The spatial distribution of hydraulic conductivity (K) in riverbeds is essential to understand and model river-groundwater interactions. However, K in riverbeds varies over several orders of magnitude and its spatial distribution is closely linked to complex geological and fluvial processes. Investigating the local distribution and spatial heterogeneity of K is therefore a challenging task. The use of direct current (DC) and time-domain-induced polarization (IP) geoelectrical methods to map qualitatively the spatial distribution of K within riverbeds is described. The approach is demonstrated for a test site situated in a typical lowland river in Belgium. Inverted geophysical parameters (resistivity, chargeability and normalized chargeability) are compared with estimates of K obtained through slug tests. In general, high values of K are observed in the middle of the river and lower values towards the banks, while the opposite is true for chargeability and normalized chargeability. Therefore, there exists an inverse correlation between K and IP geophysical parameters. Furthermore, geostatistical analyses using variograms show that all parameters have ranges of similar magnitudes. The strong correlation between K and chargeability or normalized chargeability can be explained by the fact that all three parameters are mainly controlled by clay and organic matter content.
In Flanders (Belgium), one in three journeys between home and school by adolescents (12-18 years) is made by bike. Sadly, most cycling accidents also occur in this age group. Although research and cycling policies advocate for safer school environments, their focus is often limited to a restricted area near the school gate. Not only school environments but also trajectories to school and adolescents' experience along it should be considered when designing cycling policies. Therefore, we investigated perceived cycling safety and its relation with the environment along home-to-school routes of adolescents in Flanders. Data were collected using a location based service (LBS) developed for secondary schools. Relations between perceived cycling safety and a wide range of both subjectively scored and objectively measured environmental data were analysed using multilevel linear regressions, at the level of routes, road segments, and intersections. The models show that traffic volume and cycling infrastructure have the strongest associations with perceived safety, and that accident data have a significant relation as well. Therefore, we believe that decreasing traffic volume and enhancing cycling infrastructure will increase adolescents' cycling safety perception. Furthermore, the results of this study underline the promising value of LBS to develop proactive and stimulating cycling policies.
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