Stormwater runoff is one of the main sources of pollution for urban waterways. Stormwater has traditionally been managed through concrete-based storm drainage systems, but the past twenty years have introduced an alternative in the form of green infrastructure. Green infrastructure for stormwater management involves the use of low impact development (LID), often vegetated facilities to mimic natural hydrologic systems that capture and allow infiltration of rainwater where it falls and from impervious surfaces upstream, before entering the drainage system. Portland, Oregon and Los Angeles, California have adopted green infrastructure into their stormwater management plans. For this project, bioswales, a form of vegetated LID facility, were tested in each city to determine their pollutant retention capabilities. Results from Portland show that bioswales filter out heavy metals effectively, and results from Los Angeles show that bioswales accumulate heavy metals in the soil over the course of the year (also due to filtering out metals from the stormwater). These results raise the question of whether accumulation can reach dangerous levels or saturate the soil with pollutants so that removal efficiency is diminished, indicating a need for further monitoring. However, the success of bioswales up to this point is encouraging and indicates that this method should continue to be employed.

Reframing the Ditch explores the application of native canopy using green street tools as a method to move beyond minimums and improve biological diversity of stormwater conveyances in a way that is consistent with visual landscape preference theory. Small stream water quality impairment is an issue found in 83% of stream headwaters in the Eastern United States. The Clean Water Act (1972), which regulates pollutant discharge into U.S. surface waters, mandates that municipalities create an implementation plan to improve water quality of their impaired streams. Water quality impairment is often exacerbated when headwater streams flow through urban areas. Urban areas are concentrations of human activity and as such bring concentrations of impermeable surfaces and stormwater runoff. As development increases, dedicated space for stormwater changes. Natural flow patterns that interacted with stratified layers of native vegetation often become constrained to ditches and pipes with little or no vegetation within the conveyance corridor. Reframing the Ditch creates an approach to help municipalities improve water quality of headwater streams by addressing water quality in ditches before water reaches the stream. The objective of urban conveyance systems is to move stormwater runoff into waterways as quickly as possible. When we design these conveyances to simply minimize stormwater interference, we ignore the potential contribution this land has for our public urban systems. This project looks for an intermediary between minimums and maximums. Maximums, also known as restoration, allows for messy, dynamic systems that are not hydrologically or visually appropriate in most urban environments. This thesis reveals ditches as complex landscapes that require high preforming vegetation, which ultimately limits the number of native species suitable for such harsh environments. Additionally, the more impermeable an environment is and the farther a ditch is from the top of the watershed, the more stormwater runoff there is, and the more space is required to process water and improve water quality. Cost, lack of available vegetation and lack of space may limit the application of this design in most circumstances. However, there are appropriate landscapes where this design methodology can provide valuable insight for landscape implementation plans aimed at improving water quality, while also providing public space, enriching neighborhood aesthetics and highlighting the function of our urban drainage systems. / Master of Landscape Architecture / The Environmental Protection Agency, through the Clean Water Act, dictates what is an appropriate level of contamination in streams and rivers within the United States. Waterway impairment is a widespread issue affecting 83% of headwater streams in the Eastern United States. Improving the quality of headwater streams, the smallest parts of stream and river networks, is generally thought of as the first opportunity to improve water quality downstream. Reframing the Ditch suggests an alternate first opportunity by looking at how we can improve water quality by addressing design of the urban ditch. Urban ditches, mostly in the form or open channels or curb-and-gutters, collect and move stormwater runoff. Ditches, typically have little vegetation and work to more water as quickly and efficiently as possible. When we eliminate vegetation from urban ditches, we also eliminate valuable function. In natural stream processes, vegetation slows, filters, and infiltrates water, improving water quality, while also improving biodiversity and providing habitat. However, theses natural stream processes are dynamic and messy systems that are often not appropriate for urban settings. In order to define a design method that is appropriate for urban settings, Reframing the Ditch utilizes a green street toolkit to create a strong sense of place, while processing stormwater, within our public rights-of way. By focusing on the application of native urban canopy within a drainage network, we can adhere to landscape preference and increase biodiversity. The design reveals that ditches are complex, context specific landscapes. While there is opportunity to increase utility of these spaces, there is complexity and cost to doing so. Layering utility into our stormwater conveyances is a valuable design strategy that serves individuals, neighborhoods, municipalities and watersheds. This project is an effort to help municipalities reframe their ditches, by providing ecological and social benefit, and ultimately improving water quality downstream.