2022 AIA Communities by Design Reimagining Petaluma SDAT - Report - Page 18
Petaluma DAT
Creating Connectivity
Historic landscape
At one point in time, Tidal wetlands covered over 16,000
acres along the lower Petaluma River. These wetlands
were composed of a range of estuarine habitat types.
The river entered the estuary near present day Payran
Street and ran for 17-miles to its mouth at San Pablo
Bay. Influenced by tidal flux and freshwater input, the
wetlands formed a dynamic landscape that supported a
wide variety of plants and animals. Bordering the estuary
were tidal-terrestrial transition zones, a link between
upland and fluvial habitats. Non-tidal wetlands occupied
11,400 acres throughout the watershed, large wetland
complexes existed at the Denman Flat area which
provided Important habitat to amphibians, migratory
waterfowl, and the endangered tricolored blackbird.
While flows were minimal in the dry season. The wet
season saw several periodically inundated areas along
the mainstem of the river and on the alluvial plain to the
east.
The City of Petaluma was incorporated in 1868 and
rapidly became an important shipping hub. The
Petaluma River (formerly the Petaluma Creek) is a tidal
slough that has been reshaped and renamed for human
uses. As the shipping industry grew, the river channel
was modified to become more conducive to navigation.
In the 1880’s a major effort by the Army Corps was
initiated with the purpose of dredging and straightening
the river. Railroad lines were also constructed across
the watershed in the late 19th century.
This large-scale dredging and construction of numerous
cut-offs completely altered the native ecosystem. Since
then, tidal wetland types have decreased by 58%.
Despite this loss, the Petaluma marsh remains the
largest contiguous expanse of historical tidal marsh in
San Pablo Bay. Non-tidal wetlands have decreased by
84%, given up for urban development.
In addition to the loss of tidal wetlands, non-tidal
wetlands throughout the watershed have also drastically
changed. Almost all the wet meadow that existed on
the northeastern part of the river has been eliminated.
Today most of this area is urban development. As
a direct result of this urban development and prior
agricultural use the groundwater levels have significantly
declined. Current data indicates that the groundwater
levels in areas that previously supported non-tidal
wetlands are at least 10 feet deep.
It is important to understand the historical
environmental context which informs how natural
systems existed in a particular place and how their
physical characteristics continue to influence ecological
patterns and processes in current times. This ecological
context helps identify opportunities and constraints
posed by the current conditions and any appropriate
restoration or management techniques.
Flood Risk
The climate along the Petaluma River watershed
is characterized by mild winters and dry summers,
resulting in seasonal variations in water flow. During the
wet season, flooding is common in the lower areas of the
watershed
Areas most at risk from flooding tend to concentrate
along the Petaluma River and its tributaries. The
northwestern end of the city -Denman Flats- is most
at risk from flooding since it falls right in the middle of
the FEMA floodplain. This area is predominantly zoned
as commercial with some industrial and mobile homes.
The southeastern portion of the city is also significantly
vulnerable, from here moving further south are complete
salt marsh wetlands. In the southeastern portion you
have the Petaluma Water Recycling (Treatment) Facility
and a large Agricultural/Commercial Development
which fall directly within the 100-year floodplain and will
require adaptations in the next 50-years.
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Despite all the ecological changes and a decrease in the
ecosystem functions the watershed once provided, a
large amount of undeveloped land within the watershed
still exists providing ample opportunities for the
restoration of historic wetlands, providing connectivity of
wetland habitats. Restoring these tidal, non-tidal and
fluvial habitats will provide flood mitigation, groundwater
recharge, water filtration and carbon sequestration
benefits.
Preliminary Observations
The City of Petaluma has been proactive in preparing
plans and establishing urban growth boundaries
to manage development, protect valuable natural
resources and restore a healthy watershed. Parks and
open spaces are an integral part of the community and
focus should continue to focus on the restoration of a
healthy watershed through the expansion of land for
conservation and preservation.
Petaluma River is a tidal slough that has been reshaped
to suit human purposes. Recent flooding and siltation
have affected the rivers’ water carrying capacity, creating
serious problems. Increased amounts of impervious
areas in buildings and roads accelerate the rate of
erosion and sedimentation and contribute to the poor
water quality and degradation of natural resources and
habitats along the river. Urbanization and its increased
expansion play an important role in the health of the
watershed.
As part of the investigation process our SDAT team
reviewed the following documents and extracted some of
the goals enumerated below:
• Petaluma AIA SDAT Application, 2020
• Petaluma General Plan 2025
• Petaluma Climate Emergency Framework
Equity – provide equal access to parks and open
spaces.
Reduce impervious surfaces and develop green
street standards, and stormwater management
infrastructure to slow, filter, and cleanse
stormwater runoff from impervious surfaces
(e.g., streets, sidewalks).
Expand the urban forest and integrate large,
primarily native, trees in neighborhoods to
provide shade and improve walkability, air
quality, heat attenuation, stormwater capture,
and carbon
Restore and enhance the Petaluma River,
recreating a healthy and accessible waterway
and pedestrian-oriented zone along the banks.
• Petaluma Watershed Enhancement Plan (2015):
Maintain navigability of the river
Improve flood control
Restore, create and protect natural habitats and
enhance native vegetation along river corridor
Expand public access and awareness of the river
• Petaluma Valley – Historical Hydrology and
Ecological Study, 2018
Community Input
Attendees at the community workshop on August
5, 2022, specified several challenges, assets,
and opportunities that prompted the team’s
recommendations around stronger connectivity through
green corridors:
Existing Challenges
• Limited ways to cross the freeway and the river
• Pollution of the Petaluma River
• Limited shade when walking in neighborhoods
