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Dredging in the rivers of the Ardenne is generally carried out on a smaller scale to that described in the literature and is not conducted for commercial purposes. Extractions within the river channel are made in order to prevent flooding; hence the quantity of gravel extracted is limited. This study aims to evaluate the impact of dredging and the resilience of the riverbed in the Semois. This river is found in the south of the Ardenne region and is characterized by large incised meanders, a narrow floodplain, few pebble bars, numerous bedrock outcrops and a limited stock of sediment. The bed is particularly flat and shallow and the bankfull discharge (130 m3s−1) is frequently attained (0.9 yr). Pebble tracers allowed the critical parameters (discharge, Shields criterion, and stream power), the diameter of mobilized sediment and the distance of sediment transport to be determined. A major dredging campaign resulted in the formation of a channel nearly 1 km long and 2 m deep which functioned as a sediment trap. Topographical cross‐sections made before and after the dredging campaign and again 4 yr later allowed bedload discharge to be estimated (1.1 t km−1yr−1). In order to examine the efficiency of the sediment trap, the sediment transport equations of Meyer‐Peter and Müller, Schoklitsch, Bagnold and Martin were applied. With the exception of Bagnold's equation (1980), the observed transport values and those calculated theoretically are relatively close. Between October 1997 and June 2001, 5010 t were caught in the sediment trap. For the same period the equations calculate values between 6147 and 10 571 t. The overestimation from the theoretical calculations may result from a lack of sediment supply due to the characteristics of the basin and the frequency and magnitude of flood events during the study period. From the magnitude of the sediment transport rate, a return to the initial state of the riverbed (before dredging) may be expected after approximately 10 yr. Despite the scale of the dredging campaign for a river of this size, its results are limited in terms of flood prevention. Copyright © 2005 John Wiley & Sons, Ltd.

Reach‐scale at‐a‐station hydraulic geometry (AHG) relationships are power laws that describe variations of reach‐averaged water depth, wetted width, and current velocity in stream reaches when discharge varies. Modeling AHG exponents is important, because the variations of hydraulics with discharge in stream networks influence physical habitats of aquatic species, biodiversity, water temperature, nutrient fluxes, and sediment transport. Theoretical approaches indicated that AHG exponents should depend on topographic descriptors of cross sections and roughness elements. Empirical approaches suggested that AHG exponents partly depend on hydraulic characteristics measured at a single discharge. We used a unique data set of AHG observed in 812 stream reaches (obtained from measurements at several discharge rates or from hydrodynamic models) to (1) test the consistency of theoretical and empirical predictions of AHG exponents and (2) test the generality of AHG predictions across rivers of different countries with variable landscape settings. We found that observed AHG depended on topographic predictors (describing cross‐section shape and substrate size) as expected from theory. However, AHG exponents were better predicted by empirical hydraulic characteristics of reaches: the ratio of wetted width to bankfull width and the reach Froude number. The effects of hydraulic variables were consistent with those of topographic predictors. In addition, relations between AHG and hydraulic predictors were significant and with similar direction in different data sets. Despite limited explanatory power, our results help identifying general drivers of AHG exponents. Their application still requires measurements at a single discharge rate but open perspectives of generalized AHG prediction by remote sensing. At‐a‐station hydraulic geometry of stream reaches governs habitats, sediment, nutrient, and pollutant fluxes in river catchmentsDespite low R2values, hydraulic geometry exponents in 812 reaches are consistently explained by empirical and theoretical approachesThe Froude number of reaches and the ratio of wetted to bankfull width influence hydraulic geometry similarly in different continents