Groundwater flooding in a river-connected alluvial aquifer

Abstract

Groundwater flooding can occur when the water table rises due to (a) recharge to (or decreased abstraction from) aquifers with low storativity or (b) propagation of the rising river stages into permeable, river-connected alluvial aquifers. The latter type was significant in 2013 in Alberta. A survey of 189 homes along the Elbow River in Calgary examined the basement flooding water characteristics and the initial route of floodwater entry. In homes where the initial route of entry was known, 88% were initially flooded by groundwater, and 12% reported exclusively groundwater flooding. Basement floor elevation was correlated with the severity of flooding (R2 =.61). Of the 19 surveyed homes located outside of the 100-year overland flood zone, 47% were flooded by groundwater, indicating that groundwater flooding reaches beyond overland water-flooded areas. Hydrogeological modelling demonstrated that propagation of increased river stage into the aquifer could reasonably have caused the observed groundwater flooding. Groundwater flood resilience strategies could include (a) monitoring groundwater levels in flood-prone areas to differentiate sewer backup from groundwater flooding via wastewater collection systems and to provide groundwater flooding warnings, (b) specifying minimum home basement elevation with respect to river stages for specified flood return intervals, and (c) appropriate home construction.