Hydraulic Changes to Stormwater Flow Through Wetlands
Wetlands have been increasingly identified as important in ameliorating the impacts of stormwater flow. Key to understanding the attributes of wetlands is determining the behaviour of flow through wetlands. This report presents the average flow velocities for two wetland types (scrub-shrub and emergent) found within a natural wetland through the use of dye tracer tests. The study area was divided into wetland segments using the US Fish and Wildlife Service’s National Wetland Inventory (NWI) classification scheme and mapped using a Global Positioning System (GPS).
During different flow levels, dye was pumped into the headwaters of the wetland. The dye was collected with auto- samplers at several sampling stations located at the transition zones between wetland segments. Results indicate that there is a significant difference in the flow characteristics between scrub-shrub and emergent wetland types. Differences were also found between leaf-on and leaf-off seasons. High data variability was found for samples collected furthest from the dye injection point. The range of velocities observed for scrub-shrub classified segment during the leaf-on season was from 1.11 to 23.08 m/min. For the emergent classified segment, the range of velocities was from 1.54 to 7.68 m/min. Differences in the velocities between the two types of wetlands could be attributed to the sinuosity of the stream channels and the vegetation in the floodplain that is associated with each type of wetland. The range of velocities observed for scrub-shrub classified segment during the leaf-off season was from 0.45 to 11.31 m/min. For the emergent classified segment, the range of velocities was from 0.39 to 7.64 m/min.
Differences in the velocities between seasons could be attributed to the amount and type of leaf litter found in the floodplain zones of the wetland. Currently, these results are being evaluated at a different wetland system to verify the findings. Improving our understanding of flow behavior of wetlands will lead to improved design parameters for natural wetland restoration. The findings from this study have also been used to develop a model to simulate flow through a naturally occurring wetland
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