WI_ERFO_FS_2016-1(5)_Drainage_Report.pdf

Final Hydraulics Report

WI ERFO FS 2016-1(4)&(5)

November 7, 2018

Introduction This report is a compilation of design reports for multiple culvert crossings within the Chequamegon –

Nicolet National Forest in Wisconsin. The forest was impacted by and extreme rainfall event in June

2016 that exceeded a 1,000 year storm event in some areas of the forest. Numerous culverts and bridges were damaged, breached, or completely destroyed during the 2016 storm event. The culverts studied for replacement as part of this project have been identified for replacement under the

Emergency Repairs for Federally Owned (ERFO) properties program. These culverts are all included in the WI ERFO FS 2016-1(4) and 2016-1(5) packages. The individual chapters of this report provide design details and discussion for each of the bridge crossing. The following subsections in the study introduction discuss some of the overarching observations from the design team that may / may not have fit within the individual site chapters

Design Standard and Hydrologic Methods The road system in Chequamegon National Forest consists of a mixture of asphalt paved and gravel roads. The roads are all posted for speed limits of 45 mph. Due to the low volume of traffic and rural nature of the roads, all culverts for this report are designed as a “Low-Standard” road which requires a

25-yr design storm per Chapter 7 of the Office of Federal Lands Highway Project Development and

Design Manual (PDDM).

The hydrologic analyses for each of the sites uses one of three different hydrologic analysis methods to determine discharges as recommended by PDDM. For watersheds up to 200 acres, the Rational Method was used for analysis. Generally, for watersheds between 200 and 2000 acres, Natural Resources

Conservation Service Technical Release 55 (WinTR-55) hydrologic analysis was implemented. The

WinTR-55 analysis was performed using the latest rainfall depths from National Oceanic and

Atmosphere Administration Atlas 14 (NOAA Atlas 14) web database. The Atlas 14 24-hr rainfall depths are the latest rainfall data available and are significantly greater than the default WinTR-55 rainfall depths, which reference back to either TP-40 or older regional rainfall datasets.

The United States Geologic Survey National Streamflow Statistics regional regression equations (USGS

Regional Regression Equations) were used for analysis of the largest watershed areas in the project.

Two areas / equation sets have been defined for this area of Wisconsin with the USGS regional regression study, Area 2 and Area 41. The regional regression equations were developed for watersheds ranging from 0.56 up to 1,760 square miles in Area 2 and 0.66 up to 696 square miles in Area 4.

In cases where the study area watershed was less than 2,000 acres but fell within the development parameter size for the regional regression equations, both methods were evaluated. In all instances of comparison, the TR-55 discharges were significantly higher than the USGS Regional Regression discharges. Considering the USGS Regional Regression equations are based on a large gage dataset and the TR-55 model is not calibrated to any data, more weight is given to the USGS Regional Regression data at these locations. The design team observed that the USGS Regional Regression equations include a watershed storage parameter that the peak flow discharge calculations are highly sensitive to. The TR-

55 analysis method does not include a watershed storage factor in the analyses.

1 Figure 3 from https://pubs.usgs.gov/wri/wri034250/

Culvert Design At the direction of EFLHD and the USFS, many of the project culverts are designed for aquatic organism passage (AOP). The AOP designed culverts were evaluated following the guidelines in Hydraulic

Engineering Circular 26 (HEC-26). The Forest Service prefers the design of culverts using the stream simulation procedure that places greater emphasis on bankfull plus sizing of the culverts. The WSP design team followed the HEC-26 procedure for the design of all AOP culverts, but opted for elliptical or arch structures at many locations that allowed for culvert sizing closer to the bankfull condition and better structure performance without modification to the roadway profile. The AOP designed culverts were all evaluated to include channel material embedment with furnished aggregates. On the bottom, an aggregate sized to resist the 25-yr storm is to be placed; on the top, the native streambed material.

For high energy culverts, the sizes are occasionally dictated by the embedment material depth. The channel bedding material was sized and is specified to follow the Stream Bed Simulation material following a special provision developed by the Forest Service.

All culverts are designed using corrugated steel. Closed bottom culverts are suggested for most crossings to avoid the need for scour protection through the culvert. The WSP investigated the use of concrete box culverts at several sites at the request of the Forest Service. The use of box culverts was feasible from a hydraulic review of the sites; however, review of Wisconsin DOT design standards and standard drawings show that a customized structural design is required for state standard concrete box culverts.

The WSP team performed follow-up research into local pre-cast vendors to determine if standard box culverts meeting AASHTO standards were readily available, the efforts concluded that they were not available and that each box culvert would require a customized design / custom fabrication. The short duration design schedule and aggressive construction schedule for the 2016-1(5) contract does not include sufficient time for the customized design and fabrication of concrete box culverts, thus the design team maintained the usage of standard pipe culvert options that do not have these constraints.

Following requests from the Forest Service, the team will be specifying a polymer coating meeting ASTM

A742 for all closed bottom conduits.

Per project correspondence, the Forest Service requested that all pipes be mitered to slope. This design standard was noted by the WSP Team to conflict with the PDDM recommendations for used of concrete headwalls for culverts over 48 inches to resist buoyancy. Per correspondence with EFLHD and the FS, the WSP Team designed each culvert with a mitered entrance and exit. Each culvert over 48 inches has been designed to include concrete slope protection at the inlet and outlet of the culverts. The concrete slope protection is specified in the project plans as a modification of the FLHD Standard 601-2. The detail was modified to provide measurements for elliptical pipes, corrugated metal pipe arches, and corrugated structural pipe arches. The FLHD standard detail for slope paving includes specification of pipe mitering for the upper half of the pipe, placement of a half-headwall below the slope paving. In place of the standard wingwalls with spread footer, the headwall detail will be modified to provide the spread footer.

All non-AOP designed culvert sites have been designed to include riprap pads for scour protection at the culvert outfalls. All AOP designed sites do not include riprap pads or basins and will rely upon existing scour pools for energy dissipation at the outlets. Where necessary, the AOP design stream sites will include reconstruction of the stream bed and banks to provide smooth transitions in and out of the culverts. Streambed reconstruction will be performed using the streambed simulation material specified for placement in the culvert while stream bank reconstruction will be performed using the coarser channel rock materials specified for placement in the culvert. The following tables define the gradation and sizing used for the streambed simulation material and channel rock material to be placed in the culverts.

Gradation requirements for Streambed Simulation Material (inches or sieve size)

Bed Class 100% passing 84% passing 50% passing 16% passing 10% passing

2 5 2 3/4 1/4 No. 10

4 10 4 1 3/4 1/2 No. 10

6 14 6 2 1/2 3/4 No. 10

8 22 8 3 1 No. 10

10 24 10 4 1 No. 10

12 30 12 5 1 1/2 No. 10

14 36 14 6 1 3/4 No. 10

16 42 16 7 2 No. 10

20 48 20 8 3 No. 10

24 60 24 10 3 No. 10

36 72 36 14 4 No. 10

48 96 48 18 6 No. 10

Gradation Requirement for Channel Rock (CR)

Class Mass (Pounds) Approximate Cubic Dimension

(inches)

CR - 0 12 - 90 6 - 12

CR - 1 90 - 300 12 - 18

CR - 2 300 - 700 18 - 24

CR - 3 700 - 1350 24 - 30

CR - 4 1350 - 2400 30 - 36

CR - 5 2400 - 3700 36 - 42

CR - 6 3700 - 5500 42 - 48

CR - 7 5500 - 7900 48 - 54

CR - 8 7900 - 10800 54 - 60

Note: Mass / Pounds of channel is based on a sphere of the approximate cubic dimensions composed of granite. Mass will vary with rock type. Inspection should be performed by using the cube root of the A axis * B axis * C axis of each piece.

Table of Contents

FS378 C29

FS378 C29A

FS202 W22

FS202 C23A

FS379 W37

FS1730 C37

FS191-H C14

TR63 1

T28 G

FS189-H C8

FS187 MP5.10

FS199-C S7

FS344-A S74A

FS344-B S74B

FS376 S13

FS622 S17

FS191-H S4

FS378-B S14

FS371 S19

FS198-B S6

DSRT1T2 Trail D T2

FS378 C29

Site FS378 C29

Background / Assessment The C29 culvert site is located on Wisco Road, about 1.7 miles north of the intersection with Forest Road

202. A visual field assessment was performed at Site FS378 C29 in June 5, 2018 by a WSP field team. The existing culvert and road has been washed out. Water from the perennial stream flows through a channel where the culvert had previously been. Figure 1 shows the conditions at the immediate upstream and downstream sections of the road crossing.

Figure 1: Looking Upstream (Left); and, Looking Downstream (Right). Photos taken June 5, 2018.

Upstream of the road crossing, the stream meanders and defined riffles and grade controls were observed in the field. A field measurement of the stream presented that the typical section is 3’ wide and 3’ deep.

The field assessment also revealed that roadside swales flow into the channel. Figure 2 shows a stable riffle found upstream of the road crossing as well as the roadside swales.

Figure 2: Upstream Riffle (Left); Roadside swales (Middle and Right). Photos taken June 5, 2018.

Downstream of the road crossing, the stream is a D type channel / flowing wetland. Road gravel had been washed out into the downstream wetland / stream. The stream banks are not well defined, woody vegetation is observed, and the terrain is generally flat. Figure 3 shows the woody vegetation downstream as well as a picture looking toward the downstream end of the washed-out channel. This site is not designated for AOP design and as such a detailed geomorphic investigation was not conducted.

Figure 3: Looking Downstream toward Vegetation (Left); and, Looking toward Road Crossing (Right). Photos taken June 5, 2018.

Hydrology The C29 site is located in Bayfield County and has a drainage area of 36 acres. Peak discharges at the project location were calculated using the Rational method. The Rational method is the selected method for estimating peak discharges of drainage areas less than 200 acres. Calculation is based on a simple formula:

ܳ = ܣ݅ܥ

Where Q (cfs) is the peak discharges, C is the runoff coefficient, i (in/hr) is the design rainfall intensity, and A (acres) is the drainage area.

Runoff coefficients for various types of land use, hydrologic soil groups and land slopes are provided by Wisconsin DOT Facilities Development Manual. Time of concentration was obtained from the nomograph in the WIDOT manual. The drainage area was manually delineated in ESRI GIS using County LIDAR contours. Rainfall intensity was read from the NOAA Atlas 14 point precipitation frequency estimates data center with an intensity duration determined based upon the time of concentration.

Peak discharges results are shown in Table 1.

Table 1: Peak Discharge Results

Drainage Area: 36 (acres) Return Period (year) 2 5 10 25 50 100 Rainfall Intensity (in/hr) 3.48 4.39 5.14 6.19 7.00 7.81 Peak Discharges (cfs) 25 32 37 44 50 56

Hydrology Characteristics Forests are the only land uses identified within this watershed. The soil types for this watershed are mostly type C/D soils, with small percentages of A and A/D soils. Steep slopes are prevalent throughout the upper half of the drainage area. Figure 4 shows the culvert site location, the stream channel, and the drainage area extents.

Figure 4: Site FS378 C29 Drainage Area Map

Hydrologic parameters are shown in Table 2. Using the Rational method, a t c of 0.167 hours was observed from the WIDOT nomograph. When determining the runoff coefficient (C), factors such as land use, soil type, and slope were taken into consideration. Further description of hydrologic calculations and considerations are discussed in the Appendix.

Table 2: Summary of Hydrologic Analysis

Drainage Area (Ac) Runoff Coefficient (C)

Tc (hours)

36 0.20 0.167

Hydraulic Modeling The Federal Highway Administrations (FHWA) HY-8 culvert analysis program was used for hydraulic modeling and analysis of the culvert replacement. The roadway was classified as a Low Standard Road which correlates to a 25-year design storm for the culvert following PDDM chapter 7.1.6.1 standards.

The HY-8 outlet conditions were analyzed by identifying a tailwater cross section at a grade control immediately downstream of the culvert outlet. The selected cross section is located downstream of the scour hole, at the beginning of a stable riffle. From the hydrologic analysis, the 25-year storm design flow of 44 cfs was entered into the model. Tailwater, roadway, and site station and elevation data were entered based on topographic survey data and the proposed roadway conditions.

Existing Conditions The existing roadway and culvert had been washed out. Thus, the existing conditions were not modeled in HY-8.

Proposed Conditions The HY-8 analysis resulted in a recommendation of a single barrel 49”x33” Corrugated Metal Pipe Arch Culvert (CMPAC). The proposed culvert is to be mitered to conform to the slope, following US Forest Service culvert design standards. Per project correspondence, the USFS does not prefer the use of headwalls or fabricated end sections for culvert pipes under 48 inches in diameter. Headwalls are not required per EFL-HD PDDM for culverts with an equivalent opening of 48 inches or less.

The parameters for a culvert designed to convey the 25-year design storm peak discharge are shown in Table 3.

Table 3: Summary of Culvert Design Parameters

Type Single Barrel - CMPAC Q25 44 cfs Rise 33 inches Span 49 inches Length 40 feet Upstream Invert Elev. 1251.05 Downstream Invert Elev. 1250.70 Pipe Slope 0.87% Manning’s n value (Pipe) 0.024 Inlet Configuration Mitered to Conform to Slope Channel Embedment Depth 0 inches

HW/D 1.08

Cover 1.70 feet Freeboard 1.08 feet

Per HY-8 analysis, the culvert is outlet controlled at the design storm event. For the design flow of 44 cfs, the headwater elevation is 1254.02 ft. The pipe size requires a minimum of 12” of cover; therefore, the minimum proposed roadway elevation needed to convey the design flow is 1254.80. The proposed roadway meets this minimum elevation requirement at the location of the culvert crossing.

Figure 5: Rating Curve for Proposed Condition

The downstream invert was set so that the riprap outlet apron would have a 0% slope when tied into the existing stream slope. The length of the apron determined by the FHWA EFL-HD Detail E251-50. This allows the flow to flow from the culvert outfall onto the riprap apron then to the natural stream bed without a drop. The flat outlet apron allows for velocity dissipation prior to reaching the natural channel bed and prevents potential headcut.

The upstream invert was set below the existing grade. The channel upstream will require 35-feet of grading at a 7% slope to provide a stable connection to the culvert at a lower elevation.

Design Recommendations To convey the design flow, it is recommended that a 49”x33” CMPAC with the inlet/outlet mitered to conform to slope be installed at the C29 site.

FS378 C29A

Site FS378 C29A

The C29A culvert site is located on Wisco Road, about 0.15 miles north of the intersection with Forest Road 378B. A visual assessment was performed at Site FS378 C29A in June 2018 by a WSP field team.

The existing culvert that crosses Wisco Road is a 24” CMP that is deeply buried beneath the gravel roadway. At the time of inspection, the culvert inlet could not be located, but survey information shows that the culvert inlet was buried and the outlet was completely full. Water flows down a roadside swale toward the pipe which outlets directly into Twentymile Creek, a significantly larger stream that runs parallel to the road. Figure 1 shows the conditions of the road and embankment near the location of the culvert. Figure 2 shows the larger stream, Twentymile Creek, at the downstream end of the culvert. This site is not designated for AOP design and, as such, a detailed geomorphic investigation was not conducted.

Figure 1: Looking at Road and Embankment Facing North (Left); Looking at Road and Embankment Facing South (Right). Photos taken June 5, 2018.

Figure 2: Twentymile Creek Downstream of Culvert Outlet (Left and Right). Photos taken June 4, 2018.

Hydrology The C29A site is located within Bayfield County and has a drainage area of 13 acres. Peak discharges at the project location were calculated using the Rational method. The Rational method is the selected method for estimating peak discharges of drainage areas less than 200 acres. Calculation is based on a simple formula: ܳ = ܣ݅ܥ

Where Q (cfs) is the peak discharges, C is the runoff coefficient, i (in/hr) is the design rainfall intensity, and A (acres) is the drainage area.

Runoff coefficients for various types of land use, hydrologic soil groups and land slopes are provided by Wisconsin DOT Facilities Development Manual. Time of concentration was obtained from the nomograph in the WIDOT manual. The drainage area was manually delineated in ESRI GIS using County LIDAR contours. Rainfall intensity was read from the NOAA Atlas 14 point precipitation frequency estimates data center with an intensity duration determined based upon the time of concentration.

Peak discharges results are shown in Table 1.

Table 1: Peak Discharge Results

Drainage Area: 13 (acres) Return Period (year) 2 5 10 25 50 100 Rainfall Intensity (in/hr) 4.75 5.99 7.02 8.45 9.55 10.70 Peak Discharges (cfs) 9 11 13 16 18 20

The C29A culvert discharges directly into a larger stream system, Twentymile Creek, which controls the backwater conditions through the C29A culvert. Twentymile Creek was evaluated to produce a design backwater condition for C29A. The drainage area for Twentymile Creek is 2,165 acres. Peak discharges for Twentymile Creek were determined based upon the USGS regional regression equations for

Wisconsin – Area 4. Further description of the hydrologic calculations and considerations for Twentymile Creek are discussed in the Appendix. Since the tributary stream has a drainage area more than an order of magnitude larger than C29A, peak discharge timing for extreme rainfall events between the catchments are expected to be significantly different. Evaluation of the 25-year storm results in a condition where Twentymile Creek overtops FS 378 for a significant distance of road. The scope of this project does not include corridor-wide reconstruction of FS 378 to prevent flooding from Twentymile Creek. Use of a 25-year tailwater from a significantly larger watershed in conjunction with a smaller side drainage area, results in a joint probability that exceeds the design standard of the culvert. Thus, the design team selected the 5-year storm for Twentymile Creek tailwater condition to be used in combination with the 25-year storm for the C29A tributary. The 5-year storm for Twentymile Creek is 232 cfs while the 25-year storm for the C29A tributary is 13 cfs.

Hydrology Characteristics Forest and wetlands are the only two land uses identified within this watershed. The soil types for this watershed are mostly type C/D soils, with the remainder being type A and A/D. Soils with dual grouping were categorized by either the drained or undrained condition, based upon land use and slope in the area. Upland and well drained areas were categorized as the non-D types in the grouping, while riparian, wetland, and poorly drained areas were categorized as the D type. Figure 3 shows the culvert site location, the stream channel, and the drainage area extents.

Figure 3: Site FS378 C29A Drainage Area Map

Hydrologic parameters are shown in Table 2. The runoff coefficient was based on the forested and wetland land use and the soil types. When determining the runoff coefficient (C), factors such as land use, soil type, and slope were taken into consideration. Further description of hydrologic calculations and considerations are discussed in the Appendix.

Table 2: Summary of Hydrologic Analysis

Drainage Area (Ac) Runoff Coefficient (C) Tc (hours) 13 0.14 0.05

Hydraulic Modeling The Federal Highway Administrations (FHWA) HY-8 program was used for hydraulic modeling and analysis of the culvert replacement. The roadway functional classification is low-standard which correlates to a 25-year design storm for the culvert following PDDM standards.

The HY-8 tailwater conditions were analyzed by identifying a cross section at a grade control immediately downstream of the culvert outlet. The C29A culvert discharges directly into a larger stream system, Twentymile Creek, which controls the backwater conditions through the C29A culvert.

Twentymile Creek was evaluated to produce a backwater condition for C29A. The selected cross section is located at a grade control feature in Twentymile Creek, directly downstream of the culvert.

Existing Conditions The existing culvert consists of a 24” circular corrugated metal pipe. Due to the significant inefficiencies of the existing system caused by excessive sedimentation / complete burial of the culvert, an existing condition model was not prepared.

Proposed Conditions The HY-8 analysis resulted in a recommendation of a single barrel steel 33”x49” Corrugated Metal Pipe Arch Culvert (CMPAC). The pipe arch culvert was selected for this site due to the sub-optimal cover over an equivalent CMP. The proposed culvert is to be mitered to conform to the slope, following US Forest Service culvert design standards. Per project correspondence, the USFS does not prefer the use of headwalls or fabricated end sections for culvert pipes under 48 inches in diameter. Headwalls are not required per EFL-HD PDDM for culverts with an equivalent opening of 48 inches or less.

Table 3: Summary of Culvert Design and Analysis Parameters

Q25 16 cfs Rise 33 inches Span 49 inches Length 37 feet Upstream Invert Elev. 1228.13 feet Downstream Invert Elev. 1227.42 feet Pipe Slope 1.91% Manning’s n Value (Pipe) 0.024 Inlet Configuration Mitered to Conform to Slope Channel Embedment Depth 0 inches

HW/D 0.69

Cover 1.03 feet Freeboard 0.95 feet

Per HY-8 analysis, the culvert is outlet controlled at the design storm event. For the design flow of 16 cfs, the headwater elevation is 1230.02 ft. The pipe size requires a minimum cover of 12”; therefore, the minimum proposed roadway elevation needed to convey the design flow is 1231.88 feet. The proposed roadway meets this minimum elevation requirement at the location of the culvert crossing.

Figure 4: Rating Curve for Proposed Condition the existing stream slope. The length of the apron was determined by the FHWA EFL-HD Detail E251-50.

This allows the flow to flow from the culvert outfall onto the riprap apron then to the natural stream bed without a drop. The flat outlet apron allows for velocity dissipation prior to reaching the natural channel bed and prevents potential headcut.

The upstream invert was set below the existing grade. The existing culvert invert is buried due to debris and sediment accumulation. The drainage swale upstream will be excavated. The riprap apron upstream of the culvert will have a 9% slope when tied into the existing drainage swale.

Design Recommendations To convey the design flow, it is recommended that a 33”x49” CMPAC with the inlet/outlet mitered to conform to slope replace the 24” CMPC. A berm is proposed across the drainage swale at the upstream end of the culvert to divert flow into the culvert.

FS202 W22

Site FS202 W22

The W22 site is located on Forest Road 202, about 0.9 miles south of the intersection with Forest Road 378.A visual field assessment was performed at Site FS202 W22 in June 7, 2018 by a WSP field team. The existing culvert that crosses Forest Road 202 is a circular 24” corrugated metal pipe, with approximately 4 feet of cover between the top of the pipe and the gravel roadway. Figure 1 shows the conditions at the culvert inlet and outlet.

Figure 1: Looking at Culvert Inlet (Left); and, Looking at Culvert Outlet (Right). Photos taken June 5, 2018.

A nominal amount of sediment deposition was noted at the culvert inlet and the outlet was not significantly perched above the existing stream channel. Pooling occurs immediately upstream of the culvert. The channel does not have defined stream banks, is flat, and undergoes trickle flow. The area upstream of the culvert is covered in woody vegetation. Figure 2 shows the upstream conditions of the stream.

Figure 2: Upstream of Culvert (Left, Middle, and Right). Photos taken June 5, 2018.

Downstream of the culvert, the terrain was observed to be flat very flat with no defined banks and woody vegetation. Figure 3 shows the downstream conditions of the stream. This site is not designated for AOP design and as such a detailed geomorphic investigation was not conducted.

Figure 3: Downstream of Culvert (Left and Right). Photos taken June 5, 2018.

Hydrology The W22 site is located within Bayfield County and has a drainage area of 98 acres. Peak discharges at the project location were calculated using the Rational method. The Rational method is the selected method for estimating peak discharges of drainage areas less than 200 acres. Calculation is based on a simple formula:

ܳ = ܣ݅ܥ

Where Q (cfs) is the peak discharges, C is the runoff coefficient, i (in/hr) is the design rainfall intensity, and A (acres) is the drainage area.

Runoff coefficients for various types of land use, hydrologic soil groups and land slopes are provided by Wisconsin DOT Facilities Development Manual. Time of concentration was obtained from the nomograph in the WIDOT manual. The drainage area was manually delineated in ESRI GIS using County LIDAR contours. Rainfall intensity was read from the NOAA Atlas 14 point precipitation frequency estimates data center with an intensity duration determined based upon the time of concentration.

Peak discharges results are shown in Table 1.

Table 1: Peak Discharge Results

Drainage Area: 98 (acres) Return Period (year) 2 5 10 25 50 100

Rainfall Intensity (in/hr) 2.71 3.42 4.01 4.83 5.47 6.10

Peak Discharges (cfs) 5. 67 78 94 107 119

Hydrology Characteristics Forests, lakes and roads are the land uses identified within this watershed. The soil types for this watershed are mostly type C/D soils, with small percentages of A, A/D, and D soils. Overall the terrain of the drainage area is flat. Figure shows the culvert site location, the stream channel, and the drainage area extents.

Figure 4: Site FS202 W22 Drainage Area Map

Hydrologic parameters are shown in Table 1. Using the Rational method, a tc of 0.283 hours was observed from the WIDOT nomograph. When determining the runoff coefficient (C), factors such as land use, soil type, and slope were taken into consideration. Further description of hydrologic calculations and considerations are discussed in the Appendix.

Table 1: Summary of Hydrologic Analysis

Drainage Area (Ac) Runoff Coefficient (C)

Tc (hours)

98 0.20 0.283

Hydraulic Modeling The Federal Highway Administrations (FHWA) HY-8 culvert analysis program was used for hydraulic modeling and analysis of the culvert replacement. The roadway was classified as a Low Standard Road which correlates to a 25-year design storm for the culvert following PDDM chapter 7.1.6.1 standards.

The HY-8 outlet conditions were analyzed by identifying a tailwater cross section at a grade control immediately downstream of the culvert outlet. The selected cross section is located downstream of the scour hole, at the beginning of a stable riffle.

Existing Conditions The existing culvert measures as a 24” corrugated metal pipe. From the hydrologic analysis, the 25-year storm design flow of 84 cfs was entered into the model. Tailwater, roadway, and site station and elevation data were entered based on topographic survey data and the proposed roadway conditions.

Proposed Conditions The HY-8 analysis resulted in a recommendation of a single barrel 42” Corrugated Metal Pipe Culvert (CMPC). The proposed culvert is to be mitered to conform to the slope, following US Forest Service culvert design standards. Per project correspondence, the USFS does not prefer the use of headwalls or fabricated end sections for culvert pipes under 48 inches in diameter.

The parameters for a culvert designed to convey the 25-year design storm peak discharge are shown in Table 3.

Table 3: Summary of Culvert Design Parameters

Type CMPC Q25 94 cfs Diameter 42 inches Number of Barrels 1 Length 59 feet Upstream Invert Elev. 1409.99 Downstream Invert Elev. 1407.71 Pipe Slope 3.86% Manning’s n value (Pipe / Bottom) 0.024 Inlet Configuration Mitered to Conform to Slope Channel Embedment Depth 0 inches

HW/D 1.40

Cover 3.89 feet Freeboard 2.10 feet

Per HY-8 anaysis, the culvert is outlet controlled at the design storm event. For the design flow of 94 cfs, the headwater elevation is 1414.88 ft. The pipe size requires a minimum cover of 12”; therefore, the minimum proposed roadway elevation needed to convey the design flow is 1414.49 feet. The proposed roadway meets this minimum elevation requirement at the location of the culvert crossing.

Figure 5: Rating Curve for Proposed Condition

The downstream invert was set so that the riprap outlet apron would have a 0% slope when tied into the existing stream slope. The length of the apron determined by the FHWA EFL-HD Detail E251-50. This allows the stream to flow from the culvert outfall onto the riprap apron then to the natural stream bed without a drop. The flat outlet apron allows for velocity dissipation prior to reaching the natural channel bed and prevents potential headcut.

The upstream invert was set at the existing grade. No signs of debris jam or headcut were noted.

Design Recommendations To convey the design flow, it is recommended that a 42” CMP with the inlet/outlet mitered to conform to slope replace the 24” corrugated metal pipe.

FS202 C23A

Site FS202 C23A

The C23A site is located on Old Grade Road, south of the intersection with Wisco Road. A visual field assessment was performed at Site FS202 C23A on June 8, 2018 by the WSP field team. The existing culvert that crosses Old Grade Road is a 30” CMP. At the time of inspection, the culvert inlet was more than 50% filled with fine sediment while the outfall was perched more than 2 feet and was causing erosion / soil loss on the roadway embankment. Figure 1 shows the conditions at the culvert inlet and outlet. The roadway embankments are steep on both sides of the road and are at least 10 feet above the top of the culvert.

Figure 1: Looking at Culvert Inlet (Left); and, Looking at Culvert Outlet (Right). Photos taken June 8, 2018.

Upstream of the culvert inlet, fine sediment has built up behind tree roots, in the channel, to cause ponding approximately 10 feet upstream of the culvert. The channel upstream of the culvert is not well defined due to the deposition of fine sediment (Figure 2). The watershed is defined by steep slopes upland that become more gradual closer to the culvert. The area upstream of the culvert has mature trees and a lot of undergrowth.

Figure 2: Ponding Upstream of Culvert Inlet. Photo taken June 8, 2018.

At the culvert outlet, the stream channel drops over 2 feet below the invert of the pipe. The stream banks are steep and highly eroded for approximately 10 feet downstream of the culvert. Based on the observed field conditions, the team is recommending extension of the culvert to remove stresses and grading constraints at the outfall. Further from the culvert outfall and the roadway embankment, the stream banks are less than 0.2 foot above the stream bed (Figure 3, left). Woody debris lines the channel (Figure 3, right). This site is not designated for AOP design and as such a detailed geomorphic investigation was not conducted.

Figure 3: Channel Downstream of Culvert (Left); Woody debris in Stream Channel (Right). Photos taken June 8, 2018.

Hydrology The C23A site is located within Bayfield County and has a drainage area of 20 acres. Peak discharges at the project location were calculated using the Rational method. The Rational method is the selected method for estimating peak discharges of drainage areas less than 200 acres. Calculation is based on a simple formula:

ܳ = ܣ݅ܥ

Where Q (cfs) is the peak discharges, C is the runoff coefficient, i (in/hr) is the design rainfall intensity, and A (acres) is the drainage area.

Runoff coefficients for various types of land use, hydrologic soil groups and land slopes are provided by Wisconsin DOT Facilities Development Manual. Time of concentration was obtained from the nomograph in the WIDOT manual. The drainage area was manually delineated in ESRI GIS using County LIDAR contours. Rainfall intensity was read from the NOAA Atlas 14 point precipitation frequency estimates data center with an intensity duration determined based upon the time of concentration.

Peak discharges results are shown in Table 1.

Table 1: Peak Discharge Results

Drainage Area: 20 (acres) Return Period (year) 2 5 10 25 50 100 Rainfall Intensity (in / hr) 4.49 5.66 6.63 7.99 9.04 10.12 Peak Discharges (cfs) 18 22 26 31 35 40

This watershed is covered entirely in forested land use. The soil types for this watershed are mostly type C/D soils, with small percentages of A soils. Soils with dual groupings were categorized by the drained condition, or A soils. Figure 4 shows the culvert site location and the drainage area extents.

Figure 4: Site FS202 C23A Drainage Area Map

Hydrologic parameters determined using the Rational method are shown in Table 2. The runoff coefficient was determined based on the forested land use and the mostly C soils. When determining the runoff coefficient (C), factors such as land use, soil type, and slope were taken into consideration.

Further description of hydrologic calculations and considerations are discussed in the Appendix.

Drainage Area (Ac) Runoff Coefficient (C)

Tc (hours)

20 0.20 0.1

Hydraulic Modeling The Federal Highway Administrations (FHWA) HY-8 culvert analysis program was used for hydraulic modeling and analysis of the culvert replacement. The roadway was classified as a Low Standard Road which correlates to a 25-year design storm for the culvert following PDDM chapter 7.1.6.1 standards.

The HY-8 outlet conditions were analyzed by identifying a tailwater cross section at a grade control downstream of the culvert outlet. The selected cross section is located far enough downstream to not be affected by the proposed roadway embankment regrading to a 2:1 side slope.

Existing Conditions The existing culvert is a 30” CMP. From the hydrologic analysis, the 25-year storm design flow of 32 cfs was entered into the model. Tailwater, roadway, and site station and elevation data were entered based on topographic survey data. An embedment depth of zero was selected since the existing culvert is not embedded.

Once the parameters were entered, the model was run for the culvert crossing. The results indicated that the existing culvert will convey the design storm discharge.

Table 3: Summary of Culvert Design Parameters

Type CMP Q25 32 cfs Diameter 30 inches Length 61 feet Upstream Invert Elev. 1325.8 feet Downstream Invert Elev. 1319.4 feet Pipe Slope 10.5% Channel Embedment Depth 0

HW/D 1.5

Cover 8.9 Freeboard 7.8

Proposed Conditions The HY-8 analysis resulted in a recommendation of a single barrel 36” Corrugated Metal Pipe Culvert (CMP). The proposed condition adjusted the inverts of the pipe and the length of the pipe due to the clogged and perched pipe as well as the need to extent the side slopes to meet the minimum 2:1 embankment requirements. The proposed culvert is to be mitered to conform to the slope, following US Forest Service culvert design standards. Per project correspondence, the USFS does not prefer the use of headwalls or fabricated end sections for culvert pipes under 48 inches in diameter.

Table 4.

Table 4: Summary of Culvert Design Parameters

Type Single Barrel - CMP Q25 32 cfs Diameter 36 inches Length 92 feet Upstream Invert Elev. 1326.42 feet Downstream Invert Elev. 1314.12 feet Pipe Slope 13.52% Manning’s n value (Pip) 0.049 Inlet Configuration Mitered to Conform to Slope Channel Embedment Depth 0 inches

HW/D 1.30

Cover 7.08 feet Freeboard 5.76 feet

The pipe size has been increased to adequately convey the 25-year design peak discharge. The proposed pipe length will need to be extended from 61 feet to 92 feet once the embankment side slopes are adjusted. Per HY-8 analysis, the culvert is outlet controlled at the design storm event. For the design flow of 31 cfs, the headwater elevation is 1330.34 ft. The pipe size requires a minimum cover of 12”;

therefore, the minimum proposed roadway elevation needed to convey the design flow is 1330.42 feet.

The proposed roadway meets this minimum elevation requirement at the location of the culvert crossing.

Figure 5: Rating Curve for Proposed Condition the existing stream slope. The length of the apron was determined by the FHWA EFL-HD Detail E251-50.

This allows the flow to flow from the culvert outfall onto the riprap apron then to the natural stream bed without a drop. The flat outlet apron allows for velocity dissipation prior to reaching the natural channel bed and prevents potential headcut.

The upstream invert was set at the existing grade. Due to the partially clogged, existing culvert invert, the proposed upstream culvert invert was set higher than the existing culvert invert.

Design Recommendations To meet minimum embankment side slope regulations, it is recommended that the culvert replacement be extended from 61 feet to 92 feet in length. To convey the design flow, it is recommended that a 36” CMPC with the inlet/outlet mitered to conform to slope replace the 30” corrugated metal pipe.

FS379 W37

Site FS379 W37

The W37 site is located on Federal Road, less than 1 mile east of Old Grade Road. A visual field assessment was performed at Site FS379 W37 on June 5, 2018 by a WSP field team. The existing culvert that crosses Federal Road is a 24” CMP culvert. The field team was unable to locate the culvert invert while visiting the site due to a high level of sedimentation along the upstream embankment. Figure 1(left) shows the estimated location of the culvert inlet. The culvert outlet is also buried. Part of the top of the pipe near the outlet was exposed and can be seen in Figure 1 (right). Ponding occurs both upstream and downstream of the culvert. Figure 1 shows the approximate locations of the culvert inlet and outlet.

Figure 1: Estimated Location of Buried Culvert Inlet (Left); and, Looking at Culvert Outlet (Right). Photos taken June 5, 2018.

Ponding upstream of the culvert inlet is seen in Figure 2. The ponding area is surrounded by grasses and shrubs. Trees are set back from the ponding area. Because the field team was unable to find the culvert inlet after an extensive search, it is believed that runoff from the watershed collects near the roadway and is not effectively conveyed across the road. Because the pipe is buried, the field team was unable to identify if there was flow through the pipe.

Figure 2: Ponding Upstream of Unlocated Culvert Inlet. Photos taken June 5, 2018.

Ponding also occurs downstream of the culvert outlet. Due to the poor hydraulic connectivity with the upstream ponding area, the downstream hydrology is believed to be driven by groundwater infiltration and seepage through the roadway embankment and buried pipe. Wetland plants are seen in the ponding area, with larger shrubs and trees outside of the ponding area (Figure 3). This site is not designated for AOP design and, as such, a detailed geomorphic investigation was not conducted.

Figure 3: View of Buried Pipe and Ponding Downstream of Outfall. Photos taken June 5, 2018.

Hydrology This site is located within Bayfield County and has a drainage area of 18 acres. Peak discharges at the project location were calculated using Rational method. Rational method is the selected method for estimating peak discharges of drainage areas less than 200 acres. Calculation is based on a simple formula: ܳ = ܣ݅ܥ

Where Q (cfs) is the peak discharges, C is the runoff coefficient, i (in/hr) is the design rainfall intensity, and A (acres) is the drainage area.

Runoff coefficients for various types of land use, hydrologic soil groups and land slopes are provided by Wisconsin DOT Facilities Development Manual. Time of concentration was obtained from the nomograph in the WIDOT manual. The drainage area was manually delineated in ESRI GIS using County

LIDAR contours. Rainfall intensity was read from the NOAA Atlas 14 point precipitation frequency estimates data center with an intensity duration determined based upon the time of concentration.

Peak discharges results are shown in Table 1.

Table 1: Peak Discharge Results

Drainage Area: 18 (acres) Return Period (year) 2 5 10 25 50 100 Rainfall Intensity (in / hr) 4.24 5.35 6.27 7.55 8.54 9.54 Peak Discharges (cfs) 15 19 22 27 30 34

Hydrology Characteristics Forest and wetland are the only land uses in this watershed. The watershed is comprised of type C and D soils. Figure 4 shows the culvert site location and the drainage area extents.

Figure 4: Site FS379 W37 Drainage Area Map

Hydrologic parameters are shown in Table 2. The runoff coefficient was determined based on the forest and wetland land uses and with type C and D soils. When determining the runoff coefficient (C), factors such as land use, soil type, and slope were taken into consideration. Further description of hydrologic calculations and considerations are discussed in the Appendix.

Table 2: Summary of Hydrologic Analysis

Drainage Area (Ac) Runoff Coefficient (C)

Tc (hours)

18 0.20 0.117

Hydraulic Modeling The Federal Highway Administrations (FHWA) HY-8 culvert analysis program was used for hydraulic modeling and analysis of the culvert replacement. The roadway was classified as a Low Standard Road which correlates to a 25-year design storm for the culvert following PDDM chapter 7.1.6.1 standards.

The HY-8 tailwater conditions were analyzed by identifying a cross section at a grade control immediately downstream of the culvert outlet. The selected cross section is located downstream, at the beginning of a grade control feature.

Existing Conditions The existing culvert measures as a 24”circular corrugated metal pipe. The existing pipe is buried and does not currently convey flow. Due to the significant inefficiencies of the existing system, an existing condition model was not prepared.

Proposed Conditions The HY-8 analysis resulted in a recommendation of a single barrel 42” x 29” Corrugated Metal Pipe Arch Culvert (CMPAC). The pipe arch culvert was selected for this site due to the low degree of embankment slope / cover over an equivalent CMP. The proposed culvert is to be mitered to conform to the slope, following US Forest Service culvert design standards. Per project correspondence, the USFS does not prefer the use of headwalls or fabricated end sections for culvert pipes under 48 inches in diameter.

The parameters for a culvert designed to convey the 25- year design storm peak discharge are shown in Table 3.

Table 3: Summary of Culvert Design Parameters

Type Single Barrel - CMPAC Q25 27 cfs Rise 29 in Span 42 in Length 39 ft Upstream Invert Elevation 1522.47 ft Downstream Invert Elevation 1522.35 ft Pipe Slope 0.31% Manning’s n value (Pipe / Bottom) 0.025 Inlet Configuration Mitered to conform to slope Channel Embedment Depth 0 in

HW/D 1.01

Cover 2.07 ft Freeboard 0.47 ft

Per the HY-8 analysis, the culvert is outlet controlled at the design storm event. For the design flow (Q25) of 27 cfs, the headwater elevation is 1524.92 feet. The pipe size requires a minimum cover of 12 inches; therefore, the minimum proposed roadway elevation needed to convey the design flow is

1525.89 feet. The proposed roadway meets this minimum elevation requirement at the location of the culvert crossing.

Figure 7: Rating Curve for Proposed Condition the existing stream slope. The length of the apron was determined by the FHWA EFL-HD Detail E251-50.

This allows the flow to flow from the culvert outfall onto the riprap apron then to the natural stream bed without a drop. The flat outlet apron allows for velocity dissipation prior to reaching the natural channel bed and prevents potential headcut.

The upstream invert was set below the existing grade. The existing culvert invert is buried due to debris and sediment accumulation.

Design Recommendations To convey the design flow, it is recommended that a 42”x29” CMPAC with the inlet/outlet mitered to conform to slope replace the 24” corrugated metal pipe.

FS1730 C37

Site FS1730 C37

The C37 culvert site is located on Forest Road 1730, about 0.2 miles north of the intersection with Dam Road. A field assessment was performed at Site FS1730 C37 on June 6, 2018 by a WSP field team. The existing culvert that crosses Forest Road 1730 is a circular 30” corrugated metal pipe, with approximately 1 foot of cover between the top of the pipe and the gravel roadway. At the time of inspection, the bottom of the culvert was observed to be corroded out. Figure 1 shows the conditions at the culvert inlet and outlet. At the time of inspection, the culvert outlet was observed to be 95% submerged.

Figure 1: Looking at Culvert Inlet (Left); and, Looking at Culvert Outlet (Right). Photos taken June 5, 2018.

Pooling occurs immediately upstream of the culvert. Upstream of the pool at the culvert inlet, the stream has a boulder riffle and pool sequence for approximately 100 feet. The channel is straight and has well defined banks with vegetation. Figure 2 shows the upstream conditions along with the riffles. This site is not designated for AOP design and as such a detailed geomorphic investigation was not conducted.

Figure 2: Boulder Grade Control Upstream of Culvert (Left and Right). Photos taken June 5, 2018.

Figure 3 shows the downstream conditions of the channel.

Figure 3: Looking Downstream of Culvert Toward Stream/Vegetation (Left and Right). Photos taken June 5, 2018.

Hydrology The C37 site is located in Bayfield County and has a drainage area of 481 acres. Peak discharges at the project location were calculated using the USGS regional regression equations. USGS regression equations were developed by U.S. Geological Survey (USGS) using streamflow data and log-Pearson Type III procedures. The National Streamflow Statistics (NSS) is a computer program that compiled the regression equations for calculating peak discharges at ungauged sites. The C37 watershed is located within Area 4 of the Wisconsin regional regression equations, which has a development range minimum of 422 acres (0.66 square miles). The basic input data for the regional regression equation are site location, drainage area, precipitation depth, stream reach slope, percent area that is storage, and average soil permeability. Peak discharges calculated are shown in Table 1.

Table 1: Peak Discharge Results

Drainage Area: 481 (acres) Return Period (year) 2 5 10 25 50 100 Peak Discharges (cfs) 19 32 41 52 60 68

Hydrology Characteristics Forests and roads are the land uses identified within this watershed. The soil types for this watershed are mostly type D soils, with moderate percentages of A soils. Overall the terrain of the drainage area is flat.

Figure shows the culvert site location, the stream channel, and the drainage area extents.

Figure 4: Site FS1730 C37 Drainage Area Map

Hydrologic parameters determined using USGS regression equations are shown in Table 1. Percent storage, stream slope, and mean annual snowfall are output from a StreamStat analysis of the site location. The drainage area was delineated using USGS topography. The average soil permeability is estimated from the USGS Water Resources Investigations Report.

Table 1: Summary of Hydrologic Analysis

Drainage Area (sq mi)

Percent Storage

Stream Slope 10 and 85 Method

(ft/mi)

Average Soil Permeability

(in/hr)

Mean Annual Snowfall (inches)

0.75 21 17 0.39 71.2

Hydraulic Modeling The Federal Highway Administrations (FHWA) HY-8 program was used for hydraulic modeling and analysis of the culvert replacement. The roadway was classified as a Low Standard Road which correlates to a 25-year design storm for the culvert following PDDM chapter 7.1.6.1 standards. This site does not need to account for Aquatic Organism Passage.

Outlet conditions were analyzed by identifying a tailwater cross section at a grade control immediately downstream of the culvert outlet. The selected cross section is located downstream of the scour hole, at the beginning of a stable riffle.

Existing Conditions The existing culvert measures as a 30” circular corrugated metal pipe. From the hydrologic analysis, the 25-year storm design flow of 52 cfs was entered into the model. Tailwater, roadway, and site station and elevation data were entered based on topographic survey data and the proposed roadway conditions.

Proposed Conditions The HY-8 analysis resulted in a commendation of a single barrel 49”x33” Corrugated Metal Pipe Arch Culvert (CMPAC). The proposed culvert is to be mitered to conform to the slope, following US Forest Service culvert design standards.