I. INTRODUCTION

The Best Management Practice, or "BMP", has become an important part of municipal stormwater management programs developed to address both stormwater quantity and quality problems. More specifically, structural BMPs, as distinguished from procedural, non-structural BMPs, play an important role in the ongoing effort to address nonpoint pollution. Structural BMPs are structures built or placed in the landscape, a process that requires varying degrees of manipulation of the landscape. Structural BMPs can have very rigid, well-defined forms, for example the oil separator, or can have more organic, "looser" forms, for example the constructed wetland. Procedural BMPs do not involve placing built structures in the landscape, but rather are techniques for carrying out certain activities, for example "no-till" farming.

Nonpoint pollution is recognized as the greatest threat to water resource quality in a majority of the nation's waters. This is true of both urban and rural areas, thought the dynamics of the nonpoint pollution problem and the methods used to address it in these distinct areas differ. In most stormwater management programs structural BMPs are a prominent option for improving stormwater and general water resource quality. In addition, the application of structural BMPs offers an opportunity to design structures that have the potential to perform several important - functions,- from improving water quality to improving and/or increasing habitat and ecosystem function.

The focus of this thesis is in four areas: 1) a review of the history of stormwater management as its focus moved toward addressing water quality and quantity issues; 2) a review of the literature to find structural BMPs that are currently being employed to address water quality problems; 3) a categorization of these BMPs by their pollutant removal mechanisms and hydrologic aspects; and 4) a description of the most current operational parameters (contributing drainage area, soil specifications, and land requirement) for structural BMPs used in urban and urbanizing areas to address nonpoint source pollution and the potential for the provision of other benefits through the use of structural BMPs. This document is intended to function as a tool to inform landscape architects and other stormwater management professionals about these aspects of structural BMP implementation, and increase awareness of the benefits of structural BMPs beyond water quality improvement.

The Context for this Work

Over the past two decades water quality in urban settings has been recognized as being jeopardized by pollutant loading from a variety of land uses. Legislative action taken in the late 1960s and early 1970s, resulting in the passage of the Federal Water Pollution Control Act of 1972 (FWPCA), was an important early effort to encourage attention to the problem. The primary result of the FWPCA was an effective program devoted to the reduction of point source pollution, the most obvious contributor to water quality degradation. Point source pollution has been defined as pollution that enters receiving waters Nonpoint pollution has only recently been recognized as a significant contributor to water quality degradation, and as point source pollution has been greatly reduced, it is now the main source of water-borne pollutants.

During the 1980s, as knowledge of the impacts of nonpoint source (NPS) pollution grew, structural BMPs came to play an increasing role in stormwater management programs. The recognition of NPS impacts, and the necessity of acting to reduce them, was made official in the 1987 Clean Water Act (CWA), which was an amendment to the FWPCA. The application of structural BMPs to address NPS pollution continues and has increased to the present. These BMPs have been recognized as valuable tools, in addition to tools used to reduce point source pollution, in efforts to improve water resource quality. The increase in their use has been paralleled by the pace of their evolution, such that the literature reveals thirteen structural BMPs currently seeing widespread use and an increase in structural complexity and overall functions. This thesis, as a review of the current state of structural BMPs, as they evolve and become more complex, will be a valuable tool to those who employ structural BMP technology in an effort to address NPS pollution in an urban setting.

Structural BMPs and Landscape Architecture

Structural BMPs are valuable tools in the management of water resources. Structural BMPs are important elements in most large scale design projects, often being a requirement of a municipality's stormwater management program. As designed elements within the landscape, structural BMPs have the potential for providing benefits beyond simply improving water quality. This is especially true of structural BMPs that have complex structures, large surface area requirements, and use water retention as a pollutant removal tool. Landscape architects, in the role of designer or planner, can employ structural BMPs toward multiple goals. These include water quality enhancement, habitat provision and improvement, aesthetic enhancement, and the education of the general public about both surface water quality and quantity issues. With the knowledge of the benefits these structural elements can offer within development projects, a landscape architect can be a valuable members of design teams for large-scale development projects and for stormwater management projects.