2016-01-22_SR-89_and_Fanny_Bridge_Addendum_Memorandum.pdf

T E C H N I C A L M E M O R A N D U M

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Addendum to the Preliminary Bridge Hydraulic Study for State Route 89/Fanny Bridge Community Revitalization Project (CA FLAP SR 89 [1]) PREPARED FOR: Matt Ambroziak, PE

Project Manager Central Federal Lands – Highway Division (CFL HD) 12300 West Dakota Avenue Lakewood, CO 80228

PREPARED BY: Brad Hartman, PE, CFM

DATE: January 22, 2016 (previous revisions/submittals on January 15, 2016, January 12, 2015, February 6, 2015, October 29, 2015, and December 11, 2015)

PROJECT NUMBER: 653829

REVISION NO.: 4

This memorandum is an addendum to the Preliminary Bridge Hydraulic Study for State Route (SR) 89/Fanny Bridge Community Revitalization Project in Placer County, California on SR 89 from SR‐89‐PM 7.5/9.4 to SR‐28 – PM 0.0/0.1, dated April 2014, prepared for the Tahoe Transportation District by Wood Rodgers. This addendum addresses design modifications made to the proposed SR‐89 bridge (structure RG2991) and the existing Fanny Bridge (structure RG2990) since April 2014. This memorandum also expands on discussions on the hydrologic analysis, hydraulic models, and bridge scour.

Bridge Design Modifications The preliminary design of the proposed SR‐89 Bridge and the existing Fanny Bridge to be replaced are shown in the Type, Size, and Location plans included in the bridge selection reports.

The changes to the SR‐89 Bridge since April 2014 include a lower roadway profile, elimination of all piers, a reduction in the bridge span, and the addition of pedestrian trails behind both abutments. The proposed SR‐89 bridge abutments will be of a cellular construction.

The changes made to the Fanny Bridge design since April 2014 include the full replacement of the bridge instead of restoration, and the elimination of all piers. The existing abutments will remain in place, with new abutments constructed behind the existing abutments.

Hydrologic Assessment The Wood Rodgers report lists a 505 square mile drainage area to the bridges, including the 192 square mile surface area of Lake Tahoe, which is located directly upstream of the bridges. The lake’s surface area represents more than a third of the drainage area to the bridges. Extremes in the controlled dam releases to the Truckee River are reduced due to the attenuation effect of the large surface area of the lake in relation to the drainage area. The lake is allowed to fluctuate up to 7 feet in elevation to meet water needs and to control flooding.

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Page 5 of the Wood Rodgers report states:

“For purposes of this study, it is considered sufficient to utilize the maximum historical outflow from the dam (controlled release) as the maximum flood that a downstream bridge will encounter with a 1% Chance Annual Occurrence. Considering this same maximum flow has occurred twice in the last 100 years, with two other occurrences nearly as large, Wood Rodgers considers it appropriate to apply this design flow as a “50‐year” event with the associated design freeboard considerations.”

Wood Rodgers recommended that the flood of record, which has peak discharge only 40 cubic feet per second (cfs) larger (a 1.5 percent increase) than the Federal Emergency Management Agency (FEMA) 50‐year discharge, be used as the design discharge. CH2M concurs with this statement and recommends using the flood of record as the design flow. Furthermore, given the presence of the dam, the FEMA 100‐year and 500‐year discharge rates as listed in the FEMA Flood Insurance Study (FIS) are likely too high. However, the bridges were assessed for these larger FEMA discharges anyhow, despite any unlikelihood.

Table 1 lists the discharges included in the analysis. The FEMA discharges were taken from the effective Placer County, CA FIS (06061CV001, revised November 21, 2001). The flood of record was taken from the April 2014 Wood Rodgers report. A discharge rate of 3,530 cfs was also provided by the U.S. Bureau of Reclamation (Reclamation).

Table 1. Hydrologic Discharges Hydrologic Discharges Used for the River and Bridge Assessment

Flood Discharge Rate

(cfs)

FEMA 10‐year 850

FEMA 50‐year 2,650

Flood(s) of Record (“50‐year” from 1969 and 1997) 2,690

FEMA 100‐year 3,350

Reclamation 3,530

FEMA 500‐year 4,350

Note:

cfs = cubic feet per second

Hydraulic Assessment of River and Bridges FEMA developed a HEC‐2 hydraulic model for this portion of the Truckee River in 1981. Wood Rodgers obtained the HEC‐2 model from FEMA in 2011 and converted it to HEC‐RAS. The Wood Rodgers HEC‐RAS models were then revised to reflect modifications made to the bridge designs since April 2014. Both existing conditions and proposed conditions were analyzed. The existing conditions model was revised by adding additional flood discharges and by making slight adjustments to the abutment face, overbank, and ineffective flow stations of the existing Fanny Bridge. The proposed conditions model was revised to reflect the latest design of the proposed SR‐89 Bridge including cellular abutments/columns and trails, removing the Fanny Bridge piers, and adjusting the connection between the existing abutments and the new ones, and adjusting the Fanny Bridge low chord elevations.

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Water Surface Profile Table 2 compares the existing and proposed conditions water surface elevations based on the FEMA 100‐year discharge. Consistent with the April 2014 Wood Rodgers report and current project work, all elevations listed herein from the model correspond to the NGVD29 vertical datum.

Table 2. Water Surface Profile Comparison Existing and Proposed Water Surface Elevations (in feet) for the Truckee River for the 100‐Year FEMA Discharge Rate

Cross Section/Station Existing Conditions Proposed Conditions Change

0.471 6,226.84 6,226.74 ‐0.10

0.470 6,226.83 6,226.74 ‐0.09

0.463 Fanny Bridge Proposed Fanny Bridge ─

0.457 6,226.72 6,226.65 ‐0.07

0.393 6,226.20 6,226.11 ‐0.09

0.331 6,226.09 6,225.99 ‐0.10

0.261 6,225.48 6,225.35 ‐0.13

0.258 Pedestrian Bridge Pedestrian Bridge ─

0.255 6,225.48 6,225.35 ‐0.13

0.187 6,225.11 6,224.93 ‐0.18

0.160 6,224.81 6,224.81 0.0

0.149 ─ Proposed SR‐89 Bridge ─

0.138 6,224.78 6,224.76 ‐0.02

0.114 6,224.70 6,224.70 0.0

0.085 6,224.48 6,224.48 0.0

0.084 Southwest Pacific Bridge Southwest Pacific Bridge ─

0.083 6,224.46 6,224.46 0.0

As shown in Table 2, the proposed SR‐89 Bridge and replaced Fanny Bridge do not increase water surface elevations in the river reach for the base flood (the FEMA 100‐year discharge). Therefore, it meets FEMA floodplain requirements. A “no rise” situation is also achieved for the 50‐year FEMA and 50‐year flood of record discharges. A floodplain development permit will need to be processed with the local floodplain administrator. More detailed HEC‐RAS results are provided in Appendix A.

Freeboard For both the proposed SR‐89 and Fanny bridges, Caltrans and CFL HD policy requires 2 feet of freeboard for the 50‐year flood (or the flood of record, which Wood Rodgers had equated to the 50‐year flow). Per Caltrans, no freeboard is required for the 100‐year discharge. Reclamation has requested that some freeboard be available for the 3,530 cfs discharge.

Table 3 and Table 4 list hydraulic data including average velocity, water surface elevation, and available freeboard for the proposed SR‐89 and Fanny bridges, respectively. Freeboard was based on the

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proposed bridge low‐chord elevations, which are 6233.41 feet for the proposed SR‐89 Bridge, and range from 6227.62 to 6227.00 feet for the replaced Fanny Bridge.

Table 3. SR‐89 Bridge Hydraulic Data Discharge, Velocity, Water Surface Elevation, and Available Freeboard for the Proposed SR‐89 Bridge

Proposed SR‐89 Bridge

Design Flood

Proposed Water Surface Elevation

(feet)1,2

Available Freeboard (feet)

Average Velocity (feet per second)3

Left Overbank Main

Channel Right

Overbank Overall

FEMA 10‐year 6220.71 12.70 1.30 3.57 0.75 3.52

FEMA 50‐year 6,224.00 9.41 2.35 5.11 1.96 4.38

Flood of Record 6,224.05 9.36 2.38 5.13 1.99 4.39

FEMA 100‐Year 6,224.81 8.60 2.78 5.49 2.44 4.64

Reclamation 6,225.01 8.40 2.88 5.58 2.54 4.71

FEMA 500‐Year 6,225.84 7.57 3.26 5.98 2.97 5.01

Notes:

1National Geodetic Vertical Datum of 1929 (NGVD 29) vertical datum.

2At upstream cross‐section.

3At upstream bridge face.

Table 4. Fanny Bridge Hydraulic Data Discharge, Velocity, Water Surface Elevation, and Available Freeboard for the Proposed Fanny Bridge

Proposed Fanny Bridge

Design Flood Proposed Water Surface

Elevation (feet)1,2

Available Freeboard (feet) Average Velocity (feet per second)3 Southeast Corner Northwest Corner

FEMA 10‐year 6,222.42 5.20 4.58 1.44

FEMA 50‐year 6,225.83 1.79 1.17 2.67

Flood of Record 6,225.88 1.74 1.12 2.69

FEMA 100‐Year 6,226.74 0.88 0.26 3.03

Reclamation 6,226.96 0.66 0.04 3.12

FEMA 500‐Year 6,227.94 ‐0.32 ‐0.94 3.70

Notes:

1NGVD 29 vertical datum.

2At upstream cross‐section.

3At upstream bridge face.

Adequate freeboard is available for both the 100‐year FEMA and Reclamation discharges, thereby meeting the requirements. Although only 1.12 to 1.79 feet of freeboard is available on the Fanny Bridge for the 50‐year flood of record, the following factors provide mitigation (with Figure 1 and Figure 2 provide visual support):

Other than the lake itself, no upstream tributary area is available to produce debris. Westerly winds push debris eastward. The outlet is not known to have a significant influence on lake currents.

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The dam, its associated small sluice gates, and a boom are located immediately upstream of the Fanny Bridge and substantially limit the amount of debris, if any, that would flow to and through the Fanny Bridge.

By using a larger girder depth (and the resulting reduced low‐chord), the three sets of bridge piers that exist today are eliminated for the proposed condition, further reducing the potential for debris clogging (despite the fact that debris on the existing piers is not a known issue currently).

Therefore, based on this improvement and the reduced risk of debris, the available 50‐year freeboard for the Fanny Bridge is considered sufficient from a risk‐based design perspective.

Figure 1. Aerial View of Lake Tahoe Dam Aerial View of Close Proximity of the Lake Tahoe Dam and the Fanny Bridge

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Figure 2. Lake Tahoe Dam

A View of the Lake Tahoe Dam and Sluice Gates, Immediately Upstream of the Fanny Bridge

Rafts enter the Truckee River downstream of the Fanny Bridge, but upstream of the proposed SR‐89 Bridge. The proposed SR‐89 Bridge will also provide adequate of freeboard during summer flows for recreational users and meets the United States Coast Guard preference that a bridge such as this provide at least 6 feet of freeboard over the 100‐year flood.

Bridge Scour Assessment and Countermeasures Based upon U.S. Geological Survey data, inspection of local bridges, and lack of future land use changes in the watershed, the Wood Rodgers assessment indicated there is no long term scour (degradation) evident at the bridges. Bedrock is below both the depth of scour and the proposed bridge foundations.

General channel contraction scour was estimated using standard methodologies (including an allowance for pressure flow for the 500‐year discharge at the Fanny bridge), and checked/verified by HEC‐RAS where possible.

Scour for the abutments was initially calculated using the same methods as described in the Wood Rodgers report (with the exception of pier scour since piers are no longer proposed). Per CFL HD direction in January 2015, the National Cooperative Highway Research Program (NCHRP) 24‐20 method was ultimately used to assess the local abutment scour for the FEMA 500‐year discharges, as well as the 100‐year discharges for Caltrans reporting purposes. The NCHRP method is relatively new and continues to evolve per Federal Highway Administration (FHWA) research. HEC‐RAS does not currently include the NCHRP scour computation method, so these calculations were prepared manually and checked with the

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FHWA Hydraulic Toolbox v4.1. It is noted that due to the close proximity of the Fanny bridge abutments to the main channel, the channel thalweg was used as the reference elevation for scour elevations. For the SR‐89 abutments and for scour purposes, the trail openings were assumed to be blocked. Although the columns of the SR‐89 abutments were considered piers for the hydraulic analysis, they were not assessed as piers for scour due to the concrete paving surrounding them.

Summaries of the resulting scour depths and elevations for the SR‐89 bridge are shown in Table and Table 6. Similar data is shown for the Fanny bridge in Table 7 and Table 8. More detailed scour calculations and results are provided in Appendix B.

Table 5. 100‐Year Scour Data for the Proposed SR‐89 Bridge

Proposed SR‐89/Truckee Bridge ‐ 100‐Year Scour Data (ft)

Scour Type Abutment #2 (east/left)

Main Channel

Abutment #1 (west/right)

Scour Reference Elevation 6222.04 6215.42 6222.86

Long‐term degradation depth 0.00 0.00 0.00

General Contraction Scour depth 1.35 0.00 0.74

Long‐Term Degradation + General Contraction Scour Elevation

6220.69 6215.42 6222.12

NCHRP Local Abutment Scour Depth 4.64 ‐ 5.17

Total NCHRP Abutment Scour Elevation 6217.40 ‐ 6217.69

Table 6. 500‐Year Scour Data for the Proposed SR‐89 Bridge

Proposed SR‐89/Truckee Bridge ‐ 500‐Year Scour Data (ft)

Scour Type Abutment #2 (east/left)

Main Channel

Abutment #1 (west/right)

Scour Reference Elevation 6222.04 6215.42 6222.86

Long‐term degradation depth 0.00 0.00 0.00

General Contraction Scour depth 1.48 0.00 0.87

Long‐Term Degradation + General Contraction

6220.56 6215.42 6221.99

NCHRP Local Abutment Scour Depth 5.44 ‐ 6.55

Total NCHRP Abutment Scour Elevation 6216.60 ‐ 6216.31

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Table 7. 100‐Year Scour Data for the Proposed Fanny Bridge

Proposed Fanny Bridge ‐ 100‐Year Scour Data (ft)

Scour Type Abutment #2 (east/left)

Main Channel

Abutment #1 (west/right)

Scour Reference Elevation 6215.73 6215.73 6215.73

Long‐term degradation depth 0.00 0.00 0.00

General Contraction Scour depth 0.50 0.50 0.50

Long‐Term Degradation + General Contraction

6215.23 6215.23 6215.23

NCHRP Local Abutment Scour Depth 4.11 ‐ 4.11

Total NCHRP Abutment Scour Elevation 6211.62 ‐ 6211.62

Table 8. 500‐Year Scour Data for the Proposed Fanny Bridge

Proposed Fanny Bridge ‐ 500‐Year Scour Data (ft)

Scour Type Abutment #2 (east/left)

Main Channel

Abutment #1 (west/right)

Scour Reference Elevation 6215.73 6215.73 6215.73

Long‐term degradation depth 0.00 0.00 0.00

Vertical (pressure) Contraction Scour depth 4.34 4.34 4.34

Long‐Term Degradation + General Contraction

6211.39 6211.39 6211.39

NCHRP Local Abutment Scour Depth 3.65 ‐ 3.65

Total NCHRP Abutment Scour Elevation 6212.08 ‐ 6212.08

Riprap Abutment Protection and Countermeasures Riprap countermeasures for the bridge abutments were designed per the standard method contained in HEC‐23 Design Guideline 14. For the 500‐year discharge, the calculations included as Appendix C show that a relatively small median rock size (D50) would provide scour protection. But given the special need for countermeasures on the Fanny bridge where existing abutments are being retained under pressurized flow, as well as the size of rock that exists at these bridge sites currently, it is recommended that 18‐inch riprap be used. Per FHWA guidance, the riprap will be placed out from the abutment face and into the channel a distance at least twice the flow depth beneath the bridge, or 25 feet, whichever is less. Riprap thickness will be twice the median rock size and protected with geotextile filter fabric. The extents of the riprap will be wrapped around downstream end of the Fanny Bridge to a distance of 25 feet or twice the flow depth, whichever is greater, but will terminate before the upper bank and roadway. Riprap would need to be placed in such as manner as to not damage or impede the function of the existing concrete weir located at the upstream face of the Fanny Bridge. For the proposed SR‐89 Bridge, riprap will be placed in portions of slope between the trail land the river. The top of any spread footings at the SR‐89 Bridge need to be below the elevation of long‐term degradation and general contraction scour, with the bottom of the curtain walls to be below the local abutment scour elevation.

bhartma1 Rectangle

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Conclusion The design of the proposed SR‐89 Bridge and replaced Fanny Bridge meets the client’s “no rise” requirement which also meets federal floodplain requirements. The proposed bridges meet freeboard needs and will be designed to withstand the estimated scour depths and forces.

Appendix A HEC‐RAS Results

HEC-RAS River: Truckee River Reach: Upper Reach

Reach River Sta Profile Plan Q Total Min Ch El W.S. Elev Crit W.S. E.G. Elev E.G. Slope Vel Chnl Flow Area Top Width Froude # Chl

(cfs) (ft) (ft) (ft) (ft) (ft/ft) (ft/s) (sq ft) (ft)

Upper Reach 0.471 10-year existing 850.00 6215.73 6222.45 6222.48 0.000137 1.43 595.31 119.38 0.11

Upper Reach 0.471 10-year Proposed Con3 850.00 6215.73 6222.42 6222.45 0.000139 1.44 591.64 119.30 0.11

Upper Reach 0.471 FEMA 50-year existing 2650.00 6215.73 6225.90 6226.00 0.000237 2.57 1045.51 143.18 0.16

Upper Reach 0.471 FEMA 50-year Proposed Con3 2650.00 6215.73 6225.83 6225.94 0.000244 2.60 1035.73 143.01 0.16

Upper Reach 0.471 Flood of Record existing 2690.00 6215.73 6225.96 6226.06 0.000239 2.59 1053.62 143.33 0.16

Upper Reach 0.471 Flood of Record Proposed Con3 2690.00 6215.73 6225.89 6225.99 0.000246 2.62 1043.69 143.15 0.16

Upper Reach 0.471 FEMA 100-year existing 3350.00 6215.73 6226.84 6226.97 0.000260 2.90 1180.61 145.16 0.17

Upper Reach 0.471 FEMA 100-year Proposed Con3 3350.00 6215.73 6226.74 6226.87 0.000269 2.93 1167.01 144.99 0.17

Upper Reach 0.471 BOR existing 3530.00 6215.73 6227.06 6227.20 0.000265 2.98 1213.19 145.57 0.17

Upper Reach 0.471 BOR Proposed Con3 3530.00 6215.73 6226.96 6227.10 0.000275 3.01 1198.70 145.39 0.18

Upper Reach 0.471 FEMA 500-year existing 4350.00 6215.73 6228.01 6228.18 0.000287 3.31 1352.98 147.32 0.18

Upper Reach 0.471 FEMA 500-year Proposed Con3 4350.00 6215.73 6227.95 6228.12 0.000293 3.33 1343.78 147.20 0.18

Upper Reach 0.470 10-year existing 850.00 6215.73 6222.45 6218.24 6222.48 0.000137 1.43 595.31 119.38 0.11

Upper Reach 0.470 10-year Proposed Con3 850.00 6215.73 6222.42 6218.25 6222.45 0.000139 1.44 591.64 119.30 0.11

Upper Reach 0.470 FEMA 50-year existing 2650.00 6215.73 6225.90 6219.77 6226.00 0.000240 2.59 1026.56 143.18 0.16

Upper Reach 0.470 FEMA 50-year Proposed Con3 2650.00 6215.73 6225.83 6219.77 6225.93 0.000247 2.61 1017.72 143.00 0.16

Upper Reach 0.470 Flood of Record existing 2690.00 6215.73 6225.95 6219.79 6226.06 0.000241 2.61 1034.01 143.32 0.16

Upper Reach 0.470 Flood of Record Proposed Con3 2690.00 6215.73 6225.88 6219.79 6225.99 0.000248 2.63 1024.97 143.15 0.16

Upper Reach 0.470 FEMA 100-year existing 3350.00 6215.73 6226.83 6220.22 6226.96 0.000265 2.93 1148.99 145.16 0.17

Upper Reach 0.470 FEMA 100-year Proposed Con3 3350.00 6215.73 6226.74 6220.22 6226.87 0.000275 2.96 1136.67 144.98 0.17

Upper Reach 0.470 BOR existing 3530.00 6215.73 6227.06 6220.35 6227.20 0.000271 3.01 1178.40 145.56 0.17

Upper Reach 0.470 BOR Proposed Con3 3530.00 6215.73 6226.96 6220.35 6227.10 0.000281 3.04 1165.23 145.38 0.18

Upper Reach 0.470 FEMA 500-year existing 4350.00 6215.73 6228.01 6220.84 6228.18 0.000296 3.36 1303.87 147.30 0.19

Upper Reach 0.470 FEMA 500-year Proposed Con3 4350.00 6215.73 6227.94 6220.84 6228.12 0.000302 3.38 1295.55 147.19 0.19

Upper Reach 0.463 Existing Fanny B Bridge

Upper Reach 0.457 10-year existing 850.00 6216.07 6222.41 6222.46 0.000273 1.81 469.72 111.83 0.16

Upper Reach 0.457 10-year Proposed Con3 850.00 6216.07 6222.38 6222.44 0.000277 1.82 467.21 111.73 0.16

Upper Reach 0.457 FEMA 50-year existing 2650.00 6216.07 6225.81 6225.95 0.000363 3.07 875.76 125.33 0.20

Upper Reach 0.457 FEMA 50-year Proposed Con3 2650.00 6216.07 6225.76 6225.90 0.000371 3.09 869.46 125.20 0.20

Upper Reach 0.457 Flood of Record existing 2690.00 6216.07 6225.86 6226.01 0.000365 3.10 882.87 125.48 0.20

Upper Reach 0.457 Flood of Record Proposed Con3 2690.00 6216.07 6225.81 6225.96 0.000373 3.12 876.38 125.34 0.20

Upper Reach 0.457 FEMA 100-year existing 3350.00 6216.07 6226.72 6226.91 0.000392 3.45 991.76 127.26 0.21

Upper Reach 0.457 FEMA 100-year Proposed Con3 3350.00 6216.07 6226.65 6226.84 0.000403 3.48 982.70 127.13 0.21

Upper Reach 0.457 BOR existing 3530.00 6216.07 6226.94 6227.14 0.000399 3.54 1019.71 127.67 0.21

Upper Reach 0.457 BOR Proposed Con3 3530.00 6216.07 6226.87 6227.06 0.000411 3.57 1009.87 127.52 0.21

Upper Reach 0.457 FEMA 500-year existing 4350.00 6216.07 6227.88 6228.11 0.000427 3.92 1139.46 129.41 0.22

Upper Reach 0.457 FEMA 500-year Proposed Con3 4350.00 6216.07 6227.79 6228.03 0.000441 3.96 1127.88 129.24 0.23

Upper Reach 0.393 10-year existing 850.00 6217.31 6222.13 6222.29 0.000996 3.24 266.46 78.64 0.29

Upper Reach 0.393 10-year Proposed Con3 850.00 6217.31 6222.10 6222.26 0.001021 3.27 264.31 78.41 0.30

Upper Reach 0.393 FEMA 50-year existing 2650.00 6217.31 6225.34 6225.73 0.001106 5.14 563.48 103.67 0.34

Upper Reach 0.393 FEMA 50-year Proposed Con3 2650.00 6217.31 6225.28 6225.68 0.001143 5.20 556.92 103.26 0.35

Upper Reach 0.393 Flood of Record existing 2690.00 6217.31 6225.40 6225.79 0.001109 5.18 569.01 104.01 0.34

Upper Reach 0.393 Flood of Record Proposed Con3 2690.00 6217.31 6225.33 6225.73 0.001147 5.23 562.22 103.59 0.35

Upper Reach 0.393 FEMA 100-year existing 3350.00 6217.31 6226.20 6226.67 0.001158 5.68 655.05 109.86 0.36

Upper Reach 0.393 FEMA 100-year Proposed Con3 3350.00 6217.31 6226.11 6226.59 0.001208 5.76 645.21 109.19 0.36

Upper Reach 0.393 BOR existing 3530.00 6217.31 6226.41 6226.89 0.001171 5.81 677.66 111.73 0.36

Upper Reach 0.393 BOR Proposed Con3 3530.00 6217.31 6226.31 6226.81 0.001223 5.90 666.90 110.84 0.37

Upper Reach 0.393 FEMA 500-year existing 4350.00 6217.31 6227.27 6227.85 0.001239 6.40 781.44 129.14 0.38

Upper Reach 0.393 FEMA 500-year Proposed Con3 4350.00 6217.31 6227.15 6227.75 0.001298 6.49 766.95 126.72 0.39

Upper Reach 0.331 10-year existing 850.00 6217.00 6221.90 6222.01 0.000649 2.64 354.32 121.99 0.24

Upper Reach 0.331 10-year Proposed Con3 850.00 6217.00 6221.87 6221.97 0.000673 2.67 349.98 121.77 0.24

Upper Reach 0.331 FEMA 50-year existing 2650.00 6217.00 6225.21 6225.41 0.000605 3.85 795.28 146.30 0.25

Upper Reach 0.331 FEMA 50-year Proposed Con3 2650.00 6217.00 6225.14 6225.34 0.000628 3.90 784.95 145.70 0.26

Upper Reach 0.331 Flood of Record existing 2690.00 6217.00 6225.26 6225.47 0.000606 3.87 803.15 146.75 0.25

Upper Reach 0.331 Flood of Record Proposed Con3 2690.00 6217.00 6225.19 6225.40 0.000629 3.92 792.57 146.14 0.26

Upper Reach 0.331 FEMA 100-year existing 3350.00 6217.00 6226.09 6226.32 0.000623 4.22 926.95 153.59 0.26

Upper Reach 0.331 FEMA 100-year Proposed Con3 3350.00 6217.00 6225.99 6226.23 0.000653 4.29 911.76 152.78 0.27

Upper Reach 0.331 BOR existing 3530.00 6217.00 6226.30 6226.54 0.000627 4.31 959.15 155.41 0.27

Upper Reach 0.331 BOR Proposed Con3 3530.00 6217.00 6226.19 6226.45 0.000659 4.38 942.89 154.44 0.27

Upper Reach 0.331 FEMA 500-year existing 4350.00 6217.00 6227.18 6227.47 0.000646 4.69 1101.06 165.11 0.27

Upper Reach 0.331 FEMA 500-year Proposed Con3 4350.00 6217.00 6227.06 6227.36 0.000680 4.76 1081.01 163.29 0.28

Upper Reach 0.261 10-year existing 850.00 6216.85 6221.48 6219.52 6221.66 0.001360 3.42 249.13 78.89 0.33

Upper Reach 0.261 10-year Proposed Con3 850.00 6216.85 6221.43 6219.51 6221.61 0.001440 3.48 244.79 78.43 0.34

Upper Reach 0.261 FEMA 50-year existing 2650.00 6216.85 6224.67 6221.58 6225.08 0.001269 5.21 541.97 106.20 0.36

Upper Reach 0.261 FEMA 50-year Proposed Con3 2650.00 6216.85 6224.57 6221.58 6225.00 0.001337 5.29 532.02 105.11 0.37

Upper Reach 0.261 Flood of Record existing 2690.00 6216.85 6224.72 6221.60 6225.13 0.001271 5.24 547.38 106.79 0.36

Upper Reach 0.261 Flood of Record Proposed Con3 2690.00 6216.85 6224.62 6221.60 6225.05 0.001341 5.33 537.11 105.67 0.37

Upper Reach 0.261 FEMA 100-year existing 3350.00 6216.85 6225.48 6222.16 6225.98 0.001320 5.75 632.59 115.49 0.38

Upper Reach 0.261 FEMA 100-year Proposed Con3 3350.00 6216.85 6225.35 6222.16 6225.86 0.001413 5.88 617.17 114.18 0.39

Upper Reach 0.261 BOR existing 3530.00 6216.85 6225.68 6222.29 6226.19 0.001331 5.88 655.22 117.38 0.38

Upper Reach 0.261 BOR Proposed Con3 3530.00 6216.85 6225.54 6222.29 6226.07 0.001428 6.01 638.64 115.99 0.39

Upper Reach 0.261 FEMA 500-year existing 4350.00 6216.85 6226.51 6222.93 6227.10 0.001367 6.39 755.52 123.95 0.39

Upper Reach 0.261 FEMA 500-year Proposed Con3 4350.00 6216.85 6226.34 6222.93 6226.97 0.001474 6.55 734.99 122.64 0.40

Upper Reach 0.258 Pedestrian Bridg Bridge

Upper Reach 0.255 10-year existing 850.00 6216.83 6221.44 6221.62 0.001443 3.40 250.41 84.23 0.34

Upper Reach 0.255 10-year Proposed Con3 850.00 6216.83 6221.38 6221.57 0.001537 3.47 245.57 83.65 0.35

Upper Reach 0.255 FEMA 50-year existing 2650.00 6216.83 6224.66 6225.03 0.001186 4.96 572.21 114.45 0.35

Upper Reach 0.255 FEMA 50-year Proposed Con3 2650.00 6216.83 6224.56 6224.94 0.001253 5.05 561.29 113.71 0.36

Upper Reach 0.255 Flood of Record existing 2690.00 6216.83 6224.71 6225.08 0.001187 4.99 577.98 114.84 0.35

Upper Reach 0.255 Flood of Record Proposed Con3 2690.00 6216.83 6224.61 6225.00 0.001255 5.08 566.86 114.09 0.36

Upper Reach 0.255 FEMA 100-year existing 3350.00 6216.83 6225.48 6225.92 0.001212 5.45 668.93 119.91 0.36

Upper Reach 0.255 FEMA 100-year Proposed Con3 3350.00 6216.83 6225.35 6225.80 0.001300 5.57 652.66 119.02 0.37

Upper Reach 0.255 BOR existing 3530.00 6216.83 6225.68 6226.13 0.001219 5.56 692.59 121.17 0.36

Upper Reach 0.255 BOR Proposed Con3 3530.00 6216.83 6225.54 6226.01 0.001310 5.69 675.26 120.25 0.37

Upper Reach 0.255 FEMA 500-year existing 4350.00 6216.83 6226.52 6227.04 0.001244 6.04 796.14 126.56 0.37

Upper Reach 0.255 FEMA 500-year Proposed Con3 4350.00 6216.83 6226.35 6226.90 0.001343 6.19 775.09 125.49 0.39

Upper Reach 0.187 10-year existing 850.00 6216.10 6220.97 6221.13 0.001228 3.21 264.97 82.87 0.32

Upper Reach 0.187 10-year Proposed Con3 850.00 6216.10 6220.88 6221.05 0.001328 3.31 257.14 81.53 0.33

Upper Reach 0.187 FEMA 50-year existing 2650.00 6216.10 6224.29 6224.62 0.001028 4.65 604.05 118.33 0.32

Upper Reach 0.187 FEMA 50-year Proposed Con3 2650.00 6216.10 6224.17 6224.51 0.001101 4.75 589.61 117.24 0.33

Upper Reach 0.187 Flood of Record existing 2690.00 6216.10 6224.34 6224.67 0.001030 4.68 609.90 118.77 0.33

HEC-RAS River: Truckee River Reach: Upper Reach (Continued)

Reach River Sta Profile Plan Q Total Min Ch El W.S. Elev Crit W.S. E.G. Elev E.G. Slope Vel Chnl Flow Area Top Width Froude # Chl

(cfs) (ft) (ft) (ft) (ft) (ft/ft) (ft/s) (sq ft) (ft)

Upper Reach 0.187 Flood of Record Proposed Con3 2690.00 6216.10 6224.22 6224.56 0.001104 4.78 595.23 117.66 0.34

Upper Reach 0.187 FEMA 100-year existing 3350.00 6216.10 6225.11 6225.50 0.001065 5.13 703.39 125.26 0.34

Upper Reach 0.187 FEMA 100-year Proposed Con3 3350.00 6216.10 6224.93 6225.35 0.001163 5.27 682.04 123.92 0.35

Upper Reach 0.187 BOR existing 3530.00 6216.10 6225.30 6225.71 0.001074 5.24 727.88 126.75 0.34

Upper Reach 0.187 BOR Proposed Con3 3530.00 6216.10 6225.12 6225.55 0.001174 5.39 705.22 125.37 0.35

Upper Reach 0.187 FEMA 500-year existing 4350.00 6216.10 6226.13 6226.61 0.001107 5.71 835.61 134.12 0.35

Upper Reach 0.187 FEMA 500-year Proposed Con3 4350.00 6216.10 6225.92 6226.43 0.001215 5.88 808.19 131.99 0.37

Upper Reach 0.160 10-year existing 850.00 6215.85 6220.78 6220.96 0.001193 3.43 249.82 74.38 0.32

Upper Reach 0.160 10-year Proposed Con3 850.00 6215.85 6220.71 6218.59 6220.91 0.000694 3.70 244.13 73.85 0.32

Upper Reach 0.160 FEMA 50-year existing 2650.00 6215.85 6224.03 6224.45 0.001222 5.32 542.81 104.86 0.36

Upper Reach 0.160 FEMA 50-year Proposed Con3 2650.00 6215.85 6224.00 6220.94 6224.39 0.000682 5.43 607.31 150.28 0.35

Upper Reach 0.160 Flood of Record existing 2690.00 6215.85 6224.08 6224.50 0.001227 5.36 547.83 105.19 0.36

Upper Reach 0.160 Flood of Record Proposed Con3 2690.00 6215.85 6224.05 6220.98 6224.44 0.000680 5.45 614.94 150.39 0.35

Upper Reach 0.160 FEMA 100-year existing 3350.00 6215.85 6224.81 6225.32 0.001313 5.93 626.33 110.33 0.38

Upper Reach 0.160 FEMA 100-year Proposed Con3 3350.00 6215.85 6224.81 6221.64 6225.23 0.000662 5.74 730.58 152.08 0.35

Upper Reach 0.160 BOR existing 3530.00 6215.85 6224.99 6225.53 0.001334 6.07 646.87 111.66 0.38

Upper Reach 0.160 BOR Proposed Con3 3530.00 6215.85 6225.01 6221.85 6225.43 0.000659 5.82 760.03 152.51 0.35

Upper Reach 0.160 FEMA 500-year existing 4350.00 6215.85 6225.78 6226.42 0.001418 6.67 736.93 118.28 0.40

Upper Reach 0.160 FEMA 500-year Proposed Con3 4350.00 6215.85 6225.84 6222.49 6226.29 0.000646 6.13 887.24 154.34 0.36

Upper Reach 0.138 10-year existing 850.00 6215.42 6220.65 6220.81 0.001184 3.22 263.80 79.69 0.31

Upper Reach 0.138 10-year Proposed Con3 850.00 6215.42 6220.63 6220.79 0.000830 3.25 261.85 79.42 0.32

Upper Reach 0.138 FEMA 50-year existing 2650.00 6215.42 6223.98 6224.29 0.001009 4.55 631.20 137.37 0.32

Upper Reach 0.138 FEMA 50-year Proposed Con3 2650.00 6215.42 6223.96 6224.26 0.000656 4.56 639.76 147.45 0.31

Upper Reach 0.138 Flood of Record existing 2690.00 6215.42 6224.03 6224.34 0.001010 4.57 637.99 137.88 0.32

Upper Reach 0.138 Flood of Record Proposed Con3 2690.00 6215.42 6224.01 6224.32 0.000656 4.58 647.13 148.17 0.31

Upper Reach 0.138 FEMA 100-year existing 3350.00 6215.42 6224.78 6225.14 0.001030 4.98 744.10 146.04 0.33

Upper Reach 0.138 FEMA 100-year Proposed Con3 3350.00 6215.42 6224.76 6225.11 0.000663 4.95 761.24 155.45 0.32

Upper Reach 0.138 BOR existing 3530.00 6215.42 6224.97 6225.34 0.001035 5.08 772.15 148.52 0.33

Upper Reach 0.138 BOR Proposed Con3 3530.00 6215.42 6224.96 6225.31 0.000664 5.04 791.28 157.68 0.32

Upper Reach 0.138 FEMA 500-year existing 4350.00 6215.42 6225.78 6226.21 0.001054 5.50 898.53 163.96 0.34

Upper Reach 0.138 FEMA 500-year Proposed Con3 4350.00 6215.42 6225.77 6226.18 0.000665 5.40 925.21 168.74 0.33

Upper Reach 0.114 10-year existing 850.00 6215.54 6220.52 6218.16 6220.68 0.001067 3.19 266.79 93.43 0.30

Upper Reach 0.114 10-year Proposed Con3 850.00 6215.54 6220.52 6218.16 6220.68 0.001067 3.19 266.79 93.43 0.30

Upper Reach 0.114 FEMA 50-year existing 2650.00 6215.54 6223.90 6220.34 6224.16 0.000823 4.26 707.13 144.40 0.29

Upper Reach 0.114 FEMA 50-year Proposed Con3 2650.00 6215.54 6223.90 6220.34 6224.16 0.000823 4.26 707.13 144.40 0.29

Upper Reach 0.114 Flood of Record existing 2690.00 6215.54 6223.95 6220.38 6224.21 0.000825 4.29 714.26 144.91 0.29

Upper Reach 0.114 Flood of Record Proposed Con3 2690.00 6215.54 6223.95 6220.38 6224.21 0.000825 4.29 714.26 144.91 0.29

Upper Reach 0.114 FEMA 100-year existing 3350.00 6215.54 6224.70 6221.22 6225.00 0.000859 4.70 826.87 156.88 0.30

Upper Reach 0.114 FEMA 100-year Proposed Con3 3350.00 6215.54 6224.70 6221.22 6225.00 0.000859 4.70 826.87 156.88 0.30

Upper Reach 0.114 BOR existing 3530.00 6215.54 6224.89 6221.35 6225.21 0.000867 4.80 857.06 160.25 0.31

Upper Reach 0.114 BOR Proposed Con3 3530.00 6215.54 6224.89 6221.35 6225.21 0.000867 4.80 857.06 160.25 0.31

Upper Reach 0.114 FEMA 500-year existing 4350.00 6215.54 6225.71 6221.86 6226.07 0.000894 5.21 994.04 176.81 0.32

Upper Reach 0.114 FEMA 500-year Proposed Con3 4350.00 6215.54 6225.71 6221.86 6226.07 0.000894 5.21 994.04 176.81 0.32

Upper Reach 0.085 10-year existing 850.00 6215.78 6220.37 6218.19 6220.51 0.000989 3.03 280.27 80.57 0.29

Upper Reach 0.085 10-year Proposed Con3 850.00 6215.78 6220.37 6218.19 6220.51 0.000989 3.03 280.27 80.57 0.29

Upper Reach 0.085 FEMA 50-year existing 2650.00 6215.78 6223.68 6220.09 6224.01 0.000984 4.65 621.12 173.85 0.32

Upper Reach 0.085 FEMA 50-year Proposed Con3 2650.00 6215.78 6223.68 6220.08 6224.01 0.000984 4.65 621.12 173.85 0.32

Upper Reach 0.085 Flood of Record existing 2690.00 6215.78 6223.73 6220.12 6224.06 0.000985 4.68 629.63 174.89 0.32

Upper Reach 0.085 Flood of Record Proposed Con3 2690.00 6215.78 6223.73 6220.12 6224.06 0.000985 4.68 629.63 174.89 0.32

Upper Reach 0.085 FEMA 100-year existing 3350.00 6215.78 6224.48 6220.67 6224.85 0.000997 5.05 768.72 195.09 0.33

Upper Reach 0.085 FEMA 100-year Proposed Con3 3350.00 6215.78 6224.48 6220.67 6224.85 0.000997 5.05 768.72 195.09 0.33

Upper Reach 0.085 BOR existing 3530.00 6215.78 6224.68 6220.81 6225.06 0.000993 5.13 807.08 198.39 0.33

Upper Reach 0.085 BOR Proposed Con3 3530.00 6215.78 6224.68 6220.81 6225.06 0.000993 5.13 807.08 198.39 0.33

Upper Reach 0.085 FEMA 500-year existing 4350.00 6215.78 6225.52 6221.40 6225.92 0.000962 5.41 978.49 209.16 0.33

Upper Reach 0.085 FEMA 500-year Proposed Con3 4350.00 6215.78 6225.52 6221.40 6225.92 0.000962 5.41 978.49 209.16 0.33

Upper Reach 0.084 Southwest Pacifi Bridge

Upper Reach 0.083 10-year existing 850.00 6215.66 6220.35 6218.01 6220.50 0.000945 3.04 279.36 76.78 0.28

Upper Reach 0.083 10-year Proposed Con3 850.00 6215.66 6220.35 6218.01 6220.50 0.000945 3.04 279.36 76.78 0.28

Upper Reach 0.083 FEMA 50-year existing 2650.00 6215.66 6223.68 6220.01 6223.98 0.000944 4.50 673.61 187.32 0.31

Upper Reach 0.083 FEMA 50-year Proposed Con3 2650.00 6215.66 6223.68 6220.01 6223.98 0.000944 4.50 673.61 187.32 0.31

Upper Reach 0.083 Flood of Record existing 2690.00 6215.66 6223.73 6220.05 6224.03 0.000944 4.52 682.80 189.14 0.31

Upper Reach 0.083 Flood of Record Proposed Con3 2690.00 6215.66 6223.73 6220.04 6224.03 0.000944 4.52 682.80 189.14 0.31

Upper Reach 0.083 FEMA 100-year existing 3350.00 6215.66 6224.46 6220.61 6224.79 0.000943 4.85 831.32 210.87 0.31

Upper Reach 0.083 FEMA 100-year Proposed Con3 3350.00 6215.66 6224.46 6220.61 6224.79 0.000943 4.85 831.32 210.87 0.31

Upper Reach 0.083 BOR existing 3530.00 6215.66 6224.64 6220.76 6224.98 0.000943 4.92 868.83 212.43 0.32

Upper Reach 0.083 BOR Proposed Con3 3530.00 6215.66 6224.64 6220.76 6224.98 0.000943 4.92 868.83 212.43 0.32

Upper Reach 0.083 FEMA 500-year existing 4350.00 6215.66 6225.38 6221.44 6225.75 0.000944 5.24 1028.00 218.08 0.32

Upper Reach 0.083 FEMA 500-year Proposed Con3 4350.00 6215.66 6225.38 6221.44 6225.75 0.000944 5.24 1028.00 218.08 0.32

Appendix B Scour Calculations and Results

CFL SR‐89 Truckee River Bridge 100‐Year Incipient Motion and Critical Velocity for Sediment Transport Regime

Left Channel Right

Critical velocity coefficient K = 11.17 11.17 11.17

Return Period of Discharge Tr = 100 100 100 years

Average depth of upstream flow upstream of bridge in approach section y = 1.96 7.01 2.02 ft

Median particle diameter/size of bed material D50 = 0.25 0.25 0.25 mm

Median particle diameter/size of bed material D50 = 0.00082 0.00082 0.00082 ft

Critical velocity vc = 1.17 1.45 1.18 ft/s

Actual stream velocity (upstream of bridge) v = 1.96 5.27 2.00 ft/s

Sediment regime LIVE‐BED LIVE‐BED LIVE‐BED

DyKv uc

Live‐Bed General Contraction Scour, Non‐Cohesive Materials, non‐pressurized bridge

100‐year 100‐year 100‐year

Contraction Case

Channel Section Left Overbank Main Channel Right Overbank

Gravitational constant g = 32.2 32.2 32.2 ft/s

Existing flow depth (hydraulic depth) in contracted channel before/without scour y0 = 3.07 7.70 2.36 ft

Average upstream flow depth (hydraulic depth) in uncontracted approach section of main channel y1 = 1.96 7.01 2.02 ft

Flow in main upstream channel/approach section that is under live‐bed conditions Q1 = 71 3,203 76 cfs

Bottom width of main upstream uncontracted channel/approach section W1 = 18.6 86.7 18.7 ft

Flow in contracted main channel/beneath bridge Q2 = 338 2,785 227 cfs

Bottom width of contracted channel beneath bridge W2 = 39.57 65.89 39.54 ft

Slope of upstream energy grade line (in uncontracted approach section) S1 = 0.00116 0.00116 0.00116 ft/ft

Median particle diameter/size of bed material D50 = 0.250 0.250 0.250 mm

Shear velocity v* = 0.27 0.51 0.28 ft/s

Fall velocity of D50 bed material w= 0.035 0.035 0.035 m/s

Fall velocity of D50 bed material w= 0.11 0.11 0.11 ft/s

Shear velocity divided by fall velocity of D50 particle v*/w= 2.36 4.46 2.40

Exponential coefficient from Laursen's equation k1 = 0.69 0.69 0.69

Average depth in contracted channel section including contraction scour effects y2 = 4.42 7.51 3.10 ft

General contraction scour depth ys = 1.35 ‐0.19 0.74 ft

7/6 y W W

Q Qyy k s

Discharge Return Period for Abutment Scour Estimation and Design Tr = 100 100 years

Abutment Location (left or right) LEFT (EAST) RIGHT (WEST)

Projected length of embankment impinging flow on this abutment/side L = 9.70 7.10 ft

Width of upstream floodplain/overbank only on this abutment/side (not including main channel) Bf = 18.56 18.69 ft

Ratio L/Bf = 52.3 38.0 %

Scour Condition (A or B) B B Unit discharge at approach section upstream of bridge q1 = 3.84 4.05 cfs/ft

Unit discharge at abutment toe in the constricted bridge opening q2c = 14.24 10.95 cfs/ft q2c/q1 = 3.71 2.70

Abutment type wingwall wingwall

Amplification factor based on indicated scour condition (A or B) = 1.28 1.59

Flow depth at bridge abutment, prior to scour yo = 3.07 2.36 ft

Flow depth in upstream approach section y1 = 1.96 2.02 ft

Flow depth at bridge abutment including live‐bed contraction scour yc = 6.03 4.74 ft

Maximum flow depth resulting from abutment scour ymax = 7.71 7.53 ft

Calculated maximum abutment AND contraction scour depth (scour hole) ys = 4.64 5.17 ft

HEC‐18 NCHRP 24‐20 Bridge Abutment Scour Method for LIVE‐BED CONDITIONS and NON‐COHESIVE Soils o c

As y q q yy

7/6

500‐Year Incipient Motion and Critical Velocity for Sediment Transport Regime

Left Channel Right

Critical velocity coefficient K = 11.17 11.17 11.17

Return Period of Discharge Tr = 500 500 500 years

Average depth of upstream flow upstream of bridge in approach section y = 2.41 8.00 2.66 ft

Median particle diameter/size of bed material D50 = 0.25 0.25 0.25 mm

Median particle diameter/size of bed material D50 = 0.00082 0.00082 0.00082 ft

Critical velocity vc = 1.21 1.48 1.23 ft/s

Actual stream velocity (upstream of bridge) v = 2.30 5.88 2.45 ft/s

Sediment regime LIVE‐BED LIVE‐BED LIVE‐BED

Live‐Bed General Contraction Scour, Non‐Cohesive Materials, non‐pressurized bridge

500‐year 500‐year 500‐year

Contraction Case

Channel Section Left Overbank Main Channel Right Overbank

Gravitational constant g = 32.2 32.2 32.2 ft/s

Existing flow depth (hydraulic depth) in contracted channel before/without scour y0 = 4.08 8.70 3.37 ft

Average upstream flow depth (hydraulic depth) in uncontracted approach section of main channel y1 = 2.41 8.00 2.66 ft

Flow in main upstream channel/approach section that is under live‐bed conditions Q1 = 131 4,078 141 cfs

Bottom width of main upstream uncontracted channel/approach section W1 = 23.6 86.7 21.7 ft

Flow in contracted main channel/beneath bridge Q2 = 526 3,429 395 cfs

Bottom width of contracted channel beneath bridge W2 = 39.57 65.89 39.54 ft

Slope of upstream energy grade line (in uncontracted approach section) S1 = 0.00122 0.00122 0.00122 ft/ft

Median particle diameter/size of bed material D50 = 0.250 0.250 0.250 mm

Shear velocity v* = 0.31 0.56 0.32 ft/s

Fall velocity of D50 bed material w= 0.035 0.035 0.035 m/s

Fall velocity of D50 bed material w= 0.11 0.11 0.11 ft/s

Shear velocity divided by fall velocity of D50 particle v*/w= 2.67 4.87 2.81

Exponential coefficient from Laursen's equation k1 = 0.69 0.69 0.69

Average depth in contracted channel section including contraction scour effects y2 = 5.56 8.33 4.24 ft

General contraction scour depth ys = 1.48 ‐0.37 0.87 ft

7/6 y W W

Q Qyy

Discharge Return Period for Abutment Scour Estimation and Design Tr = 500 500 years

Abutment Location (left or right) LEFT (EAST) RIGHT (WEST)

Projected length of embankment impinging flow on this abutment/side L = 14.63 13.89 ft

Width of upstream floodplain/overbank only on this abutment/side (not including main channel) Bf = 23.63 21.69 ft

Ratio L/Bf = 61.9 64.0 %

Scour Condition (A or B) B B Unit discharge at approach section upstream of bridge q1 = 5.54 6.52 cfs/ft

Unit discharge at abutment toe in the constricted bridge opening q2c = 20.45 16.89 cfs/ft q2c/q1 = 3.69 2.59

Abutment type wingwall wingwall

Amplification factor based on indicated scour condition (A or B) = 1.29 1.65

Flow depth at bridge abutment, prior to scour yo = 4.08 3.37 ft

Flow depth in upstream approach section y1 = 2.41 2.66 ft

Flow depth at bridge abutment including live‐bed contraction scour yc = 7.38 6.01 ft

Maximum flow depth resulting from abutment scour ymax = 9.52 9.92 ft

Calculated maximum abutment AND contraction scour depth (scour hole) ys = 5.44 6.55 ft

HEC‐18 NCHRP 24‐20 Bridge Abutment Scour Method for LIVE‐BED CONDITIONS and NON‐COHESIVE Soils o c

As y q

CFL Proposed Fanny Bridge

Incipient Motion and Critical Velocity for Sediment Transport Regime

Left Channel Right

Critical velocity coefficient K = 11.17 11.17 11.17

Return Period of Discharge Tr = 100 100 100 years

Average depth of upstream flow upstream of bridge in approach section y = 1.28 8.88 2.18 ft

Median particle diameter/size of bed material D50 = 0.25 0.25 0.25 mm

Median particle diameter/size of bed material D50 = 0.00082 0.00082 0.00082 ft

Critical velocity vc = 1.09 1.50 1.19 ft/s

Actual stream velocity (upstream of bridge) v = 0.63 2.93 0.99 ft/s

Sediment regime CLEAR‐WATER LIVE‐BED CLEAR‐WATER

Live‐Bed General Contraction Scour, Non‐Cohesive Materials, non‐pressurized bridge

100‐YEAR

Contraction Case

Channel Section Main Channel

Gravitational constant g = 32.2 ft/s

Existing flow depth (hydraulic depth) in contracted channel before/without scour y0 = 8.91 ft

Average upstream flow depth (hydraulic depth) in uncontracted approach section of main channel y1 = 8.88 ft/s

Flow in main upstream channel/approach section that is under live‐bed conditions Q1 = 3,317 cfs

Bottom width of main upstream uncontracted channel/approach section W1 = 127.4 ft

Flow in contracted main channel/beneath bridge Q2 = 3,350 cfs

Bottom width of contracted channel beneath bridge W2 = 118 ft

Slope of upstream energy grade line (in uncontracted approach section) S1 = 0.000269 ft/ft

Median particle diameter/size of bed material D50 = 0.250 mm

Shear velocity v* = 0.28 ft/s

Fall velocity of D50 bed material w= 0.035 m/s

Fall velocity of D50 bed material w= 0.11 ft/s

Shear velocity divided by fall velocity of D50 particle v*/w= 2.42

Exponential coefficient from Larson's equation k1 = 0.64

Average depth in contracted channel section including contraction scour effects y2 = 9.41 ft

General contraction scour depth ys = 0.50 ft

7/6 y W W

Q Qyy

CFL Proposed Fanny Bridge Scour

HEC‐18 NCHRP Bridge Abutment Scour Method for LIVE‐BED

Discharge Return Period for Abutment Scour Estimation and Design Tr = 100 100 years

Abutment Location (left or right) LEFT (SE) RIGHT (NW)

Projected length of embankment impinging flow on this abutment/side L = 7.40 20.75 ft

Width of upstream floodplain/overbank only on this abutment/side (not including main channel) Bf = 3.55 14.06 ft

Ratio L/Bf = 208.5 147.6 %

Scour Condition (A or B) A A Unit discharge at approach section upstream of bridge q1 = 26.04 26.04 cfs/ft

Unit discharge at abutment toe in the constricted bridge opening q2c = 27.02 27.02 cfs/ft q2c/q1 = 1.04 1.04

Abutment type vertical wall vertical wall

Amplification factor based on indicated scour condition (A or B) = 1.42 1.42

Flow depth at bridge abutment, prior to scour yo = 8.91 8.91 ft

Flow depth in upstream approach section y1 = 8.88 8.88 ft

Flow depth at bridge abutment including live‐bed contraction scour yc = 9.17 9.17 ft

Maximum flow depth resulting from abutment scour ymax = 13.02 13.02 ft

Calculated maximum abutment AND contraction scour depth (scour hole) ys = 4.11 4.11 ft o c

As y q

Incipient Motion and Critical Velocity for Sediment Transport Regime

Left Channel Right

Critical velocity coefficient K = 11.17 11.17 11.17

Return Period of Discharge Tr = 500 500 500 years

Average depth of upstream flow upstream of bridge in approach section y = 2.08 10.16 3.24 ft

Median particle diameter/size of bed material D50 = 0.25 0.25 0.25 mm

Median particle diameter/size of bed material D50 = 0.00082 0.00082 0.00082 ft

Critical velocity vc = 1.18 1.54 1.27 ft/s

Actual stream velocity (upstream of bridge) v = 0.87 3.31 1.30 ft/s

Sediment regime CLEAR‐WATER LIVE‐BED LIVE‐BED

Live‐Bed General Contraction Scour, Non‐Cohesive Materials, non‐pressurized bridge

500‐year

Contraction Case

Channel Section Main Channel

Gravitational constant g = 32.2 ft/s

Existing flow depth (hydraulic depth) in contracted channel before/without scour y0 = 9.19 ft

Average upstream flow depth (hydraulic depth) in uncontracted approach section of main channel y1 = 10.09 ft/s

Flow in main upstream channel/approach section that is under live‐bed conditions Q1 = 4,279 cfs

Bottom width of main upstream uncontracted channel/approach section W1 = 127.4 ft

Flow in contracted main channel/beneath bridge Q2 = 4,350 cfs

Bottom width of contracted channel beneath bridge W2 = 118 ft

Slope of upstream energy grade line (in uncontracted approach section) S1 = 0.000293 ft/ft

Median particle diameter/size of bed material D50 = 0.250 mm

Shear velocity v* = 0.31 ft/s

Fall velocity of D50 bed material w= 0.035 m/s

Fall velocity of D50 bed material w= 0.11 ft/s

Shear velocity divided by fall velocity of D50 particle v*/w= 2.69

Exponential coefficient from Larson's equation k1 = 0.64

Average depth in contracted channel section including contraction scour effects y2 = 10.75 ft

General contraction scour depth ys = 1.56 ft

7/6 y W W

Q Qyy

CFL Proposed Fanny Pressure Contraction Scour

Pressure Flow (Vertical Contraction) Scour

Return Period of Discharge Tr = 500 years

Vertical distance between low‐chord and pre‐scour stream bed at upstream bridge face hb = 9.19 ft

Vertical height of bridge superstructure, including girders, deck, and parapet/railings T = ‐ ft

Average equilibrium depth in contracted section after contraction scour y2 = 10.75 ft

Actual upstream channel flow depth (in main channel only???) hu = 10.09 ft

Distance from water surface to lower face of bridge girders ht = 0.9 ft

Weir flow height hw = 0.0 ft

Separation zone thickness t = 2.78 ft

Pressure flow contraction scour depth ys = 4.34 ft

CFL Proposed Fanny Bridge Scour

HEC‐18 NCHRP Bridge Abutment Scour Method for LIVE‐BED

Discharge Return Period for Abutment Scour Estimation and Design Tr = 500 500 years

Abutment Location (left or right) LEFT (SE) RIGHT (NW)

Projected length of embankment impinging flow on this abutment/side L = 7.79 21.42 ft

Width of upstream floodplain/overbank only on this abutment/side (not including main channel) Bf = 4.66 15.19 ft

Ratio L/Bf = 167.2 141.0 %

Scour Condition (A or B) A A Unit discharge at approach section upstream of bridge q1 = 33.59 33.59 cfs/ft

Unit discharge at abutment toe in the constricted bridge opening q2c = 33.97 33.97 cfs/ft q2c/q1 = 1.01 1.01

Abutment type vertical wall vertical wall

Amplification factor based on indicated scour condition (A or B) = 1.26 1.26

Flow depth at bridge abutment, prior to scour yo = 9.19 9.19 ft

Flow depth in upstream approach section y1 = 10.09 10.09 ft

Flow depth at bridge abutment including live‐bed contraction scour yc = 10.19 10.19 ft

Maximum flow depth resulting from abutment scour ymax = 12.84 12.84 ft

Calculated maximum abutment AND contraction scour depth (scour hole) ys = 3.65 3.65 ft o c

As y q

Appendix C Riprap Design

HEC‐23 DG14 (Isbash equation)

Froude number Fr = 0.36

Froude # less than or equal to 0.80 acceleration due to gravity g = 32.2 ft/s2 specific gravity Ss 2.65 abutment coefficient K = 1.02 characteristic average velocity in contracted section v = 6.1 ft/s

D50 = 0.7 ft

D50 = 8.7 in.

g

V

S

K D s

50 1 bhartma1 Text Box Proposed SR-89/Truckee River Bridge

HEC‐23 DG14 (Isbash equation)

Froude number Fr = 0.23

Froude # less than or equal to 0.80 acceleration due to gravity g = 32.2 ft/s2 specific gravity Ss 2.65 abutment coefficient K = 1.02 characteristic average velocity in contracted section v = 4.3 ft/s

D50 = 0.4 ft

D50 = 4.2 in.

g

V

S

K D s

50 1 bhartma1 Text Box Proposed Fanny Bridge