Before the Colwood Creek watershed was developed for modern human use, Coastal Douglas Fir
forest covered most of the land. This forest type is relatively rare in British Columbia, as the plants that compose its structure require the dry summers and wet, mild winters that characterise southeastern Vancouver Island and the Gulf Islands. The vegetation in the Coastal Douglas Fir (CDF) biogeoclimatic zone varies depending on the local conditions, such as elevation, exposure (e.g. south-facing vs. north-facing), soil types and moisture. On of the best representation of this forest type in the Colwood Creek watershed is located on Royal Roads University grounds, in the lower part of the watershed. In this area, some majestic Douglas Fir giants remain; some rank among the largest in Canada and are over 800 years old. Near the creek itself can be found large western redcedar (Thuja plicata)
, bigleaf maple (Acer macrophyllum)
, skunk cabbage (Lysichiton americanum)
and salmonberry (Rubus spectabilis)
. As the only remaining, relatively natural, old-growth forest in the urban Victoria area, this forest is most valuable for research and education opportunities, as well as for wildlife habitat. Most of the rest of CDF forest in the watershed has been previously cleared for agriculture and urban development, although some areas of older second growth forest exist in the upper watershed.
Much of the watershed once consisted of Coastal Douglas Fir forest, like this one near Mt. Wells (photo: L. Townsend)
Garry Oak meadows are a subcomponent of CDF forests, and occur in particularly dry areas that have thin and/or rocky soils, or in areas with deeper soils where First Nations maintained the open meadows with periodic burning. A large area of Garry Oak meadows previously existed between Goldstream Rd. and Sooke Rd. in the watershed, but today only isolated clumps of this ecosystem remain (see images below). Although not shown on the map below, some small Garry Oak ecosystems also still exist near Royal Roads University, as well as in Mt. Wells Regional Park.
Garry Oak coverage in lower Colwood Creek watershed, circa 1800 (orange hatched area); source: CRD Regional Community Atlas
Garry Oak coverage in lower Colwood Creek watershed, circa 1997 (purple hatched area); source: CRD Regional Community Atlas
Along Colwood Creek and surrounding the lakes within the watershed are riparian zones, ecosystems composed of saturated soil and plants adapted to growing near water. Riparian zones are important for a number of reasons, including:
- storing water and preventing downstream flooding
- filtering potentially contaminated runoff from adjacent land
- controlling water temperature through shading
- helping to dissipate the energy of high water flows, and providing sheltered pools for fish, with large woody material
- providing nutrients in the form of tree litter for freshwater and marine invertebrates and fish
- providing habitat and food for wildlife
Many of the riparian zones in the Colwood Creek watershed, particularly in the highly developed mid section, were altered when much of the land was cleared for agriculture and residential development. The stream channel in many areas was deepened in order to allow faster drainage of the surrounding land. Unfortunately, this action disconnects the stream from its floodplain, creates more potential for erosion, and contributes to a lowered functional condition of the stream. Nevertheless, healthy riparian zones exist in the upper and lower watershed, where natural vegetation remains or has regenerated. Along the lower reaches of Colwood Creek, at Royal Roads University, some sections of the riparian zone have never been logged. In this area, the creek winds through giant Western Redcedar (Thuja plicata)
, Douglas Fir (Pseudotsuga menziesii)
and Bigleaf Maple (Acer macrophyllum)
trees, and is bordered by abundant Skunk Cabbage (Lysichiton americanum)
, ferns and Salmonberry (Rubus spectabilis)
. This riparian zone is valuable to researchers as a “reference site” that shows what many of the other creeks in the area used to look like. Glen Lake, in Langford, is also bordered by a riparian zone, despite a high density of housing in this area. Lower Colwood Creek: abundant riparian vegetation and large wood indicate a healthy stream (photo: L. Townsend)
Some wetlands in the Colwood Creek watershed are located: alongside ponds on Royal Roads University property; along the shores of Esquimalt Lagoon; at the outlet of Colwood Lake on the Colwood golf course; at the outlet of Glen Lake, and near the outlet of Humpback Reservoir (see photo below). These areas are important as habitat for aquatic organisms including fish, and for breeding and feeding areas for birds and other wildlife. They also help to regulate flows in the creek, storing rainwater during times of heavy rainfall and releasing it during the dry summers. Wetland downstream from Humpback reservoir, as seen in the fall (photo: L. Townsend)
Two large lakes are located in the Colwood Creek watershed:
- Humpback Reservoir was constructed in 1913 and was used as part of the water supply for Victoria until 1995. Water was delivered to the reservoir through a pipeline from Sooke Lake.
- Glen Lake is a natural lake called an “ice kettle.” A kettle is formed after a chunk of ice is left behind from melting glacier. When the ice chunk melts, the glacial till previously on top and beside it slumps inward and forms a depression.
A pond is located near Irwin Rd. in the upper watershed, and severl small ponds and two small ice kettles are also present on Royal Roads University lands.
Near the mouth of Colwood Creek, on the northwest shore of Esquimalt Lagoon, lies a small estuary fringed on the seaward side by salt marsh. Salt-tolerant vegetation grows here, including sea asparagus (Salicornia virginica), entire-leafed gumweed (Grindelia integrifolia), and seashore saltgrass (Distichlis spicata var. spicata). Estuaries are highly productive environments and provide important habitat and food sources for invertebrates (e.g. crabs, clams, zooplankton), juvenile Pacific salmon
and cutthroat trout
, as well as many types of seabirds, shorebirds and waterfowl.