Wednesday 2nd of july – 16:30
16:30
Restoring river systems by wood addition to the channel – practical examples
AUTHORS
KINGHAN Susie, MOTT Nick
United-Kingdom
Short Abstract: Historic removal of wood and dredging have contributed to incised single-thread rivers disconnected from their floodplain. The nature-based river restoration technique of introducing large wood to river channels has multiple benefits and can be self-restorative. These include improving habitat diversity, river-bed level raising, the formation of new in-channel features, floodplain reconnection, natural flood management, development of multithread river channels and improvement to water quality. This technique mimics the natural impacts of storm events and beaver activity. While the benefits of in-channel wood are well known, less information is available of how to implement this low-cost technique in relatively constrained contexts. The method described here uses a tractor winch to pull entire riparian trees into the river channel, and chainsaw felling to add more wood into the channel to accumulate on the structures. Ideal sites have some established woodland cover which can serve as a source of material to add to the river as well as space for river-floodplain reconnection. The size of trees should at least span the width of the river in order to be reasonably stable to avoid damage to downstream infrastructure. Two examples from the UK are presented below.
16:50
Large wood transport attenuation by riparian trees: field feedback from the Rieu Sec and Clamoux Rivers (Aude) after the October 2018 floods
AUTHORS
PITON Guillaume, DUPUIS Mathieu, BENAKSAS Swann
France
Short Abstract: During floods, particularly when they are morphogenic, rivers transport large wood pieces that sometimes clog bridges, culverts, dams and other narrow channel sections. This case study describe at two rivers in the Aude department (Rieu Sec and Clamoux) that experienced strong floods in October 2018. In both cases, large wood transport was observed, extreme in the case of the Rieu Sec and moderate in the case of the Clamoux. On the Rieu Sec, the volume of driftwood exported from the catchment is considered negligible, because black poplars (populus nigra) and platanus trees massively trapped the large quantities of large wood transported. On the Clamoux, this tendency at a meander in Villegly community had been identified by the basin agency: the riparian vegetation is maintained there with a view to encouraging this natural process. The aim of this report is to describe the two sites, their characteristics and their effects on the transport of large wood, with a view to drawing inspiration from them and reproducing these trends elsewhere. This natural regulation of large wood by riparian vegetation is thus complementary to civil engineering solutions as racks or flexible barriers and can be enhanced by a suitable riparian vegetation management.
17:10
Beaver presence and hydromorphological restoration of rivers in France: situation report and feedback
AUTHORS
Vivier Anne, Tales Evelyne, Brigode Pierre, Hurel Paul, Meslin Alix, Bressan Yoann
France
Short Abstract: The expansion of the beaver’s range in France and the increase in the number of hydromorphological restoration projects on rivers are leading to increasingly frequent interactions, which are likely to increase in the future. In order to gain a better understanding of this phenomenon, a survey aimed at managers of aquatic environments was carried out to identify the restoration sites concerned and to gather information on restoration projects, the presence of beavers before, during and/or after the restoration work and the consequences of this presence for managers and environments. Carried out as part of the DAM-IT program and based on the Network of demonstration sites for the hydromorphological restoration of rivers, the survey highlighted the wide variety of interactions between beaver and restoration, as well as the interest of respondents, the majority of whom are interested in taking part in a more in-depth study on the effects of beaver dams on the restoration of watercourses as part of the DAM-IT program.
17:30
How can the flood risk related to the presence of wood in rivers be managed? Some perspectives from the Loire in an intersectoral context
AUTHORS
HORTOBAGYI Borbala, MELUN Gabriel, BRAUD Stéphane, LE ROUX Guillaume, PETIT Stéphane, PITON Guillaume, WEROCHOWSKI Antoine, RUIZ-VILLANUEVA Virginia, ENNOUINI Wafae, PERSI Elisabetta, ROSSIGNOL Benoît, PIÉGAY Hervé
France
Short Abstract: Large wood, supplied to rivers from the fluvial corridor and hillslopes, plays an important ecological role by diversifying habitats and enriching river and terrestrial biodiversity. However, it may represent a risk when it accumulates into logjams, increasing the likelihood of flooding and threatening infrastructure, particularly bridges. These phenomena are likely to be exacerbated by extreme floods and forest decline associated with climate change. To manage these risks, it is crucial to better understand the wood budget, which encompasses the flux, sources, storage and transport of wood. Recent tools, such as cameras, RFID tracking and statistical and hydraulic modeling, allow for quantifying these processes and evaluating obstruction risks. Solutions such as logjam traps and forest managed to improve its floating wood natural trapping have been successfully tested to protect vulnerable infrastructure. On the Loire River catchment, experiments combining scientific research and operational management aim to integrate this knowledge to develop strategies that reconcile infrastructure safety with ecological preservation, while adapting to future climatic and hydrological challenges.