The Water Cycle and balance

The water cycle, you were probably in the 4th grade or so when you first heard of it, and probably have hardly given it any thought in the years since. Water moves through all the different stages: evaporation, condensation, precipitation, with complicating factors like infiltration, transpiration, run-off and more. On top of the basics of how water cycles through the environment there’s also groundwater, the water balance, the water table, lake input, groundwater, etc. Here we are going to look at the way the water cycle and precipitation levels impact levels in Lesser Slave Lake, the centre of our watershed. 

Our watershed is notable for many things, my favorite of which is that we are a precipitation-based system. This means that all the water in our watershed comes from rain, sleet, hail or snow. We have no glacial headwaters, no mountain streams fed directly by the remnants of ancient ice sheets that once covered nearly all North America. The Lesser Slave Watershed is primarily fed by headwaters in the Swan Hills, approximately 119 km Southwest of the Town of Slave Lake, with a small portion of water feeding into the system from Winagami lake to the northwest of High Prairie.

Lesser Slave Lake itself is the lowest point in our watershed, which means all the land surrounding it drains into the lake. There is only one outflow from the lake, at the Lesser Slave River, which joins the Athabasca River about 75km downstream from Slave Lake. The entire basin of the Lesser Slave Watershed is approximately 20,100km2, and is made up of 6 subbasins: South Heart, East/West Prairie, Driftpile, Swan and Lesser Slave rivers, as well as a subbasin north of the lake, appropriately called the Lesser Slave Lake North subbasin. 

Water balance is a calculation of the amount of water in and out of a given system, it is an important part of decision-making processes surrounding water use and is measured in cubic meters (m3).  Annually there is just over 1,532,000,000 m3 of water that goes into our system through the various streams and rivers, plus an additional 545,000,000m3 from precipitation. That quantity is massive, but when you subtract the over 2 billion cubic metres lost through evaporation and outflow the lake levels remain well balanced, with only small changes annually. These numbers are the most up to date ones that we have at present and there is a great deal of fluctuation annually, and so it is important to remember that the numbers above are averages. The biggest factor in lake level changes is related to our overall climate: precipitation levels, and the temperature trends over a given period.

Water balances, precipitation models, inflow, output, monitoring, there’s a lot that goes into understanding our water and watershed. If you’re curious and want to know more about the watershed, LSWC’s monitoring and reporting programs, education work, or just have questions about what we do in general there are many ways you can get in touch! We’re active on Facebook, Twitter, Instagram and YouTube, as well as having our own website (www.lswc.ca), and you’re always welcome to phone our office (780-523-9800), or send us an email ([email protected])! We’re happy to answer your questions and to point you towards any relevant resources.