Lessons to learn after dike fails on CAP canal
On July 25, after days of storms, more than 3 inches of rain fell in six hours near Picacho Peak.
Floodwater began tearing through the earthen dike that was built to protect the Central Arizona Project (CAP) canal, and then, for about three-quarters of a mile, ripped up sections of the canal’s reinforced concrete lining.
Luckily, the canal is below the rest of the terrain in this area. That and the quick thinking of remote operators helped limit the damage. No canal water was lost, and though there were some temporary turbidity issues downstream, scheduled water deliveries never missed a beat.
But returning this portion of canal to how it was before the storm will likely require about $7.5 million and more than a year to fix.
And, unfortunately, it may be a harbinger of things to come.
I know. It might seem weird talking about the danger of flooding in a place that is only expected to get hotter and drier. But climate change is also expected to turn what precipitation we do get into a case of feast or famine.
Larger, longer spikes of drought could be punctuated by short-lived but heavier deluges of rain — meaning that the 200-year storm that dropped all that rain on July 25 could become more of the norm.
Yet when the roughly 340-mile CAP canal was designed in the 1970s and ‘80s, its major drainage areas were designed to accommodate 100-year storms — which at the time seemed more than enough to handle whatever temporary flooding might occur.
And they have done remarkably well at handling runoff, even if storms regularly exceed the 100-year design cutoff. Few storms over the canal’s history have impacted its operation, and only once has the canal been breached in a way that lost water (that was in 2012, on a section near Bouse in western Arizona, and it was not because of flooding).
But CAP also knows that the hydrology is changing, thanks to climate change and development, both of which can affect how much and how quickly water can run off during storms. It is working with local flood control districts to get a better sense of these changes, which in turn is informing its own analysis of which drainage areas may need modifications to handle higher levels of stormwater.
Not all areas have been fully assessed.
The plan is to focus first on those that have already been identified as most at risk, though what those fixes might entail — much less how much they could cost — remains uncertain.
Still, if there’s a lesson we’re learning — and not just in Arizona, but all over the nation — it’s that we need infrastructure that is more resilient under ever greater extremes.
We’re seeing that on the Colorado River basin, as the annual snowpack we rely on to fill our reservoirs continues to recede, deepening water shortages and putting hydropower at risk.
And in New York City, where areas that aren’t typically prone to flooding during storm surges were inundated with water, thanks to heavy rainfall from Hurricane Ida.
The Central Arizona Project serves more than 5 million people, more than 80% of the state’s population.
The last thing we need is a breach that could lose water we don’t have to lose. Or degrade the quality of that water with silt and debris, increasing the cost of treatment. Or force a lot of emergency repairs that could put the canal out of service for weeks or months at a time.
It’s important to plan for these worstcase scenarios — and it’s good to see that CAP is on it.
But making improvements across the 340-mile expanse will not be cheap. Shoring up potential weak spots could take years, if not decades, to finance, particularly if we do what we normally do and bake it into water rates.
The challenge before CAP (and countless other entities that oversee critical infrastructure nationwide) is to not only identify what needs to be done, but also to make these improvements quickly, before the worst-case scenario becomes reality.