If you’re reading this blog, there’s a good chance you’ve seen some of Green Venture’s ads for rain barrel sales, rain garden installations, and other Green Infrastructure initiatives (but if you haven’t, this is a great place to start). In this summer blog series, we’re going to take a brief journey into the processes that will help our readers understand why we care so much about these programs. Continue reading for a short primer on water pathways to kick off the series!
The Water Cycle (a.k.a. The Hydrologic Cycle)
Water is constantly in motion. While you may have noticed that rainfall and rivers have an obvious direction, you may not spend much time thinking about the places where water appears to be still (think a lake or pond), or even sometimes invisible (think the ground, plants, and the sky).
The water cycle refers to the constant movement of water between these places. When water on the ground or the surface of a waterbody is heated, it returns to the atmosphere as water vapour (evaporation). When water evaporates from the leaves of plants that take up water by their roots, it is called transpiration. When atmospheric water cools and condenses (like a sweaty glass of ice water on a hot day) we get rain!
The Paths of Precipitation
Rain and melting snow, sometimes referred to as stormwater, either soaks into the ground or runs into sewers, streams, and lakes. In this ‘land phase’ of the water cycle, water is temporarily stored in plants, deep soils, snowpacks, and water bodies. Water that soaks into the ground by a process called infiltration, is temporarily stored there as groundwater, where it slowly flows back into lakes and streams, or into aquifers (porous rock or sediment that stores groundwater). Any water that leaves your home from activities like watering lawns or washing cars and driveways is also considered stormwater, as it moves through the hydrologic cycle in the same ways.
This image shows the natural pathways water moves through the hydrologic cycle. (Dennis Cain/NOAA/NWS).
The Cycle in the City
Humans use and interact with water at every stage of the water cycle, whether it be by harvesting groundwater through a well, or flushing the toilet. One of the most apparent differences between a natural landscape and an urban area is the presence of buildings, concrete, and asphalt. These are referred to as impervious surfaces, meaning that water flows over them, increasing stormwater runoff, instead of soaking into the ground and plant matter.
This image shows how a more highly developed area will experience much less infiltration and groundwater flow, and much greater surface runoff. (Copyright © Commonwealth of Massachusetts).
How does increased stormwater affect us?
Increased Flooding
An increase in impervious surfaces means there is a greater likelihood of heavy rainfall or rapid snowmelt accumulating in an area very quickly. When the capacity of natural or manmade watercourses are exceeded, the resulting floods can cause damage to property and even loss of life. This topic will be discussed in more depth in the next blog in this series.
Undesirable stream changes
Native plant and animal diversity declines as a result of a change in stream flow. Decreased groundwater discharge into some streams can reduce the baseflow (the normally maintained water level) which allows aquatic life to survive. In other streams that receive high levels of stormwater runoff, accelerated erosion can lead to destabilized stream banks and high sediment levels, which degrades habitat quality.
Decreased water quality
With more hard surfaces, sediments suspended in stormwater have fewer opportunities to be filtered out through soils. This means that pollutants and contaminants that build up on roads from things like fertilizers, animal waste, and car emissions or spills, are more quickly transported to our waterways. Water can become less clear and oxygen may be depleted, affecting aquatic plant and animal health. Increased nutrient levels can also result in high numbers of harmful bacteria, making the water unsafe for drinking or swimming.
In the next Summer RAIN Blog, we are going to dive a little deeper into where stormwater goes, and review some stormwater management practices in Hamilton!
For those interested, more detailed information on the hydrologic cycle and stormwater management in Ontario can be found here:
