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Watershed Supply and Demand: Ladysmith

Bryan Henderson takes stock of Ladysmith's  water supplyBy Bryan A. Henderson

(For the full report click here)

My interest in the Watersheds used by Ladysmith began during my involvement in the Environmental Commission for Ladysmith in 2008. The existing Official Community Plan for Ladysmith identifies enough vacant land within the existing boundaries to reach a population of 17000. The Timberwest Couverdon land extension would simply add another 5000 people to the Town. This prompted the question, ‘Is there a sustainable water supply sufficient to meet the demand of 17000 or more, residents?’.

My experience and education gives me the theoretical and technical background to clarify and quantify this question. I worked as an Aquatic Fisheries Research Scientist for the Ontario Government for 24 years; I have a B.Sc. (UBC), M.Sc. (UBC), and Ph.D. (Aberdeen) in Zoology and Environmental Sciences. I was also an Adjunct Professor in Biological Sciences at Erindale College (University of Toronto) and the University of Windsor (Ontario).”

 

My Report, ‘Watershed Supply and Demand: Ladysmith’, is based on the Engineering Reports and Data freely provided to me by the Town of Ladysmith. The Weather Data was obtained from Environment Canada (Nanaimo Airport).

In Ladysmith we use three Watersheds (Holland, Stocking, and Banon Creeks) and two Reservoirs (Holland and Stocking Lakes). Apart from being a source of water, these Watersheds and Reservoirs are valuable ecological habitats, unique to the West Coast Rain Forests. The forests have supported a valuable Forestry Industry, and now the second growth of Douglas Fir and Hemlock, is being cut.

The Water Supply is dependent upon Precipitation (snow and rain) falling on the three Watersheds (Holland Creek, 24 square kilometre (SK); Banon Creek, 7 SK; Stocking Creek (1.7 SK)). From these Watersheds, Ladysmith has Water Licenses to use specific volumes of water from each Watershed and Reservoir. There is no formula used by the Ministry of Lands, Forests, and Natural Resources to determine how much water can be used under these Water Licenses; how these Water Licenses were determined is a mystery.

What is not a mystery, is the Recoverable Water Capacity of each Watershed, provided one knows the Area of the Watersheds, the Precipitation rates (P, rain and snow), and the Discharge rates (Q). Imagine that the Watershed is like a leaky tarp, that only allows some of the water (P), in the form of rain and snow, to flow into a downspout (Q). This Discharge rate is what forms a large part of our Water Supply. These P’s and Q’s,
Precipitation and Discharge (runoff), were collected for only one full year (May 2000 to June 2001) for one Watershed (Holland Creek). Knowing these values of P and Q, I was able to predict from an equation, the water available at Chicken Ladder to supply a major part of our Water Supply. This is a valuable equation that must be replicated for all Watersheds; until this is done, we do not know how much water is really available.

There has been much talk and controversy about the Town’s acquisition of the Holland Lake Watershed. Holland Lake can probably hold about one million cubic metres of water. This sounds like a lot of water, but in comparison, 80% of this water could be drawn in one year, if the population size and water Demand is doubled. The Holland Lake Reservoir is of critical importance to our water supply, even now. There are some critical unknowns for this theoretical Watershed: 1.) the precise volumetric capacity, and 2.) evidence that there is a Holland Lake Watershed that actually supplies water to Holland Lake. It may be, as I have calculated, that the surface area of Holland Lake is the main collection surface for the Lake. The Banon Creek Watershed could, in theory, refill Holland Lake, but the P’s and Q’s are not known for this Watershed; In essence, we know very little about the hydrology and hydrogeology of Holland Lake’s ‘Watersheds’.

So, what good information do we have, at present? Well, the most valuable information was collected in 2000 to 2001, for the Holland Creek Watershed. First, Rain was measured at Holland Lake, Chicken Ladder, and Public Works; I added the data for the Nanaimo Airport from Environment Canada. Knowing precipitation at 4 different elevations, I calculated an equation to estimate precipitation at any elevation in the
Holland Creek Watershed. This is good data, but more stations at different elevations are needed, as well as repeated sampling in future years. Second, we have flow rates (Q) at Chicken Ladder, at the same time that we have precipitation rates for the Holland Creek Watershed. We have, therefore, the best data from one year (2000-2001) to have a good basic Water Supply model. There is a critical need for comparable data for
Banon Creek, Stocking Lake, and Holland Lake. Thus, we have 1/4 of the minimum information, in one year, to predict real Water Supply.

There are important parts of the Water Supply Model that are poorly understood (Banon Creek, Holland Lake, Stocking Lake). Banon Creek Watershed is likely important, because Banon Creek could be the main supply of water to Holland Lake. Flow rates, measuring Q (discharge), could be collected fairly easily. At present, the Town is allowed to divert water from Banon Creek to Holland Lake, from November to May, by
Water License. There is concern about the Turbidity (muddiness) of the water in winter months of high flow rates. If you hike the west-side of Holland Lake, you will see the damage caused by Quads and 4×4’s, churning up the soft sandy clay, which eventually runs into Holland Lake. An comprehensive explanation should be sought for the high turbidity of water in Holland Lake.

The hydrology and hydrogeology of Holland Lake Reservoir is another critical area for field studies. Up to now, I have concentrated on the  surface flows gathering into streams and creeks, such as Holland Creek. Some of that water reaching the streams will flow at different levels in the soil and underlying rock. In the case of the Holland Lake Watershed, there are no visible streams that discharge (run-off) from the western or
eastern slopes. If there is any discharge from these slopes, then it would only come from rain infiltrating into the soil and subsequently flowing in subsurface channels into Holland Lake. From the Reports given to me, it is not clear that this subsurface flow has been measured (Hydrogeology). Further, the volume of water that can be stored in Holland Lake for later use, should be verified by a Bathymetric analysis; this would provide a ‘topographic’ map of the Reservoir. This is a simple task, done for many lakes on Vancouver Island by the Ministry of Lands, Forests, and Natural Resources.

Stocking Lake is the third poorly understood component of the Water Supply. The Watershed is smaller (1.65 KS) than the Holland Lake Watershed (1.75 KS). At least to me, it is not clear from the past Engineering Reports, that the Discharge (run-off, Q ) has been calculated. The volumetric capacity of Stocking Lake is half that of Holland Lake, and is the main source of water from October to April. Stocking Lake water is
cleaner (less turbid) that Holland Lake/Creek water, particularly from October to April. One might suspect that springs from subsurface aquifers are up-welling into Stocking Lake, possibly from the larger Banon Creek Watershed. The water is ‘cleaned’ by flowing through substrate (natural filtration) before flowing into Stocking Lake.

Once it is known from where the water comes, the next question is, ‘ how much water can we use?’. Water Consumption by Ladysmith is divided between Holland Creek/Lake and Stocking Lake. I will focus my discussion on the Water Consumption from the Holland Creek. In the past years, 600 TCM (thousand cubic metres) of water was consumed each year from May to September from the Holland Creek; the Water License only allows 400 TCM. The shortfall is met by withdrawing 200 TCM from Holland Lake. Now, I show what happens if the Demand (our consumption of water) doubles, as anticipated if the Town’s population increases to 17000 people. This is the worrying part. The increased Consumption would increase to 1200 TCM, but the Water License is only allows 400 TCM from Holland Creek. Now, 800 TCM must be drawn from Holland Lake, exceeding the annual recharging capacity of the Holland Lake Watershed. As I mentioned earlier, the evidence that the Holland Lake Reservoir is
filled naturally from the Holland Lake Watershed is questionable or not proven. The gravity feed from Banon Creek, could, in theory, provide the necessary water; the hydrology of Banon Creek, however, is not clearly understood. We seem to be entering into a risky situation. Local people have asked me why we have water restrictions in the summer, and what would happen if the Demand doubled. In addition, people are
concerned that with Climate Change, the recharging of the Holland Creek Reservoir may be reduced. It would be a useful experiment to draw 800 TCM from Holland Creek, each year, for two or more years, to assess whether Holland Lake can be recharged naturally, anticipating the expected increased Demand from 17000 people.

Climate is changing Globally, and Locally. My analyses of Air Temperatures, Precipitation, and Snowfall, is for a relatively short span of years (1948-2006). Despite this, the evidence is clear, that average yearly Temperatures have risen 2 degrees (C), from 8.5 to 10.5 degrees. As expected, snowfalls have declined over this period of time. Importantly, the persistence of these snow fields is probably declining as well. Local
people who travel near Hall and Coronation Mountains (our Watershed) have observed that the snowfields are disappearing earlier (perhaps two months earlier).

Precipitation has increased slightly over the last 60 years, but the variation from year to year may also be increasing. Rain in the ‘dry season’ (May to September) is showing a worrying trend; from the mid-1970s to the present, the amount of rain may be decreasing; this is coincident with the overall Air Temperatures rising by more than 1 degree (C) by the mid-1970s. These types of ‘Tipping Points’ are common during Climate Change.

If these trends continue for only another 20 years (the horizon of the Town’s anticipated population increase), water supply could be a problem. The Water Supply for the Fish Hatchery on Bush Creek, has decreased dramatically, so that now there is no evident flow in August, and possibly inadequate flows in mid-winter for incubating eggs and developing Salmonid larvae. The aquatic ecology of Holland Creek could well be
affected significantly unless there is a guaranteed minimum flow throughout the year.

Perhaps, we have to accept that Ladysmith should continue as a small sustainable community. At the simplest level, our water supply is limited naturally, and could become more limited in the future.

About the author: Allen McDermid

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