Asynchronicity of fine sediment supply and its effects on transport and storage in a regulated river

Open access via Springer Compact Agreement 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 “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.Peer reviewedPublisher PD

Geomorphological response to system-scale river rehabilitation II : Main-stem channel adjustments following reconnection of an ephemeral tributary

Open Access via the Jisc Wiley Agreement Research Funders United Utilities Environmental AgencyPeer reviewedPublisher PD

Geomorphological response to system-scale river rehabilitation I : Sediment supply from a reconnected tributary

Funding Information: 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 H?nter 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. Publisher Copyright: © 2020 The Authors. River Research and Applications published by John Wiley & Sons Ltd Copyright: Copyright 2020 Elsevier B.V., All rights reserved.Peer reviewe

The importance of a small ephemeral tributary for fine sediment dynamics in a main‐stem river

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

Application of Structure-from-Motion photogrammetry to river restoration

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). The authors thank Manel Llena from the University of Lleida for his help and contribution to the camera calibration experiments. We are also grateful to the three anonymous reviewers and the editors for their comments that greatly improved the manuscript.Peer reviewedPostprin

Long-term geomorphic adjustments following the recoupling of a tributary to its main-stem river

River restoration and rehabilitation projects are widespread, but rarely include the data needed to fully evaluate if they are successful in achieving their goals or how long the process of readjustment takes before a new ‘recovered’ regime state is reached. Here we present a seven-year post-project dataset detailing the morpho-sedimentary responses of a river to the reconnection of a formerly diverted tributary, and relate observed changes to conditions in the river prior to the reconnection. We describe changes in the tributary and main-stem channels, including changes in channel planform, morphology, and the export of coarse and fine sediment from the tributary to the main-stem river. We use the data to develop a conceptual model of the system's response to the reconnection. Marked geomorphic changes occurred within the first two years after the reconnection. Changes during this ‘shock phase’ included dramatic erosion and subsequent deepening and widening of the tributary channel, rapid development of a confluence bar and an increase in fine sediment delivered to the main-stem. After this shock phase, and despite the continued occurrence of high magnitude flow events, the rate of geomorphic change in the tributary began to decrease, and the rate of growth of the confluence bar slowed. Fine sediment volumes in the main-stem also decreased steadily. After an adjustment phase lasting a total of approximately 4.5 yr (including the initial 2-yr shock phase), the tributary to mainstem system appeared to reach a new dynamic equilibrium that we consider the adjusted regime state. This new regime state was characterised by, among other things, an increase in geomorphic heterogeneity in the tributary and main-stem channels. Changes in both fluvial processes and forms indicate that within 4.5 yr the project was successful in achieving its goal of augmenting sediment and increasing geomorphic heterogeneity. Our conceptual model of adjustment mirrors that developed by Petts and Gurnell (2005), with the river passing through a complex and dynamic adjustment phase before reaching a new regime state. However, unlike the responses to impoundment represented by Petts and Gurnell, our model of river response to rehabilitation charts increases in dynamism and heterogeneity.The research presented in this paper has been supported by a number of organisations. We thank United Utilities (UU) and the Environment Agency (EA) for funding and support. In particular, we thank Kat Liney and Alice Senior from UU, and Gez Foster and Jane Atkins from EA. Part of this research benefited from the methods and outcomes of the MorphHab (PID2019-104979RB-I00/AEI/10.13039/501100011033) research project. B. Marteau's contribution was in part supported by a postdoctoral fellowship from the EUR H2O'Lyon (ANR-17-EURE-0018). D. Vericat is a Serra Húnter Fellow at the University of Lleida. We are also grateful to the reviewers and editor for their comments that improved the manuscript

Terrestrial Very-Long-Baseline Atom Interferometry:Workshop Summary

This document presents a summary of the 2023 Terrestrial Very-Long-Baseline Atom Interferometry Workshop hosted by CERN. The workshop brought together experts from around the world to discuss the exciting developments in large-scale atom interferometer (AI) prototypes and their potential for detecting ultralight dark matter and gravitational waves. The primary objective of the workshop was to lay the groundwork for an international TVLBAI proto-collaboration. This collaboration aims to unite researchers from different institutions to strategize and secure funding for terrestrial large-scale AI projects. The ultimate goal is to create a roadmap detailing the design and technology choices for one or more km-scale detectors, which will be operational in the mid-2030s. The key sections of this report present the physics case and technical challenges, together with a comprehensive overview of the discussions at the workshop together with the main conclusions

Intégration en dispositifs tandem des cellules PV à contactspassivés : vers une technologie d'interface multifonctionnelleet universelle.

The photovoltaic module market is dominated by technologies based on crystalline silicon (c-Si). The use of low temperature (SHJ) or high temperature (TOPCon) passivated contacts leads to record efficiencies (26.8% and 26.2%) close to the theoretical limit of 29.4%. The option explored by the majority of institutes to overcome this limit is to combine c-Si technology with another wide bandgap (EGap) semiconductor material to enable optimum conversion of the solar spectrum over the entire energy range. The theoretical maximum efficiency of such tandem devices can then reach 42%. A two-terminal structure enables easiest module processing leading to reduced production costs. However, this places severe constraints on the interface layers between the two cells. These must provide excellent carrier lifetime in each cell, while ensuring optimal optical (minimal parasitic absorption and reflection) and electrical (efficient and highly conductive recombination junction RJ) properties.For the c-Si cell, this thesis focuses on TOPCon technology, which is expected to become market mainstream by 2030. This approach, based on poly-Si/SiOx stacks, offers great versatility for the tandem device fabrication processes (stability up to 800°C), and benefits from highly doped layers that are well suited for the formation of RJ. Among the variety of large EGap materials, perovskite (Pk) technology is the most popular solution as it benefits from both high efficiency potential and low production costs. The interface between the two cells (TOPCon and Pk) of the tandem device is usually formed by transparent conductive oxides layers such as ITO (Indium Tin Oxide), which shows excellent electrical and optical properties. However, indium is a critical material that could limit the long-term development of this technology. Therefore, the aim of this thesis is to explore indium-free approaches for the interface of Pk/c-Si tandem cells.The studies carried out in this work concern Pk/c-Si tandem cells in nip configuration, for which two alternative approaches for interface engineering are investigated. The first one uses no additional interface layer, while the second one integrates an nc-Si (n+) layer to form a silicon tunnel diode, which should provide an optimal recombination current. These two alternative approaches allowed better initial performances than the reference process, mainly by overcoming short-circuit issues in the Pk cell. Tandem devices featuring no additional interface layer show fill factors comparable to those of the world's best devices (>81%) and efficiencies close to 25%, confirming the potential of TOPCon passivated contacts to form indium-free RJ. However, these two indium-free approaches were limited by the appearance of internal series resistance over time. Advanced characterisations explain these degradations by the formation of a SiOx layer between silicon and SnO2 (the electron-selective layer - ESL- of the Pk cell).In conclusion, TOPCon passivated contacts are particularly well suited to obtain efficient recombination junctions (direct or via silicon tunnel diodes), thus eliminating the need to use indium in the interface layers. As silicon is particularly sensitive to oxidation, the choice of contacting layers (ESL in nip configuration) should be focused on a material that contains no oxygen or has a stronger affinity for oxygen than silicon.Le marché des modules photovoltaïque est dominé par les technologies basées sur le silicium cristallin (c-Si). L'utilisation de contacts passivés fabriqués à basse température (SHJ) ou haute température (TOPCon) mène à des rendements records (26,8% et 26,2%) proches de la limite théorique de 29,4%. L'option privilégiée par la majorité des acteurs pour dépasser cette limite consiste à associer la technologie c-Si avec un autre matériau semi-conducteur à large bande interdite (EGap) pour permettre une conversion optimale du spectre solaire sur toute la gamme énergétique. L'efficacité maximale théorique de tels dispositifs tandem peut alors atteindre 42%. Il semble avantageux de privilégier une structure à deux terminaux pour simplifier la mise en module et réduire les coûts associés. Cependant, cela implique de fortes contraintes sur les couches d'interface situées entre les deux cellules. En effet, ces dernières doivent alors permettre l'obtention d'excellentes durées de vie des porteurs dans chaque cellule, tout en assurant des propriétés optiques (absorption et réflexion parasites minimales) et électriques (jonction de recombinaison (JR) efficace et peu résistive) optimales.Pour la cellule c-Si, cette thèse se concentre sur la technologie TOPCon qui devrait dominer le marché d'ici 2030. De plus cette approche basée sur des empilements poly-Si/SiOx permet de disposer d'une grande versatilité pour les procédés de fabrication du dispositif tandem (stabilité jusqu'à 800°C), et de bénéficier de couches fortement dopées adaptées à la formation de JR. Le choix de l'absorbeur à large EGap s'est porté sur la technologie pérovskite (Pk) qui semble faire l'unanimité car elle combine potentiellement de faibles coûts de production et de hauts rendements. L'interface entre les deux cellules (TOPCon et Pk) du dispositif tandem est habituellement réalisée avec des couches d'oxydes transparents conducteurs comme l'ITO (Oxyde d'Indium Etain), permettant l'obtention d'excellentes propriétés électriques et optiques. L'indium est cependant un matériau critique qui pourrait limiter le développement de cette technologie à long terme. L'objectif de cette thèse consiste ainsi à explorer des approches sans indium pour l'interface des cellules tandem Pk/c-Si.Les études réalisées dans ces travaux concernent des cellules tandem Pk/c-Si en configuration nip, pour lesquelles deux approches alternatives sont étudiées pour l'ingénierie d'interface. La première n'utilise aucune couche d'interface additionnelle, et la seconde intègre une couche nc-Si (n+) pour former une diode tunnel en silicium afin d'obtenir un courant de recombinaison optimal. Ces deux approches alternatives ont mené à l'obtention de meilleures performances initiales que le procédé de référence, principalement en s'affranchissant de la problématique de court-circuits dans la cellule Pk. Les dispositifs tandem fabriqués sans couche d'interface permettent d'obtenir des facteurs de forme comparables à ceux des meilleurs dispositifs mondiaux (> 81%) ainsi que des rendements proches de 25%, démontrant le potentiel des contacts passivés TOPCon pour la formation de JR sans ITO. Ces deux technologies d'interface sans indium se sont cependant révélées limitées par l'apparition au cours du temps de résistances séries internes. Des caractérisations avancées expliquent ces dégradations par l'apparition d'une couche de SiOx entre le silicium et le SnO2 (la couche sélective d'électron - ESL- de la cellule Pk).En conclusion, les contacts passivés TOPCon sont particulièrement adaptés à la formation de jonctions de recombinaison (directes ou par le biais de diode tunnel en silicium) permettant de s'affranchir d'indium dans les couches d'interconnexion. Le silicium étant particulièrement sensible à l'oxydation, le choix de la couche de contact (ESL en configuration nip) devrait se porter sur un matériau ne comportant pas d'oxygène ou présentant une affinité pour l'oxygène plus forte que le silicium

Intégration en dispositifs tandem des cellules PV à contactspassivés : vers une technologie d'interface multifonctionnelleet universelle.

The photovoltaic module market is dominated by technologies based on crystalline silicon (c-Si). The use of low temperature (SHJ) or high temperature (TOPCon) passivated contacts leads to record efficiencies (26.8% and 26.2%) close to the theoretical limit of 29.4%. The option explored by the majority of institutes to overcome this limit is to combine c-Si technology with another wide bandgap (EGap) semiconductor material to enable optimum conversion of the solar spectrum over the entire energy range. The theoretical maximum efficiency of such tandem devices can then reach 42%. A two-terminal structure enables easiest module processing leading to reduced production costs. However, this places severe constraints on the interface layers between the two cells. These must provide excellent carrier lifetime in each cell, while ensuring optimal optical (minimal parasitic absorption and reflection) and electrical (efficient and highly conductive recombination junction RJ) properties.For the c-Si cell, this thesis focuses on TOPCon technology, which is expected to become market mainstream by 2030. This approach, based on poly-Si/SiOx stacks, offers great versatility for the tandem device fabrication processes (stability up to 800°C), and benefits from highly doped layers that are well suited for the formation of RJ. Among the variety of large EGap materials, perovskite (Pk) technology is the most popular solution as it benefits from both high efficiency potential and low production costs. The interface between the two cells (TOPCon and Pk) of the tandem device is usually formed by transparent conductive oxides layers such as ITO (Indium Tin Oxide), which shows excellent electrical and optical properties. However, indium is a critical material that could limit the long-term development of this technology. Therefore, the aim of this thesis is to explore indium-free approaches for the interface of Pk/c-Si tandem cells.The studies carried out in this work concern Pk/c-Si tandem cells in nip configuration, for which two alternative approaches for interface engineering are investigated. The first one uses no additional interface layer, while the second one integrates an nc-Si (n+) layer to form a silicon tunnel diode, which should provide an optimal recombination current. These two alternative approaches allowed better initial performances than the reference process, mainly by overcoming short-circuit issues in the Pk cell. Tandem devices featuring no additional interface layer show fill factors comparable to those of the world's best devices (>81%) and efficiencies close to 25%, confirming the potential of TOPCon passivated contacts to form indium-free RJ. However, these two indium-free approaches were limited by the appearance of internal series resistance over time. Advanced characterisations explain these degradations by the formation of a SiOx layer between silicon and SnO2 (the electron-selective layer - ESL- of the Pk cell).In conclusion, TOPCon passivated contacts are particularly well suited to obtain efficient recombination junctions (direct or via silicon tunnel diodes), thus eliminating the need to use indium in the interface layers. As silicon is particularly sensitive to oxidation, the choice of contacting layers (ESL in nip configuration) should be focused on a material that contains no oxygen or has a stronger affinity for oxygen than silicon.Le marché des modules photovoltaïque est dominé par les technologies basées sur le silicium cristallin (c-Si). L'utilisation de contacts passivés fabriqués à basse température (SHJ) ou haute température (TOPCon) mène à des rendements records (26,8% et 26,2%) proches de la limite théorique de 29,4%. L'option privilégiée par la majorité des acteurs pour dépasser cette limite consiste à associer la technologie c-Si avec un autre matériau semi-conducteur à large bande interdite (EGap) pour permettre une conversion optimale du spectre solaire sur toute la gamme énergétique. L'efficacité maximale théorique de tels dispositifs tandem peut alors atteindre 42%. Il semble avantageux de privilégier une structure à deux terminaux pour simplifier la mise en module et réduire les coûts associés. Cependant, cela implique de fortes contraintes sur les couches d'interface situées entre les deux cellules. En effet, ces dernières doivent alors permettre l'obtention d'excellentes durées de vie des porteurs dans chaque cellule, tout en assurant des propriétés optiques (absorption et réflexion parasites minimales) et électriques (jonction de recombinaison (JR) efficace et peu résistive) optimales.Pour la cellule c-Si, cette thèse se concentre sur la technologie TOPCon qui devrait dominer le marché d'ici 2030. De plus cette approche basée sur des empilements poly-Si/SiOx permet de disposer d'une grande versatilité pour les procédés de fabrication du dispositif tandem (stabilité jusqu'à 800°C), et de bénéficier de couches fortement dopées adaptées à la formation de JR. Le choix de l'absorbeur à large EGap s'est porté sur la technologie pérovskite (Pk) qui semble faire l'unanimité car elle combine potentiellement de faibles coûts de production et de hauts rendements. L'interface entre les deux cellules (TOPCon et Pk) du dispositif tandem est habituellement réalisée avec des couches d'oxydes transparents conducteurs comme l'ITO (Oxyde d'Indium Etain), permettant l'obtention d'excellentes propriétés électriques et optiques. L'indium est cependant un matériau critique qui pourrait limiter le développement de cette technologie à long terme. L'objectif de cette thèse consiste ainsi à explorer des approches sans indium pour l'interface des cellules tandem Pk/c-Si.Les études réalisées dans ces travaux concernent des cellules tandem Pk/c-Si en configuration nip, pour lesquelles deux approches alternatives sont étudiées pour l'ingénierie d'interface. La première n'utilise aucune couche d'interface additionnelle, et la seconde intègre une couche nc-Si (n+) pour former une diode tunnel en silicium afin d'obtenir un courant de recombinaison optimal. Ces deux approches alternatives ont mené à l'obtention de meilleures performances initiales que le procédé de référence, principalement en s'affranchissant de la problématique de court-circuits dans la cellule Pk. Les dispositifs tandem fabriqués sans couche d'interface permettent d'obtenir des facteurs de forme comparables à ceux des meilleurs dispositifs mondiaux (> 81%) ainsi que des rendements proches de 25%, démontrant le potentiel des contacts passivés TOPCon pour la formation de JR sans ITO. Ces deux technologies d'interface sans indium se sont cependant révélées limitées par l'apparition au cours du temps de résistances séries internes. Des caractérisations avancées expliquent ces dégradations par l'apparition d'une couche de SiOx entre le silicium et le SnO2 (la couche sélective d'électron - ESL- de la cellule Pk).En conclusion, les contacts passivés TOPCon sont particulièrement adaptés à la formation de jonctions de recombinaison (directes ou par le biais de diode tunnel en silicium) permettant de s'affranchir d'indium dans les couches d'interconnexion. Le silicium étant particulièrement sensible à l'oxydation, le choix de la couche de contact (ESL en configuration nip) devrait se porter sur un matériau ne comportant pas d'oxygène ou présentant une affinité pour l'oxygène plus forte que le silicium