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The relation between rainfall, runoff, erosion and sediment transport is highly variable in Mediterranean catchments. Their relation can be modified by land use changes and climate oscillations that, ultimately, will control water and sediment yields. This paper analyses rainfall, runoff and sediment transport relations in a meso-scale Mediterranean mountain catchment, the Ribera Salada (NE Iberian Peninsula). A total of 73 floods recorded between November 2005 and November 2008 at the Inglabaga Sediment Transport Station (114.5 km2) have been analysed. Suspended sediment transport and flow discharge were measured continuously. Rainfall data was obtained by means of direct rain gauges and daily rainfall reconstructions from radar information. Results indicate that the annual sediment yield (2.3 t km− 1 y− 1 on average) and the flood-based runoff coefficients (4.1% on average) are low. The Ribera Salada presents a low geomorphological and hydrological activity compared with other Mediterranean mountain catchments. Pearson correlations between rainfall, runoff and sediment transport variables were obtained. The hydrological response of the catchment is controlled by the base flows. The magnitude of suspended sediment concentrations is largely correlated with flood magnitude, while sediment load is correlated with the amount of direct runoff. Multivariate analysis shows that total suspended load can be predicted by integrating rainfall and runoff variables. The total direct runoff is the variable with more weight in the equation. Finally, three main hydro-sedimentary phases within the hydrological year are defined in this catchment: (a) Winter, where the catchment produces only water and very little sediment; (b) Spring, where the majority of water and sediment is produced; and (c) Summer–Autumn, when little runoff is produced but significant amount of sediments is exported out of the catchment. Results show as land use and climate change may have an important role in modifying the cycles of water and sediment yields in Mediterranean mountain catchments. ; This work was performed in the framework of research agreement between the Catalan Water Agency and the Forest Sciences Centre of Catalonia to study 'Fluvial dynamics in river basins of the Segre-Ebro in Catalonia', and within the projects CGL2009-09770/BTE and Consolider Ingenio 2010 SCARCE CSD2009-00065, financed by the Ministry of Economy and Competitiveness, and SESAM-1&2 funded by the DFG Deutsche Forschungsgemeinschaft BR 1731/11-1 & BR 1731/11-2. The study has benefited from data analysis methodology developed in the MORPHSED project, funded by the Ministry of Economy and Competitiveness and European FEDER funds (CGL2012-3639). The second author has a research contract funded by the Ramón y Cajal Program (RYC-2010-06264) with Human Capital Attraction Programme funded by funded by the Ministry of Economy and Competitiveness. Authors acknowledge the support from the Economy and Knowledge Department of the Catalan Government through the Consolidated Research Groups: RIUS -Fluvial Dynamics Research Group (2014-SGR-645).

Hydropower production involves significant impacts on the dynamics and continuity of river systems. In this paper we analyse the effects of hydropeaks on river-bed particle mobility along a 2-km river channel. For this, a total of four study reaches were stablished: one considered a control reach (no impact by hydropeaking) and three impacted (upstream and downstream from the confluence of tributaries). Mobility related to three hydrological scenarios considered representative of the entire flow conditions in the control and impacted reaches was investigated. Results indicate that sediment availability and dynamics proved different in the control reach to those observed downstream in reaches daily affected by hydropeaks. In the absence of large floods capable of resetting the system from a sedimentary point-of-view, only the role of tributaries during small flow events reduces the effects of hydropeaks on river-bed particles' availability and mobility. The effects of a hydropeaked regime are not observed for the whole spectrum of grain-sizes present in the river-bed. While the structural large elements (i.e., boulders) in the channel do not move, sand and fine gravel stored in patches of the bed are constantly entrained, transported and depleted whereas, in between, medium and large gravel are progressively winnowed. Our results point out that hydropeaked flows, which are generally not considered as disturbances in geomorphic terms, initiate frequent episodes of (selected) bed mobility and, consequently, the river-bed becomes depleted of fine sediments from patches and progressively lacks other fractions such as medium gravels, all of which are highly relevant from the ecological point of view. ; This research was undertaken under the MorphPeak (CGL2016-78874-R) project funded by the Spanish Ministry of Economy and Competiveness and the European Regional Development Fund Scheme (FEDER). Authors acknowledge the support from ENDESA S.A. at the first stage of the research. D.V. (first author) is funded through the Serra Húnter Programme (Catalan Government). F.V. (second author) has a grant funded by the Ministry of Science, Innovation and Universities, Spain (BES-2017-081850). Authors acknowledge the support from the Economy and Knowledge Department of the Catalan Government through the Consolidated Research Group 'Fluvial Dynamics Research Group' -RIUS (2017 SGR 459).

Studies of ephemeral streams have focused mainly in arid and semi‐arid regions. Such streams also occur widely in temperate regions, but much less is known about their influence on fluvial processes in main‐stem rivers here. In this paper, we present evidence of the importance of a small ephemeral temperate stream for main‐stem fine sediment dynamics. The paper focuses on a restoration project (River Ehen, North West England) which involved the reconnection of a headwater tributary to the main‐stem river. We present data on suspended sediment transport 2 years prior to and 2 years following the reconnection. Despite the small size and non‐perennial flow of the tributary, its reconnection resulted in an increase of 65% in the main‐stem sediment yield. During both the pre‐reconnection and post‐reconnection periods, a higher proportion of the annual yield was conveyed during short events with relatively high suspended sediment concentrations. Following the reconnection, the magnitude and frequency of such events increased, primarily due to sediment being delivered from the tributary at times when main‐stem flows were not elevated. Overall, the main‐stem remains supply limited and so is highly dependent on sediment delivered from the tributary. The study helps stress that even non‐perennial tributaries yielding only a small increase in catchment size (+1.2% in this case) can have a major influence on main‐stem fluvial dynamics. Their role as sediment sources may be especially important where, as in the case of the Ehen, the main‐stem is regulated and the system is otherwise starved of sediment. ; Damià Vericat is funded by a Ramon y Cajal Fellowship (RYC‐2010‐06264). Authors acknowledge the support from the Economy and Knowledge Department of the Catalan Government through the Consolidated Research Group "Fluvial Dynamics Research Group"—RIUS (2014 SGR 645), and the additional support provided by the CERCA Programme, also from the Catalan Government.

This paper is the first of a pair that report the findings of a river rehabilitation project centred on the reconnection of a formerly diverted headwater tributary (Ben Gill) to its main‐stem river (the River Ehen). The present paper describes the geomorphic evolution of the tributary in the 2 years following its reconnection, with a particular focus on assessing the volumes of sediment now being supplied to the main‐stem Ehen. Structure‐from‐Motion photogrammetry was used to produce Digital Elevation Models (DEMs) of the newly connected tributary, with successive DEMs compared to assess topographic changes in the channel and quantify volumes of material exported. 3D errors in the DEMs were small relative to the scour and fill observed in the channel (error 0.016–0.056 m compared to up to 1.7 m vertical change between consecutive surveys). Erosion was the dominant process in the tributary channel, though this varied spatially and temporally. Over the 2‐year period, an estimated minimum of 384 m3 of coarse sediment was exported from Ben Gill and delivered to the confluence zone, where a new bar feature developed as a result. This estimate is twice as high as earlier ones. Analysis of the growth of this bar suggested that much of the material supplied by Ben Gill remains here temporarily, with onward conveyance constrained by the competence of the regulated main‐stem. The work shows that, thanks to the reconnection, this small (0.55 km2) ephemeral tributary (flowing for only around 20% of the time) has become a key source of sediment for the main‐stem Ehen. The second in the pair of papers focuses on the geomorphic responses of the main‐stem to this renewed supply of sediment. ; This study was funded as part of a PhD grant by the Environment Agency UK and United Utilities. DV was funded by a Ramon y Cajal fellowship (RYC‐2010‐06264) at the time the project was developed, and is now employed as a Serra Húnter Fellow at the University of Lleida. Authors acknowledge the support from the Economy and Knowledge department of the Catalan Government through the Consolidated Research Group "Fluvial Dynamics Research Group"‐RIUS (2017‐SGR‐459), and the additional support provided by the CERCA Programme, also from the Catalan Government.

This paper describes changes in bed morpho‐dynamics and topography in the River Ehen, a regulated river in NW England (i.e., temperate climate) following a rehabilitation project that reconnected a formerly diverted headwater sub‐catchment back to its main‐stem. Sediment grain‐size distributions in the Ehen changed subtly and in rather complex ways following the reconnection. Changes were most evident in the riffle morphological unit, where gravel‐sized material accumulated in the first 2 years after the reconnection. All morphological units initially experienced an addition of fine sediment (size <8 mm) but by the end of the study the proportion of fine material in the bed matrix had returned to pre‐reconnection levels. Topographic changes were evident in some units, with net aggradation in the riffle and scour in the plane bed; there was no detectable change in the pool. Albeit limited, there was evidence of an increase in bed mobility, with field observations indicating that the new sediment is moving over the top of the largely static existing pavement, rather than interacting with it. Despite numerous uncertainties related mainly to the ephemeral nature of the tributary and, consequently, how much sediment it would deliver, evidence suggests that the main project objective is being met: there is a renewed supply of sediment now being delivered to the main‐stem Ehen at times and in quantities that are controlled by natural processes. Nevertheless, the river is still best considered to be in an adjustment phase, so assessment of its long term response to the reconnection requires continued monitoring. ; This study was funded as part of a PhD grant by the Environment Agency UK and United Utilities. DV was funded by a Ramon y Cajal fellowship (RYC‐2010‐06264) at the time of the study and is now funded by a Serra Húnter Fellowship at the University of Lleida. Authors acknowledge the support from the Economy and Knowledge department of the Catalan Government through the Consolidated Research Group "Fluvial Dynamics Research Group"‐RIUS (2014‐SGR‐645), and the additional support provided by the CERCA Programme, also from the Catalan Government.

Purpose A disconnected ephemeral tributary was reconnected to the regulated River Ehen (NW England) as part of a river restoration initiative, providing a renewed delivery of sediment to a highly stable and armoured channel. This paper (1) assesses spatial and temporal dynamics of suspended and stored sediments in the Ehen, (2) characterises the composition of stored sediment, (3) develops fine sediment budgets for downstream river reaches, and (4) assesses the controls on the storage of fine sediment in the riverbed. Materials and methods A 3-km study section in the upper part of the River Ehen was divided into two reaches. Suspended sediments were monitored at the downstream limits of each reach over a 2-year period. In-channel storage was measured in three morphological units within the upper reach, on 13 occasions over the same period. Samples were used to assess changes in volumes of stored fine sediment, as well as the grain sizes and organic content of the material. A time-lapse camera facing the confluence of the tributary was used to conceptualise different flow scenarios. These scenarios reflect the degree of synchronicity between flows in the main-stem and those in the tributary. Fine sediment budgets were developed for each reach to assess the relative contribution of different sources of sediment. Results and discussion The reconnection significantly affected suspended sediment loads in the Ehen. Bed storage increased twofold, with changes most evident in the slow-flowing morphological unit. Changes in the composition of stored sediment were less marked than changes in the quantity of material. Changes in bed storage were controlled by the degree of synchronicity between flows in the Ehen and those in the newly reconnected tributary. Results show that three generalised flow scenarios occur, with total asynchronicity between flows in the tributary and the Ehen being responsible for the main episodes of fine sediment deposition. Overall, the estimated sediment budgets provide insights into the importance of non-perennial sources of sediment in supply-limited systems such as the Ehen. Although bed storage values are within the range of those published for UK rivers, the increase observed since the reconnection, together with the persistence of a static pavement, highlights the ecologically critical conditions of the regulated main-stem River Ehen. Conclusions Intermittent sources control fine sediment transport dynamics in the upper River Ehen. In this regulated river, ongoing deposition associated with increased low- and medium-sized flow events exerts more of a control on bed storage than large but rare floods. Management actions to limit delivery of material from lateral sources could help prevent further deterio- ration of habitat conditions for biota sensitive to fine sediment. Given the ongoing adjustment in the newly reconnected tributary, continued monitoring is needed to capture further morphosedimentary response in the main-stem. ; This study was funded by the Environment Agency (EA) and United Utilities (UU) as part of a PhD grant. We would like to thank Gail Butteril, Jane Atkins, Andy Newton and Helen Reid from EA, as well as Kat Liney and Grace Martin from UU for their help and support throughout the project. Damià Vericat is funded by a Ramon y Cajal fellowship (RYC-2010-06264). Authors acknowledge the support from the Economy and Knowledge Department of the Catalan Government through the Consolidated Research Group B Fluvial Dynamics Research Group ^ — RIUS (2014 SGR 645), and the additional support provided by the CERCA Programme, also from the Catalan Government. We are also thankful to two anonymous reviewers whose comments have helped improve the paper.

Structure‐from‐Motion (SfM) photogrammetry is now used widely to study a range of earth surface processes and landforms, and is fast becoming a core tool in fluvial geomorphology. SfM photogrammetry allows extraction of topographic information and orthophotos from aerial imagery. However, one field where it is not yet widely used is that of river restoration. The characterisation of physical habitat conditions pre‐ and post‐restoration is critical for assessing project success, and SfM can be used easily and effectively for this purpose. In this paper we outline a workflow model for the application of SfM photogrammetry to collect topographic data, develop surface models and assess geomorphic change resulting from river restoration actions. We illustrate the application of the model to a river restoration project in the NW of England, to show how SfM techniques have been used to assess whether the project is achieving its geomorphic objectives. We outline the details of each stage of the workflow, which extend from preliminary decision‐making related to the establishment of a ground control network, through fish‐eye lens camera testing and calibration, to final image analysis for the creation of facies maps, the extraction of point clouds, and the development of digital elevation models (DEMs) and channel roughness maps. The workflow enabled us to confidently identify geomorphic changes occurring in the river channel over time, as well as assess spatial variation in erosion and aggradation. Critical to the assessment of change was the high number of ground control points and the application of a minimum level of detection threshold used to assess uncertainties in the topographic models. We suggest that these two things are especially important for river restoration applications. ; This research is funded by the Environment Agency and United Utilities whose support is gratefully acknowledged. Some of the methods employed in this work have been tested on the background of the results obtained in MorphSed (www.morphsed.es), a research project funded by the Spanish Ministry of Economy and Competiveness and the European Regional Development Fund Scheme (FEDER; CGL2012‐36394). The second author is funded by a Ramon y Cajal Fellowship (RYC‐2010‐06264). Authors acknowledge the support from the Economy and Knowledge Department of the Catalan Government through the Consolidated Research Group 'Fluvial Dynamics Research Group' (2014 SGR 645).

Indices of connectivity are critical means for moving from qualitative to (semi-)quantitative evaluations of material (e.g., water, sediment and nutrients) transfer across the building blocks of a terrestrial system. In geomorphology, compared to closely related disciplines like ecology and hydrology, the development of indices has only recently started and as such presents opportunities and challenges that merit attention. In this paper, we review existing indices of sediment connectivity and suggest potential avenues of development for meeting current basic and applied research needs. Specifically, we focus on terrestrial geomorphic systems dominated by processes that are driven by hydro-meteorological forcing, neglecting seismically triggered events, karstic systems and environments controlled by eolian processes. We begin by setting a conceptual framework that combines external forcings (drivers) and system (intrinsic) structural and functional properties relevant to sediment connectivity. This framework guides our review of response variables suitable for sediment connectivity indices. In particular, we consider three sample applications concerned with sediment connectivity in: (i) soil studies at the plot scale, (ii) bedload transport at the reach scale, and (iii) sediment budgets at the catchment scale. In relation to the set of response variables identified, we consider data availability and issues of data acquisition for use in indices of sediment connectivity. We classify currently available indices in raster based, object or network based, and indices based on effective catchment area. Virtually all existing indices address the degree of static, structural connectivity only, with limited attention for process-based, functional connectivity counterparts. Most recent developments in indices of sediment connectivity deal, to some extent, with different styles of anthropogenic and hydro-meteorological forcings and with the temporal variability of sediment connectivity, by incorporating additional variables and parameters in existing indices. We believe that, in order to use structural connectivity as explanatory or predictive tool, indices need to be interpretable in relation to geomorphic processes, material properties, and forcing styles and magnitude-frequency spectra. Improvements in this direction can be made through studies shaped to constrain structural-functional correlations across a range of hydro-meteorological scenarios, for example employing field-based techniques such as particle tracking and sediment provenance analysis, as well as numerical simulations. We further consider existing indices in relation to spatial and temporal scales. The latter have immediate implications on the distinction and application between indices and models of sediment connectivity. In this context, we suggest that sediment connectivity over millennial or longer time scales should be dealt with models, as opposed to indices. ; This paper forms part of the activities of the EU-funded COST action "CONNECTEUR" (ES1306; http://connecteur.info). Working group 4 (on "useable indices of connectivity") thanks CONNECTEUR for funding two workshops in Eichstaett and Tallinn during which this paper has been developed. Damià Vericat is supported by a Ramon y Cajal Fellowship (RYC-2010-06264). Authors acknowledge the support from the Economy and Knowledge Department of the Catalan Government through the Consolidated Fluvial Dynamics Research Group (2014 SGR 645), and the CERCA Programme.

Fine particles or sediments are one of the important variables that should be considered for the proper management of water quality and aquatic ecosystems. In the present study, the effect of catchment characteristics on the performance of an already developed model for the estimation of fine sediments dynamics between the water column and sediment bed was tested, using 13 catchments distributed worldwide. The model was calibrated to determine two optimal model parameters. The first is the filtration parameter, which represents the filtration of fine sediments through pores of the stream bed during the recession period of a flood event. The second parameter is the bed erosion parameter that represents the active layer, directly related to the re-suspension of fine sediments during a flood event. A dependency of the filtration parameter with the catchment area was observed in catchments smaller than ~100 km2, whereas no particular relationship was observed for larger catchments (>100 km2). In contrast, the bed erosion parameter does not show a noticeable dependency with the area or other environmental characteristics. The model estimated the mass of fine sediments released from the sediment bed to the water column during flood events in the 13 catchments within ~23% bias. ; J. A. López-Tarazón is in receipt of a Vicenç Mut postdoctoral fellowship (CAIB PD/038/2016), while Damià Vericat is a a Serra Húnter Fellow at the University of Lleida. Authors acknowledge the support from the Economy and Knowledge Department of the Catalan Government through the Consolidated Research Group 2017 SGR 459 Fluvial Dynamics Research Group (RIUS). The data in Galabre and Bès were collected during the STREAMS (Sediment TRansport and Erosion Across Mountains) project, funded by the French National Research Agency (ANR/ BLAN06-1_13915).

Hydropower is considered a renewable form of energy production, but generating electricity from rivers is not always environmentally benign. The global demand for renewables is increasing rapidly as fossil fuels are gradually phased out, so rivers will continue to be subjected to the pressures imposed by hydropower for decades to come. Finding ways of operating hydropower plants that limit impacts on downstream river ecosystems is therefore a pressing global concern. Usually, these plants cause marked and rapid fluctuations in flow in downstream river reaches, termed 'hydropeaking'. Hydropeaks result in a variety of ecological changes in the dynamic mountain rivers they typically affect; declines in fish and insect populations are evident, especially in reaches immediately downstream from the plant. While these changes are often acute and readily apparent, the underlying causal mechanisms remain unclear. We argue here that riverbed sediments are a critical but neglected causal link between hydropeaking flow regimes and ecological changes. We outline how a variety of tools from different branches of river science can now be brought together to understand precisely why hydropeaking alters sediment dynamics; these tools provide a mechanistic explanation for changes in bed sedimentary conditions and channel form across multiple scales and, consequently, a better understanding of ecological changes. By allowing us to simulate the effects of flow fluctuations on sediment dynamics and channel form, these tools also allow us to develop ways of releasing water from hydropeaking dams that limit impacts on aquatic habitat and species. ; This work was undertaken and benefited from results and discussions provided in the background of the MorphPeak (Grant No. CGL2016-78874-R) and the MorphHab (Grant No. PID2019-104979RB-I00) projects funded by the Spanish Ministry of Economy and Competiveness, Science and Innovation, and the European Regional Development Fund Scheme. Authors acknowledge the support of the Economy and Knowledge Department of the Catalan Government through the Consolidated Research Group 'Fluvial Dynamics Research Group'—RIUS (Grant No. 2017SGR-0459) and the CERCA Program. Damià Vericat is funded through the Serra Húnter Programme (Catalan Government).

Soil degradation by water is a serious environmental problem worldwide, with specific climatic factors being the major causes. We investigated the relationships between synoptic atmospheric patterns (i.e. weather types, WTs) and runoff, erosion and sediment yield throughout the Mediterranean basin by analyzing a large database of natural rainfall events at 68 research sites in 9 countries. Principal Component Analysis (PCA) was used to identify spatial relationships of the different WTs including three hydro-sedimentary variables: rainfall, runoff, and sediment yield (SY, used to refer to both soil erosion measured at plot scale and sediment yield registered at catchment scale). The results indicated 4 spatial classes of rainfall and runoff: (a) northern sites dependent on North (N) and North West (NW) flows; (b) eastern sites dependent on E and NE flows; (c) southern sites dependent on S and SE flows; and, finally, (d) western sites dependent on W and SW flows. Conversely, three spatial classes are identified for SY characterized by: (a) N and NE flows in northern sites (b) E flows in eastern sites, and (c) W and SW flows in western sites. Most of the rainfall, runoff and SY occurred during a small number of daily events, and just a few WTs accounted for large percentages of the total. Our results confirm that characterization by WT improves understanding of the general conditions under which runoff and SY occur, and provides useful information for understanding the spatial variability of runoff, and SY throughout the Mediterranean basin. The approach used here could be useful to aid of the design of regional water management and soil conservation measures. ; This research was supported by projects funded by the MINECO-FEDER: CGL2014-52135-C3-3-R, CGL2014-59946-R, CGL2015-65569-R, CGL2015-64284-C2-2-R, and PCIN-2017-061/AEI. When this manuscript was first submitted Estela Nadal-Romero and Damià Vericat received a "Ramón y Cajal" postdoctoral contract (RYC-2013-14371 and RYC‐2010‐06264, Spanish Ministry of Economy and Competitiveness, MEC). Damià Vericat is now a Serra Húnter Fellow at the University of Lleida. María Fernández-Raga received a "José Castillejo" postdoctoral grant (Spanish Ministry of Education, Culture and Sports). Carla Ferreira was supported by a post-doctoral research grant from the Portuguese Science and Technology Foundation (SFRH/BPD/120093/2016). Mariano Moreno-de las Heras received a Juan de la Cierva postdoctoral contract (IJCI-2015-26463) from the MEC. José Andrés López-Tarazón received a Vicenç Mut postdoctoral fellowship from the Autonomous Balearic Government (CAIB PD/038/2016). José Andrés López-Tarazón and Ramon Batalla also acknowledge the Secretariat for Universities and Research of the Department of the Economy and Knowledge of the Autonomous Government of Catalonia for supporting the Consolidated Research Group 2014 SGR 645 (RIUS- Fluvial Dynamics Research Group), and the CERCA Programme. This paper has benefited from the Lab and Field Data Pool created within the framework of the COST action CONNECTEUR (ES1306).