Hydraulics_Report.pdf

DONNER PASS ROAD IMPROVEMENTS

FINAL HYDRAULICS REPORT

CA FLAP NEV 40(1)

March 2019

Prepared for:

Federal Highway Administration – Central Federal Lands Highway Division

12300 W Dakota Avenue

Lakewood, CO 80228

Prepared by:

Muller Engineering Company

777 South Wadsworth Boulevard

Suite 4-100

Lakewood, Colorado 80226

303.988.4939

Muller Project Number: 15-030.02

Donner Pass Road Improvements March 2019 Final Hydraulics Report

Table of Contents

Page i

Table of Contents

1 INTRODUCTION

1.1 Location

1.2 Project Background and Objectives

1.3 Design Criteria

2 EXISTING CONDITIONS

2.1 General

2.2 Identified Work Areas

3 PROPOSED DESIGN

3.1 General

3.2 Culverts

3.3 Inlets

3.4 Ditches and Dikes/Curbs

3.5 Rundowns

3.6 Summary of Proposed Design Elements

4 CONCLUSIONS

5 REFERENCES

Appendices

A. Design Criteria

B. Photographs (from June 2015)

C. Proposed Drainage Basin Map

Soils Map & Information

NOAA Rainfall Data

Proposed Culvert Hydrology and Hydraulics

March 2019 Final Hydraulics Report

Introduction

1 INTRODUCTION

1.1 Location

The project is located on a 6.54 mile segment of Donner Pass Road (Old US 40) beginning at the I-80 /

Donner Pass Road interchange bridge in Soda Springs, CA (I-80 Exit 174), extending over Donner Pass, and ending at the Truckee, CA city limit east of the pass. Nevada County is the project applicant under the

California FLAP, but the project area encompasses portions of both Nevada County and Placer County.

Key elements of the project include comprehensive road rehabilitation, road widening to provide Class II bicycle lanes (Caltrans terminology) where feasible and establishing gravel pullouts to improve parking for trailhead, rock climbing, and historical sightseeing access. Please see Location Map below and Project

Site Map on next page.

This segment of Donner Pass Road provides access to popular recreational facilities located in and around the Tahoe National Forest, such as the Pacific Crest Trail (PCT) and Donner Summit Canyon Trail; historic emigrant trails such as Roller Pass and Coldstream Canyon; the Black Wall and Donner Pass rock climbing sites; and many prehistoric and historic features located along the 20-Mile Museum, such as the Rainbow

Bridge, the China Wall, Washoe Tribe petroglyphs, wagon train routes, and portions of the original transcontinental railroad. The PCT provides north and south access to numerous additional facilities in the

Tahoe and Eldorado National Forests. Donner Pass Road is also a frequently used route for recreational bicyclists. The proposed road improvements would be economic generators for the disadvantaged

Location Map

March 2019 Final Hydraulics Report

Introduction

Community of Soda Springs, as well as Truckee, in addition to other area businesses such as the numerous cross-country and downhill ski facilities and lodges that get access from Donner Pass Road.

1.2 Project Background and Objectives

The purpose of this project is to remedy several ongoing challenges experienced by Nevada and Placer

Counties along this segment of Donner Pass Road:

1. Moderate to severe roadway degradation that occurs as a result of extreme weather conditions in this high-altitude pass and that necessitates frequent maintenance. The proposed improvements would improve the structural issues and reduce the amount of maintenance required on the road.

2. Safety issues for bicyclists and motorists due to lack of bicycle lanes, shoulders, and recovery zone.

3. Lack of access to trails and other recreational and historic sites in or near the Tahoe National

Forest.

In general, the intent of the project is to widen the roadway, provide pavement rehabilitation, provide minor manhole and valve box adjustments, and provide roadway and bike lane signing and striping. There were no major existing drainage issues identified by the project sponsors during initial scoping. Additional scoping was completed after the 30% plans as part of the site visit however all of the issues are still minor in nature. The proposed drainage improvements are intended to continue the existing drainage patterns

Project Site Map

March 2019 Final Hydraulics Report

Existing Conditions and consist largely of extending or replacing existing pipes and adding or replacing inlets to accommodate the proposed roadway widening.

During the preliminary design phase, specific drainage issues were identified by Muller’s drainage/roadway engineers and Nevada County. Several new inlets and culvert were needed to mitigate roadway degradation from runoff in roadside ditches being blocked by the new 4’ shoulder pavement.

New curbs were required in several areas where insufficient space was available for a ditch between the rock face and new 4’ shoulder pavement or beneath guardrail. Several new inlets, culverts, and rundowns were required to capture concentrated flows.

For all new proposed inlets, culverts, and rundown structures a drainage analysis was conducted. During the preliminary design phase, two existing drainage issues were identified on the west side of the pass that also warranted a drainage analysis. All other drainage facilities were not analyzed but designed to be replaced or extended in kind to maintain existing drainage in accordance with the proposed widened roadway. All proposed drainage improvements are summarized in Section 3 of this report.

1.3 Design Criteria

The drainage design for the proposed roadway improvements was based on the proposed roadway configuration and overall historic drainage patterns. Adherence to drainage design criteria was constrained in spots by the mountainous terrain. Where feasible, new drainage improvements were based on contributing basin peak flows determined through the rational method, and the technical criteria outlined in the Federal Highway Administration/Central Federal Lands Project Development and Design

Manual (Reference 1) and the Nevada County, CA Road Standards (Reference 2). These criteria are summarized in Appendix A.

Because the primary goal of this project is to rehabilitate and expand an existing roadway, re-sizing or re-design of existing culverts and ditches was not included in the scope of this project. Delineation of drainage basins and calculation of design flows were only performed for new improvements and specific existing issues identified during the preliminary design phase. The remaining existing drainage features identified to be replaced or extended were not analyzed hydraulically. Due to the highly constrained mountainous terrain, hydraulic capacity of those features is limited to that which fits within the current geometric constraints.

2 EXISTING CONDITIONS

2.1 General

Donner Pass is located over steep mountainous terrain, and the existing roadway is typically constrained by trees, boulders, rock walls, or steep cliffs. Existing drainageways include minor roadside ditches, steep mountainside drainages, roadside inlets, and approximately 50 culverts. The existing roadway includes three bridges. No stream or structural work is planned at these bridges, and no stream restoration or fish passage work will be provided. The roadway is not located within any FEMA designated Special Flood

Hazard Areas (floodplains).

March 2019 Final Hydraulics Report

Existing Conditions

2.2 Identified Work Areas

A preliminary scoping visit in June 2015 identified potential drainage work areas in need of design improvements to accommodate the widened roadway. A site visit in July 2017 (30% field review) conducted a more in-depth evaluation of existing conditions and determined the additional drainage work needed to complete the final design. In the final design scope, specific drainage areas were identified to have a hydrologic/hydraulic analysis performed.

The project scope assumed that County maintenance forces will perform repairs on damaged culverts in advance of the project, as well as miscellaneous culvert cleanings that are not specifically identified in the scope of this project.

The drainage areas identified in the initial and final design scopes are listed below and are divided into two categories based on if they were selected to be evaluated with a hydrologic/hydraulic analysis. Please note that the roadway stationing identified below matched the final design plans and differs slightly from the estimated roadway stationing from the project scoping. See Section 3.5 Summary of Proposed Design

Elements for a detailed description of all the proposed improvements.

Drainage Areas to Match Existing Conditions: No Hydrology/Hydraulics Analysis

Station 136+75:

Existing 30” CMP culvert is too short to accommodate the proposed widened roadway. Extend pipe 2 LF and add an end section.

Station 149+57:

There is roadside ditch ponding on the driveway. A new inlet will be added, and the driveway culvert will be replaced.

Station 174+83:

Existing 18” CMP culvert is too short to accommodate the proposed widened roadway. Extend pipe 5 LF and add an end section.

Stations 184+33 to 251+44:

There are 15 existing inlets/headwalls that will need to be removed/replaced to accommodate the widened shoulder. Each specific location is designated in the table in Section 3.5 of the report.

Station 205+36:

Existing 24” CMP culvert is too short to accommodate the proposed widened roadway. Extend pipe7 LF and add an end section.

Station 280+82:

Existing 30” CMP culvert is too short to accommodate the proposed widened roadway. Extend pipe 4 LF, remove existing headwall and replace with inlet.

Station 282+55:

Existing 18” CMP culvert is too short to accommodate the proposed widened roadway. Extend pipe 4 LF, remove existing headwall and replace with inlet.

March 2019 Final Hydraulics Report

Existing Conditions

Station 283+40 to 283+69:

The driveway culvert will be removed and replaced to accommodate the widened roadway.

Station 283+85:

Existing culvert conveys flow just before a driveway which is showing signs of degradation. A new wingwall will be added to the existing headwall to prevent further erosion of the driveway.

Station 287+96:

An existing culvert is buried on the upstream end. Culvert to be extended and inlet to be added to accommodate widened roadway.

Station 343+55:

Existing 15” CMP is too short to accommodate eastbound shoulder width. Extend culvert, add end section and grade around outlet.

Station 374+25:

Ditch reconditioning on the left side to accommodate widened roadway.

Station 399+00:

Existing 15” CMP is too short to accommodate eastbound shoulder width. Extend culvert, add end section and grade around outlet.

Station 420+50:

Ditch reconditioning on the left side to accommodate widened roadway.

Drainage Areas Evaluated with Hydrology/Hydraulics

Station 128+28:

There is an existing 42” CMP culvert where the bottom is rotted out, and the culvert is too short to accommodate the widened roadway. To be removed and replaced. Left side of roadway drainage to be redesigned for widened roadway.

Station 280+82:

An existing 30” CMP culvert will need an inlet to accommodate the widened roadway and bike lane. Due to the large size of pipe, a hydrologic analysis will be conducted to size the inlet appropriately.

Station 293+31:

Existing storm drain system in the Donner Ski Ranch property and across Donner Pass Road is in poor condition. One inlet is completely covered with plywood and the outlet of the system appears to be severely damaged. The existing condition and diameter of the pipe under the roadway is unknown.

Station 310+82:

Roadway will be super elevated to convey flow to the left side of the roadway. A new headwall and pipe will be sized to accommodate flow.

Station 300+00 to 400+00

The potential need for a new dike/curb was identified in certain areas that are restricted by the mountainous terrain. In cases where the proposed roadway shoulder edge is within 1 foot of a rock wall

March 2019 Final Hydraulics Report

Existing Conditions or other constraint, a new dike/curb will be added. In cases where a roadside ditch remains at the edge of the proposed roadway shoulder, the capacity of the ditch will be governed by the existing geometric constraints. The proposed design is reflected on the roadway plans.

Station 322+63:

Roadside ditch at this location will be replaced with road and a rock outcropping will not allow for adequate space for a road side ditch on left side of the road. Refer to section 3.5.

Station 324+15:

Roadway will be super elevated to convey flow to the left side of the roadway. A new inlet and pipe will be sized to accommodate flow and prevent roadside ditch water from being dammed up by the shoulder widening and the rock face.

Station 365+87:

Roadway will be super elevated to convey flow to the left side of the roadway. A new inlet and pipe will be sized to accommodate flow.

Station 369+66:

Roadway will be super elevated to convey flow to the left side of the roadway. A new inlet and pipe will be sized to accommodate flow and prevent roadside ditch water from being dammed up by the shoulder widening and the rock face.

Station 384+24

Roadway will be super elevated to convey flow to the left side of the roadway. A new inlet and pipe will be sized to accommodate flow.

Station 392+25:

Roadway will be super elevated to convey flow to the left side of the roadway. A new inlet and pipe will be sized to accommodate flow.

March 2019 Final Hydraulics Report

Proposed Design

3 PROPOSED DESIGN

3.1 General

Due to the constraints of the steep mountainous terrain, and because no major drainage problems have been identified, the general drainage design is intended to accommodate the widened roadway, and consists of the following:

• Extension of existing roadway culverts to accommodate the widened roadway

• Replacement of existing approach road (driveway) culverts to accommodate the widened roadway

• Replacement of roadway culverts in poor condition

• Replacement or addition of new roadside inlets to accommodate the widened roadway

• Replacement or addition of dike/curb beneath guardrail or in constrained areas lacking space for a roadside ditch due to the widened roadway

• Re-grading roadside ditches to accommodate widened roadway and pullout locations

The general drainage design includes dikes/curbs and minor roadside ditches that convey water to roadside inlets and cross culverts. Cross culvert and inlet locations typically will remain unchanged from the existing conditions, except for new culverts to accommodate roadway re-grading, and a few slight realignments to accommodate the widened roadway.

3.2 Culverts

Hydrology and hydraulic calculations were not performed for existing roadway culverts or approach road culverts that are being extended. Existing size, pipe material, and slopes will be maintained in these situations. Evaluation of the need to upsize existing culverts was not done as part of this project.

Hydrology and hydraulic calculations for full replacement and new proposed culvert locations are included in Appendix C. Proposed culverts were designed to convey runoff from a 50-year storm event and checked for overtopping the roadway in the 100-year event. A headwater and diameter ratio of 1.5 was used for pipes less than or equal to 48” and a minimum cover of 12” was assumed for new proposed culverts.

Proposed new culverts were identified to accommodate the change in roadway curbing and width from the existing condition and are not due to any current drainage issues. Proposed pipes with diameters of

30” and smaller will be polyethylene while pipes 36” and larger will be reinforced concrete. Protective aprons were assumed to be used at the outfall of each proposed culvert - either fully replaced or new, except in instances where the culvert outfalls onto rock. The rocky outfall was the case for all proposed culvert locations except for the culvert replacement at Sta 128+28 (see more below). Two specific existing drainage areas identified for hydrology and hydraulic evaluation are outlined below.

Station 128+28:

The invert of the existing 42” RCP at this location has been rusted away. A new 42” RCP is proposed at this location to replace the existing CMP. The proposed pipe will need to be extended on the left side of the road to accommodate the widened roadway. Hydrology calculations confirmed a 42” pipe conveys runoff within the design criteria. The existing pipe does not meet criteria for adequate cover, therefore the new

March 2019 Final Hydraulics Report

Proposed Design pipe will be lowered to achieve appropriate cover. A class 4 riprap protective apron will be added at the culvert outlet to prevent erosion and will extend to ROW (approximately 50 ft. from center line).

Station 192+66:

The proposed roadway profile created a localized low point in the roadway. A new proposed culvert was designed to drain this low point. There are several nearby existing storm drain structures along the roadway, therefore it was assumed that conveyance capacity was adequate to convey offsite flows across the roadway. A new standard inlet and pipe are proposed to drain the roadway and reduce icing potential.

Therefore, no hydrologic or hydraulic analysis was done for this culvert.

Station 293+31:

The existing storm drain system at this location is very long and extends well outside of the roadway right of way. It consists of a long pipe that is connected by two inlets on the north side of the roadway located on property owned by the Donner Ski Ranch. The storm drain system crosses under the roadway and outfalls on private property on the south side of the roadway. Due to the unknown condition and diameter of the pipe within the project area, the proposed design will be limited to the replacement of the section of the pipe that is located directly underneath the roadway to prevent any potential failure from the existing conditions of the pipe in the vicinity of the roadway.

Hydrology calculations accounted for the contributing drainage basin and resulted in a 50-year flowrate of 101.8 cfs. A 48” pipe was selected to accommodate future improvements. The 48” RCP will connect to the existing pipe on either side of the roadway with two manhole junctions. Design challenges at this location includes the following:

• The culvert currently outfalls outside of the assumed right of way onto privately owned property.

• The alignment of the existing culvert appears to be directly under a power pole with two guy wires and electric and telephone lines that connect to the pole in all four directions. Open trench excavation of this area will be difficult.

• According to survey, the existing pipe is buried approximately 18 feet below the roadway surface.

This may provide constructability challenges including deep excavation and boulder excavation.

Design challenges of the deep pipe include daylighting the culvert within the assumed right of way.

• The existing pipe appears to go through or be connected to an existing wall of unknown composition and condition at the downstream end.

3.3 Inlets

In several locations, existing roadside inlets will be replaced by new Type 5A inlets to accommodate the widened roadway and bike lane. There are also several locations where the roadway widening would cover the existing culvert entrance, and geometric constraints do not allow for the culvert to be extended.

In these locations, a new Type 5A inlet will be added to connect surface drainage to the existing culvert.

Due to size constraints on the Type 5A inlet structures, a maximum pipe size of 24” and smaller must be used. One proposed pipe extension has an existing diameter of 30” and will require a larger Type 7B inlet to be installed. To maintain the capacity of the 30” culvert, a double Type 7B is proposed. Similarly, one

March 2019 Final Hydraulics Report

Proposed Design proposed pipe was sized to require a diameter of 30” to convey the tributary runoff. The flow to this location also warranted the larger orifice opening of a Type 7B inlet.

When possible, inlets were placed outside of the roadway limits. In areas where there is proposed curb, inlets will be placed along the curb flowline and will extend into the proposed shoulder/bike lane. In areas where there is no proposed curb and gutter, inlets were placed off the edge of the road. Proposed grade off the road to the inlet was set at 1:6 (V:H) slope, however due to the mountainous terrain some side slopes were steepened (see section 3.5 for specific details). Bike safe grates will be utilized regardless of the placement of the inlet relative to the roadway, refer to the Design Technical Memo for more information.

As previously stated, specific locations were selected for inlet sizing and placement. An orifice calculation was used to determine inlet sizing and allowable spread. The area of the opening was assumed to have a

30% reduction due the grate opening and 20% clogging factor. Newly proposed inlets were designed for no spread onto the adjacent roadway during the 50-year storm and checked to ensure that the 100-year storm does not inundate 1/3 of the traveled way. Refer to the orifice calculations in Appendix C.

3.4 Ditches and Dikes/Curbs

The widened roadway will encroach into the minor roadside ditches in several locations. In some of these locations, a portion of the roadside ditch will remain, and the hydraulic capacity will be governed by the existing geometric constraints. For proposed cross drainage, an inlet or headwall was placed at the upstream end. No evaluation for upsizing of ditches was included as part of this project. In many other locations, the existing ditch will be filled in to accommodate the widened roadway. In these situations, a dike/curb will typically be added, and new or replaced inlets will intercept the roadside drainage. In other locations, the existing ditches will remain open, and drainage from the roadside ditches will enter the existing cross culverts.

At the beginning and termination of each curb section, a transition was designed to accommodate the transition from curb to the adjacent ditch or vice versa. This transition is composed of a flare in the curb and a small section of riprap to protect the curb from erosion.

Curb will be placed under guardrail in specific locations to protect guardrail and terminus posts from sheet flow off the roadway. At these locations, curb will end before the terminus section (at the request of CFL) and the curb modified with a riprap rundown to direct flow from the roadway. Refer to the Design

Technical Memo for more information.

Several pullout locations are being improved to provide access to trails and other recreational and historic features along Donner Pass Road. Six proposed pullouts encroach on the existing roadside ditch drainage ways. Ditch grading was needed in these areas to maintain existing drainage. No hydrology or hydraulics analysis were performed at these locations. Ditches were sized to convey at least the same flow as the existing condition. Where possible 1:4 (V:H) slopes with 1’ depth was used, but some slopes were steepened to 1:3 or ditches reduced to 6” depth to accommodate terrain constraints.

March 2019 Final Hydraulics Report

Proposed Design

At several locations, where the existing ditch was filled in, the shoulder is used to convey runoff. In some instances, a shoulder breakover was utilized to keep runoff from spilling across the roadway prior to a cross drainage culvert.

3.5 Rundowns

Proposed super elevations in the roadway concentrate flow to be conveyed along proposed curbs. To protect the embankment, energy dissipation is needed at five locations where the super elevation directs flow to the right side of the roadway. At these locations, hydrology was evaluated and at any location during the 10-year event flow does not exceed 3.0 cfs. Due to the minimal flowrates, riprap class 2 was selected for all rundown structures. Refer to the plan set for rundown locations and sizes.

3.6 Summary of Proposed Design Elements

The table below gives a detailed outline of the proposed design elements.

March 2019 Final Hydraulics Report

Proposed Design

Summary of Proposed Design Elements

Project Station

50-year

Flowrat e (CFS)

Proposed Design

128+28 19.9 Remove existing 42" CMP culvert; Install new 42" RCP culvert; end section LT and RT, riprap outlet protection RT.

129+41 No H&H Remove nearby existing 18" CPP and 12" CMP approach road culverts , install 18" HDPE, LT.

136+75 No H&H Extend existing 30" CMP, install end section, LT.

149+57 No H&H Revmove nearby exisitng 18" CMP approach culvert. Install Type 5A inlet and 18" HDPE approach culvert, LT.

174+83 No H&H Extend existing 18" CMP and install end section, LT.

184+33 No H&H Remove and replace existing inlet with Type 5A and remove section of existing 18" CMP, LT. Inlet in bike lane.

185+66 No H&H Remove section of existing 18" CMP and install Type 5A inlet, LT.

187+96 No H&H Remove and replace existing inlet with Type 5A and extend existing 18" CMP, LT. Inlet in bike lane.

191+29 No H&H Remove and replace existing inlet with Type 5A and remove section of existing 18" CMP, LT. Inlet in bike lane.

192+66 No H&H Install 24" HDPE with inlet, LT. and end section RT. Inlet in bike lane

193+80 No H&H Remove and replace existing inlet with Type 5A and remove section of existing 24" CMP, LT. Inlet in bike lane.

196+87 No H&H Remove existing headwall and section of existing 24" CMP. Install Type 5A inlet, LT. Inlet in bike lane.

200+21 No H&H Remove and replace existing inlet with Type 5A and remove section of existing 18" CMP, LT. Inlet in bike lane.

202+02 No H&H Remove existing headwall, extend existing 18" CMP, and install Type 5A inlet, LT.

203+44 No H&H Extend existing 18" CMP and install Type 5A inlet, LT.

205+36 No H&H Extend existing 24" CMP and install end section, LT.

207+04 No H&H Remove and replace existing inlet with Type 5A and extend existing 18" CMP, LT. Mountainous terrain limits slope from EOP to inlet.

214+42 No H&H Remove and replace existing inlet with Type 5A and extend existing 24" CMP, LT. Mountainous terrain limits slope from EOP to inlet.

237+12 No H&H Remove and replace existing inlet with Type 5A and extend existing 24" CMP, LT. Mountainous terrain limits slope from EOP to inlet.

238+11 No H&H Remove and replace existing inlet with Type 5A and extend existing 18" CMP, LT. Mountainous terrain limits slope from EOP to inlet.

239+92 No H&H Remove and replace existing inlet with Type 5A and extend existing 18" CMP, LT. Mountainous terrain limits slope from EOP to inlet.

251+43 No H&H Remove and replace existing inlet with Type 5A and extend existing 18" CMP, LT. Mountainous terrain limits slope from EOP to inlet.

280+82 33.0 Remove existing headwall, extend 30" CMP and install (2) Type 7B inlets, LT.

282+55 No H&H Remove existing headwall, extend 18" CMP and install Type 5A inlet, LT.

283+55 No H&H Remove existing 12" CMP approach culvert and install 18" HDPE, LT.

283+85 No H&H Install wingwall to existing headwall, LT.

287+96 No H&H Install Type 5A inlet and extend existing culvert, verify size and material infield LT.

292+41 101.8 Remove section of existing pipe crossing roadway and install 48" RCP and (2) manholes LT. and RT.

310+82 9.4 Install new 24" HDPE with headwall LT. and end section RT.

318+53 to 320+64 No H&H Grade ditch around pullout location, LT.

322+63 5.2 Install rundown back into the existing roadside ditch, LT.

322+92 to 324+09 No H&H Grade ditch around pullout location, LT.

324+15 1.8 Install 24" HDPE with inlet, LT. and end section RT.

341+14 to 342+87 No H&H Grade ditch around pullout location, LT.

341+49 to 341+91 No H&H Grade ditch around pullout location, RT.

343+55 No H&H Extend existing 15" CMP and install end section, RT.

365+87 3.9 Install 24" HDPE, Type 5A inlet, LT. and end section, RT.

369+66 4.1 Install 24" HDPE with Type 5A inlet, LT and end section, RT.

372+39 to 376+16 No H&H Provide ditch reconditioning, LT.

382+57 to 382+77 No H&H Grade ditch around pullout location, LT.

383+88 to 384+21 No H&H Grade ditch around pullout location, LT.

384+24 27.9 Install 30" HDPE and Type 7B inlet, LT. Install end section, RT.

392+25 9.2 Install 24" HDPE with Type 5A inlet, LT. and end section, RT.

399+00 No H&H Remove existing headwall and extend 15" CMP, install end section, riprap outlet protection RT.

400+07 to 400+73 No H&H Grade ditch around pullout location, LT.

401+30 to 402+25 No H&H Grade ditch around pullout location, LT.

402+55 to 403+03 No H&H Grade ditch around pullout location, LT.

419+00 to 422+00 No H&H Provide ditch reconditioning, LT.

March 2019 Final Hydraulics Report

CONCLUSIONS

4 CONCLUSIONS

The final design for drainage improvements along Donner Pass includes the extension or replacement of existing culverts, the addition or replacement of drainage inlets, nine new drainage culverts, rundowns, and re-grading of ditches. Culverts that are to be extended will maintain the size, material, and slope of the existing culvert, and the proposed new culverts will be sized to convey runoff from a 50-year storm event. Existing minor roadside ditches obstructed by the widened roadway and the mountainous geometric constraints were re-graded or new dikes/curbs were added. Rundowns and drainage inlets were added where required. The project aims to continue the historic drainage patterns that exist in the vicinity of the roadway.

5 REFERENCES

1. U.S. Department of Transportation, Federal Highway Administration, Federal Lands Highway (FLH)

Project Development and Design Manual (PDDM), Chapter 7 Hydrology and Hydraulics, 2011.

2. County of Nevada, California, County Code; Title 3 Land Use and Development Code; Chapter XVII:

Road Standards (NCRS), 2017.

March 2019 Final Hydraulics Report

Appendix A Design Criteria

Drainage Design Criteria Table

Design Criteria Federal Lands Highway (FLH) Nevada County, CA

Applied Criteria

PDDM NCRS

Rainfall

Depth N/A N/A NOAA Atlas 14

Design Frequency

Cross Drainage

High-Standard road 50-year capacity

Exhibit 7.1-A

10-year capacity 5.2.A

50-year capacity

100-year no over topping 100-year no overtopping

Floodplain encroachments 100-year N/A N/A 100-year

Outlet Protection

Pipes >/= 48” design (25-

yr) Any type approved by the engineer 5.5.D

25-year (48” and greater)

Pipes <48” use detail

C251-50

Pipes < 48” = Standard Detail

C251-50

Headwater

Maximum HW/D: 1.5 for pipes <= 48”; HW/D: 1.2 pipes > 48”

N/A N/A Maximum HW/D: 1.5 for pipes <=

48”; HW/D: 1.2 pipes > 48”

Minimum cross culvert size 24”

18” for pipes < 80 ft 5.3.A 24”

24” for pipes > 80 ft

Minimum driveway culvert size 18” 12” 5.3.B 18”

Maximum Pipe Slope 10% for concrete pipes N/A N/A 10% for concrete pipes

Pavement Drainage

Capacity design (High-

Standard road) 10-year. 50-yr in sump Exhibit 7.1-A 10-year. 100-year 5.4.D 10-year, 50-yr in sump, 100-year

Spread (High-Standard road)

On grade and sags: 3’ into travel lane, not to exceed curb height.

Exhibit 7.1-A

10-Year: shall not inundate travel way

5.4.D

10-yr: shall not inundate traveled way

50-yr: 3’ into traveled lane

Sumps and Parking areas:

6” depth.

100-Year: shall not inundate more than 1/3 of traveled way

100-yr: inundate 1/3 of travel way

6” max depth

Ditches

Capacity Design 10-year Exhibit 7.1-A N/A N/A 10-year or constrained by mountainous terrain

Ditch Linings Permanent: 10-year Exhibit 7.1-A Lining approved by engineer 5.4.B

10-year or constrained by mountainous terrain

Storm Drains

Capacity Design 10-year (50-year sump) 7.3.4.2.1 N/A N/A

10-year (50-year sump)

Minimum pipe size 15” 7.3.4.2.1 15”

Hydrologic Procedure

Selection

Un-gaged Watershed

Peak Flow Methods

Based on drainage area

(DA)

DA < 200 acres: Rational

Method

7.2.4.3

DA < 640 acres: Rational

Method, NRCS TR 55 or

NRCS UH

5.1

DA < 200 acres: Rational Method

DA > 200 acres: NRCS TR

55 or Regression

Equations

DA > 640 acres: NRCS UH DA > 200 acres: NRCS TR 55 or

Regression Equations

Appendix B Photographs (from June 2015)

Typical roadside inlet to be replaced with Inlet Type 5A after roadway widening.

Driveway ponding near Station 150+00. New Inlet Type 5A and extended driveway culvert to be added.

Typical mountainous geometric constraints.

Typical driveway culvert to be extended or replaced.

Appendix C Proposed Drainage Basin Map

Soils Map & Information

NOAA Rainfall Data

Proposed Culvert Hydrology and Hydraulics

Rational Calculations

Orifice Calculations

HY8 Inputs and Calculations

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:>�#��im���� mscott Rectangle

Originator MAS

Muller Engineering Company, Inc. Date: 2/4/2019

Muller Project Number: 15030.02 Checker: WMG

Date: 2/5/2018

Land Use Types Percent Impervious

STREETS: PAVED 100

FORESTED AREA 15

RESIDENTIAL: 0.75 - 2.5 ACRES 20

PAVEMENT AREA/ROCK OUTCROPPINGS 100

STREETS: GRAVEL (PACKED) 40

(sq ft) (acre) (sq ft) % of Basin 2 (sq ft) % of Basin

2 (sq ft) % of Basin 2 (sq ft) % of Basin

2 (sq ft) % of Basin

P128L 849,667 19.51 21,169 2 0 828,498 98 0 0 22 78

P280L 1,227,712 28.18 1,572 0 1,195,022 97 0 31,118 3 0 17 83

P292L 39,480 0.91 0 0 0 39,480 100 0 100 0

P294L 2,320,706 53.28 0 1,213,955 52 0 1,106,751 48 0 56 44

P293L 156,399 3.59 0 91,132 58 0 65,268 42 0 50 50

P310L 139,130 3.19 20,405 15 18,537 13 0 100,188 72 0 89 11

P313R 7,551 0.17 7,551 100 0 0 0 0 100 0

P322L 97,973 2.25 3,643 4 55,251 56 0 39,079 40 0 52 48

P324L 39,698 0.91 0 31,420 79 0 8,278 21 0 33 67

P365L 69,878 1.60 14,188 20 32,094 46 0 23,596 34 0 61 39

P369R 3,435 0.08 3,435 100 0 0 0 0 100 0

P369L 66,888 1.54 7,299 11 21,664 32 0 37,924 57 0 72 28

P384L 506,312 11.62 0 250,429 49 0 255,883 51 0 58 42

P384R 10,347 0.24 10,347 100 0 0 0 0 100 0

P389R 8,666 0.20 8,666 100 0 0 0 0 100 0

P392L 141,976 3.26 8,848 6 27,471 19 0 105,657 74 0 84 16

P399R 4,429 0.10 3,991 90 0 0 0 439 10 94 6

Donner Pass CFL

FORESTED AREA RESIDENTIAL: 0.75 - 2.5 ACRES

PAVEMENT AREA/ROCK

OUTCROPPINGS

STREETS: GRAVEL (PACKED)

PERCENT IMPERVIOUS VALUES

WEIGHTED

PERCENT

IMPERVIOUS

WEIGHTED

PERCENT

PERVIOUS

Proposed Basin Calculations - Rational Method

BASIN ID

TOTAL AREA STREETS: PAVED

Donner Pass CFL

Proposed Basin Calculations - Rational Method Originator MAS

Muller Engineering Company, Inc. Date: 2/4/2019

Muller Project Number: 15030.02 Checker: WMG

Date: 2/5/2018

A B C/D C2 C5 C10 C25 C50 C100 % C2 C5 C10 C25 C50 C100 %

P128L 100 0.14 0.17 0.24 0.39 0.45 0.53 100 0.00 0.00 0.00 0.00 0.00 0.00 0 0.14 0.17 0.24 0.39 0.45 0.53

P280L 100 0.11 0.13 0.20 0.36 0.42 0.51 100 0.00 0.00 0.00 0.00 0.00 0.00 0 0.11 0.13 0.20 0.36 0.42 0.51

P292L 100 0.00 0.00 0.00 0.00 0.00 0.00 0 0.83 0.86 0.87 0.88 0.88 0.89 100 0.83 0.86 0.87 0.88 0.88 0.89

P294L 100 0.00 0.00 0.00 0.00 0.00 0.00 0 0.43 0.49 0.54 0.63 0.67 0.71 100 0.43 0.49 0.54 0.63 0.67 0.71

P293L 100 0.00 0.00 0.00 0.00 0.00 0.00 0 0.39 0.45 0.51 0.60 0.64 0.69 100 0.39 0.45 0.51 0.60 0.64 0.69

P310L 100 0.00 0.00 0.00 0.00 0.00 0.00 0 0.73 0.76 0.79 0.82 0.83 0.85 100 0.73 0.76 0.79 0.82 0.83 0.85

P313R 100 0.00 0.00 0.00 0.00 0.00 0.00 0 0.83 0.86 0.87 0.88 0.88 0.89 100 0.83 0.86 0.87 0.88 0.88 0.89

P322L 100 0.00 0.00 0.00 0.00 0.00 0.00 0 0.40 0.46 0.52 0.61 0.65 0.70 100 0.40 0.46 0.52 0.61 0.65 0.70

P324L 100 0.00 0.00 0.00 0.00 0.00 0.00 0 0.24 0.30 0.37 0.50 0.55 0.62 100 0.24 0.30 0.37 0.50 0.55 0.62

P365L 100 0.00 0.00 0.00 0.00 0.00 0.00 0 0.48 0.53 0.58 0.66 0.69 0.73 100 0.48 0.53 0.58 0.66 0.69 0.73

P369R 100 0.00 0.00 0.00 0.00 0.00 0.00 0 0.83 0.86 0.87 0.88 0.88 0.89 100 0.83 0.86 0.87 0.88 0.88 0.89

P369L 100 0.00 0.00 0.00 0.00 0.00 0.00 0 0.58 0.63 0.67 0.72 0.75 0.78 100 0.58 0.63 0.67 0.72 0.75 0.78

P384L 100 0.00 0.00 0.00 0.00 0.00 0.00 0 0.45 0.51 0.56 0.64 0.68 0.72 100 0.45 0.51 0.56 0.64 0.68 0.72

P384R 100 0.00 0.00 0.00 0.00 0.00 0.00 0 0.83 0.86 0.87 0.88 0.88 0.89 100 0.83 0.86 0.87 0.88 0.88 0.89

P389R 100 0.00 0.00 0.00 0.00 0.00 0.00 0 0.83 0.86 0.87 0.88 0.88 0.89 100 0.83 0.86 0.87 0.88 0.88 0.89

P392L 41 59 0.68 0.71 0.73 0.78 0.80 0.82 41 0.68 0.72 0.75 0.79 0.80 0.83 59 0.68 0.71 0.74 0.78 0.80 0.82

P399R 100 0.78 0.80 0.82 0.84 0.85 0.87 100 0.00 0.00 0.00 0.00 0.00 0.00 0 0.78 0.80 0.82 0.84 0.85 0.87

Notes:

Soil Group based on NRCS Soil Classification Map

RUNOFF COEFFIECIENTS FOR 2, 5, 10, AND 100 YEAR STORM EVENTS

BASIN ID

NRCS HYDROLOGIC SOIL GROUP

C2 C5 C10 C25 C50 C100SOIL GROUP (%)

1 SOIL GROUP B SOIL GROUP C/D

Muller Engineering Company, Inc. Date: 2/4/2019

Muller Project Number: 15030.02 Checker: WMG

Date: 2/5/2018

TOTAL tc FINAL tc

ELEV.

START

ELEV.

END

ELEV.

START

ELEV.

END

(ft) (ft) (ft) (ft) Type K

P128L 19.51 0.17 Non-Urban 500 6857.00 6820.00 0.074 19.5 1070 6820.00 6720.00 0.093 BG 10 3.1 5.8 25.3 25.3

P280L 28.18 0.13 Non-Urban 500 7650.00 7465.00 0.370 11.9 1663 7465.00 7061.00 0.243 BG 10 4.9 5.6 17.6 17.6

P292L 0.91 0.86 Urban 300 7088.00 7045.00 0.143 3.2 160 7045.00 7036.50 0.053 P 20 4.6 0.6 3.8 5.0

P294L 53.28 0.49 Non-Urban 500 7250.00 7198.00 0.104 11.4 2238 7198.00 7037.00 0.072 P 20 5.4 7.0 18.3 18.3

P293L 3.59 0.45 Non-Urban 500 7170.00 7108.00 0.124 11.5 696 7108.00 7041.50 0.096 P 20 6.2 1.9 13.3 13.3

P310L 3.19 0.76 Non-Urban 178 7165.00 7087.00 0.438 2.3 581 7087.00 7046.00 0.071 BG 10 2.7 3.6 6.0 10.0

P313R 0.17 0.86 Urban 22 7052.00 7050.00 0.091 1.0 270 7050.00 7030.00 0.074 P 20 5.4 0.8 1.8 5.0

P322L 2.25 0.46 Non-Urban 500 7245.00 6990.00 0.510 7.0 139 6990.00 6960.00 0.216 BG 10 4.6 0.5 7.5 10.0

P324L 0.91 0.30 Non-Urban 243 7015.00 6958.00 0.235 7.9 142 6958.00 6949.00 0.063 BG 10 2.5 0.9 8.9 10.0

P365L 1.60 0.53 Non-Urban 328 6745.00 6690.00 0.168 7.3 347 6690.00 6665.00 0.072 BG 10 2.7 2.2 9.4 10.0

P369R 0.08 0.86 Urban 19 6650.00 6648.00 0.105 0.9 133 6648.00 6640.00 0.060 P 20 4.9 0.5 1.3 5.0

P369L 1.54 0.63 Non-Urban 231 6745.00 6652.00 0.403 3.8 200 6652.00 6638.00 0.070 BG 10 2.6 1.3 5.1 10.0

P384L 11.62 0.51 Non-Urban 500 7385.00 7030.00 0.710 5.8 1258 7030.00 6534.00 0.394 BG 10 6.3 3.3 9.2 10.0

P384R 0.24 0.86 Urban 84 6559.00 6552.00 0.083 2.0 239 6552.00 6533.00 0.079 P 20 5.6 0.7 2.7 5.0

P389R 0.20 0.86 Urban 55 6521.00 6516.00 0.091 1.6 235 6516.00 6498.00 0.077 P 20 5.5 0.7 2.3 5.0

P392L 3.26 0.71 Non-Urban 500 6775.00 6565.00 0.420 4.5 421 6565.00 6474.00 0.216 BG 10 4.6 1.5 6.0 10.0

P399R 0.10 0.80 Urban 19 6475.00 6474.00 0.053 1.3 136 6474.00 6442.00 0.235 P 20 9.7 0.2 1.6 5.0

STANDARD FORM SF-2

TIME OF CONCENTRATION

CHANNELIZED (TRAVEL) TIME (Tt) tminimum= 5 (Urban) tminimum= 10 (Non-Urban) ti + tt

(min.)

INITIAL/OVERLAND TIME (T i) tt (min)

2CHANNELIZED

SLOPE (St) (ft/ft)

CONVEYENCE COEFFICIENT Velocity Vt

(ft/sec) Basin Type

BASIN DATA

BASIN ID C5

LENGTH

Li (ft)

OVERLAND

SLOPE (Si) (ft/ft) ti (min)

1 LENGTH

Lt (ft)

AREA

(acre)

Muller Engineering Company, Inc. 2-Year 5-Year 10-Year 25-Year 50-Year 100-Year Date: 2/4/2019

Muller Project Number: 15030.02 Checker: WMG

Date: 2/5/2018

BASIN ID

AREA

(acre) C2 C5 C10 C25 C50 C100

I2

(in/hr) I5 (in/hr)

I10

(in/hr)

I25

(in/hr)

I50

(in/hr)

I100

(in/hr)

Q2

(cfs)

Q5

(cfs)

Q10

(cfs)

Q25

(cfs)

Q50

(cfs)

Q100

(cfs)

P128L 19.51 0.14 0.17 0.24 0.39 0.45 0.53 1.09 1.42 1.67 2.01 2.27 2.53 3.0 4.6 7.7 15.2 19.9 26.1

P280L 28.18 0.11 0.13 0.20 0.36 0.42 0.51 1.32 1.72 2.03 2.44 2.76 3.07 4.0 6.2 11.3 24.6 33.0 43.9

P292L 0.91 0.83 0.86 0.87 0.88 0.88 0.89 2.13 2.77 3.28 3.93 4.44 4.95 1.6 2.2 2.6 3.1 3.6 4.0

P294L 53.28 0.43 0.49 0.54 0.63 0.67 0.71 1.29 1.68 1.99 2.39 2.70 3.01 29.6 44.0 57.6 80.1 95.6 114.0

P293L 3.59 0.39 0.45 0.51 0.60 0.64 0.69 1.51 1.96 2.32 2.78 3.14 3.50 2.1 3.2 4.2 6.0 7.2 8.7

P310L 3.19 0.73 0.76 0.79 0.82 0.83 0.85 1.70 2.21 2.62 3.14 3.54 3.95 3.9 5.4 6.6 8.2 9.4 10.7

P313R 0.17 0.83 0.86 0.87 0.88 0.88 0.89 2.13 2.77 3.28 3.93 4.44 4.95 0.3 0.4 0.5 0.6 0.7 0.8

P322L 2.25 0.40 0.46 0.52 0.61 0.65 0.70 1.70 2.21 2.62 3.14 3.54 3.95 1.5 2.3 3.0 4.3 5.2 6.2

P324L 0.91 0.24 0.30 0.37 0.50 0.55 0.62 1.70 2.21 2.62 3.14 3.54 3.95 0.4 0.6 0.9 1.4 1.8 2.2

P365L 1.60 0.48 0.53 0.58 0.66 0.69 0.73 1.70 2.21 2.62 3.14 3.54 3.95 1.3 1.9 2.4 3.3 3.9 4.7

P369R 0.08 0.83 0.86 0.87 0.88 0.88 0.89 2.13 2.77 3.28 3.93 4.44 4.95 0.1 0.2 0.2 0.3 0.3 0.3

P369L 1.54 0.58 0.63 0.67 0.72 0.75 0.78 1.70 2.21 2.62 3.14 3.54 3.95 1.5 2.1 2.7 3.5 4.1 4.7

P384L 11.62 0.45 0.51 0.56 0.64 0.68 0.72 1.70 2.21 2.62 3.14 3.54 3.95 8.9 13.1 17.1 23.5 27.9 33.1

P384R 0.24 0.83 0.86 0.87 0.88 0.88 0.89 2.13 2.77 3.28 3.93 4.44 4.95 0.4 0.6 0.7 0.8 0.9 1.1

P389R 0.20 0.83 0.86 0.87 0.88 0.88 0.89 2.13 2.77 3.28 3.93 4.44 4.95 0.4 0.5 0.6 0.7 0.8 0.9

P392L 3.26 0.68 0.71 0.74 0.78 0.80 0.82 1.70 2.21 2.62 3.14 3.54 3.95 3.8 5.2 6.3 8.0 9.2 10.6

P399R 0.10 0.78 0.80 0.82 0.84 0.85 0.87 2.13 2.77 3.28 3.93 4.44 4.95 0.2 0.2 0.3 0.3 0.4 0.4

RATIONAL FLOWS

INTENSITY VALUES

NOAA Atlas 14, Volume 6, Version 2 Norden, CA

Storm Event

One-Hour Point Rainfall Values

(P1) (inches)

0.63 0.82 0.97 1.16 1.31 1.46

28 5 ∗ �1

Muller Engineering Company, Inc. Date: 2/4/2019

Muller Project Number: 15030.02 Checker: WMG

Date: 2/5/2018

AREA CA Tc I50 Q Tc I50 Q

(acres) (acres) (min) (in/hr) (cfs) (min) (in/hr) (cfs)

P292L 0.91 0.88 0.80 5.00 4.44 3.6

P293L 3.59 0.64 2.30 13.33 3.14 7.2

P294L 53.28 0.67 35.44 18.32 2.70 95.6

18.32 37.73 2.70 101.8

P292L 0.91 0.88 0.80 5.00 4.44 3.6

P294L…