Chapman “water budget” is in deficit

On July 6, the board received an updated water supply and demand analysis for Chapman, as well as several other water-related reports. (It was a heavy day!)

Water Supply & Demand Slides (PDF)
July 6 Special Board Meeting (YouTube)

The first time such a water supply analysis was done was in 2018. As consultant Paul Nash explained, it was an an attempt to create a “water budget” for the Chapman watershed to determine how much storage is needed to meet our demand year round without going past Stage 2.

First, the caveats

Before delivering a lot of bad news, there are some important caveats here:

  • This analysis only considers Chapman Creek. It does not include other water sources such as Church Road wells, the Town of Gibsons, or the Langdale wellfield. And it also doesn’t include the use of siphons to draw down Chapman and Edwards lake below what we can normally release from the dams. So the overall picture is not quite as bleak as it sounds.
  • This analysis assumes we continue with the policy adopted by the board in 2018, which is to plan for sufficient water so that we never have to go beyond Stage 2 water restrictions. This is definitely a policy that we must revisit and reevaluate.

What hasn’t changed

A few things have not changed:

  • Population growth, as expected, is about 2% annually
  • Conservation efforts are on track to meet our goal of reducing our per capita water consumption by 20% from 2010 levels
  • The maximum length of drought used for modelling purposes is similar – 200 days vs 184

What has changed

But since consultants created this model five years ago the hydrology of the creek has changed dramatically. Once the snow melt is over, the creek dries out faster than ever before.

The creek has even “gone negative.” This was first seen last summer. We are losing water between the dam and the water intake at our treatment plant. We used to gain some water from tributaries and natural upwelling of groundwater, but now water is disappearing, either from evaporation or absorption into the parched ground. So when we release a thousand litres from the dam, we may only see 900 litres reach the water intake.

Note above the 0 line that clearly shows the creek running “negative.”

Our climate is changing so fast that past weather is no indicator of what’s going to happen.

Environmental Flow Deficit

We have a legal requirement, set by the BC government, to provide an Environmental Flow Need (EFN) of 200 L/s to the creek. This is primarily for fish habitat, and it’s more than we withdraw for drinking water. The bad news is that in a worst case scenario (a 200 day drought), we can’t even supply enough water from the lakes to provide that EFN, let alone drinking water, without using siphons or pumping in water from another source, such as a raw water reservoir.

I’ll repeat. In a severe drought all the water in the lakes will be needed for EFN, and we legally MUST supply water to the creek before we take a drop of water for our potable supply.

Other Raw Water Sources

Two “raw” (untreated) water reservoir projects are under consideration right now, either of which could be an option for supplementing creek flow. One is “Site B” up near the airport, which consultants have been investigating for a couple of years. The other, recently brought forward by the shíshálh Nation, is to repurpose two large pits at the gravel mine for water storage.

I’m not going to go into details, but here’s a really fast thumbnail. The mine makes sense because the holes have already been dug, and we’d be transforming a mined wasteland into a community benefit. However, there’s a big elevation difference, so pumping the water up from the pits to the treatment plant means high operating costs.

A Site B reservoir would have to be excavated, which has a high cost in GHG emissions as well as $$s. But it would be cheaper to operate because it would be gravity feed to the plant, and might even generate some hydroelectricity.

Both reservoir projects assume the expansion of our water treatment project, at a likely cost of over $20 million.

Moving Forward

Since the Comprehensive Regional Water Plan was passed in 2013, the world has changed, and our situation with water supply has shifted dramatically.

We are going to have to reconsider all our plans and strategies, and our expectations about how much water we use and what for.

Some of my questions:

How much water do we really need?

A few years ago we figured that $10 million was an expensive water infrastructure project (the Church Road budget was $9 million). Now we’re looking at $100 million reservoir projects. We cannot count on receiving federal or provincial grants. So how much can local taxpayers afford? And what for? Are we going to spend $100 million for green lawns?

Should we be using Chapman Creek at all?

It’s one small creek and it’s very vulnerable. In my opinion we need to diversify our sources so that we don’t receive more than a third of our water from any one source. That would make us far more resilient against drought and other disasters. (Remember earthquakes?)

How much water should we provide to the upper reaches of Chapman Creek?

Our legal requirement to provide an Environmental Flow Need (EFN) of 200 L/s is measured at the water intake, which is roughly 3 km from the mouth of the creek. In theory, we could build a raw water reservoir to supply the lower part of the creek during droughts and then let the rest of the creek (approx. 15 km) dry up between the water intake and Chapman Lake. We have no idea what impact that would have on the watershed ecosystem, but it sure couldn’t be good. And I don’t think it’s acceptable.


Posted by Donna