The potential of green infrastructure in mitigating flood impacts:
Focused on the mobility of low income and minority comunities

Date:
September 4, 2020
Source:
Portland State University
Summary:
This research advances national U.S. methods for assessing
flood vulnerability and prioritizing transportation improvement
investments, to ensure that no community is left stranded when
the next flood occurs.



FULL STORY ========================================================================== Short-term flooding from extreme storm events poses a serious
transportation challenge in U.S. cities. This problem -- which is
anticipated to grow over the next century with our global climate crisis
-- is often hardest on vulnerable populations, including low-income and minority neighborhoods. The latest report from the National Institute
for Transportation and Communities (NITC), led by Courtney Crosson
of University of Arizona (UA), advances national research methods for
assessing flood vulnerability and prioritizing transportation improvement investments to ensure that no community is left stranded when the next
flood occurs.


========================================================================== Crosson and fellow researchers Daoqin Tong (Arizona State University) and
Yinan Zhang (UA) conducted a flood vulnerability assessment of the City
of Tucson, Arizona's multi-modal transportation system in low-income and minority neighborhoods. They identified priority locations for Tucson to
invest in improvements to mitigate urban transportation system flooding,
and are now working with city and regional agencies to implement those findings. This project also serves as a proof of concept to advance
national research methods aimed at reducing the mobility impacts of
chronic flooding.

EFFECTIVE USE OF GREEN INFRASTRUCTURE IN LOW-INCOME NEIGHBORHOODS
Green infrastructure is a growing urban trend where stormwater is
managed by expanding permeable areas of natural vegetation throughout a
city. This approach to water management is intended to protect, restore,
or mimic the natural water cycle. Crosson's research team found that
building comprehensive neighborhood-scale green infrastructure in the right-of-way is effective at increasing multi-modal access in moderate
flooding conditions.

This green infrastructure solution did not address the mobility issues
that result from extreme flooding. Rather than municipalities selecting
areas that have the highest volumes of flooding or the highest volume of resident complaints, funds for green infrastructure should be invested
in low-income neighborhoods subject to moderate flooding in order to
achieve the greatest improvement of multimodal access.

Of the areas studied, 93% were part of census tracts with median household incomes below the Tucson average. Researchers intentionally focused
on low- income neighborhoods, since too often people living in those
areas are hardest hit by the impacts of natural disasters. Previous
research in this area has focused heavily on the vulnerability of the transportation infrastructure alone, largely ignoring the people in the communities. A NITC project funded in 2020 will develop a new methodology
that incorporates community socioeconomic vulnerability in the evaluation
of transportation infrastructure vulnerabilities for cities and regions
facing hazards.



========================================================================== RESEARCH METHOD FOR ASSESSING FLOOD VULNERABILITY IN TRANSPORTATION INFRASTRUCTURE Stage One -- Estimate Flood Conditions in Low-Income Neighborhoods: Researchers estimated flood conditions for a 5-year,
1-hour storm event (meaning a flood from a rainstorm lasting one hour,
of a size that occurs roughly every five years) using FLO-2D flood
modeling software and a digital elevation model constructed using LiDAR
data. This hydrological analysis was performed both at the city-scale
and at a 20-foot grid resolution.

Stage Two -- Identify Multimodal Transportation Priorities: The team then analyzed neighborhood transportation vulnerability. Using the results
from their flood model, they looked at overall transportation system performance across three modes (driving, bicycling and transit). Data from
the most recent 10 years of vehicular counts, bicycle counts, and bus stop ridership were used to identify the top ten priority locations for flood mitigation, based where usage was highest for each of the three modes.

Stage Three -- Perform Green Infrastructure Scenario Analyses:
Lastly, they took those top ten sites for each of the three modes of transportation and performed thirty green infrastructure scenario
analyses. They wanted to see the change in transportation network
accessibility after the same flood conditions, but with comprehensive neighborhood-scale green infrastructure in place. To do this, they used
ArcGIS Hydrology Analysis to find the "pour points," or places where
water flows out of the area. Then they altered their model to include
roadside basins (following design standards from NACTO and Pima County)
to control this flow.

Based on these model results, researchers identified five key green infrastructure design performance priorities.



==========================================================================
FIVE KEY DESIGN PRIORITIES FOR GREEN INFRASTRUCTURE TO MAXIMIZE MULTIMODAL ACCESSIBILITY These five principles can be used by transportation planners
and engineers, hydrologists, flood managers, and urban designers when approaching and evaluating project sites and investments to maximize
the impact on increased multimodal accessibility.

Prioritize Upstream Mitigation -- Across the thirty scenarios, the
priority segments with the greatest improved transportation access were
in areas that had substantial upstream mitigation. This suggests that
green infrastructure should not only be implemented directly adjacent
to priority transit locations, but also (and sometimes more importantly) implemented upstream of the priority segment.

Prioritize Moderate Flooding -- Across the thirty scenarios, the greatest impacts on improved transportation access were in areas that received
moderate flooding, in comparison to areas of extreme flooding. Often municipalities and transportation agencies are motivated to place green infrastructure installations in rights-of-way adjacent to areas where
there are the greatest flooding concerns and highest volume of resident complaints. But to help with extreme flooding, larger implementations
(such as underground stormwater piping or large basins) would need to be implemented in concert with smaller investments. When budget is limited
to neighborhood-scale investments, in order to visibly show an impact on reducing flooding and increasing accessibility to the multimodal network, moderately flooded sites are the best candidates.

Prioritize Network Gains -- When selecting project sites, it is critical
to consider the network gains that can be accomplished by concentrating
the green infrastructure within an area. By addressing the flooding issue
in one street or sidewalk segment, other downstream flooding concerns
may be helped as well.

Prioritize Large Right-of-Way Areas -- Across the thirty sites
and segments, the largest impacts often occurred when there was a
substantial amount of right-of-way available for implementation of green infrastructure. Taken into consideration with the other design principles,
the area (and corresponding volume) of the available right-of-way can
make a large difference in total flood reduction success.

Prioritize Pedestrian Travel Locations -- The greatest impacts of
green infrastructure on accessibility were in pedestrian access to bus
stops. The width of these designated areas to mitigate were smaller in
the pedestrian cases compared to bicycle and vehicle cases. Acting as a
buffer between road and pedestrian walking areas, the green infrastructure
most successfully supported greater access.

IMPLICATIONS FOR FUTURE RESEARCH AND PRACTICE The research expects
direct outcomes on future planning decisions made by the City of Tucson Department of Transportation, Tucson Water, Planning & Development
Services, and Pima County Regional Flood Control District (RFCD).

The NITC researchers on this project have met with the Director of
Tucson Department of Transportation and RFCD, and the leadership of
both agencies have expressed great interest in the research findings for upcoming decision-making around the allocation of green infrastructure
funds for roadway flooding mitigation.

This research can serve as a proof of concept for a larger, long-term
project to advance national research methods to reduce the impact of
chronic flooding on the multi-modal transportation network. Future
research should assess impact across time durations (rather than simple
peak event calculations) and work to optimize green infrastructure implementation across multiple benefits for multiple modes of
transportation (rather than individual modes).

By systematically prioritizing these projects in the right-of-way,
cities can move toward increased transportation network accessibility
and expanded equity.

This research was funded by the National Institute for Transportation
and Communities, with additional support from Pima County Flood Control
and Tucson Water.

The National Institute for Transportation and Communities (NITC)
is one of seven U.S. Department of Transportation national university transportation centers. NITC is a program of the Transportation Research
and Education Center (TREC) at Portland State University. This PSU-led
research partnership also includes the Oregon Institute of Technology, University of Arizona, University of Oregon, University of Texas at
Arlington and University of Utah. We pursue our theme -- improving
mobility of people and goods to build strong communities -- through
research, education and technology transfer.


========================================================================== Story Source: Materials provided by Portland_State_University. Note:
Content may be edited for style and length.


==========================================================================


Link to news story: https://www.sciencedaily.com/releases/2020/09/200904100636.htm

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