Flood-Drought Hazard Assessment for a Flat Clayey Deposit in the Canadian Prairies

Abstract

Dry climate, clayey soil, and flat topography govern water balance in the southern part of the Canadian Praries. The main purpose of this work was to assess flood-drought hazard using Regina as a typical urban centre in the region. Results indicate that extreme weather patterns are frequent and meteorological parameters have changed from 1970 to 2015: precipitation (+50 mm), air temperature (+0.9oC), relative humidity (+6%), wind speed (-1.35 km/hr), and solar radiation (+0.9 MJ/m2). In the dry climate (Dfb), 77% of the total annual precipitation (386 mm/year) occurs from April to September. The runoff coefficient of 0.6 relates to 63% impervious areas (commercial, industrial and residential) and 35% near-impervious areas (open spaces with low hydraulic conductivity). The flat topography (570 m through 600 m asl over 124 km2) along with a low channel slope of up to 0.4% results in water ponding during short-term and high-intensity rainfalls. Water is managed through the Wascana Creek that holds 98% of the total water volume (84 x 106 m3) in the city. From April to September, volume fluctuations depend on antecedent water levels and meteorological conditions. The city has recently received several events of flash floods (2010 and 2014) and long-term droughts (1984 and 2017). The negative average change in storage indicates drought-like conditions during spring-summer.

Keywords: flood-drought, hazard assessment, flat terrain, clayey deposit, dry climate