h_(2).pdf

III

Contents Section Page

Acronyms and Abbreviations ............................................................................................................... v

1 Introduction ......................................................................................................................... 1‐1

1.1 Existing Conditions ........................................................................................................... 1‐2

1.1.1 General................................................................................................................ 1‐2

1.2 Floodplain Investigation ................................................................................................... 1‐4

1.3 Wetlands .......................................................................................................................... 1‐4

2 Drainage Design Criteria and Methodology ........................................................................... 2‐1

2.1 A. General ........................................................................................................................ 2‐1

2.2 Hydrology ......................................................................................................................... 2‐1

2.3 Hydraulic Analysis ............................................................................................................ 2‐1

2.4 Roadside Ditches .............................................................................................................. 2‐2

2.5 Pavement Drainage .......................................................................................................... 2‐2

2.6 Erosion Control ................................................................................................................ 2‐2

2.7 Miscellaneous .................................................................................................................. 2‐2

3 Hydrologic Analysis ............................................................................................................... 3‐1

3.1 Major Basin Analysis ........................................................................................................ 3‐1

3.2 Minor Basin Analysis ........................................................................................................ 3‐1

4 Hydraulic Analysis ................................................................................................................ 4‐1

4.1 Major Crossing Analysis and Design ................................................................................ 4‐1

4.2 Minor (less than 48‐inch Diameter) Culverts ................................................................... 4‐1

4.3 Culvert Material Selection ............................................................................................... 4‐1

4.4 Curb Sections and Inlets .................................................................................................. 4‐1

4.5 Ditches ............................................................................................................................. 4‐1

5 Recommended Improvements .............................................................................................. 5‐1

5.1 Major Drainage Crossing .................................................................................................. 5‐1

5.2 Minor (Less than 48‐inch Diameter) Culverts .................................................................. 5‐1

5.3 New Culvert Locations ..................................................................................................... 5‐1

5.4 Storm drain and Curb ....................................................................................................... 5‐3

5.5 Ditches ............................................................................................................................. 5‐4

5.6 Underdrains ..................................................................................................................... 5‐4

6 Erosion and Sediment Control .............................................................................................. 6‐1

6.1 Construction BMPs .......................................................................................................... 6‐1

6.2 Permanent BMPs ............................................................................................................. 6‐1

7 References ............................................................................................................................ 7‐1

Appendices A Existing Culvert Inventory B FEMA Floodplain Mapping C Corrosion Test Results & Service Life Calculations

IV

Tables

2‐1 Ditch Design Criteria 2‐2 2‐2 Pavement Drainage Design Criteria 2‐2 2‐3 torm Drain Design Criteria 2‐2 5‐1 Proposed Pipe Crossings 5‐2

Figures

1‐1 Location Map and Vicinity Map 1‐2 Culvert Inlet with Sediment Deposition 1‐3 Drop Inlet with Sediment Deposition 1‐4 Typical Asphalt Curb

V

Acronyms and Abbreviations ADT Average Daily Traffic

ATV all‐terrain vehicle

BMP best management practices

CFLHD Central Federal Lands Highway Division

CMP Corrugated Metal Pipe

FEMA Federal Emergency Management Agency

FR Forest Road

HW/D headwater depth/diameter

MP Milepost

PDDM Project Development and Design Manual

SR State Route

WSEL water surface elevation

SECTION 1

1‐1

Introduction This Draft Final Hydraulics Report describes the hydrologic and hydraulic design recommendations for improvements to Kolob Canyon Road. Kolob Canyon Road is located in Washington County, Utah, and lies within the boundaries of Zion National Park. It provides access to several hiking trails including Taylor Creek, Lee Pass and South Fork Trails. See Figure 1‐1 for Location Map and Vicinity Map.

Kolob Canyon Road is classified as an Area Road and accommodates a current average daily traffic (ADT) of 280 and is maintained by the National Park Service. The general terrain of the route is mountainous with steep cut and fill slopes. The route is paved with a hot plant mix surface. Kolob Canyon Road begins at I‐15 right‐of‐way at the junction of I‐15 and Kolob Canyon Road and proceeds 5.35 miles where it terminates at Timber Creek parking lot at the top of the canyon. The paved route traverses through a section of Kolob Canyon, through mountainous terrain, along various side slopes, valleys, and crosses multiple drainages. The route is comprised of two travel lanes, shoulders and various pull outs, parking areas, and overlooks.

The project proposes pulverizing and paving Kolob Canyon Road for the entire 5.35 miles, with areas of minor roadway realignment to provide two 12‐foot travel lanes and one to three‐foot shoulders. Two areas where that have been damaged due to landslide will be reconstructed. Pavement will be removed that is outside of this roadway template and is not part of a pullout or parking lot. The project proposes grading and paving Timber Creek parking lot and improvements to the Visitor’s Center parking lot to be compliant with the Americans with Disabilities Act (ADA) requirements. Other parking lots and pull outs will be reconfigured, removed, or repaved with the focus being ADA access, improved parking delineation and an overall reduction in paved surfacing.

The majority of the proposed road reconstruction will closely follow the existing road, with minor realignments, as needed, to improve safety, maintenance and to reduce impacts. Improvements will require grading of roadside ditches, curbing to accommodate a constant typical section, and removing pullouts which will reduce the paved area along the route. Comfort station replacements and associated grading is planned at Taylor Creek, South Fork and Timber Creek parking lots. Existing culverts and drop inlets that are damaged or full of sediment will be replaced.

In steep cut areas where rockfall has been a hazard and recurring maintenance problem, curb lines will be adjusted towards the centerline to provide additional space to accommodate debris shedding from the cut slope, while maintaining the two 12‐foot travel lanes and one to three‐foot shoulders.

A secondary option is rehabilitation of Zion Canyon Scenic Drive, located in the southeasterly portion of Zion National Park, adjacent to Park’s main entrance. Rehabilitation includes milling and overlay of the existing roadway surface from the intersection of Zion‐Mount Carmel Highway to the end of the route, described as “The Narrows” trail head and Temple of Sinawava parking area, approximately 6.22 miles.

There is notable pavement rutting at the Zion Lodge, which is a key bus transit loading and unloading point. A full reconstruction of the pavement at this intersection is included as part of the Zion Canyon Scenic Drive work. There are no drainage features proposed for this option.

SECTION 1 – INTRODUCTION

1‐2

Figure 1‐1. Location Map and Vicinity Map

1.1 Existing Conditions

1.1.1 General

The 5.35‐mile route of Kolob Canyon Road consists of approximately 50 culvert crossings, 30 drop inlets with pipe outlets and 25 slope drains consisting of pipe, halfpipe, asphalt or riprap located on steep embankments. General drainage feature condition assessments were performed during an initial field visit on June 27th and 28th, 2017 and subsequently during the 70% review walkthrough held October 31 through November 2, 2017. There are 11 major culvert crossings (size 48‐inch or larger) and two drop inlets with major culvert outlets. There are two major culvert crossings that convey the South Fork of Taylor Creek under the roadway, and the other major culverts are cross culverts that convey flow from offsite drainage areas. The major culverts are in good condition and free of sediment deposition except for a 60‐inch culvert located at milepost 3.34. The outlet end of this culvert is almost completely plugged due to sediment deposition. It was agreed upon with the National Park Service (NPS) and Central Federal Lands Highway Division (CFLHD) that this culvert will not be addressed with this project.

The NPS will clean out this culvert with maintenance resources.

Begin Project Milepost 0.0

End Project Milepost 5.35

South Fork Taylor Creek Milepost 3.34

Project Location

1‐3

Figure 1‐2. Culvert Inlet with Sediment Deposition

Neither the June or November 2017 site visit revealed evidence of roadway overtopping along the route. According to Zion National Park maintenance personnel, there are no roadway overtopping problems due strictly to hydraulic capacity issues. However, it was observed, and maintenance personnel confirmed, that sediment deposition is an issue at certain locations along the route and that plugged inlets and pipes lead to mud and water flow across the roadway. Multiple inlets along the project route are currently filled with sediment and require frequent maintenance to remain functional.

Figure 1‐3. Drop Inlet with Sediment Deposition

Drainage areas contributing to existing culvert crossings are small (less than 150 acres) and have similar basin characteristics; they are steep and lightly to heavily covered with trees, brush and short grasses.

All drainage areas are conveyed by culverts under the roadway. In general, roadway drainage from the beginning of the project to milepost 3.6 drains to the South Fork of Taylor Creek or main Taylor Creek.

From milepost 3.6 to the end of the project, roadway drainage areas flow to La Verkin Creek.

1‐4

Roadside ditches within existing cut sections are vegetated, but in some cases, lack a defined shape and are full of sediment. Existing asphalt curb has been damaged by snow plows and has deteriorated over time.

Figure 1‐4. Typical Asphalt Curb

The 6.22‐mile route of Zion Canyon Scenic Drive consists of a roadside ditch on the cut side of the roadway, and ditch relief cross culverts that outlet to the north fork of the Virgin River. No additional drainage features will be added as part of this roadway rehabilitation, and all existing drainage features will be protected in place.

1.2 Floodplain Investigation

The project is not located adjacent to or within a Federal Emergency Management Agency (FEMA) mapped flood hazard area. The project area is located on FEMA Map Number 49053C0375G. See Appendix B for the project area FEMA map.

Since the project is not within a mapped FEMA Floodplain, neither a Conditional Letter of Map Revision (CLOMR) nor a Letter of Map Revision (LOMR) will be submitted. Fish passage will not be accommodated since all streams crossing the roadway are ephemeral.

1.3 Wetlands

A wetland delineation will be performed by the National Park Service as part of the Environmental Compliance Study and resource report preparation. It is not anticipated that wetlands are located within the project area.

SECTION 2

2‐1

Drainage Design Criteria and Methodology

2.1 A. General

The drainage design for Kolob Canyon Road project will be in accordance with the Federal Lands’ Project Development and Design Manual (PDDM) Chapter 7.

The full length of the roadway is classified as an Area Road. The projected Average Daily Traffic (ADT) is less than 1200, and the roadway is not designated as a critical access road.

Numerous drainages intersect the existing roadway, and culverts convey these drainages under the road. A project site visit taken in June of 2017 revealed some culverts and drop inlets were full of sediment. The culverts will be replaced with larger pipes and the drop inlets will be replaced with structures that will provide additional capacity and will improve maintenance access.

2.2 Hydrology

Existing terrain is steep and lightly to heavily vegetated with trees, bushes, sage brush and short grasses.

Drainage areas contributing to existing crossings where culverts and inlets will be replaced are small (less than 150 acres). Due to the small drainage size and very little history of overtopping, no hydrologic analysis was performed to determine peak design flows for the proposed culvert replacement. No onsite hydrologic analysis was performed due to numerous superelevation transitions that necessitate frequent interception of flow and leaving small onsite tributary areas.

2.3 Hydraulic Analysis

Since peak flows will not be developed for the culvert crossing replacements, determination of inlet vs.

outlet control and development of HD/d and hydraulic grade lines will not be made. Project minimum pipe sizes will be used.

Culverts used as cross drains that will be replaced, as well as outlet pipes of drop inlets, will match existing slopes in most cases. To minimize excavation and associated impacts, existing culvert replacements with a steep slope will be replaced with new culverts with a minimum slope of 3%. The existing culverts will be removed to the extent needed to place the new culvert, and the rest will be plugged.

New culverts shall have a minimum service life of 50 years. The gage of pipe shall be of a thickness to achieve the required minimum service life instead of using bituminous coated pipe. Because of wildfire concerns, plastic pipes shall not be used.

Minimum pipe size for ditch relief culverts and drop inlet pipe outlets will be 24 inches. Where sedimentation problems were observed or reported, the new pipe will be 36 inches. Where shallow inlet conditions will not allow the use of 36‐inch diameter pipes, 24‐inch pipes will be used.

Outlet energy dissipation and permanent erosion control will be installed for all proposed culvert crossings and where field observations determined a need for it. Final designs for outlet energy dissipation will be based on CFLHD standard for placed riprap or recommendations for energy dissipation based on recent designs in steep terrain. Stream stability shall comply with the scour analysis methods found in FHWA’s HDS 6, HEC 11, HEC 14, HEC 15, HEC 18, HEC 20, HEC 23, and NCHRP.

SECTION 2 – DRAINAGE DESIGN CRITERIA AND METHODOLOGY

2‐2

2.4 Roadside Ditches

Roadside ditches are anticipated in cut situations. Design and stabilization of roadside ditches shall comply with FHWA’s HEC 15. Roadside ditches will primarily outlet to existing cross drains, existing or proposed drop inlets, or ditch relief culverts. Design shall comply with criteria shown in Table 2‐1.

Table 2‐1 Ditch Design Criteria

Topic Capacity Design Event Min. Slope Ditch Relief Culvert Min. Size

Water Surface Elevation

Ditch Drainage 10‐year 0.5% 24 inches Not to exceed bottom of roadway aggregate base layer

2.5 Pavement Drainage

The roadway will continue to sheet flow through the majority of the project length. However, the addition of curbed sections will require additional drop inlets and storm drain pipe to meet spread criteria of half of the travel lane. Design shall comply with criteria shown in Tables 2‐2 and 2‐3 below.

Table 2‐2 Pavement Drainage Design Criteria

Topic Capacity Design Event Spread Depth Inlet Clogging

Pavement Drainage 10‐year, 50‐year in sumps Half of travel lane Curb height or 6” in sumps

50 percent in sump condition

Table 2‐3 Storm Drain Design Criteria

Topic Capacity Design Event Min. Size Min. Slope

Storm Drains 10‐year, 50‐year in sumps 24‐inch diameter Pipe‐full velocity ≥ 3 ft/sec

2.6 Erosion Control

Temporary Best Management Practices (BMP) as shown in the standard CFLHD details will be used for control of erosion during construction. Pinned wire‐enclosed riprap and loose riprap is proposed as a permanent erosion control measure for culvert outfalls.

2.7 Miscellaneous

The Kolob Canyon Road project will see a reduction in impervious areas through the elimination or reduction in area of parking lots and pull outs as well as through reducing pavement width to maintain a 26 to 30‐foot paved roadway width for the entire route. As such, peak flows resulting from impervious surfacing will be decreased throughout the project. No new mitigation of impervious based peak flows will be introduced.

SECTION 3

3‐1

Hydrologic Analysis

3.1 Major Basin Analysis

Although a number of major culvert crossings are within the project limits, replacement is not anticipated, therefore no hydrologic analysis is anticipated.

3.2 Minor Basin Analysis

Existing terrain is steep and lightly to heavily wooded with trees, brush, and short grasses. Drainage areas contributing to existing crossings are small (less than 150 acres). Onsite analysis and minor offsite analysis was deemed unnecessary. Stormwater runoff will be intercepted at existing locations with numerous new facilities. Runoff will be intercepted at every superelevation transitions, which is not the case in existing conditions. This leaves small tributary areas in curbed roadway segments that did not need to be analyzed.

SECTION 4

4‐1

Hydraulic Analysis

4.1 Major Crossing Analysis and Design

There are 11 major crossings on the project. Replacement of the major crossings is not anticipated as a part of this project, therefore, hydraulic analysis will not be required.

4.2 Minor (less than 48‐inch Diameter) Culverts

Since peak flows will not be developed, determination of inlet vs. outlet control and development of HW/D and hydraulic grade lines will not be made. Project minimum pipe sizes will be used. See discussion in Section 3, Drainage Design Criteria and Methodology.

4.3 Culvert Material Selection

Soil testing (resistivity, pH, Chloride and Sulfate) to support appropriate culvert selection was performed by CH2M. Between the beginning of the project at station 5+01.71 and station 205+00 (Lee Pass), the existing soils are rated as ‘highly corrosive’ due to low soil resistivity values averaging 778 ohm‐cm.

Using the soil resistivity of the project samples, the maximum soil pH, and Exhibit 7.3‐B, the service life for galvanized steel culverts was determined to be 36.6 years. In order to achieve the required 50‐year service life for culverts, a minimum gage of 12 will be required (0.109 inches). Between station 205+00 and the end of the project at 283+45, the soil resistivity average 2474 ohm‐cm. Using the soil resistivity of the project samples, the maximum soil pH, and Exhibit 7.3‐B in a service life for galvanized steel culverts was determined to be 58.8 years. The minimum pipe gage of 16 (0.064 inches) may be used through this section. See Appendix C for corrosion test results and service life calculations. Most areas adjacent to the roadway are forested and due to the potential for pipe damage caused by forest fire, plastic pipe will not be considered.

4.4 Curb Sections and Inlets

Sections of curbed roadway have been evaluated for flow paths at superelevation transitions, and relief inlets have been designed to intercept runoff at locations where concentrated stormwater will cross the roadway at superelevation transitions. Stormwater runoff is intercepted at all superelevation transitions on Kolob Canyon.

4.5 Ditches

Existing paved ditches will be replaced to perpetuate existing drainage patterns conveying flow to existing culvert crossings. Two new ditches are proposed at the Visitor Center parking lot to convey flow and decrease sediment buildup. These ditches have a slope of 0.50% and are not an erosion concern.

SECTION 5

5‐1

Recommended Improvements

5.1 Major Drainage Crossing

There are 11 major drainage crossings on the project. The inlet end of an existing 54‐inch culvert near station 65+85 was covered by a mud flow event in 2005 and is still buried today. Inspection from the downstream end revealed that the culvert is in good shape and clear of sediment for the majority of the pipe run. Therefore, it is recommended that the contractor excavate to locate and uncover the inlet end of the 54‐inch CMP. A catch basin and grate will be installed where stormwater runoff currently flows to, and a 48‐pipe will be installed, crossing the road at station 65+26.

Only the 60‐inch culvert on South Fork Taylor Creek at milepost 3.34 needs to be replaced due to sediment deposition on the outlet side; however, it has been decided by NPS and CFL that no remediation of this culvert will occur with this project. NPS will remove the sediment on the outlet side of the culvert with maintenance personnel.

5.2 Minor (Less than 48‐inch Diameter) Culverts

In general, existing culverts on the project are in fair to good condition. Some minor culverts will need to be replaced due to sediment deposition, rusting, or structural damage. Replacements for culverts identified as having sedimentation issues will be 12‐inches larger in diameter than the existing culvert size where cover allows.

The project was evaluated with respect to the need for outlet energy dissipation and permanent erosion control measures. In general, new culverts with outfalls on steep terrain will include loose riprap pads, and areas with extremely steep terrain wire enclosed pinned riprap (revet mattresses) will be placed at the outlet of end of pipes. Culvert cleaning will be necessary for some culverts that have minor sediment deposition and where the culverts are in good condition. Flared end sections will be added to proposed culverts to improve inlet efficiency and reduce outlet erosion and undercutting potential, and some damaged flared end sections on existing culverts will be replaced.

5.3 New Culvert Locations

Existing culverts are located at most low points and drainage channels to convey cross drainage along the project route. During the November 2017 field review, it was observed that three locations needed culverts to drain low lying areas. Culverts at these locations are included in the plans. Ditch relief culvert spacing appears to be adequate. Additional new culverts will be limited to replacing existing culverts that are damaged or full of sediment. Refer to Table 5‐1 – Proposed Pipe Crossings for information on the new culverts.

SECTION 5 – RECOMMENDED IMPROVEMENTS

5‐2

Table 5‐1. Proposed Pipe Crossings

Location (Sta.)

Diameter (inch)

Barrels Invert In (feet)

Invert Out (feet)

Length (feet)

Slope

5+21 24 1 5050.65 5050.45 38 0.53

11+20 24 1 5082.99 5080.27 55 4.94

14+52 24 1 5101.95 5101.26 7 9.83

16+53 24 1 5113.71 5111.77 65 3.01

17+70 36 1 5116.21 5110.48 56 10.36

26+35 36 1 5172.06 5168.83 84 3.87

28+73 36 1 5185.00 5183.73 42 3.00

31+26 36 1 5197.10 5195.43 56 3.01

36+12 36 1 5228.73 5221.45 45 16.01

39+58 24 1 5249.27 5248.24 34 3.01

41+54 36 1 5260.67 5258.01 53 5.01

45+54 36 1 5288.44 5287.14 43 3.04

53+34 36 1 5306.85 5304.96 63 3.00

65+27 48 1 5347.94 5345.73 74 3.01

72+15 48 1 5359.91 5354.11 55 10.60

76+22 24 1 5363.16 5362.12 35 3.00

83+49 24 1 5369.43 5368.17 42 3.01

89+83 36 1 5402.50 5401.36 35 3.22

92+33 36 1 5415.09 5413.80 42 3.11

93+74 36 1 5420.04 5418.04 46 4.34

97+02 EXISTING CULVERT CROSSING TO REMAIN

97+12 36 1 5425.57 5424.00 52 3.00

99+09 36 1 5427.52 5424.48 42 7.32

100+63 36 1 5428.76 5425.17 52 6.85

104+62 36 1 5439.43 5437.79 45 3.63

114+15 36 1 5513.42 5511.99 41 3.46

117+39 36 1 5535.21 5534.05 39 3.00

128+93 36 1 5623.42 5612.44 55 19.87

135+22 36 1 5672.84 5670.61 56 3.97

144+23 36 1 5747.93 5746.01 64 3.01

149+14 24 1 5788.04 5786.68 44 3.08

156+30 36 1 5821.58 5820.28 43 3.00

5‐3

Table 5‐1. Proposed Pipe Crossings

Location (Sta.)

Diameter (inch)

Barrels Invert In (feet)

Invert Out (feet)

Length (feet)

Slope

163+34 24 1 5866.26 5865.54 24 3.03

167+69 36 1 5901.28 5893.21 81 10.00

187+48 36 1 5983.28 5981.68 53 3.00

196+71 36 1 6041.83 6040.28 45 3.47

201+17 36 1 6064.93 6062.97 65 3.00

204+68 18 1 6076.07 6068.94 33 21.67

210+12 24 1 6081.23 6080.89 11 3.10

215+15 24 1 6087.76 6086.03 58 3.00

225+92 24 1 6069.38 6066.63 15 18.35

228+78 24 1 6048.30 6046.91 46 3.01

232+40 24 1 6021.32 6020.23 36 3.01

255+72 24 1 6034.92 6033.90 34 3.01

266+14 24 1 6103.95 6100.79 5 3.00

266+14 36 1 6097.21 6096.83 9 4.13

266+14 36 1 6096.43 Connect to existing

5 NA

285+65 24 1 6228.55 6225.58 98 3.05

5.4 Storm drain and Curb

Work proposed for the parking lots will not require removal and replacement of existing drop inlets;

these will be protected in place. However, an outlet pipe of a drop inlet in the Timber Creek parking lot will need to be removed and the new outlet pipe will be realigned to accommodate fill from a new comfort station. In areas of installation of new 6‐inch reveal curbing, existing drop inlets will be protected in place.

Where required to mitigate rockfall hazards, new 6‐inch reveal concrete curb will be placed in front of existing asphalt curb with compacted fill placed between the two curbs. This will accommodate rockfall maintenance outside the travelled way. At existing drop inlet locations, where existing asphalt curb is present, 12‐inch reveal concrete curb will replace existing asphalt curb behind the inlet. A paved asphalt shoulder will be placed around the drop inlet. The existing curb, which has become integral to the existing cut slope will remain in place throughout much of the project route. Some existing asphalt curb will be replaced with 6‐inch reveal concrete curb where existing paved asphalt ditches and aprons are needed to convey stormwater runoff to existing culverts. Lastly, existing fill‐side asphalt curb located primarily on the inside of horizontal curves will be replaced with 6‐inch reveal concrete curb.

Existing roadside rundowns that are damaged or plugged will be replaced. Other locations where rundowns exist will be modified to accommodate the new edge of pavement. Curb cuts will be placed in the new concrete curb at superelevation transitions and at low points in pullouts and parking lots as

5‐4 required. Revet mattresses or riprap aprons will be placed behind the curb cuts to prevent erosion and undercutting.

Stormwater runoff will be intercepted upstream of superelevation transitions by either drop inlets with bike safe grates along the edge of the roadway, curb cuts or tapered curbs to allow runoff to flow down existing paved ditches or aprons. Existing condition analysis showed that not all of the flow was intercepted upstream of superelevation transitions. Additional drainage features will prevent concentrated flow from crossing the roadway throughout the route.

5.5 Ditches

As a part of the typical section, roadside ditches will be established or redefined that will convey drainage away from the road section. Providing positive drainage away from the surfacing section enables a longer design life for the pavement. Existing ditches were not evaluated for capacity with respect to the requirement that the design flow WSEL be below the bottom of the road section base. All roadside ditches as part of the typical section will be paved. There are three new types of ditches proposed; one to convey concentrated runoff away from the road, one to convey flow from the outlet of a culvert, and one to convey flow to the inlet side of a culvert.

Site investigations indicated that runoff in the existing roadside ditch between station 19+45 and 24+84 has caused erosion to the road side bank. This bank will be armored with Class 3 riprap. An existing ditch with a steep grade between station 85+50 and 89+50 will have riprap check dams installed to reduce the velocity, and erosion potential, in the ditch.

5.6 Underdrains

Underdrains are recommended at locations where groundwater has been a contributing factor to landslides and roadway subgrade saturation and associated surfacing damage. See the project Geotechnical Report for additional discussion and locations of proposed underdrains.

SECTION 6

6‐1

Erosion and Sediment Control

6.1 Construction BMPs

Fiber roll, riprap or gravel bag check dams will be utilized in disturbed cut ditches and immediately upstream of existing and proposed culvert crossings to minimize the amount of sediment leaving the project within concentrated flows. Silt fencing or fiber rolls will be used at the base of disturbed slopes to minimize sediment leaving the project via sheet flow. To minimize soil tracking off the project on vehicles, stabilized construction exits will be used where construction traffic is leaving disturbed areas.

6.2 Permanent BMPs

Many slopes on the project are at or steeper than 2:1. Restoration of areas disturbed by construction will be performed by NPS.

Many of the proposed culverts outfall onto steep embankment slopes. To protect the slope from erosion caused by concentrated flow, loose riprap pads or revet mattresses at outlets will be used.

Riprap pads may also be placed at the inlet side culverts to prevent sediment deposition in the culverts.

If warranted due to erosion potential, ditches in steep areas will be riprap‐lined or riprap check dams will be installed to prevent erosion.

Additional water quality mitigation measures are not proposed.

SECTION 7

7‐1

References American Association of State Highway and Transportation Officials (AASHTO). 2011. A Policy on Geometric Design of Highways and Streets.

Federal Highway Administration (FHWA) Dec 2012. “Federal Lands Highway Project Development and Design Manual”, U.S. Department of Transportation, Washington, DC. December.

Utah Department of Transportation (UDOT) Jan 2004. Manual of Instruction, Roadway Drainage.

Appendix A Existing Drainage Facilities Inventory

Appendix A

Inventory Information

The attached inventory information was compiled based on field observations during the scoping site visit on June 27-29, 2017. A KMZ file has been compiled and is named “Kolob Canyon RD.

Drainage Features.kmz”.

Mile Post Road Width Feature Side Comment

DRAINAGE FEATURES INVENTORY

Route Begin n/a Intersection with I-15 northbound on-ramp.

C-1

24” CMP Both Some rust on bottom, inlet side needs cleaned out. Replace end section.

C-2 24” CMP Both Stone headwall in good condition; slight rust in culvert.

Retaining wall Right Shoulder retaining wall – slight deflection.

C-3 24” CMP Both Some rust on bottom. Good inlet and outlet conditions.

C-4

24” CMP Both Good inlet condition; poor outlet condition. Appears to pond at outlet causing more rust.

DI-1

DI w/ 24” CMP Right DI has screen for grate. Both grate and pipe full of sediment. REMOVE

AND REPLACE DI AND PIPE.

DI-2 DI w/ 36” CMP Both 4’ DI, looks clean. Could not find (CNF) outlet.

DD-1 12” Downdrain Left Top half cut off, clean

DI-3 DI w/ 24” CMP Right DI and pipe clear. Need end section and outlet riprap apron.

DI-4

Sediment in DI; outlet 75% plugged. REMOVE AND REPLACE DI

AND PIPE.

DI-5 DI w/ 24” CMP Right Sediment in DI; clean DI.

C-5 36” CMP Both Sediment and rock in culvert; clean out culvert.

DI-6

DI w/ 30” CMP Right Some sediment in inlet; sediment and rock in pipe. Clean out inlet and culvert.

C-6 30” CMP Both Culvert clear. Replace outlet end section.

C-7 12” CMP Right Culvert plugged. REMOVE AND REPLACE.

DI-7 DI w/ 24” CMP Right Inlet clear. CNF outlet/ heavy vegetation.

C-8 24” CMP Both Culvert clear

DI?? Right Possible Buried DI

C-9 66” CMP Both Culvert Clear

DD-2 Half Pipe DD Right Clear

C-10 36” CMP Both Half filled with rock and sediment. REPLACE

C-11

60” CMP Both Sediment deposition all the way through; clean. INSTALL INLET

RIPRAP APRON.

C-12 12” CMP Right Clear

C-13 30” CMP Both Clear (no photo)

DI-8 DI w/ 24” CMP Right Inlet clear. CNF outlet; heavy vegetation.

DI-9 DI w/ 24” CMP Right Inlet clear. CNF outlet; heavy vegetation.

DI-10 DI w/ 24” CMP Right Inlet and culvert full of sediment. REMOVE AND REPLACE.

C-14 24” CMP Both Culvert Clear

DI-11

DI w/ 48” CMP Right Bad connection between inlet and culvert. REPLACE INLET OR

REPAIR CONNECTION.

DI-12 DI w/ 24” CMP Right Inlet full of sediment. REPLACE INLET.

DI-13

Inlet full of sediment; CNF outlet. REPLACE INLET AND POSSIBLY

CULVERT.

Width Feature Side Comment

DRAINAGE FEATURES INVENTORY

DI-14

Inlet grate may need to be replaced with Bike Safety Grate.

Undercutting occurring at outlet End Section. INSTALL OUTLET

RIPRAP APRON.

C-15 12” CMP Right Culvert Clear.

C-16 66” CMP Both Culvert Clear.

DI-15

DI w/ 24” CMP Left Inlet clear. INLET AND PIPE WILL NEED TO BE REMOVED AND

RELOCATED IF PARKING LOT IS REDUCED.

C-17 24” CMP Both Outlet buried. REPLACE CULVERT.

C-18 36” CMP Both Culvert Clear.

DI-16 DI w/ 24” CMP Right Inlet and pipe clear.

C-19 24” CMP Both Culvert Clear.

DD-3 Half Pipe DD Left Clear

C-20 12” CMP Right Clear

DI-17 DI w/ 24” CMP Right Inlet and culvert clear.

C-21 36” CMP Both Culvert Clear

DD-4 Half Pipe DD Right Clear

C-22 18” CMP Both REPLACE.

C-23 60” CMP Both Culvert clear.

DI-18 DI w/ 24” CMP Right Inlet Clean. May raise grate elevation 2 to 4 inches.

C-24 12” CMP Left Outlet plugged. REPLACE.

C-25 48” CMP Both Culvert Clear

DI-19 DI w/ 36” CMP Left DI full of sediment. REPLACE DI AND INSPECT PIPE.

C-26 48” CMP Both Culvert clear.

C-27 24” CMP Both Culvert Clear.

DD-5 Half Pipe DD Right Clear

C-28

60” STEEL Both

Inlet side clear; outlet side almost completely plugged off with sediment deposition. THIS IS THE MAJOR CULVERT OF CONCERN.

DISCUSSIONS NEED TO TAKE PLACE ON REMEDIAL ACTION

MOVING FORWARD.

C-29

18” CMP Right Pipe separation above ground. NEED TO BURY PIPE, INSTALL END

SECTION, AND INSTALL RIPRAP APRON.

C-30 18” CMP Right Culvert clear. REPLACE UPSTREAM END SECTION.

C-31 24” CMP Both Culvert clear. Clear vegetation at upstream end.

DI-20 DI w/ ?? CMP Left DI almost completely Buried. REPLACE DI AND INSPECT PIPE.

C-32

48” CMP Both Culvert clear besides a couple of rocks that need to be cleaned so no sediment builds up.

C-33

12” CMP Right Outlet of pipe possibly plugged. MAY NEED TO REPLACE WITH PIPE

OR RIPRAP APRON.

DI-21

DI w/ 24” CMP Left Inlet needs cleaned. REMOVE AND REPLACE INLET; INSTALL

CURB BEHIND INLET.

DI-22 DI w/ 24” CMP Left Inlet needs cleaned; culvert clear.

C-34 12” CMP Right Culvert clear. Outlet appears to have rock in the way.

C-35 36” CMP Both Culvert clear.

C-36 48” CMP Both Culvert clear.

DI-23 DI w/ 24” CMP Right Inlet half full of shale. Clean inlet and inspect pipe.

C-37 24” CMP Both Culvert clear.

DI-24 DI w/ 24” CMP Right DI clear. END SECTION NEEDS REPLACED.

C-38 24” CMP Both Culvert clear.

DI-25 DI w/ 24” CMP Right DI clear.

C-39 48” CMP Both Culvert clear. OUTLET END SECTION NEEDS REPLACED.

C-40 12” CMP Left Culvert clear.

Width Feature Side Comment

DRAINAGE FEATURES INVENTORY

DI-26 DI w/ 24” CMP Right DI and pipe clear. Possibly add riprap at upstream end of DI.

C-41 48” CMP Both Culvert clear.

C-42

18” CMP Both Culvert clear. Sediment and vegetation on outlet side needs cleared.

REPLACE OUTLET END SECTION.

C-43 36” CMP Both Culvert clear. Clean sediment at outlet.

24” CMP

DI-27

DI w/ 48” CMP Right 4’x4’ grate w/ 48” CMP downdrain; 48” CMP outlet. Clear vegetation at outlet. INSTALL OUTLET RIPRAP APRON.

C-44 24” CMP Both Culvert clear.

DI-28 DI w/ 24” CMP Right DI and culvert clear.

C-45 30” CMP Both Culvert clear.

DI-29 DI w/ 36” CMP Right Outlet pipe 60% full. MAJOR SEDIMENT ISSUES.

C-46 12” CMP Left Culvert clear.

C-47 52” STEEL Both Culvert clear.

C-48 24” CMP Both Culvert clear.

DI-30 DI w/ 24” CMP Right Inlet clear. CNF outlet. NEED TO FIND OUTLET.

DI-31 DI w/ 24” CMP N/A In parking lot. DI clear. CNF outlet. NEED TO FIND OUTLET.

DI-32 DI w/ 24” CMP N/A In parking lot. Sediment in inlet. CNF outlet. NEED TO FIND OUTLET.

Appendix B FEMA Floodplain Mapping

Project Route

Appendix C Corrosion Test Results & Service Life

Calculations

Table 4. Laboratory Corrosivity Analysis Results

Boring ID Sample ID

Sample Depth (feet)

USCS

Class

Water Content (%) pH

Saturated Resistivity (ohm/cm)

Soil Chloride, Cl (ppm)

Soil Sulphate, SO4 (ppm)

P‐1 SS‐3 & SS‐4 5 – 11.5 GM with sand

2 8.0 732 33 33

P‐4A & 4B SS‐3 5 – 6.5 CL‐ML

with sand

6 8.1 825 48 30

B‐8 SS‐3 & SS‐4 10 – 16.5 SM with gravel

8 8.6 2304 38 55

B‐9 SS‐3 & SS‐4 5 – 11.5 SM 10 8.6 2643 29 87

Notes:

% = percent USCS = Unified Soil Classification System GM = Silty Gravel CL‐ML = Silty Clay SM = Silty Sand ppm = parts per million

H ydrology a nd H ydraulics

D ecem ber 2

R oadw ay H ydraulics

7-53

E xh ib it 7.3-B

E S

T

IM

A T

IN

G

S T

E E

L P

IP

E

S E

R V

IC

E

S L

IF

E

FEDERAL LANDS HIGHWAY MODIFIED CALIFORNIA METHOD CHART FOR

ESTIMATING SERVICE LIFE OF PLAIN GALVANIZED STEEL CULVERTS

Service Life Estimation Chart for Average Service Life of Plain Galvanized Culverts

NOTES:

1. The curves in this Chart are based on the data in FHWA-FLP-91-006 which uses the factors in California Test 643, “Method for Estimating the Service Life of Steel Culverts”. These factors increased the estimated service life by 25% after first perforation.

2. The Chart has also been modified to reflect a minimum metal thickness of 0.064 inch or 16 gage [1.63 mm]

3. Under conditions with pH between 5 and 9, and above R 1500, the average service life determined for plain galvanized culverts should be multiplied by 2.0 for Aluminum coated steel, (Type 2).

THICKNESS FACTORS

0.168

4.27

2.6

Note: Multiply the average Service Life by the Thickness Factor

0.138

3.51

2.2

0.109

2.77

1.7

0.079

2.01

1.2

0.064

1.63

1.0

0.052

1.32

0.8

THICKNESS, inch

GAGE

THICKNESS, mm

FACTOR

CALCULATIONS

Service Life = 2.39 R0.41

Service Life = 2.39 * 7780.41 = 36.6 YR Increase min. steel gage to 12 (0.109 in.)

Modified Service Life = 1.7*36.6= 62.2 YR

Service Life based on minimum observed resistivity of 778 ohm-cm

STA 5+01 to 205+00

H ydrology a nd H ydraulics

D ecem ber 2

R oadw ay H ydraulics

7-53

E xh ib it 7.3-B

E S

T

IM

A T

IN

G

S T

E E

L P

IP

E

S E

R V

IC

E

S L

IF

E

FEDERAL LANDS HIGHWAY MODIFIED CALIFORNIA METHOD CHART FOR

ESTIMATING SERVICE LIFE OF PLAIN GALVANIZED STEEL CULVERTS

Service Life Estimation Chart for Average Service Life of Plain Galvanized Culverts

NOTES:

1. The curves in this Chart are based on the data in FHWA-FLP-91-006 which uses the factors in California Test 643, “Method for Estimating the Service Life of Steel Culverts”. These factors increased the estimated service life by 25% after first perforation.

2. The Chart has also been modified to reflect a minimum metal thickness of 0.064 inch or 16 gage [1.63 mm]

3. Under conditions with pH between 5 and 9, and above R 1500, the average service life determined for plain galvanized culverts should be multiplied by 2.0 for Aluminum coated steel, (Type 2).

THICKNESS FACTORS

0.168

4.27

2.6

Note: Multiply the average Service Life by the Thickness Factor

0.138

3.51

2.2

0.109

2.77

1.7

0.079

2.01

1.2

0.064

1.63

1.0

0.052

1.32

0.8

THICKNESS, inch

GAGE

THICKNESS, mm

FACTOR

CALCULATIONS

Service Life = 2.39 R0.41

Service Life = 2.39 * 24740.41 = 58.8 YR Use min. steel gage 16 (0.064 in.)

Service Life based on minimum observed resistivity of 2474 ohm-cm

STA 205+00 to 283+45