01_ND_thro204(01)_Buck Hill Road_Final Hyd Report.pdf

Buck Hill Road

ND NP THRO 204(1)

Final Hydraulics Report

In Partnership With:

Theodore Roosevelt National Park National Park Service

Federal Highway Administration Central Federal Lands Highway Division

February 2025

2 ND NP THRO 204(1) Buck Hill Road – Final Hydraulics Report

Signature Sheet

Report prepared by: ____________________________________________________

Katie Kelehan, Hydraulic Engineer

Report reviewed by: ____________________________________________________

Aaron Estep, Hydraulic Engineer

Approved for distribution by: ____________________________________________________

Luis Calderón, Lead Hydraulic Engineer

Distribution

Electronic: N:\ND\thro204(01)\Hydraulics\9_Final‐Report

Toni Pankau, Project Management Stacy Dicciccio, Lead Designer Wilmari Valentin‐Medina, Designer Catherine Henry, Environment Dominic Monarco, Geotech Ron Andresen, Pavements Vaughn Marshall, Construction

3 ND NP THRO 204(1) Buck Hill Road – Final Hydraulics Report

Executive Summary

Project Description:

Hydrologic and hydraulic analyses were conducted for the ND NP THRO 204(1) Buck Hill Road project located in

Billings County, North Dakota. Buck Hill Trail Road, also known as Route 204, is in the Southeast portion of the

South Unit of Theodore Roosevelt National Park. The route begins at the intersection of Buck Hill Trail Road and

Scenic Loop Road. The route then proceeds southeasterly for approximately ¾ of a mile and ascends approximately 300 feet vertically to the Buck Hill Overlook parking area. The Buck Hill Overlook is a very popular location in the park, with approximately 32% of the park visitors visiting this overlook. This project proposes to rehabilitate the existing pavement, address subsurface issues observed along the route (including a previously identified slide area), and reconstruct the Buck Hill Overlook parking area at the end of the route. Along the project route, 8 existing culverts are slated for replacement or removal. An active landslide exists from approximate station 113+00 to station 122+50. Ditch reconditioning and additional inlets are recommended to reduce standing water at the base of this slide.

Design Criteria:

The Federal Lands Highway Project Development and Design Manual (PDDM) establishes the hydraulic design criteria for Buck Hill Road. With an average daily traffic (ADT) of 150 vehicles and a design speed of 15 mph, Buck

Hill Road is classified as a low‐standard road for hydraulic design.

Hydrologic Analysis:

The design flows recommended for use in hydraulic design were derived using the Rational Method.

Hydraulics Analysis:

The hydraulic performance of each of the existing culverts was analyzed. An inlet control analysis was performed for all crossings to determine required structure size.

Recommendations:

For this project, one existing culvert was not analyzed as part of this project – C08. This culvert will be removed as part of the proposed parking lot configuration thus it was not evaluated. An additional existing culvert, C04, was identified at the 30% field review. This pipe was mostly blocked by sediment and assumed to have been left behind from a previous road realignment. This pipe is recommended to be cleaned‐in‐place as it may provide additional drainage for the existing slide area.

All other existing structures will be replaced to accommodate roadway widening and to bring all structures up to the same service life. At the request of project partners, all replacement and new culverts will be HDPE to better withstand the corrosive properties of the soils within the park. Inlet and outlet end treatments are specified in

Table 1.

At the base of the existing slide area is a wide, flattened slope. Currently, runoff from the surrounding terrain ponds in this area. In addition to the paved ditches discussed in this report, superelevation of the road surface to the outboard side of this slide area is recommended with additional inlets installed to capture drainage along this reach.

With the addition of curb and gutter along much of the project reach, regular maintenance of inlets and ditches will be necessary to retain hydraulic efficiency as the erosive potential of the surrounding soils is high.

Recommendations for each crossing can be found in Table 1 following this section.

4 ND NP THRO 204(1) Buck Hill Road – Final Hydraulics Report

Outlet Protection:

Outlet protection for single barrel pipe culverts with diameters less than or equal to 48 in. and pipe slopes up to

10% may be sized in accordance with Standard Detail C251‐50, Placed Riprap at Culverts. This is applicable for culvert C01. A Standard Riprap Aprons is also recommended for C03 once the pipe is run down to a flatter slope.

Rundowns adhering to Special Detail C602‐A are recommended for culverts C02, C07, and PR04 due to pipe slopes exceeding 10% and limited surface cover. Standard riprap aprons at these outlets are recommended for if slopes allow.

The proposed location of PR05 is largely driven by grading of the proposed parking lot and results in the pipe outletting onto a fill slope. Due to sediment concerns from the surrounding hillsides which have the potential to drain to this inlet, the alignment of the pipe should remain perpendicular to the inlet. A riprap apron adhering to

Standard Detail C251‐51, Placed Riprap Between Cut and Fill, should be installed at the outlet.

Class 1, Type E, non‐woven geotextile is recommended for all aprons.

Ditches:

This project proposes to install paved ditch along much of the effected reach to help convey pavement drainage and reduce erosive sheet flow. Along the project reach, a minimum of 1‐ft deep (below the structural section) triangular ditch is recommended. This is assuming a foreslope of 1V:6H and a maximum backslope of 1V:1.0H. In addition, a minimum 6‐inch concrete curb is recommended.

A ditch lined with articulated concrete block (ACB) adhering to Special Detail 253‐A is proposed to provide flow conveyance to an existing culvert at the base of the slide area. Typical details and cross sections for this ditch have been included in the project plans as a parabolic ditch with approximate maximum side slopes of 1V:2H, minimum depth of 9 inches, and a minimum width of 3 ft. This ditch should be lined with non‐woven, Class 1, Type E geotextile.

To protect the guardrail aggregate pad from erosion, vegetated ditches are recommended throughout the project reach. These vegetated ditches should be triangular with an assumed foreslope of 1:4 and backslope of 1:3. In addition, these ditches should accommodate a minimum 6‐inch flow depth. Before permanent vegetation is established, the ditches should be lined with rolled erosion control product Type 2C.

Location‐specific ditch recommendations are included in Table 3 and additional details for the ditches lined with

ACB are included in section 6.1 of this report.

Parking Lot Drainage:

Reconfiguration of the parking at the end of the existing project reach (to replace the loop) is proposed. A detailed layout for the new parking lot has been included in the project plans. A new storm drain with curb‐opening inlet and grate is proposed near the southeast corner of the parking lot to convey drainage. NDDOT Detail D‐722‐2 for

Inlet – Type 2 will be adapted for this project and included in the plans. The location of this inlet will be reassessed as needed to account for potential changes in the parking lot grading.

Table 1: Hydraulic Recommendations

Table 2: Outlet Protection Recommendations

Table 3: Ditch Hydraulics

Ditch Start

Station End

Station Location Type

Drainage Area (ac)

10‐yr Flow

Slope Flow

Depth (ft.)

Spread2 (ft)

Avg Velocity

(fps) Recommendation

D01 100+52 101+75 RT Paved 0.3 0.4 7.6% 0.09 0.0 4.0 Paved with minimum 6 in. Concrete Curb

D02 106+00 113+80 LT Paved 1.5 1.7 8.3% 0.17 0.0 6.5 Paved with minimum 6 in. Concrete Curb

D03 108+10 119+63 RT Paved 2.2 2.4 5.1% 0.23 0.0 6.1 Paved with minimum 6 in. Concrete Curb

D04 119+64 124+00 RT Paved 1.5 1.7 10.7

0.16 0.0 7.1 Paved with minimum 6 in. Concrete Curb

D05 114+50 117+04 LT Lined 1.9 2.1 4.2% 0.15 N/A 5.8 Parabolic with minimum 0.75 ft. depth and 3 ft. width (ACB lining)

D06 117+95 125+00 LT Paved 0.8 0.9 1.0% 0.21 0.0 2.6 Paved with minimum 6 in. Concrete Curb

D07 127+50 129+75 RT Paved 0.5 0.5 9.0% 0.11 0.0 4.5 Paved with minimum 6 in. Concrete Curb

D08 131+16 131+70 LT Vegetated 1.31 1.4 7.8% 0.30 N/A 4.5 Triangular Ditch assuming max foreslope of 1V:4H and max backslope of 1V:3H

D09 131+70 136+82 LT Paved 1.3 1.4 8.7% 0.16 0.0 6.2 Paved with minimum 6 in. Concrete Curb

D10 136+82 138+15 LT Paved 1.2 1.3 9.3% 0.15 0.0 6.2 Paved with minimum 6 in. Concrete Curb 1 – D08 is proposed to provide erosion protection to the aggregate base layer of the guardrail terminal. Total drainage area to C05 used to provide conservative discharge estimate for the applicability of vegetated lining at these ditches along the project reach.

2 – Total width of paved ditch and gutter section is 3.5 ft. All flow for paved ditches contained within this section.

Table of Contents

1 Project Background Information

1.1 Project Information

1.2 Flood Insurance Study

2 Hydraulic Design Criteria

3 Hydrology

3.1 Hydrologic Setting and Topographic Data

3.2 Available Hydrologic Data

3.3 Rational Method Estimates

3.4 Regression Equation Estimates

3.5 Recommended Design Flows

4 Culvert Capacity Design

4.1 Inlet Control Analysis

4.2 Culvert Capacity Design Results

5 Culvert Stability Design

5.1 Entrance Treatment

5.2 Outlet Protection

5.3 Inlet Protection

6 Additional Considerations

6.1 Hydraulic ditches

6.2 Parking Lot Drainage

7 References

3 ND NP THRO 204(1) Buck Hill Road – Final Hydraulics Report

Tables Table 1: Hydraulic Recommendations

Table 2: Outlet Protection Recommendations

Table 3: Ditch Hydraulics

Table 4: PDDM Hydraulic Design Criteria

Table 5: Maximum Peak Flows Based on Inlet Control Conditions

Figures Figure 1: Project Location Map

Appendices Appendix A: Existing Site Information

Appendix B: Hydrology

Appendix C: Hydraulic Analyses

Appendix D: Details

4 ND NP THRO 204(1) Buck Hill Road – Final Hydraulics Report

1 PROJECT BACKGROUND INFORMATION

1.1 PROJECT INFORMATION

Buck Hill Road, also known as Route 204, is in the southeast portion of the South Unit of Theodore Roosevelt

National Park which falls within Billings County, ND. The route begins at the intersection of Buck Hill Road and the

South Unit Loop Road. The route then proceeds southeasterly for approximately ¾ of a mile and ascends approximately 300 feet vertically to the Buck Hill Overlook parking area. The Buck Hill Overlook is a very popular location in the park with approximately 32% of visitors visiting this overlook.

The present‐day condition of the road is poor; the surface is rough with broken pavement, deep cracks, and rutted to where it is marginally safe to use. One steep segment of the road has gravel surfacing; consequently, the road is subject to wash board type roughness soon after road maintenance takes place. This portion is also susceptible to severe erosion after rain events, as the deep rutting forces water to run directly down the roadway washing away much of the surface gravel. In recent years the road has been closed on occasion due to underlying drainage structures failing, resulting in large and deep sink holes in the road surface. This project proposes to rehabilitate the existing pavement, address subsurface issues observed along the route (including a previously identified slide area), and rehabilitate or reconstruct the Buck Hill Overlook parking area at the end of the route. Hydraulically, the project route has 8 existing culverts as well as stormwater inlets – all slated for replacement or removal. The project location is depicted in Figure 1 below. The existing crossings were evaluated for capacity and recommendations are provided for each structure. Existing crossing information can be found in Appendix A.

Figure 1: Project Location Map

1.2 FLOOD INSURANCE STUDY

The Federal Emergency Management Agency (FEMA) provides Flood Insurance Rate Maps (FIRMs) that detail special flood hazard areas. Lands inundated by the base flood (100‐year) are subject to National Flood Insurance

Project Start

Project End

5 ND NP THRO 204(1) Buck Hill Road – Final Hydraulics Report

Program (NFIP) floodplain management regulations. This project falls outside of all special flood hazard areas. As such, the project will not be subject to NFIP floodplain management regulations for backwater and for unregulated floodplain zones, the PDDM allows a maximum of 1‐foot rise in proposed condition base flood elevations. The

FEMA FIRM for this area has been included in Appendix A.

2 HYDRAULIC DESIGN CRITERIA

One existing culvert was not analyzed as part of this project – C08. This culvert will be removed as part of the proposed parking lot configuration. An additional existing culvert, C04, was identified at the 30% field review. This pipe was mostly blocked by sediment and assumed to have been left behind from a previous road realignment.

This pipe is recommended to be cleaned‐in‐place as it may provide additional drainage for the existing slide area.

For all other culverts, the Federal Lands Highway Project Development and Design Manual (PDDM) (Federal Lands

Highway 2012) establishes the hydraulic design criteria for Buck Hill Road. Based on the project scoping documents, Buck Hill Road will have a design speed of 15 mph and has an average daily traffic (ADT) of 150 vehicles. Per the PDDM, Buck Hill Road is classified as a low‐standard road and will have a design frequency of 25 years for culverts. Therefore, hydraulic analysis will conform to the FLH design criteria listed in Table 4. The PDDM also recommends a HW/D of 1.5 for all minor culverts with reductions made in the case of sediment or debris load concerns. Due the sandy nature of the soil along the Buck Hill project reach, a HW/D of 1.0 has been used.

Table 4: PDDM Hydraulic Design Criteria

High‐Standard Roadway

Design Frequency Check

Frequency Design Criteria

Roadway Culverts

25‐year Overtopping

New: AHW ≤ bottom of aggregate base layer

Where D ≤ 48", HW/D ≤ 1.5 & Where D > 48", HW/D ≤ 1.2

Heavy debris or sediment load concerns: 0.8 ≤ HW/D ≤ 1.0

Crossing is stable at the design flood

Minimum pipe size: 24 in. or equivalent

Roadside Ditches

10‐year N/A

New: WSEL ≤ bottom of aggregate base layer

Minimum longitudinal slope = 0.5%

Permanent Ditch Linings: Stable at the 10‐year flood

Pavement Drainage

10‐year, 50‐year in sumps

N/A

Allowable Spread = Half of one travel lane

Depth in Sumps and Parking Areas = 6” (150 mm)

Inlet Clogging Factor = 50% for grate inlets in sag or sumps

3 HYDROLOGY

3.1 HYDROLOGIC SETTING AND TOPOGRAPHIC DATA

The project is in the Missouri Plateau hydrographic region of southwestern North Dakota. The contributing drainage basins for each crossing selected for evaluation were delineated in the Watershed Modeling System version 11.1 using 1‐meter Digital Elevation Model information obtained from the USGS National Map (U.S.

Geological Survey 2023). Point precipitation depths were determined from NOAA Atlas 14 (National Oceanic and

Atmospheric Administration 2023) using the approximate centroid of the project area. Drainage basin delineations have been included in Appendix B.

6 ND NP THRO 204(1) Buck Hill Road – Final Hydraulics Report

3.2 AVAILABLE HYDROLOGIC DATA

There are no active USGS streamflow stations within the project limits. The closest stations are located on Sheep

Creek Tributary and Sheep Creek Tributary 2, both near Medora, ND. Information from these gages was not used in the hydrologic analysis for this project as the gages are both hydrologically disconnected from the project area and have drainage areas much larger than any of the basins analyzed for this project.

3.3 RATIONAL METHOD ESTIMATES

Per the PDDM, the Rational Method is applicable for basins up to 200 acres. All basins within the Buck Hill Road project fell below this 200‐ac limit.

Values for the dimensionless runoff coefficient (C) were chosen based on the land use identified from available aerial imagery. The basins are represented with a value of 0.2 per HDS‐2 (FHWA 2002). These values are associated with unimproved area surrounding the project area.

The Hydraulic Toolbox (FHWA 2022) was used to develop IDF curve equations from NOAA Atlas 14 rainfall data.

A single location was selected in NOAA Atlas 14 (approximate centroid of project) and was taken to represent all basins evaluated using the Rational Method. Times of concentration were initially computed for each basin through WMS using the Kirpich Method for overland flow on bare earth. Each basin produced a Tc less than 5 minutes so 5 minutes was used corresponding to the minimum storm duration specified by NOAA Atlas 14. Rainfall intensities were derived using this duration and computed IDF equations and the resulting Rational Method peak flows are provided in Appendix B.

3.4 REGRESSION EQUATION ESTIMATES

The U.S. Geological Survey (USGS) provides information for estimating peak flows via regional regression equations for North Dakota in Report 2015‐5096. For these equations, the basins delineated for the Buck Hill Road project fall within Hydrologic Zone B. The equations developed for this zone consider drainage area, a ruggedness number, and a compactness number.

For these equations, the ruggedness number is defined as the stream density times basin relief, where stream density is the stream length divided by the drainage area, and the basin relief is the maximum basin elevation minus the minimum basin elevation. The NDDOT Drainage Design Manual requires the total of all flowlines represented by the USGS National Hydrography Dataset (NHD) to be used when calculating the ruggedness number. For small drainage areas which do not contain any NHD stream lines, the length of a single stream line representing the longest flow path in the drainage area may be used. For Buck Hill Road, all drainage areas derived contained no NHD streamlines so the longest flow paths developed in WMS were used to compute the ruggedness numbers.

These equations also define the compactness ratio as a measure of basin shape related to basin perimeter and drainage area. It is computed as the basin perimeter length divided by two times the square root of pi times the drainage area.

For Zone B, the range of applicable drainage areas is from 0.110 to 8,342.4 mi2, the range of the ruggedness number is 68.02 and 7819.7 ft/mi, and the range of the dimensionless compaction number is 1.41 to 3.48.

Additionally, the Zone B regression equations have an average standard error of prediction of 58.8% for the 25‐yr event and 63.5% for the 100‐yr event.

7 ND NP THRO 204(1) Buck Hill Road – Final Hydraulics Report

For this analysis, the parameters determined for each crossing were developed using WMS. Variables calculated for each basin are provided in Appendix B.

3.5 RECOMMENDED DESIGN FLOWS

The selected design flows recommended for use in hydraulic design were computed using PDDM requirements for the Rational Method. Although regional regression equations are preferred by the North Dakota Department of Transportation (NDDOT) for rural basins (NDDOT 2023), the drainage areas and computed compactness numbers for each basin along Buck Hill Road were well outside the ranges typically used for the Zone B regression equations. Because of this, regional regression analysis for the existing culverts resulted in unusable peak flow estimates. Computing approximate culvert replacement sizes using the Rational Method peak flow rates resulted in most of the existing culverts (cross and side drainages) being adequately sized for the 25‐year design flow.

4 CULVERT CAPACITY DESIGN

Using the selected design flows described in Section 3, the hydraulic performance of each of the project crossings was evaluated. An inlet control analysis was initially performed for all crossings to determine required structure size.

4.1 INLET CONTROL ANALYSIS

As a rapid evaluation of hydraulic capacity, an inlet control analysis was first performed for each of the identified project culverts. This analysis is based on the inlet control equations documented in HDS‐5, Appendix A (FHWA

2012). Section A.5 of HDS‐5 describes how the inlet control equations were developed into polynomial equations for use in the HY‐8 software. The standard inlet control polynomial equation is provided in HDS‐5, Section A.5 and

Section 5.2.1.1 of the HY‐8 version 7.8 user manual. This equation was simplified as shown below for use with round pipes (barrel span equal to rise).

𝐻𝑊

𝐷

ൌ 𝑎 𝑏 𝑄 𝐷ଶ.ହ

൨ 𝑐 𝑄 𝐷ଶ.ହ

൨ ଶ 𝑑 𝑄 𝐷ଶ.ହ

൨ ଷ 𝑒 𝑄 𝐷ଶ.ହ

൨ ସ 𝑓 𝑄 𝐷ଶ.ହ

൨ ହ

𝐾௦𝑆

Where:

HW Headwater depth above inlet invert, ft

D Interior height of culvert barrel, ft

Q Discharge, ft3/s

Ks Slope correction, 0.7 for mitered to slope inlet configurations

S Culvert barrel slope, ft/ft, assumed to be 0.1 for this analysis

The coefficients a, b, c, d, e, and f are provided for various culvert shapes, materials, and inlet edge configurations in Appendix A of the HY‐8 version 7.7 user manual. The calculations for each crossing using the above equation were carried out using Microsoft Excel.

For this analysis, it is assumed that all minor culverts (diameter of 48‐in or less) will be replaced with pipe sizes as determined by the inlet control analysis only. In addition, project partners requested mitered to slope end treatments for aiding in culvert maintenance. For this reason, it is assumed that the replacement structures will be mitered with concrete toe walls for added stability. Coefficients corresponding to a Mitered to Slope inlet configuration (Ke = 0.7) were used. Maximum flow rates for various pipe sizes based on the above assumptions are provided in Table 5 below.

8 ND NP THRO 204(1) Buck Hill Road – Final Hydraulics Report

Table 5: Maximum Peak Flows Based on Inlet Control Conditions

Pipe Diameter WWA Maximum Flow (cfs)

(in) (sq ft) HW/D = 0.8 HW/D = 1.0 HW/D = 1.2 HW/D = 1.5

18 1.8 3.5 5.4 6.9 8.7

24 3.1 7.7 11.2 14.3 17.9

30 4.9 13.4 19.7 24.9 31.3

36 7.1 21.2 31.1 39.4 49.3

42 9.6 31.3 45.7 57.9 72.5

48 12.6 43.7 63.8 80.9 101.3

4.2 CULVERT CAPACITY DESIGN RESULTS

The results from the inlet control analysis indicate that all the crossings are considered minor drainages (requiring less than or equal to a single 48‐in barrel). Of the 7 existing culverts analyzed, 6 were determined to be adequately sized while 1, the existing rundown, C02, required upsizing. All culverts are proposed for replacement to accommodate the road improvements as well as to update the service life of all drainages within the project section. Additionally, the adequately sized culverts are recommended to be upsized to meet the minimum required pipe size recommended by the PDDM (24‐in for cross culvert). No culverts will be downsized.

Of the 5 culverts originally proposed, PR01 and PR02 were removed from the final scope. Reconditioning of the existing ditch at PR01 was determined to be more beneficial at the 30% field review than installing a new inlet. In addition, daylighting of the outlet for PR02 would be hindered without extensive grading of an earthen embankment across the road. Instead, an existing ditch at the base of the slide area will be reconditioned and lined to better convey flow from the proposed paved ditch along the right up station of the slide area.

Results and additional details of the inlet control analysis are provided in Appendix C. Final recommendations are provided in Table 1 of the Executive Summary of the report.

5 CULVERT STABILITY DESIGN

In addition to culvert capacity, the stability at each structure was evaluated to ensure long term success. The following suggestions discuss culvert stability considerations throughout the project.

5.1 ENTRANCE TREATMENT

At the request of project partners, C01, PR02, and C03 are recommended to have inlet end sections mitered to slope for ease of maintenance. These end sections should be anchored with a concrete toe wall for stability. C02, PR04, and C07 should be equipped with flared end sections at the inlets. Also, at the request of partners, the proposed concrete curb should be tied into these flared end sections and for C02 and C07, the asphalt paving should extend 3 inches into the inlet to provide a continuous surface such that no vegetation may grow. A Special of CFL Standard Detail 602‐5 has been included in the project plans for these culverts. Standard drop inlets with catch basins are recommended for C05, C06, and PR03. Analysis of these inlets has been included in Appendix C.

5.2 OUTLET PROTECTION

Outlet protection for single barrel pipe culverts with diameters less than or equal to 48 inches and pipe slopes up to 10% may be sized in accordance with Standard Detail C251‐50, Placed Riprap at Culverts. This is applicable for culvert C01. A Standard Riprap Apron is also recommended at C03 once the pipe is run down to a flatter slope.

9 ND NP THRO 204(1) Buck Hill Road – Final Hydraulics Report

Rundowns adhering to Special Detail C602‐A are recommended for culverts C02, C07, and PR04 due to limited surface cover. These rundowns have been successful in other areas of Theodore Roosevelt National Park.

Additional testing requirements for these rundowns will be included in the SCRs. Standard riprap aprons should be installed at the outlets if the final outlet slope allows.

PR03, C05, and C06 would require lengthening in excess of 200 feet to outlet onto flatter, more stable slopes.

These pipes should be extended away from the road surface a minimum of one pipe length to protect the road from erosion. As observed at the 30% site visit, C05 and C06 both outlet onto a slope that is well vegetated and stable.

The proposed location of PR05 is largely driven by grading of the proposed parking lot and results in the pipe outletting onto a fill slope. Due to sediment concerns from the surrounding hillsides which have the potential to drain to this inlet, the alignment of the pipe should remain perpendicular to the inlet. A riprap apron adhering to

Standard Detail C251‐51, Placed Riprap Between Cut and Fill, should be installed at the outlet. The location of this inlet may be re‐evaluated in subsequent project phases if the proposed parking lot grading allows for a different configuration.

Class 1, Type E, non‐woven geotextile is recommended for all aprons.

5.3 INLET PROTECTION

No inlet scour concerns were identified during project scoping. No additional inlet protections are proposed currently aside from entrance treatments specified in section 5.1.

6 ADDITIONAL CONSIDERATIONS

6.1 HYDRAULIC DITCHES

Paved Ditches

Proposed ditches along the project reach were analyzed to ensure they meet flow capacity requirements and convey flow to drainage structures along the corridor. Using the Hydraulic Toolbox, a capacity analysis was completed for locations throughout the project.

To compute ditch design flows, subbasins draining to each of the outlets were delineated. In addition, longitudinal slope for each section was provided by Design. For this project, curb and gutter dimensions were adopted from

NDDOT standards to create CFL Special Detail 609‐A. For these ditches, a 2‐ft wide paved section (at a 1V:6H foreslope) was used along with a 1.5‐ft wide concrete gutter and a 1‐inch relief along the gutter section.

To conform with other areas throughout the park, a 6‐inch‐tall concrete curb is recommended. Ditch typical detail and cross sections are available in the project plans. Site‐specific results of the ditch capacity analysis can be found in Table 3 included in the Recommendation Summary. The capacity analysis including a representative cross section used in the analysis can be found in Appendix C.

Lined Ditches

Lined ditches are proposed in key locations throughout the project site specifically to protect the guardrail aggregate pad from erosion. In addition, two existing ditches (one along the base of the slide area (approximate station 114+42 to 117+55) and the second behind the RT guardrail (starting at approximate station 107+56) should be reconditioned and lined to provide better flow conveyance. Like other ditches in Theodore Roosevelt National

Park, these ditches should be lined with Articulated Concrete Block adhering to Central Federal Lands Special

10 ND NP THRO 204(1) Buck Hill Road – Final Hydraulics Report

Detail 253‐A. To accommodate the use of the ACB, these ditches should be parabolic in shape with a maximum side slope of 2:1, a depth of 0.75 ft., and maximum width of 3 ft. A detail for this ditch can found in Appendix D and the project plans and analysis for these ditches has been included in Appendix C.

Vegetated Ditches

Vegetated ditches are proposed in key locations throughout the project site specifically to protect the guardrail aggregate pad from erosion. Analysis for these ditches was first completed using the Hydraulic Toolbox however, results from this analysis indicates the need for a more robust lining. From observations made in the field, many of the existing ditch reaches are well vegetated with little evidence of significant erosion. In addition, flow depths and velocities through these ditches is expected to be low.

Based on these observations, these ditches are recommended to be lined with a temporary Rolled Erosion Control

Product Type 2C until permanent vegetation is established. The capacity analysis completed for these ditches assumed a triangular section with a foreslope of 1:4 and backslope of 1:3. The ditches should accommodate a minimum flow depth of 0.5 ft. Additional details for these ditches have been included in the project plan set. Full ditch analysis for these ditches has been included in Appendix C.

6.2 PARKING LOT DRAINAGE

A 24” HDPE with rundown and riprap adhering to Standard Detail C251‐51, Placed Riprap Between Cut and Fill, should be installed in the southeast corner of the proposed parking lot (approximately 46.92661667 N,

103.39034722 W). The inlet for PR05 was sized using Hydraulic Toolbox. A 50% clogging factor was used for grates located in sump. The inlet should have a curb opening height of 6” with a minimum grate length of 12 ft. to maintain flow depths less than the curb height. The design discharge for this inlet was determined using the

Rational Method and the 50‐year design event as well as a composite runoff coefficient which was derived considering the proposed increase in impervious area.

A detail for this inlet adapted from NDDOT Detail D‐722‐02 for Inlet – Type 2 – Double has been included in the project plans. In addition, grate style “D” is recommended per NDDOT guidance as it is specifically designed for use in a sag. Analysis for this inlet has been included in Appendix C.

11 ND NP THRO 204(1) Buck Hill Road – Final Hydraulics Report

7 REFERENCES

Aquaveo. 2023. Watershed Modeling System (WMS). Provo, UT: Software version 11.1.12.

Federal Lands Highway. 2012. "Project Development and Design Manual, Chapter 7 Hydrology and Hydraulics."

https://flh.fhwa.dot.gov/resources/design/pddm/.

FHWA. 2002. "Highway Design Series No. 2, Second Edition, FHWA NHI‐02‐001."

FHWA. 2008. "Hydraulic Design Series No. 4: Introduction to Highway Hydraulics."

FHWA. 2012. "Hydraulic Design Series No. 5, Third Edition, Hydraulic Design of Highway Culverts."

FHWA. 2006. "Hydraulic Engineering Circular No. 14, Third Edition."

FHWA. 2022. Hydraulic Toolbox. Software Version 5.2, Federal Highway Administation, Aquaveo.

Multi‐Resolution Land Characteristics Consortium. 2011. National Land Cover Database 2011 (NLCD 2011). Multi‐

Resolution Land Characteristics Consortium (MRLC). https://www.mrlc.gov/data/references/national‐ land‐cover‐database‐2019‐landcover‐imperviousness‐nlcd2019.

National Oceanic and Atmospheric Administration. 2023. NOAA Atlas 14 Precipitation Frequency Data Server

(PFDS). Accessed November 2023. https://hdsc.nws.noaa.gov/pfds/pfds_map_cont.html.

Natural Resources Conservation Service. 2015. Soil Survey Geographic (SSURGO) database. Fort Worth, TX.

Accessed April 2019. http://websoilsurvey.nrcs.usda.gov.

NDDOT. 2023. NDDOT Design Manual Chapter V: Hydraulic Studies and Drainage Design. North Dakota

Department of Transportation.

U.S. Geological Survey. 2015. Regional Regression Equations to Estimate Peak‐Flow Frequency at Sites in North

Dakota Using Data through 2009. USGS.

U.S. Geological Survey. 2023. The National Map Viewer. Accessed Nov 2023.

https://apps.nationalmap.gov/viewer/.

A ND NP THRO 204(1) Buck Hill Road – Final Hydraulics Report

Appendix A

Existing Site Information

A1 | Existing Site Information ND NP THRO 204(1) Buck Hill Road – Final Hydraulics Report

Existing Structure Information

A2 | Existing Site Information ND NP THRO 204(1) Buck Hill Road – Final Hydraulics Report

FEMA Effective FIRM

THRO 204(1) Start

THRO 204(1) End

B ND NP THRO 204(1) Buck Hill Road – Final Hydraulics Report

Appendix B

Hydrology

B1 | Hydrology ND NP THRO 204(1) Buck Hill Road – Final Hydraulics Report

Hydrology Output Tables

B2 | Hydrology ND NP THRO 204(1) Buck Hill Road – Final Hydraulics Report

Culvert Basin Delineations

B3 | Hydrology ND NP THRO 204(1) Buck Hill Road – Final Hydraulics Report

Basin Delineation for Proposed Parking Lot Inlet

Note: Proposed Parking Lot layout shown in blue, proposed curb and gutter shown in yellow.

B4 | Hydrology ND NP THRO 204(1) Buck Hill Road – Final Hydraulics Report

Precipitation Frequency Data Server Information

B5 | Hydrology ND NP THRO 204(1) Buck Hill Road – Final Hydraulics Report

IDF Equations (Rational Method)

10 Year:

B6 | Hydrology ND NP THRO 204(1) Buck Hill Road – Final Hydraulics Report

25 Year:

B7 | Hydrology ND NP THRO 204(1) Buck Hill Road – Final Hydraulics Report

50 Year:

B8 | Hydrology ND NP THRO 204(1) Buck Hill Road – Final Hydraulics Report

100 Year:

C ND NP THRO 204(1) Buck Hill Road – Final Hydraulics Report

Appendix C

Hydraulic Analyses

C1 | Hydraulic Analyses ND NP THRO 204(1) Buck Hill Road – Final Hydraulics Report

Inlet Control Capacity Analysis

C2 | Hydraulic Analyses ND NP THRO 204(1) Buck Hill Road – Final Hydraulics Report

Ditch Analysis Summary:

C3 | Hydraulic Analyses ND NP THRO 204(1) Buck Hill Road – Final Hydraulics Report

Paved and Vegetated Ditch Analysis:

609-A):

1”

C4 | Hydraulic Analyses ND NP THRO 204(1) Buck Hill Road – Final Hydraulics Report

C5 | Hydraulic Analyses ND NP THRO 204(1) Buck Hill Road – Final Hydraulics Report

C6 | Hydraulic Analyses ND NP THRO 204(1) Buck Hill Road – Final Hydraulics Report

C7 | Hydraulic Analyses ND NP THRO 204(1) Buck Hill Road – Final Hydraulics Report

C8 | Hydraulic Analyses ND NP THRO 204(1) Buck Hill Road – Final Hydraulics Report

D ND NP THRO 204(1) Buck Hill Road – Final Hydraulics Report

Appendix D

Details

Varies

Varies

9”

3’ 0”