Influence of Development on Peri-urban Headwater Streams in Calgary, Alberta

Abstract

The natural connection between surface water and groundwater is inevitably altered by urban development. However, the degree of alteration is dependent on the physical and climatic characteristics of a watershed as well as the development characteristics. The goal of this study was to compare a developed and an undeveloped headwater catchment in Calgary, Alberta, to understand the influence of urbanization on streamflow response to precipitation, groundwater contributions to streamflow, and the spatial and temporal variability of streamflow in a low relief, semi-arid landscape. Hydrometric measurements of streamflow, groundwater, and precipitation were used in conjunction with electrical conductivity and stable water isotopes to compare streamflow regimes and assess the impact of development. The developed Sage Hill ravine (SHR) stream had significantly smaller runoff ratios and smaller maximum event water fractions than the undeveloped Glacier Ridge ravine (GRR) stream, which was attributed to the capture and rerouting of urban stormwater away from the stream. Groundwater was shown to be an essential source of flow to both streams. Baseflow separation and stable water isotopes showed that 95% and 86% of the cumulative streamflow volume in SHR and GRR, respectively, was from baseflow sourced from shallow groundwater. Additionally, spatial and temporal differences in streamflow between SHR and GRR were attributed to the geologic heterogeneity of the shallow subsurface. Although this study did not directly identify cause-and-effect relationships of streamflow characteristics and urban development, it did identify the importance of effective area, groundwater, and geologic heterogeneity on the generation of streamflow. These findings will be useful for improving our understanding of how future development might impact streamflow, informing urban water resource management, and protecting valuable urban ecosystems.