By Rem Westland
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.
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.
My suggestion is that readers take a look at each of the chapters, decide which one(s) they have an interest in, and dive in (so to speak). The input can be in the form of a question, asking that someone who knows the answer to propose a reply; or, the input can be substantive based upon what the reader knows or wants others to confirm. As editor of the project my plan is to review inputs every once in a while (monthly, at a minimum) and redraft the text so that the inputs are taken into account. At some stage this approach may become unwieldy (too much input?) but that won't be for a few years yet...
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.
To get a measure of inflow from White Lake, take a look at the chapter on outflow. The outflow from Bennet Lake has been measured. This means it becomes possible to back things up to Sharbot Lake (outflow at the Fall River, which flows into Bennet Lake) and to White Lake (inflow to Sharbot Lake). Our calculations suggest the inflow rate to Sharbot Lake from White Lake is in the order of 16 cubic feet per second. Over a year, therefore, this adds about 500 million cubic feet per year to the volume of our Lake.
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.
There are some estimates available for eastern Ontario lakes. Precipitation is about 35 inches per year, on average. This number can be converted to cubic feet per year (or per second, to match outflow estimates) once we have a figure for the area of our Lake. If we assume the area of Sharbot Lake is 10 square miles then the precipitation of 35 inches per year (which adds 2.92 feet to the water level) adds about 800 million cubic feet to the water volume each year.
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.
In the opening discussion we combine runoff and groundwater because that is how the data for Eastern Ontario are currently available. It reflects the logic that all precipitation that works its way into our Lake will get there either by falling directly onto the lake water (P) or by running over the land or into it (and joining the water table). Eventually, however, I would love to get to a point where we can distinguish between what washes into the Lake over our properties (we can do something about that!) and what seeps into the water table anywhere in the watershed. The latter volume of water will be affected by farming practices, management of wetlands, salting of the roads, disposal by inland residents, and so on. Both types of runoff need to be as benign as possible for our Lake but we SLPOA members can influence the inland aspect of this primarily through local and provincial politicians.
An article titled "Combating Climate Change Impacts on Phosphorous in the Grand River and to Lake Erie" by James P. Bruce (24/09/2013) concludes that, although some increase in phosphorous concentrations in water bodies is due to changes in land use and farming practices, the most important cause is heavy rain or rain on snow, and runoff events in a changing climate. It seems to me that anything we can individually do to reduce the amount and/or rate of runoff from our properties into the Lake might make more of a contribution to the improvement (or slower deterioration) of water quality than other actions. I wonder about the benefit, for example, of us property owners with shoreline spending time and effort (and a bit of money!) to create terrasses of earth and rock - covered by vegetation (and no fertilizer!) - to slow down or stop the run of rain water and Spring melt directly into the Lake. If any reader(s) have information on this...please send it in! Thanks.
Advice to me from Ralph Pentland, an at-large member of the executive, calls for another update... A separation between groundwater and surface water appears to be a distinction without much of a difference. All groundwater becomes surface water eventually. In our part of Ontario water runoff in eastern Ontario watersheds is about 1.1 cubic feet per second (cfs) per square mile. So runoff directly to Sharbot Lake will be equal to 1.1 cfs times the land portion of the Sharbot Lake watershed in square miles.
If we assume the basin land surface area around our Lake is 35 square miles the estimated run off would be about 38 cubic feet per second.
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.
I have been advised by Ralph Pentland, also on our executive, that the data currently available can provide an estimate of outflow volume via Fall River by using the measured outflow from Bennet Lake (130 cubic feet per second, from Water Survey of Canada records). The drainage area above the Bennet Lake outlet is approximately 110 square miles (includes Sharbot Lake). Since the Fall River is a major source of water for Bennet Lake, the question now becomes: if 130 cubic feet per second are flowing out of Bennet Lake, what is the volume flowing into that lake from Sharbot via the Fall River? Using an estimate of 60 square miles as the drainage area for Sharbot Lake itself, the answer (averaged over the year) would be 71 cubic feet per second.
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.
There are some estimates available for eastern Ontario. On average, the rate of evaporation has been in the order of 19 inches per year from lakes in our area. When we have a number for the area of Sharbot Lake we will be able to say what this translates into on a yearly, or per second (to match outflow measures), basis. Since the evaporation rate is 19/35 times precipitation (see chapter on Precipitation) then evaporation reduces water level by about 1.3 feet annually. What this means in water volume and rate of water loss can also be calculated using these data (434 million cubic feet, or 14 cubic feet per second).
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.<>br>
Consumption for drinking and ablutions within our homes and businesses returns about 90% of what is taken out of the Lake back into it via septic systems (hopefully!) or directly (diverted grey water and untreated sewage). My advice from Ralph Pentland is that consumptive use in eastern Canada is about .0001 cubic feet per second (cfs) per person. If we assume 2000 users of Lake water (residents, guests) then consumptive use would be 0.2 cubic feet per second. Return flow (and this is where our own contribution to the contamination challenge comes from) would be in the order of .18 cubic feet per second.
The fact is, of course, that the volume we humans take out and return is a very small amount compared to precipitation and groundwater. But we can compromise the condition of the water by what we have added to what we dispose.
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 ...