Source: http://www.fhwa.dot.gov/publications/research/infrastructure/hydraulics/05072/05.cfm
Timestamp: 2015-05-27 12:20:43
Document Index: 617037891

Matched Legal Cases: ['ART 1', 'ART 2', 'ART 3', 'ART 4', 'ART 5', 'ART 6', 'ART 7']

5. Modificationsof Thorne'S Reconnaissance Sheets - Assessing Stream Channel Stability At Bridges in Physiographic Regions, July 2006 - FHWA-HRT-05-072
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
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 RECONNAISSANCERevised for Bridge InspectionBased 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
Natural None None None
Agricultural Grass Occasional Away from river
Urban Pasture Frequent Along river
Suburban Crops Rural Shrubs Industrial Deciduous Forest/trees Cattle grazing Coniferous Forest/trees PART 3: FLOOD PLAIN
Flood Plain WidthLand UseVegetationRiparian Buffer Strip
None Natural None None
< 1 river width Agricultural Grass < 1 river width
1-5 river widths Urban Pasture 1-5 river widths
5-10 river widths Suburban Orchards > 5 river widths
> 10 river widths Rural Crops Industrial Shrubs Mining Deciduous Forest/trees Cattle grazing Coniferous Forest/trees Figure 19. Simplified and revised reconnaissance sheets based on Thorne, sheet 2. (2)
PART 4: VERTICAL CONFINEMENT
TerracesLeveesLevee Location
None None Along channel bank
Left bank Natural Setback < 1 river width
Right bank Constructed Setback > 1 river width
PART 5: LATERAL RELATION OF CHANNEL TO VALLEY
PlanformMeander Characteristics
Straight Mild bends
Meandering Moderate bends
Braided Tight bends
Anastomosed Engineered
SECTION 3-CHANNEL DESCRIPTION
PART 6: CHANNEL DESCRIPTION (select all that apply)
Bed ControlsControl TypesWidth ControlsControl TypesOther
None None None None Debris
Occasional Bedrock Occasional Bedrock Mining
Frequent Boulders Frequent Boulders Reservoir
Confined Gravel armor Confined Gravel armor Knickpoint
Bridge protection Bridge protection Grade control Bridge abutments Debris Bank stabilization Dams (beaver, engineered) Debris Flow HabitChannel Width = ___________ Perennial Flashy perennialM-B ClassificationCorps Classification (Other) Intermittent Cascade or step-pool Modified (engineered) Ephemeral Plane, pool-riffle, dune-ripple Regulated Braided Arroyo PART 7: BED SEDIMENT DESCRIPTION (select all that apply)
Bed MaterialBar TypesBar MaterialBar VegetationBar Width
Clay None Silt None None
Silt Alternate bars Sand Grasses Narrow
Sand Point bars Gravel Reeds/shrubs Moderate
GravelMidchannel bars Cobbles Trees Wide
Cobbles Diagonal bars Boulders Irregular/combination Bedrock 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 material Clay Clay
Layer material No layers No layers
Cohesive Cohesive
Bank height Bank slope
Grasses/annuals Grasses/annuals
Reeds/shrubs Reeds/shrubs
Falling trees? Yes NoFalling trees? Yes No
Tree density: Sparse DenseTree density: Sparse Dense
Tree health: Good PoorTree health: Good Poor
Tree ages: Young Mature OldTree ages: Young Mature Old
Tree diversity? Yes NoTree diversity? Yes No
Bank erosion and failure locationLocation of erosion:Location of erosion:
Outside meander bend Outside meander bend
Inside meander bend Inside meander bend
Opposite bar or obstruction Opposite bar or obstruction
Type of erosion:Type of erosion:
Geotechnical Geotechnical