HH Recommendations Report - John Dunn.pdf

John Dunn Bridge Repair #5243 and Bridge #3807 Replacement NM FLAP TAO B007(1)

Hydrology and Hydraulics Recommendations Report

Federal Highway Administration Central Federal Lands Highway Division

Prepared by HDR Engineering, Inc.

June 10th, 2020

John Dunn Bridge Repair #5243 and 1 Central Federal Lands Highway Bridge #3807 Replacement Hydrology and Hydraulics

Recommendations Report

1 Introduction HDR is preparing a Project Delivery Plan for the Federal Highway Administration, Central Federal Lands Highway Division (CFLHD) for proposed repair of the John Dunn Bridge (#5243) over the Rio Grande and the replacement of Bridge #3807 over the Arroyo Hondo (Rio Hondo) within the Bureau of Land Management (BLM) property in Taos County, New Mexico (Figure 1).

This Scope of Work (SOW) is to perform engineering, hydraulic, geotechnical, pavement design, and project management services towards delivery of a final set of plans, specifications and estimate for the Federal Highway Administration, Central Federal Lands Highway Division (CFLHD) for proposed improvements to John Dunn Bridge Repair #5243 and Bridge #3807 replacement.

1.1 Project Description

This project includes maintenance repairs to the John Dunn Bridge #5243, including replacement of safety elements, deck repair, and paint coating repair or total repainting. The John Dunn Bridge #5243 does not require a hydraulic analysis. The project also includes the replacement of Bridge #3807 located over the Arroyo Hondo 2.4 miles west of junction NM-522 along TCR B007 and approximately 700 feet from the John Dunn Bridge #5243. The hydraulic analysis of Bridge #3807 is the focus of this report.

Bridge #3807 has been identified as structurally deficient and scour critical by the New Mexico Department of Transportation (NMDOT) and is recommended to be replaced (See the Bridge Type Selection memorandum for more information). The existing roadway width at Bridge #3807 is approximately 16 feet wide at the bridge and 19 feet wide on the roadway approaches to the bridge. The bridge is constructed along a tangent between two reverse curves on Road B007. The replacement bridge is proposed to be a single lane 12-foot wide with 7 foot - 1.5-inch shoulders and metal railings for a total out to out width of 29 feet 3 inches. The proposed roadway approaches to the replacement bridge include continuation of the existing 19 feet wide roadway to the bridge with improvements to the shoulders for ditching, where possible, along with approach railing added to the shoulders on the bridge approaches. The surface of the roadway realignment will be aggregate surface course.

This report serves as the basis for hydrologic and hydraulic analysis for the proposed bridge #3807 and provides bridge scour calculations.

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Figure 1. Project Location

1.2 Project Vicinity

The proposed roadway bridge #3807 will be located at the existing bridge location, crossing the Arroyo Hondo approximately 700 feet from the confluence with the Rio Grande on BLM land (Figure 2).

Federal Emergency Management Agency (FEMA) has designated the flood hazard area within the project site as a FEMA Zone A, as determined by the Flood Insurance Rate Maps (FIRM) #35055C0625E, effective date October 6, 2010, as shown in Appendix A. Floodplains designated Zone A are subject to inundation by the 1-percent-annual-chance flood (100-year) event. Because detailed hydraulic analyses have not been performed, no Base Flood Elevations (BFEs) or flood depths are shown or available. A Zone A floodplain is designated both on the Arroyo Hondo and the Rio Grande.

Given the proximity of the proposed roadway bridge #3807 to the Rio Grande, coincident flow in the Rio Grande must be considered both as a downstream tailwater condition to local Arroyo Hondo flows and to determine if the Rio Grande itself may have the potential to backing up to the #3807 bridge location.

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Figure 2. Project Vicinity

1.3 Design Criteria

The NMDOT Drainage Design Manual (NMDOT DDM) (Smith Engineering Company et al., 2018) supplemented with Chapter 7 of the Federal Lands Highway Project Development and Design Manual (FLH PDDM) (Federal Highway Administration, 2012) are used as the basis to evaluate the proposed bridge #3807.

According to the NMDOT DDM, the design criteria for bridged waterways specify that bridges with an Average Daily Traffic (ADT) less than 400 vehicles need be designed to convey the 25-year flood with a 50-year check flood (2% AEP). The associated stability design and scour analysis is then for the 50-year flood (2% AEP) with a 100-year check flood (1% AEP). All bridges need to be designed with an additional 2 feet of freeboard. The ADT for bridge #3807 is unknown, however, it is assumed that it is less than 400 ADT.

According to the FLH PDDM, the design criteria for bridged waterways specify that bridges need to convey the 50-year flood (2% annual exceedance probability [AEP]) with appropriate freeboard (p.7-68). The required minimum freeboard height is 2 feet given that the potential for woody debris is not considered significant nor is there a potential for ice flows (p. 7-69). The check flood for water surface increases is then the greater between the 100-year flood (1% AEP) and the overtopping flood. For stability design and scour analysis, the 100-year flood (1% AEP) is specified for design and the 200-year flood (0.5% AEP) is the check flood (p. 7-68).

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Given the location of the bridge in a rural area with an assumed ADT less than 400, the NMDOT DDM will serve as the default criteria for the replacement bridge #3807 will be designed based on the following:

Conveyance of 50-year flows (2% AEP) with 2 feet of freeboard below the low chord.

This criterion is above the 25-year flow specified in the NMDOT DDM and is thus considered conservative and reflects the FLH PDDM criteria.

A check flood that considers the 100-year flows (1% AEP). This criterion is above the 50-year flow specified in the NMDOT DDM and is thus considered conservative and reflects the FLH PDDM criteria.

Abutment benches that extend above the Energy Grade Line for 25-year flows and rip rap that extends above the 50-year EGL, reflective of the NMDOT DDM.

Stability and scour analysis based on 50-year flow (1% AEP) and a check flood based on 100-year flows, reflective of the NMDOT DDM.

The Arroyo Hondo discharges to the Rio Grande about 700 feet downstream of the bridge. Neither the FLH PDDM nor the NMDOT DDM provide guidance for coincident flows in a downstream water body. The Federal Highway Administration (FHWA) also does not provide guidance specifically for bridge design but they do, however, provide guidance for urban drainage design in Table 7-3 contained in Hydraulic Engineering Circular No. 22 (FHWA, 2009).

Based on this guidance, a 10-year (10% AEP) downstream coincident flow rate is assumed in the Rio Grande. A check flood will also be evaluated assuming a 100-year (1% AEP) water surface elevation (WSE) in the Rio Grande.

2 Hydrology Flood Insurance Study (FIS) Number #35055C0625E was developed by FEMA for Taos County, New Mexico, and incorporated areas. The project area, however, is mapped as a Zone A in the FIS therefore flow rates to the project location are not available. The NMDOT DDM was therefore used as guidance for developing flows for the project location.

2.1 Arroyo Hondo

The drainage area for the Arroyo Hondo to bridge #3807 is approximately 71.5 square miles (Figure 3). There is a United States Geological Survey (USGS) stream gage (USGS Station Number: 08268500; Station Name: Arroyo Hondo at Arroyo Hondo, NM) located 1.3 miles upstream of the bridge location that was active from 1912 to 1985. Given that the drainage area is greater than 10 square miles and that there is a gage upstream, a gage analysis was performed per the NMDOT DDM (p. 4-6).

Hydrology for the Arroyo Hondo was estimated by using the published flood characteristics contained in the USGS Scientific Investigations Report (SIR) 2008–5119, Analysis of the Magnitude and Frequency of Peak Discharge and Maximum Observed Peak Discharge in New Mexico and Surrounding Areas (Waltemeyer, 2008). Flow rates for the various recurrence intervals were extracted from SIR 2008-5119 (Appendix 1, p. 51) and then area adjusted to bridge #3807 (Equation 3, p. 11). A logarithmic function was then applied to determine the 200-

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Table 1. Peak Discharges Used for Bridge #3807

Flood Return

Annual Flood Exceedance Probability

Peak Discharge at USGS Gage

08268500* (cfs)

Calculated Peak Discharge at Bridge #3807

(cfs) 500-yr 0.2% 2040 2,134 200-yr 0.5% - 1,669** 100-yr 1% 1220 1,279 50-yr 2% 945 992 25-yr 4% 717 753 10-yr 10% 470 495 5-yr 20% 319 336 2-yr 50% 154 163

*Extracted from SIR 2008-5119, p. 51 (Waltemeyer, 2008) **Based on logarithmic interpolation from surrounding calculations

Figure 3. Drainage Basin for Arroyo Hondo at Folsom South Canal

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2.2 Rio Grande

The drainage area for the Rio Grande to the John Dunn Bridge (#5243) is approximately 8,760 square miles. There is a United States Geological Survey (USGS) stream gage (USGS Station Number: 08268700; Station Name: Rio Grande near Arroyo Hondo, NM) located at the John Dunn Bridge that was active from 1963 to 2002. Given that the drainage area is greater than 10 square miles and that there is a gage at the project site, a gage analysis was performed per the NMDOT DDM (p. 4-6).

The USGS did not develop stream flow statistics and did not publish flood characteristics for gage 08268700. Hydrology for the gage was therefore estimated by developing flood characteristic using the United States Army Corps of Engineers (USACE) Hydrologic Engineering Center's (HEC) Statistical Software Package (HEC-SSP) (version 2.2) based on the flow data on record at the gage. HEC-SSP is used to develop flood flow frequency analysis based on Bulletin 17B (Interagency Advisory Committee on Water Data, 1982) and Bulletin 17C (England, et al., 2018). The output from the HEC-SSP analysis is presented in Appendix C with the results summarized in Table 2.

Table 2. Peak Discharges Used for the John Dunn Bridge (#5243)

Flood Return

Annual Flood Exceedance Probability

Peak Discharge Estimated at the

John Dunn Bridge (#5243)

(cfs) 500-yr 0.2% 16,657 200-yr 0.5% 13,737 100-yr 1% 11,689 50-yr 2% 9,774 25-yr 4% 7,436 10-yr 10% 5,803 5-yr 20% 4,270 2-yr 50% 2,328

*Developed using HEC-SSP with flow data from 1963 to 2002

3 Hydraulics A one-dimensional (1D) hydraulic model was developed using the USACE HEC River Analysis System (HEC-RAS), version 5.0.7. For this analysis, the following model scenarios were developed:

Existing Bridge 3807 Over the Arroyo Hondo Existing Rio Grande Proposed Bridge 3807 Over Arroyo Hondo

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3.1 Model Terrain

The model terrain is based a ground survey performed in September 2020 and supplemented with LiDAR collected in 2015 and published in 2019. Existing conditions survey for the Bridge and channel cross sections was performed by Woolpert, Inc. and included the following:

Survey of the existing Bridge #3807 Survey of the Arroyo Hondo 1,125 feet upstream and 720 feet downstream (to the Rio Grande) of Bridge #3807 with a total of 21 cross-sections surveyed.

Survey of the Rio Grande 530 feet upstream and 570 feet downstream of the John Dunn Bridge, with a total of 10 cross-sections surveyed.

Additional spot elevations in the vicinity of the two bridges, the Rio Grande, the Arroyo Hondo, and the existing roadways.

The survey data and the model are in the State Plane New Mexico Central Harn North American Datum 1983 (feet) horizontal datum and all elevations are referenced to NAVD 88 (feet) vertical datum. The 2015 LiDAR had to be projected from the Universal Transverse Mercator (UTM) North American Datum 1983 (meter) to the project State Plane datum.

3.2 Model Parameters

Model extents were based on the Woolpert survey, with the furthest upstream modeled cross-section corresponding to the furthest upstream surveyed cross-section for both the Arroyo Hondo and the Rio Grande.

Surface roughness, represented by the Manning’s roughness coefficient, were assigned to the channels and banks of each cross section in GIS. Values were estimated from “Open Channel Hydraulics” (Chow, 1959). This is the same reference used in the NMDOT DDM as well as the HEC-RAS Hydraulic Reference Manual (USACE, 2016). The Arroyo Hondo channel was assigned a roughness value of 0.05 for a rocky bottom river with no vegetation in the channel, steep vegetated banks, and cobbles with large boulder (Figure 4, Figure 5). The Rio Grande was assigned a roughness value of 0.04 for a sandy bottom river that is clean with some pools and shoals (Figure 6).

Given the varied roughness in the floodplains between the roads paralleling the channels, the willows transitioning into shrub in the floodplains, and the rock cliffs, numerous manning’s values were assigned.

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Figure 4. Photograph of the Arroyo Hondo Channel Looking Upstream (taken 9/8/20)

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Figure 5. Photograph Taken Across the Arroyo Hondo Channel Illustrating the Mixed Sub-Critical/Super- Critical Flow Regime (taken 9/8/20)

Figure 6. Photograph of the Rio Grande Channel Looking Downstream (Typical) (taken 6/11/19)

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The Arroyo Hondo is a fairly steep rock bottom channel with several instances of large boulders.

There are numerous instances of channel contractions and expansions. Given these channel conditions, there are several hydraulic jumps throughout the modeled area and required running a mixed flow regime. These also required several more cross-sections then what were originally surveyed. These cross-sections were developed based on the 2015 LiDAR. A total of 114 cross-sections were cut for the modeling with an average spacing of 16 channel feet. Photos taken from the existing bridge are presented in Figure 7 (upstream) and Figure 8 (downstream). The cut cross-section locations are shown in Figure 9.

The proposed condition model run replaces the existing bridge #3807 along the same alignment.

The proposed bridge will be precast, pre-stressed concrete slab structure and topping deck with no piers and 2 foot horizontal to 1 foot vertical abutments at either side. The low chord is based on the modeled 50-year WSE plus two feet of freeboard. The total width of the proposed bridge is 29 feet 3 inches and it will tie into the existing road.

Figure 7. Photo Looking Upstream from Bridge #3807- Illustration of the Rapids and Super Critical Flow Regime (taken 6/11/19)

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Figure 8. Photo Looking Downstream from Bridge #3807 (taken 6/11/19)

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Figure 9. HEC-RAS Cross Sections for Bridge #3807 over the Arroyo Hondo

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The Rio Grande is a fairly flat sandy bottom channel. A total of 16 cross-sections were cut for the modeling with an average spacing of 17 channel feet. The cut cross-section locations are shown in Figure 10Figure 9. The downstream boundary condition was set at a normal depth of 0.00027 foot per foot based on the energy grade slope of the existing channel.

Figure 10. HEC-RAS Cross Sections for the John Dunn Bridge (#5243) over the Rio Grande

The peak discharges presented in Table 1 and Table 2 were introduced at furthermost upstream cross sections of their respective models as single sets of steady state flows.

3.3 Model Results

The results of the 1D HEC-RAS model for the Rio Grande were used to set the downstream boundary condition of the Arroyo Hondo. Model results were extracted at the Arroyo Hondo confluence at cross-section 542 (Figure 10). These model results are presented in Table 3. As stated in section 1.3, the 10-year WSE of 6493.11 was used. A sensitivity analysis was also performed on the Arroyo Hondo using the Rio Grande 100-year WSE and it did not impact results at bridge #3807.

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Table 3. Model results for the Rio Grande at the Arroyo Hondo Confluence

Flood Return

Annual Flood Exceedance Probability

Water Surface Elevation in the Rio

Grande at Cross- Section 542

100-yr 1% 6499.62 50-yr 2% 6497.77 10-yr 10% 6493.11 5-yr 20% 6490.85 2-yr 50% 6487.24

The proposed bridge was sized to convey the 50-year flow (2% AEP) with 2 feet of freeboard, with freeboard defined as the vertical clearance between the design-flood water surface and the low chord of the bridge superstructure based on the criteria discussed in section 1.3. The reference datum for measuring the freeboard is the computed WSE at the cross-section upstream of the bridge. The 100-year flow is also contained under the bridge low chord. The 200-year and 500-year flows are above the bridge low chord but do not overtop the bridge. Table 4 summarizes the WSEs and resulting freeboard at the upstream face of the proposed bridge.

The 25-year (4% AEP) energy grade line is at elevation 6502.75 and the bridge abutment benches are above this elevation. The 50-year (2% AEP) energy grade line is at elevation 6503.65 and the rip rap depth is above this elevation. Table 5 tabularizes these energy grade line results.

Table 4. Modeled Water Surface Elevation at Immediately Upstream of the Proposed Bridge

Flood Return

Annual Flood Exceedance Probability

Water Surface Elevation (ft)

Flow Depth (ft) Channel Invert

Elevation: 6496.23 ft

Freeboard (ft) Bridge Low Chord Elevation: 6504.8 Bridge High Chord

Elevation: 6507 500-yr1 0.2% 6507.04 11.26 - 200-yr1 0.5% 6506.45 10.67 - 100-yr1 1% 6503.87 8.09 1.21 50-yr1 2% 6503.04 7.26 2.04 25-yr1 4% 6502.25 6.47 2.83 10-yr1 10% 6500.53 4.75 4.55 5-yr1 20% 6499.74 3.96 5.34 2-yr1 50% 6499.12 3.34 5.96

1 Model results taken at the cross-section immediately upstream of the bridge

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Table 5. Energy Grade Line Immediately Upstream of the Proposed Bridge

Flood Return

Annual Flood Exceedance Probability

Energy Grade Line Elevation (ft)

50-yr1 2% 6503.65 25-yr1 4% 6502.75

1 Model results taken at cross-section immediately upstream of the bridge

Based on the criteria discussed in section 1.3, the check flood for water surface increases is the greater between the 100-year flood (1% AEP) and the overtopping flood. The 500-year flood (0.2% AEP) is not projected to overtop the bridge, therefore the 100-year flood (1% AEP) was evaluated. Raising the bridge deck in the proposed design results in the model indicating no increases in 100-year base flood elevation within the project area other than a slight increase (less than 0.1 feet) within the first 45 feet downstream of the bridge. Otherwise, modeling indicates slight decreases in WSE around the vicinity of the bridge. Table 6 provides the 100-year (1% AEP) WSEs for the existing and proposed conditions models as well as the differences between the two.

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Table 6. 100-year (1% AEP) Water Surface Elevations

Cross Section Existing WSE

(ft) Proposed WSE

(ft) Difference 844 6504.72 6504.72 0.00 840 6504.26 6504.26 0.00 829 6503.4 6503.4 0.00 819 6504.38 6504.38 0.00 811 6503.57 6503.57 0.00 803 6503.69 6503.68 -0.01 795 6504.2 6504.19 -0.01 791 6504.21 6504.2 -0.01 785 6504.2 6504.19 -0.01 782 6504.23 6504.22 -0.01 775 6503.98 6503.97 -0.01 771 6503.96 6503.95 -0.01 760 6504 6503.87 -0.13

741.3571 JohnDunnBridge_E

711 6502.47 6502.2 -0.27 699 6501.63 6501.7 0.07 690 6501.76 6501.8 0.04 680 6501.73 6501.78 0.05 675 6501.82 6501.82 0.00 658 6500.57 6500.57 0.00 653 6501.03 6501.03 0.00 647 6500.84 6500.84 0.00 642 6500.32 6500.32 0.00 637 6499.62 6499.62 0.00

3.4 Scour

A scour analysis was performed for the Arroyo Hondo at the proposed bridge location. The scour analysis is intended to inform the structural and countermeasure design of the crossing. Results from the HEC-RAS 1D model were used.

Methodologies presented in the FHWA Hydraulic Engineering Circular No. 18 Evaluation of Scour at Bridges (HEC-18) were used for scour analysis based on direction in the NMDOT DDM. Based on the criteria discussed in section 1.3, stability and scour analysis are based on 50-year flows (2% AEP) with a check flood based on 100-year flows (1% AEP).

At the project site, the following scour components were evaluated:

Contraction Scour Abutment Scour

All scour calculations can be found in Appendix D.

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3.4.1 Contraction Scour

Contraction scour represents short-term channel degradation caused by the contraction of flow area through a restricted bridge opening. Contraction scour was calculated using the HEC-18 Contraction Scour approach as directed in the NMDOT DDM. Contraction scour was calculated for the 50- and 100-year flows. The calculation was performed using the live-bed condition since channel velocity was determined to be greater than the critical velocity for both flood events. Table 7 summarizes the contraction scour results.

Table 7. Contraction Scour Results

Flood Return Annual Flood Exceedance Probability

Live-Bed Contraction Scour (ft)

50-yr 2% 0.6 100-yr 1% 0.6

3.4.2 Abutment Scour

Abutment scour is used to determine bury depths for abutment foundations. Abutment scour was calculated using the NCHRP 24-20 approach as documented in HEC-18 and as specified in the NMDOT DDM. Abutment scour was calculated for the 50- and 100-year flows and include contraction scour in the calculations. The abutment scour results can be found in Table 8. With a

1.15 factor of safety, it is recommended that the abutment piles be at least 3.7 feet deep. The shallowest design micro pile is approximately 14 feet from the bottom of the channel.

Table 8. Abutment Scour Results

Flood Return Annual Flood Exceedance Probability

Abutment Scour depth (ft)

50-yr 2% 2.97 100-yr 1% 3.15

There are no visible nick point or head cuts downstream of the bridge that would have the potential for upstream migration. There are also no indications of channel instability. As a result, long term degradation is not anticipated. In addition, a factor of safety (1.15) was added to the abutment scour added to account for unknown conditions and even with that, the piles are much deeper than the calculated abutment scour depth.

A rip rap pad surrounding the abutments should be provided as protection from localized surface runoff. Rip rap was sized based on methods described in Bridge Scour and Stream Instability Countermeasures: Experience, Selection, and Design Guidance, Volume 2, Third Edition (HEC-23) and as specified in the NMDOT DDM (FHWA, 2009). Table 9 summarized the rip rap recommendations for bridge #3087. Assuming a 50-year design flow rate, 3.4 feet of rip rap is above the 50-year energy grade line.

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Table 9. Rip Rap Recommendations for Bridge #3807

Flood Return Annual Flood Exceedance Probability

Rip Rap Class

D50 (ft)

D100 (ft)

Rip Rap Thickness

(ft) 50-yr 2% 1/2 Ton 2.3 2.9 3.4

100-yr 1% 1/2 Ton 2.3 2.9 3.4

The riprap should be angular riprap, Class 7, with a D50 of 2.3 feet and a depth of 3.4 feet.

The slope of the riprap should not exceed 1.5 foot horizontal to 1 foot vertical (1.5:1). The generally preferred steepest slope for rip rap is 2.0 foot horizontal to 1 foot vertical, however, given the large D50 of 2.3 feet, 1.5:1 is allowed (USACE, 1994).

The upstream and downstream riprap extents is typically about 25 feet past the abutment wall.

However, given site constraints, the riprap can also be tied into the existing channel embankment by going out at a 2:1 from the abutment bench down the channel, on both the upstream and downstream site, and then wrapping the riprap around and into the embankment and tapered at a 2:1 to a 7.5 foot depth at the tie in.

4 Conclusion The purpose of this report is to provide a channel hydraulic analysis and design of the proposed bridge #3807 over Arroyo Hondo, which includes: selection of hydrologic peak discharges, hydraulic modeling of the proposed design, flood profile, floodplain analysis, and scour analysis.

Based on the hydraulic analysis, the proposed bridge opening passes the (2% AEP) with 2 feet of freeboard under the proposed low chord. Although the proposed abutments encroach the 100-year floodplain, there is only a small rise (less than 0.1 feet) that is located within 45 feet downstream of the bridge between the existing and proposed conditions. Other than this slight downstream rise, there are no other rises in the flood profile. To prevent erosion at the face of the abutments, rip rap is recommended at the upstream and downstream abutments.

The conclusions and recommendations in this report are based on the conditions of the project site and the associated watershed at the time of this study. Any modifications to the site, man-made or natural, could alter the analysis, findings, and recommendations contained herein and could invalidate the analysis, findings, and recommendations. Site conditions, completion of upstream or downstream projects, upstream or downstream land use changes, climate changes, vegetation changes, maintenance practice changes, or other factors may change over time.

Additional analysis or updates may be required in the future because of these changes.

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5 References Chow, V.T. 1959. Open Channel Hydraulics. McGraw-Hill Book Company, NY.

England, J.F., Cohn, T.A, Faber, B.A, Stedinger, J.R., Thomas, W.O., Veilleus, A.G. Mason, R.R.

2018. Guidelines for Determining Flood Flow Frequency, Bulletin 17C. Washington D.C. U.S.

Department of the Interior.

Federal Emergency Management Agency. Flood Insurance Study for Taos County, New Mexico and Incorporated Areas. Flood Insurance Study Number 35055C0625E. Effective Date October 6, 2010.

Federal Highway Administration. 2009. Bridge Scour and Stream Instability Countermeasures:

Experience, Selection, and Design Guidance (Volume 2). Third Edition. Publication No.

FHWA-NHI-09-112. Hydraulic Engineering Circular No. 23.

Federal Highway Administration. 2009. Urban Drainage Design Manual. Third Edition. Publication No. FHWA-NHI-10-009. Hydraulic Engineering Circular No. 22. Revised 2013.

Federal Highway Administration. 2012. Evaluating Scour at Bridges. Fifth Edition. Publication No.

FHWA-HIF-12-003. Hydraulic Engineering Circular No. 18.

Federal Highway Administration. December 2012. Federal Lands Highway Division Project Development and Design Manual, Chapter 7 Hydrology and Hydraulics.

Interagency Advisory Committee on Water Data. 1982. Guidelines for Determining Flood Flow Frequency, Bulletin 17B. Reston, VA. U.S. Geological Survey.

New Mexico DOT Drainage Design Manual, Section 607.3.2 (Smith Engineering Company et al.

July 2018. Drainage Design Manual New Mexico Department of Transportation).

United States Army Corps of Engineers (USACE). 1994. Hydraulic Design of Flood Control Channels. Engineer Manual No. 1110-2-1601. Section 3.3.

United States Army Corps of Engineers (USACE). 2016. HEC-RAS River Analysis System Hydraulic Reference Manual, Version 5.0.

Waltemeyer, S.D., 2008, Analysis of the magnitude and frequency of peak discharge and maximum observed peak discharge in New Mexico and surrounding areas: U.S. Geological Survey Scientific Investigations Report 2008–5119, 105 p.9, 11-12, 51

Appendix A

FEMA FIRM

Project Location

Appendix B Hydrologic Calculations for Arroyo Hondo

Project: Job No:

Subject: Computed: JAC Date: 11/13/2020 Task:

L:\jechrist\HutchinsonUtility\Comp Sheet.doc

Source:

Nearby gage: USGS 08268500 ARROYO HONDO AT ARROYO HONDO, NM Northern mountain flood region (5)—

From Page 11, Ungaged Stie on a Stream Having a Nearby Gaging Station

QT(u) = QT(g) (Au/Ag) x (Equation 3)

QT(u) = weighted flood frequency estimate at the ungaged site, in cubic feet per second;

QT(g) = flood frequency estimate at the gaging station, in cubic feet per second;

Au = drainage area at the ungaged site, in square miles;

Ag = drainage area at the gaging station, in square miles; and x =

Source of areas:

Streamstats https://streamstats.usgs.gov/ss/

Drainage area for project site:

Au = 71.506978 Drainage area at gage 08268500 Ag = 66.675054

Peak Discharge at 08268500 (cfs) x for Region 5

Calculated Peak discharge at project site (cfs)

Annual Flood Exceedance Probability

Page 51 Page 9 500 yr 2040 0.642 2134 500 0.2% 100 yr 1220 0.675 1279 100 1% 50 yr 945 0.691 992 50 2% 25 yr 717 0.709 753 25 4% 10 yr 470 0.736 495 10 10% 5 yr 319 0.761 336 5 20% 2 yr 154 0.805 163 2 50%

Interpolated flows 200 yr 1669 200 0.5%

Waltemeyer, S.D., 2008, Analysis of the magnitude and frequency of peak discharge and maximum observed peak discharge in New Mexico and surrounding areas: U.S. Geological

Survey Scientific Investigations Report 2008–5119, 105 p.

exponent of the drainage area of the applicable regional regression equation listed in table 2.

Computation CFLHD TO84 NM John Dunn 10241600 CFLHD TO86 NM SJU Cottonwood Task Local Hydrology Flow rate at the bridge y = 467.5ln(x) 808.46 R² = 0.9911

0.1%1.0%10.0%100.0% Annual Flood Exceedance Probability

Appendix C Hydrologic Calculations for Rio Grande

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File: Rio_Grande_at_Arroyo_Hondo.rpt, Page: 1

Bulletin 17C (Java) Frequency Analysis 13 Nov 2020 12:40 PM --- Input Data --- Analysis Name: Rio Grande at Arroyo Hondo Description: Annual Peak Flow Data Set Name: RIO GRANDE-ARROYO HONDO, NM-FLOW-ANNUAL PEAK DSS File Name: C:\Users\jechrist\Desktop\Projects\CFLHD NM FLAP\JohnDunnHydrology\RioGrande\RioGrandeAtRioHondo\RioGrand DSS Pathname: /RIO GRANDE/ARROYO HONDO, NM/FLOW-ANNUAL PEAK/01jan1900/IR-CENTURY/USGS/ Report File Name: C:\Users\jechrist\Desktop\Projects\CFLHD NM FLAP\JohnDunnHydrology\RioGrande\RioGrandeAtRioHondo\Bulletin XML File Name: C:\Users\jechrist\Desktop\Projects\CFLHD NM FLAP\JohnDunnHydrology\RioGrande\RioGrandeAtRioHondo\Bulletin17 Start Date:

End Date:

Skew Option: Use Station Skew Regional Skew: -Infinity Regional Skew MSE: -Infinity Plotting Position Type: Hirsch-Stedinger Upper Confidence Level: 0.05 Lower Confidence Level: 0.95 Display ordinate values using 1 digits in fraction part of value --- End of Input Data --- << EMA Representation of Data >>

RIO GRANDE-ARROYO HONDO, NM-FLOW-ANNUAL PEAK

| | Value | Threshold | | | Year Peak | Low High | Low High | Type | | 1963 655.0 | 655.0 655.0 | 1.0E-99 1.0E99 | Syst | | 1964 565.0 | 565.0 565.0 | 1.0E-99 1.0E99 | Syst | | 1965 4,400.0 | 4,400.0 4,400.0 | 1.0E-99 1.0E99 | Syst | | 1966 1,620.0 | 1,620.0 1,620.0 | 1.0E-99 1.0E99 | Syst | | 1967 1,760.0 | 1,760.0 1,760.0 | 1.0E-99 1.0E99 | Syst | | 1968 2,580.0 | 2,580.0 2,580.0 | 1.0E-99 1.0E99 | Syst | | 1969 2,560.0 | 2,560.0 2,560.0 | 1.0E-99 1.0E99 | Syst | | 1970 2,100.0 | 2,100.0 2,100.0 | 1.0E-99 1.0E99 | Syst | | 1971 1,850.0 | 1,850.0 1,850.0 | 1.0E-99 1.0E99 | Syst | | 1972 1,040.0 | 1,040.0 1,040.0 | 1.0E-99 1.0E99 | Syst | | 1973 4,290.0 | 4,290.0 4,290.0 | 1.0E-99 1.0E99 | Syst | | 1974 945.0 | 945.0 945.0 | 1.0E-99 1.0E99 | Syst | | 1975 2,640.0 | 2,640.0 2,640.0 | 1.0E-99 1.0E99 | Syst | | 1976 1,600.0 | 1,600.0 1,600.0 | 1.0E-99 1.0E99 | Syst | | 1977 712.0 | 712.0 712.0 | 1.0E-99 1.0E99 | Syst | | 1978 1,060.0 | 1,060.0 1,060.0 | 1.0E-99 1.0E99 | Syst | | 1979 6,240.0 | 6,240.0 6,240.0 | 1.0E-99 1.0E99 | Syst | | 1980 3,710.0 | 3,710.0 3,710.0 | 1.0E-99 1.0E99 | Syst | | 1981 1,020.0 | 1,020.0 1,020.0 | 1.0E-99 1.0E99 | Syst | | 1982 2,230.0 | 2,230.0 2,230.0 | 1.0E-99 1.0E99 | Syst | | 1983 3,920.0 | 3,920.0 3,920.0 | 1.0E-99 1.0E99 | Syst | | 1984 3,970.0 | 3,970.0 3,970.0 | 1.0E-99 1.0E99 | Syst | | 1985 6,940.0 | 6,940.0 6,940.0 | 1.0E-99 1.0E99 | Syst | | 1986 6,540.0 | 6,540.0 6,540.0 | 1.0E-99 1.0E99 | Syst | | 1987 7,550.0 | 7,550.0 7,550.0 | 1.0E-99 1.0E99 | Syst | | 1988 1,020.0 | 1,020.0 1,020.0 | 1.0E-99 1.0E99 | Syst | | 1989 2,280.0 | 2,280.0 2,280.0 | 1.0E-99 1.0E99 | Syst | | 1990 2,080.0 | 2,080.0 2,080.0 | 1.0E-99 1.0E99 | Syst | | 1991 3,600.0 | 3,600.0 3,600.0 | 1.0E-99 1.0E99 | Syst | | 1992 2,400.0 | 2,400.0 2,400.0 | 1.0E-99 1.0E99 | Syst | | 1993 4,590.0 | 4,590.0 4,590.0 | 1.0E-99 1.0E99 | Syst | | 1994 3,040.0 | 3,040.0 3,040.0 | 1.0E-99 1.0E99 | Syst | | 1995 6,900.0 | 6,900.0 6,900.0 | 1.0E-99 1.0E99 | Syst |

File: Rio_Grande_at_Arroyo_Hondo.rpt, Page: 2

| 1996 875.0 | 875.0 875.0 | 1.0E-99 1.0E99 | Syst | Fitted log10 Moments Mean Variance Std Dev Skew EMA at-site data w/o regional info 3.358810 0.102546 0.320228 -0.152090 EMA w/ regional info and B17b MSE(G) 3.358810 0.102546 0.320228 -0.152090 EMA w/ regional info and specified MSE(G) 3.358810 0.102546 0.320228 -0.152090 EMA Estimate of MSE[G at-site] 0.159806 MSE[G at-site systematic] 0.159806 Equivalent Record Length [G at-site] 34.000000 Equivalent Record Length [Syst+Hist-LowOutl] 34.000000 Grubbs-Beck Critical Value 0.000000 --- Final Results --- << Plotting Positions >>

RIO GRANDE-ARROYO HONDO, NM-FLOW-ANNUAL PEAK

| Events Analyzed | Ordered Events | | FLOW | Water FLOW H-S | | Day Mon Year CFS | Rank Year CFS Plot Pos | | 06 Mar 1963 655.0 | 1 1987 7,550.0 2.86 | | 12 Nov 1963 565.0 | 2 1985 6,940.0 5.71 | | 22 Jun 1965 4,400.0 | 3 1995 6,900.0 8.57 | | 11 May 1966 1,620.0 | 4 1986 6,540.0 11.43 | | 12 Aug 1967 1,760.0 | 5 1979 6,240.0 14.29 | | 01 Jun 1968 2,580.0 | 6 1993 4,590.0 17.14 | | 20 Jun 1969 2,560.0 | 7 1965 4,400.0 20.00 | | 19 Sep 1970 2,100.0 | 8 1973 4,290.0 22.86 | | 30 Mar 1971 1,850.0 | 9 1984 3,970.0 25.71 | | 17 Mar 1972 1,040.0 | 10 1983 3,920.0 28.57 | | 23 May 1973 4,290.0 | 11 1980 3,710.0 31.43 | | 16 Mar 1974 945.0 | 12 1991 3,600.0 34.29 | | 18 Jun 1975 2,640.0 | 13 1994 3,040.0 37.14 | | 31 May 1976 1,600.0 | 14 1975 2,640.0 40.00 | | 26 Jul 1977 712.0 | 15 1968 2,580.0 42.86 | | 06 Jun 1978 1,060.0 | 16 1969 2,560.0 45.71 | | 11 Jun 1979 6,240.0 | 17 1992 2,400.0 48.57 | | 26 May 1980 3,710.0 | 18 1989 2,280.0 51.43 | | 07 Aug 1981 1,020.0 | 19 1982 2,230.0 54.29 | | 01 Jun 1982 2,230.0 | 20 1970 2,100.0 57.14 | | 03 Jun 1983 3,920.0 | 21 1990 2,080.0 60.00 | | 01 Jun 1984 3,970.0 | 22 1971 1,850.0 62.86 | | 14 Jun 1985 6,940.0 | 23 1967 1,760.0 65.71 | | 11 Jun 1986 6,540.0 | 24 1966 1,620.0 68.57 | | 19 May 1987 7,550.0 | 25 1976 1,600.0 71.43 | | 11 Apr 1988 1,020.0 | 26 1978 1,060.0 74.29 | | 12 Apr 1989 2,280.0 | 27 1972 1,040.0 77.14 | | 10 May 1990 2,080.0 | 28 1988 1,020.0 80.00 | | 23 May 1991 3,600.0 | 29 1981 1,020.0 82.86 | | 16 Apr 1992 2,400.0 | 30 1974 945.0 85.71 | | 30 May 1993 4,590.0 | 31 1996 875.0 88.57 | | 04 Jun 1994 3,040.0 | 32 1977 712.0 91.43 | | 06 Jul 1995 6,900.0 | 33 1963 655.0 94.29 | | 01 Jan 1996 875.0 | 34 1964 565.0 97.14 |

* Low outlier plotting positions are computed using Median parameters.

<< Frequency Curve >>

RIO GRANDE-ARROYO HONDO, NM-FLOW-ANNUAL PEAK

Observed Events (Hirsch-Stedinger plotting positions) 95 Percent Confidence Limit 5 Percent Confidence Limit Computed Curve

Bulletin 17 Plot for Rio Grande at Arroyo Hondo

1...

1,000

10,0...

100,0...

F

1.0 1.1 .. .. ... ... 1... 5... 100...

Return Period

0.99... 0.999 0.99 0.9 0.5 0.2 0.1 0.02 0.005 0.001 0.00...

Probability

Appendix D Scour Calculations

Project: Prepared: JAC Date: 5/26/2021 Subject: Checked: Date:

Task:

Job#: No:

Reference: FHWA HEC 18 Evaluating Scour at Bridges 2012, Chapter 6

US XS: 760.0276 Proposed

Contraction Scour, Chapter 6.2

EQ 6.1

Ku 11.17 English Units y 4.55 Average depth of flow upstream of the contraction, ft (hydraulic depth at approach cross section)

D50 0.2 Particle size for Vc, mm (reasonable lower limit of D50 per HEC 18, p. 6.2, 6.15, "Because the critical shear stress reaches a minimum (Figure 6.9) at a D50 o D50 0.00065616 Particle size for Vc, ft Vc 1.25 Critical velocity above which bed material of size D and smaller will be transported, ft/s

Velocity in Channel 6.24 ft/s Average velocity at approach cross section

Contraction Scour 0.6 ft

Live bed Contraction Scour, Chapter 6.3

EQ 6 2

y2 4.7 Average depth in the contracted section, ft y1 4.55 Average depth in the upstream main channel section, ft y0 4.09 Existing depth in the contracted section before scour, ft Q2 992 Flow in the contracted channel ft3/s Q1 992 Flow in the upstream channel transporting sediment, ft3/s W1 34.98 Top width of the upstream main channel that is transporting bed material, ft (Per HEC 18, p. 6.11 "W1 and W2 are not always easily defined. In some cases, W2 33.60 Top width of the main channel in the contracted section less pier widths, ft k1 0.69 Exponent V* 0.99 Shear velocity in the upstream section, ft/s w 0.0886 Fall velocity of bed material based on the D50 g 32.2 Acceleration of gravity, 32.3 ft/s2 S1 0.006702 Slope of energy grade line of main channel, ft/ft

V*/w 11.19 ys 0.6 Average contraction scour depth, ft

Clear water Contraction Scour, Chapter 6.4

EQ 6.4

y2 17.22246408 Average equilibirium depth in the contracted section after contraction scour, ft Ku 0.0077 English Units Q 992 Discharge through the contracted section or on the set back overbank area at the section associated with the width W, ft3/s Dm 0.0008202 Diameter of the smallest nontransportable particle in the bed material (1.25*D50) in the contracted section, ft D50 0.00065616 Median diameter of the bed material, ft W 33.6 Top width of the contracted section less pier widths y0 4.094047619 Average existing depth in the contracted section, ft ys 13.13 Average contraction scour depth, ft

John Dunn Bridge Bridge 3807 Contraction Scour 50-year 10240361

Live Bed Contraction Scour

These methods and equations are also referenced in the NewMexico DOT Drainage Design Manual, Section 607.3.2 (Smith Engineering Company et al. July 2018. Drainage Design Manual NewMexico Department of Transportation)

3/16/1 DyKV uc

7/6

K

W W

Q Q y y

7/3

23/2

2 WD

QK

y m u

Task:

Job#: No:

NCHRP 24 20 Approach Reference: FHWA HEC 18 Evaluating Scour at Bridges 2012, Chapter 8

US XS: 760.0276 Proposed

Set Back Ratio and Unit Discharge

Proposed

0.0 Set back Length, ft

4.1 Average channel depth, ft

SBR 0.0 Set Back Ratio

SBR<5 both abutments Figure 8.14

A 137.6 Flow Area, ft2 Q 992.0 Total Bridge Flow, cfs V

7.21 Velocity Bridge Opening, ft/s

33.60 Top Width, ft (net top width BR)

d 4.09 Hydraulic Depth Bridge, ft q2c 29.52 Unit Bridge Discharge, cfs/ft

Projected Length

L 25.0 Project Length of Abutment, L Br 1.0 Width of Floodplain, ft

L/Br 2500.00% >75% y1 4.55 Upstream flow depth, ft Q1 992 Flow in the upstream channel transporting sediment, ft3/s W1 34.98 Top width of the upstream main channel that is transporting bed material, ft q1 28.36 Upstream unit discharge ft2/s Q1/W1 q2c 29.52 Unit discharge in the constricted opening accounting for non uniform flow distribution, ft2/s yc 4.7 Flow depth including live bed contraction scour, ft

Live Bed Abutment Scour Equation q2c/q1 1.04 A 1.50 Amplification Factor for live bed conditions from Fig 8.9 yc 4.7 Flow depth including live bed contraction scour, ft ymax 7.1 Maximum flow depth resulting from abutment scour, ft yo 4.09 Flow depth prior to scour, ft ys 2.97 Abutment Scour depth, ft

John Dunn Bridge Bridge 3807 Abutment Scour 50-Year 10240361

*** Typical velocities approaching the roadway embankments from the upstream are larger than the critical velocity from contraction scour calculations (1.22 fps). It is then assumed that enough velocity exists to allow for sediment transport indicating a live bed abutment scour condition.

These methods and equations are also referenced in the New Mexico DOT Drainage Design Manual, Section 607.3.4 (Smith Engineering Company et

al. July 2018. Drainage Design Manual New Mexico Department of Transportation) cA yy max

7/6

1 q qyy c c

Task: Riprap Design Job#: No:

Reference: Federal Highway Administration, Hydraulic Engineering Circular HEC 23

Proposed

Sizing Rock Riprap at Abutments

For Froude Numbers <0.8 HEC 23, Eq 14.1

V = 10.40 characteristic average velocity in the contracted section, ft/s Q/A Ss= 2.65 specific gravity of rock riprap g= 32.2 gravitational acceleration, 32.2 ft/s2 y= 4.09 depth of flow in the contracted bridge opening, ft K= 0.89 0.89 for spill through abutment

1.02 for a vertical wall abutment

Computed D50 = 1.81 median stone diameter, ft

21.7 median stone diameter, in

Recommended Riprap Class 1/2 ton D50 = 2.25 D100 = 2.85

For Froude Numbers >0.8 HEC 23, Eq 14.2

V = 10.40 characteristic average velocity in the contracted section, ft/s Q/A Ss= 2.65 specific gravity of rock riprap g= 32.2 gravitational acceleration, 32.2 ft/s2 y= 4.094048 depth of flow in the contracted bridge opening, ft K= 0.89 0.89 for spill through abutment

1.2 for a vertical wall abutment

Computed D50 = 2.15 median stone diameter, ft

25.8 median stone diameter, in

Recommended Riprap Class 1/2 ton

D50 = 2.25

D100 = 2.85

Recommended Riprap Class Froude Number: 0.94

1/2 ton D50 = 2.25 D100 = 2.85

Recommended Riprap Thickeness Rock riprap thickness should not be less than the larger of either 1.5 times D50 or D100

Froude Number: 0.94

1.5 * D50 = 3.375 ft

D100 = 2.85 ft

Riprap Thickness = 3.375 ft

John Dunn Bridge Bridge 3807

Federal Highway Administration. 2009. Bridge Scour and Stream Instability Countermeasures: Experience, Selection, and Design Guidance (Volume 2). Third Edition.

Publication No. FHWA NHI 09 112. Hydraulic Engineering Circular No. 23.

10240361

Task:

Job#: No:

Reference: FHWA HEC 18 Evaluating Scour at Bridges 2012, Chapter 6

US XS: 760.0276 Proposed

Contraction Scour, Chapter 6.2

EQ 6.1

Ku 11.17 English Units y 4.99 Average depth of flow upstream of the contraction, ft (hydraulic depth at approach cross section)

D50 0.2 Particle size for Vc, mm (reasonable lower limit of D50 per HEC 18, p. 6.2, 6.15, "Because the critical shear stress reaches a minimum (Figure 6.9) at a D50 o D50 0.00065616 Particle size for Vc, ft Vc 1.27 Critical velocity above which bed material of size D and smaller will be transported, ft/s

Velocity in Channel 6.76 ft/s Average velocity at approach cross section

Contraction Scour 0.6 ft

Live bed Contraction Scour, Chapter 6.3

EQ 6 2

y2 5.1 Average depth in the contracted section, ft y1 4.99 Average depth in the upstream main channel section, ft y0 4.52 Existing depth in the contracted section before scour, ft Q2 1279 Flow in the contracted channel ft3/s Q1 1279 Flow in the upstream channel transporting sediment, ft3/s W1 37.97 Top width of the upstream main channel that is transporting bed material, ft (Per HEC 18, p. 6.11 "W1 and W2 are not always easily defined. In some cases, W2 36.90 Top width of the main channel in the contracted section less pier widths, ft k1 0.69 Exponent V* 1.06 Shear velocity in the upstream section, ft/s w 0.0886 Fall velocity of bed material based on the D50 g 32.2 Acceleration of gravity, 32.3 ft/s2 S1 0.006974 Slope of energy grade line of main channel, ft/ft

V*/w 11.95 ys 0.6 Average contraction scour depth, ft

Clear water Contraction Scour, Chapter 6.4

EQ 6.4

y2 19.76122938 Average equilibirium depth in the contracted section after contraction scour, ft Ku 0.0077 English Units Q 1279 Discharge through the contracted section or on the set back overbank area at the section associated with the width W, ft3/s Dm 0.0008202 Diameter of the smallest nontransportable particle in the bed material (1.25*D50) in the contracted section, ft D50 0.00065616 Median diameter of the bed material, ft W 36.9 Top width of the contracted section less pier widths y0 4.51598916 Average existing depth in the contracted section, ft ys 15.25 Average contraction scour depth, ft

John Dunn Bridge Bridge 3807 Contraction Scour 100-year 10240361

Live Bed Contraction Scour

These methods and equations are also referenced in the NewMexico DOT Drainage Design Manual, Section 607.3.2 (Smith Engineering Company et al. July 2018. Drainage Design Manual NewMexico Department of Transportation)

3/16/1 DyKV uc

7/6

K

W W

Q Q y y

7/3

23/2

2 WD

QK

y m u

Task:

Job#: No:

NCHRP 24 20 Approach Reference: FHWA HEC 18 Evaluating Scour at Bridges 2012, Chapter 8

US XS: 760.0276 Proposed

Set Back Ratio and Unit Discharge

Proposed

0.0 Set back Length, ft

4.5 Average channel depth, ft

SBR 0.0 Set Back Ratio

SBR<5 both abutments Figure 8.14

A 166.6 Flow Area, ft2 Q 1279.0 Total Bridge Flow, cfs V 7.68 Velocity Bridge Opening, ft/s

36.90 Top Width, ft (net top width BR)

d 4.52 Hydraulic Depth Bridge, ft q2c 34.66 Unit Bridge Discharge, cfs/ft

Projected Length

L 25.0 Project Length of Abutment, L Br 1.0 Width of Floodplain, ft

L/Br 2500.00% >75% y1 4.99 Upstream flow depth, ft Q1 1279 Flow in the upstream channel transporting sediment, ft3/s W1 37.97 Top width of the upstream main channel that is transporting bed material, ft q1 33.68 Upstream unit discharge ft2/s Q1/W1 q2c 34.66 Unit discharge in the constricted opening accounting for non uniform flow distribution, ft2/s yc 5.1 Flow depth including live bed contraction scour, ft

Live Bed Abutment Scour Equation q2c/q1 1.03 A 1.50 Amplification Factor for live bed conditions from Fig 8.9 yc 5.1 Flow depth including live bed contraction scour, ft ymax 7.7 Maximum flow depth resulting from abutment scour, ft yo 4.52 Flow depth prior to scour, ft ys 3.15 Abutment Scour depth, ft

John Dunn Bridge Bridge 3807 Abutment Scour 100-year 10240361

*** Typical velocities approaching the roadway embankments from the upstream are larger than the critical velocity from contraction scour calculations (1.22 fps). It is then assumed that enough velocity exists to allow for sediment transport indicating a live bed abutment scour condition.

These methods and equations are also referenced in the New Mexico DOT Drainage Design Manual, Section 607.3.4 (Smith Engineering Company et

al. July 2018. Drainage Design Manual New Mexico Department of Transportation) cA yy max

7/6

1 q qyy c c

Task: Riprap Design 100 year Job#: 10240361 No:

Reference: Federal Highway Administration, Hydraulic Engineering Circular HEC 23

Proposed

Sizing Rock Riprap at Abutments

For Froude Numbers <0.8 HEC 23, Eq 14.1

V = 10.84 characteristic average velocity in the contracted section, ft/s Q/A Ss= 2.65 specific gravity of rock riprap g= 32.2 gravitational acceleration, 32.2 ft/s2 y= 4.52 depth of flow in the contracted bridge opening, ft K= 0.89 0.89 for spill through abutment

1.02 for a vertical wall abutment

Computed D50 = 1.97 median stone diameter, ft

23.6 median stone diameter, in

Recommended Riprap Class 1/2 ton D50 = 2.25 D100 = 2.85

For Froude Numbers >0.8 HEC 23, Eq 14.2

V = 10.84 characteristic average velocity in the contracted section, ft/s Q/A Ss= 2.65 specific gravity of rock riprap g= 32.2 gravitational acceleration, 32.2 ft/s2 y= 4.515989 depth of flow in the contracted bridge opening, ft K= 0.89 0.89 for spill through abutment

1.2 for a vertical wall abutment

Computed D50 = 2.36 median stone diameter, ft

28.4 median stone diameter, in

Recommended Riprap Class 1 ton D50 = 2.85 D100 = 3.60

Recommended Riprap Class Froude Number: 0.64 Took U/S end only due to reasonableness of result

1/2 ton

D50 = 2.25 CLASS D

D100 = 2.85

Recommended Riprap Thickeness rock riprap thickness should not be less than the larger of either 1.5 times D50 or D100

Froude Number: 0.64 Took U/S end only due to reasonableness of result

1.5 * D50 = 3.375 ft

D100 = 2.85 ft

Riprap Thickness = 3.4 ft

John Dunn Bridge Bridge 3807

Federal Highway Administration. 2009. Bridge Scour and Stream Instability Countermeasures: Experience, Selection, and Design Guidance (Volume 2). Third Edition. Publication No. FHWA NHI 09 112. Hydraulic Engineering Circular No. 23.