Aquifers and Groundwater
Living as we do in the Earth’s biosphere, our view of the world is almost entirely horizontal. Who can witness a spectacular sunset with the last golden-red rays touching the mountain tops and not be thrilled at the horizontal nature and majesty of our environment although we can also see it is being polluted.
From time to time, we may look up appreciatively at the sky, a gossamer-thin life-enabling blanket of nitrogen, oxygen, and 1% other stuff that contributes to climate change. At night, we may gaze into the infinity of outer space and realize how small we really are.
We rarely look down because we can’t. Only a few of us, miners, construction workers and the like who work underground, are first-hand witnesses of the complex layers of earth, gravel, sand, minerals and rock, much of which is permeated by precious groundwater.
About the Science of Aquifers and Groundwater
Groundwater is the term we use to describe water, usually rainfall, that has been absorbed into the soil and then drawn downward by gravity. It collects, mainly in porous underground geological formations or units that we call aquifers.
This dark underground territory and it’s aquifers involve many secrets about the whereabouts and movement of groundwater on Earth, and are studied by the sciences of geology, geoscience, Earth science, hydrology and hydrogeology.
While hydrology is the study of water on Earth's surface, which includes its distribution and movement across the land, hydrogeology is the study of groundwater and it's occurrence, distribution and movement through the Earth's crust.
So when we ask questions about aquifers, many answers will come from the study of hydrogeology, a revealing portal that helps us to understand the complex variabilities in the geologic formations below our feet where precious groundwater resources may reside.
Fresh Water
All life on Earth requires fresh clean water but 97.5% of the Earth’s water is salt water. Only 2.5% of the water on Earth is fresh water and over half of that is frozen in glaciers and polar caps. The lakes and rivers of the world cradle but a fraction of one percent of the fresh water available. This means that the groundwater, moving and stored underground is, realistically, our primary source of fresh water. In BC 28.5% of the population depend on ground water
Although the fraction of fresh water on Earth seems impossibly small, the spontaneous regeneration of fresh water in our atmosphere is simply awesome. Fresh water production begins when water evaporates from oceans, lakes and river and through plant transpiration, and during that process, salts and contaminants are left behind. The resulting pure H2O molecules rise as water vapour, eventually condensing and forming clouds. After about 10 days aloft the water falls back into the ocean or land as rain or snow. The dramatic weather and storm events we often see are all part of the hydrologic cycle, more commonly known as the water cycle. This is the process which serves to continuously replenish us with clean fresh water.
Evaporation
One cannot leave the water cycle without a quick look at evaporation. 90 percent of the moisture in the atmosphere evaporates from oceans, lakes and rivers and about 10 percent from plant transpiration. A very small amount of water changes from solid snow or ice, directly into water vapour (skipping the liquid state entirely). This process is called sublimation and occurs during Chinook wind conditions, (warm air blowing over snow or ice).
For evaporation to occur energy is required to break the bonds that hold water molecules together. Thus the process of evaporation removes heat from the local environment explaining why you feel coolness when water evaporates from your skin.
The rate of evaporation on a lake is driven by atmospheric humidity, temperature, and wind speed. The three primary conditions that increase evaporation on a lake are:
Warm lake water temperatures with overlying cold air temperatures,
low relative humidity in the overlying air, and
high wind speed across the lake.
The Fall and Winter months can introduce such conditions so evaporation rates will be high unless ice covers the surface. Hotel Lake rarely freezes over so evaporation generally continues all Winter and, in ideal conditions, can reach up to 0.6 inches a day. That loss is generally offset by the considerable rate of precipitation into the lake and its catchment area during winters.
Moving Underground
As mentioned earlier, groundwater is the term we use to describe water, usually rainfall, that has been absorbed into the soil and is then drawn downward by gravity and is then collected in porous underground geological formations that we call aquifers. The replenishment of aquifers with ground water is a process called recharging.
As you might imagine any effort to explain the hydrogeology of aquifers beneath our feet is an almost impossible task. Impossible because we really know so very little about what’s down there and there is very little for us to see from the surface. So we have approached this subject with a bit of drama and hope you enjoy the journey.
Aquifers and Karst Landscapes
Trying to understand what an aquifer is and how water behaves underground requires an open mind; after all, this is a relatively new frontier! From the hundreds of diagrams, illustrations, animations and videos online it is easy to get the impression that aquifers are underground caverns or lakes or underground rivers. However these can only be found in areas called “karst landscapes” (two examples shown above are on Vancouver Island). Karst landscapes host soluble carbonate bedrock formations such as limestone, marble, dolomite and gypsum, which dissolve over centuries thus creating sink holes, sinking streams, caves, etc.
The process that creates karst formations begins when rain drops fall through the atmosphere and while doing so pick-up CO2. After rain lands it percolates through the soil and picks up more CO2 from the carbonate bedrock thus forming a weak solution of carbonic acid: H2O + CO2 = H2CO3. Underground, the infiltrating water naturally exploits any existing joints or fractures in the bedrock and the acid causes the carbonate bedrock to slowly dissolve, creating larger openings which, over many thousands of years, eventually leads to the development of underground drainage systems and caves.
Although still largely uncharted, about 16% of BC is considered to be world-class karst areas. These are located in the Rocky Mountains, on Vancouver Island, on Haida Gwaii, along the coastal mainland, in the interior mountain ranges, the Cariboo Mountains, and in Northwest B.C. These underground caves, caverns, sink holes and the like are of greater interest as tourist attractions than as a source of drinking water.
Nevertheless, we have included this brief look at karst landscapes because they are a significant component of the hydrogeology of BC. One of the best animated videos that we could find on this subject is provided below. Produced by the Minnesota Department of Agriculture, it depicts aquifers located in the south-east Minnesota Karst landscape and while that geology is obviously very different to the geology under Hotel Lake and north Pender Harbour, the animated depictions of ground water and its movement are enlightening, perhaps even entertaining.
