UT73(2)_La_Sal_Hydraulics_Report_wAppendices.pdf

La Sal Mountain Loop Road Bureau of Land Management

US Forest Service San Juan County, UT

UT FLAP 73(2)

Final Hydraulic Report

Federal Highway Administration Central Federal Lands Highway Division

March 13, 2020

Executive Summary

Hydrology and hydraulics analyses were conducted for the US FLAP 73(2) La Sal Mountain Loop Road Project. The hydraulic analyses focused on the location of Pack Creek where the proposed roadway embankment slope will encroach into the creek. A 25-year design frequency was used in the analyses because La Sal Mountain Loop Road is considered low standard for hydraulic design. Design peak flow values were estimated using USGS regression equations for Utah. Existing and proposed conditions two-dimensional hydraulic modeling using SRH-2D was conducted to estimate water surface elevations and velocity at the project site. Based on the hydraulic results the following proposed bridge geometry was selected: Based on the hydraulic results the following bank protection measures are recommended:

• Riprap Class 6 bank protection according to FP-14 Section 705.02, protection extents as shown in the project plans.

• Minimum embedment depth below existing bed elevation of 3.5 feet.

• Top elevation of riprap to provide a minimum 2 feet freeboard from 25-year water surface elevation.

• Class 1 Type C non-woven geotextile filter according to FP-14 Section 714.01.

i UT FLAP 73(2) La Sal Loop Road - Hydraulic Report

Table of Contents

1 Project Background Information

2 Hydraulic Design Criteria

3 Hydrology

3.1 Hydrologic Setting

3.2 Floodplain Encroachment

3.3 Available Hydrologic Data

3.4 Regression Equation Estimates

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 and Bank Protection

5 Recommendations

6 References ii UT FLAP 73(2) La Sal Loop Road - Hydraulic Report

Tables Table 1: PDDM Hydraulic Design Criteria Table 2: Pack Creek Basin Properties Table 3: Available Peak Streamflow Information Table 4: StreamStats Peak Discharge Estimates at Project Location Table 5: Model Boundary Condiitons Table 6: Specified Manning’s “n” Table 7: 25-Year Existing Conditions Hydraulic Results at Selected Locations Table 8: 100-Year Existing Conditions Hydraulic Results at Selected Locations Table 9: 25-Year Proposed Conditions Hydraulic Results at Selected Locations Table 10: 100-Year Proposed Conditions Hydraulic Results at Selected Locations Table 11: 25-Year Existing and Proposed Hydraulic Results Comparison Table 12: 100-Year Existing and Proposed Hydraulic Results Comparison Table 13: Bend Scour Depth Estimate

Figures

Figure 1: Project location map Figure 2: Mill Creek Watershed and Pack Creek Basin of Interest Figure 3: FEMA National Flood Hazard Layer – Excerpt Figure 4: Project Existing Topographic Surface, Elevations in feet NAVD88 Figure 5: Project Proposed Topographic Surface, Elevations in feet NAVD88 Figure 6: SRH-2D Model Domain and Computational Mesh Figure 7: Project Land Cover Types and Manning’s Roughness Figure 8: 25-Year Water Surface Elevation – Existing Conditions Figure 9: 100-Year Water Surface Elevation – Existing Conditions Figure 10: 25-Year Velocity – Existing Conditions Figure 11: 100-Year Velocity – Existing Conditions Figure 12: Existing vs Proposed Ground at Cross Section 3 Figure 13: 25-Year Water Surface Elevation – Proposed Conditions Figure 14: 100-Year Water Surface Elevation – Proposed Conditions Figure 15: 25-Year Velocity – Proposed Conditions Figure 16: 100-Year Velocity – Proposed Conditions Figure 17: 25-Year Riprap Median Size (D50) in inches Figure 18: Riprap Bank Protection Details (source HEC-23 Figure 4.2)

Appendices

Appendix A: Hydrologic Analyses Appendix B: Hydraulic Analyses

Page 1 UT FLAP 73(2) La Sal Loop Road - Hydraulic Report

1 PROJECT BACKGROUND INFORMATION

The La Sal Mountain Loop Road project is located in San County, UT within the Manti-La Sal National Forest, see Figure 1. The project will rehabilitate and widen 2 segments of road, totaling 12.12 miles along La Sal Mountain Loop Road.

Segment 1 goes from 11+25 at the intersection of Old Airport Road to 265+00 at the intersection of Pack Creek Road. Rehabilitation and widening consists of pulverizing the existing pavement, widening the road to 30 feet from the beginning to 45+00 and 26 feet for the remainder of the road, placing aggregate base and asphalt concrete pavement, and drainage improvements. Curve widening will also be added as necessary.

Segment 2 goes from 265+00 at the intersection of Pack Creek Road, and goes to 650+85, beginning of past project UT PFH 46-1(2). Rehabilitation consists of pulverizing the existing pavement, narrowing the road to 26 feet in width, placing new aggregate base and asphalt concrete pavement, and drainage improvements. Three locations will be reconstructed consisting of raising or lowering profile, pulverizing the existing pavement, narrowing the road to 26 feet in width, placing aggregate base, and asphalt concrete pavement, and drainage improvements. Curve widening will also be added as necessary.

Due to the roadway widening the roadway embankment will extend into the outside bank of Pack Creek from approximately station 161+60 to 163+40. Due to flow in the outside of the bend the embankment must be protected from erosion. This report summarizes the hydraulic analyses conducted to determine design flows and develop required measures to protect against streambank erosion at this location.

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Figure 1: Project location map.

2 HYDRAULIC DESIGN CRITERIA

The Federal Lands Highway Project Development and Design Manual (PDDM) (Federal Lands Highway 2012) establishes the hydraulic design criteria. Based on the Design Technical Memorandum the design speed is 40mph, the design average daily traffic (ADT) is 457 vehicles, and seasonal ADT is 500 to 900 vehicles. Although based on these parameters the road is classified as low standard road for hydraulic design purposes. The applicable PDDM design criteria are listed in Table 1.

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Table 1: PDDM Hydraulic Design Criteria

Road Classification: Low-Standard Road Culverts:

Design Frequency Check Frequency Allowable Headwater

25-year flood Overtopping flood

Minimum of:

• Bottom of aggregate base layer

• HW/D ratio of 1.2 for D > 48", 1.5 for D ≤ 48”

• Unacceptable hazard to human life or property

Ditches:

Design

Frequency Stability Depth

10-year flood 10-year flood • New: WSEL ≤ bottom of aggregate base layer

• Existing: WSEL ≤ shoulder hinge point

Pavement Drainage:

Design

Frequency Spread Depth

10-year flood, 50-year in sumps

Half of one travel lane

• On-grade and Sags: Allowable spread, not to exceed curb height

• Sumps and Parking Areas: 6”

Longitudinal Embankments:

Design

Frequency Check Frequency Freeboard

25-year flood Greater of 100-year or overtopping flood 2’ minimum to bottom of aggregate base layer

3 HYDROLOGY

3.1 HYDROLOGIC SETTING

The project is located within the Mill Creek Watershed (HUC10: 1403000504), see Figure 2. A portion of the project alignment parallels Pack Creek. Pack Creek generally flows northwest from its headwaters near South Mountain to the confluence with Mill Creek approximately 9 miles northwest from the beginning of the project. The total basin area for Mill Creek is approximately 142 square miles and the ultimate outfall is the Colorado River approximately 1.5 miles west from the city of Moab.

The point of interest of the hydraulic analysis is Pack Creek near station 161+60. The contributing drainage basin and basin parameters were obtained using the StreamStats web application (U.S. Geological Survey 2016). The basin delineation is shown in Figure 2. A summary of general basin properties is shown in Table 2.

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Figure 2: Mill Creek Watershed and Pack Creek Basin of Interest

Table 2: Pack Creek Basin Properties

Stream Drainage Area (mi2) Mean Basin Elevation (ft)

Mean Annual Precipitation

(in)

Mean Basin Slope (%)

Pack Creek 32.3 8,300 29.3 33.8

3.2 FLOODPLAIN ENCROACHMENT

According to FEMA Flood Map Service Center (Federal Emergency Management Agency 2020) the project lies in an unmapped area where no studies have been completed to determine the special flood hazard area (SFHA). The SFHA comprises the land area that is shown in the FIRM as being inundated by the base flood and where the National Flood Insurance Program's (NFIP) floodplain management regulations apply.

FLH design criteria states that in an unregulated base floodplain the rise in pre- and post- water surface profiles should not exceed 1 foot. An excerpt of the applicable FIRM is shown in Figure 3.

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Figure 3: FEMA National Flood Hazard Layer – Excerpt

3.3 AVAILABLE HYDROLOGIC DATA

There are no active USGS streamflow stations on Pack Creek within the project limits. There are two inactive stations on Pack Creek located approximately 7.5 miles downstream, and 3.8 miles upstream from the point of interest. Table 3 summarizes the station location and period of record. Due to the lack of active stations and short period of record the USGS streamflow information was not used for the project.

Table 3: Available Peak Streamflow Information

USGS

Station Location Latitude Longitude Drainage

Area Period of Record Years Status

09185000

PACK CREEK

NEAR MOAB,

UTAH

38°32'25" 109°30'00" 57.4 mi2 1954 - 1959 5 Inactive

09184500

PACK CREEK

AT M4

RANCH, NR

MOAB, UTAH

38°26'10" 109°21'15" 15.8 mi2 1954-1959 5 Inactive

3.4 REGRESSION EQUATION ESTIMATES

The StreamStats web application (U.S. Geological Survey 2016) was used to estimate peak flows for Pack Creek. The Utah StreamStats application uses the regression equations presented in USGS Report 2007- 5158 (Kenney, Wilkowske and Wright 2008). The site is located in the Utah geohydrologic Region 6, which comprises most of the Colorado Plateau. The equations developed for Region 6 relate peak discharge to drainage area and mean basin elevation, and have average standard errors of prediction that vary from

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66 to 108 percent. The results for the Pack Creek basin are shown in Table 4. Additional details of the hydrologic analysis are included in Appendix A.

Table 4: StreamStats Peak Discharge Estimates at Project Location

Percent Chance Exceedance (%)

Return Period (year)

San Vicente Creek at Bridge 1 Peak Flow (cfs)

50 2 159 20 5 396 10 10 620 4 25 1,020 2 50 1,390 1 100 1,900

0.5 200 2,320

0.2 500 3,130

4 HYDRAULIC ANALYSIS

4.1 TOPOGRAPHIC INFORMATION

Existing topographic information was collected using ground survey by Central Federal Lands in 2010 for an adjacent project, and in 2018 and 2019 for the current project. The mapping information is referenced to the NAD 1983 Utah State Plane Central Zone projection with units of feet. The elevation information is referenced to the North American Vertical Datum of 1988 (NAVD 88). The existing topographic surface for the project is shown in Figure 4. There are no LiDAR sources available for this area to augment the ground survey information. The proposed topographic surface was created by merging the proposed roadway design including the proposed embankment slope and existing topographic surface as shown in Figure 5.

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Figure 4: Project Existing Topographic Surface, Elevations in feet NAVD88

Figure 5: Project Proposed Topographic Surface, Elevations in feet NAVD88

Pack Creek

Pack Creek

Proposed Embankment Slope Station 161+60 to 163+40

N

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4.2 HYDRAULIC MODEL DEVELOPMENT

Two-dimensional hydraulic modeling using SRH-2D (U.S. Bureau of Reclamation 2017) was conducted to estimate water surface elevations and flow velocities in the project reach. The model pre- and post-processing was performed using the SMS 13.0.11 interface (Aquaveo 2020). The model domain extends approximately 550 feet upstream and 375 feet downstream from the project area of interest due to the limited survey information an lack of available LiDAR to extend model limits. The model domain and computational mesh are shown in Figure 6.

Figure 6: SRH-2D Model Domain and Computational Mesh

The upstream boundary condition in the model was specified as steady inflow using the 25-year, and 100-year peak flows in Table 4. The downstream boundary condition was specified as a constant water surface elevation. The downstream water surface elevation was estimated using normal depth computations with a channel slope of 0.03 ft/ft near the model downstream boundary. The boundary conditions for the 25-year and 100-year return periods are shown in Table 5.

Table 5: Model Boundary Condiitons

Percent Chance Exceedance (%)

Return Period (year)

Upstream Inflow (cfs)

Downstream WSEL (feet – NAVD88)

4 25 1,020 963.42 1 100 1,900 963.97

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SRH-2D uses Manning’s “n” values to calculate bed friction. The land use types were delineated from aerial imagery as shown in Figure 7 and assigned typical roughness values. The roughness values used in the model are shown in Table 6.

Table 6: Specified Manning’s “n”

Land Use Manning's "n" Main Channel 0.035

Floodplain Brush 0.050

Figure 7: Project Land Cover Types and Manning’s Roughness

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 25-year and 100-year return periods. The existing conditions water surface elevation and velocity results are shown in Figure 8 to Figure 11. The hydraulic results were extracted at five cross section locations labeled in the figures below for comparison with proposed conditions results as described in Section 4.3.2. The results are summarized in Table 7 and Table 8 for the 25-year and 100-year return periods, respectively. Additional details of the hydraulic analyses are provided in Appendix B.

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Figure 8: 25-Year Water Surface Elevation – Existing Conditions

Figure 9: 100-Year Water Surface Elevation – Existing Conditions

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Figure 10: 25-Year Velocity – Existing Conditions

Figure 11: 100-Year Velocity – Existing Conditions

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Table 7: 25-Year Existing Conditions Hydraulic Results at Selected Locations

Location Velocity (ft/s) Depth (ft) WSEL (ft – NAVD88)

Average Maximum Average Maximum Average Maximum

XS 1 4.85 10.63 0.87 3.58 5328.23 5328.71

XS 2 5.94 13.69 1.59 3.24 5329.59 5330.20

XS 3 6.16 12.03 1.31 2.98 5332.09 5334.30

XS 4 4.89 12.89 0.89 2.63 5335.32 5335.62

XS 5 3.77 13.58 0.78 3.20 5337.66 5338.01

Table 8: 100-Year Existing Conditions Hydraulic Results at Selected Locations

Velocity (ft/s) Depth (ft) WSEL (ft – NAVD88)

Average Maximum Average Maximum Average Maximum

XS 1 6.78 11.95 1.31 4.29 5328.76 5329.23

XS 2 5.86 15.20 1.54 3.91 5330.82 5333.52

XS 3 5.96 13.34 1.31 3.83 5333.25 5334.80

XS 4 6.72 14.90 1.38 3.32 5335.94 5336.34

XS 5 5.63 16.04 1.22 4.00 5338.25 5338.51

4.3.2 Proposed Conditions

Proposed conditions hydraulic simulations for the 25-year and 100-year return periods were conducted using the parameters described in Section 4.2 The proposed conditions model includes the addition of the roadway embankment slope that encroaches into Pack Creek. Figure 12 shows an example comparison of the existing embankment slope and proposed embankment slope at cross section 3. The proposed conditions water surface elevation and velocity results are shown in Figure 13 to Figure 16. The proposed conditions results were extracted at five cross section locations described previously. The results are summarized in Table 9 and Table 10 for the 25-year and 100-year return periods, respectively. The existing results were subtracted from the proposed results to evaluate the effect of the proposed embankment on velocity and water surface elevations. The results of the comparison are shown in Table 11 and Table 12 for the 25-year and 100-year return periods, respectively. Positive values in these tables indicate an increase from the existing condition and negative values indicate a decrease from the existing condition.

The results show that the hydraulic impacts are minimal and localized in the vicinity of the encroachment.

In addition, the increase in the 100-year water surface elevation due to the proposed project is a maximum of 0.06 feet therefore the floodplain encroachment criteria for an unregulated zone is satisfied.

Additional details of the hydraulic analyses are provided in Appendix B.

Page 13 UT FLAP 73(2) La Sal Loop Road - Hydraulic Report

Figure 12: Existing vs Proposed Ground at Cross Section 3

Figure 13: 25-Year Water Surface Elevation – Proposed Conditions

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Figure 14: 100-Year Water Surface Elevation – Proposed Conditions

Figure 15: 25-Year Velocity – Proposed Conditions

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Figure 16: 100-Year Velocity – Proposed Conditions

Table 9: 25-Year Proposed Conditions Hydraulic Results at Selected Locations

Location Velocity (ft/s) Depth (ft) WSEL (ft – NAVD88)

Average Maximum Average Maximum Average Maximum

XS 1 4.93 10.61 0.89 3.57 5328.24 5328.70

XS 2 5.41 13.55 1.44 3.32 5329.67 5330.29

XS 3 6.67 12.20 1.29 3.04 5332.07 5334.30

XS 4 5.01 12.67 0.95 2.81 5335.41 5335.64

XS 5 3.83 13.53 0.76 3.23 5337.69 5338.00

Table 10: 100-Year Proposed Conditions Hydraulic Results at Selected Locations

Velocity (ft/s) Depth (ft) WSEL (ft – NAVD88)

Average Maximum Average Maximum Average Maximum

XS 1 6.81 11.64 1.31 4.27 5328.77 5329.24

XS 2 5.85 14.77 1.54 3.93 5330.82 5333.50

XS 3 6.57 13.43 1.31 3.79 5333.26 5334.84

XS 4 6.93 14.62 1.47 3.57 5336.08 5336.35

XS 5 5.58 15.91 1.21 4.07 5338.28 5338.57

Page 16 UT FLAP 73(2) La Sal Loop Road - Hydraulic Report

Table 11: 25-Year Existing and Proposed Hydraulic Results Comparison

Velocity (ft/s) Depth (ft) WSEL (ft – NAVD88)

Average Maximum Average Maximum Average Maximum

XS 1 0.08 -0.02 0.02 -0.01 0.01 -0.01

XS 2 -0.53 -0.14 -0.15 0.08 0.08 0.09

XS 3 0.51 0.17 -0.02 0.06 -0.02 0.00

XS 4 0.12 -0.22 0.06 0.18 0.09 0.02

XS 5 0.06 -0.05 -0.02 0.03 0.03 -0.01

Note: Positive values indicate an increase from the existing condition.

Table 12: 100-Year Existing and Proposed Hydraulic Results Comparison

Location Velocity (ft/s) Depth (ft) WSEL (ft – NAVD88)

Average Maximum Average Maximum Average Maximum

XS 1 0.03 -0.31 0.00 -0.02 0.01 0.01

XS 2 -0.01 -0.43 0.00 0.02 0.00 -0.02

XS 3 0.61 0.09 0.00 -0.04 0.01 0.04

XS 4 0.21 -0.28 0.09 0.25 0.14 0.01

XS 5 -0.05 -0.13 -0.01 0.07 0.03 0.06

Note: Positive values indicate an increase from the existing condition.

4.4 SCOUR AND BANK PROTECTION

The scour depth on the outside of the bend at the toe of the embankment slope was estimated using the HEC-23 (Federal Highway Administration 2009) Equation 4.5 for scour at protected bendways, shown below:

𝐷𝐷𝑚𝑚𝑚𝑚𝑚𝑚

𝐷𝐷𝑚𝑚𝑚𝑚𝑚𝑚

= 1.8 − 0.051 �

𝑅𝑅𝑚𝑚

𝑊𝑊

� + 0.0084 �

𝑊𝑊

𝐷𝐷𝑚𝑚𝑚𝑚𝑚𝑚

Where:

Rc = centerline radius of the bend, ft.

W = Width of bend, ft Dmxb = Maximum water depth in bend, ft Dmnc = Average water depth upstream of bend, ft.

The results are shown in Table 13. The maximum water depth in the bend is estimated as 2.4 feet, resulting in local toe scour depth of 1.4 feet. There is no contraction scour at this location and the long term degradation is assumed to equal 1 foot. The total scour estimate is 2.4 feet.

Page 17 UT FLAP 73(2) La Sal Loop Road - Hydraulic Report

Table 13: Bend Scour Depth Estimate

Parameter Value Design Frequency 25-year

Rc (ft) 88 W (ft) 81.65

Dmnc (ft) 0.96 Dmxb (ft) 2.4

Cv 1.3 Toe Scour (ft) 1.4

Long Term Degradation (ft) 1.0 Total Scour in Bend (ft) 2.4

The required bank protection median rock size (d50) was estimated using the HEC-23 Design Guideline 4 Equation 4.1 shown below:

𝑑𝑑30 = 𝑦𝑦�𝑆𝑆𝑓𝑓𝐶𝐶𝑠𝑠𝐶𝐶𝑣𝑣𝐶𝐶𝑇𝑇�

⎡ 𝑉𝑉𝑑𝑑𝑑𝑑𝑠𝑠

�𝑘𝑘1�𝑆𝑆𝑔𝑔 − 1�𝑔𝑔𝑦𝑦⎦

2.5 𝑑𝑑50 = 1.2𝑑𝑑30

Where:

d30 = particle size for which 30% is finer by weight, ft.

d50 = median particle size, ft.

y = local depth of flow, ft.

Sf = safety factor (1.1).

Cs = Stability coefficient, assumed 0.3 for angular rock.

Cv = Velocity distribution coefficient, 1.283-0.2log(Rc/W) for outside of bends.

CT = Blanket thickness coefficient, 1.0 recommended.

Vdes = Characteristic velocity, assumed to equal average velocity for straight natural channel.

K1 = Side slope correction factor, 0.87 for 2H:1V bank slope.

Sg = Specific gravity of riprap, assumed 2.5.

g = acceleration of gravity, 32.2 ft/s2.

The above equation was used in the SMS Data Calculator to estimate values based on the model water depth and velocity results. Figure 17 shows the resulting median riprap size (d50) in 3 inch increments for the for the 25-year return period. The maximum median size at the toe of the embankment slope is approximately 19 inches. The figure also shows approximate limits of the riprap bank protection. The upper elevation varies from approximately 5,337 feet at the upstream end to 5,331 feet at the downstream end to provide for 2 feet of freeboard. In addition, the bank protection extends downstream around the bend to protect against meander migration. Figure 18 shows an example detail for riprap

Page 18 UT FLAP 73(2) La Sal Loop Road - Hydraulic Report installation with buried toe. Based on the calculations the toe should be embedded a minimum of 2.4 feet below existing bed elevation, but due to practical construction requirements it is recommended that the toe is embedded a minimum of 2d50 or 3.5 feet. Geotextile filter should be Class 1 Type C non-woven according to FP-14 Section 714.01.

Figure 17: 25-Year Riprap Median Size (D50) in inches

Figure 18: Riprap Bank Protection Details (source HEC-23 Figure 4.2)

Maximum Riprap D50 at toe of slope = 19.4”

Line depicts approximate extents and upper elevation of bank protection

Page 19 UT FLAP 73(2) La Sal Loop Road - Hydraulic Report

5 RECOMMENDATIONS

Hydrology and hydraulics analyses were conducted for the US FLAP 73(2) La Sal Mountain Loop Road Project. Based on the hydraulic results the following bank protection measures are recommended:

• Riprap Class 6 bank protection according to FP-14 Section 705.02, protection extents as shown in the project plans.

• Minimum embedment depth below existing bed elevation of 3.5 feet.

• Top elevation of riprap to provide a minimum 2 feet freeboard from 25-year water surface elevation.

• Class 1 Type C non-woven geotextile filter according to FP-14 Section 714.01.

Page 20 UT FLAP 73(2) La Sal Loop Road - Hydraulic Report

6 REFERENCES

Aquaveo. 2020. Surface-water Modeling System (SMS), version 13.0.11. Provo, UT.

Federal Emergency Management Agency. 2020. FEMA Flood Map Service Center. Accessed March 11, 2020. https://msc.fema.gov/portal/home.

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

Kenney, Terry A., Chris D. Wilkowske, and Shane J. Wright. 2008. "Methods for Estimating Magnitude and Frequency of Peak Flows for Natural Streams in Utah." Scientific Investigations Report 2007-5158, U.S. Geological Survey. https://pubs.usgs.gov/sir/2007/5158/.

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

Version 3.2.

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/.

UT FLAP 73(2) La Sal Loop Road - Hydraulic Report

Appendix A – Hydrologic Analyses

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UT FLAP 73(2) La Sal Loop Road - Hydraulic Report

Appendix B - Hydraulic Analyses

SRH-2D Computational Mesh

SRH-2D Existing 25-Year WSEL

SRH-2D Existing 100-Year WSEL

SRH-2D Existing 25-Year Velocity

SRH-2D Existing 100-Year Velocity

SRH-2D Proposed 25-Year WSEL

SRH-2D Proposed 100-Year WSEL

SRH-2D Proposed 25-Year Velocity

SRH-2D Proposed 100-Year Velocity

SRH-2D Proposed 25-Year Riprap D50 (Assuming SG = 2.5)

4.3.5 Scour at protected bendways:

SRH‐2D Output from Mesh_Slope SlopOpt_25yr_1020 dataset extracted 3/12/2020

N:\UT\ut73(2)\Hydraulics\6_Hydraulic‐Design\2D\Revised\lasal_revised.sms

Ave Max Ave Max reach_1 XS 1 8.42432 143.22 0.98 4.93 10.61 0.89 3.57 reach_1 XS 2 71.6131 103.85 1.61 5.41 13.55 1.44 3.32 reach_1 XS 3 143.353 81.65 1.42 6.67 12.2 1.29 3.04 reach_1 XS 4 245.075 125.66 0.96 5.01 12.67 0.95 2.81 reach_1 XS 5 339.596 129.31 0.9 3.83 13.53 0.76 3.23

Parameter Value

Design Frequency 25‐year Rc (ft) 88

W (ft) 81.65

Dmnc (ft) 0.96

Dmxb (ft) 2.36 <‐ Scour depth estimate

Cv 1.3 <‐Velocity distribution coefficient for Equation 4.1

Toe Scour Depth (ft) 1.40

Long Term Degradation (ft) 1

Total Scour in Bend (ft) 2.4

Water Depth (ft)

Scour Estimate:

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)

Velocity (ft/s)

Location Station Width (ft) Hydraulic Depth (ft)Reach

4.4 Scour and Bank Protection