It was pointed out at last Thursday’s City Council meeting that dredging Gunlock Reservoir could increase its storage capacity by 3,000 acre-feet. That has been suggested a lot in recent months. Why not do that instead of creating the much smaller Dry Wash Reservoir?
It sounded like a good idea. The Reservoir was designed to hold 10,884 acre-feet of water. But a buildup of sediment over the years has reduced its capacity. There has been some periodic dredging, but it doesn’t hold as much water as it was designed for.
We should take advantage of every possible water source. Plus, an additional 3,000 acre-feet at Gunlock Reservoir may take away the need or at least the urgency for building Dry Wash Reservoir.
But storage capacity is just one part of a solution. The other part, call it the whale in the room, is the water source. So, I spent time yesterday looking at how the Santa Clara River behaves.
We’re seven months into the 2024 “water year.” Water years go from October 1st to September 30th. The total Santa Clara River streamflow so far is 8,000 acre-feet compared to 12,000 acre-feet in the same 7 months last year. Based on that, the estimated 2024 streamflow could be close to 16,000 acre-feet. That’s another significant wet water year… with beautiful waterfalls.
Based on that, doesn’t it make sense to dredge Gunlock Reservoir for maximum storage capacity? Another point brought up at Thursday’s meeting was the possibility of increasing the height of the Reservoir by ten feet. That would add a lot more capacity.
But two back-to-back wet years may be making us more optimistic about how easy it is to find more water. It’s not as simple as, “Dredge it and the water will come.” Sure, Kevin Costner can build a movie studio here and the actors will come. That’s close to a home run. But Mother Nature doesn’t work that way. She will deliver more strikeouts than home runs.
The Santa Clara River has delivered over 10,000 acre-feet of water in just 9 of the past 35 years (counting my 2024 estimate). That’s just 25% of the time. Half the time it delivers less than 4,000 acre-feet. Worse, streamflow topped 6,000 acre-feet just 40% of the time.
I believe it is a good idea to have as much storage capacity as possible, at least in theory, and if it makes sense. That way we can capture more water in wet years. Plus, dredging Gunlock would allow for more storage of Santa Clara River water whenever possible, which increases the reliability of that system.
But I don’t believe that just because we add 3,000 acre-feet of capacity, we can say we have 3,000 more acre-feet of water every year. If the past is any indicator, in most years that added capacity won’t give us any extra water. And the past may even overstate how much water we should expect in the future. We’re being told to expect drier, not wetter years.
Talking about whether Gunlock is a better solution than Dry Wash misses an important point. Even if we add capacity at Gunlock Reservoir, that does not do anything to create the reuse water system the Water Conservancy District is planning. The District’s 20-year plan shows the need to develop a reuse system that can deliver close to 25,000 acre-feet of reuse water annually. And Dry Wash Reservoir is meant to be a part of that reuse system.
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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