Final-Hydraulics_Recommendations.pdf

MAR-2012

FINAL HYDRAULICS RECOMMENDATIONS

TARRYALL CREEK ROAD

PIKE NATIONAL FOREST

CO PFH 81-1(4)

Prepared by:

Gerald Blackler

Technical Services Hydraulic Engineer

Central Federal Lands Highway Division

Lakewood, Colorado

Prepared by:

Gerald Blackler, PE

Hydraulic Engineer

Prepared Through:

Scott Hogan, PE

Hydraulic Team Leader

Prepared For:

Micah Leadford, PE

Project Manager

Table of Contents

Project Description and Scope

Design Standards for Project

Hydrologic Analysis

Watershed Description

Peak Flow Estimation for Large Drainages

Peak Flow Estimates for Small Drainages

Hydraulic Analysis

Existing Culvert Conditions and Capacity

Riprap Sizing and Bank Protection

Floodplain Assessment

Intermediate Hydraulic Recommendations

Culvert Replacement and Sizing

Gooseberry Gulch Discussion

Riprap Revetment and Bank Protection

FEMA Floodplain

References

List of Figures

Figure 1 – Interpolation between Rational Method and USGS Regression Equations for 25 year flow rates

Figure 2 - Detail for Stations 1458+00 and 2131+59

Figure 3 - Gooseberry Gulch Drainage Re-alignment

Figure 4 - Example Cross Sections of Existing and Encroached Channel

List of Tables

Table 1 - Variables used to Determine Time of Concentration

Table 2 - Runoff Coefficient for Small Basins at Tarryall Creek Road

Table 3 - Flow Summary Data for Tarryall Creek Road

Table 4 - Capacity Check for Existing Culverts at Tarryall Creek Road

Table 5 - Intermediate Hydraulic Recommendations for Tarryall Creek Road

Table 6 - Normal Depth Assumption Parameters for Tarryall Creek

Appendices

Appendix A – Hydrologic Information

Appendix B – Peak Flow Estimation Tables

Appendix C –Scoping Trip Summary Prepared by Roadway

Appendix D – Riprap Outlet Sizing and Embankment Protection Sizing

Appendix E – FEMA Floodplain Maps for Tarryall Creek

PROJECT DESCRIPTION AND SCOPE

This memorandum presents the intermediate hydraulic recommendations for Forest Highway (FH) 81, herein referred to as Tarryall Creek Road. Tarryall Creek Road is located in Park County, Colorado within the Pike National Forest. Additional project descriptions that contain details about other aspects of the project are available within separate reports and design documentation. This memorandum focuses on preliminary hydraulic recommendations that address peak flow estimation, culvert sizing, roadway embankment protection, and floodplain descriptions of the project area.

DESIGN STANDARDS FOR PROJECT

The estimated future average daily traffic (ADT) is between 400 and 1300, which is classified as a low volume road in the Project Development and Design Manual published by the FHWA (2008). The following standards are applied within this study:

Capacity and Stability Design for a 25 year flood.

Minimum Cross Road Culvert Diameter is 24 inches (600mm).

Headwater to Diameter Ratio (HW/D) is 1.5 for culverts less than 48 inches in diameter and 1.2 for culverts 48 inches in diameter or larger.

HYDROLOGIC ANALYSIS

WATERSHED DESCRIPTION

Major drainage basins that contribute to Tarryall Creek near the project site begin high up in the Mosquito and Ten Mile mountain ranges at the Continental Divide of the Rocky Mountains. These high peaks consist of rocky mountain sides and steep slopes that drain to a high mountain valley that is known locally as South Park, Colorado. Contributing side drainages that cross under Tarryall Creek Road originate from mountainous terrain with well established forest vegetation and moderate to steep channel slopes. Developments within the watershed are scarce and consist of ranchland and a few rural housing communities. Major drainages that will be affected by the proposed roadway improvements are, Allen Creek, Thorpe Gulch, Marksbury Gulch, and Obrien Gulch.

Sub-basins that contribute to design points on Tarryall Creek Road were divided and delineated using US Geological Survey (USGS) Digital Elevation Mapping (DEM) data (USGS 2011) and the Watershed Modeling System (Aquaeveo 2010). In total, 18 sub-basins were delineated based on major creeks and contributing areas. Figure A-1 and Table A-1 attached to this memorandum summarize each basin and the approximate roadway stationing at the outlet.

PEAK FLOW ESTIMATION FOR LARGE DRAINAGES

Regional regression equations that estimate natural stream flow are provided by the USGS in cooperation with the Colorado Water Conservation Board (CWCB) and the Colorado Department of Transportation (CDOT) and are found in the Scientific Investigations Report 2009-5136 (Capesius and Stephens 2009).

Equations for the Mountain Hydrologic Region are applicable to this study area and are defined by the basin area, slope, and mean annual precipitation as presented below.

Where, Qi = peak flow for the i return period, A = basin area in square miles, S = basin slope in percent, P

= mean annual precipitation, and are variable exponents used to predict floods for the 2 to 500 year storms. Mean annual precipitation values are taken from the Parameter-elevation Regressions on Independent Slopes Model (PRISM), which is the same data set used by the USGS in the development of the regression equations. Attachment B contains peak flow estimates for the 2 to 500 year storm events for the 18 basins included in this study.

PEAK FLOW ESTIMATES FOR SMALL DRAINAGES

Peak flow estimates for smaller drainages were developed using the Rational Method. Three drainage parameters are required within the Rational Method, including 1) rainfall intensity in inches per hour, 2) a runoff coefficient that represents the percent of flow from the drainage area, and 3) the drainage area in acres.

Rainfall intensity is a function of the Intensity Duration and Frequency (IDF) curves that are created from rainfall depths provided by NOAA (1973). The computed time of concentration (tc) determines what value from the IDF curves is appropriate. In this study, the time of concentration is determined from methodology presented in Hydraulic Design Series No. 2 (HDS 2) (McCuen et al 2002), where the total time of concentration is determined from overland flow, shallow concentrated flow, and then channelized flow. An optimization procedure built into the Hydraulic Tool Box (FHWA 2011) allows the final tc value to vary with rainfall intensity. Parameters used to compute tc are presented in Table 1 below.

Table 1 - Variables used to Determine Time of Concentration

Variable Value Description

Manning's n for Overland Flow 0.40 Woods with light underbrush

Intercept Coefficient for Velocity (k) 0.076 Forest with heavy ground litter ‐ overland flow

Manning's Roughness for Open Channel Flow

0.04 Mountain Streams, trees, brush, cobbles

Consistent land use within the study area allows for a broad application of a runoff coefficient that is representative of forested areas on relatively impermeable soil groups. Runoff coefficients for the study reach are determined from a volumetric runoff coefficient derived using the Soils Conservation Service (SCS) Runoff Curve Number Method that is described in Technical Release No. 55 (TR-55) (USDA 1986). Steps taken to derive the runoff coefficient are described below:

1. 24 Hour rainfall depths are selected from the National Oceanic and Atmospheric Administration (NOAA) Rainfall Atlas No. 2 for the 2 to 100 year storm intervals.

2. A Curve Number (CN) of 65 is selected from Table 2-2d of the TR-55 manual to represent woods in good condition hydrologic soil groupings B and C1.

3. Runoff volume is computed using equation 2-1 in the TR-55 manual.

4. The ratio of 24 hour rainfall depth to runoff volume is then used to determine the runoff coefficient.

Table 2 below presents the runoff coefficients used for small basins that drain to Tarryall Creek Road.

1 A 2/3 to 1/3 split is used between Type C Soils and Type B soils

Table 2 - Runoff Coefficient for Small Basins at Tarryall Creek Road

Tr (Years)

24 Hour Rainfall Depth (inches)

Runoff Volume (inches)

Runoff Coefficient

2 1.6 0.05 0.03

5 1.8 0.09 0.05

10 2.3 0.23 0.10

25 2.6 0.34 0.13

50 3.1 0.55 0.18

100 3.6 0.81 0.22

A comparison of the computed runoff coefficients with Table 3-1 in McCuen et al (2002) shows that the 10 to 50 year runoff coefficients in Table 2 are similar to parks, cemeteries, and sandy soils on steep slopes2.

Over 70 small drainages were analyzed using the rational method and the following was found:

Tributary drainage slopes are relatively consistent.

Peak flow values for basins 60 acres and larger were equal to or higher than the peak flow estimates for basins that are approximately one square mile (640 acres) when the USGS regression equations are applied.

Although the rational method is acceptable for computing runoff from small basins, it can also produce more conservative values and become less accurate as the basin area increases. Due to the consistency in drainage characteristics at Teryall Creek Road, a general relationship between peak flow and area can be derived for the 25 year peak flow rates. This relationship is used to bridge the gap between peak flow estimates from the rational method and the USGS regression equations. In Figure 1 below, an interpolation between the USGS regression equations and computed values from the rational method is presented.

2 The rational method is more traditionally applied to urban settings and therefore most references for runoff coefficients have land use characteristics representative of the urban environment.

Figure 1 – Interpolation between Rational Method and USGS Regression Equations for 25 year flow rates

The interpolated line presented in Figure 1 is computed by the following:

If the basin area is less than 50 acres than the peak flow is determined by Qp = 0.30A, If the basin area is greater than 50 acres and less than 640 acres than the peak flow is determined by Qp = 14*A0.075, If the basin area is greater than 640 acres than the peak flow is determined from the USGS regression equations.

Where, Qp is the peak flow in cubic feet per second (cfs) and A is the basin’s drainage area in acres.

Table 3 below presents drainage basin slope and elevation along with the resulting 25 and 50 year peak flow rates for the large basins analyzed as part of this study.

Table 3 - Flow Summary Data for Tarryall Creek Road

Basin ID Basin Area (sq mi)

Basin Slope

Average Elevation

Approximate Stationing

25 Year Design Flow

50 Year Design Flow

1B 10.51 18.85 9154 2131+59 108 134

2B 16.54 18.23 9322 2092+32 151 188

3B‐A 6.09 14 8754 2014+94 69 85

3B‐B 4.73 20.8 9450 1955+70 60 74

4B 0.43 11.25 8847 1882+42 10 12

5B 5.00 20.2 9246 1817+77 63 78

6B 0.66 17.12 8799 1759+84 15 18

0 500 1000 1500 2000

P e ak F lo w ra te cf s)

Drainage Basin Size (Acres)

Terryall Creek Road Peak Flow Comparison

USGS Regression Eq. (50 Year)

USGS Regression Eq. (25 Year)

Rational Method (25 Year)

"Rational Method (50 Year)

Interpolation

USGS (2008)

24" CMP Capacity at HW/D = 1.5 with FES and a Min. Slope of 2%

30" CMP Capacity at HW/D = 1.5 with FES and a Min. Slope of 2%

Basin ID Basin Area (sq mi)

Basin Slope

Average Elevation

Approximate Stationing

25 Year Design Flow

50 Year Design Flow

7B 1.73 27 9150 1735+24 30 37

8B 0.24 29.8 8989 1657+60 5 7

9B 0.47 26.22 9147 1620+00 11 13

10B 0.86 32.4 9501 1604+00 20 24

11B 9.70 33.1 1011 1568+91 112 138

12B 0.28 29.8 9142 1526+60 6 8

13B 0.58 34.8 9665 1483+15 13 16

14B 2.72 34.6 9963 1458+00 43 54

15B 0.70 37.8 9791 1394+25 16 19

16B 0.24 38.32 9416 1357+00 5 7

17B 0.54 40.6 9738 1325+79 12 15

18B 0.72 36.3 9747 1292+82 16 20

HYDRAULIC ANALYSIS

EXISTING CULVERT CONDITIONS AND CAPACITY

There are approximately 83 culverts that drain under Tarryall Creek Road into Tarryall Creek through the project reach. Most of these culverts consist of 12 to 15 inch corrugated metal or iron pipe. This study is focused on culverts that are larger than 48 inches in diameter or have a contributing area of approximately 200 acres or larger. Smaller cross drainages will be assessed by the roadway design engineer for appropriate sizing. Recommended runoff coefficients for the smaller basins are included in Attachment A for reference by the roadway designer.

During the scoping trip the following culvert conditions were noted by the roadway engineers:

Considerable damage on the ends of the culverts and no existing end treatment (end section or riprap) present.

Severe erosion in several locations around culverts.

Culverts that are discharging into wetland areas have a stable rundown area provided by the strong vegetation.

Most culverts ranged from ¼ full to completely buried with sediment.

There are several locations where water can build and channelize down the hillside with no culvert to allow for relief.

At approximate stations 1669+00 and 2131+50 two larger culverts have continuous water passing through them, and the culvert at 2131+50 has a history of icing issues.

Culvert capacity is assessed using the HY-8 Software developed by the Federal Highway Administration (FHWA 2009). A headwater to diameter ratio (HW/D) of 1.5 is applied for culverts less than 48 inches in diameter and a HW/D ratio of 1.2 is applied for culverts 48 inches in diameter or larger. Table 4 below summarizes the culvert capacity at the 18 locations that have larger drainages.

Table 4 - Capacity Check for Existing Culverts at Tarryall Creek Road

(acres)

Approximate Stationing

25 Year Design Flow (cfs)

Existing Culvert Does Culvert Have Adequate Capacity?

1B 6726.4 2131+59 108 54" CMP Yes

2B 10585.6 2092+32 151 48" CMP No

3B‐A 3897.6 2014+94 69 36" CMP No

3B‐B 3027.2 1955+70 60 24" CMP No

4B 275.2 1882+42 10 12" CMP No

5B 3200 1817+77 63 30" CMP No

6B 422.4 1759+84 15 18" CMP No

7B 1107.2 1735+24 30 36" CMP Yes

8B 153.6 1657+60 5 15" CMP No

9B 300.8 1620+00 11 NA No

10B 550.4 1604+00 20 NA No

11B 6208 1568+91 112 24" CMP No

12B 179.2 1526+60 6 15" CMP Yes

13B 371.2 1483+15 13 15" CMP No

14B 1740.8 1458+00 43 36" CMP No

15B 448 1394+25 16 26" Iron Pipe Yes

16B 153.6 1357+00 5 NA No

17B 345.6 1325+79 12 2 ‐ 24" Iron Pipes Yes

18B 460.8 1292+82 16 15 inch Iron Pipe No

RIPRAP SIZING AND BANK PROTECTION

During the site visit several areas were characterized by heavy slope erosion. Generally, most bank and slope erosion occurred where the roadway came close to Tarryall Creek. Stations 1345+00 LT to station 1357+00 LT were noted as being heavily eroded. Riprap lining is recommended in areas where Tarryall Creek comes close to the roadway and at any locations that slope erosion is noted. Estimation of riprap size comes from procedures in the Hydraulic Engineering Circular No. 15 (HEC 15) (FHWA 2005). A 100 year peak flow rate of 2,500 cfs is estimated from delineating a 390 square mile basin that contributes to Teryall Reservoir. Normal flow depths are computed using Manning’s equation and the channel geometry is estimated from USGS maps and photographs. A Class III riprap (D50 = 12 inches) is recommended for roadway bank protection.

Outlet protection at culverts should follow the Central Federal Lands (CFL) Standard Details. Outlet protection for culverts larger than 48 inches in diameter is designed in accordance with methodology provided in Hydraulic Engineering Circular No. 14 (HEC 14).

FLOODPLAIN ASSESSMENT

Tarryall Creek is classified by the Federal Emergency Management Agency (FEMA) as a Special Flood Hazard Area that is subject to flooding by the 1 percent annual chance flood. The flood hazard area is defined by Zone A, which is a flood zone that is determined by approximate methods and does not have base flood elevations determined. According to the Project Development and Design Manual (PDDM) the design guidance under this condition is to not exceed a 1 foot (0.3 meter) rise on own pre- and post-project water surface profile models. Attachment E contains FIRMETTE maps taken from FEMA’s website.

INTERMEDIATE HYDRAULIC RECOMMENDATIONS

CULVERT REPLACEMENT AND SIZING

The design standard for cross culverts at Teryall Creek Road requires a minimum cross culvert diameter of 24 inches and a minimum slope of 2 percent. A comparison of

Replace culverts that are less than 24 inches in diameter with 24 inch Corrugated Metal Pipe (CMPs) complete with flared end sections and outlet protection.

Replace undersized culverts as defined in Table 5 below:

Table 5 - Intermediate Hydraulic Recommendations for Tarryall Creek Road

Approximate Stationing

25 Year Design Flow

(cfs)

50 Year Design Flow

(cfs)

Existing Culvert

Proposed Culvert Notes

2131+59 108 134 54" CMP

4’x5’ Box culvert with headwalls and beveled edge

A box culvert will be constructed at this location, see icing discussion below.

2092+32 151 188 48" CMP

Twin 48 inch CMPs with headwalls and beveled edge

Culvert is undersized and needs a second 48 inch CMP to convey the

50 year peak flow.

2014+94 69 85 36" CMP

42 inch CMP with flared end sections

1955+70 60 74 24" CMP

36 inch CMP with flared end sections

1882+42 10 12 12" CMP

24 inch CMP with Flared End Sections

Approximate Stationing

25 Year Design Flow

(cfs)

50 Year Design Flow

(cfs)

Existing Culvert

Proposed Culvert Notes

1817+77 63 78 30" CMP

48 inch CMP with headwall and beveled edge

1759+84 15 18 18" CMP

24 inch CMP with Flared End Sections

1735+24 30 37 36" CMP

36 inch CMP with Flared End Sections

1657+60 5 7 15" CMP Drop Inlets A series of drop inlets will drain areas between 1603+00 to 1660+00

1620+00 11 13 NA Drop Inlets A series of drop inlets will drain areas between 1603+00 to 1660+00

1604+00 20 24 NA

30 inch CMP with Flared End Sections

See Gooseberry Gulch Discussion below

1568+91 112 138 24" CMP

Twin 54 inch CMP with Headwall and

Beveled Edge

Twin 42 inch CMPs with headwalls is also acceptable

1526+60 6 8 15" CMP

24 inch CMP with Flared End Sections

1483+15 13 16 15" CMP

30 inch CMP with

Approximate Stationing

25 Year Design Flow

(cfs)

50 Year Design Flow

(cfs)

Existing Culvert

Proposed Culvert Notes

1458+00 43 54 36" CMP

42 inch CMP with Flared End Sections

A box culvert will be constructed at this location, see icing discussion below.

1394+25 16 19 26" Iron Pipe

24 inch CMPs with Flared End Sections

This basin is split between a 24 inch at 1389+57 and a 24 inch at 1394+00

1357+00 5 7 NA

24 inch CMP with Flared End Sections

Drain to 1351+75

1325+79 12 15 2 ‐ 24" Iron

Pipes 30 inch CMP with Flared End Sections

Replace with Single 30 inch CMP

1292+82 16 20 15 inch Iron

Pipe 30 inch CMP with

Icing Problems at Stations (1458+00 and 2131+59) At Stations 1458+00 and 2131+59 there are perennial springs that create a small base flow in the drainage ways approaching the road. During winter months the base flows from the springs accumulate ice and clog the existing culverts. Local residences have complained about the amount of ice that accumulates on top of the road after the culvert clogs and overflows. A larger culvert is proposed at these two locations to reduce the likely hood if ice accumulating at the culvert’s inlet and eventually overtopping the road. In addition to a larger culvert, modifications upstream are proposed to reduce the amount of vegetation near the culvert’s entrance. Figure 2 below is a detail sketching the proposed modifications to address icing issues at Stations 1458+00 and 2131+59.

Figure 2 - Detail for Stations 1458+00 and 2131+59

GOOSEBERRY GULCH DISCUSSION

At station 1604+00 Gooseberry Gulch concentrates at Tarryall Creek Road. The proposed vertical alignment at this location cuts 3 feet into the existing roadway profile. There is no availability for drainage on the north side of the road, so a culvert under the roadway will need to be angled and have a length long enough to drain. A paved ditch in the proposed alignment begins at this location and carries water east to a series of drop inlets. To avoid having flows from Gooseberry Gulch flow onto the roadway it is recommended to drain the flows before they enter onto the roadway. Three options are viable for this crossing and are listed below in order of preference:

1. Start the paved ditch at a later station and place a 30 inch culvert under the roadway at approximate station 1605+30.

2. Place a 30 inch culvert under the roadway at approximate station 1604+00 and drain to the north west side of the roadway.

3. Grade the gulch west to drain at a 30 inch culvert at Station 1598+00. A roadside ditch with a base of 2 feet and side slopes of 4H:1V will carry the flow with a normal depth of about 1.1 feet.

The ditch should be lined with Class II (D50 = 9 inches) riprap for stability. Figure 3 below is a schematic of the proposed drainage at Station 1604+00.

Option 1 is the preferred option if it is viable with other aspects of the roadway design. Beginning the paved ditch later and utilizing the natural topography will be the least cost and maintenance of the three options. Figure 3 below presents a sketch showing the three options.

Figure 3 - Gooseberry Gulch Drainage Re-alignment

RIPRAP REVETMENT AND BANK PROTECTION

At locations where Tarryall Creek is near to or eroding into the roadway embankment provide riprap protection according to CFL’s standard details using Class 3 (D50 = 12 inches) riprap.

Outlet Sizing for Culverts Larger than 48 inches The following are riprap apron recommendations for the proposed culverts at Stations 2131+59 and 2092+32:

At Station 2131+59 provide a riprap apron outlet protection that consists of Class 5 (D50 = 1.5 feet) that is a minimum of 3.6 feet deep and has a length of at least 26 feet extended at a 3:1 angle from the culvert’s outlet.

At Station 2092+32 provide a riprap apron outlet protection that consists of Class 5 (D50 = 1.5 feet) that is a minimum of 3.6 feet deep and has a length of at least 26 feet extended at a 3:1 angle from the culvert’s outlet.

FEMA FLOODPLAIN

Under the current alignment there are minor encroachments into the FEMA floodplain as part of this project. All encroachments into the FEMA floodplain have been validated with a pre and post model that shows less than 1 foot (0.3 meters) of rise. In most locations, the alignment is taken further from the floodplain on Tarryall Creek, however, a few locations as discussed below have a minor impact within the FEMA Zone A.

Development of pre and post models are done using normal depth calculations and assuming a 100 year flow rate of 2,513 cfs and an average longitudinal slope of 0.005 feet per foot. Table 6 below presents the parameters used for Tarryall Creek 100 year floodplain estimates.

Table 6 - Normal Depth Assumption Parameters for Tarryall Creek

Manning's n

Flow Rate (cfs) Slope (ft/ft) Left OB Center Right OB

2513 0.005 0.045 0.035 0.045

A compound channel cross section was used with left and right overbank (OB) roughness values of 0.045.

A normal depth value of 6.1 for the full channel was compared with an encroachment that continues up to the low flow channel, or 100 feet from the existing bank. The resulting depth for the fully encroached section is 6.8 feet, which is less than a 1 foot rise. Figure 4 below presents the two conditions.

Figure 4 - Example Cross Sections of Existing and Encroached Channel

The entire alignment was reviewed for any potential encroachments that would exceed the condition presented in Figure 4. Based on a review of the alignment and the hydraulic assumptions presented in this section, there are no encroachments that result from the adjusted alignment that would produce a 1 foot rise or greater.

REFERENCES

Aquaveo (2010) Watershed Modeling System Version 8.4 © 2009 (www.aquaveo.com)

Capesius and Stephens (2009) “Regional Regression Equations for Esimtation of Natural Streamflow Statistics in Colorado” US Dept. of Interior and US Geol. Washington, DC.

Federal Highway Administration (2009) “HY-8 7.2” Software developed by the FHWA in cooperation with Aquaveo and the Environmental Modeling Research Laboratory.

Federal Highway Administration (2008) “Project Development and Design Manual” Federal Lands Highway Division. US Department of Transportation. Chp 7.

Federal Highway Administration (2005) “Design of Roadside Channels with Flexible Linings” Hydraulic Engineering Circular No. 15. Chp. 6. US Dept. of Transportation, Federal Highway Administration.

Federal Highway Administration (2001) “Hydraulic Design of Highway Culverts” Hydraulic Design Series No. 5. US Dept. of Transportation, Federal Highway Administration.

USGS (2011) Seamless Data Warehouse accessed July 2011 at http://seamless.usgs.gov/

Attachment A – Hydrologic Information

Figure A – 1 Basin Delineation for Terryall Creek Road

Table A1 – Basin Parameters for Terryall Creek Road

(sq. mi.)

Basin Slope

Average Elevation

(feet) Approximate

Stationing at outlet

1B 10.51 18.85 9154 2131+59

2B 15.17 18.23 9322 2092+32

3B 0.77 17.9 8754 2014+94

4B 0.89 11.25 8847 1882+42

5B 5 20.2 9246 1817+77

6B 0.66 17.12 8799 1760+11

7B 1.73 27 9150 1735+24

8B 0.24 29.8 8989 1657+60

9B 0.47 26.22 9147 1620+00

10B 0.86 32.4 9501 1604+00

11B 9.7 33.1 1011 1568+91

12B 0.28 29.8 9142 1526+60

13B 0.58 34.8 9665 1483+15

14B 2.72 34.6 9963 1496+62

15B 0.7 37.8 9791 1394+60

16B 0.24 38.32 9416 1357+00

17B 0.54 40.6 9738 1325+79

18B 0.72 36.3 9747 1282+00

Attachment B –Peak Flow Estimation Tables

Project ID CO PFH 81‐1(4) Terryall Creek Road

Description Preliminary Hydraulic Recommendations

Engineer Gerald Blackler, Hydraulic Engineer

Station 2131+59 Station 2092+32

Basin ID 1B Basin ID 2B*Basin ID 1B Basin ID 2B

A= 10.51 sq. mi. A= 16.54 sq. mi.

S = 18.85 % S = 18.23 %

P= 18.5 inches P= 18.5 inches

Q Q

Q2 ‐2.05 0.78 0.17 2.1 42 Q2 ‐2.05 0.78 0.17 2.1 60

Q5 ‐1.51 0.77 0.16 1.85 67 Q5 ‐1.51 0.77 0.16 1.85 94

Q10 ‐1.2 0.77 0.14 1.71 86 Q10 ‐1.2 0.77 0.14 1.71 121

Q25 ‐0.9 0.75 0.16 1.55 108 Q25 ‐0.9 0.75 0.16 1.55 151

Q50 ‐0.68 0.75 0.16 1.45 134 Q50 ‐0.68 0.75 0.16 1.45 188

Q100 ‐0.46 0.75 0.14 1.35 157 Q100 ‐0.46 0.75 0.14 1.35 219

Q200 ‐0.28 0.75 0.13 1.26 177 Q200 ‐0.28 0.75 0.13 1.26 248

Q500 ‐0.06 0.74 0.15 1.14 215 Q500 ‐0.06 0.74 0.15 1.14 299

*2B Collects 3B + 10.45 sq. mi

Station 2014+94 Station 1882+42

Basin ID 3B‐A* Basin ID 4B

A= 6.09 sq. mi. A= 0.43 sq. mi. Minimum Area of 1 sq. mi. Used

S = 14 % S = 11.25 %

P= 18.5 inches P= 18.5 inches

Q Q

Q2 ‐2.05 0.78 0.17 2.1 26 Q2 ‐2.05 0.78 0.17 2.1 6

Q5 ‐1.51 0.77 0.16 1.85 42 Q5 ‐1.51 0.77 0.16 1.85 10

Q10 ‐1.2 0.77 0.14 1.71 54 Q10 ‐1.2 0.77 0.14 1.71 13

Q25 ‐0.9 0.75 0.16 1.55 69 Q25 ‐0.9 0.75 0.16 1.55 17

Q50 ‐0.68 0.75 0.16 1.45 85 Q50 ‐0.68 0.75 0.16 1.45 21

Q100 ‐0.46 0.75 0.14 1.35 100 Q100 ‐0.46 0.75 0.14 1.35 25

Q200 ‐0.28 0.75 0.13 1.26 113 Q200 ‐0.28 0.75 0.13 1.26 28

Q500 ‐0.06 0.74 0.15 1.14 137 Q500 ‐0.06 0.74 0.15 1.14 35Q500 0.06 0.74 0.15 1.14 137 Q500 0.06 0.74 0.15 1.14 35

*2B Collects 3B‐B + 1.36 sq. mi

Station 1817+77 Station 1759+84

Basin ID 5B Basin ID 6B

A= 5 sq. mi. A= 0.66 sq. mi. Minimum Area of 1 sq. mi. Used

S = 20.2 % S = 17.12 %

P= 18.5 inches P= 18.5 inches

Q Q

Q2 ‐2.05 0.78 0.17 2.1 24 Q2 ‐2.05 0.78 0.17 2.1 7

Q5 ‐1.51 0.77 0.16 1.85 38 Q5 ‐1.51 0.77 0.16 1.85 11

Q10 ‐1.2 0.77 0.14 1.71 49 Q10 ‐1.2 0.77 0.14 1.71 14

Q25 ‐0.9 0.75 0.16 1.55 63 Q25 ‐0.9 0.75 0.16 1.55 18

Q50 ‐0.68 0.75 0.16 1.45 78 Q50 ‐0.68 0.75 0.16 1.45 23

Q100 ‐0.46 0.75 0.14 1.35 91 Q100 ‐0.46 0.75 0.14 1.35 27

Q200 ‐0.28 0.75 0.13 1.26 102 Q200 ‐0.28 0.75 0.13 1.26 30

Q500 ‐0.06 0.74 0.15 1.14 125 Q500 ‐0.06 0.74 0.15 1.14 37

Engineer Gerald Blackler, Hydraulic Engineer

Station 1735+24 Station 1657+60

Basin ID 7B Basin ID 8BBasin ID 7B Basin ID 8B

A= 1.73 sq. mi. A= 0.24 sq. mi. Minimum Area of 1 sq. mi. Used

S = 27 % S = 29.8 %

P= 18.5 inches P= 18.5 inches

Q Q

Q2 ‐2.05 0.78 0.17 2.1 11 Q2 ‐2.05 0.78 0.17 2.1 7

Q5 ‐1.51 0.77 0.16 1.85 18 Q5 ‐1.51 0.77 0.16 1.85 12

Q10 ‐1.2 0.77 0.14 1.71 22 Q10 ‐1.2 0.77 0.14 1.71 15

Q25 ‐0.9 0.75 0.16 1.55 30 Q25 ‐0.9 0.75 0.16 1.55 20

Q50 ‐0.68 0.75 0.16 1.45 37 Q50 ‐0.68 0.75 0.16 1.45 25

Q100 ‐0.46 0.75 0.14 1.35 43 Q100 ‐0.46 0.75 0.14 1.35 29

Q200 ‐0.28 0.75 0.13 1.26 48 Q200 ‐0.28 0.75 0.13 1.26 32

Q500 ‐0.06 0.74 0.15 1.14 60 Q500 ‐0.06 0.74 0.15 1.14 40

Station 1620+00 Station 1604+00

Basin ID 9B Basin ID 10B

A= 0.47 sq. mi. Minimum Area of 1 sq. mi. Used A= 0.86 sq. mi. Minimum Area of 1 sq. mi. Used

S = 26.22 % S = 32.4 %

P= 18.5 inches P= 18.5 inches

Q Q Q Q

Q2 ‐2.05 0.78 0.17 2.1 7 Q2 ‐2.05 0.78 0.17 2.1 7

Q5 ‐1.51 0.77 0.16 1.85 12 Q5 ‐1.51 0.77 0.16 1.85 12

Q10 ‐1.2 0.77 0.14 1.71 15 Q10 ‐1.2 0.77 0.14 1.71 15

Q25 ‐0.9 0.75 0.16 1.55 20 Q25 ‐0.9 0.75 0.16 1.55 20

Q50 ‐0.68 0.75 0.16 1.45 24 Q50 ‐0.68 0.75 0.16 1.45 25

Q100 ‐0.46 0.75 0.14 1.35 28 Q100 ‐0.46 0.75 0.14 1.35 29

Q200 ‐0.28 0.75 0.13 1.26 32 Q200 ‐0.28 0.75 0.13 1.26 33

Q500 ‐0.06 0.74 0.15 1.14 40 Q500 ‐0.06 0.74 0.15 1.14 41

Station 1568+91 Station 1526+60

Basin ID 11B Basin ID 12B

A= 9.7 sq. mi. A= 0.28 sq. mi. Minimum Area of 1 sq. mi. Used

S = 33.1 % S = 29.8 %

P= 18.5 inches P= 18.5 inches

Q Q

Q2 ‐2.05 0.78 0.17 2.1 44 Q2 ‐2.05 0.78 0.17 2.1 7

Q5 ‐1.51 0.77 0.16 1.85 69 Q5 ‐1.51 0.77 0.16 1.85 12

Q10 ‐1.2 0.77 0.14 1.71 87 Q10 ‐1.2 0.77 0.14 1.71 15

Q25 ‐0.9 0.75 0.16 1.55 112 Q25 ‐0.9 0.75 0.16 1.55 20

Q50 ‐0.68 0.75 0.16 1.45 138 Q50 ‐0.68 0.75 0.16 1.45 25

Q100 ‐0.46 0.75 0.14 1.35 160 Q100 ‐0.46 0.75 0.14 1.35 29

Q200 ‐0.28 0.75 0.13 1.26 180 Q200 ‐0.28 0.75 0.13 1.26 32

Q500 ‐0.06 0.74 0.15 1.14 220 Q500 ‐0.06 0.74 0.15 1.14 40

Engineer Gerald Blackler, Hydraulic Engineer

Station 1483+15 Station 1458+00

Basin ID 13B Basin ID 14BBasin ID 13B Basin ID 14B

A= 0.58 sq. mi. Minimum Area of 1 sq. mi. Used A= 2.72 sq. mi.

S = 34.8 % S = 34.6 %

P= 18.5 inches P= 18.5 inches

Q Q

Q2 ‐2.05 0.78 0.17 2.1 7 Q2 ‐2.05 0.78 0.17 2.1 16

Q5 ‐1.51 0.77 0.16 1.85 12 Q5 ‐1.51 0.77 0.16 1.85 26

Q10 ‐1.2 0.77 0.14 1.71 15 Q10 ‐1.2 0.77 0.14 1.71 33

Q25 ‐0.9 0.75 0.16 1.55 20 Q25 ‐0.9 0.75 0.16 1.55 43

Q50 ‐0.68 0.75 0.16 1.45 25 Q50 ‐0.68 0.75 0.16 1.45 54

Q100 ‐0.46 0.75 0.14 1.35 29 Q100 ‐0.46 0.75 0.14 1.35 62

Q200 ‐0.28 0.75 0.13 1.26 33 Q200 ‐0.28 0.75 0.13 1.26 70

Q500 ‐0.06 0.74 0.15 1.14 41 Q500 ‐0.06 0.74 0.15 1.14 87

Station 1394+25 Station 1357+00

Basin ID 15B Basin ID 16B

A= 0.7 sq. mi. Minimum Area of 1 sq. mi. Used A= 0.24 sq. mi. Minimum Area of 1 sq. mi. Used

S = 37.8 % S = 38.32 %

P= 18.5 inches P= 18.5 inches

Q Q Q Q

Q2 ‐2.05 0.78 0.17 2.1 8 Q2 ‐2.05 0.78 0.17 2.1 8

Q5 ‐1.51 0.77 0.16 1.85 12 Q5 ‐1.51 0.77 0.16 1.85 12

Q10 ‐1.2 0.77 0.14 1.71 15 Q10 ‐1.2 0.77 0.14 1.71 15

Q25 ‐0.9 0.75 0.16 1.55 21 Q25 ‐0.9 0.75 0.16 1.55 21

Q50 ‐0.68 0.75 0.16 1.45 26 Q50 ‐0.68 0.75 0.16 1.45 26

Q100 ‐0.46 0.75 0.14 1.35 30 Q100 ‐0.46 0.75 0.14 1.35 30

Q200 ‐0.28 0.75 0.13 1.26 33 Q200 ‐0.28 0.75 0.13 1.26 33

Q500 ‐0.06 0.74 0.15 1.14 42 Q500 ‐0.06 0.74 0.15 1.14 42

Station 1325+79 Station 1292+82

Basin ID 17B Basin ID 18B

A= 0.54 sq. mi. Minimum Area of 1 sq. mi. Used A= 0.72 sq. mi. Minimum Area of 1 sq. mi. Used

S = 40.6 % S = 36.3 %

P= 18.5 inches P= 18.5 inches

Q Q

Q2 ‐2.05 0.78 0.17 2.1 8 Q2 ‐2.05 0.78 0.17 2.1 8

Q5 ‐1.51 0.77 0.16 1.85 12 Q5 ‐1.51 0.77 0.16 1.85 12

Q10 ‐1.2 0.77 0.14 1.71 16 Q10 ‐1.2 0.77 0.14 1.71 15

Q25 ‐0.9 0.75 0.16 1.55 21 Q25 ‐0.9 0.75 0.16 1.55 21

Q50 ‐0.68 0.75 0.16 1.45 26 Q50 ‐0.68 0.75 0.16 1.45 26

Q100 ‐0.46 0.75 0.14 1.35 30 Q100 ‐0.46 0.75 0.14 1.35 29

Q200 ‐0.28 0.75 0.13 1.26 34 Q200 ‐0.28 0.75 0.13 1.26 33

Q500 ‐0.06 0.74 0.15 1.14 42 Q500 ‐0.06 0.74 0.15 1.14 42

Attachment C – Scoping Trip Summary Prepared by Roadway Design

CO PFH 81‐1(4)

TARRYALL CREEK ROAD

HYDRAULICS ISSUES FOR THE “SCOPE OF WORK” PREPARATION

Pre‐30% Scoping Trip

Narrative:

The scoping trip for the final phase of Tarryall Creek Road took place from May 16 to May 18, 2011. While on site, many hydraulic features were visited and concerns noted. The features noticed included roadside ditches and culverts. While on the scoping trip, several areas of concern and a total of 15 culverts not in the mapping file for the project were noted. Some of these concerns include culvert and drainage basin sizing, undercutting around culverts, piping, roadway overtopping, slope erosion and channeling around outlets.

There were several concerns noted with culverts. The first is that there was considerable damage on the ends of the culverts as no existing end treatment (end section or riprap) was present on any culvert with the exception of one, which had a dry stack head wall on the inlet. The absence of end treatments is allowing for severe erosion in several locations, which are more noticeable from just north of the town of Tarryall through the end of the project. However, in areas where the existing culverts are discharging into wetland areas, the soil is heavily rooted with vegetation, which has created a strong, stable rundown area. The need for a riprap end treatment may not be necessary in these locations.

Secondly, the majority of existing culverts ranged from ¼ full to completely buried. Third, there are several locations at which water can build and channelize traveling down the hillside, with no culvert to allow for relief or passage of the water across and away from the roadway, which is creating an overtopping condition. Additionally, in two areas, approximately stations 1669+00 and 2131+50, two larger culverts have continuous water passing through them, and the culvert at 2131+50 has a history of icing issues. At the Landis curve, there is one culvert allowing a large amount of water being carried from far down‐station to discharge away from the road. This culvert should be redesigned to accommodate this large volume of water, it will most likely require the use of a headwall with wing walls. Finally, it appeared that the majority of the culverts are undersized and need to be evaluated.

There are several areas on the project were heavy slope erosion exists. Most noticeably were the road is in close proximity to the creek, irrigation ditches, wetlands, or near major hillside channels.

Areas such as station 1345+00 LT to station 1357+00 LT, 2022+00 Lt and various other locations have considerable erosion. A larger sized riprap or slope armoring treatments should be considered. There are also locations where the roadway grade is considerably steep. Roadside ditches in these areas have shown signs of erosion and have items such as cobbles and branches present. Riprap lining should be considered in these locations.

Photographs of several of the items mentioned above as well as an existing culvert inventory of the proposed 15% mainline used for the scoping trip is shown below. For more information on the project, a drainage basin delineation file is located in the Roadway/design/Drainage Jeff file, the Hydraulic Toolbox for the project is located in: Roadway/design/design documentation/ misc/ tarryall(4) and current plan sheets can be found in the Roadway/sheets/C Sheets, and Old C Sheets folders.

Figure 1: Station 1351+00, Undercutting of Culvert by Tarryall Creek

Figure 2: Station 1429+50 Existing Culvert

Figure 3: Station 1469+50 Rt, Existing Historic Dry Stack Headwall

Figure 4: Station 1678+00 Lt. Slope Erosion

Figure 5: Station 1780+80 Lt. Erosion and Channeling from Culvert Discharge

Figure 6: Station 2022+00 Lt. Slope Erosion and Piping

Design and Hydraulics Responsibilities and Potential Design Considerations:

Drainage Basin Delineation

Culvert Sizing and Placement

Culvert End Treatments

Headwalls and Wing walls

Ditch Lining and Grading

Slope Stability and Armoring

Delegation of Design Work and QA/QC of All Design Work

Table 1: Tarryall Creek Road Mainline Culvert Inventory

Note: “not shown” indicated that the culvert is not present in the mapping file

Note: “unknown” indicates that neither the diameter or length of the culvert is present in the mapping file

Note: all stations are approximate as the horizontal alignment will be modified for the 30% PS&E Submittal.

CO PFH 81‐1(4) Tarryall Creek Road

Existing Culvert Inventory ‐ MAINLINE

Station

Findings Remarks

Field Review Mapping File

1265+76.31 15" CMP 15" X 40' CMP

1273+21.4 unknown 24" X 60' Iron Pipe Unable to verify size, culvert was buried

1282+00. 15" Iron Pipe not shown

1292+75.

2 ea 30" Iron Pipes not shown

1301+50. 15" Iron Pipe not shown

1303+58.64 24" Iron Pipe 24" Iron Pipe

1315+17.16 30" Iron Pipe unknown replace right on streamline

1325+79.11

2 ea 24" Iron Pipes

2 ea 24" Iron Pipes

1344+64.07 15" CMP 12" CMP

1351+05.65 15" CMP 15" CMP

Signs of scouring, may need heavy riprap or slope armoring as roadway is close to creek

1367+60.71 15" CMP 15" X 40' CMP

1385+43.39 12" CMP 12" X 40' CMP

Found 100 ft up station. Mapping showed 1384+43

1389+63.4

12" Iron Pipe 26" X 60' Iron Pipe

1394+59.73

26" Iron Pipe 26" X 60' Iron Pipe

1412+74.22

15" CMP

15" X 40' Iron Pipe Has existing berm built in

1429+50.96 15" CMP 12" X 50' CMP

1442+98.99 15" CMP 14" X 30' CMP

1450+50. 15" CMP not shown

1457+82.18 12" Iron Pipe 36" X 50' CMP

1459+00. 36" CMP not shown

1469+61.61 36" CMP 24" X 50' CMP Has dry stack headwall, possibly historic

1474+50. 15" CMP not shown

1483+15.22 15" CMP 15" X 32' CMP

1487+00.87 12" CMP 12" X 45" CMP

1501+68.93 18" CMP 18" X 60' CMP Has existing berm built in

1511+90. 15" CMP 14" X 40' CMP

1518+24.8 15" CMP unknown

1526+59.69 15" CMP 14" X 40' CMP

1540+96.86 15" CMP 14" X 40' CMP

1549+50. 15" CMP not shown

1555+67.21 15" CMP unknown

1568+75. 12" CMP not shown

1568+91.52 24" CMP 24" X 45' CMP constantly flowing stream present

1591+86.01 15" CMP 14" X 40' CMP

1637+00. 15" CMP not shown

1640+20.92 15" CMP 12" X 40' CMP

1651+34.78 12" CMP 12" X 40' CMP

1657+58.66 15" CMP 12" X 40' CMP

1666+93.85 12" CMP 12" X 40' CMP

1679+59.04 15" CMP 15" X 45' CMP

1685+56.53 24" CMP 24" CMP

1696+59.76 18" CMP 24" CMP

1701+32.5 24" CMP unknown

1706+22.44 12" CMP 12" X 50' CMP

1718+81.02 24" CMP 24" X 75' CMP

1727+85.14 15" CMP unknown

CO PFH 81‐1(4) Tarryall Creek Road

Existing Culvert Inventory ‐ MAINLINE

Station

Findings Remarks

Field Review Mapping File

1735+23.66 36" CMP 36" X 54' CMP

1760+11.28 18" CMP 14" X 50' CMP

1771+42.44 12" CMP 12" X 50' CMP

1775+77.65 36" CMP 36" X 50' CMP Ask forest what to do with this culvert

1782+42.49 12" CMP 12" X 50' CMP

1817+76.78 30" CMP unknown

1829+68.45 15" CMP 12" X 40' CMP

1834+12.02 15" CMP 12" X 40' CMP

1841+51.39 15" CMP 12" X 40' CMP

1855+59.27 12" CMP 12" X 40' CMP

1864+31.65 18" CMP 18" X 50' CMP

1874+00. 12" CMP unknown

1883+05.73 15" CMP 12" X 40' CMP

1890+46.81 24" CMP 24" X 75' CMP

1891+51.94 24" CMP 24" X 75' CMP

1927+36.29 15" CMP 14" X 60' CMP

1929+00. 15" CMP not shown

1937+78.54 15" CMP 14" X 60' CMP Earthen Dam present. Must avoid.

1947+50. 18" CMP 18" X 60' CMP

1955+53.59 24" CMP 24" X 80' CMP

1971+56.01 15" CMP 12" X 55" CMP

1981+70.45 15" CMP unknown

1992+00. 15" CMP not shown

2006+23.97 15" CMP unknown

2014+94.25 36" CMP 42" X 60' CMP

2031+95.88 18" CMP unknown

2042+08.89 18" CMP unknown

2053+00. 15" CMP not shown

2056+75. 18" CMP not shown

2066+01.47 18" CMP 12" X 55' CMP

2077+50. 18" CMP not shown

2085+00. 18" CMP not shown

2092+32.53 48" CMP unknown

2109+50. 15" CMP not shown

2117+50. 12" CMP not shown

2126+91.54 12" CMP 12" X 32' CMP

2131.59.24 54" CMP unknown Has icing issues in winter, constant stream

Attachment D – Riprap Outlet Sizing and Embankment Protection Sizing

Project Terryall Creek Road CO PFH 81‐1(4)

Description Roadway Riprap Protection Design

Engineer Gerald Blackler, Hydraulic Engineer

0.66323 Radians

0.01 Radians

Longitudinal Slope 0.01 K1 0.84 0.79756089

SG of Rock 2.65 0.38051 Radians

Angle of Repose 38 deg

Input

Angle of Repose 38 deg

Side Slopes 2.5

Design Input Taken from Hydraulic Tool Box

Return Period

Design

Discharge

(cfs)

Flow Depth

(ft)

Velocity

(ft/sec)

Shear

Velocity

(ft/sec)

Reynolds

Number

Safety

Factor

Sheilds

Parameter

(F*) d s p 0 D50 (ft) sin( ' SF

D50

(delta)

2 763 4.70 3.20 1.23 54754.01 1.04 0.055 2.93 2.45 3.05 0.80 0.70 1.15 0.54 0.54 0.64991627 0.662816513 0.90392 0.62

5 1162 5 10 3 60 1 28 59590 53 1 05 0 058 3 18 2 66 3 35 0 79 0 69 1 16 0 57 0 57 0 64476354 0 651648596 0 91201 0 655 1162 5.10 3.60 1.28 59590.53 1.05 0.058 3.18 2.66 3.35 0.79 0.69 1.16 0.57 0.57 0.64476354 0.651648596 0.91201 0.65

10 1473 5.40 3.80 1.32 63209.35 1.06 0.060 3.37 2.81 3.59 0.78 0.69 1.16 0.58 0.58 0.64094354 0.643505421 0.918 0.68

25 1750 5.60 4.10 1.34 65618.41 1.07 0.061 3.49 2.92 3.75 0.78 0.68 1.16 0.59 0.59 0.6384174 0.638182516 0.92195 0.69

50 2170 5.90 4.34 1.38 69227.48 1.08 0.063 3.68 3.07 3.99 0.77 0.68 1.17 0.61 0.61 0.63465808 0.6303508 0.92782 0.71

100 2513 6.10 4.60 1.40 71630.94 1.09 0.065 3.81 3.18 4.15 0.77 0.67 1.17 0.62 0.62 0.6321713 0.625227993 0.9317 0.73

0.00

Minsum 2E‐08

Notes

1 Design Procedure Follows Methodology in Hydraulic Engineer Circular No. 15 (HEC 15)

2 Normal channel computations are taken from the Hydraulic Tool Box Version 2.1

3 Channel geometry is course and estimated from USGS topographic data

4 Proposed Riprap is increased 1 class size due to coarseness of data

Recommended Size

Class III D50 = 12"Class III D50 12

Riprap Apron Sizing based on HEC 14 (CU) Project ID:

Location:

Date:

Riprap Apron Variable Value Notes

Q (ft3/s) 151.0

D (ft) 4.0 TW (ft) 1.3 Normal Depth (feet) 2.9 g (ft/s2) 32.2 Yes S (rock specific gravity) 2.5 No Outlet Velocity (ft/s) 8.62 Is flow Super Critical? Yes TW (ft) 1.3 D50 (ft) 1.67 D50 (ft) 2.34 D50 (ft) 0.532

D50 (ft) max 1.514

D50 (ft) for design 1.500 Adjusted Culvert Rise 3.450 Apron length (ft) 12.2 Apron depth (ft) 3.6

Class D50 (inch) D50 (ft) 1 6 0.50 2 9 0.75 3 12 1.00 4 15 1.25 5 18 1.50 6 21 1.75 7 24 2 8 30 2.5

9 36 3 10 42 3.5

Average

Select from Table 1

Use 26'

Table 1 - FHWA Riprap Class

Used in calculation

UD&FCD

Fletcher and Grace Eq 10-6 (HEC 14)

Default = 2.5

CO PHF 83-1(4)

2092+32 Twin 48" 4/17/12 version 070919 1 4/17/2012

Riprap Apron Sizing based on HEC 14 (CU) Project ID:

Location:

Date:

Riprap Apron Variable Value Notes

Q (ft3/s) 134.0

D (ft) 4.5 TW (ft) 1.19 Normal Depth (feet) 3.08 g (ft/s2) 32.2 Yes S (rock specific gravity) 2.5 No Outlet Velocity (ft/s) 11.55 Is flow Super Critical? Yes TW (ft) 1.2 D50 (ft) 1.59 D50 (ft) 1.93 D50 (ft) 0.956

D50 (ft) max 1.490

D50 (ft) for design 1.500 Adjusted Culvert Rise 3.790 Apron length (ft) 13.1 Apron depth (ft) 3.6

Class D50 (inch) D50 (ft) 1 6 0.50 2 9 0.75 3 12 1.00 4 15 1.25 5 18 1.50 6 21 1.75 7 24 2 8 30 2.5

9 36 3 10 42 3.5

Average

Select from Table 1

Use 26'

Table 1 - FHWA Riprap Class

Used in calculation

UD&FCD

Fletcher and Grace Eq 10-6 (HEC 14)

Default = 2.5

CO PHF 83-1(4)

2131+59 54" Culvert 4/17/12 version 070919 1 4/17/2012

Attachment E – FEMA Floodplain Maps for Terryall Creek gerald.blackler Callout 1292+82 gerald.blackler Text Box 1340+00 to 1353+00 gerald.blackler Text Box 1363 to 1385 gerald.blackler Text Box 1430 to 1445