Sue L. Niezgoda

The purpose of this review paper is to summarize the literature on the behavior and performance of permeable asphalt (PA), examine the feasibility of applying PA to arterial streets in cold climates, and present recommendations to improve the success of PA in wider applications. The review presented here required examining existing data sources and scientific journal papers, along with interviewing professionals who have conducted studies or dealt with PA in a variety of locations. The conclusions and recommendations drawn from this evaluation are intended to be guidelines for agencies looking to potentially apply PA to arterial streets in cold climate regions. Literature selected for review included PA sites that had several of the following characteristics: high volume traffic, cold climate region, abundant annual snowfall and extreme average temperatures, used sand, salt, plows, and deicers in winter maintenance activities, and experienced studded snow tires. In addition, sites reviewed also had subgrade soils with adequate infiltration rates, deep groundwater, relatively little annual precipitation, and area frost depths of 24 in. below finished grade. It was not possible to have each case study reviewed address all criteria, but all of these factors were considered important to the review to provide accurate literature comparison, and they allowed us to ascertain and present general behavior and patterns regarding PA. In addition, a summary of recommendations on the application of PA to arterial streets in cold climates with respect to water quality treatment performance, hydrologic performance, materials and durability, and maintenance practices are also presented.

The selection of an appropriate design discharge that best approximates the channel forming discharge is critical to channel design and dictates the success of restoration projects in improving channel stability. Channel forming discharge is defined as the theoretical discharge that if constantly maintained in an alluvial stream over a period of time will produce the same channel geometry that is produced by the long-term hydrograph, and it is often estimated as the bankfull, effective, or recurrence interval discharge. The determination of the channel forming flow often focuses on the physical and erosional characteristics of the stream at a reach scale (analyzing sediment transport characteristics or identifying bankfull indicators). However, with wide variability in streamflow and flood timing across regions, it is critical to examine hydrologic and watershed characteristics and their relationship to channel forming flow. Obtaining a good estimate of the channel forming discharge requires looking beyond the reach scale and gaining an understanding of regional watershed hydrology and runoff characteristics (e.g., rainfall, snowfall, geology, soil type, land use, basin topography). The purpose of this work was to conduct an investigation to determine relationships between channel forming discharge and hydrologic and watershed characteristics for snow-melt dominated streams in Wyoming and Colorado. Significant relationships between bankfull/effective discharge and watershed and hydrologic characteristics were determined. In particular, it was determined that certain characteristics directly related to snowmelt hydrology and runoff (e.g., drainage area above 9000 ft and snow water equivalent) are most significant in estimating a channel forming discharge. The results of this study provide regional characteristics of snowmelt dominant systems that are important when determining a design discharge for stream restoration projects.

Stream stabilization designers are often faced with the challenge of selecting effective bank stabilization measures. The potential benefits of stream stabilization measures can be economic, environmental, or social. Depending on the level of the potential benefit, a designer may be willing to take higher risks in implementing a given measure. A risk-benefit analysis is presented here that involves a qualitative analysis of risk and benefit (using failure modes and effects analysis) and risk and benefit quantification in terms of cost. The initial result of the method is the establishment of risk priority numbers (RPNs) and benefit priority numbers (BPNs), which provide a relative qualitative measure of the potential risk and benefit and can be used to prioritize and rank measures. The results of the qualitative analysis are then used to estimate risk and benefit quantitatively in terms of cost. These quantitative values are then compared for several stabilization alternatives to provide justification and guidance on selecting the most effective alternative. The risk-benefit method is applied to select a stream stabilization measure for a stream rehabilitation project in Indiana.