Online

Lawson, Kenneth Scott Feasley

Civil and Environmental Engineering

2023

M.S.

Proper characterization of river flow is essential for the development of structural and non-structural measures to reduce flood damages, restore ecosystem functions, and manage environmental contaminants in riparian zones. In particular, the duration of flood events is an important feature of floods that drives riverine processes such as erosion, geomorphic adjustment, habitat suitability, nutrient and water quality dynamics, and structural damage. Despite this, most flood characterization methods focus solely on relating the magnitude of annual-maximum discharges to frequency, without addressing the duration of flood events. We investigated event-specific discharge-duration dynamics at 33 USGS stream gages within the US state of Vermont. Building on the method of Feng et al. 2017, flood events from 15-minute discharge timeseries were extracted using an automated threshold method, and a statistical model was fit at each gage for both frequency of discharge exceedance and conditional duration of discharge exceedance. This Duration-Over-Threshold model can estimate the arrival rate of a flowrate threshold, q, being exceeded for a given duration, d. Fitted model parameters were compared to basin and channel physiographical characteristics to develop regional regression equations and examine potential watershed processes underlying the duration dynamics. Flood duration and hydrograph rate of recession were found to be best predicted by drainage area, mainstem slope, and soil depth/type. The regional regression equations enable design event estimation in ungauged catchments of the study region, which may be used to improve the predictive capacity of hydraulic and ecosystem models, outline a range of potential geomorphic trajectories, or inform emergency management plans and flood damage rating curves.