Barrie Creeks, Lovers Creek, and Hewitt's Creek Subwatershed Plan

The Barrie Creeks, Lovers Creek and Hewitt’s Creek Subwatershed Plan
intercept and treat stormwater prior to its entering watercourses or waterbodies. However, in
many older urban areas stormwater typically still reaches watercourses untreated
As the amount of impervious area increases, the natural water balance is disrupted.
Evapotranspiration is decreased as there is little vegetation and the permeable soil surface is
paved over; infiltration to groundwater is significantly reduced; and thus the runoff
characteristics change. This results in increases in the frequency and magnitude of runoff
events, a decrease in baseflow, and an increase in flow velocities and energy (further changes
to the hydrologic regime are discussed in greater detail in Chapter 4 - Water Quantity). These
changes further affect the form of the morphology of the stream, including channel widening,
under cutting, sedimentation, and channel braiding.
One of the most significant impacts of stormwater runoff though, is to water quality (discussed in
more depth in Chapter 3 – Water Quality). Problems with degraded water quality directly affect
the aquatic ecosystem. This occurs as pollutants are washed off of streets, parking lots,
rooftops and roadways into storm drains or ditches which discharge to watercourses and lakes.
Generally, concentrations of pollutants such as bacteria (e.g. Escherichia coli, faecal coliform,
Pseudomonas aeruginosa and faecal streptococci), nutrients (e.g. phosphorus, nitrogen),
phenolics, metals and organic compounds are higher in urban stormwater runoff than the
acceptable limits established in the PWQO (MOE, 1994). Other associated impacts include
increased water temperature and the collection of trash and debris.
All of these changes can cause considerable stress to aquatic biota, and can cause a shift from
a community containing more sensitive species to one containing species more tolerant of
degraded conditions (Figure 5-11).
Figure 5-11: Pathways by which impervious surfaces may impact aquatic biological communities
(ORMCP Technical Paper Series, #13).
Chapter 5: Aquatic Natural Heritage 230