Preliminary Drainage Design Report for NEON for the P3...

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December 2013

Preliminary Drainage Design Reportfor NEON for the P3 Improvements

December 2013

Preliminary Drainage Design Report CH2M HILL#473216 Project NEON for the P3 Improvements I

EXECUTIVE SUMMARY

Project Neon is a corridor program developed to redesign I-15 between Sahara Avenue

and US-95 in order to increase the capacity of the busiest stretch of I-15 in Nevada. The

project extends 3.7 miles through the Las Vegas Valley, including freeway widening,

realignment, and reconstruction. Project Neon provides a direct connection from the I-15

Express Lanes to the US-95 High Occupancy Vehicle (HOV) lanes. This connection will

provide continuity and the ability for NDOT to ultimately have HOV or managed lanes

from Ann Road on US-95, through the Spaghetti Bowl, and continue south to the Russell

Road interchange, and eventually further to the south. Additionally, improvements will

be made to the freeway ramps and the local street network, including reconfiguring the

Charleston Interchange into a more traditional tight-diamond interchange, connecting

Grand Central Parkway to Western Avenue at an at-grade intersection with Charleston

Boulevard, a northbound slip ramp connection to Alta Drive, and improvement of

Martin Luther King Boulevard from Alta Drive to Oakey Boulevard. The project limits

beginning at Interstate 15 milepost 39 and extending through to milepost 43.

This Preliminary Drainage Design Report is provided to document the drainage analysis

and design that has been performed for the development of the 30% design level

Drainage Plans for Project Neon – P3 Phase. This Preliminary Submittal for the P3

phase of Project Neon builds upon the previous analysis performed for the Preliminary

30% Design for Phase I that was submitted in January 2011. Since that time there have

been considerable changes to the project including:

• Addition of full MLK Improvements from Alta Drive to Oakey Boulevard with a

grade separation at Charleston Boulevard

• I-15 alignment shift south of Alta Drive to the ultimate alignment

• Addition of southbound Collector-Distributor lanes and ramp braiding for access

to Charleston Boulevard and Sahara Avenue

• Addition of a full tight-diamond interchange and widening at Charleston

Boulevard

• At-grade intersection at Western/Grand Central and Charleston Boulevard

• ES Ramp widening and relocation of existing RCB

• Alta Drive Improvements between Desert Lane and Grand Central Parkway

December 2013

Preliminary Drainage Design Report CH2M HILL#473216 Project NEON for the P3 Improvements II

This report provides a level of drainage analysis above the preliminary designation per

the NDOTDM requirements and includes a discussion of the proposed P3 Phase

improvements, 30% design level calculations and drainage plans, allows for a basis of

verifying P3 Phase drainage right-of-way needs, and provides design information for the

continued coordination and resolution of interdisciplinary coordination elements.

Design and coordination has been provided for major offsite drainage facility

relocations, minor offsite facilities impacted by the project, and onsite systems to

accommodate the P3 Phase improvements. The P3 Phase Project Summary based on the

30% drainage design is:

• The proposed drainage facilities are designed per the criteria presented in the

NDOT Drainage Manual, and the Clark County Regional Flood Control District’s

(CCRFCD) Hydrologic Criteria and Drainage Design Manual, except at otherwise

noted.

• The project site lies within FEMA-designated shaded Zone X. Areas designated as

Zone X are outside the regulatory 100-year floodplain.

• The drainage facility improvements include:

o Additional onsite storm drain facilities between Desert Inn Road and the

north side of Sahara Avenue to improve flow spread conditions

o Realignment of the existing Freeway Channel MPU storm drain facility from

just north of Sahara Avenue to just south of Charleston Boulevard to

accommodate the freeway widening and realignment of I-15

o Realignment of the existing US-95 Channel MPU storm drain facility to

accommodate “ES1” ramp widening

o Onsite storm drain improvements to accommodate roadway improvements

according to NDOT drainage criteria

o Offsite storm drain improvements in the local jurisdiction roadways to meet

local drainage criteria

• The proposed drainage improvements will perpetuate existing conditions flow

patterns and the proposed improvements do not adversely impact adjacent

properties or facilities.

December 2013

Preliminary Drainage Design Report CH2M HILL#473216 Project NEON for the P3 Improvements i

TABLE OF CONTENTS

PAGE 1.0 INTRODUCTION AND PURPOSE ............................................................................................ 1

1.1 PROJECT LOCATION AND DESCRIPTION ........................................................................ 2 1.2 P3 PHASE PROJECT SCOPE SUMMARY ............................................................................ 2 1.3 DRAINAGE DESIGN SCOPE ................................................................................................. 3

2.0 DESIGN PRODEDURES AND CRITERIA ............................................................................... 5

2.1 DRAINAGE CRITERIA .......................................................................................................... 5 2.2 COMPLIANCE ........................................................................................................................ 6 2.3 PROJECT DESIGN DATA ...................................................................................................... 6

3.0 EXISTING CONDITIONS ........................................................................................................... 7 3.1 SUMMARY OF EXISTING CONDITIONS ........................................................................... 7 3.1.1 PREVIOUS REPORTS ................................................................................................. 8 3.1.2 DRAINAGE BASIN CHARACTERISTICS ................................................................ 9 3.1.3 HISTORIC FLOW PATTERNS ................................................................................... 9 3.1.4 FEMA INFORMATION ............................................................................................. 10 3.1.5 REGIONAL FLOOD CONTROL MASTER PLAN INFORMATION ..................... 10 4.0 OFFSITE DRAINAGE FACILITIES ........................................................................................ 13 4.1 I-15 FREEWAY CHANNEL – SAHARA AVE. TO SYMPHONY PARKWAY ................ 13 4.1.1 DESERT INN ROAD TO SAHARA AVENUE ......................................................... 14 4.1.2 SAHARA AVENUE TO OAKEY BOULEVARD ..................................................... 14 4.1.3 OAKEY BOULEVARD .............................................................................................. 15 4.1.4 OAKEY BOULEVARD TO WALL STREET ........................................................... 16 4.1.5 WALL STREET TO CHARLESTON BOULEVARD ............................................... 17 4.1.6 CHARLESTON BOULEVARD / GRAND CENTRAL PARKWAY ....................... 18 4.1.7 CHARLESTON-ALTA SLIP RAMP & CHARLESTON-GRAND CENTRAL SLIP .

RAMP .......................................................................................................................... 18 4.1.8 FREEWAY CHANNEL HYDRAULIC ANALYSIS ................................................. 19

4.2 FREEWAY CHANNEL LATERALS ................................................................................... 23 4.2.1 OAKEY BOULEVARD LATERAL........................................................................... 23 4.2.2 WALDMAN AVENUE LATERAL ........................................................................... 24 4.2.3 WESTERN AVENUE LATERAL .............................................................................. 25 4.2.4 CHARLESTON BOULEVARD LATERAL .............................................................. 26 4.2.5 US-95 CHANNEL ....................................................................................................... 26 4.2.6 PINTO LANE LATERAL ........................................................................................... 26 4.2.7 ALTA DRIVE LATERAL .......................................................................................... 27

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Preliminary Drainage Design Report CH2M HILL#473216 Project NEON for the P3 Improvements ii

4.3 LOCAL OFFSITE SYSTEMS ............................................................................................... 27 4.3.1 EAST SIDE OF I-15, DESERT INN ROAD TO SAHARA AVENUE .................... 28 4.3.2 EAST SIDE OF I-15, SAHARA AVENUE TO WYOMING AVENUE .................. 28 4.3.3 EAST SIDE OF I-15, WYOMING AVENUE TO WALL STREET .......................... 29 4.3.4 WEST SIDE I-15 – MLK BLVD., OAKEY BLVD. TO ALTA DRIVE ................... 30 4.3.5 WEST SIDE I-15, ALTA DRIVE TO SYMPHONY PARKWAY ............................ 31 4.4 WESTERN AVENUE CORRIDOR OVERLAND FLOW .................................................. 31 5.0 ONSITE DRAINAGE FACILITIES.......................................................................................... 34 5.1 ONSITE DESIGN CRITERIA ............................................................................................... 34 5.2 ONSITE DRAINAGE DESIGN FLOW SPREAD CRITERIA EXCEPTIONS ................... 35 5.3 I-15 CORRIDOR .................................................................................................................... 38 5.3.1 I-15, DESERT INN RD. TO SAHARA AV. (CRUMB RUBBER PROJECT)... ........ 38 5.3.2 I-15, SAHARA AVENUE TO OAKEY BLVD.... ....................................................... 39 5.3.3 SOUTHBOUND I-15, OAKEY BLVD. TO CHARLESTON BLVD.... ..................... 39 5.3.4 NORTHBOUND I-15, OAKEY BLVD. TO CHARLESTON BLVD.... .................... 39 5.3.5 I-15, CHARLESTON BLVD. TO ALTA DRIVE... .................................................... 40 5.3.6 I-15, ALTA DRIVE TO SYMPHONY PARKWAY... ................................................ 40 5.3.7 I-15, SYMPHONY PARKWAY TO US-95... ............................................................. 41 5.4 US-95 CORRIDOR ................................................................................................................ 41 5.4.1 US-95 DIRECT CONNECT – AT-GRADE... ............................................................. 41 5.4.2 US-95 DIRECT CONNECT VIADUCT... ................................................................... 44 5.4.3 “MLK-515” AND “EN” RAMPS................................................................................. 47 5.5 LOCAL ROADS ..................................................................................................................... 48 5.5.1 SAHARA AVENUE... ................................................................................................. 48 5.5.2 OAKEY BLVD. / WYOMING AVENUE... ................................................................ 48 5.5.3 MARTIN LUTHER KING BOULEVARD... .............................................................. 48 5.5.4 CHARLESTON BOULEVARD... ............................................................................... 49 5.5.5 ALTA DRIVE / BONNEVILLE AVENUE... .............................................................. 50 5.5.6 WESTERN AVENUE – GRAND CENTRAL PARKWAY... .................................... 50 6.0 SUMMARY .................................................................................................................................. 51 7.0 REFERENCES ............................................................................................................................. 54

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Preliminary Drainage Design Report CH2M HILL#473216 Project NEON for the P3 Improvements iii

LIST OF TABLES

PAGE TABLE 2.1 SUMMARY OF DESIGN FLOW FREQUENCIES ...................................................... 5 TABLE 3.1 REFERENCE STUDIES ................................................................................................. 8 TABLE 3.1.5.1 2008 MPU FACILITIES DIRECTLY IMPACTED BY PROJECT ............................. 11 TABLE 3.1.5.2 ADDITIONAL CCRFCD 2008 MPU MASTER PLANNED FACILITIES ................ 12 TABLE 4.1.8 FREEWAY CHANNEL WATER SURFACE COMPARISON SUMMARY ............. 22 TABLE 5.2 PROJECT NEON – P3 PHASE – FLOW SPREAD CRITERIA EXCEPTIONS ........ 36

LIST OF FIGURES FOLLOWING PAGE

FIGURE 1 VICINITY MAP ................................................................................................................. 1 FIGURE 2 PROJECT AREA ................................................................................................................ 2 FIGURE 3 PROJECT DRAINAGE IMPROVEMENTS ..................................................................... 4

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Preliminary Drainage Design Report CH2M HILL#473216 Project NEON for the P3 Improvements iv

APPENDICES

APPENDIX A OFFSITE HYDROLOGIC INFORMATION & COMPUTATIONS

A-1 OFFSITE SUBBASIN MAPS

A-1.1 OFFSITE SUBBASIN MAP – EXISTING CONDITIONS

A-1.2 EXISTING CONDITIONS - FLOW EXHIBIT

A-1.3 PROPOSED CONDITIONS - FLOW EXHIBIT

A.1.4 OFFSITE SUBBASIN MAP – ULTIMATE CONDITIONS

A-1.5 ULTIMATE CONDITIONS - FLOW EXHIBIT

A-1.6 OVERALL - FLOW EXHIBIT

A-2 EXISTING CONDITIONS - HYDROLOGIC MODELS

A-2.1 100-YEAR STORM EVENT HEC-1 MODELS

A-2.1.1 SDN3 STORM DISTRIBUTION 100-YEAR HEC-1 MODEL A-2.1.2 SDN4 STORM DISTRIBUTION 100-YEAR HEC-1 MODEL A-2.1.3 SDN5 STORM DISTRIBUTION 100-YEAR HEC-1 MODEL

A-3 PROPOSED CONDITIONS - HYDROLOGIC MODELS


A-3.1.1 SDN3 STORM DISTRIBUTION 100-YEAR HEC-1 MODEL A-3.1.2 SDN4 STORM DISTRIBUTION 100-YEAR HEC-1 MODEL A-3.1.3 SDN5 STORM DISTRIBUTION 100-YEAR HEC-1 MODEL

A-4 ULTIMATE CONDITIONS HYDROLOGIC MODELS


December 2013

Preliminary Drainage Design Report CH2M HILL#473216 Project NEON for the P3 Improvements v

A-4.1.1 SDN3 STORM DISTRIBUTION 100-YEAR HEC-1 MODEL A-4.1.2 SDN4 STORM DISTRIBUTION 100-YEAR HEC-1 MODEL A-4.1.3 SDN5 STORM DISTRIBUTION 100-YEAR HEC-1 MODEL A-5 FLOW SUMMARY TABLE A-6 REINFORCED CONCRETE BOX (PRECAST & CAST-IN-PLACE) EXHIBIT A-7 2008 MPU FIGURES A-8 NOAA ATLAS 14 A-9 FEMA FIRM MAP APPENDIX B HYDRAULIC CALCULATIONS – OFF-SITE FACILITIES B-1 I-15 FREEWAY CHANNEL

B-1.1 WSPG ANALYSIS; EXISTING I-15 CHANNEL

B-1.2 PROPOSED & ULTIMATE FREEWAY CHANNEL STATIONING EXHIBIT AND PROFILE

B-1.2.1 WSPG ANALYSIS; I-15 CHANNEL MODIFICATIONS – EXISTING FLOWS

B-1.2.2 WSPG ANALYSIS; I-15 CHANNEL MODIFICATIONS– ULTIMATE 2008 MPU FLOWS

B-1.3 WSPG ANALYSIS – I-15 CHANNEL LATERALS

B-1.3.1 OAKEY BOULEVARD LATERAL

B-1.3.2 WALDMAN AVENUE LATERAL

B-1.3.3 WESTERN AVENUE LATERAL

B-1.3.4 CHARLESTON BOULEVARD LATERAL

B-1.3.5 PINTO LANE LATERAL

B-1.3.6 ALTA DRIVE LATERAL

B-2 LOCAL OFFSITE SYSTEMS

B-2.1 LOCAL ROADS HYDROLOGIC / HYDRAULIC CALCULATIONS B-2.1.1 LOCAL ROAD SUBBASIN MAP

B-2.1.2 LOCAL ROAD RATIONAL METHOD CALCULATIONS

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Preliminary Drainage Design Report CH2M HILL#473216 Project NEON for the P3 Improvements vi

B-2.1.3 LOCAL ROAD NORMAL DEPTH CALCULATIONS

B-2.1.4 INLET INTERCEPTION CALCULATIONS

B-2.2 FIELD INELT CALCULATIONS

B-2.3 DITCH AND CHANNEL CALCULATIONS

B-3 WESTERN AVENUE CORRIDOR ANALYSIS

B-3.1 EXISTING CONDITIONS HEC-RAS ANALYSIS

B-3.2 PROPOSED CONDITIONS HEC-RAS ANALYSIS

B-3.3 WESTERN AVENUE OVERLAND FLOW EXHIBIT

APPENDIX C HYDROLOGIC/HYDRAULIC CALCULATIONS – ON-SITE FACILITIES C-1 I-15 MAINLINE / US-95 & US-95 VIADUCT

C-1.1 ONSITE SUBBASIN MAPS

C-1.2 ONSITE RATIONAL METHOD CALCULATIONS

C-1.3 INLET INTERCEPTION CALCULATIONS – CONTINUOUS GRADE

C-1.4 INLET INTERCEPTION CALCULATIONS - SUMP

APPENDIX D: QA/QC ITEMS D-1 DESIGN REVIEW COMMENTS D-2 DRAINAGE FLOW SPREAD CRITERIA EXCEPTIONS APPENDIX E: SUPPLEMENTAL DOCUMENTATION CD E-1 PROJECT NEON P3 DESIGN DRAINAGE PLANS E-2 PREVIOUS REPORTS/HISTORIC INFORMATION

E-2.1 FREEWAY CHANNEL RECORD DRAWINGS

E-2.2 OFFSITE HYDROLOGY REPORT

E-2.3 EXISTING SOUTH RANCHO OVERLAND FLOW EXHIBITS

E-3 PROJECT NEON PHOTO LOG

December 2013

Preliminary Drainage Design Report CH2M HILL#473216 Project NEON for the P3 Improvements 1

1.0 INTRODUCTION AND PURPOSE

This Preliminary Drainage Design Report is provided to document the drainage analysis

and design that has been performed for the development of the 30% design level

Drainage Plans for Project Neon – P3 Phase. This Preliminary Submittal for the P3

phase of Project Neon builds upon the previous analysis performed for the Preliminary

30% Design for Phase I that was submitted in January 2011. Since that time there have

been considerable changes to the project including:

• Addition of full MLK Improvements from Alta Drive to Oakey Boulevard with a

grade separation at Charleston Boulevard

• I-15 alignment shift south of Alta Drive to the ultimate alignment

• Addition of southbound Collector-Distributor lanes and ramp braiding for access

to Charleston Boulevard and Sahara Avenue

• Addition of a full tight-diamond interchange and widening at Charleston

Boulevard

• At-grade intersection at Western/Grand Central and Charleston Boulevard

• ES Ramp widening and relocation of existing RCB

• Alta Drive Improvements between Desert Lane and Grand Central Parkway

Project Neon provides a direct connection from the I-15 Express Lanes, which extend

between approximately Russell Road and Sahara Avenue, to the US-95 High Occupancy

Vehicle (HOV) lanes, which currently extend from approximately Lake Mead Boulevard

to west of Rancho Drive. This connection will provide continuity and the ability for

NDOT to ultimately have HOV or managed lanes from Ann Road on US-95, through the

Spaghetti Bowl, and continue south to the Russell Road interchange, and eventually

further to the south. Additionally, improvements will be made to the freeway ramps and

the local street network, including reconfiguring the Charleston Interchange into a more

traditional tight-diamond interchange, connecting Grand Central Parkway to Western

Avenue at an at-grade intersection with Charleston Boulevard, a northbound slip ramp

connection to Alta Drive, and improvement of Martin Luther King Boulevard from Alta

Drive to Oakey Boulevard. The project limits beginning at Interstate 15 milepost 39 and

extending through to milepost 43. Refer to Figure 1 – Vicinity Map.

Vicinity Map

PPRROOJJEECCTT NNEEOONN –– PP33 IIMMPPRROOVVEEMMEENNTTSS Preliminary Drainage Design Report

Figure 1

12/2013

Project Location

December 2013


1.1

Project Location and Description

Project Neon is located within the City of Las Vegas, in Clark County, Nevada, Township

21 South, Range 61 East, Sections 8, 9, 4, and Township 20 South, Range 61 East,

Sections 33, 28, 29. The improvements proposed with Project Neon – P3 Phase are

located primarily along I-15 between Desert Inn Road and US-95, and along US-95

between I-15 and Rancho Drive. Refer to Figure 2 – Project Area.

1.2

P3 Phase Project Scope Summary

Project Neon is a corridor program developed to redesign I-15 between Sahara Avenue

and US-95 in order to increase the capacity of the busiest stretch of I-15 in Nevada. The

project extends 3.7 miles through the Las Vegas Valley, including freeway widening,

realignment, and reconstruction. The overall project was originally divided into several

phases to accommodate limitations in funding. The P3 delivery method allows this P3

Phase portion of the project to include multiple original phases of the project. The

remaining phases of the project would need to be accommodated with the final P3 Phase

design. The P3 Phase roadway improvements generally consist of:

• A high-occupancy vehicle (HOV) connector bridge structure from the center of I-

15, south of the system interchange, to the center of US-95, west of the system

interchange

• A direct HOV access ramp at approximately Wall Street with access to Western

Avenue

• Reconstruction of the Charleston Boulevard Interchange to a tight-diamond

configuration

• Ramp improvements at Sahara Avenue, Charleston Boulevard, Alta Drive, and

US-95

• Widening and realignment of the I-15 freeway from Sahara Avenue to the system

interchange with US-95

• Southbound CD lanes with ramp braiding to provide access to Charleston

Boulevard and Sahara Avenue

• Martin Luther King Boulevard improvements from Alta Drive to Oakey

Boulevard with grade separation at Charleston Boulevard

Project Area

PROJECT NEON – P3 IMPROVEMENTS Preliminary Drainage Design Report

Figure 2

12/2013

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Project Neon P3 Limits Township/Range Boundaries

December 2013


• Local roadway improvements on Oakey Boulevard, Charleston Boulevard, Alta

Drive, Martin Luther King Boulevard, Desert Lane, and Grand Central Parkway.

• Western Avenue–Grand Central Parkway at-grade intersection with Charleston

Boulevard

There are several proposed major projects in the vicinity of Project Neon that have been

considered for this 30% design and would need to be further analyzed by the P3

Developer during the final design of the P3 Phase of this project. These proposed

projects include, but may not be limited to:

• Future northbound collector distributor road to US95 with access from Sahara

Avenue and Charleston Boulevard

• A connector bridge over the UPRR from Grand Central Parkway to Industrial

Road currently under design by the City of Las Vegas

• City of Las Vegas future design project for the Alta Drive widening

• Grade separation of Grand Central Parkway-Industrial Road connection over

Charleston Boulevard

• Oakey/Wyoming grade separation over the UPRR

1.3

Drainage Design Scope

The drainage facility improvements incorporated into the 30% Preliminary Design Level

for Project NEON – P3 Phase include:

• Additional onsite storm drain facilities between Desert Inn Road and the north

side of Sahara Avenue to improve flow spread conditions as a result of shoulder

reductions from the recent Crumb-Rubber Overlay Project

• Realignment of the existing Regional storm drain facility to accommodate the

Freeway Widening on I-15 from just north of Sahara Avenue to the south side of


• Realignment of the existing US-95 Channel MPU storm drain facility to


• Onsite storm drain improvements to accommodate roadway improvements

according to NDOT drainage criteria including:

December 2013


1. Freeway Widening and mainline alignment shifts on I-15 from Sahara

Avenue to the Spaghetti Bowl

2. Ramp braiding from the southbound US95 ramp along southbound I-15

including exit ramps at both Charleston Boulevard and Sahara Avenue

3. Direct Connector Ramps from the high-occupancy vehicle (HOV) lanes

out to Western Avenue between Oakey Boulevard and Charleston

Boulevard

4. Reconstruction of the Charleston Blvd Interchange into a tight-diamond

configuration and widening on Charleston Boulevard

5. Alta slip ramp construction

6. Realignment of the SB US 95 entrance ramp

7. A high-occupancy vehicle (HOV) direct connector ramp from the center of

US 95, west of the Spaghetti Bowl, to the center of I-15, south of the

Spaghetti Bowl

8. MLK-US 95 loop ramp construction

• Offsite storm drain improvements in the local jurisdiction roadways to meet local

drainage criteria including:

1. Martin Luther King Boulevard improvements from Alta Drive to Oakey

Boulevard with bridge over Charleston Boulevard

2. Charleston Boulevard widening

3. Pinto Lane storm drain

4. Western Avenue–Grand Central at-grade intersection with Charleston

Boulevard

5. Western Avenue improvements

6. Alta Drive improvements

7. Iron Horse loop reconstruction

Refer to Figure 3 – Project Drainage Improvements for a high-level map of the drainage

improvements.

Project Drainage Improvements

PROJECT NEON – P3 IMPROVEMENTS Preliminary Drainage Design Report

Figure 3

12/2013

Limits of Onsite Drainage Improvements for Mainline WideningLimits of Drainage Improvements for Crumb Rubber Project Shoulder Reductions Limits of Existing CCRFCD MPU Drainage Facilities

Limits of MPU Drainage Facility to be Realigned

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TTTooowww nnnssshhhiiippp 222111 SSSooouuuttthhh,,, RRRaaannngggeee 666000 EEE aaasssttt

Limits of Proposed CCRFCD MPU Drainage Facilities

Limits of Local Roadway Improvements

December 2013


2.0 DESIGN PROCEDURES AND CRITERIA

2.1

Drainage Criteria

Multiple design storm return frequencies were considered for the design of drainage

facilities within the project area, depending on the type of drainage facility, the location

of the drainage facility, and jurisdiction of the proposed improvements. Table 2.1

provides a summary of various design storm frequencies used for analysis of facilities

along the corridor.

TABLE 2.1

SUMMARY OF DESIGN FLOW FREQUENCIES

Jurisdiction Design Condition Design Storm

Return Frequency (years)

NDOT NDOT Offsite Facility Design - Culverts, Channels, Bridges 50

NDOT No adverse impacts to Existing Condition Drainage Patterns 100

NDOT NDOT Onsite Drainage Design - I-15 Mainline, US-95 Mainline, Viaduct, Ramps, CD Roads 25

CLV/CCRFCD CCRFCD Regional Facility Design 100

CLV/RTC CCRFCD Local “Major” Event Facility Design (Local Streets) 100

CLV/RTC CCRFCD Local “Minor” Event Facility Design (Local Streets) 10

As with the previous design level analysis, hydraulic analysis of the major offsite facilities

in this report has been performed using the 100-year storm event flows based on the

following:

• The majority of existing offsite drainage facilities are Clark County Regional

Flood Control District (CCRFCD) MPU facilities, designed for a 100-year

return frequency.

• Proposed Project NEON improvements will widen the freeway footprint and

impact existing MPU facilities and 100-year flow patterns.

December 2013


• Both I-15 and US-95 freeways are elevated and isolated from direct effects of

the 50 and 100-year offsite storm flows. The 100-year flows are generally

conveyed in the MPU facility on the west side of I-15 and south side of US-95

or conveyed in the major cross streets under the freeways.

2.2

Compliance

The drainage design criteria utilized on the Project are based on the standards as

outlined in the Nevada Department of Transportation Drainage Manual (Reference 2,

hereinafter referred to as the NDOTDM). The Clark County Regional Flood Control

District 2008 Master Plan Update (Reference 3, hereinafter referred to as the 2008

MPU) and the Clark County Regional Flood Control District Hydrologic Criteria and

Drainage Design Manual (Reference 4, hereinafter referred to as the HCDDM) have also

been used for relevant design criteria.

2.3 Project Design Data

Existing ground elevations are based on topography and digital terrain modeling

obtained throughout the P3 Phase design process. Aerial mapping was provided by

NDOT. As-built field survey information for the roadway and storm drain facilities was

obtained throughout the design process for additional detail. In addition, potholes on

storm drain facilities and utility facilities have been taken at critical design points to

accurately determine existing locations where manhole access is not available or

additional information is needed.

December 2013


3.0 EXISTING CONDITIONS 3.1

Summary of Existing Conditions

The need for Project Neon is driven by the current overcapacity condition on I-15. The

existing congestion levels on the freeway contribute to traffic issues including high-

frequency accidents, air pollution, noise pollution, travel delay, and decreased quality of

life. Project Neon will improve traffic operations by separating mainstream freeway

travel from local traffic. It will enhance safety by making freeway entrance and exits

easily accessible. Increasing I-15 capacity will simultaneously increase mobility and

improve access to downtown Las Vegas.

The existing drainage facilities within the project corridor consist of CCRFCD master

planned facilities, local offsite systems, local roadway storm drain facilities, and freeway

onsite systems. In general, the existing onsite facilities on I-15 between Sahara Avenue

and the Spaghetti Bowl will be replaced with new facilities to accommodate the widening

and realignment, and the existing onsite facilities on US-95 between the Spaghetti Bowl

and Rancho Drive will be utilized as much as possible and supplemented to

accommodate the viaduct installation in the middle of the existing freeway. The existing

onsite facilities between Desert Inn Road and Sahara Avenue will be supplemented to

reduce the flow spread as much as possible given the minimal shoulder widths through

this segment.

The existing offsite drainage facilities within the project limits include:

• Freeway Channel – Sahara Avenue to Symphony Parkway (CCRFCD 2008 MPU

facilities FW15 0000 to FW15 0175)

• Oakey Boulevard lateral (CCRFCD 2008 MPU facility FWOK 0000)

• Waldman Avenue lateral (CCRFCD 2008 MPU facility FWWL 0000)

• Western Avenue lateral (CCRFCD 2008 MPU facility FWUP 0000)

• Charleston Boulevard lateral (CCRFCD 2008 MPU facility FWCH 0000)

• US-95 Channel (CCRFCD 2008 MPU facility LCCH 0000)

• Pinto Lane storm drain lateral

• Alta Drive storm drain lateral

December 2013


• Local offsite channel on East side of I-15 from Desert Inn Road to Wall Street

• Local roadway storm drain facilities in Sahara Avenue, Oakey Boulevard, Richard

Court, Desert Lane, Charleston Boulevard, Western Avenue, Grand Central

Boulevard, Martin Luther King Boulevard, Alta Drive, and Symphony Parkway.

3.1.1 Previous Reports

There are several reference studies that have been previously completed for

Project Neon or for other projects in the vicinity of the project. Table 3.1 is a list

of the previous studies that were reviewed for the 30% design of the P3 Phase of

Project NEON.

TABLE 3.1 REFERENCE STUDIES

Reference Study Date

1 30% Phase I - Drainage Design Report for Project NEON, by VTN Nevada January 2011

2 Overall Drainage Design Report for Project NEON, by VTN Nevada April 2010

3 Existing Offsite Hydrology Report for Project NEON, by VTN Nevada (based on 2008 MPU) February 2010

4 2008 CCRFCD Flood Control Master Plan Update of the Las Vegas Valley, by PBS&J September 2008

5 Offsite Hydrology Update Memorandum, by VTN Nevada (based on 2002 MPU) July 2004

6 Preliminary Offsite Hydrology Report for Project NEON, by VTN Nevada (based on 2002 MPU) April 2004

7 Offsite Hydrology Update Memorandum, by VTN Nevada (based on 2002 MPU) August 2005

8 Martin Luther King Blvd. Widening Alta Dr. to Carey Ave. – Preliminary Design and Drainage Report, by VTN Nevada January 2004

9 Meadows Detention Basin Improvements & Las Vegas Springs Preserve Cienaga Grading – 100% Design Report, by VTN Nevada

May 2001

10 Oakey Storm Sewer Conveyance System Corridor Study, by Carter-Burgess February 2000

11 I-15 Freeway Channel Pre-design Report, by Parsons Brinckerhoff May 1999

12 City of Las Vegas City Wide Hydrology Analysis, by PBS&J 1997

13 Spring Mountain Rd. Interchange and I-15 Median Widening, by Louis Berger and Associates November 1996

December 2013


3.1.2 Drainage Basin Characteristics

Offsite hydrologic analysis, including drainage basin delineation and

establishment of subbasin characteristics, was performed in the previous Project

Neon – Phase I studies and agreed upon by the reviewers. This study includes

further investigation and some subdividing of the subbasins when necessary

within the vicinity of I-15 to obtain flowrates at more specific locations along the

corridor. Three design conditions were investigated for this study: Existing

Condition, Proposed Condition, and Ultimate Condition. The Proposed Condition

is the existing tributary area with the 30% design P3 Phase improvements in

place. The Ultimate Condition features a fully developed offsite watershed, based

on the 2008 MPU analysis, with the 30% design P3 Phase improvements in

place. The Existing Conditions Subbasin Map and the Ultimate Conditions

Subbasin Map have been included in Appendix A for reference. For this study,

the Proposed Conditions offsite subbasins are the same as the Existing

Conditions subbasins.

3.1.3 Historic Flow Patterns

Offsite flows are generally conveyed to the east toward the I-15 corridor as

overland flow or in existing storm drain facilities to the existing Freeway Channel

(CCRFCD 2008 MPU facilities FW15 0000 to 0175). The existing Freeway

Channel is located on the west side of the I-15 freeway from the south side of

Sahara Avenue to Wall Street, where is crossed under the freeway and turns

north along the east side of I-15. In the Existing Conditions, the Freeway

Channel is under capacity due to the fact that a significant portion of the

upstream master planned facilities have not yet been constructed. Therefore,

overland flow that is in excess of the Freeway Channel capacity bypasses the

channel and is conveyed under the existing I-15 freeway at major street crossings.

The overland flow is then conveyed to the north between I-15 and the elevated

UPRR tracks to the low-point in Charleston Boulevard under the UPRR Bridge.

In order to determine the existing flow patterns at the project site, a preliminary

analysis was performed at the Phase 1 30% design level to investigate the existing

capacity of the Freeway Channel. The capacity analysis has been updated for this

December 2013


30% design level P3 Phase study to account for additional as-built information

that was obtained since the initial Phase 1 30% study.

The channel capacity analysis consisted of ‘balancing’ the HEC-1 hydrologic

model peak flow results and flow diversions with the WSPGW hydraulic model to

determine a maximum hydraulic grade line (HGL) in the existing facility. For the

initial analysis, the initial maximum capacity of the channel was assumed to be

the flowrate that resulted in an HGL elevation that was the same as the existing

grade above the Freeway Channel. The initial analysis was updated for this study,

and the iterative process was redone in order to establish an Existing Condition

HGL in the Freeway Channel that not only takes into consideration the grade

above the RCB facility, but also the elevation of existing inlet facilities in the

vicinity of the Freeway Channel, since flow would begin to leave the system once

the HGL reaches the elevation of the adjacent inlet facilities. Further discussion

of this analysis is contained in Section 4.1.8.

3.1.4 FEMA Information

An exhibit is provided in the Appendix A-9 showing the Federal Emergency

Management Agency (FEMA) Flood Insurance Rate Maps (FIRM) containing

Community Panel Numbers 32003C2170E revised September 27, 2002. The

project site lies within FEMA-designated shaded Zone X. Areas designated as Zone

X are outside the regulatory 100-year floodplain.

3.1.5 Regional Flood Control Master Plan Information

As shown on Figure F-31 of the 2008 Las Vegas Valley Flood Control Master Plan

Update, refer to Appendix A-7, there are several existing and proposed Regional

storm drain facilities in the project vicinity. Refer to Table 3.1.5.1 for the list of

the 2008 Master Plan Update facilities that are directly affected by the 30% P3

Phase of Project Neon, and Table 3.1.5.2 for additional CCRFCD 2008 MPU

Master Planned Facilities in the vicinity of the project.

December 2013


TABLE 3.1.5.1 2008 MPU FACILITIES DIRECTLY IMPACTED BY PROJECT

ID / River Mile Exist. / Prop. Facility Description

2008 MPU Data Length

(ft) Flow (cfs)

Slope (%)

FREEWAY CHANNEL FROM DESERT INN TO EXPRESSWAY FW15 0010 Existing 3: 12’x10’ RCB 677 3403 0.17 FW15 0038 Existing 3: 12’x10’ RCB 1945 3344 0.17 FW15 0050 Existing 3: 12’x10’ RCB 870 2613 0.17 FW15 0089 Existing 3: 12’x10’ RCB 980 2448 0.17 FW15 0100 Existing 3: 12’x 9’ RCB 1575 2295 0.17 FW15 0125 Existing 3: 12’x 8’ RCB 1350 1450 0.80 FW15 0150 Existing 3: 12’x 8’ RCB 1067 1450 0.80 OAKEY DRAIN FWOK 0000 Existing 10’x8’ RCB 1350 928 0.62 FREEWAY CHANNEL BYPASS FACILITY FWUP 0000 Existing 10’x 9’ RCB 350 242 0.37 FREEWAY CHANNEL – WALDMAN AVENUE FWWL 0000 Existing 6’x6’ RCB 1000 418 0.20 LAS VEGAS CREEK CHANNEL LCCH 000 Existing 2: 12’x 7’ RCB 730 2894 1.28 LCCH 0013 Existing 2: 12’x 6’ RCB 2035 2894 0.82

December 2013


TABLE 3.1.5.2 ADDITIONAL CCRFCD 2008 MPU MASTER PLANNED FACILITIES

ID / River Mile Exist. / Prop. Facility Description

2008 MPU Data

Length (ft)

Flow (cfs)

Slope (%)

BOULDER HIGHWAY SAHARA AVENUE BHSA 0331 P1 14’x11’ RCB 2000 3232 1.00 FREEWAY CHANNEL FROM DESERT INN TO EXPRESSWAY FW15 0000 Existing 3: 12’x10’ RCB 2170 3728 0.17

Refer to Table 3.1.5.1 for the FW15 facilities directly impacted by Project FW15 0175 Existing 3: 12’x 8’ RCB 985 1450 0.75 FW15 0214 P1 2: 12’x10’ RCB 1610 4104 0.73 FW15 0242 P1 2: 12’x 9’ RCB 1500 3968 0.93 FW15 0271 P1 2: 12’x10’ RCB 1520 3674 0.59 FW15 0301 P1 Concrete Channel 12’W 4’D 2:1 SS 1300 433 0.42 WEST CHARLESTON DRAINS FWCH 0000 Existing 10’x 7’ RCB 1710 1008 0.74 PALMYRA / SIRIUS DRAIN FWPS 0000 P1 12’x11’ RCB 3000 3240 1.50 FREEWAY CHANNEL – RAILROAD CHANNEL FWR2 0000 Existing 5’x5’ RCB 377 1.60 FWR2 0020 Existing Earthen Channel 10’W 4’D 2:1 SS 650 0.50 FREEWAY CHANNEL BYPASS FACILITY RR BRANCH FWRR 0000 Existing 48” RCP 70 1.22 FWRR 0010 Existing Concrete Channel 4’W 4’D 0:1 SS 220 1.22 FREEWAY CHANNEL – SAHARA FWSA 0000 P1 7’x5’ RCB 5700 486 1.49 FREEWAY CHANNEL BYPASS FACILITY

Refer to Table 3.1.5.1 for the FWUP facilities directly impacted by Project FWUP 0010 Existing 10’x 8’ RCB 804 242 0.37 FWUP 0059 Existing 10’x 6’ RCB 2680 242 0.40 FWUP 0100 Existing 8’x 4’ RCB 1440 242 0.47 LAS VEGAS CREEK CHANNEL

Refer to Table 3.1.5.1 for the LCCH facilities directly impacted by Project LCCH 0051 Existing 2: 14’x 7’ RCB 3113 2894 0.60 LCCH 0110 Existing Transition Structure 220 2798 LCCH 0114 Existing 2: 14’x 7’ RCB 670 2329 0.80 LAS VEGAS CREEK - RANCHO LCRA 0000 Existing 12’x 8’ RCB 380 783 0.60 WASHINGTON AVENUE CHANNEL LVWH 0484 Existing Confluence Structure 455 4978 0.15

December 2013


4.0 OFFSITE DRAINAGE FACILITIES

The offsite drainage facilities for Project NEON – P3 Phase have been designed to

accommodate the modifications to the freeway geometry and perpetuate existing

conditions flow patterns. The existing offsite drainage facilities within the project limits

include:

• Freeway Channel – Sahara Avenue to Symphony Parkway (CCRFCD 2008 MPU

facilities FW15 0000 to 0175)





• US-95 Channel (CCRFCD 2008 MPU facilities LCCH 0000 to 0114)



• Local offsite channel on East side of I-15 from Desert Inn Road to Wall Street

• Local roadway storm drain facilities in Sahara Avenue, Oakey Boulevard, Richard

Court, Desert Lane, Charleston Boulevard, Western Avenue, Grand Central

Boulevard, Martin Luther King Boulevard, Alta Drive, and Symphony Parkway.

4.1

I-15 Freeway Channel – Sahara Avenue to Symphony Parkway

The existing Freeway Channel is 2008 MPU facilities FW15 0000 to FW15 0175. The

Freeway Channel parallels I-15, from Sahara Avenue to Symphony Parkway. In addition,

the 2008 MPU proposes to upsize the existing channel facility from Desert Inn Road

north to Sahara Avenue, 2008 MPU facilities FW15 0214 to FW15 0301. Refer to 2008

MPU Figure 31 in Appendix A-7. The existing Freeway Channel was designed for the

smaller Ultimate Condition flows and does not have capacity to convey the entire

Existing Condition 100-year storm event flow that reaches the facility. As a result,

overland flow is conveyed along the west side of I-15 and under I-15 at major road

crossings. Future upstream MPU facilities and the Sahara Avenue storm drain will

reduce the flow conveyed to the Freeway Channel and eliminate the overland flow that

bypasses the facility in the existing condition. The funding for design and construction of

the upstream MPU facilities is currently unknown, and anticipated to be several years

December 2013


out. As a result, per NDOT criteria, the Freeway Channel and associated lateral facilities

have been designed to match the existing flow patterns at the site and to not result in any

additional adverse impacts to the Project area.

4.1.1 Desert Inn Road to Sahara Avenue

The proposed 2008 MPU facilities have not been constructed south of Sahara

Avenue. However, there is an existing open channel along the west side of I-15

that intercepts overland offsite flows from the tributary area west of Rancho

Drive between Desert Inn Road and Sahara Avenue. The existing channel begins

as a 12-ft wide, 4-ft deep riprap lined trapezoidal channel at Desert Inn Road and

conveys runoff to the north to Teddy Drive, approximately 0.3 miles south of

Sahara Avenue. At Teddy Drive the channel transitions to a concrete rectangular

channel for approximately 880-ft and then transitions to an existing 2-10’ x 8’

RCB. This RCB continues north, along the west edge of I-15, across Sahara

Avenue.

The 2008 MPU proposes to replace the upstream 1,300 feet of the existing riprap

channel with a 12’ wide x 4’ deep concrete trapezoidal channel with 2:1 side

slopes. Downstream of the trapezoidal channel, the 2008 MPU features proposed

dual 12’ wide by either 9’ or 10’ tall RCBs to complete the Regional storm drain

and connect to the existing 2-10’ x 8’ RCB just south of Sahara Avenue. There are

no proposed P3 Phase improvements along this reach that would impact the

geometry of the existing open channel; therefore existing drainage patterns at

this location will remain unchanged.

4.1.2 Sahara Avenue to Oakey Boulevard

The existing 2-10’ x 8’ RCB (2008 MPU facilities FW15 0125, FW15 0150, and

FW15 0175) is located between Sahara Avenue and Oakey Boulevard. Between

Sahara Avenue and station “MS” 754+36.1, the RCB is located below the existing

southbound exit ramp to Sahara Avenue. Minor changes to the existing off-ramp

are proposed in this reach, but the roadway changes will not impact the existing

RCB, therefore the RCB will remain in place and the existing drainage patterns

will remain unchanged.

December 2013


Widening of the southbound I-15 mainline and the addition of the southbound

CD ramps will result in additional loading from the roadway and embankment

fills over the box alignment. Record drawings indicate that the existing RCB was

not designed to sustain this additional loading. At station “MS” 754+36.1, the

regional storm drain facility will be realigned approximately 75 feet to the west to

accommodate the freeway improvements proposed with the P3 Phase 30%

design. The widening of the freeway footprint with the addition of the

southbound CD ramps requires right-of-way acquisition of the private residences

along Loch Lomond Way. The 2-10’ x 8’ RCB alignment shift extends for 224.6

feet and then transition to a 20’ x 10’ rectangular concrete open channel that

continues north parallel to the freeway for approximately 940 feet. The open

channel is aligned outside of the new freeway control of access, within the new

right-of-way along Loch Lomond Way. Approximately 300 feet south of Oakey

Boulevard, the storm drain transitions back to a 2-10’ x 8’ RCB for 208 feet

before transitioning to a 2-14’ x 6’ RCB under Oakey Boulevard. The Freeway

Channel alignment shift continues across Oakey Boulevard to accommodate the

proposed abutments of the new southbound CD road SA3 Bridge.

4.1.3 Oakey Boulevard

The proposed CD road SA3 Bridge at Oakey Boulevard results in a conflict with

the existing Freeway Channel RCB and confluence structure on the west side of I-

15 (2008 MPU facilities FW15 0125 and FW15 0100). The Freeway channel and

the confluence with the Oakey storm drain will be relocated to the west to avoid

the conflict with the bridge footprint.

The existing 2-10’x8’ RCB in the vicinity of Oakey Boulevard has a relatively flat

profile with minimal cover to the roadway finished grade. In addition, there is an

existing 54” sanitary sewer and a 36” waterline facility in Oakey Boulevard.

Realignment of the RCB to the west decreases the available clearance between the

existing sewer and the finished ground. As a result, the RCB was transitioned to

a 2-14’x6’ RCB facility across the roadway to maintain channel capacity and avoid

a direct conflict with the 54” sanitary sewer. The 36” waterline has been

December 2013


relocated by LVVWD since the last submittal to accommodate the RCB

realignment at this location.

4.1.4 Oakey Boulevard to Wall Street The Freeway Channel realignment to the north of Oakey Boulevard has been

designed in conjunction with the proposed local roadway improvements of

Martin Luther King Boulevard. The freeway footprint widening north of Oakey

Boulevard places additional fill loads and retaining walls on top of the existing 3-

12’ x 9’ RCB Freeway Channel, which would require significant structural

improvements to accommodate and create a situation where access to the storm

drain would be limited. As a result, the Freeway Channel has been realigned

under the proposed local roadway, which allows for convenient maintenance

access to the facility and results in more reasonable fill on the facility.

There is an existing 8” sewer line located parallel with the west edge of the

existing RCB facility, and is extremely close to the existing westerly right-of-way

line. The Freeway Channel realignment requires the 8” sewer to be relocated.

The new right-of-way for Martin Luther King Boulevard creates a corridor for the

relocated sewer facility on the west side of the storm drain.

Drop inlets have been placed at the low points in the Martin Luther King

Boulevard profile to convey the 10-year storm event runoff into the Freeway

Channel. In the Proposed Condition 100-year storm event, the Freeway Channel

is over capacity and the HGL is at or slightly above the finished grade in some

locations along the alignment between Oakey Boulevard and Wall Street. The

proposed inlets may require check valves to allow runoff collection but prevent

backwater from the Freeway Channel backing out into the roadway during the

100-year event. This should be investigated further at the next design level to

ensure that storm event criteria are met.

The existing Freeway Channel crosses I-15 from west to east on the Wall Street

alignment. The Wall Street access under I-15 will be removed with the P3 Phase

of Project Neon. As a result, the existing Wall Street Bridge will be removed and

December 2013


additional fill in excess of 35 feet will be placed above the existing Freeway

Channel. The existing 3-10’ x 12’ RCB facility under the Wall Street alignment will

be replaced prior to demolition of the bridge with an RCB facility capable of

withstanding the additional fill loading.

In addition to manhole access to the Freeway Channel, access for larger

equipment has been provided in two locations between Oakey Boulevard and

Wall Street. The existing Freeway Channel features a very large open section at

the confluence with the Oakey Lateral. Prior to the construction of the Oakey

Lateral, this opening was used to collect the runoff that was conveyed overland in

Oakey Boulevard to the Freeway Channel. This large opening will be replaced

with a grated access point to the realigned confluence structure at this same

location. The second large access point is located just over ¼ mile north of Oakey

Boulevard to the north of the fire station. This access grate is located

approximately 50 feet west of the Freeway Channel off of Martin Luther King

Boulevard and connects to the Freeway Channel with a 12’ x 8’ RCB.

4.1.5 Wall Street to Charleston Boulevard

The Freeway Channel is located on the east side of I-15 between Wall Street and

Charleston Boulevard. The P3 Phase freeway improvements include a new

northbound exit ramp from I-15 to Charleston Boulevard for the proposed tight-

diamond interchange on the west side of the existing Freeway Channel and the

realigned Western Avenue on the east side of the Freeway Channel for the

proposed at-grade intersection with Charleston Boulevard. The existing

confluence structure with the Western Avenue Lateral is located just north of

Wall Street. Pothole investigation indicated that the storm drain has experienced

settlement in the vicinity of the confluence structure and there are low points in

the storm drain invert. The existing confluence with the Western Avenue Lateral

and approximately 102 feet of the 3-10’ x 12’ RCB facility will be realigned in

order to maintain positive drainage through the confluence, accommodate the

proposed roadway improvements, and to align the Freeway Channel through this

reach to accommodate the future phase northbound CD ramp roadway

improvements. The Freeway Channel realignment/reconstruction ends

December 2013


approximately 450 feet south of Charleston Boulevard. The existing

4.1.6 Charleston Boulevard / Grand Central Parkway

The existing Freeway Channel will be protected in place at this location for the P3

Phase. The future phase Project Neon configuration includes a northbound CD

road with a bridge over Charleston Boulevard. The northbound CD alignment

will likely result in additional roadway fills and a bridge structure over both the

existing 3-12’x10’ RCB facility (2008 MPU facility FW15 0050) and the

Charleston confluence structure located just north of Charleston Boulevard. In

addition, there is a possible future phase project that includes a grade-separated

roadway connection between Western Avenue and Grand Central Parkway that

features a second bridge structure over Charleston Boulevard in this location. The

existing RCB facility and the existing Charleston confluence structure may need

to be reconstructed/realigned in a future phase of Project Neon to accommodate

these improvements.

4.1.7 Charleston-Alta Slip Ramp and Charleston-Grand Central Slip Ramp The northbound I-15 (east side) footprint north of Charleston Boulevard will be

reconfigured and widened to accommodate slip ramps from Charleston

Boulevard to both Alta Drive and Grand Central Parkway. The existing Freeway

Channel between Charleston Boulevard and Alta Drive is located parallel to the

freeway, outside of the right-of-way. The Charleston-Alta slip ramp and the

daylight from the new ramp are completely within the existing right-of-way and

will not impact the existing Freeway Channel. The Charleston-Grand Central slip

ramp extends north from Charleston Boulevard and turns east over the existing

major storm drain to connect to Grand Central Parkway. This slip ramp will

reduce the amount of cover over the existing 3-12’ x 9’ RCB facility where is

crosses the facility. According to record drawings, the existing Freeway Channel

RCB facility in this location was designed for a large amount of cover. The RCB

should be analyzed at the next design level to determine if a structural solution

will be necessary to accommodate the reduction in cover over the facility.

December 2013


4.1.8 Freeway Channel Hydraulic Analysis A detailed hydraulic analysis was performed on both the existing Freeway

Channel system and the re-aligned Freeway Channel system to ensure the

proposed system re-alignment would not adversely affect conveyance capacity

and existing flow conditions. The hydraulic analysis was extended significantly

upstream and downstream of the project limits to ensure that accurate boundary

conditions were obtained for the WSPGW analysis. The existing condition

analysis models the existing system geometry with existing condition 100-year

flows (prior to construction of the proposed upstream MPU Facilities). The

proposed condition analysis models the proposed realignment of the system,

based on the existing condition 100-year flows. The ultimate condition analysis

models the ultimate 2008 MPU based flows with the P3 Phase proposed

realignment of the system.

Since the existing Freeway Channel is undersized for the existing conditions

flowrates conveyed to the west side of I-15, the channel capacity analysis for both

the existing conditions and proposed conditions consisted of ‘balancing’ the

HEC-1 hydrologic model peak flow results and flow diversions with the WSPGW

hydraulic model to determine a maximum hydraulic grade line (HGL) in the

Freeway Channel facility. The maximum capacity of the Freeway Channel in both

the existing and proposed condition analyses was calculated for this analysis to

be the flowrate that resulted in an HGL elevation that was the same as the ground

surface elevation above the Freeway Channel or the elevation of existing or

proposed inlet facilities adjacent to the Freeway Channel, since flow would begin

to leave the system or no longer enter the system when the HGL reaches the

elevation of the inlet grates. The flow in excess of the Freeway Channel capacity

was routed in the HEC-1 analysis either north along the west side of I-15 or east

at major street crossings to the Western Avenue corridor between I-15 and the

UPRR.

The flow balancing analysis was performed by adding the flow from the HEC-1

model at the upstream end of the facility and using WSPGW to model the

channel. The flow at the next junction point downstream was then included in

December 2013


the WSPG analysis and the HGL was checked to verify that it was at or below

finished ground/inlet grate elevations. If the HGL was above finished

ground/inlet elevation, the inflow at the junction point was adjusted until the

HGL came down to the controlling elevation. This process was repeated adding

additional flows in the downstream direction until the flowrates along the entire

Freeway Channel alignment were balanced between the HEC-1 model and the

WSPGW model.

The existing condition flowrate at the upstream (south) end of the existing

Freeway Channel is 2542 cfs. The initial step in balancing the hydraulic model

involved running the existing condition flowrate of 2542 cfs, beginning at the

point where the Freeway Channel transitions from a rectangular concrete

channel to a 2-10’x8’ RCB just south of Sahara Avenue, and continuing

throughout the entire system. For this analysis, all of the flow at the RCB

entrance south of Sahara Avenue enters the dual RCB facility, as the Freeway

Channel has sufficient capacity to convey the 2542 cfs all the way through the

system. Flow from the Oakey Boulevard lateral was added into the system until

the HGL reached the control elevation at Oakey Boulevard.

Based on the elevation of the existing inlets for the Waldman lateral, which are

located approximately 400 feet upstream of the Freeway Channel, adding the

entire 313 cfs at that confluence in the existing Freeway Channel to match the

HEC-1 design point at this location resulted in an HGL above the control

elevation. The flow added to the existing Freeway Channel from the Waldman

lateral facility was revised until it was determined that 275 cfs could be added

before raising the HGL above the control elevations at either the Waldman

confluence or the upstream Oakey confluence. The remaining flow above the 275

cfs would be conveyed overland to the north along the west side of I-15 to

Charleston Boulevard in the Existing Condition. In the Proposed Condition, the

Freeway Channel will transition to a 2-18’ x 10’ RCB just upstream of the

Waldman confluence. The additional capacity allows for the entire 313 cfs to be

conveyed into the Freeway Channel in the Proposed Condition.

December 2013


The HGL in the Freeway Channel at the Western Avenue lateral confluence

location showed that the facility was already at maximum capacity, resulting in

essentially no flow entering the Freeway Channel system at Western Avenue. The

WSPGW analysis shows 1 cfs entering the Freeway Channel at the Western

Avenue confluence for both the Existing and Proposed Conditions. The

confluence with the Charleston lateral is located just downstream of the Western

confluence and is a similar situation in that the Freeway Channel is at maximum

capacity relative to the adjacent inlet grate elevations. Therefore, the analysis

shows that essentially no flow is able to get into the Freeway Channel during the

100-year design storm event. The WSPG analysis shows 1 cfs entering the

Freeway Channel at the Charleston confluence in the Existing Condition. In the

Proposed Condition, 10 cfs was able to enter the Freeway Channel before the

HGL reached the adjacent inlet elevations.

In the Existing Condition, the entire 85 cfs from the Pinto Lane RCB, and the 121

cfs in the 66” RCP at Alta Drive were able to be added into the Freeway Channel,

and the HGL in the channel at both of these locations was still well below existing

ground. In the Proposed Condition, the Pinto Lane lateral conveys runoff

collected from the intersection of Pinto Lane and Desert Lane to the Alta Lateral

storm drain. As a result, there is no flow entering the Freeway Channel in the

Proposed Condition at the Pinto Lane location. The Pinto Lane and Alta Drive

flows combine to add 329 cfs into the Freeway Channel from the Alta Drive

lateral in the Proposed Condition. The entire 329 cfs was able to be added into

the Freeway Channel at Alta Drive.

The analysis described above was the result of an iterative process of hydraulic

modeling of the Freeway Channel to determine channel capacity and hydrologic

modeling to investigate the impacts of the channel capacity on the offsite flow

splits and overland conveyance. Table 4.1.8 is a comparison of the results of the

Existing Condition and Proposed Condition Freeway Channel analysis. The

points shown in the table are located just upstream of the confluence structures,

so that the flow value listed is the flow in the Freeway Channel just before the

lateral combines with the mainline.

December 2013


TABLE 4.1.8 FREEWAY CHANNEL WATER SURFACE COMPARISON SUMMARY

APPROX. LOCATION CONDITION1 STATION FACILITY

FACILITY FLOW2

(cfs)

Difference (%)

HGL (ft)

Difference (ft)

Symphony Parkway

Existing 141+54.24 (3) 12'x9' RCB 3299 +1.6

2029.65 +0.14

Proposed 141+96.78 (3) 12'x9' RCB 3353 2029.79

Alta Drive Existing 118+01.06 (3) 12'x9' RCB 3062

-1.2 2036.25

+0.42 Proposed 118+43.60 (3) 12'x9' RCB 3024 2036.67

Pinto Lane Existing 109+33.54 (3) 12'x10' RCB 2977

+1.6 2038.14

+0.15 Proposed 109+57.03 (3) 12'x10' RCB 3024 2038.29


Existing 92+24.00 (3) 12'x10' RCB 2976 +1.3

2041.13 +0.22

Proposed 92+66.54 (2) 18'x10' RCB 3014 2041.35

Western Avenue

Existing 83+56.30 (3) 12'x10' RCB 2975 +1.3

2042.90 +0.41

Proposed 84+15.09 (2) 18'x10' RCB 3013 2043.31

Waldman Avenue

Existing 73+28.58 (3) 12'x10' RCB 2700 0.0

2045.33 +0.30

Proposed 72+00.00 (2) 18'x10' RCB 2700 2045.63

Oakey Boulevard

Existing 57+50.10 (2) 10'x8' RCB 2542 0.0

2048.57 -0.08

Proposed 57+11.22 (2) 14'x6' RCB 2542 2048.49

Sahara Avenue

Existing 10+00.00 (2) 10'x8' RCB 2542 0.0

2079.03 0.00

Proposed 10+00.00 (2) 10'x8' RCB 2542 2079.03

1. Existing Condition is the current offsite hydrologic condition and Freeway Channel configuration. Proposed

Condition is the current offsite hydrologic condition with the realigned Freeway Channel for the P3 Phase improvements.

2. Facility Flow shown is the flow just upstream of the confluence structure for the “Approx. Location” lateral

An ultimate condition hydraulic analysis was also performed to analyze the

Freeway Channel realignment configuration with the reduced ultimate condition

100-year flows, based on full build-out of the proposed CCRFCD facilities

featured in the 2008 MPU. The hydraulic grade lines for both the proposed and

ultimate condition analysis have been provided on the channel profile sheets.

December 2013


4.2

Freeway Channel Laterals

Several CCRFCD and local offsite facilities collect offsite flows west of I-15 and convey

them to the Freeway Channel. As discussed above, the Freeway Channel does not have

sufficient capacity to convey the existing flowrates until the upstream MPU facilities are

constructed. As a result, during the 100-year storm event in the existing conditions, the

lateral facilities to the Freeway Channel do not fully collect and convey the entire storm

event flows into the Freeway Channel due to the lack of capacity in the mainline system.

Flows above the system capacity are conveyed within major surface streets to the east or

north along the west side of I-15.

Realignment of several of the Freeway Channel laterals is necessary to eliminate conflicts

with the proposed roadway footprint and/or tie in points and to accommodate

modifications to the Freeway Channel alignment. Proposed facilities are designed to

maintain existing conveyance capacity. The Freeway Channel laterals include:





• US-95 Channel (CCRFCD 2008 MPU facility LCCH 0000 and LCCH 0013)



4.2.1 Oakey Boulevard Lateral The existing Oakey Boulevard Lateral (FWOK 0000) is a 10’x 8’ RCB that

includes a series of drop inlets in Oakey Boulevard to collect and convey runoff

into the system. The RCB connects to the Freeway Channel at Oakey Boulevard,

on the west side of I-15, at an open confluence structure. A portion of the Oakey

Boulevard Lateral will need to be re-aligned in order to tie into the realigned

Freeway Channel at a new confluence structure. Based on discussions with the

City of Las Vegas, the open confluence structure will be replaced with a capped

December 2013


confluence structure with a grated access. The valley gutter across Martin Luther

King Boulevard at this location is no longer necessary to convey overland flow

from Oakey Boulevard into the Freeway Channel since the upstream Oakey

Boulevard Lateral inlet facilities have capacity to collect the 100-year storm event

flow in Oakey Boulevard. The re-aligned lateral facility crosses the existing 54”

Sanitary Sewer at a point further upstream than the existing conditions, which

reduces the available cover on the facility. Therefore, the lateral is replaced with

a 14’ x 6’ RCB facility to maintain minimal clearances to the 54” sewer and

finished grade, as well as cleanly tie into the 6-ft tall RCB of the Freeway Channel.

Based on existing condition hydrologic and hydraulic flow balance analysis for

the I-15 Channel, the I-15 channel does not have capacity to convey the flow that

the Oakey Boulevard Lateral has the potential to intercept. The additional flow

will be conveyed in Oakey Boulevard and bypass the Freeway Channel facility.

Approximately 158 cfs will be conveyed into the Freeway Channel at Oakey

Boulevard, and approximately 745 cfs continues east in Oakey Boulevard to the

east side of I-15 during the 100-year storm event.

4.2.2 Waldman Avenue Lateral

The existing Waldman Avenue Lateral (FWWL 0000) is a 6’ x 6’ RCB with a

series of drop inlets in Waldman Avenue, which is located approximately 400-ft

upstream (west) of the Freeway Channel. This RCB facility connects directly into

the side of Freeway Channel. The existing Freeway Channel increases in size

from a 3-12’ x 9’ RCB to a 3-12’ x 10’ RCB at the junction with the 6’ x 6’ RCB in

order to convey the additional flow.

The realignment of the Freeway Channel to the west of the existing alignment to

keep it under the Martin Luther King Boulevard improvements will require a

portion of the Waldman Avenue Lateral be realigned also. The mainline RCB will

increase from a 3-12’ x 9’ RCB to a 2-18’ x 10’ RCB facility at a vertical grade

break located approximately 200-ft upstream of the junction point with the 6’ x 6’

RCB lateral. This configuration will maximize the hydraulic capacity of the

Freeway Channel facility in this location.

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The realigned Freeway Channel facility features a maintenance access opening

approximately 75-ft upstream of the junction with the Waldman Avenue lateral.

This maintenance access opening is a 12’ x 8’ RCB with an access grate large

enough to allow a small maintenance vehicle to be lowered into the RCB facility.

The access grate for the maintenance opening will be set approximately 1-ft above

the existing grade so that the proposed condition HGL in the Freeway channel,

which is at existing ground, will not exit the facility at this location.

4.2.3 Western Avenue Lateral The existing Western Avenue lateral (FWUP system) is a 10’ x 9’ RCB facility that

is aligned in Western Avenue from Sahara Avenue to the confluence with the

Freeway Channel at Wall Street. Based on pothole investigation, the existing

lateral facility does not completely drain due to a low point in the invert.

Approximately 306 feet of the lateral will be reconstructed/realigned to eliminate

the low point in the RCB and connect to the realigned Freeway Channel.

Based on the flow balancing analysis performed for the 100-year storm event,

there is a significant amount of flow that is conveyed in the major street

alignments across I-15 and is conveyed north in the Western Avenue corridor in

the Existing Condition and Proposed Condition. A 100-year peak flow of 1,678 cfs

is conveyed to the north in the Western Avenue corridor between I-15 and the

UPRR tracks at Sahara Avenue. The 100-year peak flow increased to 1,878 cfs at

Western Avenue and Oakey/Wyoming. The existing Western Avenue lateral RCB

has capacity to convey 520 cfs. The remaining 1,158 cfs and 1,358 cfs at Sahara

Avenue and Oakey/Wyoming, respectively, is conveyed overland to the north and

results in significant overland inundation of the Western Avenue corridor

between Sahara Avenue and Charleston Boulevard. The overland flow is

conveyed to the low point in Charleston Boulevard under the UPRR bridge. This

condition would be mitigated or reduced once the proposed upstream MPU

facilities are constructed. Refer to Section 4.4 for additional discussion of the

overland flow in the Western Avenue corridor.

December 2013


4.2.4 Charleston Boulevard Lateral The existing Charleston Boulevard Lateral (FWCH 0000) is a 10’ x 9’ RCB that

conveys offsite runoff from the west side of I-15 to the Freeway Channel on the

east side of the freeway. This facility ties into the existing Freeway Channel at the

confluence structure located at the northeast corner of Charleston Boulevard and

I-15.

The Freeway Channel and the Charleston confluence structure is not proposed to

be reconstructed for the P3 Phase, as described in Section 4.1.6. However, future

phase Project Neon improvements will likely require realignment/reconstruction

of the Charleston Boulevard lateral confluence with the Freeway Channel.

4.2.5 US-95 Channel

The US-95 Channel (2008 MPU facility segments LCCH 0000 and LCCH 0013)

is located along the south side of US-95 and wraps around the southwest

quadrant of the I-15/US-95 interchange to Symphony Parkway, below the ES

ramp. The eastbound US-95 to southbound I-15 ramp will be widened and

realigned for the P3 Phase and a new bridge will be constructed across Symphony

Parkway, along the west side of I-15, for the southbound CD road. The ES ramp

reconfiguration will require relocation of the 2-12’ x 6’ RCB US-95 Channel to

avoid the new bridge piers and the additional fill placed on the RCB due to the

realignment of the ramp. In addition, below the ES ramp, the MLK loop ramp

will be realigned with the P3 Phase improvements. The realignment will shift the

roadway over the top of the existing storm drain facility.

4.2.6 Pinto Lane Lateral

The existing local offsite Pinto Lane Lateral is an 8’x3’ RCB that collects offsite

runoff from a localized offsite low point along the west side of I-15 at Martin

Luther King Boulevard and Pinto Lane. This facility crosses I-15 and connects

with the Existing Freeway Channel on the east side of the freeway.

December 2013


The P3 Phase improvements include widening of I-15 to the west, southbound

ramp braiding, and full street improvements to the new Martin Luther King

Boulevard alignment. As a result, the upstream end of the existing 8’ x 3’ RCB

would be approximately 250 feet under the new freeway. The existing ground

slope to the west along the Pinto Lane alignment is relatively flat such that

extending the 8’ x 3’ RCB to the west of the P3 Phase roadway improvements at a

minimum slope would result in the RCB coming half way out of the ground.

Lowering the 8’x 3’ RCB to allow cover at the west end was not considered

feasible, since it would require significant disturbance to I-15. As a result, the P3

Phase improvements include inlet facilities at Pinto Lane and Desert Lane to

collect the runoff conveyed to this location and a storm drain system to convey

the flow north in Martin Luther King Boulevard to the Alta Drive storm drain

system. The addition of the flow from Pinto Lane requires that the existing 66”

storm drain in Alta Drive be upsized to convey the flow to the Freeway Channel.

Additional coordination with the City’s Alta Drive widening project will be

necessary as design progresses to verify facility sizes and ensure that the

proposed P3 Phase improvements will accommodate the City’s plans for Alta

Drive.

4.2.7 Alta Drive Lateral

The existing 66” Alta Drive lateral is upsized to accommodate the additional flow

added from the Pinto Lane lateral. The improvements to the Alta Drive lateral

will begin approximately 400 feet west of the proposed confluence, where the 66”

Alta Drive storm drain will be upsized to a 72” storm drain. The confluence with

the 66” Pinto Lane Lateral is an 8’ x 8’ structure. The storm drain between the

confluence and the Freeway Channel will be upsized to an 8’ x 5’ RCB. Continued

coordination with the City’s Alta Drive widening improvements project will be

necessary as design progresses.

4.3

Local Offsite Systems

The existing Local Offsite Systems consist of pipe and open channel facilities located

adjacent to I-15 that convey offsite flows and discharge from freeway onsite facilities.

December 2013


The local offsite systems were analyzed for this study to ensure that the improvements

maintain the existing conveyance capacity in the facilities and the flow patterns from

localized offsite drainage systems adjacent to I-15 are perpetuated. Significant

coordination between the various design disciplines has been performed to ensure

drainage, roadway and structural (retaining wall) demands are met, while minimizing or

eliminating the need for additional right-of-way acquisition.

4.3.1 East Side of I-15, Desert Inn Road to Sahara Avenue

The existing local offsite facility through this reach is a 10’ wide, 3.5’ deep riprap

lined channel along the east side of I-15. This facility conveys offsite flows,

discharged from an existing 42” RCP crossing Desert Inn Road, offsite flows

conveyed across I-15 via existing 36” RCPs, and onsite flows from the northbound

side of the freeway, and local offsite flows to the north along I-15.

There are no proposed P3 Phase roadway widening improvements within this

segment. However, due to shoulder reductions resulting from the crumb

rubber/restriping project through the corridor, there are six proposed onsite

inlets on the northbound side of the freeway that will discharge in to the existing

offsite channel. In addition, to meet spread criteria and minimize the amount of

new inlets, the barrier rail on the east side of the freeway will be replaced with

guardrail between “MN” 709+08.88 and “MN” 728+15.97 so that onsite runoff

will be conveyed off of the roadway into the existing channel. The top of the

existing channel bank will be riprap lined to prevent erosion.

4.3.2 East Side of I-15, Sahara Avenue to Wyoming Avenue

There is an existing 8’ wide, 1’ deep concrete channel located at the east toe of the

I-15 roadway embankment slope between Sahara Avenue and Highland Avenue.

This channel is immediately inside of the existing east right-of-way boundary

along I-15. This facility conveys flows discharged by an onsite system in Sahara

Avenue, local offsite flows from adjacent properties and onsite flows from

northbound I-15. This segment of the P3 Phase improvements includes 16 onsite

inlets on the northbound side of I-15 that will convey the onsite flows into the

December 2013


local offsite channel. A normal depth analysis of this channel shows it is capable

of conveying a maximum flow of approximately 70 cfs.

The P3 Phase improvements include widening of northbound I-15 starting at

approximate Station “MN” 749+00, approximately 1,100 feet north of Sahara

Avenue. The widening will put the edge of freeway directly adjacent to the right-

of-way and eliminate the existing local offsite channel. Through this area there

are several commercial properties with structures immediately adjacent to the

right-of-way boundary.

The P3 Phase improvements include a headwall within the existing channel to the

south of the widening and a 42” storm drain pipe to convey the flow from the

channel under the freeway for approximately 1,100 feet. The 42” storm drain pipe

will discharge into a proposed 12’ x 2.5’ rectangular concrete local offsite channel

that begins adjacent to Highland Avenue on the east side of I-15 at “MN” 758+80.

The concrete channel will convey flow to just south of Wyoming Avenue, where a

drop inlet will collect and convey the flow into an existing storm drain system in

Highland Avenue, similar to the existing channel configuration.

4.3.3 East Side of I-15, Wyoming Avenue to Wall Street There is an existing 8’ wide, 1’ deep concrete channel located along the east side

of I-15 adjacent to the existing right-of-way boundary between Wyoming Avenue

and Wall Street. This channel is located at the bottom of existing roadway

embankment slope and retaining wall. This existing channel conveys flows

discharged from onsite systems. Similar to the upstream reach, existing

structures are located immediately east of the existing right-of-way.

The P3 Phase improvements include widening of the northbound I-15 lanes to the

east in this area. In addition, a new bridge structure is proposed near station

“MN” 786+00 in order to provide access for the access road to the managed

lanes, Neon Gateway. The roadway widening requires additional right-of-way to

the east to accommodate the improvements through this area. As a result, the

entire local offsite channel through this reach will be eliminated by the freeway

December 2013


widening. Since the area on the east side of I-15 slopes away from the Freeway

toward Western Avenue, the channel will be replaced by an onsite system to

collect the freeway onsite runoff and convey it to a proposed storm drain system

in the Neon Gateway roadway, and north to the Freeway Channel. The proposed

storm drain system has been design to fit within proposed right-of-way takes

needed for roadway construction.

4.3.4 West Side I-15 - Martin Luther King Boulevard, Oakey Blvd. to Alta Drive

The P3 Phase roadway improvements include Martin Luther King Boulevard full

street section improvements from Oakey Boulevard to the north side of Alta

Drive. The Martin Luther King Boulevard alignment is along the west side of the

southbound Sahara Avenue exit ramp as it extends to the north. At Ellis Avenue,

the proposed roadway profile climbs to provide a grade separation over

Charleston Boulevard. The Martin Luther King Boulevard profile is back to

existing grade at approximately Hastings Avenue. The Martin Luther King

Boulevard alignment will replace Desert Lane between Hastings Avenue and Alta

Drive. Refer to Section 5.5.3 for additional discussion of the Martin Luther King

Boulevard improvements.

Inlets and storm drain facilities have been provided in Martin Luther King

Boulevard at low points in the profile and other locations as necessary to meet

street flow criteria and closely match existing flow patterns. The realigned

Freeway Channel is aligned in Martin Luther King Boulevard from approximately

Oakey Boulevard to Wall Street and will provide 100-year protection in the

ultimate condition through this reach. In the Proposed Condition, the Freeway

Channel is over capacity and the HGL is slightly above the finished ground

elevation in a couple locations along the alignment. Inlets at these low points may

require additional considerations at the next design level in order to prevent

ponding in the street in excess of City, RTC, and CCRFCD criteria.

December 2013


4.3.5 West Side I-15, Alta Drive to Symphony Parkway

The proposed I-15 freeway widening and the addition of the southbound CD road

along the west side of I-15 between Alta Drive and Symphony Parkway will create

an embankment fill slope that extends into the existing properties west of the

existing right-of-way boundary. The proposed improvements will cover both an

existing concrete channel at the toe of the existing slope and an existing 48”

storm drain located along the west edge of I-15. To accommodate the P3 Phase

improvements, the 48” storm drain will be relocated inside the proposed right-of-

way limit along Martin Luther King Boulevard. In addition, new ditch grading

will be provided at the toe of the embankment to convey runoff that reaches the

embankment north to Symphony Parkway, as it does in the Existing Condition.

The 100-year HEC-1 analysis was used to determine the offsite flow conveyed to

the ditches assuming that the offsite flow generated on the west side of Martin

Luther King Boulevard would be conveyed across the roadway into the proposed

earthen ditch facilities. The runoff in the ditches would be conveyed toward

Symphony Parkway, where a proposed field inlet would collect minor storm flows

and the major storm flows would be conveyed in Symphony Parkway across the

freeway, which matches the existing condition flow patterns.

The ditch facilities at the toe of the proposed embankment feature a 15-foot

bottom to accommodate maintenance access. Parcel 139-33-601-001, the Walker

Furniture main building, is not a part of the P3 Phase right-of-way acquisition.

This creates a right-of-way “pinch-point”, where the two ditch segments on either

side are connected with a 36” storm drain to convey the flows from the upstream

ditch to the downstream ditch and north to Symphony Parkway.

4.4

Western Avenue Corridor Overland Flow

A flow balancing analysis, as discussed in Section 4.1.8, was used to determine the

Existing Condition capacity of the Freeway Channel. The analysis showed that a

significant amount of runoff will bypass the Freeway Channel and be conveyed to the

east side of I-15 along the major cross streets. The bypass runoff will be conveyed north

December 2013


in the Western Avenue corridor between I-15 and the UPRR to the low point in

Charleston Boulevard under the UPRR bridge. A 100-year storm event peak flow of 1,678

cfs is conveyed to the north in the Western Avenue corridor at Sahara Avenue. The 100-

year storm event peak flow in the Western Avenue corridor increased to 1,878 cfs at

Oakey/Wyoming. The existing 10’ x 9’ Western Avenue lateral RCB has capacity to

convey 520 cfs. The remaining 1,158 cfs and 1,358 cfs at Sahara Avenue and

Oakey/Wyoming, respectively, is conveyed overland to the north and results in

significant overland inundation of the Western Avenue corridor between Sahara Avenue

and Charleston Boulevard.

Project Neon – P3 Phase roadway improvements include widening of the freeway to the

east, the addition of the Neon Gateway on the east side of the freeway to provide access

from Western Avenue to the HOV lanes, and also includes realignment of Western

Avenue to provide for the Western Avenue-Grand Central at-grade intersection with

Charleston Boulevard. These improvements will change the configuration of the

overland conveyance area between I-15 and the UPRR tracks between Sahara Avenue

and Charleston Boulevard.

A HEC-RAS hydraulic analysis was performed for the Western Avenue corridor to

investigate the Existing Condition flow conditions through the corridor. An additional

HEC-RAS analysis was performed to investigate the Proposed Condition configuration

and analyze the impacts that the P3 Phase improvements may have on the existing flow

conditions through the corridor. The Proposed Condition analysis showed that the P3

Phase improvements would have a very minor impact on the existing flow conditions

through the Western Avenue corridor. The Proposed Condition HEC-RAS analysis

showed that flow will be conveyed to the north toward Charleston Boulevard in the

existing earthen channel that is adjacent to the UPRR and in Western Avenue alignment.

In the 100-year storm event, flow will be conveyed into Charleston Boulevard from the

Western Avenue connection to Charleston Boulevard and over the weir at the UPRR

channel, as it does in the existing condition. Results of the HEC-RAS analysis are

included in Appendix B-3.

Some of the Existing Condition flow conditions through the Western Avenue corridor

that were determined from the Existing Condition HEC-RAS analysis include:

December 2013


• Existing 100-year flow conditions include overtopping of the UPRR tracks

starting approximately 900 feet south of Charleston Boulevard. Any

improvements within the corridor must not adversely impact the current

overtopping condition.

• Roadway grades for the HOV lanes at the Neon Gateway were established to be

above the existing condition 100-year HGL in the Western Avenue corridor. The

HOV lanes on the freeway must remain above the 100-year HGL in the corridor

as design progresses.

• In the Existing and Proposed Conditions, before the upstream MPU facilities are

constructed, the HGL of the overland flow in the Western Avenue corridor will

essentially be the same as the HGL in the Freeway Channel. Therefore, no

additional flow will be conveyed into the Freeway Channel at Western Avenue in

the 100-year storm event.

December 2013


5.0 ONSITE DRAINAGE FACILITIES

This 30% preliminary design study includes a detailed onsite analysis for the proposed

roadway improvements. The P3 Phase onsite analysis is broken out into three different

areas: I-15 corridor, US-95 corridor, and Local Roads.

5.1

Onsite Design Criteria

Design of onsite drainage facilities was performed in general accordance with the Design

Criteria and Guidelines presented in the Nevada Department of Transportation’s

Drainage Manual (Manual). The following criteria were used for the onsite analysis:

• Onsite facilities were designed in accordance with FHWA’s HEC-22, Urban

Drainage Design Manual.

• The Rational Method was used to determine onsite flowrates for the design of

onsite inlets and storm drain facilities.

• The 25-year storm event was used as the design storm for all freeway onsite

facilities.

• A minimum time of concentration, Tc, of 5 minutes was used for the analysis per

the Manual, since the onsite roadway consists of directly connected impervious

drainage basins.

• A Manning’s ‘n’ value of 0.015 was used for the roadway surface flow spread

calculations.

• The maximum allowable concentrated flow across a traveled way or onto bridges

per the Manual is 0.25cfs. This criterion was followed whenever possible, and

design exceptions were discussed with NDOT Hydraulics for areas where it was

not possible to limit the concentrated flow. Refer to Appendix D-2 for flow

spread criteria exceptions exhibits.

• Onsite inlet facilities were placed in order to intercept flow and meet the spread

criteria per Table 3-1 of the Manual (25-year design storm and zero flow spread

allowed outside of the roadway shoulder).

• Except in sag locations, a clogging factor was not used for the onsite inlets, since

they are located on an elevated freeway surface and debris is not expected to be a

problem for the inlet grates.

December 2013


• Flanker inlets were used in sag locations when necessary, per the Manual.

• Inlets were placed at the 1% cross-slope locations in superelevation transitions,

and if necessary, additional drop inlets were added further into the transition.

• When necessary, the instantaneous longitudinal slope at an inlet grate was

calculated by determining the slope between the grate and a point 10-feet

upstream of the grate.

5.2

Onsite Drainage Flow Spread Criteria Exceptions

Any areas on the Project that did not meet the criteria and guidelines in the Manual were

discussed with NDOT Hydraulics and agreed upon in concept. In general, the flow

spread criteria violations were identified in areas outside of the proposed roadway

improvement limits but within the area of analysis (i.e. crumb rubber area south of

Sahara Avenue, existing US-95 bridge over Rancho Drive, etc.). Table 5.2 shows the flow

spread criteria violations on the project. Exhibits showing the onsite drainage flow

spread criteria violation locations are included in Appendix D-2. Criteria exceptions that

were used for the onsite analysis include:

• Based on the direction of NDOT Hydraulics, the NOAA Atlas 14 rainfall intensity

values were used for the Rational Method analysis instead of the Clark County

Regional Flood Control values for rainfall intensity, as stated in the Manual. The

NOAA Atlas 14 rainfall intensity used for the project was 4.26 in/hr versus the

5.52 in/hr that is suggested in the CCRFCD HCDDM.

• Since placing manholes on the freeway is not ideal, NDOT Hydraulics is allowing

inlets to be used in place of manholes on this Project, provided the inlets are not

exceptionally deep. The onsite inlet facilities on the Project are generally 3-ft to

5-ft deep. In some cases, modified inlets have been proposed to facilitate

maintenance access.

December 2013


TABLE 5.2 PROJECT NEON – P3 PHASE - FLOW SPREAD CRITERIA EXCEPTIONS

ALIGNMENT/STATION/DIRECTION FLOW CRITERIA C

rum

b R

ubbe

r Se

gmen

t – D

eser

t Inn

to S

ahar

a

FLOW SPREAD CRITERIA EXCEPTION: DESERT INN Additional inlets/slotted drain necessary to mitigate spread criteria exception would be installed on the existing bridge approach within existing retaining wall limits.

“Le” 644+92.01 to 675+76.30 SB

Allowable Spread 6.00'

Flow Spread at Drop Inlet (with slotted drain calc) 9.29'

Flow in Travel Lane (with slotted drain calc) 3.29'

FLOW SPREAD CRITERIA EXCEPTION: DESERT INN Existing drop inlet with 10' slotted drain does not meet criteria.

“Le” 678+18.22 to 680+31.09 SB


Flow Spread at Drop Inlet (without slotted drain calc) 6.53'

Flow in Travel Lane (with slotted drain calc) 2.03'

FLOW SPREAD CRITERIA EXCEPTION: SOUNDWALL BETWEEN DESERT INN AND SAHARA Survey points indicate cross slope is beginning to slope away from the Drop Inlet. Flow spread is based on a near zero cross slope of 0.01 to complete the calculation.

“Le” 703+60.00 to 705+07.81 SB



Flow in Travel Lane (without slotted drain calc) 208.66'

FLOW SPREAD CRITERIA EXCEPTION: SOUNDWALL BETWEEN DESERT INN AND SAHARA Additional inlets along basins Le705 and Le706 will be difficult to construct due to existing soundwall on top of barrier rail.

“Le” 703+49.80 to 706+06.84 SB




FLOW SPREAD CRITERIA EXCEPTION: SOUNDWALL BETWEEN DESERT INN AND SAHARA Additional inlets along basins MS709 and MS712 will be difficult to construct due to existing soundwall on top of existing barrier rail.

“Le” 706+06.84 to 709+48.76 SB




December 2013


Saha

ra B

ridg

e

FLOW SPREAD CRITERIA EXCEPTION: SAHARA BRIDGE This basin is at the south edge of the existing bridge structure and does not meet criteria.

“MS” 736+57.76 to 735+79.24 SB


Flow Spread at Basin (no inlet at this location) 9.18'

Flow in Travel Lane (no inlet at this location) 5.68'

FLOW SPREAD CRITERIA EXCEPTION: SAHARA BRIDGE Existing drop inlet currently does not meet flow spread criteria. Adding 25 feet of slotted drain will allow existing drop inlet to meet flow spread criteria.

"MS" 742+00.48 to 745+77.92 SB




FLOW SPREAD CRITERIA EXCEPTION: SAHARA BRIDGE Existing drop inlet currently does not meet flow spread criteria. Adding 25 feet of slotted drain will allow existing drop inlet to meet flow spread criteria.

"MS" 745+77.92 to 746+88.59 SB




Us9

5 /

Ran

cho

Bri

dge

FLOW SPREAD CRITERIA EXCEPTION: RANCHO BRIDGE New Type 2 drop inlet location

"L" 1194+18.22 to 1192+23.00 EB




FLOW SPREAD CRITERIA EXCEPTION: RANCHO BRIDGE Existing drop inlet currently does not meet flow spread criteria.

"L" 1192+23.00 to 1192+50.00 EB




FLOW SPREAD CRITERIA EXCEPTION: RANCHO BRIDGE Existing drop inlet with 5-foot slotted drain currently does not meet flow spread criteria.

"L" 1192+50.00 to 1192+38.38 EB




FLOW SPREAD CRITERIA EXCEPTION: RANCHO BRIDGE This basin is on the existing overpass bridge structure and does not meet flow spread criteria.

"L" 1192+38.38 to 1198.82.00 EB




December 2013


5.3

I-15 Corridor

The limits of the I-15 Corridor onsite analysis include the Crumb Rubber section, Desert

Inn Road to Sahara Avenue, north to the US-95 interchange. The onsite basin maps for

this area are included in Appendix C-1.1. The preliminary onsite runoff calculations for

the 25-year storm event have been included in the Appendix C-1.2. On-grade inlet

interception calculations for paved areas have been included in Appendix C-1.3 and

sump inlet interception calculations for NDOT type 2 drop inlets have been included in

Appendix C-1.4. The P3 Phase 30% plans are included in Appendix E-1.

5.3.1 I-15, Desert Inn Road to Sahara Avenue (Crumb Rubber Project) NDOT recently completed the I-15 Crumb Rubber Project, which included

restriping of I-15 between Desert Inn Road and Sahara Avenue to improve traffic

operations. The restriping resulted in reduced shoulder widths that no longer

met flow spread criteria. An analysis was performed to investigate the existing

flow spread and identify locations for new inlets to increase the collection

capacity of the existing storm drain system. Despite constant design grades

shown on the record drawings for this portion of the freeway, the existing

roadway longitudinal and transverse slopes are as-built and therefore not

necessarily constant through each segment. Slopes used for the analysis of this

portion of the project were calculated by interpolating between aerial topography

and some available hard survey points. Slopes were then checked at points

within each subbasin, not just at the downstream end, to look for any possible

flow spread problem areas within the subbasin.

Within this segment of the freeway, the existing onsite systems drain to open

channels, both the west and east sides of I-15. New onsite inlets proposed along

the outside edge of the roadway will discharge directly to the open channels.

Riprap lining will be added along the north side slope of the existing flat bottom

ditch from Stations “MN” 707+13 to “MN” 728+21. There are eight locations were

slotted drain is proposed to help meet flow spread criteria within the Crumb

Rubber segment. There are two locations in the vicinity of Desert Inn Road

where flow spread criteria violations occur. There are three locations where the

December 2013


soundwall is on top of existing barrier rail, flow criteria is not met and

constructability could be difficult, therefore an exception for a flow spread

criteria violation has been identified. There are three locations in the vicinity of

the Sahara Bridge where there are flow spread criteria violations. Refer to Table

5.2 for a list of the flow spread criteria violation locations.

5.3.2 I-15, Sahara Avenue to Oakey Boulevard Between Sahara Avenue and Oakey Boulevard, widening of both the northbound

and southbound I-15 and the addition of the southbound CD ramp to Sahara

Avenue are proposed. Existing drop inlets located on the southbound side of the

road drain directly into the existing I-15 Channel RCB. These inlets will be

removed and relocated, in conjunction with roadway widening, and inlets from

mainline I-15 and the CD road will to discharge to the relocated Freeway Channel

system on the west side of the freeway. Existing drop inlets located on the

northbound side of the road currently drain to the existing 8’ wide, 2’ deep

concrete channel located east of the roadway. Inlets will be relocated, along with

roadway widening, and drain to an onsite storm drain system and then to a

proposed 12’ x 2.5’ concrete channel along Highland Avenue.

5.3.3 Southbound I-15, Oakey Boulevard to Charleston Boulevard Between Oakey Boulevard and Charleston Boulevard, southbound I-15 and the

southbound CD ramp drains to the outside shoulder. Inlets are located as

necessary to collect the 25-year storm event onsite runoff and convey it in onsite

storm drain systems. These onsite systems convey collected runoff to the

realigned Freeway Channel or to the existing 10’ x 9’ RCB in Charleston

Boulevard.

5.3.4 Northbound I-15, Oakey Boulevard to Charleston Boulevard Northbound I-15 between Oakey boulevard and Charleston Boulevard is super

elevated and drains to the inside shoulder. The I-15 profile contains a low point

and is elevated above the proposed managed lanes drop down ramps, using

December 2013


retaining walls. These geometrics necessitate closely spaced inlets to meet spread

criteria.

Since these drainage systems are adjacent to retaining walls, it is likely that the

walls will be cantilever retaining walls. This allows system trunk lines to be

located parallel with the wall, both on the high and low side. This minimizes the

number of manholes and wall penetrations, while facilitating construction

phasing; however, a large number of closely spaced inlets remain necessary along

I-15.

5.3.5 I-15, Charleston Boulevard to Alta Drive For southbound I-15, there is a superelevation transition just north of Charleston

Boulevard and the freeway drains to the inside shoulder. Onsite inlets have been

located as necessary to collect onsite runoff and a proposed onsite storm drain

system will convey the runoff from the I-15 mainline and the CD road to the

existing Freeway Channel on the east side of I-15.

The existing drainage facilities along the northbound I-15 widening will be

removed and new inlets will be provided in conjunction with roadway

improvements. Inlet facilities on the northbound side of I-15 will convey flow to

an onsite storm drain system that will discharge to the existing Freeway Channel

on the east side of I-15. Proposed inlets on the Alta Slip Ramp will discharge to

the storm drain facility in Alta Drive.

5.3.6 I-15, Alta Drive to Symphony Parkway Southbound I-15 remains superelevated to the middle of the roadway between

Alta Drive and Symphony Parkway. Onsite flows are intercepted by a series of

proposed drop inlets located in the inside shoulder adjacent to the viaduct

approach retaining wall. A second series of inlets is located south of the approach

touchdown, adjacent to the center barrier rail. These systems discharge to the

west, into the proposed ditch grading along the west side I-15. Onsite inlets

December 2013


associated with the managed lanes approach also connect to the southbound I-15

trunk line and utilize the same discharge point.

Minor modifications to the northbound I-15 edge of pavement are proposed with

the P3 Phase improvements. Where roadway edge modification occurs, inlets will

be relocated in conjunction with the roadway geometry. Inlets on the northbound

side of I-15 will discharge into the existing Freeway Channel on the east side of

the freeway.

5.3.7 I-15, Symphony Parkway to US-95 Analysis of I-15 through this segment shows that there is adequate shoulder

available without the need for additional storm drain facilities. Runoff from the

US-95 to southbound I-15 entrance Ramp, “ES1”, drains to the west side of the

roadway and is discharged to existing RCB storm drain facility adjacent to the

ramp. Flows along northbound I-15 drain to the east and are collected and

conveyed in existing facilities at Symphony Parkway.

5.4

US-95 Corridor

The limits of the US-95 Corridor onsite analysis extend from west of Rancho Drive to the

I-15/US-95 interchange and include the direct connect viaduct. Onsite analysis of the

“MLK-515” and “EN” alignment ramp modifications are also included in this section.

The onsite basin maps are included in Appendix C-1.1. The onsite runoff calculations for

the 25-year storm event have been included in the Appendix C-1.2. On-grade inlet

interception calculations for paved areas have been included in Appendix C-1.3, and

sump inlet interception calculations for NDOT type 2 drop inlets have been included in

Appendix C-1.4. The P3 Phase 30% plans are included in Appendix E-1.

5.4.1 US-95 Direct Connect - At-Grade

The roadway configuration along US-95, between Rancho Drive and I-15 will

realign the lanes toward the outside shoulder, along with minor widening where

possible, essentially within the existing roadway footprint. The approach to the

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proposed viaduct is located west of Rancho Drive, and stripping was modified to

direct traffic onto the approach. East of the viaduct approach, the managed lanes

will be supported on piers, and a median was provided in the center of US-95 to

accommodate the pier locations. Modified stripping reduces shoulder widths

from 12’ to generally between 8’ and 4’. This reduction of shoulder width requires

the addition of inlets to maintain onsite spread criteria.

Along eastbound US-95, west of “L” 1190+82, the existing roadway surface is

superelevated and drains to the inside shoulder. Proposed re-striping reduces the

available shoulder from 12’ to 8’. West of the Rancho Bridge, additional inlets

have been added on the inside shoulder. These are connected via a trunk line and

discharge at an existing lateral location to the north.

As-built survey of the eastbound Rancho Bridge reveals that the roadway surface

has a very flat cross-slope (less than 0.5% in some areas). In addition, a deck

drain proposed with the US-95 Widening Project 3C was not constructed. This

condition, along with the reduced shoulder, results in the onsite flows exceeding

allowable spread on the bridge. A potential solution includes the addition of a

deck drain as a retrofit to the bridge structure. An initial look has determined that

a deck drain could potentially be incorporated into the bridge deck, outside of the

structural box section, without excessive impacts to the bridge structure. Outfall

from this deck drain would be discharged via a pipe system below the bridge

deck, routed down a bridge pier, and discharged to the existing storm drain

system in Rancho Drive. Additional development of this concept is needed to

determine feasibility and cost of the deck drain retrofit. In addition, a

superelevation crossover occurs immediately west of the bridge, and flows in

excess of 0.25cfs crosses the roadway. An additional inlet has been placed at this

location to minimize this bypass.

East of Rancho, between stations “L” 1190+00 left and “L” 1167+63 left, the

roadway utilizes a proposed retaining wall and widens to the outside to maximize

the shoulder east of the existing Rancho entrance ramp. Due to the shift in the

roadway, existing storm drain systems along the shoulder are being removed and

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replaced with new inlets and trunk lines. These systems will utilize existing

laterals for outfall.

There is no roadway widening proposed to the east of station “L” 1167+63,

however striping revisions will reduce available spread area. The existing drop

inlets and trunk line will be maintained through this reach, and several new inlets

will be connected to the existing system to meet onsite spread criteria.

Along westbound US-95 between the Rancho Bridge and station “L” 1177+90

right, minor widening of the roadway is proposed to the outside. The proposed

striping for the viaduct approach will reduce the available spread width. The

existing storm drain system is being removed to accommodate the widening in

this location and new inlets and storm drain is being proposed. This system

continues to utilize the existing lateral discharge points.

Between stations “L” 1180+84 right and “L” 1175+29 right, the westbound

roadway is superelevated to the inside, and the viaduct approach limits the

available shoulder to 4’. A number of new inlets are proposed at this location that

will tie into storm drain systems within the center median below the viaduct

structure.

Between stations “L” 1175+29 right and “L” 1172+00 right, a median area is

proposed to accommodate the viaduct piers. This median will be separated from

traffic by barrier rail, and the interior area will be maintained near existing

roadway elevations. Immediately east of the viaduct approach, an angle point in

the barrier rail provides an entrance point for maintenance. The angle of this

median significantly widens the available shoulder and allows onsite flows

developed from the superelevated westbound US-95 to be conveyed into the

median, without the need for inlets along the shoulder.

Between stations “L” 1170+93 right and “L” 1165+93 right, westbound US-95

remains superelevated with a 4’ inside shoulder. To minimize the number of

inlets needed to maintain spread criteria, a series of barrier rail scuppers has

been proposed at a 15’ typical spacing. Runoff from these scuppers drains to the

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center median area, where an asphalt ditch will convey flows to a Type 2 drop

inlet and then to the south in an existing storm drain lateral.

Between stations “L” 1160+91 right and “L” 1172+00 right, westbound US-95

continues to be superelevated. The center median is proposed to be filled to the

top of the center barrier rail, which precludes the use of barrier rail scuppers. A

series of inlets is proposed in this location to maintain spread criteria. The

proposed inlets are connected via a trunk line and discharge to an existing lateral

crossing.

East of station “L” 1172+00, westbound US-95 resumes a normal crown, and

again drains to the outside shoulder. The shoulder is unaltered through this

reach, and the existing drainage system is capable of meeting spread criteria.

Analysis does show that a barrier rail “popout” near station “L” 1157+00 has been

constructed to accommodate a sign foundation. This popout narrows the

shoulder locally, and an additional inlet is proposed immediately west of the sign

to ensure spread is not violated.

5.4.2 US-95 Direct Connect Viaduct

The direct connect viaduct features a 62’ wide bridge deck, supported on concrete

piers. Each pier will be supported by a large pile cap and piles. Proposed striping

for the facility incorporates 1 lane in each direction. Roadway striping on the

structure has been designed to maximize the available spread width in

superelevated areas by providing a 10’ inside shoulder along the westbound lane

and a 10’ outside shoulder along the eastbound lane. Shoulder configurations that

create sufficient capacity to convey the flow spread over the majority of the

viaduct allows interception facilities to be located at pier locations. The portion of

the viaduct between stations “MC” 849+00 and “MC” 864+00 is superelevated at

8%, which supplies enough shoulder capacity to allow this portion to drain over

several pier locations without interception. Mid-span inlets are only required at

“MC” 845+40 in order to accommodate a superelevation crossover.

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Deck drains are specially designed steel inlets that are to be incorporated into the

bridge deck. Deck drains located along the outside shoulder are 18” long

perpendicular to the structure, and 4.5’ wide. Drains along the inside shoulder

are 18” long and 4.0’ wide. This geometry has been proposed to avoid conflict

with the preliminary design of the steel girders located below the deck and to

visually hide the drain piping behind the girders as much as possible.

Based on discussions with NDOT Hydraulics staff, fiberglass reinforced pipe

(FRP) has been chosen over steel material for several reasons for the 30% design.

FRP construction utilizes bonding at connection points and does not require field

welding during construction. FRP is lighter than steel and requires fewer

hangers. In addition, a wide selection of pipe fittings is available, which facilitates

incorporation of cleanouts throughout the deck drainage system.

At Pier locations, each inlet will discharge vertically, alongside the steel girders.

To accommodate minor movement at non-expansion joints, the 8” vertical pipe

will discharge to a 12” x 8” FRP expansion fitting, eliminating a hard connection

where the steel girders rest on the concrete pier caps. The fitting effectively

operates as a funnel and allows the superstructure and vertical pipe to move in

relation to the pier. Where expansion joints are proposed, the vertical discharge

pipe will utilize two spherical elastomeric expansion joints; the first located

immediately below the inlet and deck, and the second located at the bottom of the

steel superstructure. These expansion joints will allow for both vertical and

angular movement of the discharge pipe and allow for substantial movements

between the superstructure and pier cap. The upper expansion joint will utilize

control rods between its two flanges to support the weight of the discharge pipe.

Pier discharge locations have been determined by the availability of at-grade

drainage facilities. Existing storm drain facilities are not available near the piers

adjacent to the Symphony Parkway Bridge (“MC” 846+33 and “MC” 848+83). To

avoid new at-grade storm drain systems and roadway lateral cuts, the deck drains

utilize discharge pipes hung below, and parallel, to the bridge deck. Two parallel

pipes are used for the inside and outside inlets, respectively. This is necessary to

avoid crossing the steel bridge beams. These pipes convey flows to the pier

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located at “MC” 844+58, where the down drain system can discharge to proposed

at-grade onsite facilities proposed on the inside of southbound I-15.

Parallel discharge systems are proposed below the bridge deck east of MLK, to

consolidate discharge to a single down drain at “MC” 867+28.25. At this

location, a new lateral cut is needed, adjacent to the approach slab, to provide an

at-grade discharge point.

Deck drains between “MC” 869+82 and “MC” 873+87 utilize a single down drain,

located at “MC” 873+87, to avoid new roadway lateral cuts. The down drain at

this location discharges to an existing lateral that crosses US-95.

Similarly, Deck drains between “MC” 875+77 and “MC” 880+17 drain to a single

down drain at “MC” 880+17. This down drain, along with the remaining pier

down drain locations, discharge to a proposed at-grade ditch within the center

median of US-95. This ditch ultimately drains to proposed inlets within the

median and across eastbound US-95, via existing laterals. The layout of the

parallel piping systems currently does not cross anticipated deck expansion joint

locations, and therefore horizontal pipe expansion joints may not be needed.

Both the US-95 and I-15 center approaches to the viaduct structure are elevated

above the adjacent mainline using retaining wall. Retaining walls have not been

designed at this preliminary design level, however it is anticipated that cantilever

retaining wall will be needed where inlets are located at the outside shoulder and

MSE walls could be used for segments of the approaches that do not require

inlets on the outside shoulder.

A profile low point, along with a super elevation transition, is proposed near

“MC” 895+51 right. Examination of the composite design slopes in this area

shows a minimum roadway surface grade of 0.50% will be maintained. However,

to accommodate construction tolerances, and minimize the chance of

uncontrolled ponding, a 20’ slotted drain is proposed both up-station and down-

station of the sump inlet, in lieu of typical flankers.

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5.4.3 “MLK-515” and “EN” Ramps

Project NEON proposes to re-align the Martin Luther King to eastbound US-95

(“MLK-515”) ramp to bypass the I-15/US-95 Bridge. This alignment utilizes the

existing US-95 eastbound to I-15 northbound (“EN”) bridge to cross I-15. This

also necessitates a re-alignment of the “EN” ramp and Martin Luther King to

northbound I-15 (“MLK-NB15”) ramps.

West of I-15, the ramp alignments are bounded by barrier rail and retaining

walls. The ES ramp reconfiguration will require relocation of the existing 2-12’ x

6’ RCB US-95 Channel to avoid the new bridge piers and the additional fill placed

on the RCB due to the reconfiguration of the ramp. Proposed onsite systems and

trunk lines will connect to the relocated RCB facility (“ESB” alignment).

In addition to roadway storm drain systems, it is anticipated that the retaining

walls will utilize a concrete gutter to collect local runoff above the walls. Wall

gutter drains would be provided at gutter low points that will discharge to the

proposed drop inlets.

Portions of the at-grade ramps are protected from direct rainfall by existing

overhead structures. Based on discussions with NDOT Hydraulics, onsite analysis

conservatively assumes that the overhead structures do not shade the at-grade

roadway from rainfall, and the systems have been designed based on full rainfall

landing on the roadways.

East of I-15, onsite runoff from both the “MLK-515” and “EN” ramps will drain to

roadside ditches. These ditches convey runoff to field inlets that eventually

discharge to an existing 48” storm drain within the infield south of US-95. A

maximum ditch side slope of 6:1 was used adjacent to the ramps. To maintain

positive drainage, the ditch flow lines along the “MLK-515” ramp diverge from

the edge of pavement. This design will necessitate rework of some landscaped

mounding elements.

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5.5

Local Roads

The P3 Phase of Project NEON includes modifications and improvements to the local

roadways in the vicinity of the project to accommodate the proposed widening. In

general, local roadway improvements have been designed to perpetuate existing flow

patterns and maintain existing drainage system configurations. The hydrologic and

hydraulic analysis for the local roadway improvements is included in Appendix B-2. The

P3 Phase 30% drainage plans are included in Appendix E-1.

5.5.1 Sahara Avenue The P3 Phase proposes roadway improvements, including “SA3-R” ramp ties-ins,

to Sahara Avenue with barrier rail, drop inlets and a small v-ditch to convey

flows.

5.5.2 Oakey Boulevard / Wyoming Avenue Existing drop inlets in Oakey Boulevard extend west of I-15 and have been

designed to intercept onsite and offsite flows. As described in the Existing Offsite

Hydrology Report, the Oakey Boulevard Lateral is currently under capacity in the

existing 100-year condition, due to capacity limitations of the Freeway Channel.

Minor reconfiguration of inlets and laterals is needed where re-alignment of the

Oakey Boulevard lateral is proposed. Since the Oakey Boulevard Lateral has

capacity to convey the 100-year flow in Oakey Boulevard, and based on

discussions with the City, the existing MPU inflow structure and the valley gutter

at Oakey Boulevard has been eliminated and an access grate has been provided in

the reconfigured Oakey confluence structure. The Oakey Boulevard/Martin

Luther King Boulevard intersection has been reconfigured to accommodate the

improvements to the Martin Luther King Boulevard alignment.

5.5.3 Martin Luther King Boulevard The P3 Phase roadway improvements include Martin Luther King Boulevard full

street section improvements from Oakey Boulevard to the north side of Alta

Drive. Onsite analysis of Martin Luther King Boulevard falls under City of Las

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Vegas and RTC criteria. Drop inlets were designed for 100-year major events and

10-year minor events. Heading north from Oakey Boulevard, the Martin Luther

King Boulevard alignment is along the west side of the southbound CD Sahara

Avenue exit ramp. The realigned Freeway Channel is located in the Martin Luther

King Boulevard alignment and provides a tie in for the proposed onsite storm

drain facilities between Oakey Boulevard and Ellis Avenue. Since the Freeway

Channel is over capacity in the Proposed Condition, inlets at these low points

may require additional considerations at the next design level in order to prevent

ponding in the street in excess of City, RTC, and CCRFCD criteria.

The Richard Court cul-de-sac will be removed with the P3 Phase improvements.

Martin Luther King Boulevard features a grade separation over Charleston

Boulevard. The bridge is a high point that drains to the north and south of

Charleston Boulevard. North of Charleston Boulevard, Martin Luther King

Boulevard is aligned adjacent to the Desert Lane alignment, which will be

removed with the P3 Phase improvements. A slip ramp to the southbound CD

road is provided at Pinto Lane. The Pinto Lane storm drain collects the runoff in

Pinto Lane and conveys flow north in the Martin Luther King Boulevard

alignment to Alta Drive. Inlets and storm drain facilities have been provided in

Martin Luther King Boulevard at low points in the profile and other locations as

necessary to meet street flow criteria and closely match existing flow patterns.

Please refer to Appendix B-2 for all of the Martin Luther King Boulevard onsite

calculations.

5.5.4 Charleston Boulevard Charleston Boulevard will be widened with the P3 Phase improvements. Existing

drop inlets in Charleston Boulevard extend west of I-15 and have been designed

to intercept onsite and offsite flows. As previously described in the Existing

Offsite Hydrology Report, the Charleston Boulevard Lateral is currently under

capacity in the existing 100-year condition, due to capacity limitations of the

Freeway Channel. Proposed widening of Charleston Boulevard will require

removal and replacement of drop inlets in conjunction with the proposed curb

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alignments. Inlets relocated to the new curb line will be connected into either the

existing storm drain facilities in Charleston Boulevard or a proposed storm drain

facility on the north side of the widened roadway.

5.5.5 Alta Drive / Bonneville Avenue Existing drop inlets in Alta Drive extend west of I-15 and have been designed to

intercept onsite and offsite flows. As previously described, the Alta Drive Lateral

is currently under capacity in the existing 100-year condition, due to capacity

limitations of the Freeway Channel. Proposed widening of Alta Drive/Bonneville

Avenue will require removal and replacement of drop inlets in conjunction with

the proposed curb alignments. The existing 66” storm drain lateral to the

Freeway Channel will be upsized to an 8’ x 5’ RCB to accommodate the additional

flow added by the proposed Pinto Lane storm drain facility.

5.5.6 Western Avenue-Grand Central Parkway The P3 Phase improvements include an at-grade intersection of Western Avenue-

Grand Central Parkway with Charleston Boulevard. Proposed inlets on Western

Avenue, just south of Charleston Boulevard, will be conveyed to the Freeway

Channel to the west. Proposed inlets on the realigned Grand Central Parkway leg

of the intersection will convey collected runoff to an existing storm drain system

in Grand Central Parkway that conveys flow to the north. Iron Horse Court will

be reconfigured for the P3 Phase improvements and proposed inlet facilities will

convey flow to the existing storm drain system in Grand Central Parkway.

Refer to Appendix E-1 - P3 Phase 30% Drainage Plans.

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6.0 SUMMARY

The 30% drainage design for Project Neon – P3 Phase provides preliminary design for

proposed facilities required for the project. Design and coordination has been provided

for major offsite drainage facility relocations, minor offsite facilities impacted by the

project, and onsite systems to accommodate the P3 Phase improvements. This report

provides a level of drainage analysis above the preliminary designation per the

NDOTDM requirements and includes a discussion of the proposed P3 Phase

improvements, 30% design level calculations and drainage plans, allows for a basis of

verifying P3 Phase drainage right-of-way needs, and provides design information for the

continued coordination and resolution of interdisciplinary coordination elements.

NDOT Drainage Manual and CCRFCD criteria were followed in the hydrologic and

hydraulic analysis in this report. Flow spread criteria violation locations have been

reviewed with NDOT Hydraulics. The 25-year storm event was used as the design storm

for all freeway onsite facilities. Onsite facilities were designed in accordance with

FHWA’s HEC-22, Urban Drainage Design Manual. The Rational Method was used to

determine onsite flowrates for the design of onsite inlets and storm drain facilities. A

minimum time of concentration, Tc, of 5 minutes was used for the analysis per the

Manual, since the onsite roadway consists of directly connected impervious drainage

basins. Refer to Appendix C for all the onsite hydrologic and hydraulic calculations.

Refer to Appendix A for offsite hydrologic analysis models and back-up information and

specifically Appendix A-5 for the peak offsite flow summary table. Refer to Appendix B

for the offsite hydraulic calculations and exhibits. The Response to Design Review

Comments has been included in Appendix D along with the flow spread criteria

exceptions Exhibits. Please refer to the CD in Appendix E for the P3 Phase 30%

Drainage Plans, Previous Reports/Historic Information, and a Project Neon Photo Log.

The P3 Phase Project Summary based on the 30% drainage design is:

1. The proposed drainage facilities for Project Neon – P3 Phase are designed per the

criteria presented in the NDOT Drainage Manual, and the Clark County Regional

Flood Control District’s (CCRFCD) Hydrologic Criteria and Drainage Design Manual,

except at otherwise noted.

2. The project site lies within FEMA-designated shaded Zone X. Areas designated as Zone

X are outside the regulatory 100-year floodplain.

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3. The drainage facility improvements incorporated into the P3 Phase of Project NEON

include:

• Additional onsite storm drain facilities between Desert Inn Road and the

north side of Sahara Avenue to improve flow spread conditions as a result of

shoulder reductions from the recently completed Crumb-Rubber Overlay

Project

• Realignment of the existing MPU storm drain facility to accommodate the

freeway widening and realignment of I-15 from just north of Sahara Avenue

to the south side of Charleston Boulevard

• Realignment of the existing US-95 Channel MPU storm drain facility to


• Onsite storm drain improvements to accommodate roadway improvements

according to NDOT drainage criteria including:

1. Freeway Widening and realignment of I-15 from Sahara Avenue to the

Spaghetti Bowl

2. Direct Connector Ramps from the high-occupancy vehicle (HOV)

lanes out to Western Avenue located between Oakey Boulevard and


3. Reconstruction of the Charleston Boulevard Interchange to provide a

tight-diamond interchange

4. Alta slip ramp construction

5. Southbound collector distributor road with ramp braiding to provide

ramps to Charleston Boulevard and Sahara Avenue

6. A high-occupancy vehicle (HOV) direct connector ramp from the

center of US 95, west of the Spaghetti Bowl, to the center of I-15, south

of the Spaghetti Bowl

7. MLK-US 95 loop ramp construction

• Offsite storm drain improvements in the local jurisdiction roadways to meet

local drainage criteria including:

1. Reconstruction of drop inlets in Sahara Avenue, Oakey Boulevard,

Charleston Boulevard, and Alta Drive to maintain existing conditions

2. Alta Drive improvements from Martin Luther King Boulevard to

Grand Central Parkway

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3. Western Avenue–Grand Central Parkway at-grade intersection with


4. Martin Luther King Blvd improvements from Oakey Boulevard to Alta

Drive

5. BRT loop construction

4. The proposed drainage improvements will perpetuate existing conditions flow

patterns.

5. Proposed flow depths and velocities at the right-of-way lines are comparable to

existing conditions.

6. The proposed improvements do not adversely impact adjacent properties or facilities.

December 2013


7.0 REFERENCES

1. NDOT, Drainage Manual, December, 2006. 2. CCRFCD, Hydraulic Criteria and Drainage Design Manual, August 1999. 3. CCRFCD, PBS&J, Flood Control Master Plan Update of the Las Vegas Valley,

September, 2008. 4. FHWA “Urban Drainage and Design Manual” (HEC-22), August 2001. 5. FHWA “Hydraulic Design of Culverts” (HDS5), September 2001. 6. U.S. Army Corps of Engineers, Hydraulic Design of Flood Control Channels,

Engineer Manual No. 1110-2-1601, July 1991. 7. NDOT, VTN Nevada, Existing Offsite Hydrology Report for Project Neon, February

2010. 8. NDOT, VTN Nevada, 30% Drainage Design Report for Project Neon, January 2011. 9. NDOT, VTN Nevada, 15% Overall Drainage Design Report for Project Neon, April

2010 10. CCRFCD, PBS&J, City of Las Vegas – City Wide Hydrology Analysis, 1997. 11. NDOT, Parsons Brinckerhoff, I-15 Freeway Channel Pre-design Report, May 1999. 12. NDOT, Louis Berger and Associates, Spring Mountain Rd. Interchange and I-15

Median Widening, April 2000. 13. LVVWD, VTN Nevada, Meadows Detention Basin Improvements & Las Vegas

Springs Preserve Cienaga Grading – 100% Design Report, May 2001. 14. CCRFCD, Carter-Burgess, Oakey Storm Sewer Conveyance System Corridor Study,

February 2000. 15. CLV, VTN Nevada, Martin Luther King Blvd. Widening Alta Dr. to Carey Ave. –

Preliminary Design and Drainage Report, January 2004. 16. CLV, G.C. Wallace, Inc., Wyoming Ave., Grade Separations Alternatives At Union

Pacific Railroad Tracks – Draft Feasibility Study, November 2003. 17. CLV, G.C. Wallace, Inc., Industrial Rd. Sahara Ave. to Wyoming Draft Alignment

Study, November 2003. 18. CLV, Chiatovich Engineering, Drainage Study for Alta Dr. From Rancho Dr. to

Martin Luther King Blvd., January 1998.

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