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. Copyright © 2016 John Wiley & Sons, Ltd.

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

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 deterioration 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 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 m 3 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 km 2) 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.

Given the actual trajectory of greenhouse gases emissions, in situ actions are needed to limit rivers water warming. Riparian tree planting has been shown as a successful mitigation strategy, but most studies have been conducted on upland forested rivers. The hydraulic, geomorphic and thermal conditions of lowland rivers, subject to straightening and fragmentation, are very different from upland systems. In this study, the role of riparian cover relative to the presence of weirs was investigated in lowland slow‐flowing rivers within the agricultural context of the Bresse region, France. Using airborne thermal infrared (TIR) imaging, nine reaches of 20 to 30 km each were mapped to quantify water temperature, riparian vegetation and assess weir location. Campaigns were carried out during the hot summer 2018. Results have comforted that riparian vegetation is capable of limiting increase in temperature during warm events by 2 to 3°C, but with varying success depending on the rivers' thermal regimes. Rivers with a ‘colder’ regime (i.e., ground/karstwater‐fed) are thermally less influenced by riparian vegetation but also more resilient to the presence of weirs. Rivers with the highest degree of thermal alteration showed the highest positive response to riparian shading. Riparian vegetation prevents stagnant water from extreme warming but does not prevent alteration of the thermal regime, for example thermal stratification, likely to occur on a daily basis and to large extents (> 80%) during warm and low‐flow events in impounded rivers. Thermal conditions were sub‐optimal for most fish species that could be expected in these streams. Although the direct relation with thermal alteration is not proved, hydrobiological scores of flow alteration are correlated with our metric of thermo‐physical alteration. Management strategies to limit temperature increase should carefully consider restoring the thermal regime of rivers through weir removal when it is possible, combined with riparian tree planting as an additional mitigation measure.

Gravel augmentation has become common practice to mitigate the effects of decline in upstream sediment supply in gravel‐bed rivers. However, the functional aspects of river systems are often left out of rehabilitation monitoring programmes. Despite temperature being a fundamental parameter determining the general health of rivers, a limited number of studies have tested whether gravel augmentation can aid restoring thermal functions. Using airborne thermal infrared (TIR) imagery, this paper explores potential positive outcomes through the monitoring of gravel augmentation actions on three rivers in France using hydro‐morphological indicators within a trajectory‐based before–after control–impact (BACI) framework. This design, combining long‐term geomorphic evolution with TIR‐based CI strategy, indicated that restoring forms was not sufficient to restore thermal functions in their spatial dimension. Despite forms showing various degrees of recovery, the thermal regime of rehabilitated reaches (i.e. temperature gradient, cold‐water patches density, etc.) failed to recover. Nonetheless, hydro‐morphological indices can be used to estimate long‐term evolution of groundwater‐surface water interactions. We emphasise the benefits of trajectory‐based BACI assessment to identify current conditions, understand the past evolution (trajectory) of the system to define the framework within which rehabilitation can be objectively assessed, especially when assessing hydrological (here thermal) processes. From a hydrological perspective, the gap between restored forms and restored thermal processes stems from the alteration of connectivity pathways, which potentially require more time (or efforts) to be recovered than forms do. With an increasing number of rehabilitation schemes and increasing pressure of global changes on rivers, we suggest that monitoring of water temperature becomes a routine part of rehabilitation projects.

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 mainstem. 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

The annual global loss of organic carbon from terrestrial ecosystems into rivers is similar to the organic carbon stored in soils each year. Dissolved organic matter (DOM) flows through the food web to macroinvertebrates, but little is known about the effect of DOM increase on stream food webs and how much macroinvertebrates may contribute to the regulation of carbon fluxes in rivers. Using a before and after control impact (BACI) experimental design, we increased by 12% (+ 0.52 mg C L−1) the concentration of DOM in a stream for three weeks by adding sucrose, with a distinctive δ13C signature, to simulate a pulse of natural DOM supply from soils. We partitioned the diet of macroinvertebrates from carbon sources according to the green pathway (autotrophs) and detrital pathways (bacteria and terrestrial organic matter). Our flow food web approach based on C fluxes, with bacteria as a key node, showed the dominant contribution of the detrital pathways for macroinvertebrates in the reference stream. DOM addition induced changes in the diets of individual taxa, but did not have any strong effects on the relative overall contribution of the detrital pathways versus the green pathway. Autotrophic uptake of CO2 respired by bacteria was much larger than bacterial C flux to invertebrates (that is, the classic microbial loop) and allowed a significant fraction of natural allochthonous organic carbon to make its way to macroinvertebrates via autotrophs fixing CO2 respired by bacteria. Overall macroinvertebrates did not regulate directly to any great extent the flux of stream DOM towards downstream ecosystems.