The Saint‐Sauveur dam was built in 1992 in the middle section of the Buëch River. Downstream of the dam, a channel incision by several meters was observed. A gravel replenishment operation was planned in order to restore the active channel. An equivalent of two times the mean annual bedload‐transport capacity (43,500 m3) was replenished downstream of the dam in September 2016. The aim of this paper is to quantify morphological change associated with sediment remobilization in order to evaluate the efficiency of the restoration works. The monitoring was based on a combination of (a) change detection using sequential high‐resolution digital elevation models (from airborne LiDAR data), (b) bedload tracing using active ultrahigh‐frequency radio‐frequency identification technology, and (c) complementary field surveys of channel grain‐size distribution and morphology for bedload‐transport computation. Field monitoring allows us to capture a net aggradation along a 2‐km reach after the first post‐replenishment flood. A sediment balance analysis was performed to back‐calculate bedload supply coming from the sluicing operation during the flood. Although the sediment replenishment operation clearly had a positive impact on the morphological conditions of the starved river reach, the effective bedload supply from artificial berms (22,650 m3) was insufficient to initiate substantial channel shifting along the restored reach and a subsequent amplification of the sediment recharge. The combination of high‐resolution topographic resurveys and sediment tracing was successful to evaluate the downstream propagation of sediment replenishment effects.

RESUMETo sector a stream, classify It and choose the study reaches which could give o reliable picture of it, It is necessary to have a good knowledge of the morphological feotures (faciès) types llkely to be encountered.The Identification of thèse units wlll t>e done In the fleld using some simple crlterlo such as water depth, stream veloclty, sédiment size, cross section shape, longitudinal profile and plan vIew.ThIs wlll be carried out during low flow stage In order to observe the more varled flow conditions, whichIs not the case when the discharge Increases and smoothes the free water surface.

RÉSUMÉLa détermination visuelle des faciès des cours d'eau lors d'une visite de terrain est toujours délicate. Elle peut donner lieu à des appellations et des interprétations différentes de la part de plusieurs observateurs. Afin de mieux standardiser ce type d'observation, nous proposons une clé de détermination empirique basée sur une expérience d'expert. Cette clé est applicable en l'état pour les cours d'eau de taille moyenne à grande (jusqu'à plus de 100 m de large) mais peut demander des adaptations pour les très petits cours d'eau (largeur inférieure à 2 m).Les variables discriminantes de premier niveau conseillées sont la hauteur d'eau (supérieure ou inférieure à 60 cm) et la vitesse d'écoulement (supérieure ou inférieure à 30 cm/s). Elles sont facilement observables lors d'un étiage moyen. D'autres critères complémentaires sont également discutés comme la forme du profil en travers. Des conseils opératoires sont prodigués.Lorsque l'on veut établir un lien entre la nature des faciès et la biologie, il est prudent de tenir compte également de l'hydrologie et donc de la dynamique temporelle des variables physiques d'habitat. Les mesures quantitatives simples proposées permettent de renseigner les équations de géométrie hydraulique qui établissent les relations entre la largeur mouillée, la hauteur d'eau, la vitesse et le débit, grandeurs plus pertinentes pour établir un lien avec la biologie. Mots-clés : faciès morphodynamiques, géométrie hydraulique, mésohabitat.Bull. Fr. Pêche Piscic. (2002) ABSTRACTThe direct visual appreciation of geomorphic unit (GU) in running waters is always delicate. Some misinterpretation is frequent among different observers. To standardized the GU description, we proposed a decision key, based on expert' experience. The first discriminative variables are the water depth (limit at D = 60 cm) and water velocity (limit at V = 30 cm/s). They are easily observable at an average interannual low flow. Else complementary criteria are also argued, particularly the transversal water profile. Any operating advices are also given.In order to link GU and biology, it is advisable to take into account the hydrology as a dynamic physical control factor of the aquatic system. Quantitative measurements are usefull to work with the hydraulic geometry equations. These equations linked width, depth, velocity with discharge. All of them are more pertinent variables to rely physics and biology.

SUMMARYHydrobiology sludies deal more oit en with pollution problems in running waters than with those concerning sire a m régulation or détérioration of physical integrity of streams and ri vers.Il is more and more obvious lhat running water ecology is strongly related to hydrotogical charade ristics which structure aquatic habitats.

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