Water temperature variability at culvert replacement sites and river thermal impacts related to the removal of an old sediment pond: application on the Barnet Brook and a tributary of the Nerepis River (New Brunswick, Canada)

Culverts are very important hydraulic structures for stream crossing, and they come in various shapes and materials. There are generally two different types of culverts, i.e., closed bottom and open bottom structures. In the present study, two closed bottom culverts have been replaced by open bottom structures (arch culverts) during the summer of 2018. The objective of the present study was to analyze water temperature variability along the impacted sites, one year after the replacement, i.e., 2019 to assess potential impacts of the streamside vegetation removal on the thermal conditions of these streams. Results showed a significant (p < 0.05) change in mean summer temperatures at both sites. Changes in stream temperatures at Barnet Brook were attributed to the removal of an old sediment pond, whereas changes in stream temperatures at the tributary of the Nerepis River were likely due to the removal of the streamside vegetation. Increases in water temperatures (> 4 °C) were more pronounced during low flow periods compared to high flow conditions at both sites.

Urban buried streams: Abrupt transitions in habitat and biodiversity

Stream burial, the rerouting of streams into underground culverts, is common in industrialized and densely populated urban areas. While stream burial is common in urban environments, direct characterization of the within-culvert environment is rare and it is unclear if buried reaches reflect neighboring open reaches regarding habitat, biota, and water chemistry. Additionally, for a buried stream, the entrance and exit of the culvert are abrupt habitat transitions within the stream channel, and it is unknown if these transitions lead to similarly abrupt responses in biotic and abiotic characteristics or if responses are gradual. Quantifying the within-culvert environment and transitions upon entering/exiting the culvert has rarely been done but can help inform management practices regarding how these systems are impacted and establish a baseline for evaluating daylighting or stream restoration projects. To understand how culverts affect longitudinal biotic and abiotic characteristics of urban streams, we evaluated longitudinal patterns of physical habitat characteristics, stream water physiochemistry, periphyton biomass, and macroinvertebrate density and diversity in two urban streams that included long (>100 m) culvert reaches. Abrupt transitions in a suite of abiotic and biotic variables were observed at the entrances and exits of the culverts whereas some variables showed no response to the culvert presence. Periphyton biomass and macroinvertebrate density were reduced by 98% and 92%, respectively, by culverts in the two streams. Within the culverts, we observed greater water depths (average of 10 cm outside vs 26 cm within the culvert), finer benthic substrate, and diversity of macroinvertebrates was reduced by 50%. Nutrient concentrations, in contrast, showed no response to the presence of a culvert. Within 60-90 m downstream of the culvert exits, most of the measured parameters returned to levels similar to those observed upstream of the culvert, suggesting that the ecosystem impacts of urban culverts, though dramatic, may be spatially constrained.

A web-based geovisual analytics platform for identifying potential contributors to culvert sedimentation

Sediment accumulation at culverts involves large-scale and interlinked environmental processes that are difficult to address with experimental or physical modeling methods. This article presents an alternative data-driven investigation for shedding insights into these processes. Accordingly, a web-based geovisual analytics application, the IowaDOT platform, was developed, which allows users to explore the complex processes associated with the sediment deposition at culverts. The platform provides systematic procedures for (1) collecting and integrating analytical variables into a single dataset, (2) quantifying the degree of culvert sedimentation using time series of aerial images, (3) identifying drivers that contribute to culvert sedimentation processes from a variety of culvert structural and upstream landscape characteristics using a tree-based feature selection algorithm, and (4) facilitating the understanding of complex spatial and relational patterns of culvert sedimentation processes using multivariate geovisualizations supported by a self-organizing map (SOM). As the outcomes of this study, these patterns identify culvert sedimentation-prone regions in Iowa and quantify empirical relationships between the drivers and culvert sedimentation degrees. A simple evaluation of the platform was performed to assess the usefulness and user satisfaction of the tool by professional users, and positive feedbacks are received.