Sue L. Niezgoda

Applying Risk-Benefit Analysis to Select an Appropriate Streambank Stabilization Measure

AbstractStream 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 justifica...

Defining a Stream Restoration Body of Knowledge as a Basis for National Certification

DOI: 10.1061/(ASCE)HY.1943-7900.0000814IntroductionThe practice of stream restoration has become widely accepted asan essential component to improving ecosystem function andenhancing aquatic biodiversity (Wohl et al. 2005). Despite theabundance of projects being implemented, a lack of definitivetrainingrequirements,designprocedures,andmonitoringprotocolsremain for the practice of stream restoration. Given the lack ofconsistency, many restoration projects end in frustration, excessivecosts, and poor results (e.g., Williams et al. 1995; Kondolf 1998;Johnson and Brown 2001; Roni et al. 2002; Wohl et al. 2005;Bernhardt et al. 2007; Roni et al. 2008). The fact that methodand experience are both varied and even poorly defined in anew and emerging profession is not surprising; however, the com-bination of diverse and inconsistent training and methodologymakes progress in transforming the practice of stream restorationinto a mature profession difficult. The widespread practice of re-storation, now a billion dollar a year industry in the United States(Bernhardt et al. 2005), coupled with highly inconsistent results,demands its conversion into a profession with broadly acceptedprinciples and methods of tested reliability.As a profession advances, it must have ways to assess andassure the adequacy of education and training curricula and thecompetency of individual professionals (Ford and Gibbs 1996;Pomeroy-Huff et al. 2009). At the core of the process of maturinga profession is the establishment of a body of knowledge (BOK), adocument generated by experts to identify and delineate theconcepts, facts, and skills that practitioners in that profession areexpected to master (Morris et al. 2006; Pomeroy-Huff et al.2009). For example, project management professionals saw a clearneed to formulate a common and consistent set of core competen-cies on which they could base a project management certificationand advance their emerging profession (Morris et al. 2006; Winteret al. 2006). In the emerging profession of stream restoration, asimilar call exists for the establishment of consistent training stan-dards, standards of practice, and professional certification, drivenlargely by the lack of agreed on criteria for judging restoration suc-cess and highly inconsistent project results (Palmer et al. 2005;Marr 2009; Kite 2009; Fischenich 2009). The development of aprofession with standards of practice and/or certification first re-quires establishment of a training and education structure that pro-vides consistency and can support and incorporate advances inunderstanding (Morris et al. 2006).A fully effective symbiosis among research, training, andpractice has yet to emerge in stream restoration; however, severalattemptsweremadeduringthepast10yearstoestablishthecurrentandfutureneedsinstreamrestoration educationandtraining [RiverRestoration Northwest (RRNW) 2003; (AFS Curriculum WorkingGroup, unpublished data, 2003); P. Wilcock, unpublished internalreport, December 2006 RRNW, in cooperation with Oregon StateUniversity and Portland State University, sought to advance thequality of the river restoration practice by identifying restorationeducational needs (RRNW 2003). In 2003, RRNWand its partnersimplemented a survey to assess the job tasks, educational back-grounds, and training needs of professionals working on river re-storation projects in the northwestern United States and Canada.The key results are as follows.1. Available training is multidisciplinary with most universityand short courses focused on ecology, fluvial geomorphology,fisheries, restoration, and soils. Fisheries biologists and civilengineershavethegreatestrangeoftrainingacrossdisciplines.2. Improved skills and competence in fluvial geomorphology,field techniques, restoration techniques, and biology/ecologywere identified as important for a practicing professional.

ESTIMATING A STREAM RESTORATION DESIGN DISCHARGE

A primary assumption of the natural channel design method for stream restoration is that the bankfull design discharge is the dominant discharge. Dominant 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. The dominant discharge appears typically in two forms, the effective discharge and the bankfull discharge. The bankfull discharge is the most commonly used form in stream restoration projects. The selection of an appropriate design discharge that best approximates the dominant discharge is critical to the natural channel design methodology and will dictate the success of restoration projects in improving channel stability and water quality. In this paper, we present several existing methods of estimating dominant discharge, including methodology, assumptions, limitations, and appropriate applications. The goal of this paper is to offer the stream restoration community an introduction to dominant discharge and provide a reference that will aid in the selection of an appropriate design discharge for restoration projects.

A Critical Review of Permeable Asphalt Behavior and Performance to Guide Application to Arterial Streets in Cold Climates

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.

Relationships Between Watershed and Stream Characteristics and Channel Forming Discharge in Snowmelt Dominated Streams

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.

Developing Probability of Failure Estimates for Stream Restoration Design Components

Stream restoration projects are proliferating in all regions of the country to provide improvements to streams disturbed by highway construction, urbanization, and channel modifications. The morphologically-based natural channel design method is commonly used to design stream restoration projects; however, the design approach is often vague, qualitative, and lacking in guidance. This can lead to an increase in project uncertainty and costs. A two-step method of incorporating uncertainty and risk in stream restoration design has been developed as a combination of Design Failure Modes and Effects Analysis (DFMEA) and risk quantification. The purpose of DFMEA is to prioritize failures in accordance with their risk. The definition of risk contains two components: (1) probability of failure and (2) consequence of failure. Probability of failure of stream restoration design components is often difficult to determine due to lack of published failure data. In the existing risk assessment method, the likelihood of occurrence ratings from the DFMEA are used to estimate the probability of failure. A set of tasks were carried out to improve the application of the two-step risk assessment method by developing better estimates of probability of failure for stream restoration design components. A literature review was performed to compile potential failure modes, causes of failure, associated predictor variables, and uncertainty in the predictor variables for stream restoration design components. Following this, advanced probabilistic techniques, namely Logistic Regression Analysis (LRA) and Monte Carlo Simulation (MCS), were applied to develop improved failure probabilities for stream restoration design. MCS was used to incorporate the results of the literature review and to select values for the predictor variables for use in the LRA. The LRA provided a model that was used for prediction of the probability of occurrence of an event. The results were incorporated into the existing risk assessment method to create a better decision making tool for stream restoration design. The incorporation of the resulting risk assessment method in the design phase of stream restoration projects can be important to decision making and will improve the likelihood of success.

APPLYING COST-BASED RISK ASSESSMENT TO STREAM RESTORATION DESIGN

A low-risk, stream restoration design includes methods that validate design assumptions, incorporate uncertainty in the decision-making process during the project design phase, and reduce uncertainty by checking the final design. A twostep method of incorporating uncertainty and risk in stream restoration design has been developed as a combination of Design Failure Modes and Effects Analysis (DFMEA) and risk quantification. As a first step, DFMEA is applied to identify risk in terms of ratings with respect to consequence of failure, the likelihood of occurrence of a failure, and the ability to detect a failure. Due to its evolutionary nature, the DFMEA can be revised to account for design modifications and relative ratings are re-evaluated to examine reductions in uncertainty, and thereby, risk. The second step of the method is quantifying risk using initial and expected failure costs. Expected failure cost is defined as the product of probability of failure and the cost associated with failure. Since failure probability and cost of failure are both difficult to determine directly in stream restoration, the consequence and likelihood of occurrence ratings from the DFMEA can be used to estimate the expected cost and probability of failure, respectively. Using this method, risk can be estimated for several restoration design alternatives and compared to provide justification and guidance on selecting the most cost effective design alternative. The two-step, riskbased method is illustrated through application to a stream relocation project in Pennsylvania and a stream restoration project in North Carolina. Overall, the twostep method presented here can prove valuable in decision-making and will improve the likelihood of success in stream restoration design.

Urban Stream Restoration: Guidance for Monitoring and Assessment Protocols

Stream restoration over the past decade has become big business, with annual expenditures in the billions of dollars. Many projects have been completed in urban watersheds because of changing hydrology and sediment budgets have resulted in excessive bank erosion that threatens urban infrastructure. Though many projects have been completed nationally, post-project monitoring and assessments are not routinely conducted. If assessments are conducted, they are rarely reported in publicly accessible documents. Professionals involved in stream restoration have expressed the need for greater monitoring and assessment of projects, particularly in urbanizing watersheds where undisturbed reference streams are not common. The Urban Streams Committee of the Urban Water Resources Research Council and the River Restoration Committee jointly formed a task committee with the goal of producing a guidance document for monitoring and assessment of urban stream restoration projects. This paper summarizes the progress to date of the committee.

Panel Discussion of Stream Classification Systems

Classification systems provide one means for generalizing, organizing, and categorizing sets of diverse items into groups. Stream channels tend to fit into broad categories (e.g., braided, meandering, sinuous, and straight) that suggest the utility of having some type of stream classification system. Recently, natural channel design has been advocated as a goal for stream alterations and has become the heart of some stream classification systems. Similarly, channel evolution has been recommended as one means for gaining insight to dominant channel processes. Both approaches rely on observations and comparisons of channel condition and geomorphic form. However, the physical appearances of streams can be misleading, as they often represent only fleeting glimpses at conditions, usually transitory, that reflect many different states of anthropogenic disturbance. This poses a particular difficulty in terms of stream channel restoration efforts, as there are few or no undisturbed streams in many regions of the country against which to make reference in order to understand what types of restoration goals and potentials may be relevant. Nevertheless, several classification systems have been developed that are used to assist in or even to guide stream alteration activities, including stream restoration. This panel reviews the features of classification systems and considers their pros and cons for various applications, including stream restoration.