Norris_Peak_Road_Realignment_Hydraulics_Report_08-18-2015_Signed.pdf

Norris Peak Road Realignment Hydraulics Recommendation Report – 100% Submittal

Table of contents

Chapter Pages

1. Introduction

1.1 Project Description

1.2 Site Location

2. Design Criteria

2.1 Hydrologic Methodology

2.2 Hydraulic Methodology

3. Hydrology

3.1 Precipitation

3.2 Soils

3.3 Peak Flow Summary

4. Hydraulics

4.1 Culverts

4.2 Drainage Ditch

5. Design Recommendations

6. Summary

7. References

Appendices Appendix A – Hydrology Appendix B – Hydraulics Appendix C – Soil Map

Figure 1 Site Location Map

Figure 2 Basin Delineation

Table 3-1 Rainfall Intensities

1. Introduction

The purpose of this Hydraulics Recommendation Report is to provide a summary of the Norris Peak Road Realignment hydraulic recommendations for improvements to a 100% design level.

1.1 Project Description

The South Dakota Federal Lands Access Program (SD FLAP) Federal Highway Administration (FHWA) – Central Federal Lands Highway Division (CFLHD) is funding this project as part of Moving Ahead for Progress in the 21st Century (MAP-21). Norris Peak Road north of South Dakota Highway 44 has two (2) sharp reverse curves that will be removed by this project. Because of this realignment, Norris Peak Road will cross an existing drainageway twice. Also, this realignment will place Norris Peak Road in the path of normal sheet flow to the natural drainage path.

Two new culverts will be placed where Norris Peak crosses the existing drainageway. A roadside ditch on the uphill side of the proposed road. Runoff will be intercepted in this ditch and conveyed to the two aforementioned culverts and the culvert at the low point near the middle of the alignment.

1.2 Site Location

The SD FLAP CR 223801(1) Norris Peak Road is located in Pennington County, South Dakota west of Rapid City, off of South Dakota Highway 44 (SD 44). The project begins approximately

0.3 miles north of the intersection with SD 44, 300 feet past the cattle guard. The project ends approximately 1.4 miles north of the intersection with SD 44, at the end of the guardrail. This project is located in Sections 30 and 31 of Township 2 North and Range 6 East.

Figure 1 Site Location Map

2. Design Criteria

Hydrologic and hydraulic analysis follows the criteria and guidelines outlined by FHWA, CFLHD in the Project Development and Design Manual, DRAFT Chapter 7 (April 2011) [1]. Since the drainage analysis is within Pennington County and near Rapid City, the criteria for these jurisdictions is also referenced [2] [3].

This project does not impact any irrigation ditches.

2.1 Hydrologic Methodology

Hydrology was determined using two methods, the USGS Regression Equation and the Rational Method. The 25-year design storm was utilized. There are seven drainage basins in this project area as seen in Figure 2.

The largest basin (668 acres) is the area that is west of the new alignment. The USGS Regression Equation was used to analyze this basin [1]. See Appendix A for results. The existing roadway will remain as access to private properties. The proposed alignment crosses the existing drainageway at the outfall for this drainage area. Culvert sizing at this location accommodates the rainfall for this western basin as well as the top four basins to the east of the new alignment.

To the east of the new alignment there are six drainage basins. These basins were analyzed using the Rational Method.

The two highest basins (41 acres) drain directly to the existing drainageway before the new alignment’s upper crossing. The culvert sizing at this location accommodates the rainfall for these two basins.

The middle two drainage basins (74 acres) drain to a low point along the new alignment. Culverts have been sized to convey design runoff under Norris Peak Road.

The lowest two drainage basins (60 acres) drain into the natural drainageway downstream of the lowest crossing of the new alignment, therefore no new drainage features are recommended for accommodating these basins. See Appendix A for the Rational Method results.

Hydraulic Methodology

The roadside drainage ditch was designed to handle the 25-year storm flow. Pennington County’s minimum size for a roadside drainage ditch of 4:1 for the front slope and 1.1:1 for the back slope with a 2 foot depth. This size of ditch can adequately handle the 25-year design storm flows. Ditch sizing was confirmed with Flowmaster, see Appendix B.

The culverts were designed to transfer the 25-year storm drainage. HY-8 was used to find the appropriate size to convey these flows. See Appendix B for results.

3. Hydrology

3.1 Precipitation

The rainfall intensities for a 25-year storm are shown in Table 3.1.

Table 3-1 Rainfall Intensities

3.2 Soils

Soil types for the project area have been determined using the Natural Resources Conservation Service (NRCS) Soil Survey [5]. Soils consist of Type C and D soils. The breakdown of each soil type can be found in Appendix C.

Type C and D soils have a very slow infiltration rate (high runoff potential) when thoroughly wet.

These consist chiefly of clays that have a high shrink-swell potential, soils that have a high water table, soils that have a clay pan or clay layer at or near the surface, and soils that are shallow over nearly impervious material.

3.3 Peak Flow Summary

Seven basins were analyzed for this project. The peak flow rates associated with these basins quantify flow rates associated with the 25-year design storm at the drainage crossings. The cross-section for the new alignment provides a ditch on the upslope side of the roadway. The ditch provides adequate conveyance of the design flowrate to prevent overtopping of the proposed improvements.

The calculations for the peak flow for these seven basins are provided in Appendix A of this report.

4. Hydraulics

4.1 Culverts

The drainage under the roadway will be conveyed by culverts. Corrugated metal pipes (CMP) will be utilized for this project. Culvert sizing was performed using HY8.

At the upper crossing a single 36” CMP will be used. At the middle crossing two 36” CMPs will be used. At the lower crossing two 48” CMPs will be used.

Notably, the road grading at the lower 48” CMPs does alter the drainage path in events greater than the 25-year design event. Due to the impoundment that occurs from the realigned Norris Peak Road at the culverts, flow will overtop to the west at the intersection with the existing roadway alignment where it will continue southerly for approximately ¼ mile, where it combines with Rapid Creek, just slightly upstream of where it confluences in the historic condition.

Return Rainfall Intensity in Inches Per Hour at Time Duration

Period 5-min 10-min 15-min 30-min 1-hr 2-hr 3-hr 6-hr 24-hr

25-yr 9.19 7.33 6.15 4.25 2.71 1.68 1.25 0.74 0.25

4.2 Drainage Ditch

A ditch two (2) feet deep with 4:1 front slope and 1.1:1 backslope will be used for conveyance along the uphill side of the new alignment.

5. Design Recommendations

The drainage concepts outlined in Section 4 adequately drain the design flows associated the new Norris Peak Road alignment per the Project Development and Design Manual [3] and the Pennington County [4] and Rapid City Drainage Criteria [5].

6. Summary

The drainage analysis presented in this report was completed based on the current standards developed by CFLHD for the 30% design level. Any further design modifications will be discussed in additional memorandum or reports.

Figure 2 Basin Delineation

7. References

[1] National Resources Conservation Service, Web Soil Survey.

[2] City of Rapid City, Infrastructure Design Criteria, Rapid City, South Dakota, 2012.

[3] Pennington County, “Ordinance 14,” 110 May 2005. [Online]. Available:

http://www.pennco.org/index.asp?SEC=37E226F5-74EC-42A3-A414- 536208BD5909&Type=B_BASIC.

[4] Office of Federal Lands, Project Development and Design Manual, Federal Highway Administration, 2014.

[5] S. K. Sando, “Techniques for Estimating Peak-Flow Magnitude and Frequency Relations for South Dakota Streams,” United States Geological Survey, Rapid City, 1998.

Appendix A – Hydrology

NORRIS PEAK ROAD REALIGNMENT

Regression Analysis

Pennington County

8/17/2015

Job # 100045199

Area Slope

785 AC 0.09 ft/ft

1.2 sq.mi. 475.2 ft/mi

Per USGS Regression Equation***:

Q25 = 0.406 x CA 0.888 x S 1.06

- Subregion F, 25-year Frequency

Flow 335 cfs

Regression Analysis for Basin West of New Alignment

RATIONAL METHOD FOR BASINS EAST OF NEW ALIGNMENT

A B C D E F D&E C-5-yr C-25-yr* K

Areas [ft^2] 0.1 0.3 7

955202 798265 2762924 553161 1448284 1168976 *assumed as average of C10 and

C100 Areas [acre] Eff. Area

21.93 18.33 63.43 12.70 33.25 26.84 14

Overall Length [ft]

1877 2314 2663 2109 2031 2189

Overland Flow Length [ft]

500 500 500 500 500 500

Start Overland Flow Elevation [ft]

4736 4985 4985 4786 4786 4784

End Overland Elevation [ft]

4726 4762 4774 4723 4671 4696

Overland Slope [ft/ft]

0.53 9.64 7.92 2.99 5.66 4.02 Upper Middle Drainage

Overland Time of Concentration [min] Crossing Crossing Ditch E

51.5 19.8 21.1 29.1 23.6 26.4 Routed Routed

Swale Flow Length [ft] Ditch 32.6 76.8 49.1

1377 1814 2163 1609 1531 1689 757

Start Swale Flow Elevation [ft]

4726 4762 4774 4723 4671 4696 4453

End Swale Elevation [ft]

4554 4554 4438 4438 4335 4335 4363

Swale Slope [ft/ft]

0.12 0.11 0.16 0.18 0.22 0.21 0.12

Swale Velocity [ft/s]

2.5 2.4 2.8 2.9 3.3 3.2 2.4

Swale Time of Concentration [min]

9.3 12.8 13.1 9.1 7.8 8.7 5.2

Total Time of Concentration [min]

60.7 32.6 34.2 38.2 31.4 35.1 43.5

Intensity [in/hr] Comb. Int.

2.70 4.12 4.04 3.83 4.18 3.99 3.56

Peak Flowrate [cfs] Routed

17.7 22.6 76.8 14.6 41.7 32.1 49.1

Appendix B – Hydraulics

Appendix C – Soil Map