Here is the presentation I made at last night’s “Water Talkabout” at Rocky Vista University.
Patty and I like movies. A lot. They often help us come to grips with big issues. One movie we liked, “The Shape of Water,” won the Best Movie Oscar in 2017. It’s about saving a strange, watery, scaled creature from South America that lives in… well, basically… a bathtub.
We never understood the title of the movie. Water seemed shapeless to us. That is, it made no sense until we started looking at water trends in the Virgin River watershed. So, let’s take a look at some very important shapes of water.
Streamflow Trend
This chart looks at the amount of water flowing in the Virgin and Santa Clara rivers. Only 66,000 acre-feet flowed down these rivers in the 12 months ending June 2021. That’s well below the long-term trend. Flows have been improving since then, with 105,000 acre-feet in the past 12 months.
Reservoir Storage
Our reservoirs follow a repeating pattern, adding water each winter and spring then drawing it down each summer. The 12-month trend had been falling until a few months ago. Water levels fell only about 500 acre-feet since October compared to almost 2,000 acre-feet in the same period the year before. That fits the river flow trend over the past couple of years.
New Water Sources
What matters is, do we have enough water to continue growing? We get contradictory answers.
The Water Conservancy District’s Impact Study says we used 99% of our available water last year and will run out of water for growth in 2023. Yet the District says we have enough water for at least a few more years of growth. What gives?
We can increase our water supply three ways: Finding new sources, conservation, and reuse. The District’s Master Plan shows four new sources of water scheduled to come online in the next 10 years. These are expected to add 4,000 acre-feet a year. That would support 7,000 new homes.
There are other potential new sources, but none are scheduled yet. The Master Plan lists 18 major capital projects that cost close to $400 million planned over the next ten years.
Conservation
The second way we can increase our water supply is conservation. It is expected conservation will free-up 12,000 acre-feet a year between now and 2035, supporting another 20,000 homes.
Conservation Case Study
Conservation works. Based on population growth, Ivins would be using over 70 million gallons a month now. We’re using 60 million. And we didn’t even have any “tools” to use to help with conservation until recently.
What About Reuse
The third way we can add to our water supply is reuse. Let’s say we use 150 to 200 gallons a person every day. Harvard Health says we should drink about a half-gallon a day. Where does all the rest go? Some goes on our lawns and pools. Some evaporates.
Potential From Reuse
The rest goes down the drain. If we capture that and use it as a secondary water source outdoors, we’d recycle 22,000 to 34,000 acre-feet a year. That frees up enough water for 38,000 to 57,000 new homes. We won’t get there any time soon. But it is a potential source.
Two Water Supply Models
So, back to the original question: Do we have enough water to keep growing, or are we out of water? If you use what I call the “Leading Supply Model,” we have enough. If you use a “Lagging Supply Model,” we’re out. And a third question – why are we getting contradictory answers?
The Leading Supply Model
The Leading Supply Model lets us commit to new construction today even though we are technically out of water today because it assumes that by the time the new homes are built and occupied, conservation and reuse will increase to meet that new demand.
The Cart Before The Horse
That can work. But it puts the cart before the horse. We’re already dealing with so much uncertainty from Mother Nature. The Leading Supply model just compounds that risk.
What if There is a Shortfall?
What if the Leading Supply Model overestimates how much we’ll get from a new water source, or conservation, or reuse? Or underestimates how much water new construction will consume? Or overestimates how much we’ll get from the Virgin River? What then? That’s a lot of unknown variables.
I believe the model relies on our reservoirs and the aquifer under Sand Hollow as a backup source of water. It would dip into these to cover shortfalls, and then reassess the situation.
I believe we should only dip into our reservoirs when we have extremely low water years. Other than that, we should add water each year to fill our reservoirs. They are our safety net.
Donald Rumsfeld could have been talking about our water situation when he said there are things we know we know, things we know we don’t know, and things we don’t know we don’t know.
The Lagging Supply Model deals with the things we know we don’t know and the things we don’t know we don’t know. It doesn’t add new construction until new sources, conservation, or reuse actually produce additional water. It’s a more conservative model. But given the uncertainty Mother Nature brings to the table, it’s a lot safer.
The leading supply model minimizes disruption in our economy. The lagging supply model maximizes water security. We can label these as the “eat well model” and the “sleep well model.”
The bottom line: We need to understand what model is being used. And we need to be comfortable that it will protect us.
Please share your comments on this topic and tell me about
other Ivins issues I have not addressed in recent posts.
Email me at Mike@MikeScott4Ivins.com.
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