Evaluating the Function and Filtration Capabilities of a Retrofitted
Parking Lot Bioswale in Detroit, MI
Abstract
In long-established cities such as Detroit, MI, stormwater runoff from
impervious surfaces (roads, roofs, etc.) is combined with sanitary waste
and piped beneath the city to a wastewater treatment plant. These
engineered methods of water management, termed gray infrastructure,
currently dominate management practices but have drawbacks due to issues
of cost, capacity, reliability, and maintenance requirements. In
addition, combined sewer systems in cities like Detroit can become
overwhelmed during extreme storm events, requiring the diversion of
untreated sewage into local bodies of water. In a world of growing
urbanization and intensifying storm events, the development of
innovative approaches to stormwater management is expected to play a
large role in mitigating negative environmental impacts from polluted
urban runoff and flooding. The eco-friendly counterpart of gray
infrastructure, known as green infrastructure (green roofs, rain
gardens, bioswales, etc.), is an integrated approach to stormwater
management that utilizes decentralized infiltration systems to mimic the
natural processes of water filtration and deceleration. Correspondingly,
our research focuses on a bioswale that was retrofitted into the center
island of a previously designed parking lot in the post-industrial urban
ecosystem of Detroit. The main goals of our work are to: 1) quantify
potential pollutant removal, 2) quantify runoff infiltration capacity,
and 3) provide qualitative insight into best management practices for
future bioswale retrofits. We collected soil samples from 2 depths (30
and 45 cm) at 9 points from the bioswale for characterization (pH,
organic matter, electric conductivity, and texture). We also collected
and analyzed undisturbed soil cores with and without added metal
contaminants common to Detroit and with a surface addition of biochar to
test infiltration and determine the potential of increased contaminant
sorption. The results will allow us to advance with an improved design
and methodology and convey a strong argument for the expansion of
bioswales and other forms of green infrastructure across the greater
Detroit area, potentially leading to a more robust system of controlling
stormwater that brings aesthetics, health, and a wide array of ecosystem
services to a redeveloping concrete jungle.