Water flows in the Koksilah are out of balance. During winter storms water rushes in torrents down the streams and river scouring the channels and degrading fish habitat. In the summer flows reach critically low levels and are no longer able to meet the needs of fish and residents.

Koksilah flows are naturally variable as a result of:

  • Location – east side of Vancouver Island where summers are warm and dry.

  • Elevation -headwaters are in the maritime rain-snow transition zone where the precipitation changes frequently beween rain and snow and snow pack cannot be counted on to store water into the spring.

  • Flow Regulation -water is stored and released from the small lakes, numerous wetlands and underground aquifers of the watershed. Without a big lake to store and gradually release water throughout the year, stream flows tend to change rapidly and often dramatically when it rains. Flash floods in the winter and low flow conditions in the summer are common.

And today water supply is more erratic due to:

  • Land Use – Tree removal, including, extensive short rotation clearcutting, a dense road system, and water use have exacerbated the natural “flashiness” and low flows. Imagine stepping back in time several hundreds of years to when the landscape was dominated by towering old growth forests. Those forests combined with the 4 small lakes and many wetlands meant that precipitation percolated slowly into the ground and into the streams. While flows were naturally sensitive to rain the landscape functioned more like a sponge, holding the water for slow release through the year.

  • Climate Crisis – we are experiencing warmer, wetter winters and hotter drier summers and it is going to get worse. Scientists are predicting an extreme drought event now will be an average summer 30 years from now.

Koksilah River

low water

Koksilah River

high water

Flow

In August 2019, as once again Koksilah River flows reached critically low levels (0.18 m3/s), the province restricted water use for the irrigation of forage crops such as hay and corn. Following the drought work a study was undertaken to find out if the order had been effective and it was determined that flows increased by about 50% (0.31 m3/s) by early September.

River flow data

Publicly accessible real time and historic measurements of water levels and flow are available for the Water Survey of Canada monitoring station located near the Koksilah Road bridge. Keep in mind that these measurements require manual calibration so they are labelled “provisional” (unverified) until the calibration is complete (final). i.e. If the line is green or yellow, the data is provisional. Disruptions to the water flow around the gauge can impact real-time accuracy.

  • A streamflow which is greater than the 75th percentile is considered above normal
  • A streamflow which is between 25th and 75th percentiles is considered normal
  • A streamflow which is less than the 25 percentile is considered below normal
  • A Streamflow which is less than 10 percentile is considered much below normal
  • The flow category Low indicates that the estimated streamflow is the lowest value ever measured for the day of the year

This means, for example, a river discharge at the 90th percentile is equal to or greater than 90 percent of the discharge values recorded on this day of the year during all years that measurements have been made. The Koksilah River seasonal summer low-flow data are available from 1914 to 1916, 1955 to 2011, and 2013 to 2018.

Estimated flows based on the Water Survey data are also compared to long term historical flows for that day and are expressed as a percentile. Click here to see current Koksilah flows

Protected Networks
Gallery

Protected Networks

Learn about the context and rationale for a network of protected areas designed for the Koksilah River watershed.

Watershed Character and Condition
Gallery

Watershed Character and Condition

The Koksilah River watershed is a place of deep human history and immense ecological richness.