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Publication Number: FHWA-HRT-05-072
Date: July 2006

Assessing Stream Channel Stability At Bridges in Physiographic Regions

 

5. MODIFICATIONS OF THORNE'S RECONNAISSANCE SHEETS

The stream stability assessment method developed in chapter 4 is self-contained and does not require any other data or formal method of data collection other than the descriptors given in table 8. However, it is prudent to develop field forms that help observers focus attention on specific aspects of a stream, be consistent in those observations, and systematically record their observations. For this purpose, the Thorne reconnaissance field sheets are the best method available for systematically collecting stream channel data. There are several problems with using the reconnaissance field sheets developed by Thorne for highway-related purposes. (2) First, it is not clear that this highly detailed and time-consuming level of data collection is necessary to assess stream stability or stream response at a bridge. In addition, bridge inspectors generally cannot and will not take the time to collect this level of data, as it is out of line with the overall inspection process. Second, even when all of the detailed data are collected, there is no guidance within the method for interpreting the data. Third, few inspectors and hydraulic engineers have appropriate backgrounds to identify geological parameters, such as rock type. To develop a rapid stability assessment method, a simplified version of the Thorne reconnaissance sheets should be created specifically for use in training and data collection associated with assessing stream stability at bridges.

The stream stability method developed for this report is based on data collected through the reconnaissance. However, given that bridge inspection requires only assessment of stream stability in the short term and since each bridge is inspected at least every 2 years, data collection requirements can be simplified to reflect this less detailed and rapid assessment. In addition, several aspects of the sheets required minimal revision. Interpretive observations, while critical to communicating between observers, are neglected in the revised sheets because, in a rapid assessment, most of the qualitative data are collected by an inspector who is interpreting what he or she observes. All inspections require written reports in which the inspector provides his or her judgment on the status of the overall bridge condition and maintenance needs. In addition, items on the sheet that cannot be assessed in a very brief site visit are excluded from the revised sheets. The simplified and revised data collection sheets, based strongly on Thorne's reconnaissance sheets, are given in figures 18-20.

In addition to the stability assessment, keeping a record of channel dimensions upstream and downstream of the bridge will provide a history of changes in width and depth. Although detailed surveys are not part of a bridge inspection, a simple measurement of station and elevation upstream of the bridge taken annually will provide adequate cross-sectional information to assess longer term changes. Without this information, gradual but continual changes in the channel may be overlooked.

Figure 18. Simplified and revised reconnaissance sheets based on Thorne, sheet 1. (2)
STREAM RECONNAISSANCE
Revised for Bridge Inspection
Based on Thorne (1998)
SECTION 1-SITE DESCRIPTION
ROAD NAME/NUMBER DATE 
BRIDGE NUMBER   
STREAM NAME   
GPS COORDINATES   
SECTION 2-REGION AND VALLEY DESCRIPTION
PART 1: WATERSHEDPART 2: RIVER VALLEY CONDITION
Land UseVegetationValley Side FailuresFailure Locations
checkbox Naturalcheckbox Nonecheckbox Nonecheckbox None
checkbox Agriculturalcheckbox Grasscheckbox Occasionalcheckbox Away from river
checkbox Urbancheckbox Pasturecheckbox Frequentcheckbox Along river
checkbox Suburbancheckbox Crops  
checkbox Ruralcheckbox Shrubs  
checkbox Industrialcheckbox Deciduous Forest/trees  
checkbox Cattle grazingcheckbox Coniferous Forest/trees  
PART 3: FLOOD PLAIN
Flood Plain WidthLand UseVegetationRiparian Buffer Strip
checkbox Nonecheckbox Naturalcheckbox Nonecheckbox None
checkbox < 1 river widthcheckbox Agriculturalcheckbox Grasscheckbox < 1 river width
checkbox 1-5 river widthscheckbox Urbancheckbox Pasturecheckbox 1-5 river widths
checkbox 5-10 river widthscheckbox Suburbancheckbox Orchardscheckbox > 5 river widths
checkbox > 10 river widthscheckbox Ruralcheckbox Crops 
 checkbox Industrialcheckbox Shrubs 
 checkbox Miningcheckbox Deciduous Forest/trees 
 checkbox Cattle grazingcheckbox Coniferous Forest/trees 
Figure 19. Simplified and revised reconnaissance sheets based on Thorne, sheet 2. (2)
PART 4: VERTICAL CONFINEMENT
TerracesLeveesLevee Location
checkbox Nonecheckbox Nonecheckbox Along channel bank
checkbox Left bankcheckbox Naturalcheckbox Setback < 1 river width
checkbox Right bankcheckbox Constructedcheckbox Setback > 1 river width
PART 5: LATERAL RELATION OF CHANNEL TO VALLEY
PlanformMeander Characteristics
checkbox Straightcheckbox Mild bends
checkbox Meanderingcheckbox Moderate bends
checkbox Braidedcheckbox Tight bends
checkbox Anastomosedcheckbox Engineered
SECTION 3-CHANNEL DESCRIPTION
PART 6: CHANNEL DESCRIPTION (select all that apply)
Bed ControlsControl TypesWidth ControlsControl TypesOther
checkbox Nonecheckbox Nonecheckbox Nonecheckbox Nonecheckbox Debris
checkbox Occasionalcheckbox Bedrockcheckbox Occasionalcheckbox Bedrockcheckbox Mining
checkbox Frequentcheckbox Boulderscheckbox Frequentcheckbox Boulderscheckbox Reservoir
checkbox Confinedcheckbox Gravel armorcheckbox Confinedcheckbox Gravel armorcheckbox Knickpoint
 checkbox Bridge protection checkbox Bridge protection 
 checkbox Grade control checkbox Bridge abutments 
 checkbox Debris checkbox Bank stabilization 
 checkbox Dams (beaver, engineered) checkbox Debris 
Flow HabitChannel Width = ___________   
checkbox Perennial     
checkbox Flashy perennialM-B ClassificationCorps Classification (Other)  
checkbox Intermittentcheckbox Cascade or step-poolcheckbox Modified (engineered)  
checkbox Ephemeralcheckbox Plane, pool-riffle, dune-ripplecheckbox Regulated  
 checkbox Braidedcheckbox Arroyo  
PART 7: BED SEDIMENT DESCRIPTION (select all that apply)
Bed MaterialBar TypesBar MaterialBar VegetationBar Width
checkbox Claycheckbox Nonecheckbox Siltcheckbox Nonecheckbox None
checkbox Siltcheckbox Alternate barscheckbox Sandcheckbox Grassescheckbox Narrow
checkbox Sandcheckbox Point barscheckbox Gravelcheckbox Reeds/shrubscheckbox Moderate
checkbox GravelcheckboxMidchannel barscheckbox Cobblescheckbox Treescheckbox Wide
checkbox Cobblescheckbox Diagonal bars   
checkbox Boulderscheckbox Irregular/combination   
checkbox Bedrockcheckbox Braided   
  Percent Sand in Bed = ____________%
Figure 20. Simplified and revised reconnaissance sheets based on Thorne, sheet 3. (2)
SECTION 4-BANK SURVEY (select all that apply)
Bank CharacteristicLeft BankRight Bank
Bank materialcheckbox Claycheckbox Clay
checkbox Siltcheckbox Silt
checkbox Sandcheckbox Sand
checkbox Gravelcheckbox Gravel
checkbox Cobblescheckbox Cobbles
checkbox Boulderscheckbox Boulders
checkbox Bedrockcheckbox Bedrock
Layer materialcheckbox No layerscheckbox No layers
checkbox Cohesivecheckbox Cohesive
checkbox Sandcheckbox Sand
checkbox Gravelcheckbox Gravel
checkbox Cobblescheckbox Cobbles
checkbox Boulderscheckbox Boulders
Bank height  
Bank slope
checkbox Steepcheckbox Steep
checkbox Moderatecheckbox Moderate
checkbox Shallowcheckbox Shallow
Bank vegetation
checkbox Nonecheckbox None
checkbox Grasses/annualscheckbox Grasses/annuals
checkbox Reeds/shrubscheckbox Reeds/shrubs
checkbox Treescheckbox Trees
Falling trees? checkbox Yes checkbox NoFalling trees? checkbox Yes checkbox No
Tree density: checkbox Sparse checkbox DenseTree density: checkbox Sparse checkbox Dense
Tree health: checkbox Good checkbox PoorTree health: checkbox Good checkbox Poor
Tree ages: checkbox Young checkbox Mature checkbox OldTree ages: checkbox Young checkbox Mature checkbox Old
Tree diversity? checkbox Yes checkbox NoTree diversity? checkbox Yes checkbox No
Bank erosion and failure locationLocation of erosion:Location of erosion:
checkbox Outside meander bendcheckbox Outside meander bend
checkbox Inside meander bendcheckbox Inside meander bend
checkbox Opposite bar or obstructioncheckbox Opposite bar or obstruction
checkbox Generalcheckbox General
Type of erosion:Type of erosion:
checkbox Fluvialcheckbox Fluvial
checkbox Geotechnicalcheckbox Geotechnical

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The Federal Highway Administration (FHWA) is a part of the U.S. Department of Transportation and is headquartered in Washington, D.C., with field offices across the United States. is a major agency of the U.S. Department of Transportation (DOT).
The Federal Highway Administration (FHWA) is a part of the U.S. Department of Transportation and is headquartered in Washington, D.C., with field offices across the United States. is a major agency of the U.S. Department of Transportation (DOT). The hydraulics and hydrology research program at the TFHRC Federal Highway Administration's (FHWA) R&T Web site portal, which provides access to or information about the Agency’s R&T program, projects, partnerships, publications, and results.
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