Bowker Creek Watershed
Concerns
Stream channel degradation
A major limiting factor on Bowker Creek is the high degree of channel degradation that has occurred over the years. Natural stream channels are in balance with the landscape and with the amount of sediment transportation that occurs in the system. Features such as meanders in the channel, large rocks and fallen trees help to dissipate the energy of high flows and protect the stream channel from damage due to erosion. They also create new floodplains when sediment is deposited between obstacles and along the banks. Floodplains and riparian vegetation in turn help to soak up excess water and provide food and habitat for wildlife. Bowker Creek, like many urban streams, has been straightened, deepened and “armoured” with materials such as rock and cement, in order to speed the transfer of water off the land. The stream has been disconnected with its floodplain, which has been converted to urban land. The drawback to these modifications is that very little is left in place to slow down the flow of water in the creek, and with no riparian zones or floodplains remaining, little excess water is soaked up or stored. This results in erosion of stream banks, flooding of adjacent properties and degradation of aquatic and riparian habitat.
The good news is that restoration options for certain sections of the creek are being investigated, with a focus on restoring some natural features. Although the creek will probably never return to its original state, reincorporating some features such as floodplains and constructed wetlands will help improve ecological function and will help to reduce the risk of flooding.
Impervious surfaces
A large percentage of the surrounding land in the watershed consists of impervious surfaces such as roofs, roads and parking lots. These areas create problems for adjacent streams because rain water does not soak into the ground as it would in natural vegetated areas. Rather, it rushes quickly into storm drains which are in turn connected to streams and marine waterbodies. Large volumes of quickly flowing water contain a lot of energy that can cause erosion of stream banks and flooding of adjacent land, particularly in channels that have been degraded, as described above. Contaminants from these surfaces, such as automotive oil and fluids, are also flushed into streams and marine areas (see Pollution for more information on these and other toxic substances). Fortunately, knowledge about this concern is growing, and many options are now available for reducing impervious surfaces in new developments or in retrofits of existing infrastructure.
Habitat loss and degradation
A tremendous amount of wildlife habitat in the Bowker Creek watershed was lost when the land was cleared, first for agriculture and later for urban development. Riparian zones adjacent to streams are particularly important for habitat as well as for filtering contaminants and for preventing damage due to floods and high flows. Much of this vegetation has been removed and the stream banks have been armoured with materials that prevent its regeneration. This has decreased the available habitat for aquatic organisms, birds and mammals. Invasive plant species also tend to crowd out native varieties and create monocultures that are less valuable as wildlife habitat.
Although some habitat loss is inevitable in a growing urban area, key ecosystems can still be protected and restored. For example, some areas along Bowker Creek have been replanted with riparian vegetation by volunteers including school children. The District of Saanich undertakes Garry Oak restoration projects in the Bowker Creek watershed; one ongoing project is located at Campus View Elementary school, across from the University of Victoria (see the Garry Oak Restoration Project webpage for more information). See the following links for more information about how habitat loss and degradation occurs, and what you can do to help prevent habitat loss and degradation.
Water quality
The water quality of Bowker Creek limits the types of freshwater species that can live in the creek, and also affects the marine ecosystems in the receiving environment, i.e. Ross Bay. For example, excess sediment, which is introduced when large volumes of rainwater cause erosion of the stream banks, can bury bottom-dwelling organisms such as mussels and oysters. Cloudy water also decreases the amount of sunlight that penetrates, making it difficult for freshwater algae, marine kelp and eelgrass to grow. A study undertaken in 2000 found that the water quality in Bowker Creek was “acceptable” for aquatic life most of the time, but in the first flush after a rainstorm a major increase in contamination occurred. Potential contaminants in this creek include: oil, gasoline and other auto fluids washed off roads; excess nutrients from fertilizers applied to lawns and gardens as well as from pet droppings; and various chemicals and rubbish that may be disposed of in the creek and/or in storm drains that feed into the creek.
Flooding and safety
Certain sections of Bowker Creek flood during heavy rainstorms, for example upstream of Trent Street near St. Patrick’s school. Local governments are considering options to mitigate this problem, and the channel near St. Patrick’s has recently been upgraded to allow better water flows. Certain strategies, such as creating wetlands and/or ponds next to the stream channel, can create more water storage area and help prevent downstream flooding, while also increasing wildlife habitat. Opportunities for these types of projects are fairly limited in Bowker Creek since so much of the adjacent land is tied up in private property.
Invasive species
Invasive species are a concern in the Bowker Creek watershed, and have been introduced in a variety of ways: some are escaped garden ornamentals; many grasses were used for grazing and haying; and some were introduced in unknown ways. Some of the main invasive species present in this area include: Scotch broom (Cytisus scoparius), Himalayan blackberry (Rubus discolor), yellow willow (Salix lutea), weeping willow (Salix babylonica), holly (Ilex aquifolium), daphne (Daphne laureola), English ivy (Hedera helix) and Kentucky bluegrass (Poa pratensis). Invasive species tend to out-compete native species, and may create monocultures that reduce the biodiversity of the ecosystems in which they live. The non-native willows also tend to clog the stream channel with their aggressive root systems.
