Description of flow through a natural wetland using dye tracer tests

Abstract A series of dye tracer tests was performed to determine average flow velocities through various segments of a natural wetland located in Westchester, NY. The wetland was divided into segments using the US Fish and Wildlife Service's National Wetlands Inventory (NWI) classification scheme and mapped using a Global Positioning System (GPS). During different levels of flow, 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 a significant difference in flow characteristics between two classification types, scrub–shrub and emergent. High data variability was found for samples collected furthest from the dye injection point. Velocities observed for the scrub–shrub-classified segment ranged from 1.11 to 23.08 m/min; for the emergent-classified segment, velocities ranged from 1.54 to 7.68 m/min. Differences in the velocities between the two wetland types can be attributed to sinuosity of the stream channels and vegetation in the flood plain associated with each type of wetland. Results have been used to develop a model to simulate flow through a naturally occurring wetland and could be used to improve design parameters for natural wetland restoration.