MANAGING STABLE WATERWAYS AT BRIDGES IN THE MID-ATLANTIC

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MANAGING STABLE WATERWAYS AT BRIDGES IN THE MID-ATLANTIC

Abstract

In this study, a methodology is developed for creating stable channel transitions at bridge stream intersections. A methodology is developed to assess the level of success of a channel transition project based on the project’s attainment of a multi-criteria definition of a successful transition. In addition, the methodology guides the design type selection process for new construction.  For existing channel transitions, the assessment method provides an objective way of rating the ability of a channel transition project to address the complexities presented at a site. The design type selection methodology guides the designer to select a design that addresses the instabilities identified in a rapid channel stability assessment.  The rapid channel stability assessment is also used to identify bridge crossings where “do nothing” is a potentially valid solution. Once a design type is selected, the designer can check for trends in potential for sediment mobilization or deposition using a velocity ratio analysis, and to identify design weaknesses through a design failure modes and effects analysis.  Based on the sites included in this study this methodology aptly assesses existing transitions and provides valuable input to decision makers considering constructing transitions at existing or new bridges. Based on the sample of bridges in this study, do nothing is a potentially valid solution when the stability analysis results in a rating of

excellent or good.  This methodology can be applied to existing and new bridges and at locations both within and outside of the Mid-Atlantic.

Table of Contents

List of Figures……………………………………………………………………………………………………………….. vi

List of Tables………………………………………………………………………………………………………………… ix

Acknowledgements…………………………………………………………………………………………………………. x

Introduction……………………………………………………………………………………………………………………. 1

Literature Review……………………………………………………………………………………………………………. 6

Recent Advances in Scour and Channel Instability Practices…………………………………………….. 6

Stream Stabilization Practices……………………………………………………………………………………….. 7

Incorporating Stream Stabilization Practices into Bridge Countermeasures………………………. 10

Current State Guidance for Stream Modification at Road Crossings………………………………… 12

Methodology for Assessing Degree of Success of Existing Waterway Transitions at Bridges… 14

Damage States…………………………………………………………………………………………………………… 14

Complexity Table………………………………………………………………………………………………………. 17

Methodology for Guiding Design Selection……………………………………………………………………… 23

Rapid channel stability assessments (Lagasse et al. 2012)………………………………………………. 23

V/Vc Analysis……………………………………………………………………………………………………………. 25

Shield’s – Manning Equation for Critical Velocity……………………………………………………………. 25

DFMEA……………………………………………………………………………………………………………………. 27

Site Summaries and Field Observations…………………………………………………………………………… 28

MD 36 over Georges Creek………………………………………………………………………………………… 36

MD 17 over Middle Creek………………………………………………………………………………………….. 38

MD 28 over Tuscarora Creek………………………………………………………………………………………. 43

MD 223 over Piscataway Creek…………………………………………………………………………………… 46

MD 25 over Georges Run…………………………………………………………………………………………… 50

MD 165 over W. Branch of Winters Run……………………………………………………………………… 57

MD 136 over Broad Run…………………………………………………………………………………………….. 62

MD 7 over James Run………………………………………………………………………………………………… 66

PA SR 220 – US 220 over Vaughns Run………………………………………………………………………. 68

PA LR 405 over Bald Eagle Creek………………………………………………………………………………. 70

PA SR 3036 over South Fork of Sugar Creek………………………………………………………………… 71

Results…………………………………………………………………………………………………………………………. 73

Damage States…………………………………………………………………………………………………………… 73

Complexity Table………………………………………………………………………………………………………. 76

V/Vc…………………………………………………………………………………………………………………………. 79

Case Studies…………………………………………………………………………………………………………………. 84

MD 25 over Georges Run…………………………………………………………………………………………… 84

MD 7 over James Run………………………………………………………………………………………………… 90

MD 136 over Broad Run…………………………………………………………………………………………….. 90

Conclusions and Recommendations………………………………………………………………………………… 92

References……………………………………………………………………………………………………………………. 95

Appendix A: Location Maps…………………………………………………………………………………………… 98

Appendix B: Historical Imagery……………………………………………………………………………………. 106

MD 36 over Georges Creek………………………………………………………………………………………. 106

MD 17 over Middle Creek………………………………………………………………………………………… 110

MD 28 over Tuscarora Creek…………………………………………………………………………………….. 114

MD 223 over Piscataway Creek…………………………………………………………………………………. 119

MD 25 over Georges Run…………………………………………………………………………………………. 128

MD 165 over W. Branch Winters Run………………………………………………………………………… 132

MD 136 over Broad Run…………………………………………………………………………………………… 136

MD 7 over James Run………………………………………………………………………………………………. 141

Appendix C: HEC-RAS Longitudinal Profiles………………………………………………………………… 144

Appendix D: DFMEA………………………………………………………………………………………………….. 152

Introduction

Creating and managing stable transitions of streams through bridge openings is of vital importance to protecting infrastructure and the public.  Bridge crossings can be impositions on the local hydraulic conditions of the waterways they span; they can modify the flow of water, sediment, and woody debris (Johnson et al. 2010).  Hydraulic failure, including scour, flood, tidal, and debris buildup, is the primary failure mechanism of bridges in the United States (Wardhana and Hadipriono 2003).  Bridges are expensive capital investments that can cost millions of dollars to construct and maintain.  When it is cost prohibitive to build a bridge that spans the entire floodplain, flow altering devices can aid creating a stable channel transition that maintains the transport of materials through the bridge opening (Johnson et al. 2010).

 

Bridges over streams and rivers are susceptible to erosional processes during a wide range of flows (Johnson and Carroll 2016). Local and contraction scour erodes sediment from bridge piers and abutments, potentially affecting the safety of the bridge. There has been considerable focus on assessing scour, designing countermeasures to protect bridges against scour, and designing foundations to resist scour. Stream channel instability, on the other hand, including bank failure, lateral migration, and bed degradation, has the potential to impact safety at bridges as much or more than local and contraction scour. Figures 1-5 provide examples of unstable channels at bridges in the mid-Atlantic area. Figures 1 and 2 show channel widening upstream of the bridge that could threaten the bridge wing walls and abutments. Figure 3 shows an example of upstream bank failures that have resulted in unstable conditions at the bridge and significant deposition of sediment. Figure 4 provides an example of channel degradation that has exposed foundations and is causing the banks to become unstable. Deposition of sediment at bridge openings can also create unstable conditions by clogging the waterway (Johnson and Carroll 2016). Aggradation can cause the restricted waterway to concentrate such that scour is increased at abutments and/or piers in the remaining opening and to develop large, mobile bars, as shown in Figure 5, that increase lateral migration of the channel. The restricted waterway might also result in increased backwater, causing flooding upstream of the bridge.

 

There are a variety of techniques available for countering stream channel instability at bridges. Countermeasures are typically categorized into three groups: armoring, hydraulic control, and grade control (Lagasse et al. 2009). The treatment of stream channel instability and selection of countermeasures are dependent on the physical conditions at the bridges, such as reach-wide channel degradation, aggradation, or lateral channel movement or widening. The feasibility of and confidence in each of the various countermeasures is a function of multiple factors, including effectiveness, cost, maintenance, constraints, and the ability to detect failure. Some countermeasures have been systematically tested, while others may have been laboratory tested, but not field tested (Johnson et al. 2010). Certain countermeasures cannot be used effectively within existing right-of-ways. There are a wide range of costs associated with the initial design and construction of the measures as well as the maintenance costs. The ability to detect failure or impending failure of any of the countermeasures is important to assuring that the bridge will be protected during high flow events.  Few state DOTs offered transition design guidance in their hydraulics manuals.  For a majority of the manuals only general information on channel stability was available, and most referred to established federal guidance. Transition construction is often limited in scope by the right of way size, other constraining infrastructure, property, and/or environmental restrictions.

 

To limit stream impacts to bridge infrastructure and maintenance costs, a greater breadth of knowledge is needed on the effectiveness of various types of channel transitions.  There is a finite number of channel transition projects currently constructed.  To learn from this limited sample size, there is a need for a method of assessing the existing channel transition projects for effectiveness at mitigating inherent channel instabilities.  Successful transitions can be defined by building on the definition of stable channels at bridges. Johnson (2005) defines a stable channel in the vicinity of a bridge as one in which the relationship between geomorphic process and form is stationary and the morphology of the system remains relatively constant, over a defined distance upstream and downstream from bridge, and with minimal lateral movement.  Maintaining infrastructure integrity and safety is the primary goal of creating a channel transition at a bridge.  Two other goals of bridge operators are also included in our expanded definition; channel transitions should maintain the ability to convey the designed flood flow and require minimum maintenance. Combining these goals, successful channel transitions through bridge openings protect infrastructure integrity, maintain the designed flood conveyance of the bridge opening, and require minimal maintenance.  To assess existing structures attainment of these stated goals, two tools were used: damage state assessments and complexity table.  The first assesses damage to the infrastructure and channel transition.  The second tool identifies the degree of difficulty presented by inherent qualities of a site that can complicate the creation of a stable transition.

 

In addition to studying existing transitions, agencies desire to design and construct transitions that are well suited for a given location’s attributes.  Designing a potentially successful channel transition requires that the design identify and remediate instabilities in the reach.  Design checks add an additional level of confidence in a design. A rapid channel stability assessment (Lagasse et al. 2012; Johnson 2005) is used to initially identify areas of instability within a bridge reach.  Once a channel transition is designed, a velocity analysis using a ratio of channel velocity (V) over critical velocity (Vc) (V/Vc) analysis and a design failure modes and effects analysis (DFMEA) are conducted to review the design.  The V/Vc analysis shows trends in sediment mobilization.  The DFMEA is used to identify design components that have relatively higher risk priority numbers (RPNS).  These components can either be substituted for other components or redesigned to reduce the RPN.

 

The objective of this project is to improve current practices for developing and maintaining stable, resilient channels at bridges. The objective of this study will be achieved through the following goals:

 

  1. Develop a methodology to assess the degrees of success of stream channel transition designs through bridge reaches at existing bridges, based on the continued ability of these projects to protect the integrity of the bridge crossing, maintain the conveyance of the designed flow, and require minimal maintenance.
  2. Develop a methodology to guide the design selection process at existing or new bridges by identifying existing channel instabilities prior to design and by providing design checks.

 

 

Figure 1. Looking upstream from bridge, Krantz Mill Road over Big Beaver Creek, PA.

 

Figure 2. Looking downstream at bridge, Krantz Mill Road over Big Beaver Creek, PA.

 

Figure 3. Looking downstream at Hinkley Hills Road over East Branch of Rocky River in Medina County, Ohio.

 

Figure 4. Stream channel degradation at U.S. Rt. 199 N, 0.8 km S of Gandeville, WV.

 

Figure 5. Deposition and lateral migration at PA 3060 over S. Branch Sugar Creek near Troy, PA.

MANAGING STABLE WATERWAYS AT BRIDGES IN THE MID-ATLANTIC

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