Effects of hydraulic resistance by vegetation on stage dynamics of a stormwater treatment wetland

summary This work examined the potential effects of large-scale thinning of emergent vegetation on the stagedynamics in a very large (33.3 km 2 ) constructed treatment wetland in South Florida. Dense vegetativebiomass in treatment wetlands may restrict water flow and increase water levels, which may in turn haveadverse effects on vegetative community structure. Here, we developed a physically-based, spatially-dis-tributed hydrodynamic model of Stormwater Treatment Area 2, Cell 2 (STA2C2) to investigate the spatio-temporal variability of water level (stage) in response to management for thinning of emergent macro-phytes (e.g., burning and/or herbicide treatments). The model was calibrated against stage measuredat six monitoring stations for 1 year, and subsequently validated against 2 years of stage data from eightstations. Finally, the validated model was extended to simulate various vegetation management scenar-ios. The model provided an excellent fit to observed stage data in both calibration and validation periods(median model efficiency indices of 0.82 and 0.83, respectively). Higher stages in the treatment cell weredominantly associated with peak inflow magnitude and the timing of event intervals. Prolonged periodsof sustained deep water conditions were observed when one flow peak was followed by consecutivepeaks. A gradual stage gradient from the inlet to outlet was observed during peak flow periods, with ashift to a sharp gradient at approximately two-thirds distance from the inlet. Stages in the wetland werefound to be controlled less by the hydraulic resistance, as indicated by a low sensitivity of simulatedwater levels for a ±50% perturbation in flow resistance parameter. Water depths were reduced by a max-imum of 12 cm at the inlet region by thoroughly thinning the remaining emergent vegetation in STA2C2.Similarly, a maximum of only 2% of the total STA2C2 area was prevented from exceeding a water depthbelieved to be detrimental to Typha sp. (1.22 m) after the highest peak inflow. Collectively, our findingssuggested that vegetation thinning may not be effective for minimizing deep water conditions in STA2C2. 2013 Elsevier B.V. All rights reserved.