priority scour critical bridge countermeasure plan of action …gis.dot.nh.gov/bridge_scour/pelham...

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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: Beaver Brook

Feature Carried: Main Street

Owner: NHDOT

New HampshireDepartment of Transportation

Scour Critical BridgePlan of Action (POA) Report

Final Recommended Action:This bridge is an historic stone arch built 1900, with a 1929 steel multi-girder addition – no meaningful plans available. The foundations and corresponding embedment are therefore unknown. Latest underwater inspection (2006) noted no particular scour deficiencies. Currently this bridge is under a 6-month inspection frequency due to the poor condition of the substructure. This frequency should continue. This structure has experienced several significant flood event, most recently in 2006 and 2007. During CHA’s 2009 inspection it was noted that there was a scour hole on the downstream end under the newer portion of structure and large amounts of debris in the superstructure due to previous floods. Due to the extensive flood history at the bridge and the poor condition of the substructures, CHA recommends monitoring the bridge during and after significant storm events until it can be replaced. If replacement efforts are not currently defined then partially grouted riprap should also be installed at the pier. CHA recommends that the Item 113 and Item 60 both be rated 2.

Pelham 110/090

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 ACTIONPelham 110/090

1. GENERAL INFORMATIONStructure:

Year Built:

110/090

1900

City, County, State:

Pelham, Hillsborough, New Hampshire

State Highway or Facility Carried:

Main Street

Waterway Crossed:

Beaver Brook

Owner:

NHDOT

Year Rebuilt:

1929

Planned Bridge Replacement (if scheduled):

Anticipated Opening Date:

Original structure comprised of a two-span filled-spandrel split-stone arch. Structure widened on the downstream side with concrete deck on steel beams and substructure extensions. No meaningful plans available.

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)?:

Elementary school adjacent, also used for emergency vehicles.If So, Describe:

WorstAbutment: Right

WorstPier: 1

(Looking Downstream L to R)

Channel Primary Bed Material:

Sand

Channel Secondary Bed Material:

Sand & Gravel

Embedment (feet): unknown Exposure: No Exposure


Scour Summary

The bridge was originally constructed in 1900 and reconstructed (widened with concrete deck on steel beams and substructure extensions) in 1929. The FEMA FIS does not provide specific flood history for the Town of Pelham or Beaver Brook, however photos from the NHDOT inspection reports indicate that the bridge experienced flooding in May of 2006 and April 2007. USGS Gage 10965852 located 6.5 miles upstream recorded a 100 year event in 2006 and a 10-50 year event in 2007. Also NHDOT WWII Card (1942) indicates the flood of record was in 1936.

Flood History:

Two-span masonry arch bridge originally constructed in 1900 and reconstructed (widened with concrete deck on steel beams and substructure extensions) in 1929. Both abutments are composed of stone masonry, located in the channel and have unknown footing embedments. The pier is composed of stone masonry, located in the channel and has an unknown foundation. The latest NHDOT underwater inspection report (2006) did not note any significant scour issues, however it did note several voids in the masonry at the abutments and pier and that a stone at the pier was misaligned. In addition, according to the NHDOT Inspection History the bridge has been on a 6-month frequency since 1999, and inspectors have consistently noted the poor condition of the substructure elements. Bridge opening data referenced from the NHDOT WWII Card (1942) is generally consistent with the drop-line readings taken in 2009, indicating there has been no long term aggradation or degradation of the streambed within the bridge reach. During the 2009 inspection downstream of the bridge on the right side, it was observed that there was a large scour hole. Although the bridge has experienced several significant flood events since it was reconstructed in 1929 (most recently in 2006 & 2007), the potential scour depth along with the unknown and unprotected footing at the pier indicate that this bridge should remain rated as scour critical.

Field Observation:

Hillsborough Countywide FIS provides flow and water surface elevation data at the bridge. This information was used along with a field soil classification (fine to coarse sand) in order to develop a pier scour estimate. The result of this computation indicates the potential for 13.4 feet of scour at the pier during the incipient overtopping (50-year) event. Although the bridge has experienced several significant flood events since it was reconstructed in 1929 (most recently in 2006 & 2007), the potential scour depth along with the unknown and unprotected footing at the pier indicate that this bridge should be rated scour critical and a POA should be implemented.

Scour Calculations:

Current Item 113 Code: 2 Source of Scour Critical Code: Assessment

Borings:

Yes No

Bridge Maintenance Division5

20064900 Year:Total:

Text9:6/9/2010 Text9:Scour Critical Bridge - Plan of Action: Pelham 110/090 Text9: Page 1 of 6

5. MONITORING PROGRAM RECOMMENDED5a. Regular Inspection Program

Riverbed Profile Readings

Items toWatch:

According to the NHDOT Inspection History the bridge has been on a 6-month frequency since 1999, and inspectors have consistently noted the poor condition of the substructure elements. Monitor channel elevations with riverbed profile readings, making note of any significant changes. Monitor displacement of stones. Use photo documentation. MAINTAIN 6 MONTH INSPECTION FREQUENCY.

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:

Monitor channel elevations with riverbed profile readings, making note of any significant changes.

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 at low chord (apex of arch on the upstream side).

Revisit Bridge

Close Bridge (See Section 7)

Placard Location: Placard not necessary.

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

NHDOT Bridge Maintenance Divisional Superintendent Crew# 142.

NHDOT Bridge Maintenance Divisional Foreman Crew# 143.

NHDOT Bridge Design Bureau, Existing Bridge Section4.

NHDOT Bridge Design Bureau, Administrator5.

Stage (WSE)

NOAA Gage Station #

Scour Critical Riverbed Elevation(s) for Each Pier/Abutment: Pier and Abutments have unknown foundations - 1 ft below current streambed (See Attachment D)

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

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

Assess changes in channel/riverbed profiles, possible footing exposure and overall stability. Consider closing bridge.

Agency and Department Responsible for Monitoring:

NHDOT

Contact Person:

NHDOT Bridge Design Bureau (603) 271-2731

Riverbed Profile Readings (See Attachment I)

Items toWatch:

According to the NHDOT Inspection History the bridge has been on a 6-month frequency since 1999, and inspectors have consistently noted the poor condition of the substructure elements. Monitor channel elevations with riverbed profile readings, making note of any significant changes. Monitor displacement of stones.

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) Interim action - Articulated Concrete Blocks at pier and both abutments

Estimated Cost

$ 320,000

(2) $

(3) $

Consider major rehabilitation for this bridge. Install articulated concrete block system until rehabilitation schedule is defined. Deep water, but minimal embedment.

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

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:

129.5

132.5

2955

3515

5600

132.5

134

135

50 year

Flow (cfs) Elevation (ft)

100 year

500 year

Roadway

Low Chord

Flow Impacting Bridge Flow Overtopping Bridge

Yes

Yes

Yes

Yes

Yes

Yes

1545 13010 year No No


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# 142.

NHDOT Bridge Maintenance Divisional Foreman Crew# 143.

NHDOT Bridge Design Bureau, Existing Bridge Section4.

NHDOT Bridge Design Bureau, Administrator5.

Ice Jam

DischargeStage (WSE)USGS Gage Station #

Stage (WSE)NOAA Gage Station #

8. DETOUR ROUTEDetour Route Description: (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 14

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: 05

NHDOT Bureauof Traffic

Pelham 109/081 BEAVER BROOK 14.7 (6/20/2002)UOLD BRIDGE STREET unrestricted 23.9


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

0.1 Feet

9b. Criteria for Completing Bridge Reopening Process:

Above Critical Footing Elevation. (See Section 5d)


Bridge: Pelham 110/090

Date Taken: 5/21/2009 10:24:49 AM

Description: UPSTREAM FASCIA

Source: CHA

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Date Taken: 5/21/2009 10:25:01 AM

Description: DOWNSTREAM FASCIA

Source: CHA

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Text9:5/17/2010 Text9:Attachment A: Bridge Photos: Pelham 110/090 Text9: Page 1 of 3


Date Taken: 5/21/2009 10:25:03 AM

Description: DOWNSTREAM CHANNEL

Source: CHA

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Date Taken: 5/21/2009 10:24:51 AM

Description: UPSTREAM FASCIA - OVERFLOW CULVERT

Source: CHA

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Date Taken: 5/21/2009 10:24:59 AM

Description: DOWNSTREAM FASCIA - OVERFLOW CULVERT

Source: CHA

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11 King Court

Keene, NH 03431-4648 Main: (603)-357-2445

New Hampshire Scour Investigation

Pelham 110/090

Attachment B: Detour Route

Pelham 110/090

DETOUR MAP

IF GOING EAST ON MAIN ST., REVERSE DIRECTIONS.

GOING WEST ON MAIN ST.


Detour (miles): Last ADT:

Foundation Details:

KNOWN

UNKNOWN Worst Abutment: Right

Worst Pier: 1(Looking Downstream L to R)



Diving Insp Reports: 6/6/2008

FIELD VERIFICATION CARD (POA Attachment C)

Owner: NHDOT



Town, County: Pelham - Hillsborough

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

BRIDGE INFORMATION

Superstructure Type: Arch-Deck

Superstructure Material: Masonry

Scour Critical Feature: Pier


Red List: Yes

Number of Spans: 2

USGS Gage Station: 10965852 USGS Station Prox To Bridge: 6.5 miles upstream

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: Changes in streambed elevation of more than 0.1 ft or evidence of footing exposure.

(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 14

HighwayMaintenance

District: 05

NHDOT Bureauof Traffic

Streambed Elevation Drops Less than

Streambed Elevation 1.0 Feet

0.1 Feet

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

DischargeStage (WSE)USGS Gage Station #

Stage (WSE)NOAA Gage Station #

NOAA Gage Station: NOAA Station Prox To Bridge:

1 20064900 Year:Total:

Text9:5/17/2010 Text9:Attachment C: Field Verification Card: Pelham 110/090 Text9: Page 1 of 2

Upstream Low Water

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Upstream Low Water

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Downstream Elevation of Bridge at Low Water

DocID_10632.jpg

Text9:5/17/2010 Text9:Attachment C: Field Verification Card: Pelham 110/090 Text9: Page 2 of 2

ROADWAY

ELEVATION (FT)

LOW CHORD

ELEVATION (FT)

FOOTING ELEVATION (FT) STREAMBED ELEVATION (FT)

TOP BOTTOM

SUBSTR.

UNIT

2) THE SUBSTRUCTURE LABELING CONVENTION ESTABLISHED BY CHA DEFINES LEFT AND RIGHT LOOKING DOWNSTREAM.

1) UNLESS OTHERWISE SPECIFIED, ALL ELEVATIONS ARE REFERENCED TO NGVD 1929.

LEFT ABUT.

PIER 1

RIGHT ABUT.

INVESTIGATION

DDATE: 10/09

BRIDGE ELEVATION SUMMARY

NEW HAMPSHIRE BRIDGE SCOUR

4) BRIDGE 110/090 HAS AN OVERFLOW CULVERT (12FT SPAN X 8.5 FT RISE, PIPE ARCH) LOCATION APPROXIMATELY 30 FT EAST OF THE LEFT ABUTMENT.

PELHAM 110/090

132.5

132.5

132.5

129.5 (SPAN 1 APEX)

--

129.5 (SPAN 1 APEX)

UNK

UNK

UNK

UNK

UNK

UNK

NHDOT WW11

CARD (1942)

v--

120.3

v--

CHA FIELD

2009

FEMA FIS (1979)

COUNTRYWIDE (2005)

--

117.0

--

120.6

120.1

120.5

CHA 100-YEAR SCOUR

ELEVATION (FT)

v--

106.7

v--

UPSTREAM ELEVATION

N.T.S.

STREAMBED ELEVATION

(TYP)

LOW CHORD ELEVATION

(TYP)ROADWAY ELEVATION

(TYP)

RAP1LA

3) STREAMBED ELEVATIONS GIVEN ARE APPROXIMATE AT EACH SUBSTRUCTURE UNIT AND ALONG THE FASCIA INDICATED. vFOR DETAILED SUBSTRUCTURE RIVERBED PROFILE MEASUREMENTS SEE ATTACHMENT I. ATTACHMENT H PROVIDES THE LOCATION OF vSCOUR RELATED FEATURES AND OTHER MINOR STREAMBED VARIATIONS.

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BOTTOM CHA FIELD (2009)

vUPSTREAM ELEVATIONv

CHA File No:

18925.2003.1510

11 King Court

Keene, NH 03431-4648

Main: (603)-357-2445

New Hampshire Scour Investigation

Pelham 110/090 Attachment G: Scour Countermeasures

Attachment G:

Supporting Documentation, Calculations,

Estimates, and Conceptual Designs for Scour

Countermeasures

NHDOT PROTECTIVE COUNTERMEASURES 4/14/2010

ESTIMATED COST OF POTENTIAL INTERIM COUNTERMEASURE - Articulated Concrete Block System:

110/090Pelham

4619 3'-5'36 3.1 ACB Width = 2.5 times pier ftg width14 37 ACB Length is along its center25 <= width at abutment = 25 ft (less than 2 x design flow)

SSU CM TYPE Length (ft) Width (ft) Depth (ft) No. Items Quantity Unit Unit Price Subtotal1 1 LS $10,000 $10,0001 1 LS $10,000 $10,0000 0 LS $0 $0

120.5 7.75 - 2 208 SY $31 $6,485120.5 7.75 - 2 208 SY $63 $12,970120.5 7.75 - 2 208 SY $213 $44,100

0 0 LS $0 $086 25 - 2 478 SY $31 $14,93186 25 - 2 478 SY $63 $29,86186 25 - 2 478 CY $213 $101,528

Proposed work: $25,000 - diversion of water not practical - minor excavate and level area $254,875 - place filter 25% $63,719 - place ACB system $318,594

$320,000

Assumptions:Environmental impact associated with the proposed work is judged to be: potentially significantGiven the estimated quantities for this item, the unit price is judged to be higher than average unit prices.

Notes:The cost of mitigating or eliminating potential environmental impacts is not included in this estimate. The cost of environmental permit preparation is also not included herein.

Provide and place ACB system

Pier 1 ACB

Both Abutments ACB

Water Diversion System

Low Flow Water Depth

Spans Protected N/ABridge No.

In light of the overall poor condition of this bridge, CHA recommends COMPLETE REPLACEMENT. As an interim action, this countermeasure could be installed to address known scour deficiencies of the foundations. Such action might allow increasing the FHWA Item 113 scour rating from 2 (CHA’s proposed rating for current conditions) to 3 (still scour critical due to potential substructure instability during flood events). The rating condition of the substructure (FHWA Item 60) should be reduced due to its linkage with Item 113 (CHA proposes rating Item 60 as 2 for current conditions – could be increased to 3 after such action). A more careful evaluation of substructure stability would be required as part of this potential action because the countermeasure would result in “mounding” of the streambed, thereby violating the intent of HEC-23 and not allow a rating of 7.

TownSSU's Protected Pier 1 and Both Abutments

Dist. Between Abutment Faces Approved Countermeasure Type Articulated Concrete Block SystemDist. Between abut and pier

ContingencyTotal Estimated Cost

Conceptual Budget

Bridge Width

barge rental

Design Flow DepthPier Width (ft)

Pier Length (ft)

Access to pier via bargeItem

Subtotal

Excavation and site prep

Note - in light of deeper "normal low" flow, PGR is considered unacceptable due to higher costs of dewatering/diversion of water. Accordingly, use ACB system with underwater placement. Narrow and long roadway embankment drives need for barge for work access.

Mobilization

Provide and place ACB systemProvide and place filter

Water Diversion SystemExcavation and site prep Provide and place filter

5/17/2010 Attachment G

INVESTIGATION

G

NEW HAMPSHIRE BRIDGE SCOUR

DATE: 4/10

PELHAM 110/090

CONCEPTUAL COUNTERMEASURE DRAWING

UPSTREAM ELEVATION

N.T.S.

RAP1LA

N.T.S.

PLAN VIEW

LA P1 RA

PLACE ARTICULATED CONCRETE

BLOCKS

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ANNOTATION SCALE 200


BOTTOM CHA FIELD (2009)

vUPSTREAM ELEVATIONv

NHDOT POST FLOOD INSPECTION REPORT (POA Attachment I)

Bridge: Post Flood Inspection Date:Pelham 110/090GENERAL INFORMATION

Town: Pelham


Owner: NHDOT


Major Basin (HU8): Merrimack River

Functional Class: 09 - Rural Local

Detour Length: 1 (miles)

Year Built: 1900

Year ofReconstruction: 1929

ADT: 4900 Year of ADT: 2006

Overall Fed Sufficiency Rating: 15.8

RedList: Yes

Item 60: 2 Item 61: 6 Item 71: 7 Item 113: 2

Current:

HYDRAULIC INFORMATION

FEMA Study:

Whitman & Howard Information

USGS Report:

Tidal Influence: Other Hydrologic & Hydraulic Data:FEMA FIS provides flow and water surface elvation data. USGS Gage on Beaver Brook is too far away to provide flow info for bridge but was included to document flooding in the watershed. Merrimack River Watershed (Nashua River to Shawsheen River).

100-Yr Water Velocity (feet per sec): 8.9

Angle Of Attack 5

Watershed Area (sq. mi): 74.5

(Flood Flow)

BRIDGE INFORMATIONBridge Length (in feet): 46.00 Plans Available: Borings Available:

Abutment Foundation: Unknown Pier Foundation: Unknown

2005 2006 2007

Flood / Scour HistoryComments:

The bridge was originally constructed in 1900 and reconstructed (widened with concrete deck on steel beams and substructure extensions) in 1929. The FEMA FIS does not provide specific flood history for the Town of Pelham or Beaver Brook, however photos from the NHDOT inspection reports indicate that the bridge experienced flooding in May of 2006 and April 2007. USGS Gage 10965852 located 6.5 miles upstream recorded a 100 year event in 2006 and a 10-50 year event in 2007. Also NHDOT WWII Card (1942) indicates the flood of record was in 1936.

Flood History:

:

Bridge Width (in feet): 36.00

Substructure Channel Stability Hydraulic Adequacy Scour Risk

Posting 12.7 , E2

Bridge Plan File Loc: J-49

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

100-Yr Overtopping Relief: Right Approach

3/14/1980

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: 1(Looking Downstream L to R)



Diving Insp Reports: 6/6/2008

Superstructure Type: Arch-Deck

Superstructure Material: Masonry

Scour Critical Feature: Pier


Red List: Yes

Number of Spans: 2

USGS Gage Station: 10965852 USGS Station Prox To Bridge: 6.5 miles upstream

Dates:

What To Look For: Changes in streambed elevation of more than 0.1 ft or evidence of footing exposure.

NOAA Gage Station: NOAA Station Prox To Bridge:

Text9:5/17/2010 Text9:Attachment I: Post Flood Inspection Report: Pelham 110/090 Text9: Page 1 of 1

CHA File No: 18925.2003.1510

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

Pelham 110/090 Attachment J: Scour/H&H Backup

Calculations

Attachment J: Scour/H&H Backup Calculations

COMPLETED BY KKD DATE

CHECKED BY SVE PROJ. NO.

PROJ. NAME & LOCATION Pelham 110-090 SUBJECT Scour Calcs

Pier Scour Input

V1 (fps) 8.9 Average Velocity at Pier Continuity EquationY1 (ft) 11 Average Depth at Pier (134 - 123) 50-yr WSE Estimate (FEMA) / Field Measurements

θ (deg) 5 Angle of Attack Field Estimatea (ft) 3.1 Pier Width Field MeasurementL (ft) 37 Pier Length (Bottom) Field Measurement

Underlying Streambed

D95 (ft) 0.016 Sand-gravel bed Field EstimateD50 (ft) 0.008 Sand-gravel bed Field Estimate

Armoring Layer

D95 (ft) N/AD50 (ft) N/A

2/18/2010

18457

VARIABLE CALC / NOTES SOURCE

3/23/2010 Page 1 of 2 Appendix J

K4: ARMORING COEFFICIENT

PIER SCOUR COMPUTATIONSReference for methodology: HEC-18 Fourth Edition

Pelham 110-090 Incipient Overtopping (50-year) EventK4: PIER COMPONENT

Pier #1D95 (ft) = 0.0160 <---Field Estimate

D50 (ft) = 0.0080 <---Field Estimate

PIER SCOUR ANALYSIS V1: APPROACH VELOCITY (ft/s) = 8.90y: DEPTH (ft) = 11.00

Reference for methodology: HEC-18 Fourth Edition Chapter 6 a: PIER WIDTH (ft) = 3.10Ku = 11.17

PIER* Yes Vc95: CRITICAL VELOCITY FOR D95 (ft/s) = 4.20

Pier Number Pier #1 Vc50: CRITICAL VELOCITY FOR D50 (ft/s) = 3.33

V1: VELOCITY (fps) 8.9 ViC95: INITIAL SCOUR VELOCITY FOR D95 (ft/s) = 2.05Y1: DEPTH (ft) 11 ViC50: INITIAL SCOUR VELOCITY FOR D50 (ft/s) = 1.57

ATTACK ANGLE, Degrees 5 VR: VELOCITY RATIO (ft/s) = 5.71INDIVIDUAL PIER WIDTH (ft) 3.10 K4 = 1.00a: PIER WIDTH (ft) 3.10 Note: If D50 < 2mm (.007 ft) or D95 < 20mm (0.07 ft), then K4=1L: PIER LENGTH (ft) 37.00PIER SHAPE (S=SQUARE, C = CIRCULAR, SN = SHARP NOSE) SK1: SHAPE COEFFICIENT 1.10K2: ANGLE COEFFICIENT 1.59K3: BED COND. COEFFICIENT 1.10K4: BED AMORING COEFFICIENT 1.00

g: gravitational constant (ft/s2) 32.20FROUDE NUMBER, Fr 0.47LOCAL SCOUR DEPTH (ft), Yspier 13.4

Calc. By: KKD Date: 2/18/2010Check By: SVE Date: 2/20/2010

Notes: There is no foundation information for this bridge and the field visit did not indicate evidence of an exposed footing. As a result, for the purposes of this analysis CHA used the

general pier scour equation.

Sand-gravel bed

3/23/2010 Page 2 of 2 Attachment J

priority scour critical bridge countermeasure plan of action …gis.dot.nh.gov/bridge_scour/pelham...

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