Model reflects how lake could be drained out

There’s only a shortage of water in the Okanagan Valley during a drought year but they are critical.

There’s only a shortage of water in the Okanagan Valley during a drought year and even then only during a critical few weeks in August—but they are critical—so water supplies in the Okanagan Basin must be managed so the lake isn’t drained down during that period.

Such scenarios and the impact of them can now be defined thanks to the information gathered in the valley’s water supply and demand model and the Water Evaluation And Planning (WEAP) system which can be used to simulate demand and how different factors influence supply.

Brian Guy of Summit Environmental Consultants, which managed the water supply and demand project for the Okanagan Basin Water Board, and who is a member of the Okanagan Water Stewardship Council, reported to the council at its November meeting on preliminary uses of the  model to illustrate different scenarios. For instance, they’ve tried the model with all existing water licences in the basin fully used, and found that we run out of water, he said.

In other words, if all users used all the water they’re entitled to, Okanagan Lake would drop or downstream users would be cut off—even if they have prior entitlements.

In B.C., water licences are based on a principal called FITFIR—First In Time, First In Right.

That means the first licences issued have priority over the most recent licences issued.

Some of the older licences, however, are downstream, in the Osoyoos and Penticton areas, so it would be challenging to enforce FITFIR in times of a water shortage to prevent upstream users in Kelowna and Vernon from first taking more than their entitlement.

“Okanagan Lake is managed to supply downstream users, yet we’re beginning to mine the lake in some years, and the kokanee wouldn’t like that,” Guy told council members.

Another scenario involved making it a priority that the needs of fish for adequate water in valley streams take precedence over other uses of water in the basin. They found that it wouldn’t have affected other users between 1996 and 2006. Water supply and demand data from that period was used to run the model.

“We found that would not have negatively affected any other water users in that period, so any mis-trust (about giving fish flows a top priority) was mis-placed,” he commented.

Council chairman Bernie Bauer said this work is “laying the foundation to manage the resource because the model can tell us the ramifications of different decisions.”

It also highlights the need for the OBWB to play a part in a valley-wide drought management plan, Guy noted.

“All valley utilities are linked,” he said, so better coordination and more efficient management in times of shortages is possible when they’re all working together.

The new modelling is not yet available for use by different utilities, but Guy is working on the final report now and it will eventually be more widely accessible.