ASCE Permeable Pavements Report
With over 100,000 members, the American Society of Civil Engineers (ASCE) not surprisingly spends a significant amount of time developing publications to advance its profession. Many publications emerge from ASCE committees as reports, manuals of practice or national standards. After four years of work, a committee report called Permeable Pavements will be released soon by ASCE’s Environment and Water Resources Institute. It is a thorough 200-page sequel to a 2005 landmark book by landscape architect Bruce Ferguson, FASLA, called Porous Pavements.
The ASCE report will be in digital format only, available for purchase and download in its entirety, or by chapter. The report defines and standardizes terms used in permeable pavements. This should help reduce confusion between such words as subbase and subgrade, runoff and run-on, infiltration and exfiltration, underdrains and drain tiles, etc. Besides defining terms throughout the text, an appendix includes a glossary.
The chapter structure of the report is straightforward. The first chapter covers requirements common to all permeable pavements. This includes structural and hydrologic design considerations. A special feature is thorough design and construction checklists. Chapters two through six cover porous asphalt, pervious concrete, permeable interlocking concrete pavements, grid pavements and some new technologies. Chapters two through five are prefaced with fact-sheets consisting of a few pages providing an instant overview of each. The chapter after each then fills in the details.
Based on experiences of the committee and the immense amount of referenced research literature throughout the entire report, chapter seven reflects on actions required for successful projects. These include clarifying owner expectations on maintenance early in the process and holding a pre-construction meeting with the owner’s representative/engineer, contractor, material suppliers and the material testing laboratory. A key objective for this meeting is sediment control through careful construction sequencing and equipment use.
Chapter eight is on maintenance and this one required the most committee discussion. The chapter sets forth surface infiltration test methods to determine when vacuuming maintenance might be required. This includes the recently approved test method for permeable interlocking concrete pavements, ASTM C1781 Standard Test Method for Surface Infiltration Rate of Permeable Unit Pavement Systems.
Chapter nine serves as an introduction to current modeling practice, as the subject could be its own book. This chapter touches on commonly used sizing models and mentions more complicated time-based simulation models used to design permeable pavements. A key consideration in selecting models is whether site outflows only are needed or if the analysis requires modeling permeable pavement within flows through a larger drainage catchment.
Chapter 10 sets forth research needs to make permeable pavements easier to design, build and maintain. This includes full-scale load testing that informs design chart/methods for more reliable structural designs. In addition, better models on pollutant reduction are needed that process inputs on pollutants, sediment loads, and base thicknesses and subgrade soil characteristics. While there have been a few dozen full-scale runoff and pollutant monitoring projects, additional research is needed to tell designers what types of pavement systems are most effective in targeting reduction of site-specific pollutants, such as nutrients, metals or oils.
The ASCE report was spearheaded by a stakeholder committee consisting of civil engineers and regulators from cities, states, the U.S. EPA and industry. The effort represents hours of discussion, debate and in-depth review of research papers on permeable pavements as well as report drafts. The effort also led to creating a comprehensive library of technical papers on the subject.
The motivation behind this effort has been direct; ask the customer what’s needed to design, build and maintain permeable pavements. Obviously, the ultimate customer is the project owner asking about requirements for a durable and low-maintenance pavement. The civil engineer is also a customer who addresses design methods, hydrologic and water pollution models, design details and specifications. The report helps answer those questions from the engineer to better service their clients. As a bonus, the report includes guide construction specifications in chapters two through five that can be modified to project conditions by design professionals.
As a customer, regulators ask how permeable pavement performance can satisfy local or state pollution reduction goals; the ASCE report provides unvarnished information. Among other places, this information is found in the appendices, which include data on volume and pollutant reductions. Regulators also want checklists for plan review and sometimes for site inspections. The checklists in this report help address that need. The intent of the report is that state and local stormwater agencies will reference it as definitive guidance in their manuals.
While the report’s chapters and pictures come from several authors, the editing and layout were orchestrated by Bethany Eisenberg with VHB Consultants and Kelly Lindow, P.E., an independent stormwater consultant. As co-chairs and seasoned stormwater professionals, both began the journey with this committee with questions asked about permeable pavements by their clients and regulators. Having provided answers, the committee delivers a landmark report.