Using a multi-criteria analysis to identify rivers with hydromorphological restoration priority: Braided rivers in the south-eastern Subcarpathians (Romania)

A review of social-ecological system vulnerability in desertified regions: Assessment, simulation, and sustainable management

Desertified regions face considerable vulnerability due to the combined effects of climate change and human activities, which threaten regional ecological security and societal development. It is therefore necessary to assess, simulate, and manage the vulnerability of desertified regions from the perspective of the social-ecological system, to support desertification control and sustainable development. This study is a systematic review of the vulnerability of the social-ecological system in desertified regions (SESDR) based on a bibliometric analysis, and a summary of the research progresses in vulnerability assessment, simulation, and sustainable management is provided. It was found that SESDR vulnerability research started relatively late, but has developed rapidly in recent years, with an emphasis on the coupling between natural systems and human activities, and multi-scale interactions and dynamics. Using various indicators at different scales, SESDR vulnerability could be assessed in terms of exposure, sensitivity, and adaptability. Modeling the complex interactions among natural and human factors across multiple scales is essential to simulate the vulnerability dynamics of the SESDR. The sustainable management of SESDR vulnerability focuses on rational spatial planning to achieve the maximum benefits, with the right measures in the right places. Four priority research directions were proposed to develop a better understanding of the mechanisms of vulnerability and smart restoration of desertified land. The findings of this study will enable researchers, land managers, and policymakers to develop a more comprehensive understanding of SESDR vulnerability, thereby enabling them to better address the challenges posed by complex resource and environmental issues.

Improving river hydromorphological assessment through better integration of riparian vegetation: Scientific evidence and guidelines

River hydromorphology has long been subjected to huge anthropogenic pressures with severe negative impacts on related ecosystems' functioning and water quality. Therefore, improving river hydromorphological conditions represents a priority task in sustainable river management and requires proper assessment tools. It is well known that riparian vegetation plays a crucial role in sustaining river hydromorphological conditions. However, it has been nearly neglected in most hydromorphological assessment protocols, including the European Water Framework Directive (WFD). This paper reviews and synthesizes the relevance of riparian vegetation for river hydromorphology, focusing on its contribution to streamflow and sediment regime conditions. We also examine how riparian vegetation is considered in the WFD and how it is included in national hydromorphological protocols currently in use. Our findings point to a temporal mismatch between the date when the WFD came into force and the emergence of scientific and technologic advances in riparian vegetation dynamism and bio-geomorphic modeling. To overcome this misalignment, we present promising approaches for the characterization and assessment of riparian vegetation, which include the identification of vegetation units and indicators at multiple scales to support management and restoration measures. We discuss the complexity of riparian vegetation assessment, particularly with respect to the establishment of river-type-based reference conditions and the monitoring and management targets, and propose some attributes that can serve as novel indicators of the naturalness vs. artificiality of riparian vegetation. We argue that the hydromorphological context of the WFD should be revisited and offer guidance to integrate riparian vegetation in river hydromorphological monitoring and assessment.

Gravel replenishment and active-channel widening for braided-river restoration: The case of the Upper Drac River (France)

Massive gravel replenishment combined with active-channel widening could theoretically improve the morphological recovery of altered braided rivers but this restoration strategy was not yet tested in the field. A recent braided restoration project based on this principle was set up to restore a 4.2 km long reach in the Upper Drac River (French Alps) using 355.000 m³ of gravels to rise the bed level and to design a 100-m wide trapezoidal cross-section. The aim of this paper is to capture the morphological trajectory after restoration in order to evaluate efficiency and sustainability of this strategy. A Before and After Control Impact monitoring design has been used by combining a repetitive topographic survey (using airborne LiDAR data and terrestrial topographic surveys along cross-sections), an assessment of bedload supply to the restored reach using sediment tracing and active-layer surveys, and a systematic analysis of historical aerial photographs. In a particular context of low hydrological forcing after restoration, the restored reach adjusts with local braiding reference that highlights the efficiency of the restoration strategy. Despite this spontaneous braiding recovery, scouring processes are observed locally along the restored reach and the sustainability remains uncertain even if a good connection to sediment sources was observed. Feedbacks make it possible to propose recommendations to river managers who plan to use similar strategy of braided river restoration. This field study demonstrated for the first time that sediment replenishment combined with channel widening can be an efficient solution for the spontaneous recovery of braiding conditions in altered alpine gravel-bed rivers.

Hydro-Morphological Characteristics Using Flow Duration Curve, Historical Data and Remote Sensing: Effects of Land Use and Climate

Ecohydrological changes in large rivers of the world result from a long history of humandimensions and climate. The increasing human population, intensified land use, and climate change haveled to a decline in the most critical aspect of achieving sustainable development, namely, that of waterresources. This study assessed recent hydromorphological characteristics of the tropical Tana River inKenya using flow duration curve, and geospatial techniques to gain a better understanding of humanimpacts over the last two decades and their consequences for new development projects. The results showthat all extremal peak, low, and mean discharges exhibited significant increasing trends over a period of17 years. Dam construction represents a 13% reduction of the maximum discharge and a 30% decrease inlow flows, while post-regulation hydrological changes indicated an increase of 56 and 40% of high flowsand low flows respectively. Dominant flow was observed to be higher for the current decade than theprevious decade, representing a rise of the dominant streamflow by 33%. The assessment of fourmorphologically active sites at the downstream reach showed channel adjustments which support thechanges in the flow regimes observed. The channel width increased by 8.7 and 1.9% at two sites butdecreased by 31.5 and 16.2% for the other two sites under study during the time period. The resultsunderscore the contribution of other main human modifications, apart from regulation, such as increasedwater abstraction and inter basin transfer, up-stream land use and anthropogenic climate change to assessthe ecohydrological status in this river basin. Such streamflow regime dynamics may have implicationson water resource management, riverine environments, and development of new water projects.

Priorization of River Restoration by Coupling Soil and Water Assessment Tool (SWAT) and Support Vector Machine (SVM) Models in the Taizi River Basin, Northern China

Identifying priority zones for river restoration is important for biodiversity conservation and catchment management. However, limited data due to the difficulty of field collection has led to research to better understand the ecological status within a catchment and develop a targeted planning strategy for river restoration. To address this need, coupling hydrological and machine learning models were constructed to identify priority zones for river restoration based on a dataset of aquatic organisms (i.e., algae, macroinvertebrates, and fish) and physicochemical indicators that were collected from 130 sites in September 2014 in the Taizi River, northern China. A process-based model soil and water assessment tool (SWAT) was developed to model the temporal-spatial variations in environmental indicators. A support vector machine (SVM) model was applied to explore the relationships between aquatic organisms and environmental indicators. Biological indices among different hydrological periods were simulated by coupling SWAT and SVM models. Results indicated that aquatic biological indices and physicochemical indicators exhibited apparent temporal and spatial patterns, and those patterns were more evident in the upper reaches compared to the lower reaches. The ecological status of the Taizi River was better in the flood season than that in the dry season. Priority zones were identified for different hydrological seasons by setting the target values for ecological restoration based on biota organisms, and the results suggest that hydrological conditions significantly influenced restoration prioritization over other environmental parameters. Our approach could be applied in other seasonal river ecosystems to provide important preferences for river restoration.

Review of national methodologies for rivers' hydromorphological assessment: A comparative approach in France, Romania, and Croatia

Conducting hydromorphological assessments for evaluating the ecological status of rivers is a key requirement of the Directive 2000/60/EC (Water Framework Directive - WFD) within European Union (EU) Member States. This paper aims at understanding how this requirement was implemented, through an original comparative review of methodologies for rivers' hydromorphological assessment in three EU Member States, which joined the EU at different times, and with many differences in terms of hydrographic features, socio-economic and water management systems: France, Romania, and Croatia. More precisely, the paper aims at identifying and understanding the main principles guiding the hydromorphological assessment methodologies, elements and data used, giving an overview of the results of hydromorphological river status assessment, and concluding on the stage of hydromorphological assessment implementation. France developed numerous methodologies for physical habitat survey since the 1990s and it is currently conducting a rigorous hydromorphological field survey, but it does not yet have any national methodology for rivers' hydromorphological status assessment, nevertheless foreseen for the next cycle of the WFD. Besides, Romania and Croatia have already started the assessment of the hydromorphological status of rivers within the two cycles of the River Basin Management Plans and are making efforts to improve the hydromorphological monitoring activity. The methods generally differ in indicators, data used, and spatial scale of analysis, which makes it difficult to compare the results of the assessments. Despite a common water policy, the methodological dissimilarities seem to be rather usual between EU Member States. Therefore, the standardization of methodologies appears to be necessary, but the current results could be useful for setting priorities for river restoration and for achieving a better status at a national scale.