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Dynamics of groundwater floodwaves and groundwater flood events in an alluvial aquifer

By Thomas Buffin-Bélanger, Claude-André Cloutier, Catherine Tremblay, Gwénaëlle Chaillou and Marie Larocque

Abstract

In gravelly floodplains, streamflood events induce groundwater floodwaves that propagate through the alluvial aquifer. Understanding groundwater floodwave dynamics can contribute to groundwater flood risk management. This study documents groundwater floodwaves on a flood event basis to fully assess environmental factors that control their propagation velocity, their amplitude and their extension in the floodplain, and examines the expression of groundwater flooding in the Matane River floodplain (Québec, Canada). An array of 15 piezometers equipped with automated level sensors and a river stage gauge monitoring at 15-minute intervals from September 2011 to September 2014 were installed within a 0.04-km2 area of the floodplain. Cross-correlation analyses were performed between piezometric and river-level time series for 54 flood events. The results reveal that groundwater floodwave propagation occurs at all flood magnitudes. The smaller floods produced a clear groundwater floodwave through the floodplain, while the largest floods affected local groundwater flow orientation by generating an inversion of the hydraulic gradient. Propagation velocities ranging from 8 to 13 m/h, which are two to three orders of magnitude higher than groundwater velocity, were documented while the induced pulse propagated across the floodplain to more than 230 m from the channel. Propagation velocity and amplitude attenuation of the groundwater floodwaves depend both on flood event characteristics and the aquifer characteristics. Groundwater flooding events are documented at discharge below bankfull (< 0.5 Qbf). This study highlights the role of flood event hydrographs and environmental variables on groundwater floodwave properties and the complex relationship between flood event discharge and groundwater flooding. The role that groundwater floodwaves play in flood mapping and the ability of analytical solutions to reproduce them are also discussed

Topics: Aquifers, Banks (bodies of water), Groundwater, Groundwater flow, Groundwater resources, Risk management, Rivers, Time series analysis, Velocity, Aquifer characteristics, Complex relationships, Cross-correlation analysis, Environmental factors, Environmental variables, Groundwater velocity
Year: 2015
DOI identifier: 10.1080/07011784.2015.1102651
OAI identifier: oai:www.archipel.uqam.ca:8908

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