AZ NFSR 289 Tonto Creek Bridge Final Hydraulics Tech Memo.pdf

TABLE OF CONTENTS

I. PROJECT DESCRIPTION AND LOCATION

A. LOCATION AND DESCRIPTION

II. DRAINAGE BASINS

A. MAJOR BASINS

B. MINOR BASINS

III. DRAINAGE DESIGN CRITERIA

A. GENERAL CRITERIA

B. HYDAULIC CRITERIA

IV. DRAINAGE FACILITY DESIGN

A. HYDROLOGY

B. HYDRAULICS

Modeling Considerations Modeling Results

C. SCOUR AND BANK PROTECTION

V. REFERENCES

Figures 1 Bridge Aerial 1 2 Site Photographs 2 3 Project Location Map 3 4 Tonto Creek Basin 4 5 HEC-RAS 2D Existing Condition Model Mesh 8 6 Tonto Creek Bridge Section Plot Showing 30% Blockage 11 7 Tonto Creek Flow Profiles 11

Tables 1 Hydraulic Criteria 5 2 Basin Properties 6 3 Peak Discharges (cfs) 6 4 Manning’s n Roughness 9 5 HEC-RAS Hydraulic Results 10

Appendix A Existing Bridge Plan B USGS StreamStats Report for Tonto Creek Bridge C FEMA FIRMette Map 04007C0278D effective 12/04/2007 D Manning’s ‘n’ Calculation E HEC-RAS Output F Riprap Sizing Calculations (HEC-23) G Proposed Bridge Plan

I. PROJECT DESCRIPTION AND LOCATION

A. LOCATION AND DESCRIPTION

The FS 289 crossing of Tonto Creek is immediately downstream of the confluence with Horton Creek and is the site of the Horton Creek trailhead. Tonto Creek flows southerly, terminating at the Salt River at Theodore Roosevelt Lake. Figure 1 shows aerial imagery of the bridge site.

Figure 1 – Bridge Aerial

The existing bridge was built in 1956 and is a cast-in-place slab deck supported by stacked stone abutments and pier with mortar atop a concrete sill tied into bedrock. Refer to Appendix A for the existing bridge plan. Photographs from the site showing the bridge and general condition of the channel are included in Figure 2.

This project is located within the Tonto National Forest in Gila County, Arizona, at the Tonto Creek crossing at Forest Service Road 289. The project location lies north of Kohls Ranch, northeast of Payson, AZ. Access to the project is by AZ State Route 260 to Forest Service Road 289, also known as Zane Gray Highway. The project location is at Latitude 34°20'23.7"N, Longitude 111°05'44.8"W, as shown in Figure 3.

1: Bridge facing downstream, south 2: Bridge facing upstream, northwest

3: Roadway facing east-southeast 4: Channel facing upstream, northwest

Figure 2 – Site Photographs

Figure 3 – Project Location Map

II. DRAINAGE BASINS

A. MAJOR BASINS

The contributing drainage basin has an area of 13.3 square miles (mi2), a mean elevation of 6,748 feet, and a mean annual precipitation of 36.1 inches as documented in the StreamStats Report for the Tonto Creek watershed included in Appendix B. The watershed is largely forested and undeveloped with the exception of a cleared power line corridor bisecting the basin. The watershed is located along the Mogollon Rim which forms the boundary between Coconino and Gila Counties. See Figure 4 for watershed delineation.

Figure 4 – Tonto Creek Basin

B. MINOR BASINS

No minor basins were identified in this drainage analysis.

III. DRAINAGE DESIGN CRITERIA

A. GENERAL CRITERIA

Drainage criteria for the Tonto Creek bridge project is based on the guidelines outlined in Federal Highway Administration (FHWA) Hydraulic Design Series and United States Forest Service (USFS) Transportation Structures Handbook (TSH). Other criteria defaults to the Federal Lands Highway Project Development and Design Manual (PDDM).

B. HYDAULIC CRITERIA

Hydraulic design criteria for the project were obtained from both the TSH and the PDDM. FS 289 road is classified as low standard for hydraulic design purpose according to the PDDM, and the applicable criteria are listed in Table 1.

The project site is not located within a regulatory floodplain delineation by the Federal Emergency Management Agency (FEMA) as shown in the Flood Insurance Rate Map (FIRM) panel 04007C0278D effective 12/04/2007. A FEMA FIRMette map showing the project site is included in Appendix C.

TABLE 1 - HYDRAULIC CRITERIA

Bridge Design Standards

Design Frequency Check Frequency Freeboard

100-year flood (TSH 14.1.9a.10d, TSH 62.2)

N/A

>3-feet recommended + debris consideration

(TSH 62.2)

Resiliency check for 30-50% debris blockage

(TSH 62.2)

50-year flood

(PDDM 7.4.3.3.1)

Greater of 100-year flood or overtopping flood

3.5-feet minimum due to potential for woody debris

(PDDM 7.4.3.4.1)

Scour

(PDDM

7.4.3.3.2)

Design Frequency Check Frequency Countermeasure Design

Frequency

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

Floodplain Encroachment

FEMA SFHA Involvement Allowable Rise

Project outside of FEMA regulated Special Flood Hazard Area (SFHA)

1-foot maximum rise over existing condition

IV. DRAINAGE FACILITY DESIGN

A. HYDROLOGY

Following discussion with US Forest Service and FHWA staff, hydrologic analysis consisted of applying peak discharge estimates obtained from USGS StreamStats web application (U.S.

Geological Survey 2015) at a point immediately downstream of the subject bridge along Tonto Creek (see Appendix B).

A review of the USGS National Weather Water Information System (NWIS) found there are no comparable, active USGS peak streamflow stations within the project limits or nearby. The nearest active station is East Verde River Diversion from East Clear Creek near Pine, AZ, ID 09507580 which is approximately 10 miles to the west-northwest and does not include peak streamflow measurements as it is a Salt River Project (SRP) pumping operation. There is also a stream gage along Tonto Creek significantly downstream of the subject bridge at a drainage area of 675 mi²; Tonto Creek Above Gun Creek, near Roosevelt, AZ, ID 09499000.

Basin properties as reported by StreamStats are summarized in Table 2.

TABLE 2 – BASIN PROPERTIES

Site

Drainage Area (mi²)

Mean Basin

Elevation (ft)

Mean Basin Slope

Mean Annual Precip

(in)

Tonto Creek Bridge 13.3 6,748 33.5 36.1

Tonto Creek Upstream 6.8 6,750 31.8 35.7

Horton Creek Upstream 6.5 6,748 35.4 36.6

The peak flow result for a 100-year event for the project basin is 7,610 cubic feet per second (cfs). Table 3 shows the peak streamflow estimates for the bridge location.

TABLE 3 – PEAK DISCHARGES (CFS)

Return Period Tonto Creek Bridge

2-year 305

50-year 5,240

100-year 7,610

200-year 10,500

B. HYDRAULICS

Flow in Tonto Creek was modeled using US Army Corps of Engineers HEC-RAS River Analysis System version 6.6 applying an unsteady, 2D hydraulic analysis. Analyses were conducted to determine estimates of water surface elevations, freeboard, capacity, and impacts of debris accumulation. The 2D modeling option was used for all modeling.

Modeling Considerations

Model Scenarios

Three conditions were modeled: Existing, Proposed, and Proposed with partial debris blockage.

Main channel conveyance performance was assessed under 2-year, 50-year, 100-year, and 200-year design storm events with the blockage scenario applied to the 100-year design storm hydrology.

For the proposed condition, it was assumed that the existing bridge, pier, and existing bridge abutments will be removed with no channel grading proposed to the channel profile. Refer to the bridge plans in Appendix F for the proposed bank grading and bridge geometry.

As a resiliency measure for the proposed bridge, an analysis was performed considering blockage of conveyance area through the bridge opening due to the potential accumulation of woody debris. Per design guidance, blockage from runoff debris is typically estimated for 30% to 50% of the channel flow area. From field observations, it appeared that a minimum 30% blockage would be appropriate based on professional judgement and understanding the general size and condition of forest in the basin.

Topography

Topography was obtained from December 2023 LiDAR in TIFF raster format performed by Cooper Aerial Surveys Company. The data was provided as 1-foot topological contours, so the vertical accuracy is understood to be nominally 6-inches. This LiDAR data set is the basis of the existing conditions model terrain prepared in RASMapper. The proposed condition terrain is the existing terrain with the existing bridge abutments removed, but no other modifications of the channel bottom width, alignment, or elevation. Topographic elevations were provided in feet North American Vertical Datum of 1988 (NAVD88) and in feet North American Datum of 1983 (NAD83) State Plane Arizona East.

Model Geometry

The modeling domain was defined with a target cell spacing of 15 feet, although HEC-RAS supports an adaptive grid generation with variable individual grid sizes conforming to 2D breaklines defined along prominent linear topographic features including channel banks, channel flowlines, roadways and ridges in the vicinity of the existing and proposed bridges.

Figure 5 shows the computational mesh used for existing condition scenarios overlayed onto the LiDAR terrain.

The loss of conveyance due to accumulated debris was implemented by constricting the bridge’s upstream 1D cross section from both left and right banks such that the excluded flow area gave an approximate 30% reduction in conveyance area for the channel. This cross section configuration is shown in Figure 6.

Figure 5 – HEC-RAS 2D Existing Condition Model Mesh

Expansion and Contraction Coefficients

The HEC-RAS model was developed with contraction and expansion coefficients of 0.1 / 0.3 for areas outside the immediate influence of the bridge and 0.3 / 0.5 for the bridge, respectively.

These values were selected due to the relatively gradual cross-sectional and flow width variations. The application of these coefficients was applied to the internal bridge cross sections for bridges within the 2D model.

Roughness Coefficients

During the site visit, the channel conditions and overbank conditions were evaluated. The USGS Guide for Selecting Manning’s Roughness Coefficients for Natural Channels and Flood Plains was used as a reference for determining the n-values as shown in the following table. Supporting calculations with example pictures from the site are included in Appendix D. Individual land use Manning’s n values incorporated into this model are summarized in Table 4.

TABLE 4 – MANNING’S N ROUGHNESS

Land Cover n-value

Road/Pavement 0.020

Rock Cut 0.038

Proposed Rock Cut 0.031

Channel (cobble) 0.053

Channel Overbank (vegetated) 0.063

Forested Overbank 0.078

Reach Boundary Conditions

The flow boundary options were used for both upstream boundaries on Horton and Tonto Creek, and a normal depth condition was specified at the downstream boundary location on Tonto Creek. A 100-year event flow peak of 3,851 cfs was applied to the Horton Creek boundary and 3,759 cfs was applied to the upper Tonto Creek boundary such that the sum of these inputs equals the total peak flow at the bridge location downstream of the channel confluence. Other design storm flows were similarly divided between the two upstream boundaries resulting in total flow at the bridge as shown in Table 3. The normal depth boundary on lower Tonto Creek was defined with an energy grade slope of 0.026 ft/ft for all model scenarios.

Bridges and Culverts

The existing bridge was modeled in the existing conditions scenario using the standard HEC- RAS bridge options including the roadway deck and abutment data to characterize the geometry within the 2D model. The proposed bridge was also modeled using standard bridge options to reflect the new bridge design as shown in Appendix F. The proposed bridge will span the channel with a single span structure having a higher minimum chord elevation than the existing structure.

Blocked Obstructions, Levees, Dikes, and Non-Levee embankments

No levees, dikes, or non-levee embankments were modeled as part of this study. Blocking obstructions for the 100-year event were evaluated with a 30% loss of flow area at the upstream bridge face. This obstruction was modeled as ineffective flow areas blocking flow on both left and right channel banks.

Islands and Flow Splits

No islands or flow splits were intentionally modeled as part of this analysis, however these features would be resolved with the 2D mesh if present during low flow scenarios.

Supercritical Flow, Hydraulic Jump, and Drop Analysis

Review of the Froude number within the simulation reveals that flow through the bridge section is supercritical (i.e., Fr > 1.0), whereas most of the natural channel was subcritical. The energy grade slope along most of Tonto Creek in the model domain was approximately 0.016 ft/ft.

Modeling Results

Using the Water Surface Elevations (WSE) from the HEC-RAS model and the proposed bridge configuration, compliance with design criteria was assessed against with the goals shown in Table 1. Supporting HEC-RAS output data is included in Appendix E.

Freeboard calculations were performed at the upstream face of the proposed bridge, and the controlling point for the freeboard is the low chord elevation is 5,462.00 feet at the eastern abutment as shown in the bridge layout drawing included in Appendix G. The bridge superstructure thickness is 44-inches (3.61 feet) and the top of deck elevation is 5,466.06 feet.

Model results show that the bridge does not meet desired freeboard criteria (i.e., TSH 62.2 for 100-yr event and PDDM 7.4.3.4.1 for the 50-year) as shown in Table 5. However, the model suggests that the bridge will not overtop for all design storm events except for the 200-year return interval where the bridge deck just overtops. Finally, the 100-year event with 30% channel blockage from accumulated debris will raise the channel WSEL approximately 3.5 feet over the unobstructed scenario but will not overtop the roadway leaving the main lanes passable. Figure 6 shows a plot of the proposed upstream bridge section as modeled in the debris obstructed scenario. Figure 7 includes flow profiles of all design storm scenarios for Tonto Creek.

TABLE 5 - HEC-RAS HYDRAULIC RESULTS

Storm Event Q (cfs) U/S Bridge Face

Max WSE (ft) Freeboard (ft)

2-year 305 5453.01 8.99

50-year 5,240 5458.83 3.17

100-year 7,610 5460.28 1.72

100-year (30% Debris Blockage) 7,610 5463.76 NA

200-year 10,500 5466.48 NA

Figure 6 – Tonto Creek Bridge Section Plot Showing 30% Blockage

Figure 7 – Tonto Creek Flow Profiles

450 470 490 510 530 550 570

El ev at io n ft

Station (ft)

Roadway LowChord Debris Channel

0 100 200 300 400 500 600

El ev at io n ft

Station (ft)

2yr WSEL 50yr WSEL 100yr WSEL 100yr Debris WSEL 200yr WSEL Channel

Approximate Location of Proposed FS 289 Bridge

C. SCOUR AND BANK PROTECTION

As shown in the HEC-RAS model output in Appendix E, maximum velocities in Tonto Creek main channel through the proposed bridge structure are expected to be between 18 feet per second (fps) and 21.5 fps in the 100-year event. Estimated velocities in Horton Creek channel vary between 13.5 fps and 18.5 fps upstream of the proposed bridge.

Based on field observations, much of the existing site consists of bedrock at the surface, likely due to high flow velocity through the area transporting loose cobble and small boulders through the project site. The proposed bridge will be anchored to competent bedrock; thus, no scour analysis is expected to be required. A HEC-23 based design for riprap armoring suggest installation of 36-inch (median size) limestone stones with a mat depth of 54-inches will be sufficient to stabilize and protect the abutments. Riprap sizing calculations are included in Appendix F.

V. REFERENCES

1. Federal Lands Highway, Project Development and Design Manual (PDDM), Federal Highway Administration, January 2014.

2. Guide for Selecting Manning’s Roughness Coefficients for Natural Channels and

Flood Plains, Federal Highway Administration, April 1984.

3. Federal Highway Administration Hydraulic Design Series No. 2, Highway Hydrology, 2nd Edition, 2002.

4. HEC-RAS User’s Manual, Hydrologic Engineering Center – US Army Corps of Engineers, 2020.

5. Federal Highway Administration Hydraulic Engineering Circular No. 23, September

6. Federal Highway Administration Hydraulic Engineering Circular No. 18, April 2012

APPENDIX

Appendix A

Existing Bridge Plan

UPPER TONTO BRIDGE

GENERAL PLAN, ELEVATION & BRIDGE DETAILS

F.S. ROAD NO. 289 - 0.8

TONTO NATIONAL FOREST

1-13171 JULY 2013

SHEET NO.

RME

RME

KFY

KFY

engineering

2501 BELT VIEW DRIVE

HELENA, MT 59601

(406)449-8627

R

PREPARED BY:

REGION THREE

PROJECT:

DESIGNED:

DRAWN:

DESIGN CHECKED:

DRAWING CHECKED:

DATE: NO. DATEBYREVISION DESCRIPTION

NBI STRUCTURE # 3356

F.S. ROAD 289

MILEPOST

EDGE OF EXISTING ROAD

EDGE OF EXISTING ROAD

BRIDGE PROFILE LOOKING UPSTREAM

BRIDGE APPROACH LOOKING WEST

A A

T O

N T

O

C R

E E

K

TO HIGHWAY 260

Appendix B

USGS StreamStats Report

Tonto Creek Bridge Location

4/19/23, 1:16 PM StreamStats https://streamstats.usgs.gov/ss/ 1/5

StreamStats Report

Collapse All

Basin Characteristics

Parameter Code Parameter Description Value Unit

BSLDEM10M Mean basin slope computed from 10 m DEM 33.54 percent

CONTDA Area that contributes flow to a point on a stream 13.28 square miles

DRNAREA Area that drains to a point on a stream 13.28 square miles

ELEV Mean Basin Elevation 6748.13 feet

ELEVMAX Maximum basin elevation 7934.11 feet

FD_Region FD_Region 1623 dimensionless

MINBELEV Minimum basin elevation 5441.08 feet

PRECIP Mean Annual Precipitation 36.1 inches

SLOP30_10M Percent area with slopes greater than 30 percent from 10-meter NED 45 percent

STRMTOT total length of all mapped streams (1:24,000-scale) in the basin 28.74 miles

Peak-Flow Statistics

Peak-Flow Statistics Parameters [100.0 Percent (13.3 square miles) Peak Region 4 Central Highland 2014 5211]

Parameter Code Parameter Name Value Units Min Limit Max Limit

CONTDA Contributing Drainage Area 13.28 square miles 0.059 18044

ELEV Mean Basin Elevation 6748.13 feet 3274 7451

PRECIP Mean Annual Precipitation 36.1 inches 10.8 33.5

Region ID: AZ Workspace ID: AZ20230419174646890000 Clicked Point (Latitude, Longitude): 34.33909, -111.09589 Time: 2023-04-19 12:47:08 -0500 https://streamstats.usgs.gov/ss/ 2/5

Peak-Flow Statistics Disclaimers [100.0 Percent (13.3 square miles) Peak Region 4 Central Highland 2014 5211]

One or more of the parameters is outside the suggested range. Estimates were extrapolated with unknown errors.

Peak-Flow Statistics Flow Report [100.0 Percent (13.3 square miles) Peak Region 4 Central Highland 2014 5211]

Statistic Value Unit

50-percent AEP flood 305 ft^3/s

20-percent AEP flood 879 ft^3/s

10-percent AEP flood 1660 ft^3/s

4-percent AEP flood 3370 ft^3/s

2-percent AEP flood 5240 ft^3/s

1-percent AEP flood 7610 ft^3/s

0.5-percent AEP flood 10500 ft^3/s

0.2-percent AEP flood 15300 ft^3/s

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

Flood-Volume Statistics Parameters [100.0 Percent (13.3 square miles) Central highland MeanMax flows 2014 5109]

Parameter Code Parameter Name Value Units Min Limit Max Limit

CONTDA Contributing Drainage Area 13.28 square miles 1.1 7890

PRECIP Mean Annual Precipitation 36.1 inches 13.9 36.7

ELEV Mean Basin Elevation 6748.13 feet 2240 9520

FD_Region FD_Region 1623 dimensionless

Flood-Volume Statistics Flow Report [100.0 Percent (13.3 square miles) Central highland MeanMax flows 2014 5109]

PIl: Prediction Interval-Lower, PIu: Prediction Interval-Upper, ASEp: Average Standard Error of Prediction, SE: Standard Error (other -- see report)

Statistic Value Unit ASEp

1 Day 2 Year Maximum 113 ft^3/s 50.8

1 Day 5 Year Maximum 326 ft^3/s 43.7

1 Day 10 Year Maximum 600 ft^3/s 40.6

1 Day 25 Year Maximum 1290 ft^3/s 37

1 Day 50 Year Maximum 1850 ft^3/s 36.4

1 Day 100 Year Maximum 2520 ft^3/s 36.7

1 Day 200 Year Maximum 3300 ft^3/s 37.8

1 Day 500 Year Maximum 4310 ft^3/s 37.7

3 Day 2 Year Maximum 69.1 ft^3/s 52.3

3 Day 5 Year Maximum 207 ft^3/s 43.5

3 Day 10 Year Maximum 339 ft^3/s 40.4

3 Day 25 Year Maximum 566 ft^3/s 40.3 http://pubs.usgs.gov/sir/2014/5211/ https://streamstats.usgs.gov/ss/ 3/5

Statistic Value Unit ASEp

3 Day 50 Year Maximum 762 ft^3/s 39.3

3 Day 100 Year Maximum 975 ft^3/s 39.9

3 Day 200 Year Maximum 1200 ft^3/s 40.6

3 Day 500 Year Maximum 1700 ft^3/s 35.3

7 Day 2 Year Maximum 49.6 ft^3/s 52.9

7 Day 5 Year Maximum 138 ft^3/s 42.7

7 Day 10 Year Maximum 214 ft^3/s 36.1

7 Day 25 Year Maximum 353 ft^3/s 34.9

7 Day 50 Year Maximum 446 ft^3/s 32.6

7 Day 100 Year Maximum 569 ft^3/s 33.1

7 Day 200 Year Maximum 696 ft^3/s 33.6

7 Day 500 Year Maximum 879 ft^3/s 35.2

15 Day 2 Year Maximum 38.1 ft^3/s 51.3

15 Day 5 Year Maximum 93.1 ft^3/s 40.4

15 Day 10 Year Maximum 146 ft^3/s 36.4

15 Day 25 Year Maximum 235 ft^3/s 34.9

15 Day 50 Year Maximum 305 ft^3/s 32.6

15 Day 100 Year Maximum 376 ft^3/s 32

15 Day 200 Year Maximum 453 ft^3/s 31.6

15 Day 500 Year Maximum 523 ft^3/s 28.6

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

30 Day 5 Year Maximum 65.3 ft^3/s 42.7

30 Day 10 Year Maximum 110 ft^3/s 38.2

30 Day 25 Year Maximum 178 ft^3/s 36.6

30 Day 50 Year Maximum 226 ft^3/s 34.1

30 Day 100 Year Maximum 279 ft^3/s 32.6

30 Day 200 Year Maximum 331 ft^3/s 31.2

30 Day 500 Year Maximum 372 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/)

Bankfull Statistics

Bankfull Statistics Parameters [Intermontane Plateau D Bieger 2015]

Parameter Code Parameter Name Value Units Min Limit Max Limit

DRNAREA Drainage Area 13.28 square miles 3.62934 7579.9152

Bankfull Statistics Parameters [Basin and Range P Bieger 2015]

Parameter Code Parameter Name Value Units Min Limit Max Limit

DRNAREA Drainage Area 13.28 square miles 3.949803 5008.971825 http://pubs.usgs.gov/sir/2014/5109/ https://streamstats.usgs.gov/ss/ 4/5

Bankfull Statistics Parameters [USA Bieger 2015]

Parameter Code Parameter Name Value Units Min Limit Max Limit

DRNAREA Drainage Area 13.28 square miles 0.07722 59927.7393

Bankfull Statistics Flow Report [Intermontane Plateau D Bieger 2015]

Statistic Value Unit

Bieger_D_channel_width 15.8 ft

Bieger_D_channel_depth 0.736 ft

Bieger_D_channel_cross_sectional_area 10.7 ft^2

Bankfull Statistics Flow Report [Basin and Range P Bieger 2015]

Statistic Value Unit

Bieger_P_channel_width 33.1 ft

Bieger_P_channel_depth 1.29 ft

Bieger_P_channel_cross_sectional_area 35.3 ft^2

Bankfull Statistics Flow Report [USA Bieger 2015]

Statistic Value Unit

Bieger_USA_channel_width 30.8 ft

Bieger_USA_channel_depth 2.09 ft

Bieger_USA_channel_cross_sectional_area 69.1 ft^2

Bankfull Statistics Flow Report [Area-Averaged]

Statistic Value Unit

Bieger_D_channel_width 15.8 ft

Bieger_D_channel_depth 0.736 ft

Bieger_D_channel_cross_sectional_area 10.7 ft^2

Bieger_P_channel_width 33.1 ft

Bieger_P_channel_depth 1.29 ft

Bieger_P_channel_cross_sectional_area 35.3 ft^2

Bieger_USA_channel_width 30.8 ft

Bieger_USA_channel_depth 2.09 ft

Bieger_USA_channel_cross_sectional_area 69.1 ft^2

Bankfull Statistics Citations

Bieger, Katrin; Rathjens, Hendrik; Allen, Peter M.; and Arnold, Jeffrey G.,2015, Development and Evaluation of Bankfull Hydraulic Geometry Relationships for the Physiographic Regions of the United States, Publications from USDA-ARS / UNL Faculty, 17p. (https://digitalcommons.unl.edu/usdaarsfacpub/1515?

utm_source=digitalcommons.unl.edu%2Fusdaarsfacpub%2F1515&utm_medium=PDF&utm_campaign=PDFCoverPages) https://digitalcommons.unl.edu/usdaarsfacpub/1515?utm_source=digitalcommons.unl.edu%2Fusdaarsfacpub%2F1515&utm_medium=PDF&utm_campaign=PDFCoverPages https://streamstats.usgs.gov/ss/ 5/5

Maximum Probable Flood Statistics

Maximum Probable Flood Statistics Parameters [Crippen Bue Region 16]

Parameter Code Parameter Name Value Units Min Limit Max Limit

DRNAREA Drainage Area 13.28 square miles 0.1 1000

Maximum Probable Flood Statistics Flow Report [Crippen Bue Region 16]

Statistic Value Unit

Maximum Flood Crippen Bue Regional 78500 ft^3/s

Maximum Probable Flood Statistics Citations

Crippen, J.R. and Bue, Conrad D.1977, Maximum Floodflows in the Conterminous United States, Geological Survey Water- Supply Paper 1887, 52p. (https://pubs.usgs.gov/wsp/1887/report.pdf)

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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: 4.14.0

StreamStats Services Version: 1.2.22

NSS Services Version: 2.2.1 https://pubs.usgs.gov/wsp/1887/report.pdf

Appendix C

FEMA FIRMette Map04007C0278D effective 12/04/2007

National Flood Hazard Layer FIRMette

0 500 1,000 1,500 2,000250 Feet

Ü

SEE FIS REPORT FOR DETAILED LEGEND AND INDEX MAP FOR FIRM PANEL LAYOUT

SPECIAL FLOOD

HAZARD AREAS

Without Base Flood Elevation (BFE) Zone A, V, A99

With BFE or Depth Zone AE, AO, AH, VE, AR

Regulatory Floodway

0.2% Annual Chance Flood Hazard, Areas of 1% annual chance flood with average depth less than one foot or with drainage areas of less than one square mile Zone X

Future Conditions 1% Annual Chance Flood Hazard Zone X

Area with Reduced Flood Risk due to Levee. See Notes. Zone X

Area with Flood Risk due to Levee Zone D

NO SCREEN Area of Minimal Flood Hazard Zone X

Area of Undetermined Flood Hazard Zone D

Channel, Culvert, or Storm Sewer

Levee, Dike, or Floodwall

Cross Sections with 1% Annual Chance

17.5 Water Surface Elevation

Coastal Transect

Coastal Transect Baseline Profile Baseline Hydrographic Feature

Base Flood Elevation Line (BFE)

Effective LOMRs

Limit of Study Jurisdiction Boundary

Digital Data Available

No Digital Data Available

Unmapped

This map complies with FEMA's standards for the use of digital flood maps if it is not void as described below.

The basemap shown complies with FEMA's basemap accuracy standards

The flood hazard information is derived directly from the authoritative NFHL web services provided by FEMA. This map was exported on 4/1/2025 at 1:59 PM and does not reflect changes or amendments subsequent to this date and time. The NFHL and effective information may change or become superseded by new data over time.

This map image is void if the one or more of the following map elements do not appear: basemap imagery, flood zone labels, legend, scale bar, map creation date, community identifiers, FIRM panel number, and FIRM effective date. Map images for unmapped and unmodernized areas cannot be used for regulatory purposes.

Legend

OTHER AREAS OF

FLOOD HAZARD

OTHER AREAS

GENERAL

STRUCTURES

OTHER

FEATURES

MAP PANELS

B 20.2

The pin displayed on the map is an approximate point selected by the user and does not represent an authoritative property location.

1:6,000

111°6'4"W 34°20'39"N

111°5'26"W 34°20'9"N

Basemap Imagery Source: USGS National Map 2023

Appendix D

Manning’s n Calculations

DATE 3/13/2024

PROJECT FS289 Tonto Creek

SUBJECT n-value calculations

USER Daniel Selk

Land Cover Base n

Final n-value n = m(n1+n2+n3+n4)

Road/Pavement 0.020 n/a n/a n/a n/a n/a n/a n/a n/a n/a 1.0 0.020

Rock Cut 0.025 Minor 0.003 Alternating

Occasionally

0.003 Minor 0.005 Small 0.002 Minor 1.0 0.038

Proposed Rock Cut 0.025 Minor 0.003 Alternating

Occasionally

0.001 Negligible 0.000 Small 0.002 Minor 1.0 0.031

Channel (cobble) 0.030 Minor 0.003 Alternating

Occasionally

0.003 Minor 0.005 Small 0.002 Minor 1.0 0.043

Channel Overbank (vegetated) 0.025 Minor 0.003 n/a 0.000 Minor 0.010 Medium 0.025 Minor 1.0 0.063

Forested Overbank 0.025 Minor 0.003 n/a 0.000 Appreciable 0.020 Large 0.030 Minor 1.0 0.078

Site picture examples

Rock Cut Channel (cobble) Channel Overbank (vegetated) Forested Overbank

Degree of irregularity n1

Effect of obstruction n3

Variation in channel cross section n2

Amount of vegetation n4

Degree of meandering m

0.0430.043 0.053

Appendix E

HEC-RAS Output

Existing Condition 50-year Design Storm Maximum Water Surface Elevation

Existing Condition 50-year Design Storm Maximum Water Depth

Existing Condition 50-year Design Storm Maximum Water Velocity

Existing Condition 100-year Design Storm Maximum Water Surface Elevation

Existing Condition 100-year Design Storm Maximum Water Depth

Existing Condition 100-year Design Storm Maximum Water Velocity

Existing Condition 200-year Design Storm Maximum Water Surface Elevation

Existing Condition 200-year Design Storm Maximum Water Depth

Existing Condition 200-year Design Storm Maximum Water Velocity

Proposed Condition 50-year Design Storm Maximum Water Surface Elevation

Proposed Condition 50-year Design Storm Maximum Water Depth

Proposed Condition 50-year Design Storm Maximum Water Velocity

Proposed Condition 100-year Design Storm Maximum Water Surface Elevation

Proposed Condition 100-year Design Storm Maximum Water Depth

Proposed Condition 100-year Design Storm Maximum Water Velocity

Proposed Condition 200-year Design Storm Maximum Water Surface Elevation

Proposed Condition 200-year Design Storm Maximum Water Depth

Proposed Condition 200-year Design Storm Maximum Water Velocity

Appendix F

Riprap Sizing Calculations (HEC-23)

FS 289 @ Tonto Creek Type Spill through

Ss 2.65

Return Hydraulic

Interval Q Fr Depth Velocity D50 D50

(years) (cfs) (unitless) K (ft) (fps) (ft) (in)

2 305 2.50 0.61 1.20 8.00 0.48 6

50 5240 1.50 0.61 5.60 15.00 2.14 26

100 7610 1.30 0.61 7.00 14.00 2.54 30

200 10500 0.60 0.89 10.00 13.00 2.83 34

D50 Use 36" stone

Thickness 54"

K values (Fr <= 0.80)

0.89 Spill through abutments

1.02 Vertical wall abutment

K values (Fr > 0.80)

0.61 Spill through abutments

0.69 Vertical wall abutment

Note:

If SBR < 5, velocities are average for the constricted cross section.

If SBR > 5, use velocity from the overbank flow only. See HEC-23 guidance.

Matt thickness = 1.5*d50

Appendix G

Proposed Bridge Plans