&EPA

SEPTEMBER 2022

CASE STUDY | Taking Steps to Protect Our Communities

SANTA FE UNDERPASS BLAZES
A FLOOD PREVENTION TRAIL
WITH GREEN INFRASTRUCTURE

When it came time to build a new pedestrian and biking underpass at one
of the busiest intersections in the metropolitan area, the City of Santa Fe,
New Mexico, included green infrastructure innovations to ensure water
from occasional heavy storms would not pool on the newly constructed
trail. Proactively incorporating green infrastructure such as stormwater
infiltration ponds, infiltration trenches, and bioswales of native plants in this
community project helped mitigate flooding on the trail, reduced reguired
maintenance at the site, saved water, and improved the local ecosystem.

BACKGROUND

Given the dry, desert environment of
New Mexico, stormwater management
might not be the first consideration for
construction project teams in the region.

The Santa Fe metropolitan area receives
only 14 inches of rain per year, much
less than the annual U.S. average of 38
inches. However, most of this rainfall
occurs during intense storms in July and
August, referred to as "monsoon season."

The high-desert and mountain scrub
ecosystem is not able to naturally stop
the flow of stormwater or reduce nutrient
loading during major weather events.

Without proper management, runoff can
cause erosion of the local landscape and
carry pollution into the Santa Fe River,
enough for the river to be classified as
impaired due to high levels of sediment,
nutrients, bacteria, and thermal pollution.

This stormwater should be treated before
it reaches the Santa Fe River watershed.

Additonally, uncontrolled stormwater
runoff during the monsoon season can
damage private and public property.

Streets and sidewalks can be covered
in sand and gravel from runoff, trees
and power lines could fall down in bad
storms, and low-lying dwellings may
become flooded.

AT-A-GLANCE

PROJECT NAME:

The Acequia Trail Pedestrian
and Bicycle Underpass

COMPLETED:

2017

LOCATION:

Santa Fe, New Mexico

POPULATION:

84,683

PROJECT FOOTPRINT:

Nearly 100,000 square feet

GREEN INFRASTRUCTURE:

Bioswales, infiltration
trenches, infiltration ponds

RESULTS:

The site can collect up
to 437,000 gallons of
stormwater per year and
holds water from a 100-year
storm event

BENEFITS:

Local watershed protection,
reduced maintenance,
improved safety and
aesthetics

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MONSOON
SEASON

Arial image of St. Francis Drive Intersection before
the project. Courtesy Serquis + Associates

Based on its unique climate and
associated challenges, the City of Santa
Fe developed a proactive stormwater
strategy to maintain a sustainable
ecosystem and quality of life by
seeing stormwater as a "resource with
unrealized opportunities."'The city's
strategy highlights the importance of
incorporating stormwater management
into local development projects such as
the AcequiaTrail Pedestrian and Bicycle
Underpass.

The Acequia Trail Pedestrian and Bicycle
Underpass project was developed to
safely link two popular trails under a
busy intersection, allowing continuous
access to the popular retail and
community spaces such as parks, plazas,
and playgrounds in southwest Santa
Fe. Before the underpass was built, the
five-way intersection on St. Francis Drive
posed safety and accessibility challenges

The annual North American
Monsoon System impacts
New Mexico and other areas
of the Southwest. From mid

June through the end of

September, exceptionally hot

days are accompanied by an

increase in thunderstorms and

flash flooding

Finished trail and underpass. Courtesy Serquis +
Associates

for pedestrians and cyclists trying to
reach the Santa Fe Railyard. The Railyard
development, a 50-acre site that was
completed in 2008, had incorporated
green infrastructure and served as a
source of inspiration for the underpass
site design.

PLANNING AND
FINANCING

A diverse group of stakeholders
contributed input throughout the
process, including: the Santa Fe Railyard,
which owned the land for the project;
the Santa Fe School for the Deaf, which
has a campus adjacent to the site;
the City of Santa Fe Bicycle Technical
Advisory Committee; and the Santa
Fe Arts Commission. During the initial
design discussions, the project team
recommended incorporating green
infrastructure features to address the
stormwater runoff that would collect and
flood the usable areas of the trail during
"monsoon" season.

Because the trail is located near a historic
irrigation canal, the team conducted a
study of the surface and groundwater of
the proposed site for the underpass. After
discussing several options to divert water
from the trail and prevent flooding, the
team decided to capture and filter water
on site.

1 City of Santa Fe Stormwater Management Strategic Plan: https://www.santafenm.gov/document
center/document/9530

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UNDERPASS
BIOSWALES

The underpass used some of
the same green infrastructure
features as the Railyard, which
include bioswales, native
plants, infiltration ponds,
and underground storage to
capture and treat stormwater.
Bioswales are shallow and
sunken vegetated channels
that slow, direct, treat,
and filter pollutants from
stormwater runoff and direct
stormwater into infiltration
ponds.

The project team used highway funds
available for the underpass to improve
the project and prevent flooding. The city
had received $4.2 million in funding from
the Federal Highway Administration's
(FHWA) Congestion Mitigation and Air
Quality (CMAQ) Improvement Program,
which focuses on traffic calming and
air guality projects.Though the funding
program does not explicitly reguire
stormwater infrastructure aspects, the
project was allowed to include green
infrastructure components to control
erosion and provide flood protection.

PROJECT DETAILS

Once funding and site design were
approved, project construction took

The underpass was excavated to resemble
a canyon and the local landscape. Courtesy
Serquis + Associates

nine months to complete. For the first
three months, the project team built the
structure of the underpass walkway. After
the structural elements of the underpass
were complete, a drainage system
modeled after a traditional irrigation
ditch was added to both sides of the
underpass. This served to direct water
from the paved underpass trail to the
green infrastructure elements.

Following the initial stages, the adjacent
trail areas were formed to resemble a
canyon, and trenches and bioswales
were added to direct stormwater to
areas for storage and treatment without
interfering with trail usability. Stormwater
is stored in two infiltration ponds—one
upper pond and one lower pond—that
collect and filter stormwater before it
reaches groundwater. When the higher
pond fills up, water flows into the lower

A semi-circular infiltration pond and the 15,000-gallon cistern prevents flooding and standing water on
the trail when it rains. Courtesy Serquis + Associates and the City of Santa Fe

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A bioswale constructed from gravel and repurposed concrete reduces erosion and directs storm water
flow. Courtesy Serquis + Associates

pond, where it wiil filter back into the
ground. When there is too much water
in the ponds, stormwater overflow is
collected in a 15,000-galIon cistern
and slowly discharged to the aguifer to
prevent flooding. The drainage system
and green infrastructure features were
designed and built to manage the runoff
from a 100-year storm event, which is
a storm that has a 1 percent chance
of occurring in any given year; in the
Santa Fe area, that type of storm can
generate 2 inches of rainfall in one hour?
Given arid climate and compact ground
conditions, that rate of rainfall could lead
to significant flooding in low-lying areas
without stormwater practices.

Various types of ground covers were
used along the sides of the trail to slow
and direct the flow of water. For example,
concrete material from the demolition
phase was crushed and repurposed
throughout the site, which both reduced
construction waste and minimized
erosion. This intentional design created a

landscape where runoff flows directly to
areas where it will be treated and filtered
back into the groundwater system.

The project incorporated native trees
and shrubs that reduce the need for
additional irrigation, since the plants
are accustomed to the local climate.
Vegetated areas also help control erosion
while improving the aesthetics of the site.

RESULTS

This project's green infrastructure can
capture and treat up to 437,000 gallons
of stormwater per year. By reducing the
likelihood of flooding during monsoon
season, it also provides the following
benefits to the community:

HEALTHIER WATERSHED:

By capturing precipitation
before it beccomes runoff
or causes flooding, these
stormwater management
features protect nearby waterways from
pollution, improving water guality and
the local ecosystem.

2 National Weather Service, Precipitation Frequency Data Server: https://hdsc.nws.noaa.qov/hdsc/pfds/

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MORE BEAUTIFUL
LANDSCAPE: Adding native
plants along with pavers and
stones enhanced the look of
the site and made it a more
pleasant pathway to encourage cyclists
and pedestrians to use alternate forms
of transportation to reach the Railyard
development.

IMPROVED SAFETY: In

addition to making it safer
to walk or bike through this
busy intersection, capturing
stormwater on this pathway
reduced the effects of flooding.

REDUCED MAINTENANCE:

Using native plants and
preventing flooding and
erosion mean less work
for city crews to maintain the trail and
irrigate the landscape during drier
months.

LESSONS LEARNED

The community learned the following
strategies for designing and building a
successful project:

• Piggyback on existing project
funds. The City of Santa Fe accessed
federal transportation funding to build
the underpass.

•	Incorporate stormwater
management concepts early. By

incorporating green infrastructure
elements into the initial design of
the project, the project team
ensured these components met the
goals of stakeholders and would be
covered by the transportation funding.

•	Get inspired. Seeing that stormwater
management technologies were
successful in the nearby Railyard
development inspired the project
designers and ensured consistency in
the area.

•	Know your local weather
conditions. Careful planning and
local site considerations prevented
problems from arising after the project
was complete. Given the prevalence
of intense rain events, the project
team considered the flooding
potential of the underpass and
designed solutions to prevent it.

ACKNOWLEDGEMENTS

The City of Santa Fe and Serguis +

Associates provided information and

photos for this case study.

Q

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