As the city grows, the amount of natural ground cover changes dramatically. The Bowker Creek watershed once included extensive Douglas-fir forests, Garry Oak meadows as well as wetland areas. Remnant ecosystems remain but these are also under development pressure. Urbanization has replaced much of the natural vegetation and soil with concrete, asphalt, buildings and other impermeable surfaces. When it rains, water travels directly over these impermeable surfaces, into pipes and directly into the creek.
Less water is absorbed into the ground.
As a result, more water arrives in the creek channel far more quickly after it rains. Urbanization therefore tends to speed run-off and produce higher peak flows. The effect is shown in the graph below. Urbanization can also reduce summer low flows as less water is stored in the surrounding soil. A staff gauge for measuring stream flow has been installed on Bowker Creek near Trent Street.