EXHIBIT C - Hydraulic Report Dated January 14 2025.pdf

FOR HYDRAULIC DESIGN REPORT

Power Trail – Harmony Underpass

City of Fort Collins

CDOT Project No. TAP M455-123

CDOT Code: 21888

January 14, 2025

Prepared for:

CITY OF FORT COLLINS

281 North College Ave.

Fort Collins, Colorado 80524

CDOT REGION 4

10601 W. 10th Street

Greeley, Colorado 80634

Prepared by:

Wilson & Company

4065 St. Cloud Street, Suite 100

Loveland, Colorado 80538

(970) 834-6364

© 2025 Wilson & Company, Inc., Engineers & Architects

EXHIBIT C

Table of Contents

1.0 Introduction

1.1 Project Location

1.2 Description of Project

2.0 Hydrology

2.1 Major Basin Description

2.2 Existing Drainage Conditions and Basin Description

2.3 Channel Description

2.4 Precipitation Data

2.5 Flood History

2.6 Design Flood Frequency

2.7 Prediction of Design Discharge

3.0 Existing Structure

3.1 Description

4.0 Design Discussion

4.1 General Concept

4.2 MS-4 Requirements (permanent BMPs)

4.3 Erosion Control

5.0 Recommended Design

5.1 Compliance with Standards

5.2 Drainage Concept

6.0 References

Appendix A – Grading and Drainage Exhibits ................................................................ A

Appendix B – Hydrologic Calculations............................................................................. B

Appendix C – Hydraulic Calculations ..............................................................................C

Appendix D – Soil and FEMA Information .......................................................................D

Appendix E – Underpass Plans ....................................................................................... E

Power Trail – Harmony Underpass Wilson & Company, Inc., Engineers & Architects 1

1.0 Introduction

1.1 Project Location

The Power Trail Harmony Road Underpass project is located between McMurry Avenue and the Union Pacific Railroad ROW along Harmony Drive in the City of Fort Collins. Specifically, the project is in the Southeast Quarter of Section 31 Township 07 North and Northeast Quarter of Section 06 Township 06 North, Range 68 West of the Sixth Principal Meridian, Larimer

County, Colorado. Land Use in the area is Commercial. Please refer to Figure 1.1 for the

Project Location Map.

Figure 1.1 Project Location Map (not to scale).

1.2 Description of Project

The main goal of the project is to provide a grade separated pedestrian and bicycle facility at

Harmony Road. This will be accomplished with a large box culvert below the roadway. The profile of Harmony Road will not be changed. Existing sidewalks in the project area will be moved and the Power Trail will cross Harmony Road at the proposed underpass.

Power Trail – Harmony Underpass Wilson & Company, Inc., Engineers & Architects 2

The total study area used for this report is approximately 4.3 acres. Soil data from the National

Resource Conversation Service (NCRS) indicates the site soils consist of Nunn clay loam types and are considered Hydrologic Soil Group C with low surface runoff potential. Please refer to Appendix D for the soil information.

2.0 Hydrology

2.1 Major Basin Description

This portion of Harmony Road is the dividing line between the Fox Meadows Drainage Basin to the north and the McClellands Creek Drainage Basin to the south. Adjacent developments are within the City of Fort Collins.

2.2 Existing Drainage Conditions and Basin Description

All flows on the northern half of Harmony Road currently drain to an existing drainage swale and pipe system on the north that conveys flows east then north along the west side of the

Union Pacific Railroad and discharge to the Golden Meadows Regional Detention Pond. All flows on the southern half of the Harmony Road roadway currently drain off the south edge of the east bound lanes into an existing drainage swale that conveys flows east then south along the west side of the Union Pacific Railroad and discharge to the Oakridge Regional Detention

Pond and McClellands Creek.

Modifications to the existing flow paths are the result of the addition of the underpass to

Harmony Road.

The project has been divided into four sub-basins for discussion of both the existing and proposed drainage conditions. Please refer to Section 4.1 General Concept for a detailed description of the proposed basin conditions and the Drainage Exhibits in Appendix A for identification and location of these basins. The Rational Method was used to compute peak flows for the sub-basins. Calculations for the existing conditions are included in Appendix B.

The following is a discussion of the existing conditions for each basin.

Basin A is the northern portion of the project and is bounded on the south by the existing edge of asphalt along Harmony Road. This basin has been defined separately from Basin

B because it is the area in the proposed condition that will drain into the underpass and need to be pumped. This basin currently drains to the existing roadside ditch on the north side of

Harmony Road. This ditch drains east along Harmony Road and then north along the west

Power Trail – Harmony Underpass Wilson & Company, Inc., Engineers & Architects 3 side of the Union Pacific Railroad to the Golden Meadows Regional Detention Pond. North of this basin is an existing swale that receives flows from developments west of Innovation

Drive. This swale will not be modified with the project.

Basin B is the westbound lanes and median of Harmony Road in the project area. Today this basin flows to a low point in the depressed center median of Harmony Road. Flow is captured by an existing flared end section and 19”x30” elliptical pipe system at design point b. Runoff is then conveyed to the roadside ditch of Harmony Road that drains east along Harmony Road and then north along the west side of the Union Pacific Railroad to the Golden Meadows

Regional Detention Pond.

Basin C includes a small portion of the eastbound lanes of Harmony Road and the proposed underpass footprint south of Harmony. This basin has been defined separately from Basin D because it is the area in the proposed condition that will drain into the underpass and need to be pumped. Today, flow from this basin sheets southeast to a shallow roadside ditch. This swale flows to the east, then south along the west side of the Union Pacific Railroad to the

Oakridge Regional Detention Pond.

Basin D is the southern portion of the proposed project and includes the eastbound lanes of

Harmony Road to McMurry and the area south of the road that drains to the existing roadside swale. The south edge of the basin is bounded by the ridge of landscaped berms. This area drains to the same swale as Basin C.

The following is a summary of existing flows.

Power Trail – Harmony Underpass Wilson & Company, Inc., Engineers & Architects 4

Table 2.2.1 Summary of Existing Conditions Flow.

Design Tributary Area C (2, 5, & 10) C (25) C (50) C (100) Q(2) Q(5) Q(10) Q(25) Q(50) Q(100)

Point Sub-basin (ac) (cfs) (cfs) (cfs) (cfs) (cfs) (cfs) REMARKS a A 0.48 0.38 0.42 0.46 0.48 0.5 0.7 0.8 1.2 1.5 2.1

DRAINS TO EX

ROADSIDE DITCH

b B 0.92 0.65 0.71 0.78 0.81 1.1 1.7 1.9 2.8 3.6 4.7

DRAINS VIA EX SWALE

IN MEDIAN TO EX

CULVERT

c C 0.42 0.62 0.68 0.74 0.77 0.7 1.0 1.1 1.8 2.3 3.1 DRAINS TO BASIN D d D 2.44 0.57 0.62 0.68 0.71 2.5 3.6 4.2 6.2 8.1 10.8

DRAINS VIA EX SWALE

AND PAN

Power Trail – Harmony Underpass Wilson & Company, Inc., Engineers & Architects 5

2.3 Channel Description

Currently, the north portion of the project drains into an existing drainage swale and pipe system which conveys the flows east then north to the Golden Meadows Regional Detention

Pond, Fossil Creek Reservoir, Fossil Creek, and ultimately into the Cache la Poudre River.

The south portion of this project drains into an existing drainage swale which conveys the flows east then south to the Oakridge Regional Detention Pond, then McClellands Creek, Fossil Creek Reservoir, Fossil Creek, and ultimately into the Cache la Poudre River.

2.4 Precipitation Data

For the 2-, 10-, and 100-year events, the rainfall intensities used in the computation of runoff via the Rational Method were obtained from the City of Fort Collins Intensity-Duration-

Frequency Curves and Table Figure 3.4-1 & Table 3.4-1 of The City of Fort Collins Stormwater

Criteria Manual (SCM) dated December 2018. For the 5-, 25-, and 50-year events the rainfall intensities used were obtained from Figure 3-1 of the IDF Curve that was produced in 1999 and presented via Ordinance 42, 1999 to the January 1997 Revised City of Fort Collins “Storm

Drainage Design Criteria and Construction Standards”.

The following table is a summary of the total rainfall depths associated with each specified design flood frequency.

Table 2.4.1 Fort Collins Two-hour Point Rainfall Data.

2.5 Flood History

Per FEMA Flood Zone and Flood Insurance Rate Map (FIRM) panel numbers 08069C1000F, effective date December 19, 2006, this project area is not located within any designated floodplain. Please refer to Appendix D for the FEMA FIRM Map.

Rainfall

Period

2-year 5-year 10-year 25-year 50-year 100-year

Rainfall

Depth (in.)

0.98 1.36 1.71 2.31 2.91 3.67

Power Trail – Harmony Underpass Wilson & Company, Inc., Engineers & Architects 6

2.6 Design Flood Frequency

The approach to selecting the design flood frequency followed the CDOT’s Drainage Design

Manual (CDOT DDM) and the City of Fort Colins SCM.

The City of Fort Collins requires that all drainage system design and construction take into consideration three separate and distinct drainage problems. The first is the eightieth (80th) percentile storm event often referred to as the “water quality storm” or 0.6 inches. The second is the “minor storm” which is the 2-year storm or the 50th percentile storm event. The third is the “major storm” which is the 100-year storm or the one percentile storm event.

CDOT offers suggested design frequencies for each drainage type in the following table

(Table 7.2) with more specific criteria in Table 13.1.

Power Trail – Harmony Underpass Wilson & Company, Inc., Engineers & Architects 7

The City of Fort Collins offers the following street encroachment standards in Table 2.1-1 and

Table 2.1-2 and cross-street flow in Table 2.1-3.

Power Trail – Harmony Underpass Wilson & Company, Inc., Engineers & Architects 8

However, no curb is being added to the project so there are no spread calculations included in this report.

2.7 Prediction of Design Discharge

Runoff computations were prepared for the 2-year minor and 100-year major storm frequencies utilizing the Rational Method. In addition, runoff was also calculated for the 5-, 10-, 25- and 50-year storm events to better understand pump sizing and capacity for the box culvert underpass. All hydrologic calculations associated with the basins are included in

Appendix B of this report.

Percentage impervious values and runoff coefficients were based on proposed land surface types and are specified in the following Tables 3.2-2 and 4.1-3 from the City of Fort Collins

SCM. The City of Fort Collins adjusts the runoff coefficient for analysis of storms with higher intensities. These frequency adjustment factors, Cf, are listed in the following Table 3.2-3 and are applied to the composite runoff.

Power Trail – Harmony Underpass Wilson & Company, Inc., Engineers & Architects 9

Power Trail – Harmony Underpass Wilson & Company, Inc., Engineers & Architects 10

The rainfall intensities used in the Rational Method computation of runoff were obtained from the City of Fort Colins Intensity-Duration-Frequency (IDF) Curves and are tabulated in the following table.

Power Trail – Harmony Underpass Wilson & Company, Inc., Engineers & Architects 11

Figure 3-1 is used for the Fort Collins SCM IDF Curve for the 5-, 25-, 50-year event.

3.0 Existing Structure

3.1 Description

There are two regional drainage facilities in the project area. The channel north of Harmony drains east and north to Golden Meadows Regional Detention Pond, and the channel south of Harmony drains east and south to Oakridge Regional Detention Pond. Neither facility will be changed with the underpass project.

Power Trail – Harmony Underpass Wilson & Company, Inc., Engineers & Architects 12

4.0 Design Discussion

4.1 General Concept

The proposed drainage patterns follow the historic patterns until flows are redirected by proposed improvements, as described in each basin below. The proposed basins are the same as the existing basins described above for comparison. Please refer to the Power Trail

Harmony Underpass Proposed Drainage Plan in Appendix A that shows the site and the surrounding areas broken down into the following proposed condition sub-basins:

Basin A is north of Harmony Road and includes the underpass approach which will drain to new inlets and storm pipes and into the underpass. The underpass is lower than any available gravity outfall and stormwater that enters the underpass area will need to be pumped. Basin

A will be directed south to Basin C where the proposed pump is located.

Basin B is the westbound lanes and median of Harmony Road. The roadway will be shifted slightly, but the drainage pattern for this basin will remain (draining to the depressed median).

Flow is captured by a proposed CDOT Type D inlet, at design point b, that replaces an existing flared end section. Runoff is then conveyed north via a proposed pipe system to the roadside ditch of Harmony Road and to the Golden Meadows Regional Detention Pond. Basin B maintains existing flow conditions.

Basin C is a small portion of the eastbound lanes of Harmony Road south of the median and the south approach to the underpass. This area will drain to the pump system. It is proposed that this pump will discharge to the roadside swale on the south side of Harmony as the basin does today.

Basin D does not change significantly from existing conditions. It includes all of the drainage area on the south side of Harmony that is upstream of Basin C. At the underpass, the roadside swale will be rerouted south and around the underpass approaches.

The Rational Method was used to compute peak flows for the sub-basins. Calculations are included in Appendix B. The following table is a summary of proposed flows.

Power Trail – Harmony Underpass Wilson & Company, Inc., Engineers & Architects 13

Table 4. 1 Summary of Proposed Flow.

Design Tributary Area Q(2) Q(5) Q(10) Q(25) Q(50) Q(100)

Point Sub-basin (ac) C (2, 5, & 10) C (25) C (50) C (100) (cfs) (cfs) (cfs) (cfs) (cfs) (cfs) REMARKS a A 0.48 0.58 0.64 0.70 0.72 0.7 1.0 1.2 1.8 2.3 3.3

PUMPED FROM

BOX CULVERT

b B 0.92 0.63 0.69 0.75 0.79 1.1 1.5 1.8 2.6 3.4 4.6

CDOT TYPE D

INLET IN

MEDIAN

c C 0.42 0.86 0.94 1.00 1.00 1.0 1.4 1.7 2.5 3.2 4.2

PUMPED FROM

BOX CULVERT

d D 2.44 0.55 0.61 0.66 0.69 2.4 3.4 4.1 6.0 7.8 10.6

SWALE TO

SOUTH

Power Trail – Harmony Underpass Wilson & Company, Inc., Engineers & Architects 14

Inlet size and location was based on the City of Fort Collins SCM (see Table 2.4).

The Manning’s equation was used to size the proposed pipes of the storm system and

StormCAD software by Bentley® was used to model the proposed systems and analyze the proposed HGL’s. Both the minor (2-yr) and major (100-yr) storms were analyzed. In underpass, pipes were not sized as they simply need to be able to convey the maximum pump flow (much less than the 100-yr storm).

Proposed flow and pump discussion.

It is uncommon for drainage basins to change their outfall location between existing and proposed. The project is only proposed to have one pump; therefore, Basin A will now drain south rather than north. To mitigate this change and the slight increase in imperviousness

(refer to the Impervious Area Exhibit in Appendix A), the pump will be sized so that it does not discharge the full 100-year flow. A comparison of existing and proposed conditions follows:

Existing flow north (Basins A + B) = 6.8 CFS

Existing flow south (Basins C + D) = 13.9 CFS

Proposed flow north (Basin B) = 4.6 CFS

Proposed flow south (Basins A + C + D) = 18.1 CFS

With the project, flows to the north are reduced and flows to the south would be increased if the flow was allowed to discharge freely (not pumped). The pump will not be sized for the

100-year flow, the underpass will act like a detention pond where water can be stored in large events while the pump “catches up”. The total existing flow from Basins C and D is 13.9 CFS

(the existing flow on the south side of the road). The proposed flow from Basin D is reduced

(10.6 CFS), and the pump will be sized to receive Basins A and C (7.5 CFS) and discharge

3.3 CFS (approximately 1,400 GPM) or less (please refer to Appendix C for the Power Trail

Underpass Hydraulic Pump Calculations). With a maximum pumped flow of 3.3 CFS the total flow south of the project is 13.9 CFS (3.3+10.6) which matches existing conditions for Basins

C and D.

The total area draining to the pump is 0.9 acres. In a 100-year storm (3.67” of rainfall), there will conservatively be 90,000 gallons of water. At the maximum pump flow design of 1,400

GPM, it would take 64 minutes to empty the underpass.

Power Trail – Harmony Underpass Wilson & Company, Inc., Engineers & Architects 15

The 100-year flood will fill the box culvert with approximately 4’ of water if the pump failed.

The City monitors and closes flooded trails routinely. Please refer to Appendix C for the Stage

Storage Table of the box culvert.

4.2 MS-4 Requirements (permanent BMPs)

The project will only add 8,732 SF of additional impervious area and will not trigger permanent

MS-4 requirements. The long, flat existing swales and ponds do provide some water quality for the region, and this small increase in imperviousness is negligible.

4.3 Erosion Control

This site lies within a moderate rainfall and wind erodibility area with an erosion Factor K of

0.28-0.32 and a wind erodibility group rating of 6. Please refer to Appendix D for the Natural

Resources Conservation Service Web Soil Survey information. Potential also exists for tracking of mud onto existing streets which could then wash into existing and proposed storm systems on-site and offsite downstream.

Erosion and sedimentation will be controlled on-site by use of inlet protection, sediment control logs in swales, seeding and mulch. The measures will be designed to limit the overall sediment yield increase due to construction as required by the City of Fort Collins. During grading, the soil will be roughened and furrowed perpendicular to the prevailing winds.

During the performance of the work required by these specifications or any operations appurtenant thereto, whether on right-of-way provided by the City or elsewhere, the contractor shall furnish all labor, equipment, materials, and means required to comply with applicable permits. The Contractor shall conduct proper efficient measures wherever and as necessary to reduce dust nuisance, and to prevent dust nuisance that has originated from his operations from dwellings or causing naissance to persons. The Contractor will be held liable for any damage resulting from dust originating from his operations under these specifications on right-of-way or elsewhere.

Wherever construction vehicles access routes or intersect paved public roads, provisions must be made to minimize the transport of sediment by runoff or vehicles tracking onto the paved surface. The contractor will be responsible for clearing mud tracked onto city streets daily.

All temporary and permanent erosion and sediment control practices must be maintained and repaired as needed to ensure continued performance of their intended function.

Power Trail – Harmony Underpass Wilson & Company, Inc., Engineers & Architects 16

The disturbed area is greater than 1 acre and will require a State of Colorado Discharge

Permit.

5.0 Recommended Design

5.1 Compliance with Standards

This design is in compliance with the City of Fort Collins Stormwater Criteria Manual dated

December 2018 and the Colorado Department of Transportation’s Drainage Design Manual dated 2019.

5.2 Drainage Concept

The main goals of the drainage design are to maintain/improve existing drainage conditions while optimizing proposed drainage conditions.

The proposed design ensures that the Golden Meadows (north) and Oakridge (south)

Regional Detention Ponds receive equal or lesser flow than current conditions.

With Basin A rerouting to the south, Golden Meadows Regional Detention Pond will receive

4.6 CFS as opposed to existing 6.8 CFS. To mitigate the increase of flow to Oakridge Regional

Detention Pond, the pump will be designed with a maximum capacity of 3.3 CFS to maintain a total of 13.9 CFS when combined with flow from Basin D (see Appendix C Power Trail

Hydraulic Pump Calculations sheet 3).

The existing systems include grass lined channels that will provide some water quality treatment. The ultimate outfall for the project will be to the Cache la Poudre River.

6.0 References

1. “Stormwater Criteria Manual”, City of Fort Collins, dated December 2018.

2. City of Fort Collins IDF Curve that was produced in 1999 and presented via Ordinance 42, 1999 to the January 1997 Revised City of Fort Collins “Storm Drainage Design Criteria and

Construction Standards”.

3. “Drainage Design Manual”, Colorado Department of Transportation, 2019.

4. “Urban Storm Drainage Criteria Manual, Volumes I, II and III”, Urban Drainage and Flood

Control District (Mile High Flood District), Latest Revisions.

A

Appendix A – Drainage Exhibits

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Appendix B – Hydrologic Calculations

WILSON COMPANY

EXISTING - DRAINAGE SUMMARY TABLE

Design Tributary Area C (2, 5, & 10) C (25) C (50) C (100) tc (2, 5, & 10) tc (25) tc (50) tc (100) Q(2)tot Q(5)tot Q(10)tot Q(25)tot Q(50)tot Q(100)tot

Sub-basin REMARKS

Point (ac) (min) (min) (min) (min) (cfs) (cfs) (cfs) (cfs) (cfs) (cfs) a A 0.48 0.38 0.42 0.46 0.48 6.4 6.2 6.1 6.0 0.5 0.7 0.8 1.2 1.5 2.1 DRAINS TO EX 12IN FES b B 0.92 0.65 0.71 0.78 0.81 15.7 15.7 15.7 15.7 1.1 1.7 1.9 2.8 3.6 4.7 DRAINS VIA EX SWALE IN MEDIAN TO EX CULVERT c C 0.42 0.62 0.68 0.74 0.77 7.0 6.3 5.6 5.3 0.7 1.0 1.1 1.8 2.3 3.1 DRAINS TO BASIN D d D 2.44 0.57 0.62 0.68 0.71 16.4 16.4 16.4 16.1 2.5 3.6 4.2 6.2 8.1 10.8 DRAINS VIA EX SWALE AND PAN

230706 EX FLOW.xls

B1

ROADSIDE DITCH

RUNOFF COEFFICIENTS & % IMPERVIOUS

LOCATION: POWER TRAIL - HARMONY UNDERPASS - EXISTING CONDITIONS

PROJECT NO: 21-100-223

COMPUTATIONS BY: TTT

DATE: 7/6/2023

All Runoff Coefficient Calculations based on equations from

City of Fort Collins Stormwater Criteria Manual, December 2018 onless otherwise specifiec. Runoff % Recommended Runoff Coefficients from Table 3.2-2 coefficient Impervious Recommended % Impervious from Table 4.1-3

C

Streets, parking lots (asphalt): 0.95 100

Sidewalks (concrete): 0.95 100

Roofs: 0.95 90

Gravel or Pavers: 0.50 40

Landscape Areas (Average, clay) : 0.25 2

Hydrologic Soil Group C

SUBBASIN TOTAL TOTAL ROOF PAVED GRAVEL SIDEWALK LANDSCAPE RUNOFF %

DESIGNATION AREA AREA AREA AREA AREA AREA AREA COEFF. Impervious REMARKS

(ac.) (sq.ft) (sq.ft) (sq.ft) (sq.ft) (sq.ft) (sq.ft) (C)

A 0.48 21,028 0 0 0 3,961 17,067 0.38 20 DRAINS TO EX 12IN FES

B 0.92 40,227 0 22,571 0 177 17,479 0.65 57 DRAINS VIA EX SWALE IN MEDIAN TO EX 30-IN FES

C 0.42 18,217 0 9,409 0 92 8,716 0.62 53 DRAINS TO BASIN D

D 2.44 106,117 0 42,378 0 5,436 58,303 0.57 46 DRAINS VIA EX SWALE AND PAN

Total 4.26 185,589 - 74,358 - 9,666 101,565 0.57 46

Equations

- Calculated C coefficients & % Impervious are area weighted

C = Σ (Ci Ai) / At Equation 5-2

Ci = runoff coefficient for specific area, Ai

Ai = areas of surface with runoff coefficient of Ci n = number of different surfaces to consider

At = total area over which C is applicable; the sum of all Ai's

230706 EX FLOW.xls

B2

ROADSIDE DITCH

STANDARD FORM SF-2

LOCATION: POWER TRAIL - HARMONY UNDERPASS - EXISTING CONDITIONS

PROJECT NO: 21-100-223

COMPUTATIONS BY: TTT

DATE: 7/6/2023

Time of Concentration Calculations based on equations from

2, 5, and 10-yr storm Cf = 1.00 Table3.2-3 City of Fort Collins Stormwater Criteria Manual, December 2018

SUB-BASIN INITIAL /OVERLAND TRAVEL TIME / GUTTER OR CHANNEL FLOW tc CHECK FINAL REMARKS

DATA TIME (ti) (tt) (URBANIZED BASIN) tc

DESIGN SUBBASIN(s) Area C Length Slope ti Length Slope n Vel. tt tc = Total L tc=(L/180)+10

PONIT (ac) (ft) (%) (min) (ft) (%) Manning (ft/s) (min) ti + tt (ft) (min) (min)

Equation 5-5 a A 0.48 0.38 9 2.3 3.1 263 1.5 0.03 1.3 3.3 6.4 272 11.5 6.4 b B 0.92 0.65 12 8.3 1.5 1010 0.6 0.03 0.8 20.3 21.7 1022 15.7 15.7 c C 0.42 0.62 53 1.8 5.4 201 1.7 0.02 2.1 1.6 7.0 254 11.4 7.0 d D 2.44 0.57 55 2.5 5.5 1100 2.0 0.03 1.5 12.1 17.6 1155 16.4 16.4

EQUATIONS:

tc = ti + tt Equation 5-3 ti = [1.87 (1.1 - CCf ) L 0.5

] / S 1/3

Equation 3.3-2 tt = L/Vel. Equation 5-5

V=1.49/n R 2/3

S 1/2

Equation 5-4 Velocity from Manning's Equation with R=0.1 final tc = minimum of ti + tt and urbanized basin check min. tc = 5 min. due to limits of IDF curves

TIME OF CONCENTRATION - 2, 5, and 10 YR

230706 EX FLOW.xls

B3 EXHIBIT C

TIME OF CONCENTRATION - 25 YR

LOCATION: POWER TRAIL - HARMONY UNDERPASS - EXISTING CONDITIONS

PROJECT NO: 21-100-223

COMPUTATIONS BY: TTT

DATE: 7/6/2023

Time of Concentration Calculations based on equations from

25-yr storm Cf = 1.10 Table3.2-3 City of Fort Collins Stormwater Criteria Manual, December 2018

SUB-BASIN INITIAL /OVERLAND TRAVEL TIME / GUTTER OR CHANNEL FLOW tc CHECK FINAL REMARKS

DATA TIME (ti) (tt) (URBANIZED BASIN) tc

DESIGN SUBBASIN(s) Area C C*Cf Length Slope ti Length Slope n Vel. tt tc = Total L tc=(l/180)+10

PONIT (ac) (ft) (%) (min) (ft) (%) Manning (ft/s) (min) ti + tt (ft) (min) (min)

Equation 5-5 a A 0.48 0.38 0.42 9 2.3 2.9 263 1.5 0.03 1.3 3.3 6.2 272 11.5 6.2 b B 0.92 0.65 0.71 12 8.3 1.2 1010 0.6 0.03 0.8 20.3 21.5 1022 15.7 15.7 c C 0.42 0.62 0.68 53 1.8 4.7 201 1.7 0.02 2.1 1.6 6.3 254 11.4 6.3 d D 2.44 0.57 0.62 55 2.5 4.9 1100 2.0 0.03 1.5 12.1 17.0 1155 16.4 16.4

EQUATIONS:

tc = ti + tt Equation 5-3 ti = [1.87 (1.1 - CCf ) L 0.5

] / S 1/3

Equation 3.3-2 tt = L/Vel. Equation 5-5

V=1.49/n R 2/3

S 1/2

Equation 5-4 Velocity from Manning's Equation with R=0.1 final tc = minimum of ti + tt and urbanized basin check min. tc = 5 min. due to limits of IDF curves

B4 EXHIBIT C

TIME OF CONCENTRATION - 50 YR

LOCATION: POWER TRAIL - HARMONY UNDERPASS - EXISTING CONDITIONS

PROJECT NO: 21-100-223

COMPUTATIONS BY: TTT

DATE: 7/6/2023

Time of Concentration Calculations based on equations from

50-yr storm Cf = 1.20 Table3.2-3 City of Fort Collins Stormwater Criteria Manual, December 2018

SUB-BASIN INITIAL /OVERLAND TRAVEL TIME / GUTTER OR CHANNEL FLOW tc CHECK FINAL REMARKS

DATA TIME (ti) (tt) (URBANIZED BASIN) tc

DESIGN SUBBASIN(s) Area C C*Cf Length Slope ti Length Slope n Vel. tt tc = Total L tc=(l/180)+10

PONIT (ac) (ft) (%) (min) (ft) (%) Manning (ft/s) (min) ti + tt (ft) (min) (min)

Equation 5-5 a A 0.48 0.38 0.46 9 2.3 2.7 263 1.5 0.03 1.3 3.3 6.1 272 11.5 6.1 b B 0.92 0.65 0.78 12 8.3 1.0 1010 0.6 0.03 0.8 20.3 21.3 1022 15.7 15.7 c C 0.42 0.62 0.74 53 1.8 4.1 201 1.7 0.02 2.1 1.6 5.6 254 11.4 5.6 d D 2.44 0.57 0.68 55 2.5 4.3 1100 2.0 0.03 1.5 12.1 16.4 1155 16.4 16.4

EQUATIONS:

tc = ti + tt Equation 5-3 ti = [1.87 (1.1 - CCf ) L 0.5

] / S 1/3

Equation 3.3-2 tt = L/Vel. Equation 5-5

V=1.49/n R 2/3

S 1/2

Equation 5-4 Velocity from Manning's Equation with R=0.1 final tc = minimum of ti + tt and urbanized basin check min. tc = 5 min. due to limits of IDF curves

B5 EXHIBIT C

TIME OF CONCENTRATION - 100 YR

LOCATION: POWER TRAIL - HARMONY UNDERPASS - EXISTING CONDITIONS

PROJECT NO: 21-100-223

COMPUTATIONS BY: TTT

DATE: 7/6/2023

Time of Concentration Calculations based on equations from

100-yr storm Cf = 1.25 Table3.2-3 City of Fort Collins Stormwater Criteria Manual, December 2018

SUB-BASIN INITIAL /OVERLAND TRAVEL TIME / GUTTER OR CHANNEL FLOW tc CHECK FINAL REMARKS

DATA TIME (ti) (tt) (URBANIZED BASIN) tc

DESIGN SUBBASIN(s) Area C C*Cf Length Slope ti Length Slope n Vel. tt tc = Total L tc=(l/180)+10

PONIT (ac) (ft) (%) (min) (ft) (%) Manning (ft/s) (min) ti + tt (ft) (min) (min)

Equation 5-5 a A 0.48 0.38 0.48 9 2.3 2.6 263 1.5 0.03 1.3 3.3 6.0 272 11.5 6.0 b B 0.92 0.65 0.81 12 8.3 0.9 1010 0.6 0.03 0.8 20.3 21.2 1022 15.7 15.7 c C 0.42 0.62 0.77 53 1.8 3.7 201 1.7 0.02 2.1 1.6 5.3 254 11.4 5.3 d D 2.44 0.57 0.71 55 2.5 4.0 1100 2.0 0.03 1.5 12.1 16.1 1155 16.4 16.1

EQUATIONS:

tc = ti + tt Equation 5-3 ti = [1.87 (1.1 - CCf ) L 0.5

] / S 1/3

Equation 3.3-2 tt = L/Vel. Equation 5-5

V=1.49/n R 2/3

S 1/2

Equation 5-4 Velocity from Manning's Equation with R=0.1 final tc = minimum of ti + tt and urbanized basin check min. tc = 5 min. due to limits of IDF curves

B6 EXHIBIT C

RATIONAL METHOD PEAK RUNOFF

(City of Fort Collins, 2-Yr Storm)

LOCATION: POWER TRAIL - HARMONY UNDERPASS - EXISTING CONDITIONS

PROJECT NO: 21-100-223

COMPUTATIONS BY: TTT

DATE: 7/6/2023

Rational Method Calculations based on equation from

2 yr storm, Cf = 1.00 City of Fort Collins Stormwater Criteria Manual, December 2018

DIRECT RUNOFF CARRY OVER TOTAL REMARKS

Design Tributary A C Cf tc i Q (2) from Q (2) Q(2)tot

Sub-basin Design

Point (ac) (min) (in/hr) (cfs) Point (cfs) (cfs) a A 0.48 0.38 6.4 2.6 0.5 0.5 b B 0.92 0.65 15.7 1.8 1.1 1.1 c C 0.42 0.62 7.0 2.5 0.7 0.7 d D 2.44 0.57 16.4 1.8 2.5 2.5

Q = Cf C iA Equation 5-1

Q = peak discharge (cfs)

C = runoff coefficient

Cf = frequency adjustment factor i = rainfall intensity (in/hr) from City of Fort Collins IDF curve, Figure 3.4-1

A = drainage area (acres)

B7 EXHIBIT C

(City of Fort Collins, 5-Yr Storm)

LOCATION: POWER TRAIL - HARMONY UNDERPASS - EXISTING CONDITIONS

PROJECT NO: 21-100-223

COMPUTATIONS BY: TTT

DATE: 7/6/2023

Rational Method Calculations based on equation from

5 yr storm, Cf = 1.00 City of Fort Collins Stormwater Criteria Manual, December 2018

DIRECT RUNOFF CARRY OVER TOTAL REMARKS

Design Tributary A C Cf tc i Q (5) from Q (5) Q(5)tot

Sub-basin Design

Point (ac) (min) (in/hr) (cfs) Point (cfs) (cfs) a A 0.48 0.38 6.4 3.8 0.7 0.7 b B 0.92 0.65 15.7 2.8 1.7 1.7 c C 0.42 0.62 7.0 3.7 1.0 1.0 d D 2.44 0.57 16.4 2.6 3.6 3.6

Q = Cf C iA Equation 5-1

Q = peak discharge (cfs)

C = runoff coefficient

Cf = frequency adjustment factor i = rainfall intensity (in/hr) from City of Fort Collins IDF curve, Figure 3-1 from 1999 IDF Curve

A = drainage area (acres)

B8 EXHIBIT C

(City of Fort Collins, 10-Yr Storm)

LOCATION: POWER TRAIL - HARMONY UNDERPASS - EXISTING CONDITIONS

PROJECT NO: 21-100-223

COMPUTATIONS BY: TTT

DATE: 7/6/2023

Rational Method Calculations based on equation from

10 yr storm, Cf = 1.00 City of Fort Collins Stormwater Criteria Manual, December 2018

DIRECT RUNOFF CARRY OVER TOTAL REMARKS

Design Tributary A C Cf tc i Q (10) from Q (10) Q(10)tot

Sub-basin Design

Point (ac) (min) (in/hr) (cfs) Point (cfs) (cfs) a A 0.48 0.38 6.4 4.5 0.8 0.8 b B 0.92 0.65 15.7 3.1 1.9 1.9 c C 0.42 0.62 7.0 4.3 1.1 1.1 d D 2.44 0.57 16.4 3.0 4.2 4.2

Q = Cf C iA Equation 5-1

Q = peak discharge (cfs)

C = runoff coefficient

Cf = frequency adjustment factor i = rainfall intensity (in/hr) from City of Fort Collins IDF curve, Figure 3.4-1

A = drainage area (acres)

B9 EXHIBIT C

(City of Fort Collins, 25-Yr Storm)

LOCATION: POWER TRAIL - HARMONY UNDERPASS - EXISTING CONDITIONS

PROJECT NO: 21-100-223

COMPUTATIONS BY: TTT

DATE: 7/6/2023

Rational Method Calculations based on equation from

25 yr storm, Cf = 1.10 City of Fort Collins Stormwater Criteria Manual, December 2018

DIRECT RUNOFF CARRY OVER TOTAL REMARKS

Des. Area A C Cf tc i Q (25) from Q (25) Q(25)tot

Design

Point Design. (ac) (min) (in/hr) (cfs) Point (cfs) (cfs) a A 0.48 0.42 6.0 5.8 1.2 1.2 b B 0.92 0.71 15.7 4.2 2.8 2.8 c C 0.42 0.68 5.3 6.2 1.8 1.8 d D 2.44 0.62 16.1 4.1 6.2 6.2

Q = C iA Equation 5-1

Q = peak discharge (cfs)

C = runoff coefficient i = rainfall intensity (in/hr) from City of Fort Collins IDF curve, Figure 3-1 from 1999 IDF Curve

A = drainage area (acres)

B10 EXHIBIT C

(City of Fort Collins, 50-Yr Storm)

LOCATION: POWER TRAIL - HARMONY UNDERPASS - EXISTING CONDITIONS

PROJECT NO: 21-100-223

COMPUTATIONS BY: TTT

DATE: 7/6/2023

Rational Method Calculations based on equation from

50 yr storm, Cf = 1.20 City of Fort Collins Stormwater Criteria Manual, December 2018

DIRECT RUNOFF CARRY OVER TOTAL REMARKS

Des. Area A C Cf tc i Q (50) from Q (50) Q(50)tot

Design

Point Design. (ac) (min) (in/hr) (cfs) Point (cfs) (cfs) a A 0.48 0.46 6.0 6.9 1.5 1.5 b B 0.92 0.78 15.7 5.0 3.6 3.6 c C 0.42 0.74 5.3 7.3 2.3 2.3 d D 2.44 0.68 16.1 4.9 8.1 8.1

Q = C iA Equation 5-1

Q = peak discharge (cfs)

C = runoff coefficient i = rainfall intensity (in/hr) from City of Fort Collins IDF curve, Figure 3-1 from 1999 IDF Curve

A = drainage area (acres)

B11 EXHIBIT C

(City of Fort Collins, 100-Yr Storm)

LOCATION: POWER TRAIL - HARMONY UNDERPASS - EXISTING CONDITIONS

PROJECT NO: 21-100-223

COMPUTATIONS BY: TTT

DATE: 7/6/2023

Rational Method Calculations based on equation from

100 yr storm, Cf = 1.25 City of Fort Collins Stormwater Criteria Manual, December 2018

DIRECT RUNOFF CARRY OVER TOTAL REMARKS

Des. Area A C Cf tc i Q (100) from Q (100) Q(100)tot

Design

Point Design. (ac) (min) (in/hr) (cfs) Point (cfs) (cfs) a A 0.48 0.48 6.0 9.29 2.1 2.1 b B 0.92 0.81 15.7 6.36 4.7 4.7 c C 0.42 0.77 5.3 9.61 3.1 3.1 d D 2.44 0.71 16.1 6.28 10.8 10.8

Q = C iA Equation 5-1

Q = peak discharge (cfs)

C = runoff coefficient i = rainfall intensity (in/hr) from City of Fort Collins IDF curve, Figure 3.4-1

A = drainage area (acres)

B12 EXHIBIT C

Interwest Consulting Group

PROPOSED - DRAINAGE SUMMARY TABLE

Design Tributary Area C (2, 5, & 10) C (25) C (50) C (100) tc (2, 5, & 10) tc (25) tc (50) tc (100) Q(2)tot Q(5)tot Q(10)tot Q(25)tot Q(50)tot Q(100)tot

Sub-basin REMARKS

Point (ac) (min) (min) (min) (min) (cfs) (cfs) (cfs) (cfs) (cfs) (cfs) a A 0.48 0.58 0.64 0.70 0.72 7.1 6.5 5.9 5.7 0.7 1.0 1.2 1.8 2.3 3.3 Pumped from Box Culvert b B 0.92 0.63 0.69 0.75 0.79 15.9 15.9 15.9 15.9 1.1 1.5 1.8 2.6 3.4 4.6 North to Existing Swale c C 0.42 0.86 0.94 1.00 1.00 5.0 5.0 5.0 5.0 1.0 1.4 1.7 2.5 3.2 4.2 Pumped from Box Culvert d D 2.44 0.55 0.61 0.66 0.69 16.0 16.0 16.0 16.0 2.4 3.4 4.1 6.0 7.8 10.6 South to Existing Swale

230706 PROP FLOW.xls

B13 EXHIBIT C

RUNOFF COEFFICIENTS & % IMPERVIOUS

LOCATION: POWER TRAIL - HARMONY UNDERPASS - PROPOSED

PROJECT NO: 21-100-223

COMPUTATIONS BY: TTT

DATE: 7/6/2023

Runoff Coefficient Calculations based on equations from

City of Fort Collins Stormwater Criteria Manual, December 2018

Hydrologic Soil Group C Runoff % Recommended Runoff Coefficients from Table 3.2-2 coefficient Impervious Recommended % Impervious from Table 4.1-3

C

Streets, parking lots (asphalt): 0.95 100

Sidewalks (concrete): 0.95 100

Roofs: 0.95 90

Gravel or Pavers: 0.50 40

Landscape Areas (Average, clay) : 0.25 2

SUBBASIN TOTAL TOTAL ROOF PAVED GRAVEL SIDEWALK LANDSCAPE RUNOFF %

DESIGNATION AREA AREA AREA AREA AREA AREA AREA COEFF. Impervious REMARKS

(ac.) (sq.ft) (sq.ft) (sq.ft) (sq.ft) (sq.ft) (sq.ft) (C)

A 0.48 21,028 0 0 0 9,902 11,126 0.58 48

B 0.92 40,227 0 21,726 0 0 18,501 0.63 55

C 0.42 18,217 0 9,480 0 6,312 2,425 0.86 87

D 2.44 106,117 0 40,068 0 5,445 60,604 0.55 44

Total 4.26 185,589 - 71,275 - 21,658 92,656 0.60 51

Equations

- Calculated C coefficients & % Impervious are area weighted

C = Σ (Ci Ai) / At Equation 5-2

Ci = runoff coefficient for specific area, Ai

Ai = areas of surface with runoff coefficient of Ci n = number of different surfaces to consider

At = total area over which C is applicable; the sum of all Ai's

B14 EXHIBIT C

LOCATION: POWER TRAIL - HARMONY UNDERPASS - PROPOSED

PROJECT NO: 21-100-223

COMPUTATIONS BY: TTT

DATE: 7/6/2023

Time of Concentration Calculations based on equations from

2, 5, and 10-yr storm Cf = 1.00 Table3.2-3 City of Fort Collins Stormwater Criteria Manual, December 2018

SUB-BASIN INITIAL /OVERLAND TRAVEL TIME / GUTTER OR CHANNEL FLOW tc CHECK FINAL REMARKS

DATA TIME (ti) (tt) (URBANIZED BASIN) tc

DESIGN SUBBASIN(s) Area C Length Slope ti Length Slope n Vel. tt tc = Total L tc=(L/180)+10

PONIT (ac) (ft) (%) (min) (ft) (%) Manning (ft/s) (min) ti + tt (ft) (min) (min)

Equation 5-5 a A 0.48 0.58 26 1.0 5.0 272 4.1 0.03 2.2 2.1 7.1 298 11.7 7.1 b B 0.92 0.63 11 8.9 1.4 1050 0.5 0.03 0.8 23.1 24.5 1061 15.9 15.9 c C 0.42 0.86 63 2.9 2.5 166 6.6 0.03 2.8 1.0 3.5 229 11.3 5.0 d D 2.44 0.55 58 2.2 6.0 1024 0.9 0.03 1.0 16.6 22.7 1082 16.0 16.0

EQUATIONS:

tc = ti + tt Equation 5-3 ti = [1.87 (1.1 - CCf ) L 0.5

] / S 1/3

Equation 3.3-2 tt = L/Vel. Equation 5-5

V=1.49/n R 2/3

S 1/2

Equation 5-4 Velocity from Manning's Equation with R=0.1 final tc = minimum of ti + tt and urbanized basin check min. tc = 5 min. due to limits of IDF curves

TIME OF CONCENTRATION - 2, 5, and 10 YR

B15 EXHIBIT C

TIME OF CONCENTRATION - 25 YR

LOCATION: POWER TRAIL - HARMONY UNDERPASS - PROPOSED

PROJECT NO: 21-100-223

COMPUTATIONS BY: TTT

DATE: 7/6/2023

Time of Concentration Calculations based on equations from

25-yr storm Cf = 1.10 Table3.2-3 City of Fort Collins Stormwater Criteria Manual, December 2018

SUB-BASIN INITIAL /OVERLAND TRAVEL TIME / GUTTER OR CHANNEL FLOW tc CHECK FINAL REMARKS

DATA TIME (ti) (tt) (URBANIZED BASIN) tc

DESIGN SUBBASIN(s) Area C C*Cf Length Slope ti Length Slope n Vel. tt tc = Total L tc=(l/180)+10

PONIT (ac) (ft) (%) (min) (ft) (%) Manning (ft/s) (min) ti + tt (ft) (min) (min)

Equation 5-5 a A 0.48 0.58 0.64 26 1.0 4.4 272 4.1 0.03 2.2 2.1 6.5 298 11.7 6.5 b B 0.92 0.63 0.69 11 8.9 1.2 1050 0.5 0.03 0.8 23.1 24.3 1061 15.9 15.9 c C 0.42 0.86 0.94 63 2.9 1.6 166 6.6 0.03 2.8 1.0 2.6 229 11.3 5.0 d D 2.44 0.55 0.61 58 2.2 5.4 1024 0.9 0.03 1.0 16.6 22.0 1082 16.0 16.0

EQUATIONS:

tc = ti + tt Equation 5-3 ti = [1.87 (1.1 - CCf ) L 0.5

] / S 1/3

Equation 3.3-2 tt = L/Vel. Equation 5-5

V=1.49/n R 2/3

S 1/2

Equation 5-4 Velocity from Manning's Equation with R=0.1 final tc = minimum of ti + tt and urbanized basin check min. tc = 5 min. due to limits of IDF curves

B16 EXHIBIT C

TIME OF CONCENTRATION - 50 YR

LOCATION: POWER TRAIL - HARMONY UNDERPASS - PROPOSED

PROJECT NO: 21-100-223

COMPUTATIONS BY: TTT

DATE: 7/6/2023

Time of Concentration Calculations based on equations from

50-yr storm Cf = 1.20 Table3.2-3 City of Fort Collins Stormwater Criteria Manual, December 2018

SUB-BASIN INITIAL /OVERLAND TRAVEL TIME / GUTTER OR CHANNEL FLOW tc CHECK FINAL REMARKS

DATA TIME (ti) (tt) (URBANIZED BASIN) tc

DESIGN SUBBASIN(s) Area C C*Cf Length Slope ti Length Slope n Vel. tt tc = Total L tc=(l/180)+10

PONIT (ac) (ft) (%) (min) (ft) (%) Manning (ft/s) (min) ti + tt (ft) (min) (min)

Equation 5-5 a A 0.48 0.58 0.70 26 1.0 3.9 272 4.1 0.03 2.2 2.1 5.9 298 11.7 5.9 b B 0.92 0.63 0.75 11 8.9 1.1 1050 0.5 0.03 0.8 23.1 24.1 1061 15.9 15.9 c C 0.42 0.86 1.00 63 2.9 1.0 166 6.6 0.03 2.8 1.0 2.0 229 11.3 5.0 d D 2.44 0.55 0.66 58 2.2 4.8 1024 0.9 0.03 1.0 16.6 21.4 1082 16.0 16.0

EQUATIONS:

tc = ti + tt Equation 5-3 ti = [1.87 (1.1 - CCf ) L 0.5

] / S 1/3

Equation 3.3-2 tt = L/Vel. Equation 5-5

V=1.49/n R 2/3

S 1/2

Equation 5-4 Velocity from Manning's Equation with R=0.1 final tc = minimum of ti + tt and urbanized basin check min. tc = 5 min. due to limits of IDF curves

B17 EXHIBIT C

TIME OF CONCENTRATION - 100 YR

LOCATION: POWER TRAIL - HARMONY UNDERPASS - PROPOSED

PROJECT NO: 21-100-223

COMPUTATIONS BY: TTT

DATE: 7/6/2023

Time of Concentration Calculations based on equations from

100-yr storm Cf = 1.25 Table3.2-3 City of Fort Collins Stormwater Criteria Manual, December 2018

SUB-BASIN INITIAL /OVERLAND TRAVEL TIME / GUTTER OR CHANNEL FLOW tc CHECK FINAL REMARKS

DATA TIME (ti) (tt) (URBANIZED BASIN) tc

DESIGN SUBBASIN(s) Area C C*Cf Length Slope ti Length Slope n Vel. tt tc = Total L tc=(l/180)+10

PONIT (ac) (ft) (%) (min) (ft) (%) Manning (ft/s) (min) ti + tt (ft) (min) (min)

Equation 5-5 a A 0.48 0.58 0.72 26 1.0 3.6 272 4.1 0.03 2.2 2.1 5.7 298 11.7 5.7 b B 0.92 0.63 0.79 11 8.9 1.0 1050 0.5 0.03 0.8 23.1 24.1 1061 15.9 15.9 c C 0.42 0.86 1.00 63 2.9 1.0 166 6.6 0.03 2.8 1.0 2.0 229 11.3 5.0 d D 2.44 0.55 0.69 58 2.2 4.5 1024 0.9 0.03 1.0 16.6 21.1 1082 16.0 16.0

EQUATIONS:

tc = ti + tt Equation 5-3 ti = [1.87 (1.1 - CCf ) L 0.5

] / S 1/3

Equation 3.3-2 tt = L/Vel. Equation 5-5

V=1.49/n R 2/3

S 1/2

Equation 5-4 Velocity from Manning's Equation with R=0.1 final tc = minimum of ti + tt and urbanized basin check min. tc = 5 min. due to limits of IDF curves

B18 EXHIBIT C

(City of Fort Collins, 2-Yr Storm)

LOCATION: POWER TRAIL - HARMONY UNDERPASS - PROPOSED

PROJECT NO: 21-100-223

COMPUTATIONS BY: TTT

DATE: 7/6/2023

Rational Method Calculations based on equation from

2 yr storm, Cf = 1.00 City of Fort Collins Stormwater Criteria Manual, December 2018

DIRECT RUNOFF CARRY OVER TOTAL REMARKS

Design Tributary A C Cf tc i Q (2) from Q (2) Q(2)tot

Sub-basin Design

Point (ac) (min) (in/hr) (cfs) Point (cfs) (cfs) a A 0.48 0.58 7.1 2.53 0.7 0.7 b B 0.92 0.63 15.9 1.81 1.1 1.1 c C 0.42 0.86 5.0 2.85 1.0 1.0 d D 2.44 0.55 16.0 1.81 2.4 2.4

Q = Cf C iA Equation 5-1

Q = peak discharge (cfs)

C = runoff coefficient

Cf = frequency adjustment factor i = rainfall intensity (in/hr) from City of Fort Collins IDF curve, Figure 3.4-1

A = drainage area (acres)

B19 EXHIBIT C

(City of Fort Collins, 5-Yr Storm)

LOCATION: POWER TRAIL - HARMONY UNDERPASS - PROPOSED

PROJECT NO: 21-100-223

COMPUTATIONS BY: TTT

DATE: 7/6/2023

Rational Method Calculations based on equation from

5 yr storm, Cf = 1.00 City of Fort Collins Stormwater Criteria Manual, December 2018

DIRECT RUNOFF CARRY OVER TOTAL REMARKS

Design Tributary A C Cf tc i Q (5) from Q (5) Q(5)tot

Sub-basin Design

Point (ac) (min) (in/hr) (cfs) Point (cfs) (cfs) a A 0.48 0.58 7.1 3.7 1.0 1.0 b B 0.92 0.63 15.9 2.6 1.5 1.5 c C 0.42 0.86 5.0 4.0 1.4 1.4 d D 2.44 0.55 16.0 2.6 3.4 3.4

Q = Cf C iA Equation 5-1

Q = peak discharge (cfs)

C = runoff coefficient

Cf = frequency adjustment factor i = rainfall intensity (in/hr) from City of Fort Collins IDF curve, Figure 3-1 from 1999 IDF Curve

A = drainage area (acres)

B20 EXHIBIT C

(City of Fort Collins, 10-Yr Storm)

LOCATION: POWER TRAIL - HARMONY UNDERPASS - PROPOSED

PROJECT NO: 21-100-223

COMPUTATIONS BY: TTT

DATE: 7/6/2023

Rational Method Calculations based on equation from

10 yr storm, Cf = 1.00 City of Fort Collins Stormwater Criteria Manual, December 2018

DIRECT RUNOFF CARRY OVER TOTAL REMARKS

Design Tributary A C Cf tc i Q (10) from Q (10) Q(10)tot

Sub-basin Design

Point (ac) (min) (in/hr) (cfs) Point (cfs) (cfs) a A 0.48 0.58 7.1 4.32 1.2 1.2 b B 0.92 0.63 15.9 3.09 1.8 1.8 c C 0.42 0.86 5.0 4.87 1.7 1.7 d D 2.44 0.55 16.0 3.08 4.1 4.1

Q = Cf C iA Equation 5-1

Q = peak discharge (cfs)

C = runoff coefficient

Cf = frequency adjustment factor i = rainfall intensity (in/hr) from City of Fort Collins IDF curve, Figure 3.4-1

A = drainage area (acres)

B21 EXHIBIT C

(City of Fort Collins, 25-Yr Storm)

LOCATION: POWER TRAIL - HARMONY UNDERPASS - PROPOSED

PROJECT NO: 21-100-223

COMPUTATIONS BY: TTT

DATE: 7/6/2023

Rational Method Calculations based on equation from

25 yr storm, Cf = 1.10 City of Fort Collins Stormwater Criteria Manual, December 2018

DIRECT RUNOFF CARRY OVER TOTAL REMARKS

Des. Area A C Cf tc i Q (25) from Q (25) Q(25)tot

Design

Point Design. (ac) (min) (in/hr) (cfs) Point (cfs) (cfs) a A 0.48 0.64 5.7 5.7 1.8 1.8 b B 0.92 0.69 15.9 4.0 2.6 2.6 c C 0.42 0.94 5.0 6.3 2.5 2.5 d D 2.44 0.61 16.0 4.0 6.0 6.0

Q = C iA Equation 5-1

Q = peak discharge (cfs)

C = runoff coefficient i = rainfall intensity (in/hr) from City of Fort Collins IDF curve, Figure 3-1 from 1999 IDF Curve

A = drainage area (acres)

B22 EXHIBIT C

(City of Fort Collins, 50-Yr Storm)

LOCATION: POWER TRAIL - HARMONY UNDERPASS - PROPOSED

PROJECT NO: 21-100-223

COMPUTATIONS BY: TTT

DATE: 7/6/2023

Rational Method Calculations based on equation from

50 yr storm, Cf = 1.20 City of Fort Collins Stormwater Criteria Manual, December 2018

DIRECT RUNOFF CARRY OVER TOTAL REMARKS

Des. Area A C Cf tc i Q (50) from Q (50) Q(50)tot

Design

Point Design. (ac) (min) (in/hr) (cfs) Point (cfs) (cfs) a A 0.48 0.70 5.7 6.9 2.3 2.3 b B 0.92 0.75 15.9 4.9 3.4 3.4 c C 0.42 1.00 5.0 7.6 3.2 3.2 d D 2.44 0.66 16.0 4.9 7.8 7.8

Q = C iA Equation 5-1

Q = peak discharge (cfs)

C = runoff coefficient i = rainfall intensity (in/hr) from City of Fort Collins IDF curve, Figure 3-1 from 1999 IDF Curve

A = drainage area (acres)

B23 EXHIBIT C

(City of Fort Collins, 100-Yr Storm)

LOCATION: POWER TRAIL - HARMONY UNDERPASS - PROPOSED

PROJECT NO: 21-100-223

COMPUTATIONS BY: TTT

DATE: 7/6/2023

Rational Method Calculations based on equation from

100 yr storm, Cf = 1.25 City of Fort Collins Stormwater Criteria Manual, December 2018

DIRECT RUNOFF CARRY OVER TOTAL REMARKS

Des. Area A C Cf tc i Q (100) from Q (100) Q(100)tot

Design

Point Design. (ac) (min) (in/hr) (cfs) Point (cfs) (cfs) a A 0.48 0.72 5.7 9.43 3.3 3.3 b B 0.92 0.79 15.9 6.32 4.6 4.6 c C 0.42 1.00 5.0 9.95 4.2 4.2 d D 2.44 0.69 16.0 6.30 10.6 10.6

Q = C iA Equation 5-1

Q = peak discharge (cfs)

C = runoff coefficient i = rainfall intensity (in/hr) from City of Fort Collins IDF curve, Figure 3.4-1

A = drainage area (acres)

B24 EXHIBIT C

B25 EXHIBIT C

B26 EXHIBIT C

B27

C

Appendix C – Hydraulic Calculations

Wilson Company

Inlet Flow Calculation for Area Inlets Project: Powertrail Basin B

Job Number : 21-100-223-00

Calculations by : ES

Date : 8/26/2024

Objective: to find the number of grates required for area inlets in grassy areas December 2018, Fort Collins Stormwater Criteria Manual, Chapter 9

Geometry at inlet :

Width (W): 2.92 feet

Length (L): 2.92 feet

Opening Ratio (R): 0.7 sq ft/sq ft

Reduction Factor (F): 50%

Grate Flow:

Use the orifice equation Qi = C*A*SQRT(2*g*H) to find the ideal inlet capacity.*

C = Orifice discharge coefficient= 0.6

A = Orifice area (ft ) - open area of grate g = gravitational constant = 32.2 ft/s d = head on grate centroid, ponding depth (feet)

Then multiply by the reduction factor for the allowable capacity.

QG = Qi * (1-F)

DP b

Q = 4.6 cfs d = 0.5 ft

Type C Inlet

A = W*L*R

= 5.97 ft

Qi = C*A*SQRT(2*g*d)

= 20.32 cfs

QG = Qi * F

= 10.16 cfs ok, > 4.6 CFS

USE : Type C Inlet (MINIMUM SIZE FOR THE INLET, TYPE D INLET IS CONSIDERED TO BE TWO TYPE C INLETS)

Grate Dimensions and information:

WSEL

Page1 C1

Wilson Company

Page2C2

Scenario: 100-yr

P1

FES

TYPE C INLET DP b

MH-1

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StormCAD [10.04.00.158]Bentley Systems, Inc. Haestad Methods Solution CenterBasin B CAD.stsw

C3

D

Conduit FlexTable: Combined Pipe/Node Report Energy Grade

Line (Out) (ft)

Energy Grade Line (In)

(ft)

Hydraulic Grade Line

(Out) (ft)

Hydraulic Grade Line

(In) (ft)

Velocity (ft/s)

Flow (cfs)

Invert (Stop) (ft)

Stop NodeInvert (Start) (ft)

Start NodeMaterialSpan (ft)

Rise (ft)

Section TypeManning's nLabel

4,970.954,971.044,970.824,970.922.831.104,970.59MH-14,970.50FESConcrete1.91.2Ellipse0.013P1

4,971.074,971.524,971.014,971.412.821.104,971.08TYPE C INLET DP b4,970.59MH-1Concrete1.91.2Ellipse0.013P2

Page 1 of 176 Watertown Road, Suite 2D Thomaston, CT 06787 USA +1-203-755-16668/1/2023

StormCAD [10.04.00.158]Bentley Systems, Inc. Haestad Methods Solution CenterBasin B CAD 2yr.stsw

C4

2-YR

Profile Report

Engineering Profile - Profile - 1 (Basin B CAD 2yr.stsw)

4,970.00

4,975.00

-0+50 0+00 0+50 1+00 1+50

Station (ft)

E le v a ti o n ft

MH-1

Rim: 4,973.03 ft Invert: 4,970.59 ft

TYPE C INLET DP b Rim: 4,973.48 ft Invert: 4,971.08 ftFES

Rim: 4,971.63 ft Invert: 4,970.50 ft

P2: 97.7 ft @ -0.005 ft/ft

Ellipse - 1.9 x 1.2 ft Concrete P1: 18.0 ft @ -0.005 ft/ft

Ellipse - 1.9 x 1.2 ft Concrete

Page 1 of 176 Watertown Road, Suite 2D Thomaston, CT 06787 USA +1-203- 755-1666

8/1/2023

StormCAD [10.04.00.158]Bentley Systems, Inc. Haestad Methods Solution CenterBasin B CAD 2yr.stsw

C5

Conduit FlexTable: Combined Pipe/Node Report Energy Grade

Line (Out) (ft)

Energy Grade Line (In)

(ft)

Hydraulic Grade Line

(Out) (ft)

Hydraulic Grade Line

(In) (ft)

Velocity (ft/s)

Flow (cfs)

Invert (Stop) (ft)

Stop NodeInvert (Start) (ft)

Start NodeMaterialSpan (ft)

Rise (ft)

Section TypeManning's nLabel

4,971.484,971.574,971.184,971.284.404.604,970.59MH-14,970.50FESConcrete1.91.2Ellipse0.013P1

4,971.664,972.064,971.514,971.774.404.604,971.08TYPE C INLET DP b4,970.59MH-1Concrete1.91.2Ellipse0.013P2

Page 1 of 176 Watertown Road, Suite 2D Thomaston, CT 06787 USA +1-203-755-16668/1/2023

StormCAD [10.04.00.158]Bentley Systems, Inc. Haestad Methods Solution CenterBasin B CAD 100yr.stsw

C6

100-YR

Profile Report

Engineering Profile - Profile - 1 (Basin B CAD 100yr.stsw)

4,970.00

4,975.00

-0+50 0+00 0+50 1+00 1+50

Station (ft)

E le v a ti o n ft

MH-1

Rim: 4,973.03 ft Invert: 4,970.59 ft

TYPE C INLET DP b Rim: 4,973.48 ft Invert: 4,971.08 ftFES

Rim: 4,971.63 ft Invert: 4,970.50 ft

P2: 97.7 ft @ -0.005 ft/ft

Ellipse - 1.9 x 1.2 ft Concrete P1: 18.0 ft @ -0.005 ft/ft

Ellipse - 1.9 x 1.2 ft Concrete

Page 1 of 176 Watertown Road, Suite 2D Thomaston, CT 06787 USA +1-203- 755-1666

8/1/2023

StormCAD [10.04.00.158]Bentley Systems, Inc. Haestad Methods Solution CenterBasin B CAD 100yr.stsw

C7

Culvert Calculator Report

2-15" RCP

m:\...\culvertmaster\2 15in culvert.cvm

08/26/24 11:51:58 AM

Wilson & Co

© Bentley Systems, Incorporated Haestad Methods Solution Center Watertown, CT 06795 USA +1-203-755-1666

Project Engineer: EDSchneider@wilsonco.com

CulvertMaster v10.3 [10.03.00.03]

So…