The Upper Chiquita Reservoir poses no significant safety risks to nearby residents and improves regional water supply reliability.

The purpose of the Upper Chiquita Reservoir is to protect the public from water emergencies, and its location was carefully selected to maximize the ability of the member agencies to provide water in the event of such an emergency – it is located in a seismically stable area, at an elevation that will allow water to flow into the pipeline system even if there is no power.

Of course, whenever a reservoir is built, public safety must be a major consideration. This section details how public safety concerns have driven the design process for the Upper Chiquita Reservoir.

History has proven that earthen embankment reservoirs, like the one being proposed at Upper Chiquita, are inherently safe. The design of the Upper Chiquita Reservoir goes beyond typical reservoir design to provide an even greater level of safety, so it will be able to withstand extreme seismic activity, very heavy and prolonged rainfall, high winds, wildfires and natural deterioration.

Minimizing the Risk of Flooding

Engineers have closely studied the Upper Chiquita site and the reservoir plans for several years, and a risk analysis has shown the potential for a flood caused by reservoir failure is less than one in one million. Below are steps SMWD has taken to ensure the project is safe for local residents and students.

The First Fill
Poor construction can lead to failure when the reservoir is filled the first time. In California, the design and construction of reservoirs like this one is regulated by State safety officials, which sets stringent design criteria, and monitors all phases of construction and initial filling to safeguard the public. Reservoirs constructed to this standard have never failed. The Department of Safety of Dams experts won’t just review the plans – they will be on-site during construction and first fill, monitoring all activities.

Earthquake Protection
Earthen embankment reservoirs perform much better in earthquakes than concrete dams because they can flex with earth movement. With the Upper Chiquita Reservoir’s design, only a very small risk of failure would be present in the strongest of all possible seismic events - those that occur only once every 5,000 years. Because these rare, strong events would normally cause only some damage, not failure, the risk of failure from a seismic event is so minuscule that seismic and dam experts say that it would take a very, very strong earthquake – one likely to occur only once in a million years or more – to cause the facility to completely collapse.

Removing the Greatest Risk
The most frequent cause of failure in earthen embankment reservoirs is flooding, when heavy rainfall causes a reservoir to overflow, weakening the reservoir walls. The Upper Chiquita Reservoir facility is protected from this threat from this in several ways:

• Water Sources: Unlike most reservoirs, this one will not be joined with any natural water source, such as a stream or river, allowing SMWD to control the amount of water in the reservoir at all times.
• Cover: The facility will be covered with an impervious barrier, so rainwater will not fall into it. Rain that does fall on the cover will be pumped to surrounding storm drains, and the drains will also catch and divert runoff from the small area around the reservoir.
• Spillway: A concrete spillway, which will protect the reservoir's structural integrity in the event of rising water, is incorporated into the design to provide an extra measure of safety, even though the design prevents over-topping.
• Dual-Lining: The reservoir will be dual-lined and covered with a heavy, impervious barrier, greatly reducing the prospect of seepage and preventing overspills.
• Sub-Drains: Even if the liner were to fail, a system of sub-drains built under the liner would capture and divert the water, so it can’t weaken soils.
• Monitoring: High-tech moisture sensors and other devices will constantly monitor the reservoir and sub-drain system, allowing for up-to-the-moment detail on water levels within the structure, immediate notification of any structural irregularities or vulnerabilities, and timely diagnostics for routine maintenance.

Even with this highly unlikely probability of reservoir failure, SMWD is working with Orange County’s coordinated emergency response system to create an early warning and emergency response protocol. Because both Capistrano Unified School District and the Transportation Corridor Agencies participate in the County’s emergency program, this can be a coordinated effort, benefiting from the input of all agencies with facilities in the area.