Hydraulics Report January 2021.pdf

Buffalo Crossing Bridge Apache-Sitgreaves National Forest

US Forest Service Greenlee County, AZ

AZ FS 24(1)

Hydraulics Report

Federal Highway Administration

Central Federal Lands Highway Division

January 2021

Executive Summary

Hydrologic and hydraulic analyses were conducted for the AZ FS 24(1) Buffalo Crossing Bridge Project. For the preliminary recommendations, the 50-year and 100-year floods were evaluated as the hydraulic design flood in accordance with Federal Lands Highway (FLH) and U.S. Forest Service (USFS) design criteria, respectively. The peak flow values were estimated using both USGS regression equations for Arizona and NRCS method rainfall-runoff modeling conducted using HEC-HMS. The rainfall-runoff analysis peak flow values were selected as design flows because they were more conservative and more closely aligned with an approximate comparison with gaged Black River stream flows.

Existing and proposed conditions two-dimensional hydraulic modeling using SRH-2D was conducted to estimate water surface elevations, depths and flow velocities at the project site. The proposed bridge was assumed to be a single span structure with the existing abutments remaining in place. The USFS uses the 100-year flood as the hydraulic design flood, requires a 3-foot minimum freeboard, and recommends simulating debris blockage in the bridge opening where conditions warrant. Based on input from USFS the selected criteria were the 100-year flood with 3-foot of freeboard with no additional blockage due to debris.

The proposed structure is a 100-ft long bridge with an approximate low chord of 7,534.8 feet at the southeast abutment. The bridge has a 1% slope, with deck elevations varying from 7538.56 feet to 7539.56 feet. Based on the results of the hydraulic analyses, the proposed bridge meets both FLH and USFS freeboard criteria as summarized in the following table:

Summary of Bridge Freeboard Results

Design Criteria

Hydraulic Capacity Design

Frequency

Bridge Waterway

Width (ft)

Minimum Freeboard

(ft)

Maximum

WSEL 36-

feet Upstream

(ft)

Proposed Low Chord Elevation

(ft)

Provided Freeboard

(ft)

Existing Low Chord Elevation

(ft)

FLH PDDM 50-year 88 2 7,530.4 7,534.8

4.4 7531.0

USFS TSH 100-year 88 3 7,531.8 3.0

Scour depth estimates were conducted in accordance with HEC-18 using a 100-year scour design flood and 200-year scour check flood. Scour elevation results are summarized in the following table:

Summary of Bridge Scour Results

Parameter 100-Year 200-Year Total Scour (ft) 3.89 5.24

Channel Thalweg Elevation (ft) 7521.5 7521.5 Potential Scour Elevation (ft) 7517.6 7516.3 i AZ FS 24(1) Buffalo Crossing – Hydraulic Report

Table of Contents

1 Project Background Information

2 Hydraulic Design Criteria

3 Hydrology

3.1 Hydrologic Setting

3.2 FEMA Flood Insurance Study

3.3 Available Hydrologic Data

3.4 Regression Equation Estimates

3.5 Rainfall-Runoff Model Estimates

3.5.1 Precipitation

3.5.2 Basin Parameters

3.6 Recommended Design Discharges

4 Hydraulic Analysis

4.1 Topographic Information

4.2 Hydraulic Model Development

4.3 Hydraulic Model Results

4.3.1 Existing Conditions

4.3.2 Proposed Conditions

4.4 Scour Assessment

4.4.1 Site Visit Observations

4.4.2 Geotechnical Investigation

4.4.3 Scour Estimates

5 Summary of Results

6 References ii AZ FS 24(1) Buffalo Crossing – Hydraulic Report

Tables Table 1: FLH Hydraulic Design Criteria Table 2: USFS Bridge Hydraulic Design Criteria Table 3: Basin Properties Table 4: Available Peak Streamflow Information Table 5: StreamStats Peak Flow Estimates and 90-Percent Prediction Intervals at Project Site Table 6: NOAA Atlas 14 24-Hour Point Precipitation – Basin Centroid Table 7: Basin Parameters (NRCS Method) Table 8: HEC-HMS Peak Discharge Estimates at Project Site Table 9: Peak Flow at USGS 09489100 and Project Site Table 10: Recommended Design Flows Table 11: Project Land Cover Types and Manning’s Roughness Table 12: 50-year and 100-year Existing Conditions Hydraulic Results Table 13: 50-year and 100-year Existing Conditions Freeboard Table 14: 50-year Proposed Conditions Selected Hydraulic Results Table 15: 100-year Proposed Conditions Selected Hydraulic Results Table 16: 50-year and 100-year Proposed Conditions Hydraulic Results Table 17: 50-year and 100-year Proposed Conditions Freeboard Table 18: Contraction Scour Estimates Table 18: Summary of Bridge Freeboard Results

Figures

Figure 1: Project location map Figure 2: Drainage Basin Map Figure 3: Peak Flow Comparison Figure 4: Topographic Surface, Elevations in feet referenced to NAVD88 Figure 5: Project Land Cover Types and Manning’s Roughness Figure 6: Existing Conditions SRH-2D Mesh Detail near Bridge Figure 7: 50-year and 100-year Existing Conditions WSEL at Bridge Looking Downstream Figure 8: 200-year and 500-year Existing Conditions WSEL at Bridge Looking Downstream Figure 9: Proposed WSEL Profile Baseline Figure 10: Proposed 50-year and 100-year WSEL Profile Figure 11: Streambed Sample Particle Size Distribution

Appendices

Appendix A: Hydrologic Analyses Appendix B: Existing Condition Hydraulic Analyses Appendix C: Proposed Condition Hydraulic Analyses Appendix D: Site Visit Documentation

Page 1 AZ FS 24(1) Buffalo Crossing – Hydraulic Report

1 PROJECT BACKGROUND INFORMATION

The Buffalo Crossing Bridge project is located in Greenlee County, AZ within the Apache-Sitgreaves National Forest. The existing bridge carries National Forest Route 24 over the North Fork East Fork Black River, see Figure 1.

Figure 1: Project location map.

2 HYDRAULIC DESIGN CRITERIA

Two design references were evaluated to establish the hydraulic capacity design criteria: The Federal Lands Highway Project Development and Design Manual (PDDM) (Federal Lands Highway 2012) and the USFS

Transportation Structures Handbook (TSH) (U.S. Forest Service 2014). Based on the project scoping summary, the road is classified as a Forest Service Maintenance Level 4 with an average daily traffic (ADT) of 82 vehicles.

Buffalo Crossing Bridge

Page 2 AZ FS 24(1) Buffalo Crossing – Hydraulic Report

Based on these parameters, the road is classified as low standard for hydraulic design purposes according to the PDDM. The applicable FLH and TSH design criteria are listed in Table 1 and.

Table 2, respectively. Both FLH and USFS reference HEC-18 (Federal Highway Administration 2009) for scour estimates, therefore the scour criteria shown in Table 1 will be applied to the project.

Table 1: FLH Hydraulic Design Criteria

Road Classification: Low-Standard Road (ADT 82 vpd)

Bridges

Design Frequency Check Frequency Freeboard

50-year flood

Greater of 100-year or overtopping flood

• Minimum of 2 feet

• 3.5 feet to 5 feet when woody debris potential is significant

• 5 feet to 10 feet when ice flow potential is significant

Scour

Scour Design

Frequency Scour Check Frequency Scour Countermeasure Design Frequency

100-year flood 200-year flood 200-year flood

Floodplain Encroachment

FEMA SFHA Involvement Allowable Rise Project within FEMA regulated special flood hazard area (SFHA) – Zone A Maximum 1-foot rise in water surface profile over existing conditions

Table 2: USFS Bridge Hydraulic Design Criteria

Bridges

Design Frequency Check Frequency Freeboard

100-year flood Not specified • Minimum of 3 feet

3 HYDROLOGY

3.1 HYDROLOGIC SETTING

The project is located within the North Fork East Fork Black River Subwatershed (HUC12: 150601010106) The total contributing drainage area to the bridge is approximately 111.5 square miles. The North Fork generally flows from north to south from its headwaters near Pool Knoll west of Route 261 to the confluence with the West Fork Black River located approximately 0.75 miles downstream of the project site. The contributing drainage basin was delineated using available 10-meter digital elevation model (DEM) information obtained from the USGS National Map as shown in Figure 2. A summary of general basin properties is shown in Table 3.

Page 3 AZ FS 24(1) Buffalo Crossing – Hydraulic Report

Table 3: Basin Properties

Site Drainage Area (mi2)

Mean Basin Elevation (ft)

Mean Basin Slope (%)

Mean Annual Precipitation (in)

Buffalo Crossing Bridge 111.5 8,802 13.6 28.1

Figure 2: Drainage Basin Map

Page 4 AZ FS 24(1) Buffalo Crossing – Hydraulic Report

3.2 FEMA FLOOD INSURANCE STUDY

According to FEMA Flood Insurance Rate Map (FIRM) panels 04011C0025D and 04001C5075E, the project is located within a FEMA Zone A special flood hazard area (SFHA). The SFHA comprises the land area that is shown in the FIRM as being inundated by the 1% chance (100-year) base flood and where the National Flood Insurance Program's (NFIP) floodplain management regulations apply. The boundaries of FEMA Zone A are determined using approximate methods therefore no base flood elevations (BFEs) are shown in the FIRM. The PDDM criteria for Zone A allows a maximum of 1-foot rise in proposed conditions base flood elevations when compared to the existing condition.

3.3 AVAILABLE HYDROLOGIC DATA

According to the USGS National Water Information System (NWIS) there are no active USGS peak streamflow stations within the project limits. The closest USGS active station is located on the Black River approximately 36 miles downstream of the project site. Although listed as “active” peak streamflow collection stopped in 2015. An inactive station is located approximately 9 miles downstream from the project site. Data from both of these stations was included in the development of the USGS regression equations for Arizona described in Section 3.4. Table 4 summarizes the station locations and period of record.

Table 4: Available Peak Streamflow Information

USGS

Station Location Latitude Longitude Drainage

Area Period of Record

Total Peak Streamflow

Records Status

09489500 Black River BLW

Pumping Plant, near Point of Pines, AZ

33°28'36" 109°45'48" 560 mi2 1954- 2015 62 Active

09489100 Black River near Maverick, AZ 33°42'27" 109°26'48" 315 mi2 1963-

1983 20 Inactive

3.4 REGRESSION EQUATION ESTIMATES

The StreamStats web application (U.S. Geological Survey 2016) was used to estimate peak flows for the project sites. The Arizona StreamStats application uses the regression equations presented in USGS Report 2014-5211 (Paretti, et al. 2014). According to the report the project basin is located hydrologic region 1 – High Elevation, which comprises areas above elevation 7,500 feet. The region 1 equations relate peak discharge to drainage area. According to the study the average standard errors of prediction for the equations vary from 56 to 86 percent. The report also includes a methodology for estimating 90-percent prediction intervals. The peak flow results and prediction intervals for the project basin are shown in Table 5.

Page 5 AZ FS 24(1) Buffalo Crossing – Hydraulic Report

Table 5: StreamStats Peak Flow Estimates and 90-Percent Prediction Intervals at Project Site

Percent Chance

Exceedance

Return Period (year) Peak Flow Estimate Lower Prediction

Interval Upper Prediction

Interval

(cfs) (cfs) (cfs)

50 2 382 110 1,320 20 5 801 301 2,140 10 10 1,180 479 2,900 4 25 1,780 755 4,180 2 50 2,310 982 5,440 1 100 2,910 1,220 6,970

0.5 200 3,620 1,470 8,920

0.2 500 4,700 1,810 12,200

3.5 RAINFALL-RUNOFF MODEL ESTIMATES

Rainfall-runoff modeling using HEC-HMS was conducted to compare the peak flow estimates from the regression equations as described in the following sections.

3.5.1 Precipitation

The point precipitation values for the project were obtained from NOAA Atlas 14 Volume 1 (Perica, Dietz, et al. 2011) using the Precipitation Frequency Data Server (National Oceanic and Atmospheric Administration 2011). The precipitation values at the basin centroid were assumed to represent the precipitation over the entire project basin area. The point precipitation values for a duration of 24 hours and various return periods are shown in Table 6.

Table 6: NOAA Atlas 14 24-Hour Point Precipitation – Basin Centroid

Percent Chance Exceedance (%)

Return Period (year)

Point Precipitation (inches)

50 2 2.07 20 5 2.54 10 10 2.92 4 25 3.43 2 50 3.91 1 100 4.39

0.5 200 4.89

0.2 500 5.60

3.5.2 Basin Parameters

The NRCS curve number (CN) method (Natural Resources Conservation Service 1997) was used to estimate runoff. SSURGO soil information (Natural Resources Conservation Service 2015) is not available for the project basin, a hydrologic soil group (HSG) of B was assumed based on information from the

Page 6 AZ FS 24(1) Buffalo Crossing – Hydraulic Report

Gridded National Soil Survey Database. Land cover was obtained from the national land cover dataset (Multi-Resolution Land Characteristics Consortium 2018). Land cover for the project basin consists primarily of grassland/herbaceous areas, with small areas of shrub/scrub, herbaceous wetlands, deciduous forests and developed/open space interspersed throughout. Time of concentration was estimated by the NRCS lag time method. The NRCS and unit hydrograph was used to estimate peak flows from the basins. An SCS (now NRCS) Type 2 rainfall distribution was selected based on the project location.

A summary of basin parameters is shown in Table 7.

Table 7: Basin Parameters (NRCS Method)

Basin Parameter Site 1 Drainage Area (sq. mi.) 111.5

Composite Curve Number (CN) 64.2

Lag Time (min) 479

The hydrologic computations were carried out using HEC-HMS (U.S. Army Corps of Engineers 2017). The results for various return periods are shown in Table 8.

Table 8: HEC-HMS Peak Discharge Estimates at Project Site

Percent Chance Exceedance (%) Return Period (year) Peak Flow (cfs)

50 2 670 20 5 1,420 10 10 2,190 4 25 3,440 2 50 4,800 1 100 6,310

0.5 200 8,020

0.2 500 10,640

3.6 RECOMMENDED DESIGN DISCHARGES

As discussed in Section 3.3 there is no streamflow data near the project to calibrate the peak flow results the USGS 09489100 Black River gage is useful for comparison. The project site has a drainage area of 11.5 square miles or 35% of the 315 square mile area at the gage. This falls outside the 0.5-1.5 drainage area range of applicability for weighting the regression equation estimates presented in the USGS report.

Although outside of the applicability range, the StreamStats data collection report shows that the regression equations underestimated the gage peak flows significantly. Table 9 shows this comparison and a theoretical estimate at the project site using the ratio of drainage areas.

Page 7 AZ FS 24(1) Buffalo Crossing – Hydraulic Report

Table 9: Peak Flow at USGS 09489100 and Project Site

Return Period (year) Flood Frequency (cfs) Regression Estimate (cfs)

Peak Flow at Project Site Assuming 35% of the Flood Frequency

Gage (cfs) 2 1,730 752 606 5 4,020 1,530 1,407

10 6,260 2,220 2,191 25 10,000 3,310 3,500 50 13,600 4,290 4,760

100 17,900 5,420 6,265 200 23,100 6,740 8,085 500 31,300 8,720 10,955

Figure 3 shows a comparison between the regression equation and rainfall-runoff model peak flow estimates. As shown, the regression equations peak flow estimates are closer to the lower 90% prediction interval and the rainfall-runoff model peak flow estimates are close to the upper 90% prediction interval.

Based on this comparison, the rainfall-runoff model results were selected for the project as shown in Table

10. Additional details of the hydrologic analysis are provided in Appendix A.

Figure 3: Peak Flow Comparison

Page 8 AZ FS 24(1) Buffalo Crossing – Hydraulic Report

Table 10: Recommended Design Flows

Percent Chance Exceedance (%) Return Period (year) Peak Flow (cfs)

50 2 670 20 5 1,420 10 10 2,190 4 25 3,440 2 50 4,800 1 100 6,310

0.5 200 8,020

0.2 500 10,640

4 HYDRAULIC ANALYSIS

Hydraulic analyses were conducted for Buffalo Crossing bridge. The objective of the analyses was to establish water surface elevations, freeboard, and hydraulic capacity requirements using the available data and two-dimensional hydraulic modeling. The input data, model development, and results are discussed in the following sections.

4.1 TOPOGRAPHIC INFORMATION

Field survey information collected by Central Federal Lands was used to develop the hydraulic models for the sites. The survey information was processed to create triangular irregular network (TIN) surfaces to represent the topography in the streambed and floodplain areas near the existing crossings as shown in Figure 4. All elevations for the study are in units of feet and are referenced to the North American Vertical Datum of 1988 (NAVD 88).

Page 9 AZ FS 24(1) Buffalo Crossing – Hydraulic Report

Figure 4: Topographic Surface, Elevations in feet referenced to NAVD88

4.2 HYDRAULIC MODEL DEVELOPMENT

Preliminary two-dimensional hydraulic simulations were conducted using SRH-2D (U.S. Bureau of Reclamation 2017) to estimate water surface elevations, water depth and flow velocities at the project site. The SRH-2D computational mesh generation and model pre- and post-processing was performed using the SMS 13.0.11 interface (Aquaveo 2019).

Page 10 AZ FS 24(1) Buffalo Crossing – Hydraulic Report

The upstream boundary conditions in the model were specified as a constant discharge using the peak flow values shown in Table 10. The downstream boundary conditions were specified as known water surface elevations obtained using Manning’s equation and a energy grade line slope assumed to equal the streambed slope near the model downstream boundary.

SRH-2D uses Manning’s “n” values to calculate bed friction. The land use types were delineated from aerial imagery as shown in Figure 5 and assigned standard roughness values. The roughness values used in the model are shown in Table 11. The roughness values will be confirmed during the 30% site visit.

Table 11: Project Land Cover Types and Manning’s Roughness

Land Use Manning's "n" Main Channel 0.035

Floodplain Trees 0.100 Bare Ground 0.040

Page 11 AZ FS 24(1) Buffalo Crossing – Hydraulic Report

Figure 5: Project Land Cover Types and Manning’s Roughness

Page 12 AZ FS 24(1) Buffalo Crossing – Hydraulic Report

For the existing conditions simulations, the existing bridge was modeled as a pressure boundary condition including overtopping. The bridge low chord was assumed to be a constant 7531-ft and the overtopping elevation a constant 7533-ft. The existing bridge piers were simulated as holes in the mesh as shown in Figure 6.

Figure 6: Existing Conditions SRH-2D Mesh Detail near Bridge

The objective of the proposed conditions simulations is to estimate the required bridge low chord elevation and waterway opening to satisfy the freeboard requirements. For cost savings and to reduce environmental impacts, it is assumed at this stage that the existing bridge abutments will remain in place and that the proposed bridge abutments will be constructed behind the existing. Two proposed condition scenarios were evaluated for the 50-year and 100-year return periods based on the criteria shown in Section 2. Based on input from the USFS partners the proposed bridge opening is based on a 100-year return period, 3-feet of freeboard, with no additional blockage due to debris.

Buffalo Crossing Bridge

Pier

Pier

Page 13 AZ FS 24(1) Buffalo Crossing – Hydraulic Report

4.3 HYDRAULIC MODEL RESULTS

4.3.1 Existing Conditions

Existing conditions hydraulic simulations using the parameters described in Section 4.2 were conducted for the 2-, 5-, 10-, 25-, 50-, 100-, 200-, and 500-year return periods. A summary of existing conditions results were extracted at the upstream bridge face and approximately one bridge width upstream. For design purposes, freeboard is typically computed a distance upstream of the bridge to avoid uncertainty associated with the rapid drawdown of water as flow accelerates through the bridge opening. The results are summarized in Table 12 for the 50-year and 100-year return periods, respectively. Maps showing the two-dimensional water surface elevation and velocity results are included in Appendix B.

Table 12: 50-year and 100-year Existing Conditions Hydraulic Results

Location Return Period (year)

Velocity (ft/s) Depth (ft) WSEL (ft) Average Maximum Average Maximum Average Maximum

At Bridge (Upstream Face)

50 9.4 12.2 6.1 7.3 7528.9 7529.5 100 10.2 13.1 7.3 8.6 7530.1 7530.8

36 feet Upstream of Bridge

50 7.6 11.7 5.3 8.2 7529.8 7530.5 100 7.0 11.8 5.4 9.6 7531.4 7532.0

The results show that the existing bridge can pass 50-year and 100-year event without a pressure flow condition although freeboard is limited as shown in Table 13. Based on the values estimated 36 feet upstream, the existing bridge does not meet design criteria. Figure 7 illustrates the water surface elevation results at the bridge.

Table 13: 50-year and 100-year Existing Conditions Freeboard

Location Return Period (year)

Maximum WSEL (ft)

Freeboard (ft)

At Bridge (Upstream Face)

50 7529.5 1.5 100 7530.8 0.2

36 feet Upstream of Bridge

50 7530.5 0.5 100 7532.0 -1.0

Page 14 AZ FS 24(1) Buffalo Crossing – Hydraulic Report

Figure 7: 50-year and 100-year Existing Conditions WSEL at Bridge Looking Downstream

For the less frequent 200-year and 500-year events, the results show significant overtopping of the bridge and the approach embankments as shown in Figure 8.

Figure 8: 200-year and 500-year Existing Conditions WSEL at Bridge Looking Downstream

Page 15 AZ FS 24(1) Buffalo Crossing – Hydraulic Report

4.3.2 Proposed Conditions

Proposed conditions hydraulic simulations using the parameters described in Section 4.2 were conducted for the 50-year and 100-year return periods. The proposed structure is a 100-ft long bridge with an approximate low chord of 7,534.8 feet at the southeast abutment. The bridge has a 1% slope, with deck elevations varying from 7538.56 feet to 7539.56 feet. The proposed bridge layout is included in Appendix C. For illustration purposes, Figure 10 shows 50-year and 100-year water surface profiles measured along the channel profile baseline shown in Figure 9. Due to the two-dimensional model domain, the profiles do not represent the maximum water surface elevations. Average and maximum hydraulic results along the profile baseline are shown in Table 14 and Table 15 for 50-year and 100-year return periods, respectively.

Figure 9: Proposed WSEL Profile Baseline

Bridge

WSEL Profile Baseline

Page 16 AZ FS 24(1) Buffalo Crossing – Hydraulic Report

Figure 10: Proposed 50-year and 100-year WSEL Profile

Table 14: 50-year Proposed Conditions Selected Hydraulic Results

Station Velocity (ft/s) Depth (ft) WSEL (ft)

Average Maximum Average Maximum Average Maximum 0 8.5 13.0 4.7 7.8 7526.7 7527.0

100 7.4 12.2 5.3 8.0 7528.1 7528.6 200 10.3 12.8 5.5 7.2 7528.7 7529.8 300 5.5 10.3 5.8 8.8 7530.6 7530.9 400 5.1 9.8 5.0 9.0 7531.3 7531.6

Table 15: 100-year Proposed Conditions Selected Hydraulic Results

Station Velocity (ft/s) Depth (ft) WSEL (ft)

Average Maximum Average Maximum Average Maximum 0 9.9 14.4 5.5 8.6 7527.4 7527.8

100 8.2 13.5 6.1 9.1 7529.1 7529.7 200 11.2 13.8 6.8 8.3 7529.9 7531.3 300 5.8 10.6 6.9 10.3 7532.0 7532.4 400 4.9 9.8 5.5 10.3 7532.7 7533.1

50-year

Low chord 7534.8’

Page 17 AZ FS 24(1) Buffalo Crossing – Hydraulic Report

For freeboard documentation purposes, the proposed conditions results were extracted at the upstream bridge face and approximately one bridge width upstream. Selected hydraulic results summarized in Table

16. The provided freeboard for the 50-year and 100-year return periods is shown in Table 17. Maps showing the two-dimensional water surface elevation, velocity and additional hydraulic results are included in Appendix C.

Table 16: 50-year and 100-year Proposed Conditions Hydraulic Results

Location Return Period (year)

Velocity (ft/s) Depth (ft) WSEL (ft) Average Maximum Average Maximum Average Maximum

At Bridge (Upstream Face)

50 10.6 12.4 6.1 7.2 7528.7 7529.3 100 11.5 13.4 7.0 8.3 7529.8 7530.5

36 feet Upstream of Bridge

50 9.5 12.6 5.4 7.7 7529.5 7530.4 100 10.0 13.2 6.2 8.9 7530.7 7531.8

Table 17: 50-year and 100-year Proposed Conditions Freeboard

Location Return Period (year)

Maximum WSEL (ft)

Proposed Low Chord Elevation (ft)

Provided Freeboard (ft)

At Bridge (Upstream Face)

50 7529.3

7534.8

5.5 100 7530.5 4.3

36 feet Upstream of

Bridge

50 7530.4 4.4

100 7531.8 3.0

4.4 SCOUR ASSESSMENT

4.4.1 Site Visit Observations

A site visit was conducted for the AZ 24(1) Buffalo Crossing project on 11/17/2020. The East Fork Black River reach in the vicinity of the bridge is a single thread channel. The channel bed consists mainly of sand, gravel and cobble material. Riparian vegetation consists primarily of willows and grasses. Vegetation in the floodplain is characterized by conifers, shrubs and brush. The channel reach in the vicinity of the bridge is straight.

The channel appears generally stable laterally and vertically upstream and downstream of the bridge, with only local stability problems observed. At the bridge, significant aggradation was noted in the south and center spans, with a well-developed mid-channel bar downstream of the south and center spans. The main low flow channel is located in the north span but some flow was observed in the center span. Some local degradation was present near the north abutment, most likely due to the aggradation in the south and center spans limiting conveyance. Flow through the bridge will be significantly improved by the removal of the existing piers. Site visit details are included in Appendix D.

Page 18 AZ FS 24(1) Buffalo Crossing – Hydraulic Report

4.4.2 Geotechnical Investigation

A gradation analysis of streambed material was conducted as part of the geotechnical investigation documented in the project Geotechnical Report. Based on the laboratory results the sample is classified as GW or a well graded gravel. The median particle size (D50) is 24 mm. The particle size distribution is shown in Figure 11.

Figure 11: Streambed Sample Particle Size Distribution

4.4.3 Scour Estimates

Scour depth estimates were conducted in accordance with HEC-18 (Federal Highway Administration 2012). Total scour is the combination of long term degradation, contraction scour and local scour. For this study local scour was estimated using the NCHRP 24-20 method. As discussed previously, the site investigation did not observe potential for long term degradation. Also, the USFS inspection report did not observe degradation concerns. The flow distribution through the bridge will be vastly improved by the removal of the two existing pier walls, reducing potential degradation induced by local shear. For this analysis 1-foot of long term degradation was assumed to account for potential bed elevation changes.

Contraction scour was estimated using the 100-year scour design flood and 200-year scour check flood.

Based on the critical velocity of the streambed materials a live bed scour condition can be expected. In this condition sediment is being transported into the bridge opening from upstream flow. Due to the uncertainties with the scour lateral location it is referenced to the thalweg elevation of the channel cross

D50 = 24mm

Page 19 AZ FS 24(1) Buffalo Crossing – Hydraulic Report section at the bridge. A summary of contraction scour including long term degradation is shown in Table 18.

Table 18: Contraction Scour Estimates

Parameter 100-Year 200-Year D50 (ft) 0.0775

Average Flow Depth Upstream of Contraction(ft) 8.80 10.17

Critical Velocity (ft/s) 6.84 7.01 Average Velocity Upstream (ft/s) 9.97 10.04

Scour Condition Live Bed Live Bed Contraction Scour Depth (ft) 2.89 4.24 Long Term Degradation (ft) 1.0 1.0

Total Scour (ft) 3.89 5.24 Channel Thalweg Elevation (ft) 7521.5 7521.5 Potential Scour Elevation (ft) 7517.6 7516.3

Abutment scour was estimated using the NCHRP 24-20 method which applies an amplification factor to the contraction scour at the abutments, i.e. it includes contraction scour at each abutment as part of the estimate. The estimated 100-year abutment scour depths were 2.71 feet and 2.26 feet for the left and right abutments, respectively. The estimated 200-year abutment scour depths were 4.0 feet and 3.44 feet for the left and right abutments, respectively. Since the abutment scour depths are shallower than the contraction scour depths. It is recommended that the scour elevations shown in Table 18 are used in the design of the bridge foundations. Additional details of the scour assessment are included in Appendix B.

5 SUMMARY OF RESULTS

Hydrology and hydraulics analyses were conducted for the Buffalo Crossing Bridge project as discussed in the preceding sections. Table 19 shows the that the proposed low chord elevation satisfies both FLH PDDM criteria and USFS TSH freeboard criteria.

Table 19: Summary of Bridge Freeboard Results

Design Criteria

Hydraulic Capacity Design

Frequency

Bridge Waterway

Width (ft)

Minimum Freeboard

(ft)

Maximum WSEL 36-feet Upstream (ft)

Proposed Low Chord

Elevation (ft)

Provided Freeboard (ft)

FLH PDDM 50-year 88 2 7,530.4 7,534.8

4.4

USFS TSH 100-year 88 3 7,531.8 3.0

Page 20 AZ FS 24(1) Buffalo Crossing – Hydraulic Report

6 REFERENCES

Aquaveo. 2019. Surface-water Modeling System (SMS), version 13.0.5. Provo, UT.

Federal Highway Administration . 2009. "Bridge Scour and Stream Instability Countermeasures - Experience, Selection, and Design Guidelines, Hydraulic Engineering Circular No. 23, Third Edition, FHWA-NHI 09-111 (Vol. 1), FHWA-NHI-09-112 (Vol. 2)." Federal Highway Administration, Washington, DC.

Federal Highway Administration. 2012. "Evaluating Scour at Bridges, Hydraulic Engineering Circular No.

18, Fifth Edition, FHWA-HIF-12-003." Washington D.C.

Federal Highway Administration. 2017. HY-8 Culvert Analysis Program. Version 7.50.

Federal Lands Highway. 2012. "Project Development and Design Manual, Chapter 7 Hydrology and Hydraulics." https://flh.fhwa.dot.gov/resources/design/pddm/.

Lewis, Jason M. 2010. "Methods for Estimating the Magnitude and Frequency of Peak Streamflows for Unregulated Streams in Oklahoma." U.S. Geological Survey Scientific Investigations Report 2010- 5137. https://pubs.usgs.gov/sir/2010/5137/.

Multi-Resolution Land Characteristics Consortium . 2018. National Land Cover Database 2011 (NLCD 2011). Multi-Resolution Land Characteristics Consortium (MRLC).

https://data.nal.usda.gov/dataset/national-land-cover-database-2011-nlcd-2011.

National Oceanic and Atmospheric Administration. 2011. Precipitation Frequency Data Server (PFDS).

Silver Springs, MD. Accessed April 2019. https://hdsc.nws.noaa.gov/hdsc/pfds/index.html.

Natural Resources Conservation Service. 1997. "National Engineering Handbook, Part 630 Hydrology."

Washington, DC. https://directives.sc.egov.usda.gov/viewerFS.aspx?hid=21422.

Natural Resources Conservation Service. 2015. Soil Survey Geographic (SSURGO) database. Fort Worth, TX. Accessed April 2019. http://websoilsurvey.nrcs.usda.gov.

New Mexico Department of Transportation. 2018. "Drainage Design Manual."

https://dot.state.nm.us/content/dam/nmdot/Infrastructure/Drain_Design_Manual.pdf.

Paretti, Nicholas V., Jeffery R. Kennedy, Lovina A. Turney, and Andrea G. Veilleux. 2014. Methods for estimating magnitude and frequency of floods in Arizona, developed with unregulated and rural peak-flow data through water year 2010. Scientific Investigaitons Report 2014-5211, U.S.

Geological Survey. https://doi.org/10.3133/sir20145211.

Perica, Sanja, Deborah Martin, Sandra Pavlovic, Ishani Roy, Michael St. Laurent, Carl Trypaluk, Dale Unruh, Michael Yekta, and Geoffrey Bonnin. 2013. "Precipitation Frequency Atlas of the United States Volume 8 Version 2.0: Midwestern States (Colorado, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, Oklahoma, South Dakota, Wisconsin)." NOAA Atlas 14, Silver Spring, MD.

Page 21 AZ FS 24(1) Buffalo Crossing – Hydraulic Report

Perica, Sanja, Sarah Dietz, Sarah Heim, Lillian Hiner, Kazungu Maitaria, Deborah Martin, Sandra Pavlovic, et al. 2011. "Precipitation Frequency Atlas of the United States Volume 1 Version 5.0: Semiarid Southwest (Arizona, Southeast California, Nevada, New Mexico, Utah)." NOAA Atlas 14, Silver Spring, MD.

U.S. Army Corps of Engineers. 2017. HEC-HMS, Hydrologic Engineering Center Hydrologic Modeling System. Version 4.2.1. Davis, CA.

U.S. Bureau of Reclamation. 2017. SRH-2D, Sedimentation and River Hydraulics – Two-Dimensional model.

Version 3.2.

U.S. Forest Service. 2014. "Transportation Structures Handbook." FSH 7709.56b.

U.S. Geological Survey. 2016. StreamStats Program. http://streamstats.usgs.gov.

U.S. Geological Survey. 2018. The National Map. Accessed March 2019.

https://viewer.nationalmap.gov/advanced-viewer/.

Waltenmeyer, Scott 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.

AZ FS 24(1) Buffalo Crossing – Hydraulic Report

Appendix A – Hydrologic Analyses

StreamStats Information

2/19/2020 StreamStats https://streamstats.usgs.gov/ss/ 1/7

Buffalo Crossing Bridge - AZ FS 24(1)

Basin Characteristics

Parameter Code Parameter Description Value Unit

CONTDA Area that contributes flow to a point on a stream 111.53 square miles

ELEV Mean Basin Elevation 8802.264 feet

PRECIP Mean Annual Precipitation 28.1 inches

FD_Region FD_Region 1623 dimensionless

APRAVTMP Mean AprilTemperature 38.9 degrees F

AUGAVPRE Mean August Precipitation 4.4 inches

AUGAVTMP Mean August Temperature 57.2 degrees F

Region ID: AZ Workspace ID: AZ20200219155230179000 Clicked Point (Latitude, Longitude): 33.76106, -109.35701 Time: 2020-02-19 08:52:37 -0700 https://streamstats.usgs.gov/ss/ 2/7

Parameter Code Parameter Description Value Unit

AZ_HIPERMA Percent basin surface area containing high permeability aquifer units as defined for Arizona in SIR 2014-5211

94 percent

AZ_HIPERMG Percent basin surface area containing high permeability geologic units as defined for Arizona in SIR 2014-5211

94 percent

BASINPERIM Perimeter of the drainage basin as defined in SIR 2004-5262

91.31 miles

BSLDEM10M Mean basin slope computed from 10 m DEM 13.55 percent

CH92_01DEV Percent Difference between 1992 and 2001 area covered by developed land using NLCD

0 percent

CH92_01FOR Percent Difference between 1992 and 2001 area covered by forest using NLCD

-3 percent

DECAVPRE Mean December Precipitation 2.4 inches

DRNAREA Area that drains to a point on a stream 111.53 square miles

DRNDENSITY Basin drainage density defined as total stream length divided by drainage area.

2.21 dimensionless

EL5000 Percent of area above 5000 ft 100 percent

EL6000 Percent of area above 6000 ft 100 percent

EL7500 Percent of area above 7500 ft 100 percent

ELEVMAX Maximum basin elevation 9765.67 feet

FEBAVPRE Mean February Precipitation 2.4 inches

IMPNLCD01 Percentage of impervious area determined from NLCD 2001 impervious dataset

0 percent

JANAVPRE Mean January Precipitation 2.5 inches

JULAVPRE Mean July Precipitation 3.4 inches

JULYAVTMP Mean July Temperature 59.1 degrees F

JUNAVPRE Mean June Precipitation 0.8 inches

JUNEAVTMP Mean June Temperature 55.6 degrees F

LAT_CENT Latitude of Basin Centroid 33.878 decimal degrees

LC01BARE Percentage of area barren land, NLCD 2001 category 31

0 percent https://streamstats.usgs.gov/ss/ 3/7

Parameter Code Parameter Description Value Unit

LC01DEV Percentage of land-use from NLCD 2001 classes 21-24

0 percent

LC01FOREST Percentage of forest from NLCD 2001 classes 41-

67 percent

LC01HERB Percentage of herbaceous upland from NLCD 2001 class 71

32 percent

LC92FOREST Percentage of forest from NLCD 1992 classes 41-

70 percent

LONG_CENT Longitude Basin Centroid -109.3265 decimal degrees

LU92DEV Percent of area covered by all densities of developed land using 1992 NLCD

0 percent

MARAVPRE Mean March Precipitation 2.6 inches

MARAVTMP Mean March Temperature 33.4 degrees F

MAYAVPRE Mean May Precipitation 0.9 inches

MAYAVTMP Mean May Temperature 46.8 degrees F

MINBELEV Minimum basin elevation 7520.81 feet

NFSL30_10M Percent area with north-facing slopes greater than 30 percent from 10-meter NED.

3 percent

NOVAVPRE Mean November Precipitation 2.3 inches

NOVAVTMP Mean November Temperature 33.9 degrees F

OCTAVPRE Mean October Precipitation 2.6 inches

OCTAVTMP Mean October Temperature 43.2 degrees F

OUTLETELEV Elevation of the stream outlet in thousands of feet above NAVD88.

7520.81 feet

RELIEF Maximum - minimum elevation 2244.86 feet

RELRELF Basin relief divided by basin perimeter 24.59 feet per mi

SEPAVPRE Mean September Precipitation 2.5 inches

SEPAVTMP Mean September Temperature 52.4 degrees F

SLOP30_10M Percent area with slopes greater than 30 percent from 10-meter NED

9 percent

STRMTOT total length of all mapped streams (1:24,000-scale) in the basin

246.09 miles https://streamstats.usgs.gov/ss/ 4/7

Parameter Code Parameter Description Value Unit

TEMP Mean Annual Temperature 42.08 degrees F

Peak-Flow Statistics Parameters[Peak Region 1 High Elev 2014 5211]

Parameter Code Parameter Name Value Units Min Limit Max Limit

CONTDA Contributing Drainage Area

111.53 square miles 1.26 711

ELEV Mean Basin Elevation 8802.264 feet

Peak-Flow Statistics Flow Report[Peak Region 1 High Elev 2014 5211]

PIl: Prediction Interval-Lower, PIu: Prediction Interval-Upper, SEp: Standard Error of Prediction, SE:

Standard Error (other -- see report)

Statistic Value Unit PIl PIu SEp

2 Year Peak Flood 382 ft^3/s 110 1320 86.1

5 Year Peak Flood 801 ft^3/s 301 2140 64.4

10 Year Peak Flood 1180 ft^3/s 479 2900 58.2

25 Year Peak Flood 1780 ft^3/s 755 4180 55

50 Year Peak Flood 2310 ft^3/s 982 5440 55.1

100 Year Peak Flood 2910 ft^3/s 1220 6970 56.3

200 Year Peak Flood 3620 ft^3/s 1470 8920 58.5

500 Year Peak Flood 4700 ft^3/s 1810 12200 62.7

Peak-Flow Statistics Citations

Paretti, N.V., Kennedy, J.R., Turney, L.A., and Veilleux, A.G.,2014, Methods for estimating magnitude and frequency of floods in Arizona, developed with unregulated and rural peak-flow data through water year 2010: U.S. Geological Survey Scientific Investigations Report 2014-5211, 61 p., http://dx.doi.org/10.3133/sir20145211.

(http://pubs.usgs.gov/sir/2014/5211/)

Flood-Volume Statistics Parameters[100 Percent (111 square miles) Central highland MeanMax flows 2014 5109] http://pubs.usgs.gov/sir/2014/5211/ https://streamstats.usgs.gov/ss/ 5/7

Parameter Code Parameter Name Value Units

Min Limit

Max Limit

Parameter Code Parameter Name Value Units

Min Limit

Max Limit

CONTDA Contributing Drainage Area

111.53 square miles 1.1 7890

PRECIP Mean Annual Precipitation 28.1 inches 13.9 36.7

ELEV Mean Basin Elevation 8802.264 feet 2240 9520

FD_Region FD_Region 1623 dimensionless

Flood-Volume Statistics Flow Report[100 Percent (111 square miles) Central highland MeanMax flows 2014 5109]

PIl: Prediction Interval-Lower, PIu: Prediction Interval-Upper, SEp: Standard Error of Prediction, SE:

Standard Error (other -- see report)

Statistic Value Unit SEp

1 Day 2 Year Maximum 254 ft^3/s 50.8

1 Day 5 Year Maximum 591 ft^3/s 43.7

1 Day 10 Year Maximum 1030 ft^3/s 40.6

1 Day 25 Year Maximum 1950 ft^3/s 37

1 Day 50 Year Maximum 2780 ft^3/s 36.4

1 Day 100 Year Maximum 3790 ft^3/s 36.7

1 Day 200 Year Maximum 4980 ft^3/s 37.8

1 Day 500 Year Maximum 6630 ft^3/s 37.7

3 Day 2 Year Maximum 271 ft^3/s 52.3

3 Day 5 Year Maximum 433 ft^3/s 43.5

3 Day 10 Year Maximum 642 ft^3/s 40.4

3 Day 25 Year Maximum 937 ft^3/s 40.3

3 Day 50 Year Maximum 1240 ft^3/s 39.3

3 Day 100 Year Maximum 1580 ft^3/s 39.9

3 Day 200 Year Maximum 1960 ft^3/s 40.6

3 Day 500 Year Maximum 2750 ft^3/s 35.3

7 Day 2 Year Maximum 185 ft^3/s 52.9

7 Day 5 Year Maximum 322 ft^3/s 42.7

7 Day 10 Year Maximum 396 ft^3/s 36.1

7 Day 25 Year Maximum 547 ft^3/s 34.9

7 Day 50 Year Maximum 666 ft^3/s 32.6 https://streamstats.usgs.gov/ss/ 6/7

Statistic Value Unit SEp

7 Day 100 Year Maximum 832 ft^3/s 33.1

7 Day 200 Year Maximum 1010 ft^3/s 33.6

7 Day 500 Year Maximum 1260 ft^3/s 35.2

15 Day 2 Year Maximum 134 ft^3/s 51.3

15 Day 5 Year Maximum 223 ft^3/s 40.4

15 Day 10 Year Maximum 298 ft^3/s 36.4

15 Day 25 Year Maximum 389 ft^3/s 34.9

15 Day 50 Year Maximum 475 ft^3/s 32.6

15 Day 100 Year Maximum 559 ft^3/s 32

15 Day 200 Year Maximum 652 ft^3/s 31.6

15 Day 500 Year Maximum 812 ft^3/s 28.6

30 Day 2 Year Maximum 99.4 ft^3/s 49.5

30 Day 5 Year Maximum 224 ft^3/s 42.7

30 Day 10 Year Maximum 233 ft^3/s 38.2

30 Day 25 Year Maximum 302 ft^3/s 36.6

30 Day 50 Year Maximum 358 ft^3/s 34.1

30 Day 100 Year Maximum 423 ft^3/s 32.6

30 Day 200 Year Maximum 483 ft^3/s 31.2

30 Day 500 Year Maximum 595 ft^3/s 27.1

Flood-Volume Statistics Citations

Kennedy, J.R., Paretti, N.V., and Veilleux, A.G.,2014, Methods for estimating magnitude and frequency of 1-, 3-, 7-, 15-, and 30-day flood-duration flows in Arizona: U.S. Geological Survey Scientific Investigations Report 2014–5109, 35 p.

(http://pubs.usgs.gov/sir/2014/5109/)

USGS Data Disclaimer: Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data for other purposes, nor on all computer systems, nor shall the act of distribution constitute any such warranty.

http://pubs.usgs.gov/sir/2014/5109/ https://streamstats.usgs.gov/ss/ 7/7

USGS Software Disclaimer: This software has been approved for release by the U.S. Geological Survey (USGS). Although the software has been subjected to rigorous review, the USGS reserves the right to update the software as needed pursuant to further analysis and review. No warranty, expressed or implied, is made by the USGS or the U.S. Government as to the functionality of the software and related material nor shall the fact of release constitute any such warranty. Furthermore, the software is released on condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from its authorized or unauthorized use.

USGS Product Names Disclaimer: Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

Application Version: 4.3.11

Precipitation Frequency Data Server Information

7/27/2020 Precipitation Frequency Data Server https://hdsc.nws.noaa.gov/hdsc/pfds/pfds_printpage.html?lat=33.8780&lon=-109.3265&data=depth&units=english&series=pds 1/4

NOAA Atlas 14, Volume 1, Version 5 Location name: Eagar, Arizona, USA*

Latitude: 33.878°, Longitude: -109.3265° Elevation: 8754.64 ft**

* source: ESRI Maps ** source: USGS

POINT PRECIPITATION FREQUENCY ESTIMATES

Sanja Perica, Sarah Dietz, Sarah Heim, Lillian Hiner, Kazungu Maitaria, Deborah Martin, Sandra Pavlovic, Ishani Roy, Carl Trypaluk, Dale Unruh, Fenglin Yan, Michael Yekta, Tan Zhao, Geoffrey

Bonnin, Daniel Brewer, Li-Chuan Chen, Tye Parzybok, John Yarchoan

NOAA, National Weather Service, Silver Spring, Maryland

PF_tabular | PF_graphical | Maps_&_aerials

PF tabular PDS-based point precipitation frequency estimates with 90% confidence intervals (in inches)1

Duration Average recurrence interval (years)

1 2 5 10 25 50 100 200 500 1000

5-min 0.280 (0.243‑0.322)

0.358 (0.311‑0.412)

0.463 (0.402‑0.531)

0.540 (0.466‑0.619)

0.643 (0.550‑0.734)

0.719 (0.612‑0.823)

0.797 (0.672‑0.914)

0.874 (0.730‑1.01)

0.974 (0.800‑1.14)

1.06 (0.855‑1.25)

10-min 0.426 (0.370‑0.491)

0.544 (0.473‑0.627)

0.705 (0.611‑0.808)

0.822 (0.710‑0.941)

0.978 (0.837‑1.12)

1.09 (0.931‑1.25)

1.21 (1.02‑1.39)

1.33 (1.11‑1.54)

1.48 (1.22‑1.73)

1.61 (1.30‑1.90)

15-min 0.528 (0.459‑0.609)

0.675 (0.586‑0.777)

0.874 (0.758‑1.00)

1.02 (0.880‑1.17)

1.21 (1.04‑1.38)

1.36 (1.15‑1.55)

1.50 (1.27‑1.73)

1.65 (1.38‑1.90)

1.84 (1.51‑2.14)

1.99 (1.61‑2.35)

30-min 0.710 (0.618‑0.820)

0.908 (0.790‑1.05)

1.18 (1.02‑1.35)

1.37 (1.18‑1.57)

1.63 (1.40‑1.86)

1.83 (1.55‑2.09)

2.02 (1.71‑2.32)

2.22 (1.86‑2.56)

2.47 (2.03‑2.89)

2.68 (2.17‑3.17)

60-min 0.879 (0.765‑1.01)

1.12 (0.977‑1.30)

1.46 (1.26‑1.67)

1.70 (1.47‑1.95)

2.02 (1.73‑2.31)

2.26 (1.92‑2.59)

2.51 (2.11‑2.88)

2.75 (2.30‑3.17)

3.06 (2.51‑3.57)

3.32 (2.69‑3.92)

2-hr 0.985 (0.852‑1.14)

1.25 (1.08‑1.43)

1.60 (1.39‑1.84)

1.89 (1.62‑2.16)

2.27 (1.95‑2.61)

2.58 (2.18‑2.96)

2.90 (2.43‑3.33)

3.22 (2.68‑3.72)

3.66 (2.99‑4.26)

4.02 (3.24‑4.71)

3-hr 1.05 (0.922‑1.21)

1.33 (1.16‑1.52)

1.68 (1.47‑1.93)

1.97 (1.71‑2.26)

2.38 (2.04‑2.72)

2.70 (2.30‑3.10)

3.04 (2.56‑3.50)

3.39 (2.81‑3.92)

3.88 (3.15‑4.52)

4.28 (3.42‑5.02)

6-hr 1.29 (1.14‑1.48)

1.61 (1.42‑1.85)

2.01 (1.76‑2.31)

2.35 (2.05‑2.70)

2.83 (2.45‑3.25)

3.22 (2.76‑3.71)

3.64 (3.07‑4.20)

4.07 (3.38‑4.71)

4.66 (3.79‑5.45)

5.14 (4.11‑6.06)

12-hr 1.58 (1.39‑1.82)

1.98 (1.73‑2.28)

2.45 (2.14‑2.82)

2.85 (2.48‑3.28)

3.42 (2.94‑3.95)

3.87 (3.30‑4.47)

4.34 (3.67‑5.04)

4.84 (4.03‑5.65)

5.54 (4.52‑6.54)

6.09 (4.89‑7.25)

24-hr 1.67 (1.52‑1.85)

2.07 (1.88‑2.29)

2.54 (2.31‑2.85)

2.92 (2.64‑3.32)

3.43 (3.09‑3.99)

3.91 (3.44‑4.52)

4.39 (3.78‑5.09)

4.89 (4.12‑5.71)

5.60 (4.57‑6.60)

6.15 (4.90‑7.32)

2-day 2.04 (1.84‑2.25)

2.53 (2.29‑2.79)

3.10 (2.81‑3.42)

3.57 (3.23‑3.94)

4.21 (3.79‑4.64)

4.71 (4.22‑5.19)

5.21 (4.65‑5.75)

5.73 (5.08‑6.33)

6.42 (5.64‑7.13)

6.96 (6.07‑7.77)

3-day 2.25 (2.04‑2.49)

2.79 (2.53‑3.09)

3.44 (3.11‑3.79)

3.96 (3.57‑4.37)

4.66 (4.19‑5.14)

5.21 (4.67‑5.75)

5.78 (5.14‑6.38)

6.35 (5.62‑7.03)

7.12 (6.24‑7.91)

7.72 (6.71‑8.62)

4-day 2.46 (2.23‑2.73)

3.06 (2.77‑3.39)

3.77 (3.40‑4.16)

4.34 (3.91‑4.79)

5.12 (4.59‑5.64)

5.72 (5.11‑6.31)

6.34 (5.64‑7.01)

6.97 (6.16‑7.72)

7.82 (6.85‑8.70)

8.47 (7.36‑9.47)

7-day 2.97 (2.70‑3.29)

3.69 (3.35‑4.08)

4.51 (4.08‑4.98)

5.17 (4.68‑5.71)

6.07 (5.47‑6.70)

6.76 (6.07‑7.47)

7.47 (6.67‑8.26)

8.19 (7.27‑9.08)

9.16 (8.05‑10.2)

9.90 (8.62‑11.1)

10-day 3.43 (3.13‑3.80)

4.24 (3.87‑4.69)

5.15 (4.70‑5.69)

5.90 (5.36‑6.51)

6.91 (6.25‑7.63)

7.69 (6.94‑8.49)

8.50 (7.62‑9.38)

9.31 (8.30‑10.3)

10.4 (9.17‑11.6)

11.2 (9.82‑12.5)

20-day 4.68 (4.25‑5.16)

5.78 (5.24‑6.37)

6.96 (6.30‑7.67)

7.89 (7.14‑8.69)

9.13 (8.23‑10.0)

10.1 (9.03‑11.1)

11.0 (9.83‑12.1)

11.9 (10.6‑13.1)

13.1 (11.6‑14.5)

14.0 (12.3‑15.6)

30-day 5.79 (5.29‑6.33)

7.15 (6.53‑7.82)

8.55 (7.80‑9.35)

9.62 (8.77‑10.5)

11.0 (10.0‑12.0)

12.0 (10.9‑13.1)

13.0 (11.8‑14.2)

13.9 (12.6‑15.3)

15.1 (13.6‑16.6)

16.0 (14.3‑17.6)

45-day 7.19 (6.61‑7.82)

8.87 (8.14‑9.63)

10.5 (9.67‑11.4)

11.8 (10.8‑12.8)

13.3 (12.2‑14.5)

14.4 (13.2‑15.7)

15.5 (14.1‑16.9)

16.5 (15.0‑18.0)

17.7 (16.0‑19.4)

18.5 (16.7‑20.4)

60-day 8.40 (7.72‑9.14)

10.4 (9.54‑11.3)

12.3 (11.3‑13.4)

13.7 (12.6‑15.0)

15.5 (14.2‑16.9)

16.7 (15.3‑18.2)

17.9 (16.3‑19.5)

18.9 (17.3‑20.7)

20.2 (18.4‑22.2)

21.1 (19.1‑23.2)

1 Precipitation frequency (PF) estimates in this table are based on frequency analysis of partial duration series (PDS).

Numbers in parenthesis are PF estimates at lower and upper bounds of the 90% confidence interval. The probability that precipitation frequency estimates (for a given duration and average recurrence interval) will be greater than the upper bound (or less than the lower bound) is 5%. Estimates at upper bounds are not checked against probable maximum precipitation (PMP) estimates and may be higher than currently valid PMP values.

Please refer to NOAA Atlas 14 document for more information.

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PF graphical https://www.commerce.gov/ http://www.noaa.gov/ https://hdsc.nws.noaa.gov/hdsc/pfds/pfds_printpage.html?lat=33.8780&lon=-109.3265&data=depth&units=english&series=pds 2/4

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Maps & aerials

Small scale terrain https://hdsc.nws.noaa.gov/hdsc/pfds/pfds_printpage.html?lat=33.8780&lon=-109.3265&data=depth&units=english&series=pds 3/4

Large scale terrain

Large scale map

Large scale aerial

3km

2mi

100km

60mi

100km

60mi https://hdsc.nws.noaa.gov/hdsc/pfds/pfds_printpage.html?lat=33.8780&lon=-109.3265&data=depth&units=english&series=pds 4/4

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Disclaimer

100km

60mi https://www.commerce.gov/ http://www.noaa.gov/ http://www.nws.noaa.gov/ http://www.nws.noaa.gov/oh/ mailto:HDSC.Questions@noaa.gov http://www.nws.noaa.gov/disclaimer.html

FEMA FIRM Information

7/29/2020 FLH Hydraulics Project Scoping https://fhwapolicy.maps.arcgis.com/home/webmap/print.html 1/1

Airbus,USGS,NGA,NASA,CGIAR,NCEAS,NLS,OS,NMA,Geodatastyrelsen,GSA,GSI and the GIS User Community | Source: USGS; NOAA; and the GIS Community | Source: USDA NRCS, Esri | Copyright:© 2013 National Geographic Society, i-cubed | Esri | USGS TNM – National Hydrography Dataset. Data

Refreshed July, 2020. | USGS WBD - Watershed Boundary Dataset. Data refreshed July, 2020. | National Geographic, Esri, Garmin, HERE, UNEP-WCMC, USGS, NASA, ESA, METI, NRCAN, GEBCO, NOAA, increment P Corp.

FLH Hydraulics Project Scoping

NFHL

FIRM Panels

Political Jurisdictions

Flood Hazard Zones 1% Annual Chance Flood Hazard

Regulatory Floodway

Special Floodway

Area of Undetermined Flood Hazard 0.2% Annual Chance Flood Hazard Future Conditions 1% Annual Chance Flood Hazard Area with Reduced Risk Due to Levee

0.6mi

USGS NWIS Information

HEC-HMS Information

Basin Model:

Input Parameters:

Results:

Appendix B - Existing Condition Hydraulic Analyses

Selected SRH-2D Information – Existing Conditions

Scatter Data (Topographic Surface)

Selected SRH-2D Information – Existing Conditions (cont.)

SRH-2D Computational Mesh

Materials (Manning’s Roughness)

Existing Conditions Profile Baseline and Reference Stations

Existing Conditions Water Surface Profile

200-year

Hydraulic Results Tables for Selected Return Periods

2 Year Q= 670 CFS

Profile Station Shear Stress (lb/ft2) Froude Velocity (ft/s) Depth (ft) WSEL (ft) Ave Max Ave Max Ave Max Ave Max Ave Max

0 0.86 1.42 0.66 0.81 5.02 7.72 2.00 3.25 7522.26 7522.31 100 1.47 3.98 0.67 1.08 4.73 7.93 1.48 3.07 7523.33 7523.57 200 0.65 1.16 0.61 1.88 4.35 6.76 1.97 3.27 7524.57 7524.91 300 0.59 1.15 0.47 0.72 3.41 7.02 1.68 3.40 7525.14 7525.20 400 0.98 1.27 0.62 0.79 5.04 7.37 2.09 3.62 7525.89 7525.95

50 Year Q= 4800 CFS

Profile Station Shear Stress (lb/ft2) Froude Velocity (ft/s) Depth (ft) WSEL (ft)

Ave Max Ave Max Ave Max Ave Max Ave Max 0 1.97 2.85 0.74 1.28 8.44 12.74 4.79 7.79 7526.71 7526.99

100 3.37 11.55 0.52 0.87 6.92 11.93 5.22 8.00 7528.16 7528.55 200 2.38 9.08 0.69 0.92 9.09 11.71 5.95 7.92 7529.31 7530.12 300 1.12 2.82 0.39 0.66 4.83 10.03 5.05 8.83 7530.60 7530.78 400 1.88 4.06 0.50 0.85 6.00 10.42 5.19 8.84 7531.06 7531.21

100 Year Q= 6310 CFS

Shear Stress (lb/ft2) Froude Velocity (ft/s) Depth (ft) WSEL (ft) Ave Max Ave Max Ave Max Ave Max Ave Max

0 2.42 3.43 0.77 1.23 9.44 14.08 5.19 8.63 7527.47 7527.84 100 4.04 14.46 0.53 0.88 7.55 13.08 6.06 9.07 7529.22 7529.67 200 2.25 9.48 0.64 0.87 8.06 12.21 5.97 9.31 7530.85 7532.02 300 1.12 3.05 0.35 0.62 4.85 10.20 5.88 10.27 7532.02 7532.24 400 1.54…