CO FLAP LPL 10(1) Lake Nighthorse Access Final Hydraulics Report.pdf

CENTRAL FEDERAL LANDS

LAKE NIGHTHORSE

100-PERCENT HYDRAULICS REPORT

LA PLATA COUNTY, COLORADO

APRIL 03, 2025

LAKE NIGHTHORSE

100-PERCENT

HYDRAULICS REPORT

LA PLATA COUNTY,

COLORADO

CENTRAL FEDERAL LANDS

FINAL

PROJECT NO.: 73012219.

DATE: APRIL 03, 2025

WSP USA ENVIRONMENT & INFRASTRUCTURE INC.

2000 S. COLORADO BLVD., SUITE. 2-1000

DENVER, CO 80222

T: 303-935-65051

WSP.COM

Lake Nighthorse 100-Percent Hydraulics Report Project No. 73012219.

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EXECUTIVE SUMMARY

Hydrologic and hydraulic analyses were conducted for the Lake Nighthorse project located in La Plata County, CO. The hydraulic design frequencies are the 50-year flood for culvert design and the 10-year flood for roadside ditch capacity and stability.

The design flows were estimated using rainfall-runoff analyses (USACE, 2023). Hydraulic performance for each cross culvert was evaluated using HY-8 (FHWA, 2022).

The ditch design was evaluated using Bentley FlowMaster (2020 Bentley Systems) and includes both grass-lined and paved sections as necessary to avoid underground utilities and to maintain compliance with CFL criteria.

A Hydrodynamic Separator is included in the design to manage runoff that flows over the proposed paved parking lot. Table 1 summarizes the existing conditions and proposed upgrades for ten existing cross culvert locations and two new cross culvert locations (Abbreviations: CMP – Corrugated Metal Pipe). See Figure 1 for an overview of the project location.

Table 1: Culvert Summary Matrix

LOCATION STATION EXISTING CONDITIONS PROPOSED UPGRADES

Culvert 1 100+30 Single 36’’ CMP Flush culvert Culvert 2 103+52 Single 24’’ CMP Flush culvert Culvert 3 107+87 Single 36’’ Double Broken-back

CMP

Flush culvert

Culvert 4 109+83 Single 42’’ Double Broken-back

CMP

Plug and abandon

Culvert 5 113+72 Single 36’’ CMP Flush Culvert and add riprap Culvert 10 115+11 Buried – Conditions Unknown Replace with 25” CMP Culvert and add riprap Culvert 6 117+26 Single 24’’ CMP Flush Culvert and add riprap Culvert 7 120+00 Single 24’’ CMP Plug and abandon Culvert 8 124+62 Single 24’’ CMP Flush Culvert Culvert 9 130+72 Single 60’’ CMP Flush Culvert Culvert 11 120+00 N/A (no existing culvert) Install new single 24” CMP and add riprap Culvert 12 0+591 N/A (no existing culvert) Install new Single 36” CMP and add riprap

1. Station 0+59 refers to the stationing used for the Overflow Parking Lot Access Road.

The following is a summary of the proposed drainage upgrades:

Flush (clean) and reuse existing Culverts 1, 2, 3, 5, 6, 8 and 9;

Plug and abandon Culverts 4 and 7;

Install new 24” CMP Culvert 10 at Station 115+11 to replace buried culvert;

Install new 24” CMP Culvert 11 at Station 120+00 to carry flows from abandoned Culvert 7;

Install new 36” CMP Culvert 12 at Station 0+59 near bottom of parking lot driveway, to reroute all flows previously entering Culvert 4 under the parking lot towards Culvert 3; and

Install storm sewer and catchbasin manholes within parking lot to re-route all parking lot flow through storm system, into a Hydrodynamic Separator and finally into Culvert 3 before re-entering the lake.

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Figure 1: Project Location Map

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TABLE OF

CONTENTS

1 PROJECT BACKGROUND

INFORMATION

2 HYDROLOGY

2.1 Hydrologic Setting

2.2 Available Hydrologic Data

2.3 FEMA Flood Insurance Study

3 DETERMINATION OF DESIGN

DISCHARGE

3.1 Hydraulic Design Criteria

3.1.1 Drainage Basin Delineations

3.1.2 Soils and Land Cover

3.1.3 Rainfall Data

3.1.4 Loss Methodology

3.1.5 Subbasin Lag Time

3.1.6 Transform Methodology

3.1.7 Summary of Hydrologic Parameters

3.2 Design Peak FLows

4 EXISTING CONDITIONS HYDRAULICS

ANALYSES

4.1 Cross Culverts

5 PROPOSED CONDITIONS HYDRAULICS

ANALYSES

5.1 Existing Cross Culverts (to be reused)

5.2 New Cross Culverts

5.3 Roadside Ditches

5.4 Proposed Scour Countermeasures

5.4.1 Proposed Culvert Outlet Protection

5.4.2 Proposed Ditch Scour Countermeasures

5.5 Parking Lot Drainage

5.5.1 Inlet Drainage Design

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5.5.2 Hydrodynamic Separator Design

6 REFERENCES

TABLES

TABLE 1: CULVERT SUMMARY MATRIX .......................................... III

TABLE 2: DESIGN CRITERIA

TABLE 3: HYDROLOGIC PARAMETERS FOR THE

DETERMINATION OF DESIGN

FLOWS

TABLE 4: CURVE NUMBER AND LAG TIME FOR

HEC-HMS SUBBASINS

TABLE 5: PEAK FLOWS AS ESTIMATED USING

RAINFALL-RUNOFF MODELING

FOR EXISTING CONDITIONS

TABLE 6: PEAK FLOWS AS ESTIMATED USING

RAINFALL-RUNOFF MODELING

FOR PROPOSED CONDITIONS,

TABLE 7: PEAK FLOWS FOR PAVED AND

DETACHED DITCHES AS

ESTIMATED USING RAINFALL-

RUNOFF MODELING

TABLE 8: EXISTING CONDITIONS HYDRAULIC

RESULTS FOR 25-YEAR

TABLE 9: PROPOSED CONDITIONS HYDRAULIC

RESULTS FOR 25-YEAR DESIGN

EVENT (EXISTING CULVERTS)

TABLE 10: PROPOSED CONDITIONS

HYDRAULIC RESULTS FOR 25-

YEAR DESIGN EVENT (NEW

CULVERTS)

TABLE 11: PRELIMINARY GRASS-LINED DITCH

DESIGN HYDRAULIC RESULTS

FOR 10-YEAR

TABLE 12: PRELIMINARY PAVED AND

DETACHED DITCH DESIGN

HYDRAULIC RESULTS FOR 10-

YEAR

TABLE 13: PROPOSED CULVERT RIPRAP

APRON DESIGN (NEW AND

EXISTING CULVERTS)

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FIGURES

FIGURE 1: PROJECT LOCATION MAP ............................................... IV

FIGURE 2: PORTION OF FIRM PANEL

08067C0700G, EFFECTIVE

APRIL 25, 2024

FIGURE 3: DRAINAGE AREA DELINEATION MAP

FIGURE 4: LONGEST FLOWPATH

FIGURE 5: SUBBASIN CURVE NUMBER

FIGURE 6: PARKING LOT INLETS

FIGURE 7. HYDRODYNAMIC SEPARATOR

PROFILE VIEW

APPENDICES

A HYDROLOGY

B EXISTING CONDITIONS CULVERT HYDRAULIC

MODELING

C PROPOSED CONDITIONS CULVERT HYDRAULIC

MODELING

D CULVERT PROPOSED OUTLET PROTECTION

E ROADSIDE DITCH DESIGN

F INLET DRAINAGE

G WATER QUALITY DESIGN

ABBREVIATIONS AND ACRONYMS

BFE Base Flood Elevation CN Curve Number CFS Cubic Feet per Second CFLHD Central Federal Lands Highway Department CLOMR Conditional Letter of Map Revision CMP Corrugated Metal Pipe CWCB Colorado Water Conservation Board DEM Digital Elevation Model FEMA Federal Emergency Management Agency FHWA Federal Highway Administration FIRM Flood Insurance Rate Map FLH Federal Lands Highway FPS Feet per Second FT Feet HEC-HMS Hydrologic Engineering Center - Hydrologic

Modeling System

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HW/D Headwater to Structure Depth Ratio H:V Horizontal to Vertical i Rainfall Intensity IN Inches NED National Elevation Dataset NFIP National Flood Insurance Program NOAA National Oceanic and Atmospheric Association NRCS Natural Resources Conservation Service PDDM Project Development and Design Manual PFDS Precipitation Frequency Data Server SCS Soil Conservation Service SSURGO Soil Survey Geographic Database Tc Time or Concentration TR-55 Technical Report 55 USACE United States Army Corps of Engineers USGS U.S. Geological Survey

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1 PROJECT BACKGROUND

INFORMATION

This project includes the evaluation of ten existing cross culverts and two new culverts along the roadway connecting County Road 210 to the Lake Nighthorse Boat Dock just east of Lake Nighthorse.

These cross culverts convey flows under the roadway from east to west and drainage eventually reaches Lake Nighthorse.

The analyses detailed in this report include hydrology and hydraulics for all existing and proposed cross culverts, the addition of a side drainage ditch, and hydrologic implications of new pavement over the existing (unpaved) parking lot. New drainage including curbs, inlets, and water quality measures that were evaluated for the proposed parking lot.

Cross culverts and side drainages that convey design flows were evaluated for capacity and upgraded/replaced as needed. Some of these culverts show some damage to the end treatments, most likely due to the short length and no end sections.

Peak flows were estimated across the project area using rainfall runoff modeling. Culvert hydraulics were evaluated using the Federal Highway Administration’s (FHWA) HY-8 software, and ditch hydraulics evaluated using Bentley FlowMaster.

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2 HYDROLOGY

2.1 HYDROLOGIC SETTING

The project is located entirely within La Plata County, Colorado southwest of the City of Durango.

The design road runs along a ridgeline between steep forest land and Lake Nighthorse. Runoff flows generally drain toward the design road and are conveyed downstream to Lake Nighthorse.

2.2 AVAILABLE HYDROLOGIC DATA

The project site does not include any National Hydrography Dataset (NHD) stream crossings. No flow records are available at the project site and no nearby gages are available.

2.3 FEMA FLOOD INSURANCE STUDY

The Federal Emergency Management Agency (FEMA) provides flood insurance rate maps that detail special flood hazard areas. Land that is inundated by the base (100-year) flood are subject to National Flood Insurance Program (NFIP) floodplain management regulations.

The national flood hazard map indicates that a portion of the project limits for the Lake Nighthorse Road rehabilitation falls within Zone A (See Figure 2). FEMA Zone A is defined as an area with a one-percent annual chance of flooding.

The project will be classified as “working within the floodplain” but “no significant encroachment.”

The Colorado Water Conservation Board (CWCB) oversees floodplain management within the State of Colorado. According to CWCB regulations, any project within a Zone A floodplain may result in a maximum rise of 0.50 feet in the base flood elevation (BFE), the regulatory 100-year water surface elevation, before a Conditional Letter of Map Revision (CLOMR) is required.

The proposed roadway improvements will not impact the floodplain as no roadway modifications will be made within this zone (i.e., no additional embankment fill, etc.). However, since the roadway work will be close to the area of impact a floodplain permit will be required to complete the work.

Coordination with the La Plata County Floodplain Administrator should be conducted as needed to meet the local permitting requirements.

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Figure 2: Portion of FIRM Panel 08067C0700G, Effective April 25, 2024

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3 DETERMINATION OF DESIGN

DISCHARGE

3.1 HYDRAULIC DESIGN CRITERIA

The design and analysis of the proposed culverts evaluated for this project were developed in accordance with the design criteria outlined in the Federal Lands Highway (FLH) Project Development and Design Manual (PDDM).

Table 2 shows the FLH design criteria for culverts and roadside ditches.

Table 2: Design Criteria

DESIGN CRITERIA FLH

Culvert Design Event 25-year Minimum Cross Culvert Size 24’’

Roadside Ditch Capacity/Stability Design

Flood 10-year

Maximum Allowable Culvert Headwater to Structure

Depth Ratio

≤48-inch depth:

Max HW/D = 1.5

>48inch depth:

Max HW/D = 1.2

A HEC-HMS Version 4.11 model (USACE, 2023) was developed to perform rainfall-runoff analyses at the existing and proposed culverts. HEC-HMS methodology was determined to be the best approach for analysis as the drainage conditions in this location act primarily as a network (i.e., flows from one ditch segment/culvert entering another), resulting in cumulative flows. HEC-HMS is a popular choice for this type of project as it allows for individual analysis of flow concentration times, providing a more accurate depiction of cumulative peak flows. Rational Method was also considered as a viable option due to the small drainage basin sizes (<200 acres), however this was determined to be overly conservative for this type of analysis as it does not include calculations for individual timing of the various peak flows. This would result in a higher than anticipated peak flow, as the multiple flow paths leading into a culvert would be assumed to converge at the same time.

Sub-basin boundaries, land use, and hydrologic soil groups were spatially intersected to generate an accurate runoff curve number for each sub-basin in accordance with NRCS Runoff Curve Number (CN) methodology paired with an SCS Type II rainfall distribution.

The development of rainfall runoff parameters is detailed in the subsections below. See Figure 3 for a schematic of the drainage area delineations and the existing culvert locations. Subbasin hydrologic parameters are summarized in Table 3.

3.1.1 DRAINAGE BASIN DELINEATIONS

For these calculations, basins were delineated against a 1-meter Digital Elevation Model (DEM) published by the United States Geological Survey (USGS) in 2022 (USGS, 2022).

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3.1.2 SOILS AND LAND COVER

Soil datasets were downloaded from the Soil Survey Geographic Database (SSURGO) website (NRCS, 2015). Soils within the basin are a relatively even combination of hydrologic soil groups C and D with a few small areas of B soils.

Various cover types exist within the watershed including deciduous forests, evergreen forest, and shrub/scrub.

3.1.3 RAINFALL DATA

Precipitation datapoints for the analysis were obtained from the National Oceanic and Atmospheric Association (NOAA) Atlas 14 Precipitation Frequency Data Server (PFDS). A precipitation grid dataset was downloaded from the PFDS for each required recurrence interval and were spatially averaged using ArcGIS Pro Version 3.1.2 for each subbasin to obtain a single average precipitation depth.

3.1.4 LOSS METHODOLOGY

Land cover types and hydrologic conditions were intersected with their respective hydrologic soil groups. CN values were then assigned based on the tables within the TR-55 Urban Hydrology for Small Watersheds (SCS, 1986), made available by the United States Department of Agriculture Natural Resources Conservation Service (NRCS). Table 4 summarizes the CN values used in each subbasin.

3.1.5 SUBBASIN LAG TIME

The time of concentration for each basin was calculated following the methodology outlined in TR-55.

First, the longest flow paths for each basin were delineated in ArcGIS Pro (Esri Inc., 2023).

The longest flow paths were then subdivided into overland, shallow, and channel flow sections.

Channel flow sections were provided with roughness characteristics. Finally, the length, slope, and average velocity of each flow path segment were calculated from the DEM. The 2-year NOAA Atlas 14 rainfall depths were input for channel flow path segments.

The time of concentration for each subbasin was calculated from the flow metrics listed above.

The subbasin lag time for input to HEC-HMS was calculated as 60 percent of the time of concentration. A minimum lag time was considered times under 5 minutes, however as further detailed in Section 3.1.7, WSP elected to apply shorter lag time estimates in the HEC-HMS model to better account for peak flow timing throughout the flow network. Refer to Appendix A for mapped flow paths corresponding to each subbasin.

3.1.6 TRANSFORM METHODOLOGY

The SCS Unit Hydrograph transform methodology was applied to transform the rainfall-runoff volume from each subbasin into runoff hydrographs. The SCS Unit Hydrograph uses the lag time, which accounts for different types of basins land use, storage, and the average slope of the basin, to shape the resulting runoff hydrographs. Table 3 summarizes the lag time for each subbasin.

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3.1.7 SUMMARY OF HYDROLOGIC PARAMETERS

Figure 3: Drainage Area Delineation Map

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Figure 4: Longest Flowpath

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Figure 5: Subbasin Curve Number

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Table 3: Hydrologic Parameters for the Determination of Design Flows

SUBBASIN

AREA

(MI2)

CURVE

NUMBER

LAG TIME

(MIN)

2-YEAR

RAINFALL

DEPTH

(IN)

10-YEAR

RAINFALL

DEPTH

(IN)

25-YEAR

RAINFALL

DEPTH

(IN)

50-YEAR

RAINFALL

DEPTH

(IN)

SS16B 0.036 78 38.5 1.67 2.26 2.65 2.96

SS16A 0.0043 79 2.16 1.67 2.26 2.65 2.96

SS04B 0.063 78 65.93 1.67 2.26 2.65 2.96

SS04C 0.049 76 40.38 1.67 2.26 2.65 2.96

SS04D 0.0039 78 4.61 1.67 2.26 2.65 2.96

SS05A 0.0080 78 5.47 1.67 2.26 2.65 2.96

SS0809A 0.0072 76 4.55 1.67 2.26 2.65 2.96

SS0706A 0.0017 95 1.10 1.67 2.26 2.65 2.96

SS04A 0.0015 95 0.80 1.67 2.26 2.65 2.96

SS01A 0.020 79 13.36 1.67 2.26 2.65 2.96

SS02A 0.0029 79 0.37 1.67 2.26 2.65 2.96

SS1415A 0.0068 79 5.44 1.67 2.26 2.65 2.96

SS1415B 0.0026 79 1.54 1.67 2.26 2.65 2.96

SS10A 0.0059 77 7.22 1.67 2.26 2.65 2.96

SS18A 0.0058 77 5.55 1.67 2.26 2.65 2.96

SS17A 0.0036 79 2.43 1.67 2.26 2.65 2.96

SS1213A 0.0035 79 2.68 1.67 2.26 2.65 2.96

SS11A 0.0032 78 1.74 1.67 2.26 2.65 2.96

SS03A 0.0019 79 0.66 1.67 2.26 2.65 2.96

SS0405A 0.00046 73 0.40 1.67 2.26 2.65 2.96

WSP evaluated watershed lag times using the methodology outlined in the Soil Conservation Service’s Technical Report 55, Urban Hydrology for Small Watersheds, commonly referred to as TR-55.

The lag times for the subbasins contributing to each culvert were calculated as 60 percent of the time of concentration (Tc) estimated using TR-55 equations. Necessary input includes land cover and roughness coefficients, length of the longest flowpath from the upper elevations to the subbasin outlet, slope of the hydraulic grade line (assumed equal to the bed slope), hydraulic radius of channelized flow sections, and the 2-year, 24-hour rainfall.

Point precipitation depths for the 2-year 24-hour storm were sourced from NOAA precipitation grids. These grids were developed for durations ranging from a minimum of 5 minutes up to 60 days. Although it is recommended to assume a minimum time of concentration (Tc) value of 5 minutes to maintain correlation with the NOAA point precipitation frequency estimates, WSP elected to apply shorter Tc and subsequent lag time estimates in the HEC-HMS modeling to better account for peak flow timing throughout the flow network.

This approach is conservative because increasing shorter lag times to 5 minutes would decrease the peak flow estimates for affected subbasins. Additionally, because the PDDM recommends a minimum cross-culvert pipe diameter of 24 inches and because peak flows calculated with the shorter lag times were all within the existing culvert’s design capacities, Central Federal Lands

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April 2025 it was determined that comparing results against the 5-minute values would not provide any design benefit.

Table 4: Curve Number and Lag Time for HEC-HMS subbasins

CULVERT SUBBASIN

SUBBASIN 25-YEAR PEAK

FLOW

(CFS)

DESIGN (25-YEAR) PEAK

FLOW*

(CFS)

Culvert 1 St 100+30

SS01A 11.1

12.1

SS02A 2.4

Culvert 2 St 103+52

SS03A

1.5 1.5

Culvert 3 St 107+87

SS0809A 4.7

22.8

SS05A 5.8

SS04B 11.7

SS04C 11.2

SS04D 2.9

Culvert 5 St 113+72

SS10A

3.6

3.6

Culvert 10 St 115+11

SS17A

2.9

2.9

Culvert 6 St 117+26

SS11A

2.5

2.5

Culvert 7 St 120+00

SS1213A

2.8

2.8

Culvert 8 St 124+62

SS1415A 5.3

7.5

SS1415B 2.2

Culvert 9 St 130+72

SS16A 3.5

10.3

SS16B 9.9

*The design peak flow accounts for timing (modeled lag time as listed in Table 3) rather than assuming concurrent peak flows; the design peak flow is not necessarily equal to the sum of the contributing subbasin peak flows.

3.2 DESIGN PEAK FLOWS

A summary of peak flows for culvert estimates for existing conditions is included below in Table 5. A summary of peak flows for culvert estimates for proposed conditions is included below in Table 6. Culvert 4 is removed, and flows are redirected to Culvert 3 for proposed conditions, and Culvert 7 is also removed with flows being directed into Culvert 11. A summary of peak flows for paved and detached ditch estimates is included in

Table 7.

Table 5: Peak Flows as Estimated using Rainfall-Runoff Modeling for Existing Conditions

CULVERT

25-YEAR

(CULVERT DESIGN FREQUENCY)

CFS

Culvert 1 St 100+30

12.1

Culvert 2 St 103+52

1.5

Culvert 3 21.4

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St 107+87 Culvert 4 St 109+83

11.4

Culvert 5 St 113+72

3.6

Culvert 6 St 117+26

2.5

Culvert 7 St 120+00

2.8

Culvert 8 St 124+62

7.5

Culvert 9 St 130+72

10.3

Table 6: Peak Flows as Estimated using Rainfall-Runoff Modeling for Proposed Conditions, CULVERT

25-YEAR

(CULVERT DESIGN FREQUENCY)

CFS

10-YEAR

(DITCH DESIGN FREQUENCY)

CFS

Culvert 1 St 100+30

12.1 8.4

Culvert 2 St 103+52

1.5 1.1

Culvert 3 St 107+87

22.8 14.4

Culvert 5 St 113+72

3.6 2.5

Culvert 10 St 115+11

2.9 2.1

Culvert 6 St 117+26

2.5 1.8

Culvert 8 St 124+62

7.5 5.3

Culvert 9 St 130+72

10.3 7.1

Culvert 11 St 120+00

2.8 2.1

Culvert 12 St 0+59

4.7 3.2

Parking lot access road station 1+55, 20’

RT

6.8 4.9

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Proposed improvements to the parking lot hydraulics include rerouting all parking lot runoff into a storm drain system consisting of three catch basin manholes, draining stormwater flow into an Hydrodynamic Separator and finally into Culvert 3 before re-entering the lake. Addition of the storm drainage infrastructure will provide a more efficient drainage and storage system for the parking lot runoff before re-entering the surrounding drainage network.

Table 7: Peak Flows for Paved and Detached Ditches as Estimated using Rainfall-Runoff Modeling

STATIONING TYPE

10-YEAR

CFS

135+50 to 141+50 Paved 4.6 125+00 to 128+50 Paved 3.8

111+50 to 113+00 Paved 0.64

110+00 to 111+50 Detached 2.56 105+00 to 106+00 Paved 2.10

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4 EXISTING CONDITIONS

HYDRAULICS ANALYSES

4.1 CROSS CULVERTS

The hydraulic performance of the culverts was evaluated using the FHWA’s HY-8 Version 7.80.2 software package (FHWA, 2022). Required input included design discharge, upstream and downstream invert elevations, culvert dimensions, culvert material, inlet type, tailwater data, and roadway data.

All culvert analyses were based on the flows reported in Table 6. Based on the analysis described above, the existing conditions for each culvert are provided in Table 8.

Table 8: Existing Conditions Hydraulic Results for 25-year

CROSS

CULVERT

CULVERT

SIZE

ALLOWABLE

HW/D

CULVERT

DISCHARGE

(CFS)

HEADWATER

DEPTH

(FT)

HW/D

CULVERT

OUTLET

DEPTH

(FT)

CULVERT

OUTLET

VELOCITY

(FPS)

Culvert 1 St 100+30

Single 36’’

CMP

1.5 12.1 1.61 0.5 0.85 7.31

Culvert 2 St 103+52

Single 24’’

CMP

1.5 1.5 0.52 0.3 0.22 8.01

Culvert 3 St 107+87

Single 36’’

CMP

1.5 21.4 2.29 0.8 1.28 7.41

Culvert 4 St 109+83

Single 42’’

CMP

1.5 11.4 1.5 0.4 1.01 4.99

Culvert 5 St 113+72

Single 36”

CMP

1.5 3.6 0.85 0.3 0.49 4.8

Culvert 10 St 115+11

Unknown (Buried)

Unknown Unknown Unknown Unknown Unknown Unknown

Culvert 6 St 117+26

Single 24’’

CMP

1.5 2.5 0.79 0.4 0.46 4.61

Culvert 7 St 120+00

Single 24’’

CMP

1.5 2.8 0.75 0.4 0.32 8.52

Culvert 8 St 124+62

Single 24’’

CMP

1.5 7.5 1.16 0.6 0.43 15.08

Culvert 9 St 130+72

Single 60’’

CMP

1.2 10.3 1.22 0.3 0.58 8.11

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5 PROPOSED CONDITIONS

HYDRAULICS ANALYSES

5.1 EXISTING CROSS CULVERTS (TO BE REUSED)

The design for every culvert must meet the Federal Lands Highway HW/D requirements for the 25-year design event. Culvert 4 is abandoned with flows redirected to Culvert 3, and Culvert 7 is also abandoned with flows rerouting to Culvert 11 for proposed conditions. Based on the analysis described above, the proposed conditions for each existing culvert are provided in Table 9. The design headwater elevation is below the aggregate base course at all crossings and HW/D requirements are met for all culverts. No roadway overtopping is observed during the design event.

Table 9: Proposed Conditions Hydraulic Results for 25-year Design Event (Existing Culverts)

CROSS

CULVERT

CULVERT

SIZE

(FT)

ALLOWABLE

HW/D

CULVERT

DISCHARGE

(CFS)

HEADWATER

DEPTH

(FT)

HW/D

CULVERT

OUTLET

DEPTH

(FT)

CULVERT

OUTLET

VELOCITY

(FPS)

EXISTING VS.

PROPOSED

COMPARISON

Culvert 1 St 100+50

Single

36’’ CMP

1.5 12.1 1.61 0.5 0.85 7.31 No change.

Culvert 2 St 103+50

Single

24’’ CMP

1.5 1.5 0.52 0.3 0.22 8.01 No change.

Culvert 3 St 107+90

Single

36’’ CMP

1.5 22.8 2.38 0.8 1.33 7.53

Revised drainage area due to parking lot regrading/rerouting from Culvert 4.

Culvert 5 St 113+72

Single

36’’ CMP

1.5 3.6 0.85 0.3 0.49 4.80 No change.

Culvert 6 St 117+26

Single

24’’ CMP

1.5 2.5 0.79 0.4 0.46 4.61 No change.

Culvert 8 St 124+62

Single

24’’ CMP

1.5 7.5 1.16 0.6 0.43 15.08 No change.

Culvert 9 St 130+72

Single

60’’ CMP

1.2 10.3 1.22 0.3 0.58 8.11 No change.

As indicated previously, Culvert 4 will be plugged and abandoned, and all flow will be rerouted to Culvert 3. Culvert 3 flows represented in Table 8 reflect the combined drainage areas of Culverts 3 and

4. Flows previously directed to Culvert 7 are shown below under Culvert 11.

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5.2 NEW CROSS CULVERTS

The proposed drainage system includes the installation of three new culverts (Culvert 10 replacement and new culverts 11 and 12), as shown in Table 10.

Table 10: Proposed Conditions Hydraulic Results for 25-year Design Event (New Culverts)

CROSS

CULVERT

CULVERT

SIZE

(FT)

ALLOWABLE

HW/D

CULVERT

DISCHARGE

(CFS)

HEADWATER

DEPTH

(FT)

HW/D

CULVERT

OUTLET

DEPTH

(FT)

CULVERT

OUTLET

VELOCITY

(FPS)

Culvert 10 St 115+11

Single 24”

CMP

1.5 3.9 0.97 0.5 0.47 6.86

Culvert 11 St 120+00

Single 24’’

CMP

1.5 2.8 0.85 0.4 0.54 4.05

Culvert 12 St 0+59

Single 36’’

CMP

1.5 4.7 0.98 0.3 0.61 4.52

Per consultation with CFL and the design team, it was determined that Culverts 4 and 7 shall be abandoned and plugged. Culvert 4 shall be abandoned to improve the aesthetics and usability of the public swim beach directly downstream. Re-routing of these flows under the parking lot through Culvert 12, and then into Culvert 3 will direct peak flows away from the beach and improve the recreational beach space available for public use. Culvert 7 shall be abandoned to improve the alignment of the channel and replaced with Culvert 11, which will have a smaller impact as it is shorter than Culvert 7.

Upon completion of the hydrologic and hydraulic analysis, it was determined that due to the varying time of concentrations between the subbasins for Culverts 3 and 4, the re-routing of Culvert 4 flows through Culvert 12 and into Culvert 3 did not drastically increase the overall flow volumes and was found to be within the 25-year design capacity for the existing system.

5.3 ROADSIDE DITCHES

A ditch system has been designed to run along the roadway and convey runoff to the culverts. The PDDM requires that roadside ditches be designed to convey the 10-year event with a maximum water surface elevation no higher than the bottom of the aggregate base layer. Proposed roadside ditch cross-sections were designed using Bentley FlowMaster V8i (Bentley Systems, Inc., 2009).

The ditch system design is primarily driven by the need to avoid existing underground utilities while also meeting CFL criteria. As a result, the proposed ditch includes sections of grass-lined, paved, and detached sections. A summary of the ditch design parameters is presented in Table 11.

The grass-lined ditch cross-section is triangular with 3:1 and 2:1 (H:V) side slopes. Roughness coefficients were estimated based on existing imagery and range from 0.04 to 0.045. A summary of the grass-lined ditch design parameters is presented in Table 11.

For the grass-lined portions of the ditch, the distance between the top of the pavement and the bottom of the ditch is designed to be 2 ft, and the pavement is designed to be 8 in. As per the design criteria listed in Table 2, the 10-year water surface elevation within the ditch must remain below the proposed aggregate base course, so the maximum normal depth for the 10-year event through the ditch is 16 inches.

Central Federal Lands

WSP

April 2025

The paved ditch cross-section is triangular with 10:1 (H:V) and 0.625:1 (H:V) side slopes. This cross-section was assumed for the entire length of the proposed ditch. Roughness values were estimated as 0.015.

The detached ditch cross-section is triangular with 3:1 (H:V) and 3:1 (H:V) side slopes. This cross-section was assumed for the entire length of the proposed ditch. Roughness values were estimated as 0.015.

Riprap countermeasures will be placed at each intersection between paved and unpaved ditch sections. These riprap sections were designed according to the methods of HEC-14 on the assumption that the flow behaves like culvert outflows. See Section 5.4.2 for proposed ditch riprap sizing and Appendix E for a detailed presentation of the roadside ditch design.

Table 11: Preliminary Grass-Lined Ditch Design Hydraulic Results for 10-year

CROSS

CULVERT

STATION

NORMAL

DEPTH IN

THE DITCH

(IN)

ROUGHNES

S

COEFFICIEN

T

LEFT SIDE

SLOPE

(H:V)

RIGHT SIDE

SLOPE

(H:V)

VELOCITY

(FPS)

FLOW TYPE

Culvert 1 St 100+50

100+30 10.6 0.045 3 2 4.31 Supercritical

Culvert 2 St 103+50

103+52 8.6 0.045 3 2 0.85 Subcritical

Culvert 3 St 107+90

107+87 20.6 0.040 3 2 2.07 Subcritical

Culvert 4 St 109+83

109+83 15.1 0.040 3 2 1.84 Subcritical

Culvert 5 St 113+72

113+72 10.9 0.045 3 2 1.21 Subcritical

Culvert 6 St 117+26

117+26 6.4 0.045 3 2 2.56 Subcritical

Culvert 7 St 120+00

120+00 5.8 0.045 3 2 3.61 Supercritical

Culvert 8 St 124+62

124+62 10.1 0.045 3 2 2.99 Subcritical

Culvert 9 St 130+72

130+72 10.1 0.045 3 2 4.04 Supercritical

Table 12: Preliminary Paved and Detached Ditch Design Hydraulic Results for 10-year

STATION TYPE

NORMAL

DEPTH IN

THE DITCH

(IN)

ROUGHNESS

COEFFICIENT

LEFT SIDE

SLOPE

(H:V)

RIGHT

SIDE

SLOPE

(H:V)

VELOCITY

(FPS)

FLOW TYPE

135+50 to 141+50

Paved 4.2 0.015 10 0.625 7.03 Supercritical

125+00 to 128+50

Paved 3.7 0.015 10 0.625 7.35 Supercritical

111+50 to 113+00

Paved 3.5 0.015 10 0.625 1.38 Subcritical

110+00 to 111+50

Detached 5.3 0.015 3 3 4.30 Supercritical

Central Federal Lands

WSP

April 2025

105+00 to 106+00

Paved 3.0 0.015 10 0.625 6.45 Supercritical

5.4 PROPOSED SCOUR COUNTERMEASURES

5.4.1 PROPOSED CULVERT OUTLET PROTECTION

The outlet protection design was conducted according to the methods outlined in the FHWA’s CFLHD Detail for Placed Riprap at Culvert Outlets (FHWA, 2006).

Table 13 shows the calculations of the minimum riprap diameters to protect against outlet scour at each culvert. A site visit was completed by WSP at the Project 30-percent design level. During the site visit it was noted that many of the existing culverts (to be flushed rather than replaced) had adequate scour protection from riprap placed along the roadway embankment. WSP therefore recommends installation of new riprap at new culvert installations and any existing areas that have experienced erosion. Refer to Appendix D Culvert Proposed Outlet Protection for further details.

Table 13: Proposed Culvert Riprap Apron Design (New and Existing Culverts)

CROSS CULVERT

PROPOSED SCOUR

UPGRADES

DESIGN RIPRAP

DIAMETER (IN)1

DESIGN APRON

LENGTH (FT)2

DESIGN APRON

DEPTH (FT)3

Culvert 1 St 100+30

None – existing riprap at outlet

N/A N/A N/A

Culvert 2 St 103+50

None – existing riprap at outlet

N/A N/A N/A

Culvert 3 St 107+90

None – existing riprap at outlet

N/A N/A N/A

Culvert 5 St 113+72

None – existing riprap at outlet

N/A N/A N/A

Culvert 10 St 115+11

New outlet apron only/inlet as is

5 8 1.5

Culvert 6 St 117+26

New outlet apron only/inlet as is

5 8 1.5

Culvert 8 St 124+62

None – existing riprap at outlet

N/A N/A N/A

Culvert 9 St 130+72

None – existing riprap at outlet

N/A N/A N/A

Culvert 11 St 120+00

New outlet apron only/inlet as is

5 8 1.5

Culvert 12 St 0+59

New outlet apron only/inlet as is

5 12 1.5

Notes:

1. Minimum required D50 sizing was determined using Equation 10.4 from Chapter 10 of the FHWA HEC-14 guidelines.

2 & 3. Proposed Apron length and Apron Depth were determined using Table 10.1 from Chapter 10 of the FHWA HEC-14 guidelines.

Per Table 10.1 of the HEC-14 guidelines, a minimum D50 of 5” requires a Class 1 riprap. However, as indicated in the CFL design standards, all culverts under a 10% grade shall have a minimum of Class 3 riprap used for scour protection. The proposed riprap classification has therefore been upgraded to Class 3 riprap for all locations.

Central Federal Lands

WSP

April 2025

5.4.2 PROPOSED DITCH SCOUR COUNTERMEASURES

The preliminary calculations show that the minimum D50 diameter riprap of 6 inches (Class 2) is sufficient to protect against outlet scour at each paved and detached ditch. Per Chapter 10 of the HEC-14 guidelines, a minimum apron length of 8 ft and minimum apron depth of 1.65 ft is required.

As indicated in Section 5.4.2, a Class 3 riprap has been proposed for all culverts.

As requested by CFL, for the purposes of simplifying construction procedures (i.e., managing payment items, tracking material quantities, etc.) the proposed riprap classification for all ditch scour protection shall be Class 3.

5.5 PARKING LOT DRAINAGE

5.5.1 INLET DRAINAGE DESIGN

The inlet design was conducted according to the methods outlined in the Mile High Flood District MHFD’s Street and Inlet Hydraulics Workbook (MHFD, 2023). Inlets 1, 2 and 3 are shown in Figure 6. A five-foot Curb Inlet opening was used as the inlet type for all three inlets.

Figure 6: Parking Lot Inlets

The Mile High Flood District (MHFD) does not include analysis for parking lots within the Inlet Workbook, nor is there any specific criteria listed in the MHFD volumes regarding allowable spread within parking lots. As inlet design calculations were not available for parking lots using the MHFD

Inlet 1

Inlet 2

Inlet 3

Central Federal Lands

WSP

April 2025 guidelines, the maximum allowable spread widths calculated for the three inlets were designed to meet MHFD’s rural street standards. This approach is reasonable because the parking lot entrance is adjacent to what the MHFD would consider a rural street.

The MHFD’s Inlet Workbook was used to determined required flow capacity of the proposed curb and gutter under minor and major storm event scenarios (see Table 14).

Table 14: Curb and Gutter Analysis

INLET

MAX SPREAD

MAJOR/MINOR

(FT)

MAX DEPTH AT

GUTTER

MAJOR/MINOR

(INCHES)

ALLOWABLE

CAPACITY

MAJOR/MINOR (CFS)

1 7.0 6.0 5.4 2 7.0 6.0 4.8 3 7.0 6.0 4.8

Refer to Appendix F Inlet Drainage for further details on curb and gutter design.

5.5.2 HYDRODYNAMIC SEPARATOR DESIGN

A Hydrodynamic Separator is proposed at the parking lot access road station 1+55, 20’ RT to collect and treat the parking lot runoff. See Figure 5 below.

Figure 7. Hydrodynamic Separator Profile View

Following The City of Durango Storm Drainage Design Criteria Manual, the MS4 General Permit defines that new development and redevelopment locations shall be designed to treat a minimum runoff flow equivalent to the 80th percentile storm event, corresponding to a storm depth of 0.6 inches and shall reduce the event mean concentration of total suspended solids (TSS) to a median

Central Federal Lands

WSP

April 2025 value of 30 mg/L of less. Following the Mile High Flood District (MHFD) Urban Storm Drainage Criteria Manual Volume 3, the Water Quality Peak Flow (WQPF) was determined to be 2.34 CFS.

The specific Hydrodynamic Separator dimensions will be designed according to the manufacturer’s specifications. Similarly to other water quality systems along this project reach, the proposed Hydrodynamic Separator shall be a hydrodynamic treatment system capable of separating oil from the parking lot runoff in addition to containment of debris, trash and sediments. Available products were reviewed for compliance and multiple Contech Engineering Solutions’ hydrodynamic separator treatment options were found to be compatible with the City of Durango’s water quality design criteria, such as the CDS and Cascade Separator units.

Central Federal Lands

WSP

April 2025

6 REFERENCES

Bentley Systems, Inc. (2009). FlowMaster V8i (SELECTseries1). Watertown, CT: Bentley.

Esri Inc. (2023). ArcGIS Pro Version 3.1.2.

FHWA. (2006). Hydraulic Engineering Circular No. 14 – Hydraulic Design of Energy Dissipators for Culverts and Channels, Chapter 10: Riprap Basins and Aprons. U.S. Department of Transportation.

FHWA. (2021). FP-14 Standard Specifications: Table 705-1 Gradation Requirements for Riprap. U.S.

Department of Transportation, Federal Lands Highway.

FHWA. (2022). HY-8 7.80.2. Environmental Modeling Research Laboratory: Aquaveo LLC.

FLH. (2012). Project Development and Design Manual, Chapter 7 Hydrology and Hydraulics. Federal Highway Administration.

Google. (2021). Google Earth Pro Version 7.3.4.8248 (64-bit). Retrieved from Imagery July 2, 2021:

Trinity County, CA

NOAA. (2017). NOAA Atlas 14, Volume 6, Version 2: Point Precipitation Frequency Server. Silver Spring, MD: National Weather Service.

NRCS. (2015). Soil Survey Geographic (SSURGO) Database. http://websoilsurvey.nrcs.usda.gov: Natural Resources Conservation Service.

SCS. (1986). TR-55 Urban Hydrology for Small Watersheds. U.S. Department of Agriculture.

USACE. (2023). HEC-HMS Version 4.11. Davis, CA: U.S. Army Corps of Engineers, Institute for Water Resources, Hydrologic Engineering Center.

USGS. (2019). StreamStats Application Version 4.3.0. (37.10455 N, 106.00619 W):

https://streamstats.usgs.gov/ss.

USGS. (2022). 20220316, USGS 1 Meter 12 x77y413 CO_Southwest_NRCS_2018_D18. U.S. Geological Survey.

APPENDIX

A HYDROLOGY

B EXISTING

CONDITIONS

CULVERT

HYDRAULIC

MODELING

HY-8 Culvert Analysis Report

Crossing Discharge Data

Discharge Selection Method: Specify Minimum, Design, and Maximum Flow

Minimum Flow: 0.00 cfs

Design Flow: 12.10 cfs

Maximum Flow: 15.10 cfs

Table 1 - Summary of Culvert Flows at Crossing: SS01

Headwater Elevation (ft)

Total Discharge (cfs)

Culvert 1 Discharge (cfs)

Roadway Discharge (cfs)

Iterations

6890.10 0.00 0.00 0.00 1

6890.64 1.51 1.51 0.00 1

6890.87 3.02 3.02 0.00 1

6891.05 4.53 4.53 0.00 1

6891.20 6.04 6.04 0.00 1

6891.34 7.55 7.55 0.00 1

6891.47 9.06 9.06 0.00 1

6891.59 10.57 10.57 0.00 1

6891.71 12.10 12.10 0.00 1

6891.82 13.59 13.59 0.00 1

6891.93 15.10 15.10 0.00 1

6900.00 85.72 85.72 0.00 Overtopping

Culvert Data: Culvert 1

Table 1 - Culvert Summary Table: Culvert 1

Total Disch arge (cfs)

Culve rt Disch arge (cfs)

Head water Elevat ion (ft)

Inle t Cont rol Dep th (ft)

Outl et Cont rol Dep th (ft)

Fl ow Ty pe

Nor mal Dep th (ft)

Criti cal Dep th (ft)

Out let De pth (ft)

Tailw ater Dept h (ft)

Outl et Velo city (ft/s

Tailw ater Veloc ity (ft/s)

0.00 cfs

0.00 cfs

6890.1

0.00 0.00

0-

NF

0.00 0.00 0.0

0.00 0.00 0.00

1.51 cfs

1.51 cfs

6890.6

0.54 0.0* 1- S2 n

0.31 0.38 0.3

0.06 3.96 1.62

3.02 cfs

3.02 cfs

6890.8

0.77 0.0* 1- S2 n

0.43 0.54 0.4

0.09 4.89 2.14

4.53 cfs

4.53 cfs

6891.0

0.95 0.0* 1- S2 n

0.52 0.67 0.5

0.12 5.50 2.51

6.04 cfs

6.04 cfs

6891.2

1.10 0.0* 1- S2 n

0.60 0.77 0.6

0.14 5.98 2.82

7.55 cfs

7.55 cfs

6891.3

1.24 0.0* 1- S2 n

0.67 0.87 0.6

0.16 6.39 3.08

9.06 cfs

9.06 cfs

6891.4

1.37 0.0* 1- S2 n

0.74 0.95 0.7

0.18 6.74 3.31

10.57 cfs

10.57 cfs

6891.5

1.49 0.0* 1- S2 n

0.80 1.03 0.8

0.20 7.04 3.51

12.10 cfs

12.10 cfs

6891.7

1.61 0.0* 1- S2 n

0.85 1.10 0.8

0.22 7.31 3.71

13.59 cfs

13.59 cfs

6891.8

1.72 0.0* 1- S2 n

0.90 1.17 0.9

0.23 7.56 3.88

15.10 cfs

15.10 cfs

6891.9

1.83 0.0* 1- S2 n

0.96 1.24 0.9

0.25 7.79 4.04

* Full Flow Headwater elevation is below inlet invert.

Culvert Barrel Data

Culvert Barrel Type Straight Culvert

Inlet Elevation (invert): 6890.10 ft, Outlet Elevation (invert): 6886.33 ft

Culvert Length: 105.07 ft, Culvert Slope: 0.0359

Water Surface Profile Plot for Culvert: Culvert 1

Site Data - Culvert 1

Site Data Option: Culvert Invert Data

Inlet Station: 0.00 ft

Inlet Elevation: 6890.10 ft

Outlet Station: 105.00 ft

Outlet Elevation: 6886.33 ft

Number of Barrels: 1

Culvert Data Summary - Culvert 1

Barrel Shape: Circular

Barrel Diameter: 3.00 ft

Barrel Material: Corrugated Steel

Embedment: 0.00 in

Barrel Manning's n: 0.0240

Culvert Type: Straight

Inlet Configuration: Thin Edge Projecting

Inlet Depression: None

Crossing Discharge Data

Discharge Selection Method: Specify Minimum, Design, and Maximum Flow

Minimum Flow: 0.00 cfs

Design Flow: 1.50 cfs

Maximum Flow: 1.90 cfs

Table 2 - Summary of Culvert Flows at Crossing: SS03

Headwater Elevation (ft)

Total Discharge (cfs)

Culvert 2 Discharge (cfs)

Roadway Discharge (cfs)

Iterations

6908.42 0.00 0.00 0.00 1

6908.60 0.19 0.19 0.00 1

6908.68 0.38 0.38 0.00 1

6908.73 0.57 0.57 0.00 1

6908.78 0.76 0.76 0.00 1

6908.83 0.95 0.95 0.00 1

6908.87 1.14 1.14 0.00 1

6908.91 1.33 1.33 0.00 1

6908.94 1.50 1.50 0.00 1

6908.97 1.71 1.71 0.00 1

6909.00 1.90 1.90 0.00 1

6914.98 31.59 31.59 0.00 Overtopping

Culvert Data: Culvert 2

Table 2 - Culvert Summary Table: Culvert 2

Total Disch arge (cfs)

Culve rt Disch arge (cfs)

Head water Elevat ion (ft)

Inle t Cont rol Dep th (ft)

Outl et Cont rol Dep th (ft)

Fl ow Ty pe

Nor mal Dep th (ft)

Criti cal Dep th (ft)

Out let De pth (ft)

Tailw ater Dept h (ft)

Outl et Velo city (ft/s

Tailw ater Veloc ity (ft/s)

0.00 cfs

0.00 cfs

6908.4

0.00 0.00

0-

NF

0.00 0.00 0.0

0.00 0.00 0.00

0.19 cfs

0.19 cfs

6908.6

0.18 0.0* 1- S2 n

0.08 0.15 0.0

0.02 4.46 0.99

0.38 0.38 6908.6 0.26 0.0* 1- 0.11 0.21 0.1 0.04 5.34 1.30 cfs cfs 8 S2 n

0.57 cfs

0.57 cfs

6908.7

0.31 0.0* 1- S2 n

0.14 0.26 0.1

0.05 6.03 1.53

0.76 cfs

0.76 cfs

6908.7

0.36 0.0* 1- S2 n

0.16 0.30 0.1

0.06 6.52 1.72

0.95 cfs

0.95 cfs

6908.8

0.41 0.0* 1- S2 n

0.18 0.34 0.1

0.06 7.01 1.87

1.14 cfs

1.14 cfs

6908.8

0.45 0.0* 1- S2 n

0.19 0.37 0.1

0.07 7.38 2.01

1.33 cfs

1.33 cfs

6908.9

0.49 0.0* 1- S2 n

0.21 0.40 0.2

0.08 7.69 2.14

1.50 cfs

1.50 cfs

6908.9

0.52 0.0* 1- S2 n

0.22 0.42 0.2

0.08 8.01 2.25

1.71 cfs

1.71 cfs

6908.9

0.55 0.0* 1- S2 n

0.23 0.45 0.2

0.09 8.33 2.36

1.90 cfs

1.90 cfs

6909.0

0.58 0.0* 1- S2 n

0.25 0.48 0.2

0.10 8.58 2.46

* Full Flow Headwater elevation is below inlet invert.

Culvert Barrel Data

Culvert Barrel Type Straight Culvert

Inlet Elevation (invert): 6908.42 ft, Outlet Elevation (invert): 6886.93 ft

Culvert Length: 96.43 ft, Culvert Slope: 0.2286

Water Surface Profile Plot for Culvert: Culvert 2

Site Data - Culvert 2

Inlet Station: 0.00 ft

Inlet Elevation: 6908.42 ft

Outlet Station: 94.00 ft

Outlet Elevation: 6886.93 ft

Number of Barrels: 1

Culvert Data Summary - Culvert 2

Barrel Shape: Circular

Barrel Diameter: 2.00 ft

Barrel Material: Corrugated Steel

Inlet Depression: None

Crossing Discharge Data

Discharge Selection Method: Specify Minimum, Design, and Maximum Flow

Minimum Flow: 0.00 cfs

Design Flow: 21.40 cfs

Maximum Flow: 27.50 cfs

Table 3 - Summary of Culvert Flows at Crossing: SS04

Headwater Elevation (ft)

Total Discharge (cfs)

Culvert 3 Discharge (cfs)

Roadway Discharge (cfs)

Iterations

6889.60 0.00 0.00 0.00 1

6890.34 2.75 2.75 0.00 1

6890.66 5.50 5.50 0.00 1

6890.91 8.25 8.25 0.00 1

6891.14 11.00 11.00 0.00 1

6891.35 13.75 13.75 0.00 1

6891.55 16.50 16.50 0.00 1

6891.74 19.25 19.25 0.00 1

6891.89 21.40 21.40 0.00 1

6892.12 24.75 24.75 0.00 1

6892.31 27.50 27.50 0.00 1

6898.00 77.60 77.60 0.00 Overtopping

Culvert Data: Culvert 3

Table 3 - Culvert Summary Table: Culvert 3

Total Disch arge (cfs)

Culve rt Disch arge (cfs)

Head water Elevat ion (ft)

Inle t Cont rol Dep th (ft)

Outl et Cont rol Dep th (ft)

Fl ow Ty pe

Nor mal Dep th (ft)

Criti cal Dep th (ft)

Out let De pth (ft)

Tailw ater Dept h (ft)

Outl et Velo city (ft/s

Tailw ater Veloc ity (ft/s)

0.00 cfs

0.00 cfs

6889.6

0.00 0.00

0-

NF

0.00 0.00 0.0

0.00 0.00 0.00

2.75 cfs

2.75 cfs

6890.3

0.74 0.0* 1- S2 n

0.00 0.52 0.4

0.15 4.13 2.25

5.50 5.50 6890.6 1.06 0.0* 1- 0.00 0.74 0.6 0.23 5.06 2.95 cfs cfs 6 S2

8.25 cfs

8.25 cfs

6890.9

1.31 0.0* 1- S2 n

0.00 0.91 0.7

0.30 5.68 3.45

11.00 cfs

11.00 cfs

6891.1

1.54 0.0* 1- S2 n

0.00 0.91 0.9

0.36 6.17 3.85

13.75 cfs

13.75 cfs

6891.3

1.75 0.0* 1- S2 n

0.00 0.91 1.0

0.41 6.57 4.19

16.50 cfs

16.50 cfs

6891.5

1.95 0.00

1- S2 n

0.00 0.91 1.1

0.46 6.91 4.48

19.25 cfs

19.25 cfs

6891.7

2.14 0.09

1- S2 n

0.00 0.91 1.2

0.51 7.20 4.75

21.40 cfs

21.40 cfs

6891.8

2.29 0.17

1- S2 n

0.00 0.91 1.2

0.54 7.41 4.94

24.75 cfs

24.75 cfs

6892.1

2.52 0.31

1- S2 n

0.00 0.91 1.3

0.59 7.70 5.21

27.50 cfs

27.50 cfs

6892.3

2.71 0.45

1- S2 n

0.00 0.91 1.4

0.63 7.91 5.42

* Full Flow Headwater elevation is below inlet invert.

Culvert Barrel Data

Culvert Barrel Type Double Broken-back Culvert

Inlet Elevation (invert): 6889.60 ft, Upper Break Elevation (invert): 6888.32 ft, Lower Break Elevation (invert): 6888.32 ft, Outlet Elevation (invert): 6886.49 ft

Culvert Length: 120.04 ft, Upper Culvert Section Slope: 0.0291

Steep Culvert Section Slope: 0.0000

Runout Culvert Section Slope: 0.0241

Water Surface Profile Plot for Culvert: Culvert 3

Site Data - Culvert 3

Inlet Station: 0.00 ft

Inlet Elevation: 6889.60 ft

Upper Break Station: 44.00 ft

Upper Break Elevation: 6888.32 ft

Lower Break Station: 44.00 ft

Lower Break Elevation: 6888.32 ft

Outlet Station: 120.00 ft

Outlet Elevation: 6886.49 ft

Number of Barrels: 1

Culvert Data Summary - Culvert 3

Barrel Shape: Circular

Barrel Diameter: 3.00 ft

Upper & Middle Section Material: Corrugated Steel

Lower Section Material: Corrugated Steel

Embedment: 0.00 in

Upper & Middle Section Manning's n: 0.0240

Lower Section Manning's n: 0.0240

Culvert Type: Double Broken-back

Inlet Configuration: Thin Edge Projecting

Inlet Depression: None

Crossing Discharge Data

Discharge Selection Method: Specify Minimum, Design, and Maximum Flow

Minimum Flow: 0.00 cfs

Design Flow: 11.40 cfs

Maximum Flow: 14.50 cfs

Table 4 - Summary of Culvert Flows at Crossing: SS08SS09

Headwater Elevation (ft)

Total Discharge (cfs)

Culvert 4 Discharge (cfs)

Roadway Discharge (cfs)

Iterations

6886.76 0.00 0.00 0.00 1

6887.27 1.45 1.45 0.00 1

6887.49 2.90 2.90 0.00 1

6887.66 4.35 4.35 0.00 1

6887.81 5.80 5.80 0.00 1

6887.94 7.25 7.25 0.00 1

6888.06 8.70 8.70 0.00 1

6888.17 10.15 10.15 0.00 1

6888.26 11.40 11.40 0.00 1

6888.37 13.05 13.05 0.00 1

6888.46 14.50 14.50 0.00 1

6898.50 127.02 127.02 0.00 Overtopping

Culvert Data: Culvert 4

Table 4 - Culvert Summary Table: Culvert 4

Total Culve Head Inle Outl Fl Nor Criti Out Tailw Outl Tailw

Disch arge (cfs) rt Disch arge (cfs) water Elevat ion (ft) t Cont rol Dep th (ft) et Cont rol Dep th (ft) ow Ty pe mal Dep th (ft) cal Dep th (ft) let De pth (ft) ater Dept h (ft) et Velo city (ft/s ater Veloc ity (ft/s)

0.00 cfs

0.00 cfs

6886.7

0.00 0.00

0-

NF

0.00 0.00 0.0

0.00 0.00 0.00

1.45 cfs

1.45 cfs

6887.2

0.51 0.33

1- S2 n

0.00 0.36 0.3

0.16 2.72 1.10

2.90 cfs

2.90 cfs

6887.4

0.73 0.33

1- S2 n

0.00 0.51 0.5

0.25 3.36 1.44

4.35 cfs

4.35 cfs

6887.6

0.90 0.34

1- S2 n

0.00 0.62 0.6

0.32 3.77 1.68

5.80 cfs

5.80 cfs

6887.8

1.05 0.34

1- S2 n

0.00 0.72 0.7

0.39 4.10 1.88

7.25 cfs

7.25 cfs

6887.9

1.18 0.35

1- S2 n

0.00 0.81 0.8

0.44 4.38 2.04

8.70 cfs

8.70 cfs

6888.0

1.30 0.36

1- S2 n

0.00 0.89 0.8

0.50 4.62 2.19

10.15 cfs

10.15 cfs

6888.1

1.41 0.37

1- S2 n

0.00 0.96 0.9

0.55 4.83 2.31

11.40 cfs

11.40 cfs

6888.2

1.50 0.38

1- S2 n

0.00 1.02 1.0

0.59 4.99 2.42

13.05 cfs

13.05 cfs

6888.3

1.61 0.40

1- S2 n

0.00 1.10 1.0

0.64 5.18 2.54

14.50 cfs

14.50 cfs

6888.4

1.70 0.42

1- S2 n

0.00 1.16 1.1

0.69 5.34 2.64

Culvert Barrel Data

Culvert Barrel Type Double Broken-back Culvert

Inlet Elevation (invert): 6886.76 ft, Upper Break Elevation (invert): 6885.89 ft, Lower Break Elevation (invert): 6885.89 ft, Outlet Elevation (invert): 6884.95 ft

Culvert Length: 100.02 ft, Upper Culvert Section Slope: 0.0290

Steep Culvert Section Slope: 0.0000

Runout Culvert Section Slope: 0.0134

Water Surface Profile Plot for Culvert: Culvert 4

Site Data - Culvert 4

Inlet Station: 0.00 ft

Inlet Elevation: 6886.76 ft

Upper Break Station: 30.00 ft

Upper Break Elevation: 6885.89 ft

Lower Break Station: 30.00 ft

Lower Break Elevation: 6885.89 ft

Outlet Station: 100.00 ft

Outlet Elevation: 6884.95 ft

Number of Barrels: 1

Culvert Data Summary - Culvert 4

Barrel Shape: Circular

Barrel Diameter: 3.50 ft

Upper & Middle Section Material: Corrugated Steel

Lower Section Material: Corrugated Steel

Embedment: 0.00 in

Upper & Middle Section Manning's n: 0.0240

Lower Section Manning's n: 0.0240

Culvert Type: Double Broken-back

Inlet Configuration: Thin Edge Projecting

Inlet Depression: None

Crossing Discharge Data

Discharge Selection Method: Specify Minimum, Design, and Maximum Flow

Minimum Flow: 0.00 cfs

Design Flow: 2.50 cfs

Maximum Flow: 3.10 cfs

Table 5 - Summary of Culvert Flows at Crossing: SS11

Headwater Elevation (ft)

Total Discharge (cfs)

Culvert 6 Discharge (cfs)

Roadway Discharge (cfs)

Iterations

6891.29 0.00 0.00 0.00 1

6891.56 0.31 0.31 0.00 1

6891.67 0.62 0.62 0.00 1

6891.76 0.93 0.93 0.00 1

6891.84 1.24 1.24 0.00 1

6891.91 1.55 1.55 0.00 1

6891.97 1.86 1.86 0.00 1

6892.03 2.17 2.17 0.00 1

6892.08 2.50 2.50 0.00 1

6892.13 2.79 2.79 0.00 1

6892.18 3.10 3.10 0.00 1

6903.00 37.42 37.42 0.00 Overtopping

Culvert Data: Culvert 6

Table 5 - Culvert Summary Table: Culvert 6

Total Disch arge (cfs)

Culve rt Disch arge (cfs)

Head water Elevat ion (ft)

Inle t Cont rol Dep th (ft)

Outl et Cont rol Dep th (ft)

Fl ow Ty pe

Nor mal Dep th (ft)

Criti cal Dep th (ft)

Out let De pth (ft)

Tailw ater Dept h (ft)

Outl et Velo city (ft/s

Tailw ater Veloc ity (ft/s)

0.00 cfs

0.00 cfs

6891.2

0.00 0.00

0-

NF

0.00 0.00 0.0

0.00 0.00 0.00

0.31 cfs

0.31 cfs

6891.5

0.27 0.0* 1- S2 n

0.17 0.19 0.1

0.03 2.49 1.34

0.62 cfs

0.62 cfs

6891.6

0.38 0.0* 1- S2 n

0.23 0.27 0.2

0.04 3.07 1.77

0.93 cfs

0.93 cfs

6891.7

0.47 0.0* 1- S2 n

0.28 0.33 0.2

0.06 3.45 2.09

1.24 cfs

1.24 cfs

6891.8

0.55 0.0* 1- S2 n

0.32 0.38 0.3

0.07 3.76 2.33

1.55 cfs

1.55 cfs

6891.9

0.62 0.0* 1- S2 n

0.36 0.43 0.3

0.08 4.01 2.55

1.86 cfs

1.86 cfs

6891.9

0.68 0.0* 1- S2 n

0.39 0.47 0.3

0.08 4.23 2.74

2.17 cfs

2.17 cfs

6892.0

0.74 0.0* 1- S2 n

0.43 0.51 0.4

0.09 4.43 2.91

2.50 cfs

2.50 cfs

6892.0

0.79 0.0* 1- S2 n

0.46 0.55 0.4

0.10 4.61 3.08

2.79 cfs

2.79 cfs

6892.1

0.84 0.0* 1- S2 n

0.48 0.58 0.4

0.11 4.76 3.22

3.10 cfs

3.10 cfs

6892.1

0.89 0.0* 1- S2 n

0.51 0.61 0.5

0.12 4.91 3.35

* Full Flow Headwater elevation is below inlet invert.

Culvert Barrel Data

Culvert Barrel Type Straight Culvert

Inlet Elevation (invert): 6891.29 ft, Outlet Elevation (invert): 6888.47 ft

Culvert Length: 90.04 ft, Culvert Slope: 0.0313

Water Surface Profile Plot for Culvert: Culvert 6

Site Data - Culvert 6

Inlet Station: 0.00 ft

Inlet Elevation: 6891.29 ft

Outlet Station: 90.00 ft

Outlet Elevation: 6888.47 ft

Number of Barrels: 1

Culvert Data Summary - Culvert 6

Barrel Shape: Circular

Barrel Diameter: 2.00 ft

Barrel Material: Corrugated Steel

Barrel Manning's n: 0.0240

Culvert Type: Straight

Inlet Configuration: Thin Edge Projecting

Inlet Depression: None

Crossing Discharge Data

Discharge Selection Method: Specify Minimum, Design, and Maximum Flow

Minimum Flow: 0.00 cfs

Design Flow: 2.80 cfs

Maximum Flow: 3.50 cfs

Table 6 - Summary of Culvert Flows at Crossing: SS12SS13

Headwater Elevation (ft)

Total Discharge (cfs)

Culvert 7 Discharge (cfs)

Roadway Discharge (cfs)

Iterations

6912.54 0.00 0.00 0.00 1

6912.80 0.35 0.35 0.00 1

6912.91 0.70 0.70 0.00 1

6912.99 1.05 1.05 0.00 1

6913.06 1.40 1.40 0.00 1

6913.13 1.75 1.75 0.00 1

6913.19 2.10 2.10 0.00 1

6913.24 2.45 2.45 0.00 1

6913.29 2.80 2.80 0.00 1

6913.34 3.15 3.15 0.00 1

6913.39 3.50 3.50 0.00 1

6921.00 36.36 36.36 0.00 Overtopping

Culvert Data: Culvert 7

Table 6 - Culvert Summary Table: Culvert 7

Total Disch arge (cfs)

Culve rt Disch arge (cfs)

Head water Elevat ion (ft)

Inle t Cont rol Dep th (ft)

Outl et Cont rol Dep th (ft)

Fl ow Ty pe

Nor mal Dep th (ft)

Criti cal Dep th (ft)

Out let De pth (ft)

Tailw ater Dept h (ft)

Outl et Velo city (ft/s

Tailw ater Veloc ity (ft/s)

0.00

0.00 cfs

6912.5

0.00 0.00

0-

NF

0.00 0.00 0.0

0.00 0.00 0.00

0.35 cfs

0.35 cfs

6912.8

0.26 0.0* 1- S2 n

0.12 0.20 0.1

0.04 4.63 1.64

0.70 cfs

0.70 cfs

6912.9

0.37 0.0* 1- S2 n

0.16 0.29 0.1

0.06 5.65 2.16

1.05 cfs

1.05 cfs

6912.9

0.45 0.0* 1- S2 n

0.20 0.35 0.2

0.08 6.35 2.53

1.40 cfs

1.40 cfs

6913.0

0.52 0.0* 1- S2 n

0.23 0.41 0.2

0.10 6.95 2.84

1.75 cfs

1.75 cfs

6913.1

0.59 0.0* 1- S2 n

0.26 0.46 0.2

0.11 7.39 3.09

2.10 cfs

2.10 cfs

6913.1

0.65 0.0* 1- S2 n

0.28 0.50 0.2

0.13 7.83 3.32

2.45 cfs

2.45 cfs

6…