Dams and Hicks

For my bike friends who regularly ride Hicks from New Almaden, you likely marvel at the beauty of two water bodies, Almaden Reservoir and Gaudalupe Reservoir. Birds, streams, the ability to lose oneself while riding, to forget about the woes of the world - aren't we lucky to have these areas just a short pedal away?

Beyond admiration as you pedal by, what do you know about these two reservoirs? Before I was elected to the Water District, more commonly referred to as Valley Water, I knew very little. But after my ride last Friday (the first ride on my brand new road bike) I figured it would be cool to help fellow Hicks riders get to know these two reservoirs a little better. Read on so you can impress your friends with some dam knowledge on your next bike ride.

First, Santa Clara Valley Water District (Valley Water) owns and operates 10 dams and reservoirs. The biggest is Anderson reservoir in Morgan Hill at around 90,000 acre feet and the smallest Vasona at ~500 AF. (An acre foot is the amount of water it takes to cover one acre one foot deep.)

Why do we have dams and reservoirs? The basic functions of a dam are to control water for flood protection and water supply in service of human needs. These days, as we have realized the error of our water ways, dams are now being managed in a way that restores the health of our ecosystems too. As it turns out, dams are not that great for fish that need to swim upstream and we've got to fix that.

So, there are three important functions of reservoirs:

1. Supply so that we have water to drink and the land doesn't sink due to subsidence,

2. Flood protection so that we’re safe, and

3. Ecosystem health so that nature is able to sustain life on earth.

As a sidenote, while these are the reasons dams exist overall, in Santa Clara County, the flood protection function is minimal or in Valley Water speak, "incidental."

Managing reservoirs to balance all these needs is quite an endeavor. Is it going to be a wet year? If so, what levels do you keep a reservoir at in order to have water to drink long-term? How dry has it been for a few years and so how much will the mountains absorb before water run-off fills the reservoirs? Will there be enough water so that the fish can survive during their migration upstream? What about the water temperature and amount of oxygen as it relates to a healthy fish habitat, especially with higher temperatures under climate change? With ten reservoirs to manage in combination with nature doing its thing, achieving those three goals is incredibly complicated across Santa Clara County.

Sidenote: Thank goodness the Water District has some of the best people in the industry and that our employee retention rates are high. Continuity in knowledge and staffing means we are better able to meet these challenges.

In Santa Clara County, 6 of our 10 reservoirs were built in the 1930’s. That's old which is part of the reason why, of those ten, 5 are currently considered seismically sketchy. That means if there’s a decent earthquake, they may not hold. As a result, both reservoirs are kept below capacity, and have been kept that way for years. Almaden, the second smallest reservoir at 1,500 AF, is required to be at only 93% capacity and Guadalupe which can hold just over 3,000 AF is at 66% capacity.

Both reservoirs are important for water supply, in particular groundwater recharge. That means water is released in a very planned and intentional way so that, as it flows in our creeks, water can seep into the soil and into recharge ponds to refill water stored naturally underground. (And by the way, the amount of water we store in our underground aquifers surpasses all the water stored in our ten reservoirs.) One of the problems with both these reservoirs is that due to mercury mining, much of the water that flows into the reservoirs is contaminated. For more information about what the District is doing about that, click here.

Seismically upgrading these dams costs money. That is why this year as a part of the rate setting process, one of the baseline assumptions is that we are continuing to move forward with these two projects. The other three Valley Water dams that need seismic upgrades are some of our largest:  Anderson (90,000 AF -restricted to deadpool), Coyote (23,200 AF – restricted to 12,400), and Calero (9,900 AF – restricted to 4,600).

I'm only scratching the surface on all the interesting information about these two reservoirs so for more info click here (Guadalupe) and here (Almaden)

I hope the combination of your natural curiosity about these water bodies as you ride Hicks along with the little bit of information provided here inspires you to click through the links, poke around and learn more. Doing so WILL grow your appreciation for what it takes to operate the ten dams and reservoirs owned, operated, and paid for by you through Valley Water.

And, next time you go for a ride with your friends, you can impress them with your dam knowledge!

Happy riding and keep the rubber side down.