Hydraulics Engineering - Photos from the 1998 Scanning Review of
European Practice for Bridge Scour and Stream Instability Counter Measures
Observations on Specific Countermeasures
Photos from the Scanning Tour
Of the more than 575,000 bridges in the national bridge inventory, approximately 84 percent are over water. Each year in the United States, highway bridge failures cost millions of dollars as a result of both direct costs necessary to replace or restore bridges and indirect costs related to disruption of transportation facilities. Of even greater consequence is the loss of life from bridge failures. Hydraulic factors such as stream instability, degradation, contraction scour, and local scour account for more of our bridge failures (approximately 60 percent) than all other factors combined.
On-going screening and evaluation of the vulnerability of the nations' highway bridges to scour by State Departments of Transportation have identified more than 18,000 bridges that are considered scour-critical and in need of repair or replacement. Almost 100,000 bridges with unknown foundations have been identified. As State Departments of Transportation develop Plans of Action to address the effects of scour and stream instability, there is a need for innovative, effective, and economical countermeasures to be considered for the design of new bridges and for repairing existing bridges.
With this in mind the Federal Highway Administration (FHWA), the American Association of State Highway and Transportation Officials (AASHTO), and the Transportation Research Board (TRB) sponsored a scanning review of European practice for bridge scour and stream instability countermeasures in October 1998. This review involved a Panel of representatives from FHWA, state departments of transportation (California, Illinois, Maryland, Minnesota, Oregon, and South Carolina), universities, and the private sector. The Panel included a State Bridge Engineer and three members of the AASHTO Task Force on Hydraulics and Hydrology. The review included visits to highway research institutes, hydraulic research laboratories, and field sites in four countries: Switzerland, Germany, the Netherlands, and the United Kingdom. Scanning review objectives were to:
- Review and document innovative techniques used to mitigate the effects of scour and stream instability at bridges.
- Evaluate these techniques for potential application in the United States.
- Share information on United States' practice with counterparts in the countries visited.
While the review concentrated on bridge scour and stream instability countermeasures, the Panel's inquiries were wide-ranging and included basic scour technology for evaluation and design, laboratory and field research programs, environmental issues, and bioengineering techniques.
Scour Manuals. In the United States, bridge scour technology is contained primarily in three FHWA publications:
- HEC-18; Evaluating Scour at Bridges
- HEC-20; Stream Stability at Highway Structures
- HEC-23; Bridge Scour and Stream Instability Countermeasures
Copies of these publications were provided to each host agency in all four countries visited. During the scanning review, several recently published or draft documents were obtained that summarize bridge scour and countermeasure technology in Europe. These documents, which will be reviewed in more detail by the Panel in preparation of the final report for the scanning review, may enhance our basic scour technology and do suggest a number of potentially useful countermeasure design and installation techniques. Specific manuals include: (1) a recently published Scour Manual by hydraulic engineers at the Delft Hydraulics Laboratory in the Netherlands, (2) Handbook 47 for Bridge Scour Assessment prepared by British Railtrack, (3) a draft Advice Notice on Assessment of Scour at Highway Bridges being prepared for the Highway Agency in the United Kingdom, and (4) a River and Channel Revetment Design Manual published recently by the H.R. Wallingford Laboratory in the United Kingdom. In the Netherlands the Panel was provided a copy of a new publication on Dikes and Revetments by Pilarczyk. Engineers in all four countries visited referred to a manual on the Use of Rock in Hydraulic Engineering (CUR Report #169) as an extremely important reference book.
Design Philosophy. The general design approach in Switzerland, Germany, and the Netherlands is to prevent scour from occurring or move scour away from the structure by including scour and stream instability countermeasures in the initial design and construction of their bridges. In general, these countries feel that they do not have a significant bridge scour problem, largely because of this design approach. The fact that their major navigable waterways and canals have been stabilized by extensive river training works, obviously contributes to the success of this approach.
The bridge scour problem in the United Kingdom is similar to that faced in the United States. Both countries are applying the latest scour technology to the design of new bridges, but both face significant problems with scour and stream instability at thousands of bridges on an aging infrastructure. As a result of a catastrophic railroad bridge failure with fatalities at Glanrhyd in 1987, Railtrack has taken the lead in developing scour assessment techniques and countermeasures in the United Kingdom.
Risk Analysis. Some form of risk analysis is used to determine the level of effort and investment in countermeasure design and installation in all countries visited. For example, Switzerland uses a matrix to code flood hazard zones into increasing degrees of hazard (yellow, blue, red) and infrastructure design and maintenance decisions are guided by the degree of risk involved. The Netherlands uses both a regional risk analysis, considering such factors as distance from the coast and vulnerability to storm surge, and a detailed analysis of the risk of failure of individual components of a project. These factors influence the decision on investment in scour countermeasures. In all four countries both a design flood and a larger "check" flood are used in bridge and scour countermeasures design, comparable to the 100-year frequency design flood and 500-year frequency (or super flood) check flood used for scour assessment in the United States. In the United Kingdom the "super flood" has a 200-year return period.
Environmental Policy. Environmental impacts are considered for scour and stream instability countermeasure selection, design and installation in all countries visited. In the United Kingdom, the Environmental Agency through the National Centre for Risk Analysis and Options Appraisal has prepared a Guidance Note (No. 18) on River Geomorphology: A Practical Guide which outlines a geomorphological approach to river management. In general, their approach is to emphasize environmental enhancement and sustainability, without creating an undue risk to lives and property in applying environmental policy to structures in a riverine system.
River Geomorphology. In the United States, FHWA's HEC-20 stresses the need to take a river system/geomorphic approach to channel instability problems. All four countries in Europe recognize the value of a geomorphic analysis in bridge and countermeasure design. At the University of Nottingham in the United Kingdom, in particular, research in applying geomorphic reconnaissance techniques to river engineering problems has produced useful and practical guidance for the hydraulic engineer. Such techniques support geomorphic classification of a river system and permit a detailed investigation of form and process for critical reaches where instability could affect bridge design or countermeasure selection, design and maintenance. The Panel obtained two recent publications from Nottingham, a Stream Reconnaissance Handbook, and a text on Applied Fluvial Geomorphology for River Engineering and Management which will be reviewed in more detail for the final report.
Scour Prediction. While investigating improved scour prediction techniques was not the primary purpose of the scanning review, methods to calculate scour, particularly in complex flow situations, were obviously of interest to the Panel. For example, at both the Delft Hydraulics Laboratory in the Netherlands and the H.R. Wallingford Laboratory in the United Kingdom, researchers are working on the problem of scour at very wide piers, which is a high priority research need in the United States. The approach in both cases is to develop techniques to estimate the time rate of scour and determine the point at which the process makes the transition from scour on a "slender" pier (influenced largely by pier width) to scour on a wide pier (influenced primarily by water depth). The investigations encompass both unidirectional (riverine) flow and reversing (tidal) flow. At the H.R. Wallingford Laboratory, specialized apparatus has been developed to investigate the time rate of scour in cohesive materials.
In Switzerland, the Netherlands, and the United Kingdom, the estimation of turbulence intensity in relation to the structure (bridge, storm surge barrier, etc.) is considered to be a key factor for estimating scour potential and designing scour countermeasures. For example, at the New Waterway storm surge barrier near Rotterdam, the size of riprap channel protection is graded from larger stone near the barrier to smaller stone away from the barrier, based on an estimate of turbulence intensity from a physical model of the storm surge barrier.
In estimating scour at a bridge pier, researchers in the Netherlands consider the interaction between the various scour components (long-term degradation, general or contraction scour, and local scour) when calculating total scour. The interaction between scour holes on adjacent substructure elements is considered indeterminate. At Delft, research has been conducted on the combined effects of lateral channel migration and local scour, specifically the development of scour on groins in meander bends. The Dutch consider the most pressing research needs in scour prediction to be:
- Prediction of bed levels during floods in relation to the general morphological behavior of the river.
- Determination of the relationship between the flood wave and the speed with which the riverbed responds (i.e., the relationship between scour development and flood duration).
- Development of techniques to estimate the superposition of general and local scour (e.g., scour at a pier in a river bend or the interaction of contraction scour and local scour in a straight reach of river).
The problems of estimating scour at wide piers, calculating scour under tidal flow conditions, the time rate of scour, particularly in cohesive materials, and the interaction of the various scour components are recognized in the United States as among our most pressing research needs in scour.
Modeling. Both physical hydraulic modeling in a laboratory and numerical computer modeling are among the standard techniques available to analyze the scour problem and design countermeasures. The Panel had the opportunity to visit hydraulic modeling laboratories with exceptional facilities and capabilities at the laboratory of Hydraulics, Hydrology, and Glaciology of the Swiss Federal Institute (VAW/ETH) in Zurich, Switzerland; the Federal Waterways Engineering and Research Institute (BAW) in Karlsruhe, Germany; and the H.R. Wallingford Laboratory in Wallingford, United Kingdom. In Europe it is much more likely that physical modeling, often in conjunction with computer modeling, will be used as an integral part of the hydraulic design process for bridge foundations and countermeasures than we are accustomed to in the United States.
A major effort is underway in Europe to develop 1-, 2-, and 3-dimensional computer models with hydrodynamic, sediment transport, and in some cases, morphologic capabilities. In fact, it was apparent that the Delft Hydraulics Laboratory, as a recently privatized entity, has made a business decision to transition from maintaining extensive physical modeling capabilities to establishing Delft as a center of expertise in computer modeling in Europe. As an initial reaction, it appears that our 1- and 2-dimensional hydrodynamic modeling capabilities to support scour predictions and countermeasures design are comparable with what is currently available in Europe.
Inspection and Monitoring. Most of the countries visited, have initiated efforts to develop a bridge inspection or scour evaluation program comparable to the National Bridge Inspection Standards (NBIS) in the United States. In Switzerland, some specific guidance on the stability of structures in water has recently been published (1998) as a multi-agency guideline by the Federal Office for Highways (ASTRA), the Federal Office for Transport (BAV), the Federal Office for Water Management (BWW), and the Swiss Federal Railways (SBB). This document is presented as a "Recommendation for the preservation and maintenance of existing structures/Hints for the construction of new structures." In Germany, the Federal Highway Research Institute (BAST) is investigating the use of the FHWA PONTIS bridge management system.
The Railtrack Handbook 47 on scour prepared in the United Kingdom apparently contains some guidance on inspection, but a copy of this document was not available for review. In response to the Glanrhyd bridge failure in 1987, high water marks were painted on most railroad bridges in the United Kingdom to guide inspectors decisions on caution or closure, but this approach apparently met with only mixed success as it resulted in unnecessary bridge closures.
Only in the United Kingdom was an effort made comparable to the U.S. National Cooperative Highway Research Program (NCHRP) Project 21-3 to develop fixed instrumentation for measuring and monitoring scour at bridge piers and abutments. This resulted in the patented Wallingford "Tell-Tail" device which was installed on several railroad bridges following the Glanrhyd bridge failure. Again, this approach appears to be viewed in the United Kingdom as only marginally successful.
In none of the four countries was technology available to determine the characteristics of unknown bridge foundations, that is, foundations for which design or as-built drawings do not exist. In the United Kingdom there are numerous unknown foundation bridges and the problem is considered as serious as it is in the United States.
OBSERVATIONS ON SPECIFIC COUNTERMEASURES
Riprap. The use of riprap, that is, armor stone in combination with a geotextile or granular filter, is by far the most common scour and stream instability countermeasure in all countries visited in Europe. Its availability, economy, ease of installation, and flexibility are considered highly desirable characteristics in all four countries visited. As a result, considerable effort has been devoted to techniques for determining size, gradation, layer thickness and horizontal extent, filters, and placement techniques and equipment for revetment and coastal applications. They consider riprap an effective and permanent countermeasure against channel instability and scour, including local scour at bridge piers.
Generally, riprap is sized using the Hudson formula (coastal applications), Shields diagram, or methods developed in New Zealand, the Netherlands, the United Kingdom, or the United States. The need for designing the riprap for a specific site was emphasized. Great care is taken in placing the riprap at critical locations, and in many cases stones are placed individually in the riprap matrix. Highly specialized equipment has been developed by construction contractors in Europe for placing riprap, particularly for coastal installations. The use of bottom dump or side dump pontoons (barges) is common in both Germany and the Netherlands. For large installations, vessels for placing riprap are equipped with dynamic positioning systems using Differential Global Positioning System technology and thrusters to maintain position, and echo sounders (or divers) to verify the coverage of the riprap layer. Some of the smaller pontoon systems, particularly the bottom dump pontoons developed in Germany could be used to place riprap in water at larger bridges.
At the BAW in Germany, the Panel observed wave tank testing of prototype scale partially grouted riprap. In general, the objective is to increase the stability of the riprap without sacrificing all of the flexibility. Contractors in Germany have developed techniques and equipment to achieve the desired grout coverage (fill about 40 percent of the voids at the surface) and the right penetration (decreasing grout fill with depth into the riprap matrix and no grout in contact with the geotextile filter). With the correct slurry mix (recipe) partial grouting can be achieved underwater with minimal environmental impact. Even though engineers in the Netherlands and United Kingdom and current guidance in the United States tend to discourage the use of grouted riprap, BAW engineers believe that partial grouting, if done correctly, will ensure that the riprap retains sufficient flexibility while adding to stability.
A number of references on partially grouted riprap from the Permanent International Association of Navigation Congresses (PIANC) were obtained in Germany. The Panel plans to review the work at BAW in detail.
Filters. As in the United States, a properly designed geotextile or granular filter is considered essential to the success of riprap and most other countermeasures on sand or fine-grained material. In Germany and the Netherlands, a significant investment has been made in the development and testing of geosynthetic materials, and innovative installation techniques have been developed that could find application for bridge pier and abutment countermeasures in the United States.
At the BAW in Karlsruhe, Germany, a highly specialized laboratory is available for testing a wide range of geotextile characteristics, including: (1) impact test (to determine punching resistance, e.g., when large stone is dropped on the geotextile); (2) abrasion test; (3) permeability, clay clogging, and sand clogging tests; and (4) tests of material characteristics such as elongation and strength. Through this testing program, geotextile materials have been developed that permit innovative approaches to filter placement for riprap and other countermeasures.
Geotextile containers (large sand bags) made of mechanically bonded non-woven fabrics up to 1.25 cubic meters in volume have been used to provide a filter layer for riprap installation at several large projects in Germany. The containers are sewn on three sides at a factory and filled on-site to approximately 80 percent of capacity with sand/gravel filter material using a hopper system. The final seam is sewn on site. The containers are placed in layers using a side-dump pontoon. The elongation capabilities of the fabric and partial filling allow the containers to adjust to irregularities of the substrate at the installation site. Riprap is then placed over the layer of geotextile containers.
At the Eidersperrwerk storm surge barrier on the Eider estuary in Germany, a filter layer of more than 48,000 geotextile containers was used to repair a 30 meter deep scour hole at the barrier. An armor layer of 1 to 6 ton stone and toe stabilization using a fascine mat (see below) with smaller stone completed the installation. Similarly, a geotextile bag filter and riprap protection were used as a countermeasure against pier scour at a new bridge on the Peena River in Germany. The Dutch used a similar concept to place a filter at the Eastern Scheldt storm surge barrier completed in 1986. Instead of individual sand bags, large sand mats or mattresses consisting of two layers of non-woven geotextile with granular material in between were fabricated on land and placed with large barge mounted rollers as a foundation for individual precast dam components and as a filter for riprap placed for scour protection.
Three countries, Germany, Netherlands, and the United Kingdom use fascine mats, a very old, traditional approach for scour protection, as a means of placing a geotextile filter in deep water. The fascines consist of a matrix of willow or other natural material woven in long bundles (15- to 20-cm in diameter) to form a matrix which is assembled over a layer of woven geotextile. The geotextile has ties which permit fastening it to the fascine mat. The fascine mattress, sometimes called a "sinker mat" is floated into position and sunk into place by dropping riprap-size stone on it from a barge. Fascine sinker mats and riprap have been used to protect the toe of the geotextile container/riprap protection at the Eider estuary storm surge barrier in Germany and for coastal applications in the Netherlands.
River Training. River training and stabilization techniques against lateral channel migration in the major navigable waterways of Europe are similar to those employed by the U.S. Army Corps of Engineers on navigable waterways in the United States (e.g., the Mississippi, Ohio, and Missouri river systems). Groins and jetties projecting roughly perpendicular to the river bank, dikes placed parallel to the river bank, or revetment placed on the river bank are the most common river training works in Europe. Generally, riprap is the preferred construction material. Scour at the nose of groins and jetties, at the head of dikes, and at the toe of revetment are the most commonly cited problems.
River training has been an ongoing process on Europe's navigable rivers (or on canals in the Netherlands) for hundreds of years, and there are few unprotected reaches of river. Thus, lateral instability due to river meander is a rare occurrence and is not considered a threat to bridges. The Panel noted that on the Rhine River from Koblenz to Mainz, the only reach of river we had the opportunity to observe in detail, that the use of long parallel dikes placed roughly one third of the channel width from the river bank to constrict the flow is much more common than in the United States, where a groin field would be used for the same purpose. Flow is allowed to pass through the area between the dike and the river bank, sometimes over a submerged groin or weir.
To protect the toe of river bank (or canal bank) revetment, two approaches are usually employed. Either a toe trench is excavated and riprap is placed in the trench, or a "falling apron" approach is used. While the former is common in the United States, the latter is not. The falling apron or self launching of riprap revetment was mentioned in all four countries. With this approach, stone is placed in a windrow along a bankline or at the toe to be protected, and as the river erodes into the bankline or toe it launches the material along the face of the slope and onto the toe. Methods are available to estimate the amount of extra material required to protect the revetment toe and to compensate for not having a filter.
Riverbed Degradation. Sills, grade control structures, low check dams, or weirs constructed of a variety of materials are commonly used in Europe to protect against vertical channel instability (degradation) as they are in the United States. However, innovative approaches to the problem were presented in Switzerland and Germany, that justify further consideration.
In Switzerland, the flood control agency (BWW) has experimented in the field with local channel widening in lieu of replacing deteriorating check dams as a means of grade control on the Emental River near Zurich. Enhanced environmental diversity on a narrowly channelized river is seen as a benefit, but some local instability and the need to protect the shoulders of the widened section may be a detriment.
In Germany, the approach to the problem of degradation on the Rhine River has involved sediment management on a large scale. Here, it is recognized that long-term degradation problems are generally related to a deficiency in the supply of sediment to a river reach or river system. As a result, a system-wide sediment management program has evolved which involves as one component, an attempt to replenish the sediment supply by "feeding the Rhine." As much as 150,000 tons of material annually is extracted from local quarries and placed in the Rhine above critical reaches to replenish the sediment supply and reverse degradational trends. A four volume handbook on sediment management on the Rhine was made available to the Panel.
The Swiss also recognize the impacts of sediment deficiency on river system stability. Prior to 1970, gravel mining (or harvesting) from rivers was allowed in Switzerland, but when scour problems were noted in adjacent reaches, the practice was restricted. Now gravel mining is allowed only in sediment detention basins.
Alternative Countermeasures. Among the areas of particular interest to the Panel during the scanning review were alternative countermeasures such as flow altering devices or alternatives to riprap (particularly for the pier scour problem). The following paragraphs outline some of the Panel's observations on alternative countermeasures in relation to United States practice.
In 1987, the Swiss experienced a near catastrophic failure of a major highway bridge when the Reuss River migrated laterally and undermined the foundation of a bridge pier. The countermeasure system developed by the VAW/ETH laboratory included large concrete groins to correct and prevent further channel migration. The river bank between the groins was protected by very large precast concrete prisms, triangular in cross section, placed individually as revetment. In lieu of smaller interlocking armor units that would be costly to fabricate, the decision was made to cast much larger prisms with a simple shape and use the mass of the prisms to protect against river bank scour. The precast, hollow prisms were filled with concrete after they were placed in their final position. The groin field and prism revetment were then covered with a layer of natural stone for aesthetic and environmental reasons. The economics of the trade-offs between smaller, high cost interlocking shapes for artificial riprap and simpler shapes with more mass are worth further consideration.
In general, proprietary products such as interlocking block, articulating cable-tied block, and articulating grout filled mattresses for revetment and channel bed protection are not considered as effective as riprap in Europe. The need for adequate toe protection and anchoring was emphasized. Block and mattress manufacturers in the United States and Europe are developing design criteria based on full-scale laboratory testing of specific products. Such tests should provide the necessary guidance for the successful design and installation of proprietary products for revetment and channel protection.
Recent laboratory testing by NCHRP, FHWA, and others in the United States indicates that when articulating mat products are used as a pier scour countermeasure, the joint between the mattress and the pier must be protected to prevent scour under the mat. The Panel encountered two approaches to solving this problem that justify further evaluation. In Germany, reference was made to a proprietary system for installing a collar and tying the geotextile filter underlying a block mattress to the bridge pier using a pneumatic tie. This approach appears feasible for circular piers. In the Netherlands, the recommended approach is to place granular filter material to a depth of 1 meter below the stream bed for 5 meters around the pier. The geotextile filter and block mat placed on the stream bed overlap this granular filter layer and the remaining gap between the mat and the pier is filled with riprap. Successful field installations have apparently been made using this technique.
Recent laboratory research by NCHRP, FHWA, and others in the United States has shown that flow altering devices such as scour collars, sacrificial piles, and guide vanes as countermeasures against pier scour are only marginally effective. The Panel did not encounter any successful applications of flow altering devices as a pier scour countermeasure in any of the countries visited. However, researchers at the VAW hydraulic laboratory in Switzerland studied pressure flow at a bridge using devices to modify the flow. Pressure flow occurs when flood waters are high enough to submerge bridge superstructure elements or overtop the bridge deck. One of the devices studied was a curved plate, called a pressure flow shield, that is placed on the upstream side of a bridge. The study concluded that the pressure flow shield could prevent overtopping and improve flow conditions through the bridge opening. In another experiment at VAW the upstream, bottom edge of each bridge girder was modified by the addition of a rounded "nose." This improved flow conditions through the bridge under pressure flow and reduced backwater upstream of the bridge. This approach also appeared to decrease scour under the bridge and improve the passage of debris (trees and other vegetation) through the bridge opening.
Protecting bridges from the accumulation of debris and predicting the increase in scour at a bridge caused by debris is a problem world wide. The Panel did not encounter any applications of "debris deflectors" or other devices at a bridge during the scanning review. The Swiss were, however, experimenting with the design of large "trash racks" at sedimentation basins to catch vegetative debris before it moves downstream to a bridge. At the University of Nottingham in the United Kingdom, a substantial effort has been made to develop software to aid in the prediction of scour when debris accumulates at a bridge.
Bioengineering. Based on familiarity with the literature prior to the scanning review, Panelists considered Europe a leader in the use of bioengineering techniques for river instability problems. While bioengineering techniques are integrated with traditional engineering countermeasures for river system management in Europe, hydraulic engineers in all four countries visited would not recommend the reliance on bioengineering countermeasures as the only countermeasure technique when there is a risk of damage to property or a structure, or where there is potential loss of life. The primary concern expressed was a lack of knowledge about the properties of the materials being used in relation to force and stress generated by flowing water, and the difficulties in obtaining consistent performance from countermeasures relying on living materials.
During the scanning review a number of case studies were presented to the Panel from which potentially valuable "lessons learned" can be derived for the final report. The following tables summarize these case studies.
Lessons Learned From Bridge Failures.
||Items of Interest
||Lateral channel migration and use of "prisms" as countermeasure to correct channel instability.
||1997 and 1998 floods. Hundreds of bridges damaged or destroyed due to inadequate foundation design or inadequate waterway opening. Over 8,000 bridges in need of repair.
|Salzach River, Salzburg
||Effect of installation of a temporary access dike for bridge repair. Unavoidable construction delays extended into the flood season and led to a 12 m deep scour hole at main bridge pier on spread footing which then required structural underpinning.
Lessons Learned From Successful Installation of Countermeasures.
||Items of Interest
||Geotextile containers as filter layer. Use of fascine mat as toe protection. Extent of riprap mat. Specialized equipment.
||Use of geotextile container and riprap for pier protection.
|Eastern Scheldt Barrier
||Geotextile mat as filter layer. Individually placed riprap stone. Extent of riprap mat. Specialized equipment.
|New Waterway, Rotterdam
||Riprap sizing based on turbulence intensity.
The scanning review Panel had the unique opportunity to visit four European countries and discuss and observe design philosophy, scour prediction techniques, inspection and monitoring practices and numerous specific countermeasures for bridge scour and stream instability problems. The Panel is in the process of preparing a final report which will provide detailed descriptions of findings and our final recommendations. Based on a preliminary review of our observations, the following items may provide recommendations for implementation or further evaluation.
- The economics of including scour and stream instability countermeasures in the initial construction of a bridge.
- The applicability of risk analysis in bridge and countermeasure design, particularly in the selection and design of countermeasures for existing scour critical or unknown foundation bridges.
- Consideration of risk to the structure, lives, or property in relation to environmental policy.
- Review of European inspection and monitoring programs and manuals in relation to the National Bridge Inspection Standards (NBIS).
- Recognition of the importance of geomorphic reconnaissance and analysis in selection and design of countermeasures.
- Improved techniques to analyze and predict scour, particularly for complex flow situations such as wide piers, pressure flow, tidal scour, debris, and the interaction of general and local scour components.
- Investigation of the role of turbulence intensity and the time rate of scour.
- Consideration of increased use of physical hydraulic models and development of computer models to evaluate scour in complex flow situations and for the design of countermeasures.
- Re-evaluate design and installation techniques for riprap and reconsider its viability as a permanent countermeasure against pier scour.
- Review of techniques for design and installation of partially grouted riprap and evaluate its applicability to United States practice.
- Evaluate the use of innovative techniques for placing filters under riprap and other countermeasures, including geotextile containers, geotextile mattresses, and the use of fascine mats.
- Evaluate the placement of riprap revetment using falling apron or self launching techniques.
- Evaluate the applicability of sediment management as a means to counteract long-term river bed degradation problems.
- Consider the relative merits of proprietary products (interlocking block, cable-tied block, articulating block, and mattresses) in relation to the use of riprap for channel protection and as local scour countermeasures.
- Suggest techniques to prevent scour at the "joint" between articulating mattresses and a bridge pier when these products are used as a pier scour countermeasure.
- Develop "lessons learned" from case studies.
During the final Panel meeting initial steps were taken to develop an implementation plan. The following activities were discussed.
Papers could be presented at the following conferences or meetings:
- Prepare paper for ASCE Water Resources Division Specialty Conference in Seattle, August 1999 (Pagan and Lagasse, Abstract submitted October 15, 1998)
- AASHTO presentation, November 1998, Boston (Hulbert)
- TRB A2A03, A2K03, and A2C06 Committee presentations, January 1999, Washington, D.C.
- AASHTO Bridge Conference, San Diego, May 1999
- AASHTO Task Force meeting and Western Regional Hydraulic Engineers Conference, Lake Tahoe, May 1999 (Bryson, Ghere, Hulbert)
- TRB 5th Bridge Conference, Tampa, Florida, April 2000 - Discussion with program committee on submitting abstract (due November 30, 1998 - Bryson, Ghere, Hulbert)
- International Society for Soil Mechanics and Geotechnical Engineering (ISSMGE) Year 2000 Conference, Melbourne, Australia (Briaud)
Other activities that would continue the dialogue with European counterparts or disseminate information to other groups include:
- Incorporate new technology into FHWA planned update of HEC-18, 20, and 23 and in NHI planned revisions to Stream Stability and Scour at Bridges courses (NHI No. 13046 and 13047) and Highways in the River Environment course (NHI No. 13010)
- Invite/provide support for selected hydraulic engineers from countries visited during the scanning review to an appropriate conference in the United States for continued dialogue. At least one excellent candidate was identified in each country visited
- FHWA International Programs and NHI schedule a Stream Stability and Scour course in cooperation with the H.R. Wallingford Laboratories in the United Kingdom. Primary purpose would be to build on the exceptional rapport established with scour researchers and practitioners during the visit to the United Kingdom. Staff the course with FHWA and Ayres instructors to increase the opportunities for productive exchange.
- Explore opportunities to reach the Association of General Contractors regarding techniques, equipment, quality control, specifications, etc. for riprap and other countermeasure placement
- Seek support for a study of AASHTO riprap specifications and work with AASHTO on recommendations for improvement
1998 Scanning Review of European Practice for
Bridge Scour and Stream Instability Countermeasures
October 16-20, 1998
Laboratory of Hydraulics, Hydrology and Glaciology (VAW); Swiss Federal Institute of Technology (ETH)
October 21, 1998
Federal Research Institute for Water Construction (BAW)
Rhine River - Koblenz to Mainz, Germany
October 22, 1998
Federal Research Institute for Water Construction (BAW)
Bergisch-Gladbach (Cologne), Germany
October 23, 1998
Federal Institute for Transportation Research (BAST)
The Hague, Netherlands
October 24-25, 1998
Mid-Tour Panel Meeting
Eastern Scheldt Barrier, Netherlands
October 26, 1998
Directorate General of Public Works and Water Management
Delft Hydraulics Institute, Delft and New Waterway Storm Surge Barrier,
October 27, 1998
Delft Hydraulics Institute
Wallingford, United Kingdom
October 28-29, 1998
H.R. Wallingford Hydraulics Research Station
Nottingham, United Kingdom
October 30, 1998
University of Nottingham
London, United Kingdom
October 31 - November 1, 1998
Final Panel Meeting
1998 Scanning Review of European Practice for
Bridge Scour and Stream Instability Countermeasures
Don Flemming (Co-Chairman)
State Bridge Engineer
Minnesota Department of Transportation
Jorge E. Pagán-Ortiz (Co-Chairman)
Office of Engineering, Bridge Division, FHWA
Senior Bridge Engineer
Department of Civil Engineering
Texas A&M University
David W. Bryson
Oregon Department of Transportation
Illinois Department of Transportation
William H. Hulbert
South Carolina Department of Transportation
J. Sterling Jones
Research Hydraulics Engineer
Office of Engineering Research and Development, FHWA
Andrzej J. Kosicki
Bridge Hydraulics Engineer
Peter F. Lagasse (Report Facilitator)
Senior Vice President
FHWA Region 7, Iowa Division Office
Arthur Parola, Jr.
Department of Civil and Environmental Engineering
University of Louisville