A riser structure in the middle of Lake Johnson to lower water levels

Lowering Water Levels

Managing a high-hazard dam from our office

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Checking the Lake Lower Water Levels Benefits

This pilot program uses a camera and new system to help prepare for major flooding. We now automatically lower the dam at Lake Johnson and can respond more quickly during a rainstorm.

A high-hazard dam – high risk for people living downstream if the dam fails and causes flooding. We designed the dam at Lake Johnson so that water flows over the dam into Walnut Creek. These new features help protect you from the water flow and preserve the lake.

Checking the Lake

We use a camera to track the lake’s water level and storm flows in real time. We can see when we need to:

  1. Safely lower water levels to limit impacts from flooding;
  2. Make sure water isn’t leaving the dam too fast (only two feet per day); and,
  3. Fix issues with water flow that could impact residents downstream.

The camera takes a photo every five minutes (Images aren’t recorded/saved.) You can see what we see on the US Geological Survey’s website.

Lower Water Levels

Before the pilot program, we manually lowered water levels at Lake Johnson. This included taking a boat to the structure in the lake and turning the wheel to open the dam spillway. Doing this was unsafe. The structure’s ladder is slippery during bad weather and covered in algae from the water.

Now, we can lower water levels right from our office keeping you and our staff safe in the process. (An alarm will sound when the lake water is being lowered.)


More efficient.
It used to take staff up to a day to lower water levels at a lake. Now, we can respond within minutes.

More prepared.
We see conditions in real time and notify first responders sooner to prepare for flooding.

More focused on the environment.
We control the flow of water to protect the shorelines of the lake.



Brad Cole, PE
Stormwater Asset Manager

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