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Agir en amont sur le ruissellement en plantant ou en restaurant des haies est présenté dans certains documents comme une excellente solution pour atténuer les inondations. Pour d’autres, ces effets sont plus mesurés. Pour comprendre ces désaccords, les auteurs de cet article ont analysé la littérature scientifique sur l’effet des actions en versant, et en particulier des haies, sur le ruissellement. Ils attirent notamment l’attention sur la manière dont les résultats scientifiques sont présentés et cités, car elle peut être à l’origine de mauvaises interprétations.

Les inondations par ruissellement sont peu prises en compte dans la gestion des territoires, et en particulier par la nouvelle compétence GEMAPI. Or, le ruissellement intense peut contribuer de manière significative à des inondations en versant et à la hausse des débits d’eau lors des épisodes d’inondation et au transfert des polluants stockés dans les sols des versants. Dans cet article, l'auteur propose d'évaluer le potentiel d'interception du ruissellement par les zones humides de tête de bassin versant (TBV), qu'elles soient fonctionnelles ou potentielles.

La compétence GEMAPI appelle aujourd’hui les collectivités territoriales à mettre en œuvre des solutions innovantes permettant d’accorder la prévention des inondations avec la gestion intégrée des milieux aquatiques. Comment les solutions fondées sur la nature, basée sur l’utilisation d’ouvrages de génie écologique et végétal, complémentaires à des ouvrages de génie civil, peuvent répondre aux enjeux croisés de prévention des inondations et de restauration des milieux, et comment évaluer leur plus-value écologique et sécuritaire dans ce contexte ? Ce article fait le point sur ces questions.

La gestion intégrée des inondations à l’échelle du bassin versant offre des perspectives intéressantes pour poser un diagnostic pertinent et trouver des solutions de gestion de l’aléa, notamment à l’amont des enjeux. Cet article s'intéresse ici aux différentes étapes de l'estimation de l'aléa inondation et nous présente les principes et méthodes de diagnostic d'efficacité probabiliste pour améliorer la gestion des inondations par des ouvrages de prévention dispersés sur le bassin versant.

Pluvial floods caused by extreme overland flow inland account for half of all flood damage claims each year along with fluvial floods. In order to increase confidence in pluvial flood susceptibility mapping, overland flow models need to be intensively evaluated using observations from past events. However, most remote-sensing-based flood detection techniques only focus on the identification of degradations and/or water pixels in the close vicinity of overflowing streams after heavy rainfall. Many occurrences of pluvial-flood-induced damages such as soil erosion, gullies, landslides and mudflows located further away from the stream are thus often unrevealed. To fill this gap, a transferable remote sensing fusion method called FuSVIPR, for Fusion of Sentinel-2 & Very high resolution Imagery for Pluvial Runoff, is developed to produce damage-detection maps. Based on very high spatial resolution optical imagery (from Pléiades satellites or airborne sensors) combined with 10 m change images from Sentinel-2 satellites, the Random Forest and U-net machine/deep learning techniques are separately trained and compared to locate pluvial flood footprints on the ground at 0.5 m spatial resolution following heavy weather events. In this work, three flash flood events in the Aude and Alpes-Maritimes departments in the South of France are investigated, covering over more than 160 km2 of rural and periurban areas between 2018 and 2020. Pluvial-flood-detection accuracies hover around 75% (with a minimum area detection ratio for annotated ground truths of 25%), and false-positive rates mostly below 2% are achieved on all three distinct events using a cross-site validation framework. FuSVIPR is then further evaluated on the latest devastating flash floods of April 2022 in the Durban area (South Africa), without additional training. Very good agreement with the impact maps produced in the context of the International Charter "Space and Major Disasters" are reached with similar performance figures. These results emphasize the high generalization capability of this method to locate pluvial floods at any time of the year and over diverse regions worldwide using a very high spatial resolution visible product and two Sentinel-2 images. The resulting impact maps have high potential for helping thorough evaluation and improvement of surface water inundation models and boosting extreme precipitation downscaling at a very high spatial resolution. [ABSTRACT FROM AUTHOR]

The IRIP method, or "indicator of intense pluvial runoff" in English, is a geomatics method that allows mapping the susceptibility of a 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) on runoff. These factors are summed up to provide susceptibility maps for 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, direct 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 pieces of 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, which 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 a comprehensive database of runoff-related impacts collected on an 80 km railway line in Normandy (north of France) and covering the whole 20th century. The results show that the evaluation method is robust, relevant and generic enough for evaluating a non-quantitative method of runoff hazard mapping using localized runoff-related proxy data. In addition, the good performance of the IRIP model in the case study confirms 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Water & Land Development is the property of Polish Academy of Sciences and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editors talks about the International Symposium on Ecohydrology, Biotechnology and Engineering: Towards Harmony and discuss the papers presented at the symposium, which was held in Łódz, Poland from September 17 to 19, 2013.

Copyright of Natures Sciences Sociétés is the property of EDP Sciences and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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. [ABSTRACT FROM AUTHOR]

The industrial symbiosis (IS) landscape is evolving rapidly. While previous studies have argued for the importance of municipalities participating in the governing of IS, research on the implications of different forms of municipal organization is still lacking. This paper aims to investigate how municipal administration and municipally-owned corporations, as two forms of organization, impact the governing of IS in the water and sewage sector. This is explored in relation to the Swedish municipality Simrishamn, which recently underwent changes in the form of organization. Results show that municipal administration contributes to a more inclusive process where many actors can influence and bring ideas and perspectives on how to develop an IS. The risk, however, is that other issues within the municipality are seen as more pressing and, therefore, get prioritized before IS. In corporate form, the development of IS becomes more business-like as the focus is kept on core business. Technology development is strengthened as skills and competencies are promoted through the expertise of the employees. Drawbacks include processes becoming less transparent and political goals, such as citizen welfare not receiving the same level of priority as within municipal administration. There is also a risk that fewer perspectives are included in the process of developing IS, which may inhibit innovation, even if the results also indicate that an increased business focus of the corporate form strengthens the innovation capacity. [ABSTRACT FROM AUTHOR]

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 (a) surface and subsurface flow (i.e., hyporheic flow) and (b) 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 coinjected 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, and (c) N‐uptake and microbial community 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 contributes 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 its 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. [ABSTRACT FROM AUTHOR]

For sustainable and integrated flood management, small actions in the hillslopes and non-structural measures appear interesting, either to diminish the need for large flood mitigation infrastructures (whether sewerage networks or hydraulic structures in the river – which may have severe impact on the river ecosystems), or as complementary to these structures. However, the effect on flood mitigation of land-use modification and small storage or runoff control facilities is still debated in scientific literature. The effect of various structures spread over the catchment is difficult to assess, and hazardous to generalize from one studied catchment to another, which explains why the debate is still open. This study contributes to identify context features that could also explain constrasting results. Focusing on a West-Mediterranean Northern and Southern countries literature, we compare first traditionnal and modern hillslope actions against runoff in both countries. Then, we search in the physical contexts differences that might explain why actions in the hillslopes are more studied in Europe than in Maghreb. But the priorities of national or regional policies also explain differences in the perception of efficiency: the interest of hillslope actions is different if the aim is to limit erosion and pollutant transfer and/or to mitigate large floods. Pollution and how ecological status is taken into account in flood mitigation project assessment are also crucial points.

IRIP – 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.