Atmospheric River Capture (ARC) Project - General Project Information

Why Regional Water Supply Collaboration Matters

PROJECT STATUS AND ENVIRONMENTAL REVIEW What environmental studies are being conducted?

Marin Water is currently preparing a draft Environmental Impact Report (EIR) in accordance with the California Environmental Quality Act (CEQA). The draft EIR will evaluate a range of environmental topics, including: Traffic and transportation Noise Biological resources (such as wetlands and oak woodlands) Cultural and archaeological resources Air quality and other environmental factors

North Bay and broader regional water systems are interconnected, and agencies regularly work together during droughts, emergencies, and other periods of urgent need to help maintain reliable water supplies.

Environmental surveys are also underway to better understand existing site conditions, including areas that may contain sensitive habitats or resources.

How will environmental impacts be addressed?

The draft EIR will identify potential environmental impacts of the project and evaluate ways to avoid, minimize or mitigate those impacts where feasible. This includes consideration of construction-related impacts as well as operational effects.

The proposed ARC Project would strengthen regional water resilience by capturing and storing excess winter water during specific storm conditions for later use during dry periods. By storing available winter water locally during wet periods, the project can help improve drought preparedness in Marin while supporting more flexible use of shared regional water supplies during future dry conditions.

Marin Water and neighboring agencies have a long history of working together to support regional water resilience during changing conditions, droughts and emergencies.

The ARC Project would leverage existing infrastructure to create a connecting pipeline to access and store water during key storm events for use during dry periods.

As part of the Environmental Impact Report (EIR) process now underway, a range of alternatives will continue to be formally evaluated and analyzed before any project approval is considered.

Connecting winter water to storage for a more resilient water supply Marin Water is proposing to construct the Atmospheric River Capture (ARC) Project, a water supply project designed to improve Marin Water’s resilience during dry periods. It would provide the infrastructure needed to deliver high flows from the Russian River during and following key winter storms to Nicasio Reservoir for storage, where the water can be used later during dry periods.

HOW IT WORKS From Storm to Storage

Why ARC over other options like more storage tanks, increasing reservoir capacity, etc.?

Over the last five years, Marin Water has developed and evaluated a wide range of water supply and storage options as part of its long-term planning, including reservoir expansion, the creation of new reservoirs, desalination, recycled water, direct potable reuse, bolstered demand management efforts, and increased use of supplemental Russian River supplies. Based on that evaluation, the ARC Project was identified as the most practical and cost-effective near-term option for improving long-term water supply reliability.

ATMOSPHERIC RIVER CAPTURE (ARC) PROJECT

Drought Response (2021) – Residential Preparedness

During the most recent drought, Marin Water and North Marin Water District worked with the County of Marin and other partners to prepare for providing emergency potable water supplies for rural residents relying on wells that were at risk of running dry. These measures were ultimately not needed due to changing conditions.

Even in dry years with below-average rainfall, intense atmospheric river storms can temporarily swell the Russian River with high winter flows.

The ARC Project would operate during these dry year storm windows to capture and store water that would otherwise flow to the ocean.

Winter water captured during key storm windows

Drought Response (2021) – Agricultural Use

Both water districts also worked with the County of Marin to support water needs in areas outside both districts’ service areas, including allowing West Marin ranchers to purchase and truck untreated reservoir water for agricultural use over several months during the drought.

The Russian River watershed is much larger than Marin Water’s Mt. Tam watershed. As a result, storms there can generate sustained runoff and elevated river flows – even in dry years – creating opportunities to capture water.

Novato Landslide (2023)

Travels through existing North Marin Aqueduct

Nicasio Reservoir

A landslide in Novato raised concerns about access to local water supply. Marin Water coordinated with North Marin Water District and was prepared to support emergency interconnections if needed to help maintain service for North Marin Water District customers.

Future Opportunity – Stafford Lake Winter Water Storage

The ARC Project would include infrastructure connecting to Stafford Lake, creating a potential future opportunity for North Marin Water District to more efficiently capture and store available winter water during key storm events. By leveraging infrastructure used by both agencies, this could support additional drought resilience and more efficient use of available regional winter water sources.

Future Opportunity – Supporting North Bay Water Resilience

By allowing Marin Water to store water captured during key winter storm events for later use, the ARC Project could help reduce reliance on shared regional water supplies during droughts. This added flexibility may help support broader North Bay water resilience during periods when water supplies are limited.

MORE PROJECT INFORMATION:

Visit Project webpage marinwater.org/ARCproject

Email Project team ARCproject@marinwater.org

Watch Project video Scan code

The captured winter water would travel through existing infrastructure already used by Marin Water. Today, this water flows directly to the distribution system, not into local reservoirs.

Conveyed to storage via new pipeline and pump system

The ARC Project builds a new connection between the Aqueduct and Nicasio Reservoir, providing the missing link that allows for captured winter water to be stored for later use.

Stored in Nicasio Reservoir for later use

Stored water would supplement Marin Water’s supply during extended dry periods. Diversions from the Russian River would be closely coordinated with weather forecasts and reservoir levels and would only occur when storage space is available and local conditions in the Russian River Watershed allow.

CAPTURING WINTER RAIN DURING DRY PERIODS THE FULL PROJECT AT A GLANCE What Would Be Built

Even in dry years, historical data shows that large winter storms can still produce significant flows in the Russian River watershed, which is about 40 times larger than the watershed feeding Marin Water’s seven local reservoirs.

New infrastructure would connect the North Marin Aqueduct to Nicasio Reservoir, allowing captured winter flows to be stored for use during dry periods.

These flows can remain elevated for weeks or even months, and much of this water flows to the Pacific Ocean, even after environmental requirements are met. The ARC Project would allow Marin Water to capture a limited portion of that water during these storm windows and store it for use later during dry periods.

Amount of water flowing to Pacific Ocean from Russian River Russian River at Hacienda Bridge gage (CFS)

Cubic feet per second (CFS)

100,000

PROJECT TIMELINE Estimated as of May 2026 and may change based on environmental review, property acquisitions and permitting.

2025-2026 Preliminary Design 2025-2027 Environmental Review

(Environmental Impact Report prepared in compliance with the California Enviornmental Quality Act)

The full Project would include a 13.2-mile pipeline, two pumping stations, a dechlorination facility and points of delivery at both Stafford Lake and Nicasio Reservoir.

1

Scoping: Initiate Environmental Review with Notice of Preparation (NOP) & Public Outreach Comments on EIR scope collected March 13 – April 13, 2026

CURRENT ESTIMATED PROJECT COST AND FUNDING $195 million, with a potential range of $137 million to $293 million

2

Publish Draft EIR Anticipated fall 2026

Marin Water is funding the design of the ARC Project through its capital budget program and plans to finance construction through bond funding. In parallel, the Project team is also actively investigating all available state and federal funding opportunities that may help offset some of the Project costs.

3

4

Improve Drought Resilience Captures excess winter water resulting from storm events, and stores it in local reservoirs for use during dry periods.

Strengthen Regional Collaboration Strengthens regional water resiliency by leveraging infrastructure shared with neighboring agencies, creating opportunities for more efficient use of shared water sources and mutual aid during future dry periods.

2026-2027 Final Design & Permitting 2027-2030 Construction

45,000 MGD (million gallons per day)

10,000

1,000

65 MGD

100

1920 1940 1960 1980 2000 Russian River flows typically range from 100 CFS (65 MGD) to over 70,000 CFS (45,000 MGD) depending on water year type (wet or dry)

HOW THE PROJECT WOULD HAVE WORKED IN PREVIOUS DROUGHTS The project would operate during dry years when there are low reservoir storage levels in Marin, extended dry periods and high flow in the Russian river from atmospheric river storm events. When these conditions align, the project can operate during key storm windows to store water for later use.

Even in 1976-1977, the dryest year of record, approximately 27,000 acre-feet of excess Russian River water flowed out into the ocean, well above in-stream requirements. The ARC project would have enabled the District to capture and store some of this surplus water.

During the last drought in 2021, Nicasio Reservoir had enough available storage capacity that the ARC Project could have delivered over 16,000 acre-feet of additional water supply over a four-year period. At the time, the District was considering building an expensive emergency pipeline across the Richmond Bridge to ensure adequate water supply, which would not have been necessary had the ARC Project been in place.

Drought of Record – 1976-1977 (Winter months when ARC Project would operate) Russian River at Hacienda Bridge gage (CFS)

Public Comment Period for Draft EIR (45 days) Anticipated fall 2026 Address Public Comments on Draft and Publish Final EIR Anticipated late 2026 / early 2027

Drought of record 1976-1977

10

Minimum instream flow requirments (CFS)

1,000 900

Align with Community Priorities Marin Water is coordinating with local agencies as the project develops to identify opportunities, where feasible, to align the project with local priorities and provide added community value.

Cubic feet per second (CFS)

*This connection to Stafford Lake creates a potential future opportunity for North Marin Water District to more efficiently capture and store available winter water during dry periods.

KEY BENEFITS

Minimum instream flow requirments (CFS)

800 700 600

139 days of available surplus water (~27,000 acre-feet)

500 400 300 200 100 Oct. 1 1976

Nov. 1 1976

Dec. 1 1976

Jan. 1 1977

Feb. 1 1977

Mar. 1 1977

Apr. 1 1977

May 1 1977

CAPTURING WINTER RAIN DURING DRY PERIODS THE FULL PROJECT AT A GLANCE What Would Be Built

Even in dry years, historical data shows that large winter storms can still produce significant flows in the Russian River watershed, which is about 40 times larger than the watershed feeding Marin Water’s seven local reservoirs.

New infrastructure would connect the North Marin Aqueduct to Nicasio Reservoir, allowing captured winter flows to be stored for use during dry periods.

These flows can remain elevated for weeks or even months, and much of this water flows to the Pacific Ocean, even after environmental requirements are met. The ARC Project would allow Marin Water to capture a limited portion of that water during these storm windows and store it for use later during dry periods.

Amount of water flowing to Pacific Ocean from Russian River Russian River at Hacienda Bridge gage (CFS)

Cubic feet per second (CFS)

100,000

PROJECT TIMELINE Estimated as of May 2026 and may change based on environmental review, property acquisitions and permitting.

2025-2026 Preliminary Design 2025-2027 Environmental Review

(Environmental Impact Report prepared in compliance with the California Enviornmental Quality Act)

The full Project would include a 13.2-mile pipeline, two pumping stations, a dechlorination facility and points of delivery at both Stafford Lake and Nicasio Reservoir.

1

Scoping: Initiate Environmental Review with Notice of Preparation (NOP) & Public Outreach Comments on EIR scope collected March 13 – April 13, 2026

CURRENT ESTIMATED PROJECT COST AND FUNDING $195 million, with a potential range of $137 million to $293 million

2

Publish Draft EIR Anticipated fall 2026

Marin Water is funding the design of the ARC Project through its capital budget program and plans to finance construction through bond funding. In parallel, the Project team is also actively investigating all available state and federal funding opportunities that may help offset some of the Project costs.

3

4

Improve Drought Resilience Captures excess winter water resulting from storm events, and stores it in local reservoirs for use during dry periods.

Strengthen Regional Collaboration Strengthens regional water resiliency by leveraging infrastructure shared with neighboring agencies, creating opportunities for more efficient use of shared water sources and mutual aid during future dry periods.

2026-2027 Final Design & Permitting 2027-2030 Construction

45,000 MGD (million gallons per day)

10,000

1,000

65 MGD

100

1920 1940 1960 1980 2000 Russian River flows typically range from 100 CFS (65 MGD) to over 70,000 CFS (45,000 MGD) depending on water year type (wet or dry)

HOW THE PROJECT WOULD HAVE WORKED IN PREVIOUS DROUGHTS The project would operate during dry years when there are low reservoir storage levels in Marin, extended dry periods and high flow in the Russian river from atmospheric river storm events. When these conditions align, the project can operate during key storm windows to store water for later use.

Even in 1976-1977, the dryest year of record, approximately 27,000 acre-feet of excess Russian River water flowed out into the ocean, well above in-stream requirements. The ARC project would have enabled the District to capture and store some of this surplus water.

During the last drought in 2021, Nicasio Reservoir had enough available storage capacity that the ARC Project could have delivered over 16,000 acre-feet of additional water supply over a four-year period. At the time, the District was considering building an expensive emergency pipeline across the Richmond Bridge to ensure adequate water supply, which would not have been necessary had the ARC Project been in place.

Drought of Record – 1976-1977 (Winter months when ARC Project would operate) Russian River at Hacienda Bridge gage (CFS)

Public Comment Period for Draft EIR (45 days) Anticipated fall 2026 Address Public Comments on Draft and Publish Final EIR Anticipated late 2026 / early 2027

Drought of record 1976-1977

10

Minimum instream flow requirments (CFS)

1,000 900

Align with Community Priorities Marin Water is coordinating with local agencies as the project develops to identify opportunities, where feasible, to align the project with local priorities and provide added community value.

Cubic feet per second (CFS)

*This connection to Stafford Lake creates a potential future opportunity for North Marin Water District to more efficiently capture and store available winter water during dry periods.

KEY BENEFITS

Minimum instream flow requirments (CFS)

800 700 600

139 days of available surplus water (~27,000 acre-feet)

500 400 300 200 100 Oct. 1 1976

Nov. 1 1976

Dec. 1 1976

Jan. 1 1977

Feb. 1 1977

Mar. 1 1977

Apr. 1 1977

May 1 1977

CAPTURING WINTER RAIN DURING DRY PERIODS THE FULL PROJECT AT A GLANCE What Would Be Built

Even in dry years, historical data shows that large winter storms can still produce significant flows in the Russian River watershed, which is about 40 times larger than the watershed feeding Marin Water’s seven local reservoirs.

New infrastructure would connect the North Marin Aqueduct to Nicasio Reservoir, allowing captured winter flows to be stored for use during dry periods.

These flows can remain elevated for weeks or even months, and much of this water flows to the Pacific Ocean, even after environmental requirements are met. The ARC Project would allow Marin Water to capture a limited portion of that water during these storm windows and store it for use later during dry periods.

Amount of water flowing to Pacific Ocean from Russian River Russian River at Hacienda Bridge gage (CFS)

Cubic feet per second (CFS)

100,000

PROJECT TIMELINE Estimated as of May 2026 and may change based on environmental review, property acquisitions and permitting.

2025-2026 Preliminary Design 2025-2027 Environmental Review

(Environmental Impact Report prepared in compliance with the California Enviornmental Quality Act)

The full Project would include a 13.2-mile pipeline, two pumping stations, a dechlorination facility and points of delivery at both Stafford Lake and Nicasio Reservoir.

1

Scoping: Initiate Environmental Review with Notice of Preparation (NOP) & Public Outreach Comments on EIR scope collected March 13 – April 13, 2026

CURRENT ESTIMATED PROJECT COST AND FUNDING $195 million, with a potential range of $137 million to $293 million

2

Publish Draft EIR Anticipated fall 2026

Marin Water is funding the design of the ARC Project through its capital budget program and plans to finance construction through bond funding. In parallel, the Project team is also actively investigating all available state and federal funding opportunities that may help offset some of the Project costs.

3

4

Improve Drought Resilience Captures excess winter water resulting from storm events, and stores it in local reservoirs for use during dry periods.

Strengthen Regional Collaboration Strengthens regional water resiliency by leveraging infrastructure shared with neighboring agencies, creating opportunities for more efficient use of shared water sources and mutual aid during future dry periods.

2026-2027 Final Design & Permitting 2027-2030 Construction

45,000 MGD (million gallons per day)

10,000

1,000

65 MGD

100

1920 1940 1960 1980 2000 Russian River flows typically range from 100 CFS (65 MGD) to over 70,000 CFS (45,000 MGD) depending on water year type (wet or dry)

HOW THE PROJECT WOULD HAVE WORKED IN PREVIOUS DROUGHTS The project would operate during dry years when there are low reservoir storage levels in Marin, extended dry periods and high flow in the Russian river from atmospheric river storm events. When these conditions align, the project can operate during key storm windows to store water for later use.

Even in 1976-1977, the dryest year of record, approximately 27,000 acre-feet of excess Russian River water flowed out into the ocean, well above in-stream requirements. The ARC project would have enabled the District to capture and store some of this surplus water.

During the last drought in 2021, Nicasio Reservoir had enough available storage capacity that the ARC Project could have delivered over 16,000 acre-feet of additional water supply over a four-year period. At the time, the District was considering building an expensive emergency pipeline across the Richmond Bridge to ensure adequate water supply, which would not have been necessary had the ARC Project been in place.

Drought of Record – 1976-1977 (Winter months when ARC Project would operate) Russian River at Hacienda Bridge gage (CFS)

Public Comment Period for Draft EIR (45 days) Anticipated fall 2026 Address Public Comments on Draft and Publish Final EIR Anticipated late 2026 / early 2027

Drought of record 1976-1977

10

Minimum instream flow requirments (CFS)

1,000 900

Align with Community Priorities Marin Water is coordinating with local agencies as the project develops to identify opportunities, where feasible, to align the project with local priorities and provide added community value.

Cubic feet per second (CFS)

*This connection to Stafford Lake creates a potential future opportunity for North Marin Water District to more efficiently capture and store available winter water during dry periods.

KEY BENEFITS

Minimum instream flow requirments (CFS)

800 700 600

139 days of available surplus water (~27,000 acre-feet)

500 400 300 200 100 Oct. 1 1976

Nov. 1 1976

Dec. 1 1976

Jan. 1 1977

Feb. 1 1977

Mar. 1 1977

Apr. 1 1977

May 1 1977

Why Regional Water Supply Collaboration Matters

PROJECT STATUS AND ENVIRONMENTAL REVIEW What environmental studies are being conducted?

Marin Water is currently preparing a draft Environmental Impact Report (EIR) in accordance with the California Environmental Quality Act (CEQA). The draft EIR will evaluate a range of environmental topics, including: Traffic and transportation Noise Biological resources (such as wetlands and oak woodlands) Cultural and archaeological resources Air quality and other environmental factors

North Bay and broader regional water systems are interconnected, and agencies regularly work together during droughts, emergencies, and other periods of urgent need to help maintain reliable water supplies.

Environmental surveys are also underway to better understand existing site conditions, including areas that may contain sensitive habitats or resources.

How will environmental impacts be addressed?

The draft EIR will identify potential environmental impacts of the project and evaluate ways to avoid, minimize or mitigate those impacts where feasible. This includes consideration of construction-related impacts as well as operational effects.

The proposed ARC Project would strengthen regional water resilience by capturing and storing excess winter water during specific storm conditions for later use during dry periods. By storing available winter water locally during wet periods, the project can help improve drought preparedness in Marin while supporting more flexible use of shared regional water supplies during future dry conditions.

Marin Water and neighboring agencies have a long history of working together to support regional water resilience during changing conditions, droughts and emergencies.

The ARC Project would leverage existing infrastructure to create a connecting pipeline to access and store water during key storm events for use during dry periods.

As part of the Environmental Impact Report (EIR) process now underway, a range of alternatives will continue to be formally evaluated and analyzed before any project approval is considered.

Connecting winter water to storage for a more resilient water supply Marin Water is proposing to construct the Atmospheric River Capture (ARC) Project, a water supply project designed to improve Marin Water’s resilience during dry periods. It would provide the infrastructure needed to deliver high flows from the Russian River during and following key winter storms to Nicasio Reservoir for storage, where the water can be used later during dry periods.

HOW IT WORKS From Storm to Storage

Why ARC over other options like more storage tanks, increasing reservoir capacity, etc.?

Over the last five years, Marin Water has developed and evaluated a wide range of water supply and storage options as part of its long-term planning, including reservoir expansion, the creation of new reservoirs, desalination, recycled water, direct potable reuse, bolstered demand management efforts, and increased use of supplemental Russian River supplies. Based on that evaluation, the ARC Project was identified as the most practical and cost-effective near-term option for improving long-term water supply reliability.

ATMOSPHERIC RIVER CAPTURE (ARC) PROJECT

Drought Response (2021) – Residential Preparedness

During the most recent drought, Marin Water and North Marin Water District worked with the County of Marin and other partners to prepare for providing emergency potable water supplies for rural residents relying on wells that were at risk of running dry. These measures were ultimately not needed due to changing conditions.

Even in dry years with below-average rainfall, intense atmospheric river storms can temporarily swell the Russian River with high winter flows.

The ARC Project would operate during these dry year storm windows to capture and store water that would otherwise flow to the ocean.

Winter water captured during key storm windows

Drought Response (2021) – Agricultural Use

Both water districts also worked with the County of Marin to support water needs in areas outside both districts’ service areas, including allowing West Marin ranchers to purchase and truck untreated reservoir water for agricultural use over several months during the drought.

The Russian River watershed is much larger than Marin Water’s Mt. Tam watershed. As a result, storms there can generate sustained runoff and elevated river flows – even in dry years – creating opportunities to capture water.

Novato Landslide (2023)

Travels through existing North Marin Aqueduct

Nicasio Reservoir

A landslide in Novato raised concerns about access to local water supply. Marin Water coordinated with North Marin Water District and was prepared to support emergency interconnections if needed to help maintain service for North Marin Water District customers.

Future Opportunity – Stafford Lake Winter Water Storage

The ARC Project would include infrastructure connecting to Stafford Lake, creating a potential future opportunity for North Marin Water District to more efficiently capture and store available winter water during key storm events. By leveraging infrastructure used by both agencies, this could support additional drought resilience and more efficient use of available regional winter water sources.

Future Opportunity – Supporting North Bay Water Resilience

By allowing Marin Water to store water captured during key winter storm events for later use, the ARC Project could help reduce reliance on shared regional water supplies during droughts. This added flexibility may help support broader North Bay water resilience during periods when water supplies are limited.

MORE PROJECT INFORMATION:

Visit Project webpage marinwater.org/ARCproject

Email Project team ARCproject@marinwater.org

Watch Project video Scan code

The captured winter water would travel through existing infrastructure already used by Marin Water. Today, this water flows directly to the distribution system, not into local reservoirs.

Conveyed to storage via new pipeline and pump system

The ARC Project builds a new connection between the Aqueduct and Nicasio Reservoir, providing the missing link that allows for captured winter water to be stored for later use.

Stored in Nicasio Reservoir for later use

Stored water would supplement Marin Water’s supply during extended dry periods. Diversions from the Russian River would be closely coordinated with weather forecasts and reservoir levels and would only occur when storage space is available and local conditions in the Russian River Watershed allow.

Why Regional Water Supply Collaboration Matters

PROJECT STATUS AND ENVIRONMENTAL REVIEW What environmental studies are being conducted?

Marin Water is currently preparing a draft Environmental Impact Report (EIR) in accordance with the California Environmental Quality Act (CEQA). The draft EIR will evaluate a range of environmental topics, including: Traffic and transportation Noise Biological resources (such as wetlands and oak woodlands) Cultural and archaeological resources Air quality and other environmental factors

North Bay and broader regional water systems are interconnected, and agencies regularly work together during droughts, emergencies, and other periods of urgent need to help maintain reliable water supplies.

Environmental surveys are also underway to better understand existing site conditions, including areas that may contain sensitive habitats or resources.

How will environmental impacts be addressed?

The draft EIR will identify potential environmental impacts of the project and evaluate ways to avoid, minimize or mitigate those impacts where feasible. This includes consideration of construction-related impacts as well as operational effects.

The proposed ARC Project would strengthen regional water resilience by capturing and storing excess winter water during specific storm conditions for later use during dry periods. By storing available winter water locally during wet periods, the project can help improve drought preparedness in Marin while supporting more flexible use of shared regional water supplies during future dry conditions.

Marin Water and neighboring agencies have a long history of working together to support regional water resilience during changing conditions, droughts and emergencies.

The ARC Project would leverage existing infrastructure to create a connecting pipeline to access and store water during key storm events for use during dry periods.

As part of the Environmental Impact Report (EIR) process now underway, a range of alternatives will continue to be formally evaluated and analyzed before any project approval is considered.

Connecting winter water to storage for a more resilient water supply Marin Water is proposing to construct the Atmospheric River Capture (ARC) Project, a water supply project designed to improve Marin Water’s resilience during dry periods. It would provide the infrastructure needed to deliver high flows from the Russian River during and following key winter storms to Nicasio Reservoir for storage, where the water can be used later during dry periods.

HOW IT WORKS From Storm to Storage

Why ARC over other options like more storage tanks, increasing reservoir capacity, etc.?

Over the last five years, Marin Water has developed and evaluated a wide range of water supply and storage options as part of its long-term planning, including reservoir expansion, the creation of new reservoirs, desalination, recycled water, direct potable reuse, bolstered demand management efforts, and increased use of supplemental Russian River supplies. Based on that evaluation, the ARC Project was identified as the most practical and cost-effective near-term option for improving long-term water supply reliability.

ATMOSPHERIC RIVER CAPTURE (ARC) PROJECT

Drought Response (2021) – Residential Preparedness

During the most recent drought, Marin Water and North Marin Water District worked with the County of Marin and other partners to prepare for providing emergency potable water supplies for rural residents relying on wells that were at risk of running dry. These measures were ultimately not needed due to changing conditions.

Even in dry years with below-average rainfall, intense atmospheric river storms can temporarily swell the Russian River with high winter flows.

The ARC Project would operate during these dry year storm windows to capture and store water that would otherwise flow to the ocean.

Winter water captured during key storm windows

Drought Response (2021) – Agricultural Use

Both water districts also worked with the County of Marin to support water needs in areas outside both districts’ service areas, including allowing West Marin ranchers to purchase and truck untreated reservoir water for agricultural use over several months during the drought.

The Russian River watershed is much larger than Marin Water’s Mt. Tam watershed. As a result, storms there can generate sustained runoff and elevated river flows – even in dry years – creating opportunities to capture water.

Novato Landslide (2023)

Travels through existing North Marin Aqueduct

Nicasio Reservoir

A landslide in Novato raised concerns about access to local water supply. Marin Water coordinated with North Marin Water District and was prepared to support emergency interconnections if needed to help maintain service for North Marin Water District customers.

Future Opportunity – Stafford Lake Winter Water Storage

The ARC Project would include infrastructure connecting to Stafford Lake, creating a potential future opportunity for North Marin Water District to more efficiently capture and store available winter water during key storm events. By leveraging infrastructure used by both agencies, this could support additional drought resilience and more efficient use of available regional winter water sources.

Future Opportunity – Supporting North Bay Water Resilience

By allowing Marin Water to store water captured during key winter storm events for later use, the ARC Project could help reduce reliance on shared regional water supplies during droughts. This added flexibility may help support broader North Bay water resilience during periods when water supplies are limited.

MORE PROJECT INFORMATION:

Visit Project webpage marinwater.org/ARCproject

Email Project team ARCproject@marinwater.org

Watch Project video Scan code

The captured winter water would travel through existing infrastructure already used by Marin Water. Today, this water flows directly to the distribution system, not into local reservoirs.

Conveyed to storage via new pipeline and pump system

The ARC Project builds a new connection between the Aqueduct and Nicasio Reservoir, providing the missing link that allows for captured winter water to be stored for later use.

Stored in Nicasio Reservoir for later use

Stored water would supplement Marin Water’s supply during extended dry periods. Diversions from the Russian River would be closely coordinated with weather forecasts and reservoir levels and would only occur when storage space is available and local conditions in the Russian River Watershed allow.