Colquitz River Watershed
Physical changes to the creek channel from historical agricultural activities including ditching, draining and channelization to improve crop land, and removal of water for crop irrigation and livestock have left a legacy of decreased ecological functioning of the Colquitz. Fertilizer and pesticide use on both agricultural and residential lands has also contributed to decreased water quality and contributed to algal blooms and low oxygen levels in places like Swan Lake.
Urbanization and the increased amount of impervious surfaces such as roads, parking lots and roofs have also caused significant changes to the watershed, increasing the flooding frequency and severity, and the “flashiness” of the Colquitz and its tributaries. Clearing of land for agriculture and residential use also brought a significant decrease in vegetation cover which in turn contributes to decreased water quality, creek bank erosion and flood potential.
Changes to creek morphology have resulted in areas where the creek has been separated from its natural floodplain, causing flooding of roads and properties during heavy rain events.
Several industries and commercial operations adjacent to the Colquitz also used the creek and its tributaries as a water source as well as a dumping ground for septic waste and municipal sewage treatment plant effluent. For over 40 years, two wineries discharged their untreated effluent into Swan Creek.
Home heating oil spill incidents have spiked in recent years (2011/12), affecting salmon and other sensitive species in the watershed. On the positive side, this has led to improved response times by local agencies to clean up and remediate affected areas. An awareness campaign for homeowners outlining their responsibilities regarding oil tanks on their property has been undertaken by the District of Saanich (http://saanich.ca/living/environment/pdf/OilTanks2012.pdf). These oil spills have also prompted the initiation of a restoration project on Swan Creek (http://peninsulastreams.ca/.
Removal of the native riparian vegetation for ditching, draining and straightening the Colquitz, and other disruptive activities in the watershed paved the way for the introduction of invasive plants. These generally have few natural controls, and spread rapidly along watercourses and adjacent areas. They are often difficult to remove or eradicate, and degrade natural areas by reducing habitat quality and diversity, and providing low food value for wildlife and birds. They frequently cause the disappearance of native plants upon which many other species depend. Many plants are “garden escapees” that have originated in residential gardens and are now proliferating in natural areas. In some cases introductions of invasive plants are due to people dumping yard and garden waste into riparian and other natural areas.
Invasive species that pose the biggest problem in the Colquitz watershed include:
|Common Name ||Scientific Name |
|English hawthorn ||Crataegus monogyna |
|Holly ||Ilex aquifolium |
|Spurge laurel ||Daphne laureola |
|Scotch broom ||Cytisus scoparius |
|Himalayan blackberry ||Rubus armeniacus |
|English ivy ||Hedera helix |
|Japanese knotweed ||Fallopia japonica |
|Morning glory ||Ipomoea indica |
|Yellow-flag iris ||Iris pseudocorus |
|Purple loosestrife ||Lythrum salicaria |
|Reed canary grass ||Phalaris arundinacea |