Project_8_-_26th_Ave_-_Drainange_Memo.pdf

CITY OF WHEAT RIDGE

PROJECT 8 -26TH AVE,

OAK ST TO

PARAMOUNT PKWY

SIDEWALK GAP PROGRAM

Prepared for:

City of Wheat Ridge Colorado

Wheat Ridge, Colorado

Prepared by:

Olsson

1525 Raleigh Street, Suite 400

Denver, CO 80204

July 2026

Olsson Project No. B25-03001

Project 8 – 26th Ave, Oak St to Paramount Pkwy Sidewalk Gap Program

City of Wheat Ridge Project No. 025-029B July 2026

B25-03001 1

TABLE OF CONTENTS

1. Introduction

1.1 Project Location and Purpose

1.2 Description of Property

1.2.1 Ground Cover and Topography

1.2.2 Soils Description

1.2.3 Major Drainageways

2. Hydrology

2.1 Drainage Basin Map

2.2 Major Basin Description

2.3 On-Site Description

2.4 Precipitation Data

2.5 Design Flood Frequency

3. Existing Structures

4. Design Discussion

5. Recommended Design

5.1 Inlets and Street Capacity

5.2 Storm Drain

5.3 Detention/Water Quality

6. Variances

References

Appendix A Hydrology

Appendix B Hydraulics

Appendix C Reference Information

B25-03001 2

1. INTRODUCTION

Project 8 consists of sidewalk improvements along the north side of West 26th Avenue between

Oak Street and Paramount Parkway as part of the City of Wheat Ridge Sidewalk Gaps

Program. The project includes construction of a new sidewalk, curb and gutter, chase drain, and associated roadway patching. The project also includes drainage improvements consisting of a storm sewer pipe extension and swale regrading near Paramount Parkway, as well as extension of the Wattrus Ditch irrigation pipe near Nelson Street.

1.1 Project Location and Purpose

Project 8 will improve pedestrian connectivity along the north side of 26th Avenue by closing an existing sidewalk gap between Oak Street and Paramount Parkway. The project is located within a residential area of the City of Wheat Ridge, Colorado. A vicinity map is provided in

Figure 1.

Figure 1 - Site Vicinity Map

B25-03001 3

1.2 Description of Property

1.2.1 Ground Cover and Topography

The improvements include adding sidewalk, curb and gutter, pipe extensions, a chase drain, a swale, and driveways on the north side of West 26th Avenue. The project area is fully developed, and ground cover is comprised of pavement, grass, gravel, and bare earth.

An existing high point along West 26th Avenue near Nelson Street divides the project flows.

Runoff west of the high point flows west until Oak Street where it is then diverted north via curb and gutter along Oak Street. Runoff east of the high point flows east to Skyline Drive and then north along Skyline Drive in an indistinct, roadside swale. East of Skyline Drive, runoff continues east toward Paramount Parkway, where it diverted north through a roadside swale.

1.2.2 Soils Description

The project area includes soils in Hydrologic Soil Group Type C which are characterized as having low to moderate infiltration rates and moderate to high runoff potentials. According to the

United States Department of Agriculture (USDA) Natural Resources Conservation Service

(NRCS), the soils in the project area are comprised of 2.1 acres of Nunn-Urban land complex,

2.9 acres of Urban land-Ciancio-Englewood complex. The full soils report is included in

Appendix C.

1.2.3 Major Drainageways

There are no major drainageways within the project area. The project is located within the Lena

Gulch watershed and flows will eventually drain to Lena Gulch via street conveyance, storm infrastructure, and tributary swales.

2. HYDROLOGY

2.1 Drainage Basin Map

Drainage basins were delineated using survey information, supplemented with 2020 LiDAR data outside of the project area. The Rational Method was used to complete hydrological calculations using the MHFD rational spreadsheet. A drainage map of the proposed conditions is included in

Appendix A.

2.2 Major Basin Description

There are no major cross-drainage waterways that pass through the project area, and no major offsite basin delineation was required for the project. The project site eventually flows to Lena

Gulch.

B25-03001 4

2.3 On-Site Description

Four basins were delineated under proposed conditions, and one basin was delineated under existing conditions, for a total of five basins.

8.01 - This basin does not have any proposed improvements and is based on existing conditions. Flows from this basin are captured at a valley grate and conveyed via 12-inch RCP to a swale at the downstream most portion of basin 8.02. Flow from this basin combines with basin 8.02 flows and is conveyed north along Paramount Parkway.

8.02 - This basin delineates flow along the north side of West 26th Avenue between Paramount

Parkway and Skyline Drive. Flow is conveyed east along the street and is combined with flows from basin 8.01 travelling north along Paramount Parkway.

8.03 - This basin is smallest and delineates flow along the northeastern curb ramp at the corner of Skyline Drive and West 26th Avenue. Flow from this basin is conveyed along the street and leaves the site north along Skyline Drive.

8.04 - This basin is the largest and delineates flow along the north side of West 26th Avenue between Skyline Drive and Nelson Street. Flow from this basin is conveyed east along the street and leaves the site north along Skyline Drive.

8.05 - This basin delineates flow along the north side of West 26th Avenue between Nelson

Street and Oak Street. Flow from this basin is conveyed west along the street and leaves the site north along Oak Street.

Table 1 - Peak Flow Summary

Basin 5-year Flows (cfs) 100-year Flows (cfs)

8.01 4.66 10.73

8.02 (before combining with 8.01) 1.12 3.14

8.02 (after combining with 8.01) 5.78 13.87

8.03 0.07 0.16

8.04 3.48 10.20

8.05 0.88 2.02

2.4 Precipitation Data

The project is located in the City of Wheat Ridge; therefore, the City of Wheat Ridge drainage design criteria was applied and supplemented with Mile High Flood District (MHFD) Criteria as required. Precipitation data was determined in accordance with the MHFD guidance using the point precipitation frequency estimates from NOAA Atlas 14, Volume 8, Version 2 for Wheat

Ridge, Colorado at the project location. Precipitation data is included in Appendix A.

B25-03001 5

2.5 Design Flood Frequency

The Jefferson County criteria was referred to determine a minor and major flood frequency of 5-years and 100-years, respectively. MHFD Criteria and Jefferson County criteria were referenced to determine the allowable overtopping and street capacity for collector streets. The more stringent of the two criterion, MHFD criteria, was used. Figure 2 and Figure 3 show the MHFD street capacity criteria used for this project.

For this project, the minor storm flow must leave at least one lane free of water and must not exceed 6-inches in depth as to not overtop the curb. The major storm flow may spread to the crown of the street and must not exceed 12-inches in depth.

Figure 2 - MHFD Minor Storm Street Capacity Criteria

B25-03001 6

Figure 3 - MHFD Major Storm Street Capacity Criteria

3. EXISTING STRUCTURES

There are no existing structures within the project limits aside from the Wattrus Ditch irrigation pipe near Nelson Street and the storm sewer pipe east of Paramount Parkway. Project flows are primarily conveyed through small, roadside swales until they flow north along side streets.

4. DESIGN DISCUSSION

The proposed drainage does not change the existing drainage patterns and ties into the existing drainage infrastructure. Existing conditions were not evaluated, and it is assumed that the existing downstream infrastructure has capacity for the design flows.

This project does not disturb more than one acre and therefore does not require water quality treatment per the City’s MS4 permit.

5. RECOMMENDED DESIGN

5.1 Inlets and Street Capacity

No street inlets are proposed with this project. Proposed and existing streets will convey flows and meet street capacity requirements without the need for inlets.

Within basins 8.02 and 8.05, a maximum ponding depth of 3-inches was used for the minor storm to verify roadway capacity at reduced-height driveways. Under existing conditions, B25-03001 7 driveways within these basins slope towards the properties, therefore, to avoid increasing runoff onto the properties during the minor storm event, the driveways were designed to rise 3 inches before sloping towards the properties. Within basin 8.04, the reduced-height driveways are located on the upstream portion of the basin. A maximum ponding depth of 3-inches could not be achieved with the total basin flow; however, since the driveways are located on the upstream half of the basin, a 3-inch maximum ponding depth could be achieved when half of the flow is assumed to flow along the gutters adjacent to the driveways in that basin. Full calculations for the street capacity evaluation are included in Appendix B.

5.2 Storm Drain

It is assumed that the existing downstream storm drain has capacity for the flows conveyed to existing infrastructure. Analysis of the entire downstream storm system is not included in the scope of this project.

A small swale exists behind the sidewalk between Skyline Drive and Circle Drive. The swale is lower than the sidewalk and local flows would be trapped behind the sidewalk. To mitigate issues with ponding on the adjacent properties, a 22-inch-wide chase drain is proposed at the northwest corner of Skyline Drive and West 26th Avenue. Full calculations for the chase drain evaluation are included in Appendix B.

5.3 Detention/Water Quality

This project is not required to provide detention. The increase in percent imperviousness compared to existing conditions is 2.5%, which will produce minimally increased runoff – maximums of 0.26 cfs and 0.34 cfs during the minor and major storms, respectively.

The project disturbs less than one acre; therefore, no water quality is required.

6. VARIANCES

No variances from the criteria are requested with this project.

REFERENCES

Mile High Flood District. April 2025. MHFD-Culvert Workbook, Version 4.01.

Mile High Flood District. August 2025. MHFD-Inlet Workbook, Version 6.00.

Mile High Flood District. August 2025. MHFD-Rational Workbook, Version 3.00.

National Oceanic and Atmospheric Administration. 2026. NOAA Atlas 14, Volume 8, B25-03001 8

Version 2.

United States Department of Agriculture. 2026. Custom Soil Resource Report for

Golden Area, Colorado, Parts of Denver, Douglas, Jefferson, and Park Counties.

Urban Drainage and Flood Control District, Volume 1. March 2024. Urban Storm

Drainage Criteria Manual: Volume 1.

Urban Drainage and Flood Control District, Volume 2. January 2016. Urban Storm

Drainage Criteria Manual: Volume 2.

APPENDIX A

HYDROLOGY

Designer:

Company:

Date:

Project:

Location:

Provide subcatchment names on the Rational Calcs worksheet to open up the table below.

Imperviousness

Source

Imperviousness

Category Calculated

Imperviousness

(Optional)

Override

Imperviousness

WQE

2-yr

5-yr 10-yr 25-yr 50-yr 100-yr 500-yr

WQE

2-yr

5-yr 10-yr 25-yr 50-yr 100-yr 500-yr Comments

EX 8.01 1 1.98 C/D 95.0% 95.0% 0.79 0.81 0.83 0.85 0.86 0.87 0.89 0.79 0.81 0.83 0.85 0.86 0.87 0.89

1.98 C/D Surface Type Roadways and Paved Streets 95% 0.79 0.81 0.83 0.85 0.86 0.87 0.89

EX 8.02 2 0.58 C/D 62.8% 62.8% 0.51 0.55 0.59 0.67 0.70 0.74 0.79 0.51 0.55 0.59 0.67 0.70 0.74 0.79

0.33 C/D Surface Type Roadways and Paved Streets 95% 0.79 0.81 0.83 0.85 0.86 0.87 0.89

0.25 C/D Surface Type Disturbed Soil 20% 0.14 0.20 0.28 0.43 0.49 0.57 0.65

EX 8.03 2 0.03 C/D 81.6% 81.6% 0.67 0.70 0.73 0.78 0.80 0.82 0.84 0.67 0.70 0.73 0.78 0.80 0.82 0.84

0.02 C/D Surface Type Roadways and Paved Streets 95% 0.79 0.81 0.83 0.85 0.86 0.87 0.89

0.00 C/D Surface Type Disturbed Soil 20% 0.14 0.20 0.28 0.43 0.49 0.57 0.65

EX 8.04 2 2.16 C/D 57.2% 57.2% 0.46 0.50 0.55 0.64 0.68 0.72 0.77 0.46 0.50 0.55 0.64 0.68 0.72 0.77

1.07 C/D Surface Type Roadways and Paved Streets 95% 0.79 0.81 0.83 0.85 0.86 0.87 0.89

1.09 C/D Surface Type Disturbed Soil 20% 0.14 0.20 0.28 0.43 0.49 0.57 0.65

EX 8.05 2 0.31 C/D 91.3% 91.3% 0.76 0.78 0.80 0.83 0.84 0.86 0.88 0.76 0.78 0.80 0.83 0.84 0.86 0.88

0.29 C/D Surface Type Roadways and Paved Streets 95% 0.79 0.81 0.83 0.85 0.86 0.87 0.89

0.02 C/D Surface Type Disturbed Soil 20% 0.14 0.20 0.28 0.43 0.49 0.57 0.65

PR 8.01 1 1.98 C/D 95.0% 95.0% 0.79 0.81 0.83 0.85 0.86 0.87 0.89 0.79 0.81 0.83 0.85 0.86 0.87 0.89

1.98 C/D Surface Type Roadways and Paved Streets 95% 0.79 0.81 0.83 0.85 0.86 0.87 0.89

PR 8.02 2 0.58 C/D 66.2% 66.2% 0.54 0.57 0.62 0.69 0.72 0.75 0.80 0.54 0.57 0.62 0.69 0.72 0.75 0.80

0.36 C/D Surface Type Roadways and Paved Streets 95% 0.79 0.81 0.83 0.85 0.86 0.87 0.89

0.22 C/D Surface Type Disturbed Soil 20% 0.14 0.20 0.28 0.43 0.49 0.57 0.65

PR 8.03 2 0.03 C/D 90.9% 90.9% 0.75 0.78 0.80 0.83 0.84 0.86 0.87 0.75 0.78 0.80 0.83 0.84 0.86 0.87

0.02 C/D Surface Type Roadways and Paved Streets 95% 0.79 0.81 0.83 0.85 0.86 0.87 0.89

0.00 C/D Surface Type Disturbed Soil 20% 0.14 0.20 0.28 0.43 0.49 0.57 0.65

PR 8.04 2 2.16 C/D 61.5% 61.5% 0.50 0.54 0.58 0.66 0.70 0.74 0.78 0.50 0.54 0.58 0.66 0.70 0.74 0.78

1.19 C/D Surface Type Roadways and Paved Streets 95% 0.79 0.81 0.83 0.85 0.86 0.87 0.89

0.96 C/D Surface Type Disturbed Soil 20% 0.14 0.20 0.28 0.43 0.49 0.57 0.65

PR 8.05 2 0.31 C/D 95.0% 95.0% 0.79 0.81 0.83 0.85 0.86 0.87 0.89 0.79 0.81 0.83 0.85 0.86 0.87 0.89

0.31 C/D Surface Type Roadways and Paved Streets 95% 0.79 0.81 0.83 0.85 0.86 0.87 0.89

0.00 C/D Surface Type Disturbed Soil 20% 0.14 0.20 0.28 0.43 0.49 0.57 0.65

Determination of Runoff Coefficients for Rational Method MHFD-Rational, Version 3.00 (August 2025)

Sidewalk Gaps - Project 08 Cells of this color are for required user-input

Cells of this color are for optional override values

Subcatchment

Name

# of

Subareas

Area

(ac)

NRCS

Hydrologic

Soil Group

(Optional) Override Runoff Coefficient, C

Wheat Ridge

Runoff Coefficient, C

Madison Stewart Olsson 7/30/2026

Percent Imperviousness

Project 08 _MHFD-Rational v3.xlsm, Runoff Coeffs 7/30/2026, 10:00

Designer: Select MHFD location for NOAA Atlas 14 Rainfall Depths from the pulldown list OR enter your own depths obtained from the NOAA website (click this link)

Company: WQE 2-yr 5-yr 10-yr 25-yr 50-yr 100-yr 500-yr

Date: 1-hour rainfall depth, P1 (in) = 0.61 0.77 1.04 1.28 1.64 1.92 2.22 2.98

Project: a b c

Location: Rainfall Intensity Equation Coefficients = 28.50 10.00 0.786

Subcatchment

Name

Area

(ac)

NRCS

Hydrologic

Soil Group(s)

Imperviousness

WQE

2-yr

5-yr 10-yr 25-yr 50-yr 100-yr 500-yr

Overland Flow

Length

Li (ft)

U/S Elevation

(ft)

(Optional)

D/S Elevation

(ft)

(Optional)

Overland Flow

Slope

Si (ft/ft)

Overland Flow

Time ti (min)

Channelized

Flow Length

Lt (ft)

U/S Elevation

(ft)

(Optional)

D/S Elevation

(ft)

(Optional)

Channelized

Flow Slope

St (ft/ft)

NRCS

Conveyance

Factor K

Channelized

Flow Velocity

Vt (ft/sec)

Channelized

Flow Time tt (min)

Computed tc (min)

Regional tc (min)

Selected tc (min)

(Optional)

Override tc (min)

WQE 2-yr 5-yr 10-yr 25-yr 50-yr 100-yr 500-yr WQE 2-yr 5-yr 10-yr 25-yr 50-yr 100-yr 500-yr

EX 8.01 1.98 C/D 95.0% 0.79 0.81 0.83 0.85 0.86 0.87 0.89 94.14 5581.00 5579.00 0.021 3.97 339.11 5579.00 5578.00 0.003 20 1.09 5.20 9.18 14.52 9.18 1.71 2.15 2.91 3.58 4.59 5.37 6.21 8.33 2.66 3.36 4.66 5.89 7.73 9.17 10.73 14.65

EX 8.02 0.58 C/D 62.8% 0.51 0.55 0.59 0.67 0.70 0.74 0.79 26.37 0.034 3.44 328.01 5578.25 5574.84 0.010 20 2.04 2.68 6.12 18.33 6.12 1.96 2.47 3.33 4.10 5.26 6.15 7.12 9.55 0.58 0.73 1.06 1.41 2.05 2.51 3.06 4.36

EX 8.03 0.03 C/D 81.6% 0.67 0.70 0.73 0.78 0.80 0.82 0.84 22.66 0.006 4.12 32.94 5578.68 5578.06 0.019 20 2.74 0.20 4.32 12.33 5.00 2.07 2.61 3.53 4.34 5.56 6.51 7.53 10.11 0.04 0.04 0.06 0.08 0.11 0.13 0.16 0.22

EX 8.04 2.16 C/D 57.2% 0.46 0.50 0.55 0.64 0.68 0.72 0.77 23.21 0.030 3.61 939.10 5602.01 5578.58 0.025 20 3.16 4.95 8.56 22.11 8.56 1.75 2.21 2.98 3.67 4.70 5.51 6.37 8.55 1.73 2.19 3.22 4.37 6.49 8.03 9.86 14.16

EX 8.05 0.31 C/D 91.3% 0.76 0.78 0.80 0.83 0.84 0.86 0.88 23.21 0.043 1.73 506.65 5601.86 5580.76 0.042 20 4.08 2.07 3.79 12.38 5.00 2.07 2.61 3.53 4.34 5.56 6.51 7.53 10.11 0.48 0.61 0.85 1.07 1.42 1.69 1.99 2.72

PR 8.01 1.98 C/D 95.0% 0.79 0.81 0.83 0.85 0.86 0.87 0.89 94.14 5581.00 5579.00 0.021 3.97 339.11 5579.00 5578.00 0.003 20 1.09 5.20 9.18 14.52 9.18 1.71 2.15 2.91 3.58 4.59 5.37 6.21 8.33 2.66 3.36 4.66 5.89 7.73 9.17 10.73 14.65

PR 8.02 0.58 C/D 66.2% 0.54 0.57 0.62 0.69 0.72 0.75 0.80 26.37 0.034 3.27 328.01 5578.25 5574.84 0.010 20 2.04 2.68 5.95 17.67 5.95 1.97 2.49 3.36 4.14 5.30 6.21 7.18 9.63 0.62 0.78 1.12 1.49 2.12 2.59 3.14 4.45

PR 8.03 0.03 C/D 90.9% 0.75 0.78 0.80 0.83 0.84 0.86 0.87 22.66 0.006 3.33 32.94 5578.68 5578.06 0.019 20 2.74 0.20 3.53 10.73 5.00 2.07 2.61 3.53 4.34 5.56 6.51 7.53 10.11 0.04 0.05 0.07 0.09 0.12 0.14 0.16 0.22

PR 8.04 2.16 C/D 61.5% 0.50 0.54 0.58 0.66 0.70 0.74 0.78 23.21 0.030 3.40 939.10 5602.01 5578.58 0.025 20 3.16 4.95 8.35 21.17 8.35 1.77 2.23 3.01 3.71 4.75 5.56 6.43 8.63 1.89 2.39 3.48 4.67 6.80 8.36 10.20 14.55

PR 8.05 0.31 C/D 95.0% 0.79 0.81 0.83 0.85 0.86 0.87 0.89 23.21 0.043 1.56 506.65 5601.86 5580.76 0.042 20 4.08 2.07 3.63 11.71 5.00 2.07 2.61 3.53 4.34 5.56 6.51 7.53 10.11 0.50 0.63 0.88 1.11 1.46 1.73 2.02 2.76

Calculation of Peak Runoff using Rational Method Madison Stewart

Olsson

Runoff Coefficient, C

MHFD-Rational, Version 3.00 (August 2025)

7/30/2026

Sidewalk Gaps - Project 08

Wheat Ridge

Provide input for area, soil type, and imperviousness on the Runoff Coeffs worksheet.

Cells of this color are for required user-input

Cells of this color are for optional override values

Calculation of Peak Runoff using Rational MethodCalculation of Peak Runoff using Rational Method

Rainfall Intensity, I (in/hr) Peak Flow, Q (cfs)Overland (Initial) Flow Time Channelized (Travel) Flow Time Time of Concentration

I ��/ℎ� � a ∗ P� b t� t� �

0.395 1.1 � C� L�

S� t� � L�

60K S�

L�

60V�

Computed t� � t� t�

Regional t� � 26 � 17i

L�

60 14i 9 S�

Selected t� � max t3�4�353 , min Computed t� ,Regional t� t� 3�4�353� 5 (urban) t� 3�4�353� 10 (non-urban)

Q 89: � CIA

Project 08 _MHFD-Rational v3.xlsm, Rational Calcs 7/30/2026, 9:59

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1525 Raleigh Street Suite 400 Denver, CO 80204 olsson.com

TEL 303.237.2072

DATE:

DRAWN BY:

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1PROPOSED DRAINAGE MAP

EXHIBIT

A = BASIN DESCRIPTION

B = AREA (AC)

C = COMPOSITE RUNOFF COEFFICIENTS

(5-YR, 100-YR)

D = DESIGN POINT

CB

A

LEGEND

BASIN BOUNDARY

PROPOSED STORM

EXISTING MAJOR CONTOUR

(SURVEY)

EXISTING MINOR CONTOUR

(SURVEY)

0.570.58

8.02

0.75

0.811.98

8.01

0.87

80' 160'40'0'

SCALE IN FEET

XXXX

WEST 26TH AVE

M

AT

C H

LI

N

E

PROPOSED MAJOR CONTOURS

PROPOSED MINOR CONTOURS

CHANNELIZED FLOW

OVERLAND FLOW

XXXX

M

AT

C H

LI

N

E

EXISTING MAJOR CONTOUR

(LIDAR)

EXISTING MINOR CONTOUR

(LIDAR)

FLOW PATH

XXXX

WEST 26TH AVE

0.542.16

8.04

0.74

0.780.03

8.03

0.86

0.810.31

8.05

0.87

PA

R

AM

O

U N

T

PK

W Y

SK

YL

IN

E

D R

C

IR

C

LE

D R

8.01

8.02

8.038.04

8.05

O

AK

S T

N

EL

SO

N

S T

D

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APPENDIX B

HYDRAULICS

ALLOWABLE CAPACITY FOR ONE-HALF OF STREET (Minor & Major Storm) (Based on Regulated Criteria for Maximum Allowable Flow Depth and Spread)

Project: Sidewalk Gaps - Project 08

Inlet ID: Roadway 8.02

Gutter Geometry:

Maximum Allowable Width for Spread Behind Curb TBACK = 8.0 ft

Side Slope Behind Curb (leave blank for no conveyance credit behind curb) SBACK = 0.020 ft/ft Manning's Roughness Behind Curb (typically between 0.012 and 0.020) nBACK = 0.013

Height of Curb at Gutter Flow Line HCURB = 6.00 inches

Distance from Curb Face to Street Crown TCROWN = 18.5 ft

Gutter Width W = 2.50 ft

Street Transverse Slope SX = 0.020 ft/ft Gutter Cross Slope (typically 2 inches over 24 inches or 0.083 ft/ft) SW = 0.083 ft/ft

Street Longitudinal Slope - Enter 0 for sump condition SO = 0.010 ft/ft

Manning's Roughness for Street Section (typically between 0.012 and 0.020) nSTREET = 0.013

Minor Storm Major Storm Max. Allowable Spread for Minor & Major Storm TMAX = 13.5 18.5 ft

Max. Allowable Depth at Gutter Flowline for Minor & Major Storm dMAX = 3.0 12.0 inches

Allow Flow Depth at Street Crown (check box for yes, leave blank for no)

MINOR STORM Allowable Capacity is based on Depth Criterion Minor Storm Major Storm

MAJOR STORM Allowable Capacity is based on Spread Criterion Qallow = 1.3 17.3 cfs

Minor storm max. allowable capacity GOOD - greater than the design peak flow of 1.12 cfs on sheet 'Inlet Management'

Major storm max. allowable capacity GOOD - greater than the design peak flow of 3.14 cfs on sheet 'Inlet Management'

MHFD-Inlet, Version 6.00 (August 2025)

Project: Sidewalk Gaps - Project 08

Inlet ID: Roadway 8.03

Gutter Geometry:

Maximum Allowable Width for Spread Behind Curb TBACK = 8.0 ft

Side Slope Behind Curb (leave blank for no conveyance credit behind curb) SBACK = 0.020 ft/ft Manning's Roughness Behind Curb (typically between 0.012 and 0.020) nBACK = 0.013

Height of Curb at Gutter Flow Line HCURB = 6.00 inches

Distance from Curb Face to Street Crown TCROWN = 18.5 ft

Gutter Width W = 2.50 ft

Street Transverse Slope SX = 0.020 ft/ft Gutter Cross Slope (typically 2 inches over 24 inches or 0.083 ft/ft) SW = 0.083 ft/ft

Street Longitudinal Slope - Enter 0 for sump condition SO = 0.019 ft/ft

Manning's Roughness for Street Section (typically between 0.012 and 0.020) nSTREET = 0.013

Minor Storm Major Storm Max. Allowable Spread for Minor & Major Storm TMAX = 13.5 18.5 ft

Max. Allowable Depth at Gutter Flowline for Minor & Major Storm dMAX = 6.0 12.0 inches

Allow Flow Depth at Street Crown (check box for yes, leave blank for no)

MINOR STORM Allowable Capacity is based on Spread Criterion Minor Storm Major Storm

MAJOR STORM Allowable Capacity is based on Spread Criterion Qallow = 11.4 23.8 cfs

Minor storm max. allowable capacity GOOD - greater than the design peak flow of 0.07 cfs on sheet 'Inlet Management'

Major storm max. allowable capacity GOOD - greater than the design peak flow of 0.16 cfs on sheet 'Inlet Management'

Project: Sidewalk Gaps - Project 08

Inlet ID: Roadway 8.04

Gutter Geometry:

Maximum Allowable Width for Spread Behind Curb TBACK = 6.0 ft

Side Slope Behind Curb (leave blank for no conveyance credit behind curb) SBACK = 0.020 ft/ft Manning's Roughness Behind Curb (typically between 0.012 and 0.020) nBACK = 0.013

Height of Curb at Gutter Flow Line HCURB = 6.00 inches

Distance from Curb Face to Street Crown TCROWN = 18.5 ft

Gutter Width W = 2.50 ft

Street Transverse Slope SX = 0.020 ft/ft Gutter Cross Slope (typically 2 inches over 24 inches or 0.083 ft/ft) SW = 0.083 ft/ft

Street Longitudinal Slope - Enter 0 for sump condition SO = 0.025 ft/ft

Manning's Roughness for Street Section (typically between 0.012 and 0.020) nSTREET = 0.013

Minor Storm Major Storm Max. Allowable Spread for Minor & Major Storm TMAX = 13.5 18.5 ft

Max. Allowable Depth at Gutter Flowline for Minor & Major Storm dMAX = 6.0 12.0 inches

Allow Flow Depth at Street Crown (check box for yes, leave blank for no)

MINOR STORM Allowable Capacity is based on Spread Criterion Minor Storm Major Storm

MAJOR STORM Allowable Capacity is based on Spread Criterion Qallow = 13.1 27.3 cfs

Minor storm max. allowable capacity GOOD - greater than the design peak flow of 3.48 cfs on sheet 'Inlet Management'

Major storm max. allowable capacity GOOD - greater than the design peak flow of 10.20 cfs on sheet 'Inlet Management'

Project: Sidewalk Gaps - Project 08

Inlet ID: Roadway 8.05

Gutter Geometry:

Maximum Allowable Width for Spread Behind Curb TBACK = 6.0 ft

Side Slope Behind Curb (leave blank for no conveyance credit behind curb) SBACK = 0.020 ft/ft Manning's Roughness Behind Curb (typically between 0.012 and 0.020) nBACK = 0.013

Height of Curb at Gutter Flow Line HCURB = 6.00 inches

Distance from Curb Face to Street Crown TCROWN = 18.5 ft

Gutter Width W = 2.50 ft

Street Transverse Slope SX = 0.020 ft/ft Gutter Cross Slope (typically 2 inches over 24 inches or 0.083 ft/ft) SW = 0.083 ft/ft

Street Longitudinal Slope - Enter 0 for sump condition SO = 0.042 ft/ft

Manning's Roughness for Street Section (typically between 0.012 and 0.020) nSTREET = 0.013

Minor Storm Major Storm Max. Allowable Spread for Minor & Major Storm TMAX = 13.5 18.5 ft

Max. Allowable Depth at Gutter Flowline for Minor & Major Storm dMAX = 3.0 12.0 inches

Allow Flow Depth at Street Crown (check box for yes, leave blank for no)

MINOR STORM Allowable Capacity is based on Depth Criterion Minor Storm Major Storm

MAJOR STORM Allowable Capacity is based on Spread Criterion Qallow = 2.7 35.4 cfs

Minor storm max. allowable capacity GOOD - greater than the design peak flow of 0.88 cfs on sheet 'Inlet Management'

Major storm max. allowable capacity GOOD - greater than the design peak flow of 2.02 cfs on sheet 'Inlet Management'

Worksheet for 8.04 Swale

Project Description

Manning Formula

Friction Method

DischargeSolve For

Input Data ft/ft0.025Channel Slope in2.3Normal Depth

Section Definitions

Elevation (ft)

Station (ft)

5,579.770+12

5,579.700+14

5,579.580+17

5,579.650+23

5,580.090+25

Roughness Segment Definitions

Roughness CoefficientEnding StationStart Station

0.050(0+25, 5,580.09)(0+12, 5,579.77)

Options

Pavlovskii's Method

Current Roughness Weighted Method

Pavlovskii's Method

Open Channel Weighting Method

Pavlovskii's Method

Closed Channel Weighting Method

Results cfs1.54Discharge

0.050Roughness Coefficient

5,579.6 to 5,580.1 ft

Elevation Range ft²1.4Flow Area ft11.4Wetted Perimeter in1.4Hydraulic Radius ft11.34Top Width in2.3Normal Depth in1.8Critical Depth ft/ft0.081Critical Slope ft/s1.14Velocity ft0.02Velocity Head ft0.21Specific Energy

0.581Froude Number

SubcriticalFlow Type

Page 1 of 227 Siemon Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666

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FlowMaster [10.03.00.03]

Bentley Systems, Inc. Haestad Methods Solution CenterProject 08_Roadway Swales.fm8

Worksheet for 8.04 Swale

GVF Input Data in0.0Downstream Depth ft0.0Length

0Number Of Steps

GVF Output Data in0.0Upstream Depth

N/AProfile Description ft0.00Profile Headloss ft/s0.00Downstream Velocity ft/s0.00Upstream Velocity in2.3Normal Depth in1.8Critical Depth ft/ft0.025Channel Slope ft/ft0.081Critical Slope

Page 2 of 227 Siemon Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666

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FlowMaster [10.03.00.03]

Cross Section for 8.04 Swale

Manning Formula

Friction Method

DischargeSolve For

Input Data ft/ft0.025Channel Slope in2.3Normal Depth cfs1.54Discharge

Page 1 of 127 Siemon Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666

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FlowMaster [10.03.00.03]

Worksheet for 8.04 Chase Drain Orifice

DischargeSolve For

Input Data ft0.50Headwater Elevation ft0.25Centroid Elevation ft0.00Tailwater Elevation

0.670Discharge Coefficient ft1.83Opening Width ft0.5Opening Height

Results cfs2.46Discharge ft0.25 Headwater Height Above Centroid ft-0.25 Tailwater Height Above Centroid ft²0.9Flow Area ft/s2.69Velocity

Page 1 of 127 Siemon Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666

7/30/2026

FlowMaster [10.03.00.03]

Cross Section for 8.04 Chase Drain Orifice

DischargeSolve For

Input Data cfs2.46Discharge ft0.50Headwater Elevation ft0.25Centroid Elevation ft0.00Tailwater Elevation

0.670Discharge Coefficient ft1.83Opening Width ft0.5Opening Height

Page 1 of 127 Siemon Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666

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APPENDIX C

REFERENCE INFORMATION

United States Department of Agriculture

A product of the National Cooperative Soil Survey, a joint effort of the United States Department of Agriculture and other Federal agencies, State agencies including the Agricultural Experiment Stations, and local participants

Custom Soil Resource Report for Golden Area, Colorado, Parts of Denver, Douglas, Jefferson, and Park Counties

Natural Resources Conservation Service

July 29, 2026

Preface Soil surveys contain information that affects land use planning in survey areas.

They highlight soil limitations that affect various land uses and provide information about the properties of the soils in the survey areas. Soil surveys are designed for many different users, including farmers, ranchers, foresters, agronomists, urban planners, community officials, engineers, developers, builders, and home buyers.

Also, conservationists, teachers, students, and specialists in recreation, waste disposal, and pollution control can use the surveys to help them understand, protect, or enhance the environment.

Various land use regulations of Federal, State, and local governments may impose special restrictions on land use or land treatment. Soil surveys identify soil properties that are used in making various land use or land treatment decisions.

The information is intended to help the land users identify and reduce the effects of soil limitations on various land uses. The landowner or user is responsible for identifying and complying with existing laws and regulations.

Although soil survey information can be used for general farm, local, and wider area planning, onsite investigation is needed to supplement this information in some cases. Examples include soil quality assessments (http://www.nrcs.usda.gov/wps/ portal/nrcs/main/soils/health/) and certain conservation and engineering applications. For more detailed information, contact your local USDA Service Center (https://offices.sc.egov.usda.gov/locator/app?agency=nrcs) or your NRCS State Soil Scientist (http://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/contactus/?

cid=nrcs142p2_053951).

Great differences in soil properties can occur within short distances. Some soils are seasonally wet or subject to flooding. Some are too unstable to be used as a foundation for buildings or roads. Clayey or wet soils are poorly suited to use as septic tank absorption fields. A high water table makes a soil poorly suited to basements or underground installations.

The National Cooperative Soil Survey is a joint effort of the United States Department of Agriculture and other Federal agencies, State agencies including the Agricultural Experiment Stations, and local agencies. The Natural Resources Conservation Service (NRCS) has leadership for the Federal part of the National Cooperative Soil Survey.

Information about soils is updated periodically. Updated information is available through the NRCS Web Soil Survey, the site for official soil survey information.

The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, national origin, age, disability, and where applicable, sex, marital status, familial status, parental status, religion, sexual orientation, genetic information, political beliefs, reprisal, or because all or a part of an individual's income is derived from any public assistance program. (Not all prohibited bases apply to all programs.) Persons with disabilities who require http://www.nrcs.usda.gov/wps/portal/nrcs/main/soils/health/ http://www.nrcs.usda.gov/wps/portal/nrcs/main/soils/health/ https://offices.sc.egov.usda.gov/locator/app?agency=nrcs http://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/contactus/?cid=nrcs142p2_053951 http://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/contactus/?cid=nrcs142p2_053951 alternative means for communication of program information (Braille, large print, audiotape, etc.) should contact USDA's TARGET Center at (202) 720-2600 (voice and TDD). To file a complaint of discrimination, write to USDA, Director, Office of Civil Rights, 1400 Independence Avenue, S.W., Washington, D.C. 20250-9410 or call (800) 795-3272 (voice) or (202) 720-6382 (TDD). USDA is an equal opportunity provider and employer.

Contents Preface How Soil Surveys Are Made Soil Map

Soil Map Legend Map Unit Legend Map Unit Descriptions

Golden Area, Colorado, Parts of Denver, Douglas, Jefferson, and Park Counties

106—Nunn-Urban land complex, 2 to 5 percent slopes 107—Nunn-Urban land complex, 5 to 9 percent slopes UcA—Urban land-Ciancio-Englewood complex, 0 to 3 percent slopes

References

How Soil Surveys Are Made Soil surveys are made to provide information about the soils and miscellaneous areas in a specific area. They include a description of the soils and miscellaneous areas and their location on the landscape and tables that show soil properties and limitations affecting various uses. Soil scientists observed the steepness, length, and shape of the slopes; the general pattern of drainage; the kinds of crops and native plants; and the kinds of bedrock. They observed and described many soil profiles. A soil profile is the sequence of natural layers, or horizons, in a soil. The profile extends from the surface down into the unconsolidated material in which the soil formed or from the surface down to bedrock. The unconsolidated material is devoid of roots and other living organisms and has not been changed by other biological activity.

Currently, soils are mapped according to the boundaries of major land resource areas (MLRAs). MLRAs are geographically associated land resource units that share common characteristics related to physiography, geology, climate, water resources, soils, biological resources, and land uses (USDA, 2006). Soil survey areas typically consist of parts of one or more MLRA.

The soils and miscellaneous areas in a survey area occur in an orderly pattern that is related to the geology, landforms, relief, climate, and natural vegetation of the area. Each kind of soil and miscellaneous area is associated with a particular kind of landform or with a segment of the landform. By observing the soils and miscellaneous areas in the survey area and relating their position to specific segments of the landform, a soil scientist develops a concept, or model, of how they were formed. Thus, during mapping, this model enables the soil scientist to predict with a considerable degree of accuracy the kind of soil or miscellaneous area at a specific location on the landscape.

Commonly, individual soils on the landscape merge into one another as their characteristics gradually change. To construct an accurate soil map, however, soil scientists must determine the boundaries between the soils. They can observe only a limited number of soil profiles. Nevertheless, these observations, supplemented by an understanding of the soil-vegetation-landscape relationship, are sufficient to verify predictions of the kinds of soil in an area and to determine the boundaries.

Soil scientists recorded the characteristics of the soil profiles that they studied. They noted soil color, texture, size and shape of soil aggregates, kind and amount of rock fragments, distribution of plant roots, reaction, and other features that enable them to identify soils. After describing the soils in the survey area and determining their properties, the soil scientists assigned the soils to taxonomic classes (units).

Taxonomic classes are concepts. Each taxonomic class has a set of soil characteristics with precisely defined limits. The classes are used as a basis for comparison to classify soils systematically. Soil taxonomy, the system of taxonomic classification used in the United States, is based mainly on the kind and character of soil properties and the arrangement of horizons within the profile. After the soil scientists classified and named the soils in the survey area, they compared the individual soils with similar soils in the same taxonomic class in other areas so that they could confirm data and assemble additional data based on experience and research.

The objective of soil mapping is not to delineate pure map unit components; the objective is to separate the landscape into landforms or landform segments that have similar use and management requirements. Each map unit is defined by a unique combination of soil components and/or miscellaneous areas in predictable proportions. Some components may be highly contrasting to the other components of the map unit. The presence of minor components in a map unit in no way diminishes the usefulness or accuracy of the data. The delineation of such landforms and landform segments on the map provides sufficient information for the development of resource plans. If intensive use of small areas is planned, onsite investigation is needed to define and locate the soils and miscellaneous areas.

Soil scientists make many field observations in the process of producing a soil map.

The frequency of observation is dependent upon several factors, including scale of mapping, intensity of mapping, design of map units, complexity of the landscape, and experience of the soil scientist. Observations are made to test and refine the soil-landscape model and predictions and to verify the classification of the soils at specific locations. Once the soil-landscape model is refined, a significantly smaller number of measurements of individual soil properties are made and recorded.

These measurements may include field measurements, such as those for color, depth to bedrock, and texture, and laboratory measurements, such as those for content of sand, silt, clay, salt, and other components. Properties of each soil typically vary from one point to another across the landscape.

Observations for map unit components are aggregated to develop ranges of characteristics for the components. The aggregated values are presented. Direct measurements do not exist for every property presented for every map unit component. Values for some properties are estimated from combinations of other properties.

While a soil survey is in progress, samples of some of the soils in the area generally are collected for laboratory analyses and for engineering tests. Soil scientists interpret the data from these analyses and tests as well as the field-observed characteristics and the soil properties to determine the expected behavior of the soils under different uses. Interpretations for all of the soils are field tested through observation of the soils in different uses and under different levels of management.

Some interpretations are modified to fit local conditions, and some new interpretations are developed to meet local needs. Data are assembled from other sources, such as research information, production records, and field experience of specialists. For example, data on crop yields under defined levels of management are assembled from farm records and from field or plot experiments on the same kinds of soil.

Predictions about soil behavior are based not only on soil properties but also on such variables as climate and biological activity. Soil conditions are predictable over long periods of time, but they are not predictable from year to year. For example, soil scientists can predict with a fairly high degree of accuracy that a given soil will have a high water table within certain depths in most years, but they cannot predict that a high water table will always be at a specific level in the soil on a specific date.

After soil scientists located and identified the significant natural bodies of soil in the survey area, they drew the boundaries of these bodies on aerial photographs and

Custom Soil Resource Report identified each as a specific map unit. Aerial photographs show trees, buildings, fields, roads, and rivers, all of which help in locating boundaries accurately.

Soil Map The soil map section includes the soil map for the defined area of interest, a list of soil map units on the map and extent of each map unit, and cartographic symbols displayed on the map. Also presented are various metadata about data used to produce the map, and a description of each soil map unit.

Soil Map

489790 489870 489950 490030 490110 490190 490270 490350 490430 490510

489790 489870 489950 490030 490110 490190 490270 490350 490430 490510

39° 45' 24'' N

5°

' 1 0'

' W 39° 45' 24'' N

5°

' 3

7' ' W

39° 45' 8'' N

5°

' 1

0' ' W

39° 45' 8'' N

5°

' 3

7' ' W

N

Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84 0 150 300 600 900

Feet 0 50 100 200 300

Meters Map Scale: 1:3,590 if printed on A landscape (11" x 8.5") sheet.

Soil Map may not be valid at this scale.

MAP LEGEND MAP INFORMATION

Area of Interest (AOI) Area of Interest (AOI)

Soils Soil Map Unit Polygons

Soil Map Unit Lines

Soil Map Unit Points

Special Point Features Blowout

Borrow Pit

Clay Spot

Closed Depression

Gravel Pit

Gravelly Spot

Landfill

Lava Flow

Marsh or swamp

Mine or Quarry

Miscellaneous Water

Perennial Water

Rock Outcrop

Saline Spot

Sandy Spot

Severely Eroded Spot

Sinkhole

Slide or Slip

Sodic Spot

Spoil Area

Stony Spot

Very Stony Spot

Wet Spot

Other

Special Line Features

Water Features Streams and Canals

Transportation Rails

Interstate Highways

US Routes

Major Roads

Local Roads

Background Aerial Photography

The soil surveys that comprise your AOI were mapped at 1:24,000.

Warning: Soil Map may not be valid at this scale.

Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale.

Please rely on the bar scale on each map sheet for map measurements.

Source of Map: Natural Resources Conservation Service Web Soil Survey URL:

Coordinate System: Web Mercator (EPSG:3857)

Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required.

This product is generated from the USDA-NRCS certified data as of the version date(s) listed below.

Soil Survey Area: Golden Area, Colorado, Parts of Denver, Douglas, Jefferson, and Park Counties Survey Area Data: Version 20, Aug 29, 2025

Soil map units are labeled (as space allows) for map scales 1:50,000 or larger.

Date(s) aerial images were photographed: Jul 1, 2020—Jul 2, The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background

MAP LEGEND MAP INFORMATION

imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident.

Map Unit Legend

Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI

106 Nunn-Urban land complex, 2 to 5 percent slopes

1.9 37.6%

107 Nunn-Urban land complex, 5 to 9 percent slopes

0.2 4.5%

UcA Urban land-Ciancio-Englewood complex, 0 to 3 percent slopes

2.9 57.9%

Totals for Area of Interest 5.1 100.0%

Map Unit Descriptions The map units delineated on the detailed soil maps in a soil survey represent the soils or miscellaneous areas in the survey area. The map unit descriptions, along with the maps, can be used to determine the composition and properties of a unit.

A map unit delineation on a soil map represents an area dominated by one or more major kinds of soil or miscellaneous areas. A map unit is identified and named according to the taxonomic classification of the dominant soils. Within a taxonomic class there are precisely defined limits for the properties of the soils. On the landscape, however, the soils are natural phenomena, and they have the characteristic variability of all natural phenomena. Thus, the range of some observed properties may extend beyond the limits defined for a taxonomic class.

Areas of soils of a single taxonomic class rarely, if ever, can be mapped without including areas of other taxonomic classes. Consequently, every map unit is made up of the soils or miscellaneous areas for which it is named and some minor components that belong to taxonomic classes other than those of the major soils.

Most minor soils have properties similar to those of the dominant soil or soils in the map unit, and thus they do not affect use and management. These are called noncontrasting, or similar, components. They may or may not be mentioned in a particular map unit description. Other minor components, however, have properties and behavioral characteristics divergent enough to affect use or to require different management. These are called contrasting, or dissimilar, components. They generally are in small areas and could not be mapped separately because of the scale used. Some small areas of strongly contrasting soils or miscellaneous areas are identified by a special symbol on the maps. If included in the database for a given area, the contrasting minor components are identified in the map unit descriptions along with some characteristics of each. A few areas of minor components may not have been observed, and consequently they are not mentioned in the descriptions, especially where the pattern was so complex that it was impractical to make enough observations to identify all the soils and miscellaneous areas on the landscape.

The presence of minor components in a map unit in no way diminishes the usefulness or accuracy of the data. The objective of mapping is not to delineate pure taxonomic classes but rather to separate the landscape into landforms or landform segments that have similar use and management requirements. The delineation of such segments on the map provides sufficient information for the development of resource plans. If intensive use of small areas is planned, however, onsite investigation is needed to define and locate the soils and miscellaneous areas.

An identifying symbol precedes the map unit name in the map unit descriptions.

Each description includes general facts about the unit and gives important soil properties and…