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Steering Committee
Co-Chairs
Jay Jasperse
(Sonoma County Water Agency)
F. Martin Ralph
(Center for Western Weather and Water
Extremes at Scripps Institution of Oceanography)
Members
Michael Anderson
(California State Climate Office, Department of Water Resources)
Levi Brekke
(Bureau of Reclamation)
Michael Dettinger
(United States Geological Survey)
Mike Dillabough
(US Army Corps of Engineers)
Rob Hartman
(NOAA's National Weather Service)
Christy Jones
(US Army Corps of Engineers)
Patrick Rutten
(NOAA Restoration Center)
Cary Talbot
(US Army Corps of Engineers)
Robert Webb
(NOAA's Earth System Research Laboratory)
Support Staff
Ann DuBay
(Sonoma County Water Agency)
David Ford
(David Ford Consulting Engineers)
Arleen O'Donnell
(Eastern Research Group)
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Executive Summary
The Region
Lake Mendocino is located on the East Fork of the Russian River in Mendocino County,
California. Created in 1958 by the Coyote Valley Dam (CVD), it provides flood control,
water supply, recreation and stream flow regulation. The U.S. Army Corps of Engineers (USACE)
owns and operates the dam in accordance with the Lake Mendocino Water Control Manual
(1959, revised in 1986). Sonoma County Water Agency (Water Agency) is the local partner
that manages water stored in Lake Mendocino for water supply.
The Lake Mendocino Water Control Manual (Manual) specifies elevations for an upper
volume of reservoir storage that must be kept available for capturing storm runoff
and reducing flood risk and a lower volume of storage that may be used for water supply.
During a flood event, runoff is captured by the reservoir and released soon after to
create storage space for another potential storm. The Manual is based on typical
historical weather patterns – wet during the winter, dry otherwise.
The Challenge
The Manual utilizes gross estimates of flood potential to establish reservoir storage
and release requirements. It does not account for changing conditions in the watershed — for
example, increased variation in dry and wet weather patterns and reductions to imported
flows into the Lake that have occurred since 1986. Also, the Manual’s reservoir operations
procedures were developed decades ago, without the benefit of current science that more
accurately predicts weather and streamflow.
Given reduced supplies, changed hydrologic conditions, and technological advances, some
adjustments to the current reservoir operating procedures may be possible to optimize the
goals of maintaining flood control while bolstering water supply reliability for downstream
users and the environment (e.g., to support recovery of endangered and threatened salmonids).
Modern observation and prediction technology could be used to reduce flood risk by supporting
decisions of greater reservoir level drawdown in advance of storms. Or, such technology might
be used to improve supply reliability by permitting more storm runoff to be retained for water
supply while still preserving flood risk reduction objectives.
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Map of Russian River watershed, including Sonoma County Water Agency
transmission system. Source: Sonoma County Water Agency. (Click above for full size image)
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Graph of Lake Mendocino Rule Curve. Water must be released from lake between November 1
and March 1, when water levels are above 68,000 acre feet. (Click above for full size image)
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For example, following an atmospheric river-type storm in December 2012, water was
released to create flood space according to the Manual, dropping reservoir levels by
more than 35%. 2013 was the driest year on record, resulting in little inflow to
refill the reservoir. By December 2013 lake levels were extremely low and remained
low through 2014. Ideally, water from the December 2012 event could have been retained
based on a longer-term precipitation forecasts, lessening the impact of drought.
The Potential Solution
An interagency Steering Committee was formed to explore methods for better balancing
flood control and water supply needs. The committee, consisting of state and federal
agencies, the Center for Western Water and Weather Extremes (CW3E) and Sonoma County
Water Agency are working together on a preliminary viability assessment to determine
if Forecast Informed Reservoir Operations (FIRO) at Lake Mendocino can improve water
supply, maintain flood risk reduction, and achieve additional ecosystem benefits.
Recent studies show the potential for improved predictability of atmospheric rivers,
which provide 50% of the region’s precipitation and cause most of the Russian River’s
floods. Also, recently developed modeling capabilities and detailed field studies
have provided a greater understanding of the hydrologic processes and watershed conditions
defining soil storage capacity and the relationship between runoff and recharge in the
watershed that affects the reservoir inflow from rain invents.
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FIRO is a proposed management strategy that uses data from watershed monitoring and modern
weather and water forecasting to help water managers selectively retain or release
water from reservoirs in a manner that reflects current and forecasted conditions.
FIRO’s utilization of modern technology can optimize the use of limited resources and
represents a viable climate change adaptation strategy. The goal of FIRO is to update
standard flood control guidelines in order to improve water supply and environmental
outcomes without diminishing flood risk reduction or dam safety. Examples of tangible
benefits include:
Improve Supply Reliability for Downstream Uses - When storms cause
moderate-to-high reservoir levels, normal operation is to release water to re-establish
flood control space. With FIRO, some of that water could be retained for future supply
as long as no major precipitation is predicted for several days and it can be
demonstrated that the retained water can be released past downstream flood prone areas
before the arrival of the next storm. This strategy will permit earlier supply capture
in some years, improving summer season supply reliability for downstream water users and
improving the timing and volume of releases to protect water quality and provide flows
needed for recovery of salmonid populations.
Enhance Flood Risk Reduction - When a storm is predicted to cause flooding,
normal operations call for release of reservoir water and drawdown of water levels.
With FIRO, release decisions would consider weather observations and predictions
and the current watershed conditions, which, in some cases, would indicate greater
drawdown for flood risk reduction so long as there is confidence that the amount of
precipitation and runoff will restore reservoir levels for water supply after the storm.
Tangible Outcomes
The full Lake Mendocino FIRO assessment will include identification, assessment
and enhancement of the best science available to improve operations to maximize
flood control, water supply and ecosystem benefits. The evaluation will identify
realistic, short-term steps to provide more accurate and timely information about
weather and watershed conditions. In addition to benefitting Lake Mendocino, the project
has transferability potential throughout the western U.S. Lake Mendocino is not the only
reservoir facing challenges. Water managers nationwide are grappling with the triple
challenges of water supply, flood protection and ecosystem health in the face of climate
change. In the long-term, infrastructure solutions may be required. But in the short-term,
changes in reservoir operations could result in better water management. Identifying and
navigating the steps necessary to change reservoir operations can be intimidating.
One goal of Lake Mendocino FIRO participants is to document and share a process that
can be replicated in other communities.
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