dysfonctionnements pouvant avoir comme impacts des ralentissements, des interruptions des circulations ferroviaires, voire dans des cas plus rares, des déraillements. Irstea a mis au point une méthode de cartographie du ruissellement (IRIP- Inondation par Ruissellement Intense Pluvial) qui permet d'avoir une vision globale du ruissellement et de sa dynamique potentielle depuis les zones sources jusqu'à l'aval, au niveau des zones d'accumulation. Sur la base de cette méthodologie et en collaboration avec Irstea, la direction de l'Ingénierie de la SNCF développe un logiciel dans l'optique de mieux répondre aux besoins de diagnostic et de gestion des risques liés au ruissellement sur le réseau ferré national. Des travaux de validation de la méthode et son intégration dans le contexte ferroviaire sont en cours avec des données d'incidents liés au ruissellement, recensés par le gestionnaire d'infrastructure.

Hydrological and morphological characteristics of streams and rivers influence a wide array of ecological processes and patterns ; they define the aquatic habitat template. Interdisciplinary approaches are required to study physical-biological interactions ; increased collaboration between ecologists and experts in morphology, hydrology and hydraulic engineering is particularly desirable. In this paper, we present our experience of aquatic habitat modelling. In particular, we indicate how statistical instead of mechanistic hydraulic descriptions simplify the input field data required to estimate instream habitat suitability. We have also conducted significant biological validations of habitat model predictions expressed at the fish community level. A better quantification of instream habitat suitability is meaningful when associated with the understanding of the large-scale processes governing stream equilibrium. In this context, the knowledge of bankfull discharge, at which the self-maintenance of the river morphology occurs, is of particular importance. The identification of key hydraulic variables and periods for population dynamics and vital processes are challenging for the near future. A greater understanding of physical-biological interactions will not only yield deeper insights into the ecological organization of streams and rivers, it will also improve our ability to predict how flow alterations caused by various human activities affect these vital ecosystems. Our progresses depend mainly on of our ability to produce biologically validated models.

International audience; Hydrological and biotic forces constrain brown trout (Salmo trutta) population dynamics, but tests of their role across numerous streams are uncommon. In 30 French stream reaches, using 5-8 samples (1 per year) each, we investigated whether the year-to-year seasonal hydrology influenced annual trout densities within reaches, and whether the relationships were shared by all reaches. We also searched for intraspecific interactions between and within cohorts. Trout data were age class (0+, 1+, and adults) densities. For each year, hydrology was described using 13 variables, each computed for a reproduction, emergence, and growth period related to the biological cycle of trout. We used anal-yses of covariance (ANCOVA) to test how trout densities at year n - 1 and hydrology at year n influenced trout densi-ties at year n. High flows during emergence significantly reduced the 0+ densities, consistently across the 30 reaches. Then, 1+ and adult densities were linked, respectively, to 0+ and 1+ densities from the previous year. Analyses also re-vealed density-dependent survival mechanisms for the 0+ cohort, suggesting intracohort competition. Therefore, hydrol-ogy constrains trout dynamics only during the critical emergence period, after which intracohort interactions regulate the 0+ density. Such mechanisms, validated across 30 environmentally different reaches, seem to be fundamental to trout population dynamics.; Les forces hydrologiques et biotiques imposent des contraintes à la dynamique de population des Truites brunes; cependant, on a rarement évalué leur rôle simultanément dans un grand nombre de cours d'eau. À partir de 5-8 échantillons (1 par année) récoltés dans chacun de 30 tronçons de cours d'eau français, nous avons examiné si les variations de l'hydrologie d'année en année influencent la densité annuelle des truites dans un tronçon et si les relations obtenues s'appliquent à tous les tronçons. Nous avons aussi cherché à trouver des interactions intra-spécifiques au sein des cohortes et d'une cohorte à l'autre. Nos données consistaient en des densités des différentes classes d'âges (0+, 1+ et adulte). Nous avons mesuré, chaque année, 13 variables hydrologiques, regroupées selon les périodes d'émergence, de reproduction et de croissance du cycle biologique des truites. Des analyses de covariance (ANCOVA) nous ont permis de vérifier comment la densité des truites de l'année n -1 et l'hydrologie de l'année n pouvaient influencer la densité des truites de l'année n. Des débits élevés durant l'émergence réduisaient significativement les densités des truites d'âge 0+, de façon comparable dans tous les 30 tronçons. De plus, les densités des truites d'âges 1+ et adulte étaient reliées respectivement aux densités des poissons d'âges 0+ et 1+ de l'année précédente. Les analyses ont aussi mis en évidence des mécanismes de survie reliés à la densité chez la cohorte d'âge 0+, ce qui semble indiquer l'existence de compétition au sein de la cohorte. L'hydrologie impose donc des contraintes à la dynamique de population des truites seulement durant la période critique de l'émergence, après quoi ce sont les interactions au sein de la cohorte qui contrôlent la densité des poissons d'âge 0+. De tels mécanismes, observés dans 30 tronçons qui diffèrent par leurs conditions environnementales, semblent être des caractéristiques fondamentales de la dynamique de population des truites.

International audience; The increasing global rate of urbanisation and concurrent global climate changes create new challenges and new opportunities for managing cities, water resources and related quality of life. In most strategies, however, water ecosystems, which are the fundamental component of the integrated urban water resources management (IUWRM), are regarded as objects of protection or rehabilitation; not, as postulated by ecohydrology, as management tools. This paper addresses the possibilities of: (i) the functional incorporation of aquatic ecosystems into the IUWRM; (ii) optimising their functioning by local ecohydrological approach; and (iii) integration of ecosystem functions on a city scale to build system solutions for more resilient cities. Two case studies of the UNESCO MAB/IHP demonstration network representing different urban development patterns are given. The City of Łodz´ (Poland) uses water-resource based urban retrofitting for improving the quality of life and attracting inhabitants, departing from the analysis of longitudinal dynamics of nutrient transition in the river–reservoirs system, towards proposing an alternative concept of spatial city development. The city of Lyon (France), with intensive periurban development and population growth, provides a hierarchy of stream reaches to cope with combined sewer overflows to help municipalities to better position future urban runoff outlets. This article envisions also the future management of urban waste and storm waters using urban rivers, assuming resilient cities will depend on the integrity of environmental, technical and spatial planning decisions. The virtues of ecohydrology are discussed in this respect.

[Departement_IRSTEA]Eaux [TR1_IRSTEA]ARCEAU [TR2_IRSTEA]BELCA; International audience; Urbanization subjects streams to increased nitrogen loads. Therefore studying nitrogen forms at the interface between urban stream and groundwater is important for water resource management. In this study we report results on water δ(18)O and nitrogen forms in subsurface waters of a stream (Yzeron, France). The sites studied were located upstream and downstream of combined sewer overflows (CSO) in a rural area and a periurban area, respectively. Water δ(18)O allowed us to follow the mixing of subsurface water with surface water. Dissolved organic nitrogen and organic carbon of fine sediment increased by 20-30% between rural and periurban subsurface waters in the cold season, under high flow. The highest nitrate levels were observed in rural subsurface waters in the cold season. The lowest nitrate levels were found in periurban subsurface waters in the warm season, under low flow. They corresponded to slow exchange of subsurface waters with channel water. Thus reduced exchange between surface and subsurface waters and organic-matter-rich input seemed to favor nitrate reduction in the downstream, periurban, subsurface waters impacted by CSO.

Irstea carried out in 2012 a bibliographical analysis on flood hazard assessment for the French Ministry in charge of the implementation of the Flood Directive. This work relied on a large but heterogeneous mine of information : published regional or national maps, technical notes, internet pages aimed at the general public, and research papers on various relevant fields (hydraulic models, calibration procedures, estimation of flood quantiles...). This document highlights selected conclusions of this work, and the resulting suggestions for flood hazard assessment and mapping. It is a summarized complement to the slides. The aim can not be to present all the methods in details, but to give an overview of the approaches, and to focus on some issues.

[Departement_IRSTEA]Eaux [TR1_IRSTEA]ARCEAU; In this paper we explore several indicators to evidence the impact of land use change, and particularly of urbanization/artificialization on discharge series of periurban catchments. A first set of indicators is derived from the literature and describes the monthly and annual hydrological regime, low flows and high flows, and flow components. Statistical tests are also applied to assess the existence of trends/ruptures on the longest time series. In addition, new indicators, especially built to show the impact of Sewer Overflow Devices (SODs) and infiltration into sewer networks are proposed. The method is applied to the Yzeron (150 km2) catchment, located close to Lyon city (France) where various discharge gauges with a variable time step are available on sub-catchments ranging from a few to 130 km2 (some of them nested), with a large variety of land uses (forest, agricultural land, artificialized areas). In addition, discharge is also measured in a SOD and a combined sewer network so that the relevance of the new proposed indicators can be assessed. In the largest sub-catchments, the results show a decrease of specific discharge from upstream to downstream corresponding to an increase of artificialized areas, except for high flows. When a SOD is present, the specific discharge is increased for frequencies larger than 50%, and the frequency of zero daily discharge is decreased. Waste water can be the only source of water in autumn month in a 4.1 km2 sub-catchment. Base flow is also decreased for the most urbanized catchments. Our results confirm the impact of SODs on the modification of the flood regime, with an increase of frequent floods, but a marginal impact on the largest floods, mainly governed by saturation of the rural parts of the catchments. The decomposition of the sewer discharge shows that, on an annual basis, infiltration in the sewer network accounts for 30% of the total discharge and runoff due to rainwater to about 40% (the remaining being composed of the waste water discharge). It can explain the decrease of base flow. Our analysis shows that, for periurban catchments, a long term monitoring of nested sub-catchments and infrastructures (SODs, sewer networks) with a small time step, is very valuable and provides data allowing a quantitative assessment of the impact of urbanization on the whole hydrological regime.

[Departement_IRSTEA]Eaux [TR1_IRSTEA]BELCA [TR2_IRSTEA]QUASARE [TR2_IRSTEA]ARCEAU; International audience; Fifty years after the hyporheic zone was first defined (Orghidan, 1959), there are still gaps in the knowledge regarding the role of biodiversity in hyporheic processes. First, some methodological questions remained unanswered regarding the interactions between biodiversity and physical processes, both for the study of habitat characteristics and interactions at different scales. Furthermore, many questions remain to be addressed to help inform our understanding of invertebrate community dynamics, especially regarding the trophic niches of organisms, the functional groups present within sediment, and their temporal changes. Understanding microbial community dynamics would require investigations about their relationship with the physical characteristics of the sediment, their diversity, their relationship with metabolic pathways, their inter- actions with invertebrates, and their response to environmental stress. Another fundamental research question is that of the importance of the hyporheic zone in the global metabolism of the river, which must be explored in relation to organic matter recycling, the effects of disturbances, and the degradation of contaminants. Finally, the application of this knowledge requires the development of methods for the estimation of hydro- logical exchanges, especially for the management of sediment clogging, the optimization of self-purification, and the integration of climate change in environmental policies. The development of descriptors of hyporheic zone health and of new metrology is also crucial to include specific targets in water policies for the long-term management of the system and a clear evaluation of restoration strategies.

International audience

International audience; The study highlights the relevance of integrating hydro-geomorphological typologies in pluri-disciplinary ecological researches on ecosystem functioning, in two contrasted hydrosystems: the Rhine alluvial plain and the Yzeron basin. Two hydro-geomorphological typologies of reference status in rivers, elaborated from the same conceptual scheme, are compared with two bio-typologies of ecosystem functioning characterization, one based on communities of aquatic macrophytes (Rhine plain) and the second on oligochaete assemblages (Yzeron basin). The two bio-typologies mainly reflect water exchanges between surface water and groundwater. In the Rhine plain, morphodynamics of the D3 geomorpho-type modify the tendency of increasing in the trophic level from upstream to downstream areas, this increasing being only verified for the D4 geomorpho-type. Indeed, morphodynamics of the D3 geomorpho-type prevents channel clogging and activates the limnocrene groundwater springs, inducing water oligotrophication and increase of biodiversity. In the Yzeron basin, which is impacted by polluted urban water runoffs, the B3 and A1 geomorpho-types present the highest values of ecological potentials (EPs) due to greater slopes and active surface water/groundwater exchanges. Results suggest that some biological characteristics and ecological functions could be spatialized on larger spatial scales through appropriate geomorphic river typologies.

International audience; Managing flood risks has been an integral part of the human survival efforts since historic times. During the last decades, global changes brought on by population growth, climate change, urbanization, migration and land conversion, are altering the Earth water cycle and have increased flood risks. None of these factors alone would be sufficient to explain the observed increase in the flood risk. This paper presents a study that aims to evaluate the causes for flood risk increase and to assess the effectiveness of two techniques for flood risk mitigation. One in at the stream course scale and the other at the home scale. The research was conducted in the catchment of the Yzeron River in western Lyon. The catchment area is 130 km2 and characterized by a rapidly expanding, peri-urban development. To evaluate the specific impact of urban development on the flood regimes we used a diachronic approach, with hydrologic and land-use data from two periods, the seventies and the nineties. A semi-distributed hydrological model was fitted (Radojevic et al., submitted) to and validated with a set of last decade floods and corresponding rainfall data. Keeping the same rainfall data, it was then ran with the seventies land use data. Calculated flood regimes characteristics from observations and simulations were significantly different opening the assumption that the rainfall regime would have also changed between these two decades. Model simulation was also extrapolated to expected land use on 2050. This last simulation revealed a five folds increase of the ten years flood peak. Considering that both land use change and rainfall regimes would significantly modify a flood regime, we compared the efficiency of technical solutions to mitigate land use and rainfall influence on a flood regimes. Three situations were tested based on one dry reservoir, two dry reservoirs and home scale temporary rainfall retention facility. It results that dry reservoir number and location are strategic considerations to avoid concomitancy of floods at a main confluence. The home scale rain water temporary retention would be a very efficient strategy but test including the effect of their distribution at a basin scale is required.

PurposeGlobal change results both from climatic and land practice evolution in response to anthropogenic needs for development and human safety. The purpose of this paper is to describe a method to assess the respective effect of both sources of change on the flood regimes.Design/methodology/approachThe research takes place in the Western periurban part of Lyon (France), which is characterized by a rapidly expanding, scattered urban development since the 1970s. An increase in frequency of large floods is reported. At the same time, a long daily rainfall time series exhibits sensitive changes in rainfall durations and intensities. Independent analysis of global change components is performed using observed rainfall and land‐use data from two disconnected decades. A marked difference in natural climatic regime variability between decades is used as a surrogate to study effect of climate change.FindingsAnthropogenic activity at the observed rate of land use change, in particular urban change, mainly influences the frequent flood distribution. The observed large flood increase results both of longer rainfall events and more heavy daily rainfall. From simulations, a 43 percent urban cover as planned from 2025 projection would have a very sensitive effect also on larger floods, giving the hand to a more anthropogenic‐based flood control.Originality/valueDespite an expected increase in rainfall and flow variability regimes as a result of climate change and a projected growing of the world urban population, there is a lack of methodology to address combination of both processes on the flood regimes. A method is proposed to judge on the respective importance and interplay of these processes.

International audience; Two approaches are proposed for developing adapted metrics, proposing realistic and sustainable ecologic objectives, and suggesting a management strategy for stream rehabilitation. The first approach implemented a harmonization system of French standardized biotic indices. The second one was based on the development of functional traits (FTrs), which were defined by oligochaete assemblages inhabiting coarse surface sediments and the hyporheic system. The harmonization system allowed to define a weighted general ecological quality. The FTrs characterized an ecological potential (EP) resulting from interactions between physical factors (dynamics of hydrologic exchanges between surface water and groundwater) and chemical factors. An example of using both approaches at the same urbanized site is presented and serves for planning of rehabilitation activities. The benefits, drawbacks and progress of both approaches are discussed.; Utilisation combinée des bio-indicateurs standardisés et d'un bio-indicateur fonctionnel du substrat pour l'évaluation du bon potentiel écologique d'un cours d'eau périurbain.

International audience; The objective of this chapter is to explore how flow variability affects SGW interactions and thereby functions of the fluvial ecosystem along the hyporheic corridor' from head waters to river mouth (Stanford and Ward, 1993). The chapter begins by defining fluvial ecosystems in terms of two aspects of their structure and functionbiogeochemical processes and biotic structurethat are expected to respond to flow variability and SGW exchange. Data from a field experiment serve to illustrate dimensions and variability of SGW exchange at one location in space and time. The range of space and time scales over which SGW interactions occur is then considered in a case study. This analysis takes the form of a cross-continental comparison of river basins in humid (Europe) and arid/semi-arid (southwestern USA) settings, generalizing the dynamics of SGW exchange to contrasting environments as recommended by Poff et al. (2006). Finally, the relationship between patterns of flow variability and biotic processes is explored, considering important biological and anthropogenic influences on SGW exchange at different spatio-temporal scales within the fluvial ecosystems.