ENVIRONMENT YUKON






Lakes and Rivers

Extreme high and low water in lakes and rivers

Significance

Water levels in Yukon, both river flows and lake levels, are susceptible to change from a range of processes, including:

  • changes to the timing of snowmelt,
  • the phase and magnitude of precipitation,
  • permafrost thaw,
  • shifts in vegetation, and
  • melting glaciers.

These are just some of the processes that can alter the flows in lakes and rivers. The response in water flows to these processes may be different in different regions of the territory.

Higher flows in lakes and rivers can cause:

  • Increased sedimentation and contaminants in river systems, affecting human health, drinking water and ecosystems.
  • Increased flooding potential if peak flows affect populated areas, which can result in infrastructure loss and economic costs.

Low flows in lakes and rivers can cause:

  • Increased concentrations of ions, such as dissolved metals, which can negatively affect aquatic ecosystems.

Changes in water flows and groundwater can affect resource development, such as hydro power production, mining practices or agriculture, as well as the availability of water for communities and other local needs.

Increased water flows in the winter, which is generally a low-flow time of year, are a climate change driven trend. It results from warming air temperatures, degrading permafrost, and in some locations, increased precipitation. This trend is expected to continue with future warming, particularly in areas of permafrost where thaw results in increased groundwater flow connections.

Takhini River flowing into Kusawa Lake.

What is happening?

Annual river flow

Thirty-two stations across Yukon monitor for trends in annual minimum and maximum river flows:

  • Yukon River: 25 stations
  • Alsek River: 3 stations
  • Liard River: 3 stations
  • Peel River: 2 stations
  • Porcupine River: 1 station

28 of 32 long-term river stations measured significant increases over time in the volume of water flowing when the river was at its minimum. No stations indicated that there were declining flows over time (Figure 1).

Stations with increasing low flow trends (Figure 1) had a median trend fit of +10 per cent per decade.

Figure 2 shows that most (33 of 34) long-term river stations did not show a significant trend for maximum river flow.

The Whitehorse station measured a significant decrease in annual peak flow volumes (Figure 2), but it has flow volumes which are affected by the Whitehorse dam.

The majority of stations examined are large rivers (29 of 34 are greater than 1,000 km2).

FIGURES 1-2: Annual minimum and maximum river flow. Period of record varies by station and has information to 2013.

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Annual lake levels

In Yukon, there is monitoring for trends in the annual minimum and maximum water levels at six Yukon lakes:

  • Bennett Lake
  • Kluane Lake
  • Marsh Lake
  • Mayo Lake
  • Aishihik Lake
  • Teslin Lake

Three lakes (Bennett, Kluane and Marsh Lake) showed significant declines in low water levels over time (Figure 3); Marsh Lake levels are influenced by the control structure associated with the Whitehorse dam.

Marsh Lake showed a significant increasing trend in high water levels of 0.5 cm per decade (Figure 4); Marsh Lake is a regulated system because of the Whitehorse dam, but the control structure has a minimal effect during periods of high water levels.

Mayo Lake showed significant increases in both low and high water levels; these levels are influenced by the Mayo dam.

FIGURES 3-4: Annual minimum and maximum lake levels. Period of record varies by station and has information to 2013.

[[slider::./images/report-water-extreme-flow-figure-3.jpg|./images/report-water-extreme-flow-figure-4.jpg]]

Taking action

Two research projects are underway in collaboration with the Emergency Measures Organization to help Yukon communities prepare for flooding events:

  • Yukon flood risk mapping: using high resolution LiDAR elevation data to identify flood prone areas near Yukon communities.
  • Development of flood hazard perception stages: categorizing water level stages into severity indices ("Action Stage", "Minor Flooding", "Moderate Flooding" and "Major Flooding") that determine when and what action should be taken with an impending flood.

Profile

Measuring water velocity

Testing the Acoustic Doppler Profiler on the Yukon River.

The traditional way that the Department of Environment's Water Resources Branch has measured discharge (volume of flow) in the creeks and rivers we monitor is to wade into the water and measure the depth and velocity at multiple points using a mechanical instrument, and use this information to calculate the total flow. One of the biggest challenges is that when the water levels rise, the creeks become impossible or dangerous to wade into. Therefore, we become unable to get measurements at the high flow water levels that are often of the most interest. Previous alternatives to wading into the water were often elaborate, expensive, time- consuming, and did not always produce quality data.

The new instrument Water Resources Branch will start using in spring 2016 is a type of Acoustic Doppler Profiler. The sensor is mounted on a pontoon that floats across the surface of the water; it shoots high frequency sound waves into the water column which are reflected off particles in the water. Using the Doppler Effect (the same effect you notice when the pitch of an ambulance siren moving towards you sounds different then when it’s moving away from you) the sensor can determine how fast the water is moving throughout the water column. The sensor produces a visual of this (see the figure), where different colours show different velocities. It also maps out the precise shape of the stream bottom and so is able to produce high resolution data which is used to calculate the total flow.

This technology will produce better data, it will reduce the time needed to perform a measurement, and it will keep field workers safer.

Data quality

  • The Water Survey of Canada conducts long-term measurements of large rivers and lakes. They provide summaries of annual peak high and low flows based on daily mean flows and water levels.
  • The Water Survey of Canada provides public access to hydrometric data,
  • All stations included in the analysis are active sites that have at least 30 years of peak flow data. The oldest station on record began collecting data in 1943.
  • Data from the Water Survey of Canada is typically released two years after data collection; currently data is available to 2013.
  • The majority of stations have a minimal number (less than 5 per cent) of missing years in the record.

Further information

Measuring water levels on Boulder Creek.

References

Environment and Climate Change Canada. n.d. Water Survey of Canada Historical Hydrometric Data. Available from: www.wateroffice.ec.gc.ca

Helsel, D.R., D.K. Mueller, and J.R. Slack. 2006. Computer Program for the Kendall Family of Trend Tests: U.S. Geological Survey Scientific Investigations Report 2005–5275. U.S. Geological Survey, Reston, Virginia U.S.A. Available from: http://pubs.usgs.gov/sir/2005/5275/pdf/sir2005-5275.pdf.