Dam Safety Program

MMWD manages seven reservoirs to capture and store 75% of the water we supply to our customers. Our reservoirs include Phoenix, Lagunitas, Bon Tempe, Alpine and Kent on Mt. Tamalpais, and Nicasio and Soulajule in west Marin. Together they hold 79,566 acre-feet of water, or about 30 billion gallons.

We have a comprehensive Dam Safety Program to ensure all of our dams and spillways are safe and functioning properly. This program includes three main components: monitoring, routine inspection and maintenance, and emergency preparedness and response planning. The district also works closely with state and federal regulators and local emergency response partners to ensure public safety.


MMWD continuously monitors conditions at the dams and spillways to ensure they are functioning as intended. Instruments placed on and in the dam’s monitor, and record parameters such as water seepage, dam movement and water pressure.

The engineering technicians also perform monthly visual inspections of each dam. In addition, our rangers tour the dams frequently—often daily during rainstorms—and live onsite at Phoenix, Alpine, and Soulajule dams. Other routine visits are made by maintenance and water quality lab personnel.

Inspections and Maintenance

Through ongoing maintenance, we are able to protect the dams from deterioration and prolong their lifespans. MMWD routinely inspects the condition of each dam and spillway, and provides an annual instrumentation report to the Division of Safety of Dams (DSOD) under the California Department of Water Resources. In addition, MMWD jointly inspects each dam with DSOD every year.

Emergency Preparedness and Response

At the core of our Dam Safety Program emergency response and preparedness is our post-earthquake dam evaluation team. After significant earthquakes, trained personnel inspect the dams for any signs of damage, and the dams’ monuments are surveyed by the district surveyor to check for any vertical or horizontal movement.

In addition, MMWD works with other agencies and public safety personnel on emergency action planning and training exercises. Our Operations Center is staffed 24/7 year-round, so we are able to activate our Emergency Operations Center (EOC) at any time to coordinate the actions of MMWD first responders.

We maintain Emergency Action Plans for each of our dams in the unlikely event of a dam emergency. These plans include notification procedures and contacts with the California Office of Emergency Service to assist first responders in case of an emergency. Included in these plans are inundation maps that have been submitted to DSOD.

Inundation maps show the area downstream of each dam that could be inundated by flooding from the unlikely event of a dam failure. These maps are essential for emergency response planning as they assist in determining which downstream areas of a dam may be impacted from a dam failure so that first responders can focus their efforts.

Inundation maps are available on DSOD's website located here.

More information on DSOD Dam Safety Program can be found here.