The Story of a Lake

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The Story of a Lake

Post by admin » Tue Oct 06, 2015 9:08 am

Originally posted by Rem Westland - 22/09/2013

The story of a lake, almost any lake, begins with geological events such as those described for Sharbot Lake in the July 2013 Lake Plan. A lot of time has passed since our Lake became what it is today.

The story I am interested in developing with readers of the SLPOA website is about the present and the future of Sharbot Lake. I want to know more about the water we see when we look at our Lake, the water we boat on, the water we fish in, the water we swim in, the water many of us draw from for our home supply. I want to know how much water we are talking about, how the water gets to where it is, what keeps it in its two basins, and where it goes from here.

I believe that if we know all of those things we will be better equipped to decide what is good for our Lake and what is bad.

From discussion with other SLPOA members I know that the story I am contemplating could become extremely technical and complex. But I hope we can keep it relatively simple.

Let's begin with the fact that Sharbot Lake has a current reality. It exists. In terms of its water volume it can be described with regard to shoreline and depth. In principle the volume of water in the Lake at any point in time can be measured, although as a practical matter the accuracy of the measure may be somewhat off from true! The quality of the water at any point in time can also be stated with fair confidence, such as the Mississippi Valley Conservation Authority does at five year intervals.

Every day, every week, every month, and every year the volume of water in our Lake is impacted by a number of variables. The overall effect of those variables will be to increase volume (raise the level of the Lake) or decrease it. The amount of increase or decrease is again a measurable amount. If we use the tape measure displayed under the old railway bridge we can regularly check the line and see right away whether the Lake level is rising or falling. If we have on hand the area of the Lake in square kilometres, we could multiply the area by the change in depth and know right away what the increase or decrease in volume has been. If we do this on a set date(s) once a year we will be able to say how much water the Lake has gained or lost in the course of the previous twelve months. Simple.

I now want to share with you a formula that enables a person to explain the change in volume. This formula has been developed by experts in the study of water...but most of us would have come to it on our own. I will be proposing that each variable in the formula become a separate chapter in this Story of a Lake.

The change in water volume in the Lake has been called the net basin supply (or NBS). The net amount of water that has added to or taken away from the Lake can be explained by the difference between the amount that has been added to the Lake and the amount that has been taken away.

The formula for this (each variable is described in chapter headings 2 through 10 below) is the following:

NBS = (I + Di + G + P + R) - (O + Do + E + C).

What I propose is that this Story of a Lake be a story with ten chapters. I propose that any one of us, whether members of the SLPOA or individuals and groups having an interest in our Lake, share what we know or what we are learning with regard to any one - or more - of the chapters in the Story. As we, together, build more and more content into each of the chapters we will, one day, be able to say a whole lot about Sharbot Lake and we will be able to point with some accuracy at the variables in the equation which are causing particular worry with respect to water quality.

But first...let me elaborate upon each of the variables in the equation and thereby introduce each of the ten chapters.

Chapter 1 - Sharbot Lake
This is where we describe the Lake in all of its dimensions (location, surface area, depth, background in both geological and human time, condition at the time our Story began, and so on). This would be the place to describe the bird, fish, and animal life supported by the Lake, the watershed of the Lake, development, and whatever else may be of interest and relevant.

Chapter 2: Inflow to the Lake from upstream sources (I)
I have been told that the only inflow is from White Lake...but this may not be accurate. Some have mentioned St. George's Lake as one that empties into Sharbot Lake. There may be a creek or two (Sharbot Creek?) that some of you will know about. In principle, as always, the amount of inflow is knowable once we have identified the source of the incoming and the rate of flow of water (volume, by time) from each source.

Chapter 3: Diversions in (Di)
By this we mean human-engineered diversions. A dam constructed where the Lake empties into the Fall River, for example, would be such a diversion. I was told that when Mr. Ken Hollywood was President of the SLPOA he and other members considered opening a canal from St. George's Lake to Sharbot Lake. That too, if it had been done, would have been a diversion-in. My own guess is that we will have very little value coming from this variable for quite some time (if ever). If one day the Lake level were to be dangerously low owing the climate change, of course, the importance of this variable could grow immensely. By manipulating this variable, such as by building a dam where Fall River begins, our engineers (or beavers?) could compensate for water loss to some extent.

Chapter 4: Groundwater (G)
This will be an interesting one. When my family came to the Lake over forty years ago we were told that Sharbot is a spring-fed lake (groundwater, aquifers, underwater springs). I read somewhere that ground water flows into our Lake at such a clip that every three years the water in the Lake has been renewed entirely. But this may not be so. The ground water chapter will require contributors to think about the entire watershed. If this variable is indeed as meaningful in terms of volume as many of us have long believed then the quality of the groundwater will have a lot to say about the quality of the Lake water.

Chapter 5: Precipitation (P)
This is all about rain and snow falling onto the Lake itself. The Kennebec Lake Association made an effort to record the volume of water that fell onto their lake as rain and then to measure what happened to the level of the lake. It proved not to be a one-to-one relationship: the volume of rain that fell should have had more of an impact on water level than it did. This raised questions about the role of wetlands (did some of the rising water slosh over into the wetlands?) and the need to recalculate outflows (chapter 7 below). The content of rain, of course, impacts on water quality. We no longer talk much about acid rain...but it's still there. We also do not talk enough about pollen and dust that can be carried on air currents and deposited in our Lake when it rains. This will be an interesting chapter too.

Chapter 6: Runoff (R)
And now we get to a big one! While an accurate measure of runoff (rain that falls onto land and runs from there into the Lake) would be difficult, a rough estimate by calculating the area of land all around the Lake some 300 metres from shore could begin to tell us how much water runs into the Lake when it rains. Volume of rain, hardness of the land (early frost), cleared areas, and so on will all make a difference. Our current understanding is that runoff from land (I would include runoff from septic systems in this...but others may not agree) is a major source of nutrients which feed aquatic plants (good and bad) and can lead to toxic algae.

Chapter 7: Outflow (O)
We now hop over to the other side of the equation. Outflow refers to the rivers (Fall River) and creeks that take water naturally away from a lake. I have always believed that our only outflow is the Fall River but, again, I may be wrong. The value of O will change from season to season...and the more we know about this the better.

Chapter 8: Diversions out (Do)
These would be human-engineered diversions. As in the case of Di above I suspect this one is not much of an issue at this time unless the experts tell us that Do includes water we draw out of the lake via our pump intakes and mostly return to the Lake from seepage into the ground (water used on lawns) and from septic systems. I believe we must know more about Do engineering and marketing options. The Tay River is subject to an enormous daily draw of water away from the river and away from the watershed. I saw one of those Tay Valley trucks rolling down highway 38 the other day and I wondered if the time will ever come when our Lake water is drained in the millions of litres per year to feed some industry somewhere. I personally think that we need to set down the bylaws and the provincial prohibitions as soon as possible to stop this before it starts. I would love to get input to this chapter from anyone who also lives in Perth!

Chapter 9: Evaporation (E)
When we know the Lake area and we know the temperatures in the course of the year when water is open to the air, we can know the amount of water we lose from our Lake because of evaporation. If climate change means temperature warming in our part of Ontario then the value of E will rise in the coming years. Unless something changes on the other side of the equation it also means that Lake volume will decrease. If Lake volume decreases and Lake quality is already a problem...then increasing concentration of toxins will result. There will be a lot to say in this chapter as well.

Chapter 10: Consumption (C)
By this I mean the kind of consumption that takes water permanently away from our Lake. It includes consumption that takes water away from our watershed as well. The amount of C can likely never be known. I have read about the concept of "virtual water", which refers to the water which is consumed by farms in the growing of plants which are in turn marketed outside the watershed. Across the planet "virtual water" is becoming a cause of intense concern because of how some very dry regions are using scarce water to grow products like grapes (as only one example) and then selling the grapes (also as wine) in other regions of the world where water may actually be in great abundance.

When you have taken a look at these Chapters you will see that a rough calculation done by members of the SLPOA executive demonstrates that the inflow and outflow from our Lake is about equal at 85 cubic feet per second (or cfs) where:

I = 16 cfs; G (includes run-off and return flow after consumption) = 42 cfs; P = 27 cfs; E = 13 cfs; O = 70 cfs; and C = 2 cfs. The challenge is to get beyond estimates and to achieve a separation between factors (like surface runoff and ground water from aquifers) which we combined for reasons stated in the relevant chapters.

I invite you to read the chapters, challenge the numbers, and help us understand the dynamics of the water in Sharbot Lake better than we currently do.

Remember: The goal of this Story is to help keep our Lake in as good a condition as possible. We SLPOA members and potential members cannot do this on our own, but as we get more informed and as we pick up the strength that comes with better information, we will be able to do a better job within our own direct spheres of influence. We will also be equipped to do a better job in pressuring others (municipal, provincial, and national authorities) to be more effective at their levels as well.

Let me know what you think ...

You can join the discussion on each chapter by posting your thoughts in the appropriate chapter thread.
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SLPOA Forum Administrator

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