priority scour critical bridge countermeasure plan of ...gis.dot.nh.gov/bridge_scour/dover...

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Attachment D: Bridge Elevation Summary Showing Existing Streambed, Foundation Depth(s) and Observed and/or Calculated Scour Depths

The Following Materials Are Being Submitted With This Report:

Attachment H: Plan View Showing Location of Scour Holes, Debris, etc,

Attachment B: Map Showing Detour Route(s)

Attachment E: Boring Logs and/or Other Subsurface Information

Attachment F: Survey Cross Sections From Current and Previous Inspection Reports

Attachment G: Supporting Documentation, Calculations, Estimates, and Conceptual Designs for Scour Countermeasures

Attachment A: Photos

Attachment C: Field Verification Card (FVC)

Feature Crossed: Salmon Falls River

Feature Carried: Gulf Road

Owner: NHDOT

New HampshireDepartment of Transportation

Scour Critical BridgePlan of Action (POA) Report

Final Recommended Action:Given the poor condition of the substructure, substantial scour potential, and unknown (likely low) remaining embedment, CHA recommends considering a complete bridge replacement. The New Hampshire owned 4 span section appears less vulnerable than the 23 span Maine owned section. Until the structure can be replaced, CHA recommends that the bridge be monitored during storm tide events using portable sonar and sounding rods, as appropriate, on a slack-tide rotation. The bridge should be closed if the water surface elevation exceeds 8 ft NAVD88 or 13 ft MLLW from NOAA gage 8423898, if more than 3.5 ft of scour is observed at any bent during monitoring , if conditions are too severe to allow monitoring or if foundation movement or other signs of structural distress are observed. The underwater inspections should continue on a 2 year frequency. Significant predicted scour and deteriorated timber pile bents (unknown length) support strong consideration to replace the Maine owned section of this bridge. Countermeasures appear to be less effective on a long term basis, cost prohibitive based on a conceptual review of scour susceptability, and the duel state ownership.

Dover 182/123

POA Report

Scour POA Priority:

Attachment I: Post Flood Inspection Documentation

Post Flood Inspection Tasks

Flood Monitoring Program

Conceptual Structural / Hydraulic Countermeasures

Fixed Monitoring Devices

Increased Inspection Frequency

Priority Countermeasure

PriorityMonitoring

Attachment J: Scour / H&H Backup Calculations

Attachment K: NHDOT Underwater Inspection Report

SCOUR CRITICAL BRIDGE − PLAN OF ACTIONDover 182/123

1. GENERAL INFORMATIONStructure:

Year Built:

182/123

1982

City, County, State:

Dover, Strafford, New Hampshire

State Highway or Facility Carried:

Gulf Road

Waterway Crossed:

Salmon Falls River

Owner:

NHDOT

Year Rebuilt:

NA

Planned Bridge Replacement (if scheduled):

Anticipated Opening Date:

The structure contains 27 spans, 23 of which are located in Maine. The spans in NH are comprised of a concrete deck supported by steel beams on concrete caps and concrete encased steel H-pile bents. The spans in Maine are comprised of a concrete slab spanning between timber pile bents and timber abutment. The bridge in its current configuration was built 1982 without further reconstruction – the timber substructure in Maine predates the 1982 major reconstruction.

Structure Size and Description:

Foundation Details:

KNOWN UNKNOWN

Subsurface SoilInformation:

Bridge ADT Info:

Does the Bridge Provide Service to Emergency Facilities and/or an Evacuation Route (Y/N)?:

This bridge is of critical use, it is one of the limited access bridges to Maine. The 4900 ADT is critical.If So, Describe:

WorstAbutment: Right

WorstPier: 25

(Looking Downstream L to R)

Channel Primary Bed Material:

Sand & Gravel

Channel Secondary Bed Material:

Sand

Embedment (feet): 56 Exposure: None

Embedment (feet): unknown Exposure: Piles Exposed

Scour Summary

Strafford County FIS provides riverine discharges at the Rollingsford/Somersworth boundary approximately 4.5 miles upstream of the site. According to the FIS, Bridge 182/123 has not experienced a significant flood event since it was rebuilt in 1982. However, the FEMA Independent Evaluation of Recent Flooding in New Hampshire (7-08), indicates that the Salmon Falls River flooded in 2006 and 2007, with a recurrence interval of 10-50 years.

Flood History:

Twenty-seven span bridge built in 1982 that has not been reconstructed. The bridge carries Gulf Road over Salmon River from New Hampshire to Maine, and is tidally influenced. The abutments are concrete and located at the banks of the channel. The right abutment (NH) is founded on timber piles and the left abutment (ME) is founded on concrete piles. Three (3) piers (owned by NH) support the bridge near the right abutment, and consist of concrete on concrete encased steel H-piles. Thirty timber bents (owned by ME) support the bridge, extending from the concrete piers to the left abutment. In 2009, CHA did not observe any evidence of scour at the right abutment. In addition, the structure was protected by rounded boulders (approximately 1 ft in diameter) in fair condition. Water depth prevented an inspection of piers during the 2009 site visit. The original embedment cannot be determined from the available plans. The latest NH Bridge Inspection Report (2008) noted that some of the timber bents, located in Maine, were broken, badly damaged and/or deteriorated. The latest NH underwater inspection report (2007) included inspection of only the three concrete piers in NH. It states that the concrete that encapsulates the steel piles has failed at several locations; exposing the steel H-piles with corrosion of the steel noted. Also, local scour was noted to have exposed the steel piles below the concrete encasement level.

Field Observation:

Two storm tides were considered for the bridge: Nor’easter storm of record (1978 Nor’easter) and a Category 1 hurricane landfall. The storm tides were developed using record data, the Portland, Maine gage records, and the 100-year and 500-year water surface elevation (WSE) data from the Portsmouth, New Hampshire Flood Insurance Study. An unsteady state HEC-RAS model was developed using elevation data generated from CHA hydrographic survey (2009) supplemented with bathymetric data from the Portland Tsunami digital elevation model (DEM). The model output was used along with boring log data and a field soil classification in order to develop pier and contraction scour estimates. The result of this computation indicates the potential for 21 ft of scour at the three (NH) concrete piers and 15 ft at the (ME) timber bents during the 100-year flood event.

Scour Calculations:

Current Item 113 Code: 3 Source of Scour Critical Code: Calculation

Borings:

Yes No

Bridge Maintenance Division6

20034900 Year:Total:

Text9:6/24/2010 Text9:Scour Critical Bridge - Plan of Action: Dover 182/123 Text9: Page 1 of 6

5. MONITORING PROGRAM RECOMMENDED5a. Regular Inspection Program

Riverbed Profile Readings

Items toWatch:

Monitor any changes in channel elevations and look for any bridge distress, foundation deterioration, evidence of lateral migration, abutment and/or pier scour.

5b. Fixed Monitoring Device(s)

Type of Instrument:

Installation Location(s):

Sample Interval: 30 min 1 hr. 6 hrs. 12 hrs. Other:

Frequency of Data Download and Review: Daily Weekly Monthly Other:

Scour Critical Elevation(s) For Each Pier:

Criteria of Termination For Fixed Monitoring:

Standard 2 Year Interval

Underwater Inspection Required Items toWatch:

Lateral migration, changes in channel bed elevations, abutment scour, signs of pier scour, including scour and refill (probe for unconsolidated materials). Continue with underwater inspections every 2 years.

Standard 5 Year Interval

2 Year Interval

1 Year Interval

5c. Flood Monitoring Program

Type:

Discharge

Visual Inspection

Instrument (check all that apply)

Portable Geophysical SonarOther:

(check all that apply)

Flood Monitoring event defined by:

Stage (WSE)

Frequency of Flood Monitoring: 1 hr. 3 hrs. 6 hrs. Other:

Notified By Public

Flood Warning Issued by NWS

Notified by Fixed Monitoring Device

USGS Gage Station #

1 Year Interval

Criteria to End Flood MonitoringConditions Stable / Water Receding

Recommended Post Flood Inspection

Action(s) Required if Scour Critical Elevation Detected: (See Section 7 and Section 8)

Not Applicable:

During PrecipitationEvent, Look For:

Water surface elevation within 2 ft the low chord (Piers 24-26, NH Bridge).

Revisit Bridge

Close Bridge (See Section 7)

Placard Location: No placard necessary, use low chord for monitoring.

Contact Person(s):NHDOT Bridge Design Bureau, Bridge Inspector1.

NHDOT Bridge Maintenance Divisional Superintendent Crew# 62.

NHDOT Bridge Maintenance Divisional Foreman Crew# 63.

NHDOT Bridge Design Bureau, Existing Bridge Section4.

NHDOT Bridge Design Bureau, Administrator5.

Stage (WSE) 6 ft NAVD88 = (11 ft MLLW)

NOAA Gage Station # 8423898

Scour Critical Riverbed Elevation(s) for Each Pier/Abutment: Unknown. Bridge is founded on piles of unknown embedment.

NOTE: Additional Details for Action(s) Required May Be Included in Sections 7 and 8.

Action(s) Required if Scour Critical Riverbed Elevation Detected:

Close Bridge. Institute detour.

Agency and Department Responsible for Monitoring:

NHDOT

Contact Person:

NHDOT Bridge Design Bureau (603) 271-2731

Riverbed Profile Readings (See Attachment I)

Items toWatch:

Evidence of scour and refill; greater than 5ft total scour with respect to 2009 channel invert at any point; lateral migration; abutment scour; pier scour, settlement, tilting, debris or distress.

5d. Post-Flood Inspection Tasks Required

Visual Inspection (See Attachment I)

Profile at Substructure (See Attachment I)

Undermining (See Attachment I)


6. COUNTERMEASURE RECOMMENDATIONS

Conceptual Structural / Hydraulic Countermeasures

Basis for the Selection of the Preferred Scour Countermeasure:

Include Information on Hydraulic, Structural or Monitoring Countermeasures.

(1)

Estimated Cost

$

(2) $

(3) $

Bridge replacement should be considered before conceptual countermeasures are designed. Owned by 2 states.

Countermeasure Implementation Project Type:

Proposed Construction

Other:

Bridge Maintenance

Programmed Construction - Project Lead Agency

Bridge Design

Highway Design

Recommended Countermeasures to be Performed by:

NHDOT. Maine DOT owns 23 of 27 spans.

Contact Person:


Post Flood Inspection Tasks Required

Flood Monitoring Program

Fixed Monitoring Devices

Regular Inspection Program

Lead Agency:

Conceptual Cost Estimate:

H & H Summary Information:

8.1

11.7

8.4

9.7

50 year

Flow (cfs) Elevation (ft)

100 year

500 year

Roadway

Low Chord

Flow Impacting Bridge Flow Overtopping Bridge

Yes

Yes

No

No

10 year


7. BRIDGE CLOSURE PLAN

Scour Measurement Results / Monitoring Device (See Section 5)

Criteria For Consideration of Bridge Closure:

Observed Structure Movement / Settlement

Water Surface Elevation Reaches Low Chord

Overtopping Road or Structure

Other: Debris Accumulation Movement of RipRap/Other Armor Protection Loss of Road Embankment

Agency and Department Responsible for Closure:

Contact Person(s):

NHDOT Bridge Design Bureau, Bridge Inspector

(See Attachment C)

Water Reaches Critical Elevation:

NHDOT Municipality:Transportation Management Center

1.

NHDOT Bridge Maintenance Divisional Superintendent Crew# 62.

NHDOT Bridge Maintenance Divisional Foreman Crew# 63.

NHDOT Bridge Design Bureau, Existing Bridge Section4.

NHDOT Bridge Design Bureau, Administrator5.

Ice Jam

DischargeStage (WSE)USGS Gage Station #

Stage (WSE) 8 ft NAVD88 = (13 ft MLLW)NOAA Gage Station # 8423898

8. DETOUR ROUTEDetour Route Description:

This detour includes roads in the state of Maine. No information is available for Maine bridges.

(See Attachment B)

Bridges on Detour Route:

Bridge NumberFeatureCrossed

Load Posting (tons) (Date)

Item 113Code

Traffic Control Equipment (detour signing and barriers) and storage location(s) (NHDOT/Town): NHDOT Bridge Maintenance Divisional Crew 6

Additional Considerations or Critical Issues (susceptibility to overtopping, limited waterway adequacy, lane restrictions, etc.):


News Release, Other Public Notice (include authorized person(s), information to be provided and limitations):

NHDOT Public Information Officer, NHDOT Bridge Design Bureau (603) 271-2731

FeatureCarried

VerticalClearance

(feet)

WidthRestrictions

(feet)

HighwayMaintenance

District: 06

NHDOT Bureauof Traffic

Rollinsford 116/086 SALMON FALLS RIVER 44.5 (N/A)8NH 4 unrestricted 44.7


9. BRIDGE REOPENING PLAN9a. Criteria for Consideration to Complete Interim Bridge Reopening:

Agency and Person Responsible for Re-Opening Bridge After Inspection:


Post Flood Inspection Completed

Critical Elevation Marker Is Visible

Reasons for Closure Have Abated

Water Surface Levels Dropping

Diving Inspection Completed within 7 calendar days

Verify Riverbed Elevation (drop line readings)

Streambed Elevation Drops Less than

Streambed Elevation 1.0 Feet

3.5 Feet

9b. Criteria for Completing Bridge Reopening Process:

Above Critical Footing Elevation. (See Section 5d)


Bridge: Dover 182/123

Date Taken: 2/12/2009 3:01:16 PM

Description: Upstream Fascia

Source: CHAScourInsp

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Date Taken: 2/12/2009 3:34:36 PM

Description: Downstream Fascia from boat launch


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Text9:6/24/2010 Text9:Attachment A: Bridge Photos: Dover 182/123 Text9: Page 1 of 3


Date Taken: 2/12/2009 3:17:08 PM

Description: Downstream Left Abut - Under Bridge (Maine) & Fascia


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Date Taken: 2/12/2009 3:01:02 PM

Description: Upstream Reach Open Water


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Date Taken: 2/12/2009 3:00:10 PM

Description: Downstream Reach from Right Downstream Approach


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Date Taken: 2/12/2009 2:59:42 PM

Description: Downstream Cross Section Fascia


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11 King CourtKeene, NH 03431-4648Main: (603)-357-2445 New Hampshire Scour Investigation

Dover 182/123

Attachment B: Detour Route

Dover182/123

IF GOING WEST ON DOVER-ELIOT RD, REVERSE DIRECTIONS.

GOING EAST ON DOVER-ELIOT RD.

DETOUR MAP


Detour (miles): Last ADT:

Foundation Details:

KNOWN

UNKNOWN Worst Abutment: Right

Worst Pier: 25(Looking Downstream L to R)



Diving Insp Reports: 10/2/2007 9/23/2005

FIELD VERIFICATION CARD (POA Attachment C)

Owner: NHDOT



Town, County: Dover - Strafford

Contact Person: NHDOT Bridge Design Bureau (603) 271-2731

BRIDGE INFORMATION

Superstructure Type: Stringer/Multi-Beam or Girder

Superstructure Material: Concrete

Scour Critical Feature: R. Abutment, Bents 24-26; other bents should be probed for scour holes.


Red List: No

Number of Spans: 27

USGS Gage Station: USGS Station Prox To Bridge:

GENERAL INFORMATION

Scour Measurement Results / Monitoring Device

CRITERIA FOR CONSIDERATION OF BRIDGE CLOSURE

Observed Structure Movement / Settlement

Water Surface Elevation Reaches Low Chord

Overtopping Road or Structure

Date/TimeNotified:

Completed ProperNotification

Close BridgeRevisit BridgePost-Flood Inspection Recommendation

POST-MONITORING VERIFICATION

ACTION TAKEN

REFERENCE PHOTOS

Dates:

Water Reaches Critical Elevation:

Agency:

What To Look For: Scour at any location exceeding 3.5 ft. Lateral migration into Right abutment. Lateral migration into timber pile bent-supported segment of bridge. Check tidal gage at Ft. Point, NH.

(Left to Right Convention Looking Downstream)

CRITERIA FOR CONSIDERATION TO COMPLETE INTERIM BRIDGE REOPENING:

Agency and Person Responsible for Re-Opening Bridge After Inspection:


Critical Elevation Marker Is Visible

Reasons for Closure Have Abated

Water Surface Levels Dropping

Verify Riverbed Elevation

Above Critical Footing Elevation. (See Section 5d)

(Continued on Next Page)

Interim Reopening Date:Interim Reopening Approved By: Time:

INTERIM REOPENING COMMENTS

Traffic Control Equipment (detour signing and barriers) and storage location(s) (NHDOT/Town): NHDOT Bridge Maintenance Divisional Crew 6

HighwayMaintenance

District: 06

NHDOT Bureauof Traffic

Streambed Elevation Drops Less than

Streambed Elevation 1.0 Feet

3.5 Feet

Other: Debris Accumulation Movement of RipRap/Other Armor Protection Loss of Road Embankment Ice Jam

DischargeStage (WSE)USGS Gage Station #

Stage (WSE) 8 ft NAVD88 = (13 ft MLLW)NOAA Gage Station # 8423898

NOAA Gage Station: 8423898 NOAA Station Prox To Bridge: Fort Point, NH - Approximately 13 miles DS

8 20034900 Year:Total:

Text9:6/24/2010 Text9:Attachment C: Field Verification Card: Dover 182/123 Text9: Page 1 of 2

Upstream Elevation of Bridge at Low Water

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Downstream Elevation of Bridge at Low Water

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Scour Critical Feature at Low Water

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Text9:6/24/2010 Text9:Attachment C: Field Verification Card: Dover 182/123 Text9: Page 2 of 2

NHDOT POST FLOOD INSPECTION REPORT (POA Attachment I)

Bridge: Post Flood Inspection Date:Dover 182/123GENERAL INFORMATION

Town: Dover


Owner: NHDOT


Major Basin (HU8):

Functional Class: 17 - Urban Collector

Detour Length: 8 (miles)

Year Built: 1982

Year ofReconstruction: NA

ADT: 4900 Year of ADT: 2003

Overall Fed Sufficiency Rating: 65.6

RedList: No

Item 60: 4 Item 61: 6 Item 71: 8 Item 113: 3

Current:

HYDRAULIC INFORMATION

FEMA Study:

Whitman & Howard Information

USGS Report:

Tidal Influence: Other Hydrologic & Hydraulic Data:Strafford County FIS provides riverine discharges at the Rollinsford/Somersworth boundary approximately 4.5 miles upstream. Moderate to small tidal prism with 8 to 10 ft tide range. Poor condition of substructure makes it more vulnerable to scour. FEMA report does not extend downstream to this location. Moderate to heavy woody debris and ice. Standard large "river" survey ( Max flow depth > 10 ft).

100-Yr Water Velocity (feet per sec): 6

Angle Of Attack 10

Watershed Area (sq. mi):

(Flood Flow)

BRIDGE INFORMATIONBridge Length (in feet): 489.00 Plans Available: Borings Available:

Abutment Foundation: EB Piles Pier Foundation: EB Piles

2005 2006 2007

Flood / Scour HistoryComments:

Strafford County FIS provides riverine discharges at the Rollingsford/Somersworth boundary approximately 4.5 miles upstream of the site. According to the FIS, Bridge 182/123 has not experienced a significant flood event since it was rebuilt in 1982. However, the FEMA Independent Evaluation of Recent Flooding in New Hampshire (7-08), indicates that the Salmon Falls River flooded in 2006 and 2007, with a recurrence interval of 10-50 years.

Flood History:

:

Bridge Width (in feet): 32.00

Substructure Channel Stability Hydraulic Adequacy Scour Risk

Posting 44.5 , NPR

Bridge Plan File Loc: 2-2-1-4 / 2-12-2-12

(scale of 1-9)(worst - best)

100-Yr Overtopping Relief: Left Approach

5/17/2005

Bridge Scour ReportNov 1992 :( )

RESULTS OF POST FLOOD INSPECTION

:(Actual Metric Tons, Signed)

Date of Interim Bridge Reopening:Date of Bridge Closure:

Date of Post Flood Inspection: Post Flood Inspection Completed By:

NA NA

Foundation Details:

KNOWN

UNKNOWN Worst Abutment: Right

Worst Pier: 25(Looking Downstream L to R)



Diving Insp Reports: 10/2/2007 9/23/2005

Superstructure Type: Stringer/Multi-Beam or Girder

Superstructure Material: Concrete

Scour Critical Feature: R. Abutment, Bents 24-26; other bents should be probed for scour holes.


Red List: No

Number of Spans: 27

USGS Gage Station: USGS Station Prox To Bridge:

Dates:

What To Look For: Scour at any location exceeding 3.5 ft. Lateral migration into Right abutment. Lateral migration into timber pile bent-supported segment of bridge. Check tidal gage at Ft. Point, NH.

NOAA Gage Station: 8423898 NOAA Station Prox To Bridge: Fort Point, NH - Approximately 13 miles DS

Text9:6/24/2010 Text9:Attachment I: Post Flood Inspection Report: Dover 182/123 Text9: Page 1 of 1

CHA File No:18925.2003.1510


Dover 182/123Attachment J: Scour/H&H Backup

Calculations

Attachment J: Scour/H&H Backup Calculations

Hydraulic Data from <Dover_SalmonFalls.prj>100-hurricane-1 ApprXS 17330 500-hurricane1 Appr XS 17330Portsmouth Bridge ContXS 16131 BU Portsmouth bridge Cont XS 16131 BU

100-yr. Flood Data 500-yr. Flood Data

Hydraulic: Yo = 12.28 ft. adjacent Yo = 13.1 ft. adjacentLeft Y1 = ft. adjacent Left Y1 = ft. adjacent

Right Y1 = 0.72 ft. adjacent Right Y1 = 1.59 ft. adjacentQ1 = 20,564 cfs Q1 = 24,974 cfs

Channel Q2 = 19,215 cfs Channel Q2 = 23,547 cfsLeft Q2 = cfs Left Q2 = cfs

Right Q2 = 9 cfs Right Q2 = 38 cfsA1 = 11,055 ft.2 A1 = 16,424 ft.2

A2 = 4,651 ft.2 A2 = 4,982 ft.2

W1 = 951.0 ft. W1 = 1,566.2 ft.

Channel W2 = 345.7 ft. Channel W2 = 347.4 ft.Left W2 = ft. Left W2 = ft.

Right W2 = 13.0 ft. Right W2 = 13.0 ft.Vm = 1.86 fps Vm = 1.52 fpsD50 = 0.000656 ft. D50 = 0.000656 ft.

Energy Slope = 0.000137 ft. Energy Slope = 0.000145 ft.Gravity Acceleration = 32.2 ft/sec2 Gravity Acceleration = 32.2 ft/sec2

Fall Vel., ω = 0.091 fps Fall Vel., ω = 0.091 fps

100-year SCOUR SUMMARY for Dover Bridge over Salmon Falls

BRIDGE # 182/123Stafford County NH

September, 2009

Groundline Initial Contraction Local Total Scour Remaining Pier/Bent Elevation Embedment Scour Scour Scour Elevation Embedment

(ft-NAVD) (ft) (ft) (ft) (ft) (ft-NAVD) (ft)25-27 -14.5 0.0 9.8 11.9 21.7 -36.2 -21.720-24 -10.3 0.0 9.8 5.5 15.3 -25.6 -15.32-19 -5.0 0.0 9.8 4.5 14.3 -19.3 -14.3

500-year SCOUR SUMMARYfor Dover Bridge over Salmon Falls


September, 2009

Groundline Initial Contraction Local Total Scour Remaining Pier/Bent Elevation Embedment Scour Scour Scour Elevation Embedment

(ft) (ft) (ft) (ft) (ft) (ft-NAVD) (ft)25-27 -14.5 0.0 15.1 12.7 27.8 -42.3 -27.820-24 -10.3 0.0 15.1 5.5 20.6 -30.9 -20.62-19 -5.0 0.0 15.1 4.8 19.9 -24.9 -19.9

NOTES: These tables present potential scour depths for the associated hydraulic events. If a soil horizon exists beneath the bridge which isresistant to scour, the predicted scour depths could be reduced to reflect the competence of the material. This reduction would require examination and approval by a qualified geotechnical engineer with knowledge of the properties of the material.

Calc. By: LGG Date: 10/1/2009Check By: LWZ Date: 11/24/2009

SCOUR MODE COMPUTATIONfor Dover Bridge over Salmon Falls


September, 2009

The following computations are made using Laursen's Equation (Equation 15 in HEC-18):Vc = Ku x Y1

1/6 x D501/3

100-year Hurricane DISCHARGEMAIN CHANNEL SCOUR MODE

APPROACH SECTION MAIN CHANNEL AREA (ft2), A1 = 11,055APPROACH SECTION MAIN CHANNEL WIDTH (ft), W1 = 951APPROACH SECTION AVERAGE CHANNEL DEPTH (ft), Y1 = A1/W1 = 11.62MEDIAN GRAIN SIZE (ft), D50 = 0.000656Ku 11.17BED TRANSPORT CRITICAL VELOCITY (fps), Vc = 1.46

DISCHARGE IN APPROACH CHANNEL (cfs), Q1 = 20,564MEAN VELOCITY IN APPROACH CHANNEL (fps), Vm = 1.86MAIN CHANNEL SCOUR MODE = LIVE-BED

APPROACH SECTION MAIN CHANNEL AREA (ft2), A1 = 16,424APPROACH SECTION MAIN CHANNEL WIDTH (ft), W1 = 1,566APPROACH SECTION AVERAGE CHANNEL DEPTH (ft), Y1 = A1/W1 = 10.49MEDIAN GRAIN SIZE (ft), D50 = 0.000656Ku 11.17BED TRANSPORT CRITICAL VELOCITY (fps), Vc = 1.44

DISCHARGE IN APPROACH CHANNEL (cfs), Q1 = 24,974MEAN VELOCITY IN APPROACH CHANNEL (fps), Vm = 1.52MAIN CHANNEL SCOUR MODE = LIVE-BED


500-year DISCHARGEMAIN CHANNEL SCOUR MODE

CONTRACTION SCOUR COMPUTATIONSfor Dover Bridge over Salmon Falls


September, 2009

The following computations are made using the HEC-18 equation forLive Bed Contraction Scour:

Ys=Y2-Y0

Y2=((Q2/Q1)6/7((W1/W2)

k1))*Y1

100-year Hurricane DISCHARGEMain Channel

LIVE-BED CONTRACTION SCOUR COMPUTATIONS

ENERGY SLOPE = 1.37E-04ω FALL VELOCITY (fps) = 0.09AVERAGE UPSTREAM CHANNEL DEPTH (ft), Y1 = A1/W1 = 11.62g GRAVITATIONAL ACCELERATION (ft/sqsec) = 32.20V*

SHEAR VELOCITY IN UPSTREAM SECTION (fps) = 0.23V*/ω = 2.49k1 HEC-18 = 0.69DISCHARGE IN UPSTREAM CHANNEL (cfs), Q1 = 20,564DISCHARGE IN CONTRACTED SECTION (cfs), Q2 = 19,215WIDTH OF UPSTREAM CHANNEL SECTION (ft), W 1 = 951.0WIDTH OF MAIN CHANNEL CONTRACTED SECTION (ft), W 2 = 345.7MEDIAN GRAIN SIZE (ft), D50 = 0.000656

COMPUTED WATER DEPTH OF CONTRACTED SECTION (ft), Y 2 = 22.05AVERAGE WATER DEPTH AT BRIDGE(ft), Y0 = 12.28AVERAGE SCOUR DEPTH AT CONTRACTED SECTION, YS = 9.8


CONTRACTION SCOUR COMPUTATIONSfor Dover Bridge over Salmon Falls

Stafford County NH

September, 2009

The following computations are made using the HEC-18 equation forLive Bed Contraction Scour:

Ys=Y2-Y0

Y2=((Q2/Q1)6/7((W1/W2)

k1))*Y1

500-year DISCHARGEMain Channel

LIVE-BED CONTRACTION SCOUR COMPUTATIONS

ENERGY SLOPE = 0.00015ω FALL VELOCITY (fps) = 0.09AVERAGE UPSTREAM CHANNEL DEPTH (ft), Y1 = A1/W1 = 10.49g GRAVITATIONAL ACCELERATION (ft/sqsec) = 32.20V*

SHEAR VELOCITY IN UPSTREAM SECTION (fps) = 0.22V*/ω = 2.43k1 SEE HEC-18 = 0.69DISCHARGE IN UPSTREAM CHANNEL (cfs), Q1 = 24,974DISCHARGE IN CONTRACTED SECTION (cfs), Q2 = 23,547WIDTH OF UPSTREAM CHANNEL SECTION (ft), W 1 = 1,566.2WIDTH OF MAIN CHANNEL CONTRACTED SECTION (ft), W 2 = 347.4MEDIAN GRAIN SIZE (ft), D50 = 0.000656

COMPUTED WATER DEPTH OF CONTRACTED SECTION (ft), Y 2 = 28.19AVERAGE WATER DEPTH AT BRIDGE(ft), Y0 = 13.10AVERAGE SCOUR DEPTH AT CONTRACTED SECTION, YS = 15.1


BRIDGE # 182/123

100-year Storm Tide EventLOCAL PIER SCOUR COMPUTATIONS

for Dover Bridge over Salmon FallsBRIDGE # 182/123

Stafford County NH

September, 2009

PILE BENT SCOUR ANALYSIS FOR 100-year Hurricane discharge

Reference for methodology: HEC-18 4th Edition Chapter 6

Bent Number Bents 25-27 Bents 20-24 Bent 2-19V1: VELOCITY (fps) 6.19 6.19 3.72Y1: DEPTH (ft) 18.52 18.52 13.04ATTACK ANGLE, Degrees 20 20 20INDIVIDUAL PIER WIDTH (ft) 3.00 1.00 1.00a: PILE WIDTH (ft) 3.00 1.00 1.00L: PILE LENGTH (ft) 12.00 4.00 4.00PIER SHAPE (S=SQUARE, C = CIRCULAR) C S SK1: SHAPE COEFFICIENT 1.00 1.00 1.00K2: ANGLE COEFFICIENT 1.72 1.72 1.72K3: BED COND. COEFFICIENT 1.10 1.10 1.10K4: ARMORING COEFFICIENT 1.00 1.00 1.00g: gravitational constant (ft/sec2) 32.20 32.20 32.20FROUDE NUMBER, Fr 0.25 0.25 0.18COMPUTED LOCAL SCOUR DEPTH (ft), Yscomp 11.91 5.83 4.47MINIMUM SCOUR DEPTH (ft), Ysmin N/A N/A N/AMAXIMUM SCOUR DEPTH (ft), Ysmax=2.4aK1(K2)

1.538 16.62 5.54 5.54TOTAL SCOUR DEPTH (ft), Ys 11.9 5.5 4.5


500-year Storm Tide EventLOCAL PIER SCOUR COMPUTATIONS

for Dover Bridge over Salmon FallsBRIDGE # 182/123

Stafford County NH

September, 2009

PILE BENT SCOUR ANALYSIS FOR 500-year Hurricane discharge

Reference for methodology: HEC-18 4th Edition Chapter 6

Bent Number Bents 25-27 Bents 20-24 Bent 2-19V1: VELOCITY (fps) 7.13 7.13 4.27Y1: DEPTH (ft) 19.35 19.35 13.91ATTACK ANGLE, Degrees 20 20 20INDIVIDUAL PIER WIDTH (ft) 3.00 1.00 1.00a: PILE WIDTH (ft) 3.00 1.00 1.00L: PILE LENGTH (ft) 12.00 4.00 4.00PIER SHAPE (S=SQUARE, C = CIRCULAR) C C CK1: SHAPE COEFFICIENT 1.00 1.00 1.00K2: ANGLE COEFFICIENT 1.72 1.72 1.72K3: BED COND. COEFFICIENT 1.10 1.10 1.10K4: ARMORING COEFFICIENT 1.00 1.00 1.00g: gravitational constant (ft/sec2) 32.20 32.20 32.20FROUDE NUMBER, Fr 0.29 0.29 0.20COMPUTED LOCAL SCOUR DEPTH (ft), Yscomp 12.73 6.24 4.78MINIMUM SCOUR DEPTH (ft), Ysmin N/A N/A N/AMAXIMUM SCOUR DEPTH (ft), Ysmax=2.4aK1(K2)

1.538 16.62 5.54 5.54TOTAL SCOUR DEPTH (ft), Ys 12.7 5.5 4.8


CHA File No:18925.2003.1510


Dover 182/123Attachment K: Underwater Inspection

Reports

Attachment K: Underwater Inspection Reports

priority scour critical bridge countermeasure plan of ...gis.dot.nh.gov/bridge_scour/dover...

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