waa-jeffer134309-2_HYD_AOP Report.pdf

Memorandum

Western Federal Lands Highway Division 610 E. Fifth Street

Vancouver, WA 98661-3801

TWO TROUT CREEK CROSSING

AQUATIC ORGANISM PASSAGE HYDRAULICS REPORT

To: John Davis, WFLHD Project Manager From: Vernon Bevan, WFLHD Hydraulics Engineer Date: August 9, 2024 Project: Two Trout Creek Crossing – WA FLAP JEFFER 134309(2)

Background

Oil City Road is a rural, two-lane road located south of Forks, Washington in Jefferson County.

The road branches off US Highway 101 and travels west to Oil City, an unincorporated community at the mouth of the Hoh River. The road is primarily used to access the Oil City Trailhead in Olympic National Park, industrial timberland and a few private residences. Two Trout Creek is conveyed through the roadway embankment by two parallel 48-inch diameter culverts at Milepost

0.51. The crossing is located approximately 1,500 feet upstream of the creek’s confluence with the Hoh River (Figure 1).

The existing crossing was constructed in 1999 as an emergency repair after a head cut, which was progressing upstream, washed out the road. Jefferson County diverted the roadway north/upstream of its original alignment and installed twin 48-inch diameter CMP culverts. Figure 2 illustrates the location of the present crossing as well as the location of the original crossing and road alignment.

A 77-foot bridge was initially proposed to pass Oil City Road over Two Trout Creek. After further analysis and consideration of cost, a concrete box culvert was selected as the preferred option.

Refer to the attached Two Trout Creek TS&L Conceptional Options Memo for details.

This project aims to construct a permanent crossing of Two Trout Creek on the original roadway alignment which will facilitate aquatic organism passage (AOP). Some of the data and information for analysis and design came from a Hydraulic Engineering Analysis prepared by Watershed Science and Engineering (WSE) for a Preliminary Design Report produced by KPFF Consulting.

AOP Design Criteria

The proposed AOP structure has been designed following recommendations in Stream Simulation:

An Ecological Approach to Providing Passage for Aquatic Organisms at Road-Stream Crossings (USDA-Forest Service 2008) as well as Water Crossing Design Guidelines (Washington Department of Fish and Wildlife 2013). The structure will also be consistent with requirements of the Aquatic Restoration Biological Opinion II (ARBOII) per the National Marine Fisheries Service and the U.S. Fish and Wildlife Service.

Memo to: John Davis, WFLHD Project Manager August 2024

These documents provide design methodologies intended to mimic natural stream processes within the culvert. Sediment transport, debris conveyance and streambed morphology within the culvert should replicate these processes as they occur in the natural channel. Determination of the high and low fish passage design flows, water velocities, and water depths are not required for this method since the stream hydraulic characteristics within the culvert are intended to replicate the stream conditions upstream and downstream of the crossing. AOP culvert design utilizes streambed materials and sizes which occur in the natural channel, providing similar channel complexity, flow depth, flow velocities, and resting areas. The following requirements have been incorporated into the AOP design:

Flood and Debris Conveyance: Culvert capacity is designed to accommodate the 100-year recurrence flood without interfering with the functioning of the floodplain while providing adequate clearance above the flood stage for expected debris.

Crossing Location: Crossing structure is placed within the pre-development natural channel alignment wherever possible.

Culvert Width: Must accommodate the design channel bankfull width plus additional width for construction of stable bank rocks along both sides of the channel inside the culvert. The minimum culvert bed width is 1.3 times the bankfull channel width for non-entrenched streams. For entrenched streams (entrenchment ratio < 1.4) the minimum width is bankfull channel width plus room for natural channel banks.

Channel Vertical Clearance: Clearance from bed to ceiling must be at least 4-feet to allow for ease of construction, maintenance, and debris removal. Where possible, clearance will be 5-feet or greater.

Channel Slope: Reconstructed streambed within the culvert approximates the average slope of the stream reference reach. The slope should not deviate by more than 25% from the natural stream slope of the reference reach.

Embedment: Bottoms of round culverts should be buried below the streambed thalweg a minimum of 40% of the pipe diameter. Box or pipe arch culverts should be buried a minimum of 20% of the culvert’s rise.

Maximum Length of Road Crossing: Length should be less than 150-feet.

Fill Materials: Fill materials are generally comprised of sediment similar in size composition to natural bed materials that form the natural stream channel above and below the road crossing.

Larger material is added to assist grade retention and provide resting areas for migrating fish. A dense, well-graded mixture is specified, with washing in of fines between constructed lifts, to encourage the stream to flow on the surface.

Fill/substrate material for culverts without an adequate sediment supply, such as those situated below a lake or wetland, should be designed to resist the predicted critical shear forces of the 100-year flood.

Water Depth and Velocity: Bankfull water depths and velocities in the culvert must closely resemble those in the existing reference reach as specified in the 2021 USFW Service guidance document.

Two Trout Creek

Two Trout Creek is a single thread channel that flows approximately 0.9 miles southeast from its headwaters before reaching Oil City Road. It passes under the road through two, parallel 48-inch culverts before travelling 1,500 feet to its confluence with the Hoh River (Photos 1 and 2). Below the crossing, the channel is unstable and actions have been taken to arrest a 4-foot headcut located a short distance below the culvert outlets.

Upstream of the crossing outside the influence of the existing culverts, the stream has a gradient of 6.1% and a riffle/pool morphology. Bankfull widths measured in the field by WSE ranged from 10 to 14 feet with an average of 11.3 feet (Photo 3). The streambanks are thickly vegetated and appear relatively stable although there are some indications of minor incision. Woody debris was observed in the stream including multiple large logs which were suspended above the channel by both banks. Upstream of the crossing, the stream is relatively (hydraulically) stable, and the channel does not exhibit excessive lateral bank erosion or incision.

After passing under Oil City Road, the stream experiences a rapid drop of approximately 4 feet due to a headcut. The road embankment and the channel below the outlets was lined with large riprap during emergency repairs made in 1999 to prevent the headcut from migrating upstream and impacting the culverts and road (Photo 4). From the culvert outlets to a point approximately 200 feet downstream, the channel slope is 7.2%. Over the next 200 feet, the slope decreases to 4.6%. The stream initially assumes a step/pool morphology after passing through the culverts.

However, as the slope decreases, it generally reverts to a riffle/pool form (Photo 5).

The channel is incised with increasing severity as it travels downstream. Approximately 250 feet below the culvert outlets, incision becomes extreme and the channel is flanked by steep slopes that exceed 30 feet in height. The severity of the channel incision is depicted in Photo 6. The channel is also experiencing widespread lateral bank erosion below the crossing which has resulted in large deposits of sediment in the stream. Additionally, many mature trees have either been deposited in the channel or span the banks. As a result of this lateral bank erosion, it is not possible to estimate reliable bankfull widths in this reach.

Bed material upstream and downstream of the crossing includes sand, gravel, cobbles, and boulders. Pebble counts were carried out by WSE both above and below the crossing. A combined gradation of the upstream and downstream pebble counts yielded a D50 of 2.6 inches, a D85 of

6.3 inches and a D100 of 23.6 inches.

It is important to emphasize that Two Trout Creek is in active transition below the road crossing.

A headcut is located approximately 100 feet downstream of the existing culvert outlets and is likely to progress upstream, although the time frame is uncertain.

Morphological transition of Two Trout Creek is being driven by migration of the Hoh River to the west, which has shorted the length of the creek. Between 1994 and 2021, the right bank of the Hoh River moved approximately 90 feet to the west at the confluence of the two watercourses. In response, the slope of the stream has steepened resulting in both vertical incision and lateral bank erosion. It is likely that the stream will be in transition for the foreseeable future. In their assessment of scour, WSE advised that crossing designs should account for 5 feet of potential bed degradation resulting from future channel adjustment.

Recommendations:

The existing culverts do not meet USFWS standards for fish-bearing stream crossings and inhibit aquatic organism passage. A larger culvert is required to replace the existing culverts as well as provide space for bankfull width, a natural channel bottom, and stable banks.

• Install an 52-foot long, concrete box culvert with a 18-foot span and a 12-foot rise.

• Place the culvert at a 6.1 % slope to simulate the channel slopes upstream of the crossing by setting the inverts at elevation 241.73-feet upstream and at elevation 238.54-feet downstream (project datum).

• Embed the culvert a minimum of 5.0 feet and backfill the culvert interior with streambed material conserved during excavation of the culvert. If the conserved streambed material quantity is insufficient for backfilling the culvert, use material similar to the natural streambed material. Streambed material will be augmented with gradation which will be determined later in the Design process.

• Allow clearance for debris passage and maintenance access by providing 5.0 feet of clearance from the crown of the culvert and the installed bed material.

• Construct a channel with a bankfull width of 12 feet and depth of 12 inches including a low flow channel and streambanks inside the culvert to provide resting opportunities for fish.

• Install sediment retention sills spaced 15.5 feet through the culvert to prevent loss of streambed material and only allow a maximum 4-inch drop from the top of the sill to the top of the pool formed by the downstream sill.

• Install 5 rock weirs spaced at 12-foot intervals to help maintain banks and channel shape.

• Install 3 round boulders, approximately 24-inches in diameter, for inducing channel migration and providing low velocity fish resting areas.

• Install Class 4 riprap (FHWA FP-24), minimum 3 feet thick, at the inlet and outlet for controlling erosion near the culvert.

Construction

The Washington Department of Fish and Wildlife instream work period for the project location is between July 15 and August 15. Temporary flow deflectors placed for isolating the work area and diverting the stream flow must have a minimum height of 3 feet above the stream bottom and be stable assuming 8 feet per second parallel flow and 2 feet maximum water depth. Use plastic-lined channels or pipes to temporally convey stream flow through the construction area and protect the outfalls from erosion. Temporary stream diversions must have minimum flow capacity equal to the 2-year discharge of 32.7 ft3/s. Before installing the flow deflectors fish must be removed from the work area. Fish removal and screening must be carried out to the level and methods specified in the environmental permits. Fish passage must be maintained in accordance with environmental permits.

Full dewatering of the construction area is expected up to groundwater level for excavation as well as installing the culvert, riprap and backfill. Water pumped from the work area must be discharged to a vegetated upland treatment area near the site where it will infiltrate into the soil. If an acceptable area for the required level of treatment is not available, additional treatment systems or methods must be provided.

The State of Washington and the U.S. Fish and Wildlife Service restrict the release of turbidity from the work areas into the stream. These agencies require turbidity control and monitoring, and should be contacted for specific requirements and allowable discharge limits.

Stream Impacts

The proposed fish passage culvert is expected to dramatically improve stream flow conveyance, sediment transport, and woody debris transport to a level comparable to reaches upstream and downstream of the culvert. A moderate amount of turbidity and sediment is expected to be released when the flow barriers are removed, and stream flow is introduced into the newly constructed culvert. The amount of turbidity and sediment will be reduced by removing the flow barriers gradually in order to re-introducing stream flow into the channel over an extended two to three-hour time period.

Operation and Maintenance

Scour or aggradation of the streambed is expected to occur to some extent, as would be expected for the natural stream. Monitoring at regular intervals is important to ensure the operation and serviceability of the structure. This should occur more frequently during the first three years following construction; at least twice a year as well as following flood events. The purpose is to ensure that excessive debris accumulation, scour, or aggradation does not impair passage through the culvert. Fish boulders and rock weirs placed within the culvert and stream channel should be inspected and repositioned or replaced if they have been dislodged. Additional rock may need to be installed to correct erosion or channel degradation. Riprap placed at the culvert inlet and outlet should be also be examined and dislodged stone should be repositioned or replaced. After the initial three year period, monitoring may occur annually. If possible, inspections should also be carried out following major discharge events.

Floodplain and Flood-rise Impacts

Flood limits and elevations have not been mapped by the National Flood Insurance Program for the site. The proposed culverts will improve hydraulic conveyance and is not expected to negatively impact flooding at the site.

Hydrology

There are no active or historical streamflow gages on Two Trout Creek or similar streams in the vicinity. As a result, peak annual discharges at the project location were estimated using USGS StreamStats (Version 4.20.1). StreamStats is a web-based application for delineating watersheds and calculating discharge statistics on ungauged streams.

The drainage area for Two Trout Creek is 0.26 mi2 and approximately 60% of the watershed is covered by forest canopy. Mean annual precipitation is 120 inches. Sometime between 1985 and 1994, most of the upper watershed was clear cut. Since that time, the forest canopy in the upper watershed has recovered. Between 2021 and 2024, a small portion of the lower watershed near the road crossing was clear cut.

StreamStats estimates for flow range from 32.7 ft3/s for the 2-year discharge event to 78.4 ft3/s for the 100-year discharge event. Refer to Table 1 and the StreamStats report in the attachments for a complete range of peak annual discharges.

In their hydraulic analysis, WSE considered the effects of climate change on stream flows in Two Trout Creek. The effects of climate changes were evaluated using the Washington Department of Fish and Wildlife Culverts and Climate Change web application (Culverts And Climate Change (wa.gov)). Based on the evaluation, the 100-year discharge event is projected to increase by 21.1% by 2080. Thus, the StreamStats estimate of 78.4 ft3/s is expected to increase to 95 ft3/s. This value was rounded up to 100 ft3/s for hydraulic analysis of the proposed culvert.

Culvert Hydraulics

Hydraulic capacity and performance of the proposed culvert were evaluated using the FHWA Culvert Hydraulics Analysis Program, HY-8, version 7.7.1. The evaluation included a range of discharges from the 2-year event to the 100-year event considering climate change.

Culvert performance was modeled using the design slope of 10% and a Manning’s Roughness coefficient of 0.035 for the channel bottom while a roughness coefficient of 0.024 was used for the sides and top of the culvert. The proposed culvert has enough capacity to accommodate all of the modeled stream flows. Headwater to depth ratios based on modeling results are given in Table

2. The HY-8 Culvert Analysis Report is included in the attachments.

https://geodataservices.wdfw.wa.gov/hp/culvert-app/ https://geodataservices.wdfw.wa.gov/hp/culvert-app/

Attachments: Table 1 - Peak Discharge Estimates Table 2 – Headwater Depths and Ratios Figures 1 and 2 Photographs HY-8 Calculations USGS StreamStats Report Design Drawings Two Trout Creek TS&L Conceptual Options Memo WSE Draft Hydraulic Analysis: Oil City Road MP 0.51 Special Contract Requirements and Gradation Stability Calculations (TBD)

Tables

Table 1. Peak Discharge Estimates Peak Annual Floods Discharge (ft3/s)

2-Year 32.7 5-Year 44.4 10-Year 53.2 25-Year 62.6 50-Year 70.0 100-Year 78.4

100-Year Adjusted for Climate Change 100.0

Table 2. Peak Discharges and Headwater to Depth Ratios

Peak Annual Discharge Discharge (ft3/s)

Headwater Depth

(ft) HW/D (D = 7 ft)

2-Year 32.7 0.67 0.10 50-Year 70.0 1.10 0.16 100-Year 78.4 1.17 0.17

100-Year Adjusted for Climate Change 100.0 1.38 0.20

Figure 1. Two Trout Creek Site Location and Watershed.

Figure 2. Map of Project Area.

Photos

PHOTO 1

07/06/2023

PHOTO 2

07/06/2023

PHOTO 3

10/06/2020

Two Trout Creek

Two Trout Creek Channel approximately 100 feet upstream of the crossing.

Stream has riffle/pool morphology with well vegetated banks.

Outlet of the two 48-inch culverts. Bank around the outlets has been protected with large riprap. Riprap was also paced in the channel to prevent a 4-foot headcut from impacting the culvert.

Standing in the center of the channel and looking downstream to the southeast.

Standing in the channel and looking downstream towards the southeast.

Inlet of one of the two culverts that carry Two Trout Creek under Oil City Road. A large log has fallen across the stream banks and is suspended above the channel approximately 10 feet upstream of the culvert inlet.

Standing in the center of the channel and looking upstream towards the northwest.

Photos

PHOTO 4

07/06/2023

PHOTO 5

10/06/2020

PHOTO 6

07/06/2023

North Shore Road - MP 10.2

Channel is extremely incised and and experiencing lateral bank erosion.

Large trees have fallen into the channel.

Standing in the center of the channel and looking upstream towards the northwest.

Channel was lined with riprap in 1999 to to prevent the headcut from migrating upstream and impacting the culverts and road. Channel has a riffle pool morphology.

Standing in the center of the channel and looking upstream towards the northwest.

Channel slope decreases and stream transistions to a riffle/pool morphology.

Stream is deeply incised.

Standing on the north bank and looking across to the south bank approximately 500 feet downstream of the crossing.

HY-8 Culvert Analysis Report Crossing Discharge Data Discharge Selection Method: Specify Minimum, Design, and Maximum Flow

Minimum Flow: 32.70 cfs

Design Flow: 78.40 cfs

Maximum Flow: 100.00 cfs

Table 1 - Summary of Culvert Flows at Crossing: AOP 100 cfs Headwater Elevation (ft)

Total Discharge (cfs)

Box Culvert 1 Discharge (cfs)

Roadway Discharge (cfs)

Iterations

247.41 32.70 32.70 0.00 1

247.49 39.43 39.43 0.00 1

247.58 46.16 46.16 0.00 1

247.66 52.89 52.89 0.00 1

247.74 59.62 59.62 0.00 1

247.82 66.35 66.35 0.00 1

247.89 73.08 73.08 0.00 1

247.95 78.40 78.40 0.00 1

248.03 86.54 86.54 0.00 1

248.10 93.27 93.27 0.00 1

248.16 100.00 100.00 0.00 1

262.51 2173.09 2173.09 0.00 Overtopping

Rating Curve Plot for Crossing: AOP 100 cfs

Culvert Data: Box Culvert 1

Table 2 - Culvert Summary Table: Box Culvert 1 Total Discharge (cfs)

Culvert Discharge (cfs)

Headwater Elevation (ft)

Inlet Control Depth (ft)

Outlet Control Depth (ft)

Flow Type

Normal Depth (ft)

Critical Depth (ft)

Outlet Depth (ft)

Tailwater Depth (ft)

Outlet Velocity (ft/s)

Tailwater Velocity (ft/s)

32.70 cfs 32.70 cfs 247.41 0.68 0.0* 1-S2n 0.35 0.47 0.35 0.96 5.23 6.78

39.43 cfs 39.43 cfs 247.49 0.76 0.0* 1-S2n 0.39 0.53 0.39 1.01 5.65 7.24

46.16 cfs 46.16 cfs 247.58 0.85 0.0* 1-S2n 0.42 0.59 0.42 1.05 6.04 7.65

52.89 cfs 52.89 cfs 247.66 0.93 0.0* 1-S2n 0.46 0.64 0.46 1.09 6.37 8.03

59.62 cfs 59.62 cfs 247.74 1.01 0.0* 1-S2n 0.50 0.70 0.50 1.13 6.65 8.36

66.35 cfs 66.35 cfs 247.82 1.09 0.0* 1-S2n 0.53 0.75 0.53 1.17 6.90 8.67

73.08 cfs 73.08 cfs 247.89 1.16 0.0* 1-S2n 0.56 0.80 0.56 1.20 7.19 8.96

78.40 cfs 78.40 cfs 247.95 1.22 0.0* 1-S2n 0.59 0.84 0.59 1.23 7.41 9.18

86.54 cfs 86.54 cfs 248.03 1.30 0.0* 1-S2n 0.62 0.90 0.62 1.27 7.71 9.49

93.27 cfs 93.27 cfs 248.10 1.37 0.0* 1-S2n 0.65 0.94 0.66 1.30 7.87 9.73

100.00 cfs 100.00 cfs 248.16 1.43 0.0* 1-S2n 0.68 0.99 0.68 1.33 8.14 9.95

* Full Flow Headwater elevation is below inlet invert.

Culvert Barrel Data Culvert Barrel Type Straight Culvert

Inlet Elevation (invert): 246.73 ft, Outlet Elevation (invert): 243.54 ft

Culvert Length: 52.10 ft, Culvert Slope: 0.0613

Culvert Performance Curve Plot: Box Culvert 1

Water Surface Profile Plot for Culvert: Box Culvert 1

Site Data - Box Culvert 1 Site Data Option: Culvert Invert Data

Inlet Station: 0.00 ft

Inlet Elevation: 241.73 ft

Outlet Station: 52.00 ft

Outlet Elevation: 238.54 ft

Number of Barrels: 1

Culvert Data Summary - Box Culvert 1 Barrel Shape: Concrete Box

Barrel Span: 18.00 ft

Barrel Rise: 12.00 ft

Barrel Material: Concrete

Embedment: 60.00 in

Barrel Manning's n: 0.0120 (top and sides)

Manning's n: 0.0350 (bottom)

Culvert Type: Straight

Inlet Configuration: Square Edge (30-75º flare) Wingwall (Ke=0.4)

Inlet Depression: None

Tailwater Data for Crossing: AOP 100 cfs

Table 3 - Downstream Channel Rating Curve (Crossing: AOP 100 cfs) Flow (cfs) Water

Surface Elev (ft)

Velocity (ft/s)

Depth (ft) Shear (psf) Froude Number

32.70 244.50 0.96 6.78 6.07 1.95

39.43 244.55 1.01 7.24 6.37 1.99

46.16 244.59 1.05 7.65 6.65 2.01

52.89 244.63 1.09 8.03 6.91 2.03

59.62 244.67 1.13 8.36 7.16 2.05

66.35 244.71 1.17 8.67 7.40 2.07

73.08 244.74 1.20 8.96 7.62 2.09

78.40 244.77 1.23 9.18 7.80 2.10

86.54 244.81 1.27 9.49 8.05 2.12

93.27 244.84 1.30 9.73 8.25 2.13

100.00 244.87 1.33 9.95 8.45 2.14

Tailwater Channel Data - AOP 100 cfs Tailwater Channel Option: Irregular Channel

Channel Slope: Irregular Channel

User Defined Channel Cross-Section Coord No. Station (ft) Elevation (ft) Manning's n 1 0.00 253.14 0.0350 2 6.75 247.64 0.0350 3 27.00 246.14 0.0350 4 29.00 245.44 0.0350 5 29.70 243.64 0.0350 6 30.60 243.54 0.0350 7 35.00 244.34 0.0350 8 41.00 244.24 0.0350 9 46.50 245.34 0.0350 10 55.00 245.89 0.0350 11 62.70 252.14 0.0000

Roadway Data for Crossing: AOP 100 cfs Roadway Profile Shape: Constant Roadway Elevation

Crest Length: 26.00 ft

Crest Elevation: 262.51 ft

Roadway Surface: Gravel

Roadway Top Width: 26.00 ft

2 Trout Creek StreamStats Report

Collapse All

Basin Characteristics

Parameter Code Parameter Description Value Unit

CANOPY_PCT Percentage of drainage area covered by canopy as described in OK SIR 2009_5267 56.9 percent

DRNAREA Area that drains to a point on a stream 0.26 square miles

ELEV Mean Basin Elevation 719 feet

PRECIP Mean Annual Precipitation 120 inches

PRECPRIS10 Basin average mean annual precipitation for 1981 to 2010 from PRISM 118 inches

Peak-Flow Statistics

Peak-Flow Statistics Parameters [Peak Region 4 2016 5118]

Parameter Code Parameter Name Value Units Min Limit Max Limit

DRNAREA Drainage Area 0.26 square miles 0.18 2230

PRECPRIS10 Mean Annual Precip PRISM 1981 2010 118 inches 11.9 187

Peak-Flow Statistics Flow Report [Peak Region 4 2016 5118]

PIL: Lower 90% Prediction Interval, PIU: Upper 90% Prediction Interval, ASEp: Average Standard Error of Prediction, SE:

Standard Error, PC: Percent Correct (other -- see report)

Region ID: WA Workspace ID: WA20240620191252629000 Clicked Point (Latitude, Longitude): 47.80237, -124.26260 Time: 2024-06-20 12:13:31 -0700

Statistic Value Unit PIL PIU ASEp

50-percent AEP flood 32.7 ft^3/s 2.7 395 52.5

20-percent AEP flood 44.4 ft^3/s 3.77 523 50.6

10-percent AEP flood 53.2 ft^3/s 4.33 654 50.5

4-percent AEP flood 62.6 ft^3/s 4.55 862 51.7

2-percent AEP flood 70 ft^3/s 4.62 1060 52.9

1-percent AEP flood 78.4 ft^3/s 4.72 1300 54.2

0.5-percent AEP flood 83.5 ft^3/s 4.59 1520 55.5

0.2-percent AEP flood 94.6 ft^3/s 4.51 1980 58

Peak-Flow Statistics Citations

Mastin, M.C., Konrad, C.P., Veilleux, A.G., and Tecca, A.E.,2016, Magnitude, frequency, and trends of floods at gaged and ungaged sites in Washington, based on data through water year 2014 (ver 1.1, October 2016): U.S. Geological Survey Scientific Investigations Report 2016–5118, 70 p. (http://dx.doi.org/10.3133/sir20165118)

Bankfull Statistics

Bankfull Statistics Parameters [Pacific Mountain System D Bieger 2015]

Parameter Code Parameter Name Value Units Min Limit Max Limit

DRNAREA Drainage Area 0.26 square miles 6.1776 8079.9147

Bankfull Statistics Parameters [Pacific Border P Bieger 2015]

Parameter Code Parameter Name Value Units Min Limit Max Limit

DRNAREA Drainage Area 0.26 square miles 6.169878 3938.976756

Bankfull Statistics Parameters [USA Bieger 2015]

Parameter Code Parameter Name Value Units Min Limit Max Limit

DRNAREA Drainage Area 0.26 square miles 0.07722 59927.7393

Bankfull Statistics Parameters [Pac Maritime Mtn CastroJackson 2001]

Parameter Code Parameter Name Value Units Min Limit Max Limit

DRNAREA Drainage Area 0.26 square miles 54.8 3093

Bankfull Statistics Disclaimers [Pacific Mountain System D Bieger 2015]

One or more of the parameters is outside the suggested range. Estimates were extrapolated with unknown errors.

Bankfull Statistics Flow Report [Pacific Mountain System D Bieger 2015]

Statistic Value Unit

Bieger_D_channel_width 7.73 ft

Bieger_D_channel_depth 0.672 ft

Bieger_D_channel_cross_sectional_area 7.23 ft^2 http://dx.doi.org/10.3133/sir20165118

Bankfull Statistics Disclaimers [Pacific Border P Bieger 2015]

One or more of the parameters is outside the suggested range. Estimates were extrapolated with unknown errors.

Bankfull Statistics Flow Report [Pacific Border P Bieger 2015]

Statistic Value Unit

Bieger_P_channel_width 6.07 ft

Bieger_P_channel_cross_sectional_area 5.77 ft^2

Bieger_P_channel_depth 0.605 ft

Bankfull Statistics Flow Report [USA Bieger 2015]

Statistic Value Unit

Bieger_USA_channel_width 7.71 ft

Bieger_USA_channel_depth 0.905 ft

Bieger_USA_channel_cross_sectional_area 8.26 ft^2

Bankfull Statistics Disclaimers [Pac Maritime Mtn CastroJackson 2001]

One or more of the parameters is outside the suggested range. Estimates were extrapolated with unknown errors.

Bankfull Statistics Flow Report [Pac Maritime Mtn CastroJackson 2001]

Statistic Value Unit

Bankfull Width 6.94 ft

Bankfull Depth 0.39 ft

Bankfull Area 5.27 ft^2

Bankfull Streamflow 36.9 ft^3/s

Bankfull Statistics Flow Report [Area-Averaged]

Statistic Value Unit

Bieger_D_channel_width 7.73 ft

Bieger_D_channel_depth 0.672 ft

Bieger_D_channel_cross_sectional_area 7.23 ft^2

Bieger_P_channel_width 6.07 ft

Bieger_P_channel_cross_sectional_area 5.77 ft^2

Bieger_P_channel_depth 0.605 ft

Bieger_USA_channel_width 7.71 ft

Bieger_USA_channel_depth 0.905 ft

Bieger_USA_channel_cross_sectional_area 8.26 ft^2

Bankfull Width 6.94 ft

Bankfull Depth 0.39 ft

Bankfull Area 5.27 ft^2

Bankfull Streamflow 36.9 ft^3/s

Bankfull Statistics Citations

Bieger, Katrin; Rathjens, Hendrik; Allen, Peter M.; and Arnold, Jeffrey G.,2015, Development and Evaluation of Bankfull Hydraulic Geometry Relationships for the Physiographic Regions of the United States, Publications from USDA-ARS / UNL Faculty, 17p. (https://digitalcommons.unl.edu/usdaarsfacpub/1515?

utm_source=digitalcommons.unl.edu%2Fusdaarsfacpub%2F1515&utm_medium=PDF&utm_campaign=PDFCoverPages) Castro, J.M, and Jackson, P.L.Castro, J.M, and Jackson, P.L., 2001, Bankfull Discharge Recurrence Intervals and Regional Hydraulic Geometery Relationships: Patterns in the Pacific Northwest, USA, Journal of the American Water Resources Association, Volume 37, No. 5, 14 p. (https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1752-1688.2001.tb03636.x)

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Application Version: 4.20.1

StreamStats Services Version: 1.2.22

NSS Services Version: 2.2.1 https://digitalcommons.unl.edu/usdaarsfacpub/1515?utm_source=digitalcommons.unl.edu%2Fusdaarsfacpub%2F1515&utm_medium=PDF&utm_campaign=PDFCoverPages https://digitalcommons.unl.edu/usdaarsfacpub/1515?utm_source=digitalcommons.unl.edu%2Fusdaarsfacpub%2F1515&utm_medium=PDF&utm_campaign=PDFCoverPages https://digitalcommons.unl.edu/usdaarsfacpub/1515?utm_source=digitalcommons.unl.edu%2Fusdaarsfacpub%2F1515&utm_medium=PDF&utm_campaign=PDFCoverPages https://digitalcommons.unl.edu/usdaarsfacpub/1515?utm_source=digitalcommons.unl.edu%2Fusdaarsfacpub%2F1515&utm_medium=PDF&utm_campaign=PDFCoverPages https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1752-1688.2001.tb03636.x https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1752-1688.2001.tb03636.x https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1752-1688.2001.tb03636.x

120 100 90 80 70 60 50 40 30 20 10 0 10 20 30 40 50 60 70 80 90 100 120

OUTLETINLETPIPEHYDRAULIC INFORMATION

LENGTH: 50 ft

PIPE SLOPE: 0.61 ft/ft

HEADWALL: Concrete

FLOWLINE SLOPE: 0.61 ft/ft

Q : 32.7 CFS

Q : 65 CFS

BANKFULL CHANNEL WIDTH: 12.0 ft

TYPE: Concrete Box SPAN: 18 ft RISE: 12 ft

LOWER BEVEL HEIGHT: LOWER BEVEL HEIGHT:

BEVEL:

HEADWALL: Concrete

BEVEL:

Q : 78.4 CFS

INV N/E/EL: 241.73' 238.54'INV N/E/EL:

WALL THICKNESS: NA

HW : 248.3 feet

N

OHW : 247.3 feet

BURIAL DEPTH: 5.0 ft BURIAL DEPTH: 5.0 ft

12+81.85, 26.19 LT

PLAN AND PROFILE

TWO TROUT CREEK CULVERT

H.1

STATE PROJECT

NUMBER

SHEET

WA WA FLAP JEFFER 134309(2)

V B e v a n

/2

/2

C h e c k e d b y

D e s ig n e d b y

A O

P S h e e t c p w w o r k

\d

\w a a je f f e r

A O

P p la n .d g n

:4

P

M

A u g u s t

12+74.38, 25.27 RT

Existing ground

Concrete wingwall (Typ.)

Concrete headwall method B, class 4

Placed riprap detail Sheet H.13material per

Backfill with streambed

15.5' spacing per detail sheet G.14.

Install sediment retention sill at

Channel elev. 246.73'

Channel elev. 243.54' Slope 6.1% per detail sheet G.15.

Install rock weirs at 12' spacing concrete box culvert

18' span, 12' rise

12+78.05 centerline

New culvert

Roadway centerline

48" culverts

Remove existing

52'

:1

Two Trout Creek

Flow

SCALE IN FEET

10 0 10 20 30 40

Existing roadway alignment

1'3

2'

1V:

2H

12" depth

Bedding material, :1

6'

Proposed edge of pavement

LC

12' 15.5'

Begin channel grading

End channel grading

13.1'

SECTION A-A

PLAN

NOTE:

FOOTNOTE:

3.

2.

1.

Pipe arch culvert

W

Streambed sediment

Streambed cobble

Pipe arch culvert wall

Box culvert wall

Stagger in-channel fish passage boulders within the culvert span.

streambed cobble, and bank stone gradations.

See special contract requirements for streambed sediment, and wash in fines as specified in special contract requirements.

Mix streambed cobbles evenly throughout streambed sediment

Channel flowline

Streambed sedimentRound pipe culvert wall Streambed top

Round culvert

B D

Culvert wall

LC

Flow

BB

A

W

X (typ.)

where specified on plan per detail Sheet G.14

Sediment retention sill on plan where specified detail Sheet G.15

Rock weir per culvert boulder within

Fish passage where specified on plan per detail Sheet G.14

Sediment retention sill specified on plan boulder where

Fish passage

NO SCALE

Streambed Material.

Infill informational quantities are incidental to ITEM 64704-1000 [4] dimension.

smallest 4 3 Embed fish passage boulders within active channel [3] sediment where listed in the infill quantities table.

Construct well defined banks with bank stone and streambed[2] parabolic shape.

Slope streambed aggregate towards flowline to ensure[1]

[1]Channel flowline

[2]Bank stone

[2]Bank stone

A Flow

SECTION B-B

(typ.)

36" min.

Streambed cobble

Culvert outlet where specified on plan per detail Sheet G.14

Sediment retention sill

[3]within culvert

Fish passage boulder

Streambed sediment X (typ.)

plan sheet or Length on

4' match rock weir spacing

Stagger fish boulders each side and

LC

specified on plan

Sheet G.15 where

Rock weir per detail outlet

Culvert

LOCATION

(FT)

X

(CUYD)

COBBLE

STREAMBED

(CUYD)

SEDIMENT

STREAMBED

(CUYD)

STONE

BANK

GRADATION

COBBLE

STREAMBED

(FT)

W

MITIGATION

FISH PASSAGE BOULDER

(IN)

DIA. NO.

[4]STREAMBED MATERIAL

TOTAL

TWO TROUT CREEK 15.5 12 24 3TBD

(IN)

BD

d e p th B u r ia l

B u r ia l d e p th

BD/3

3% (typ.)

Slope

TBD

TBD

TBD

TBD

TBD

TBD

:5 u g u s t

D e s ig n S u r v

F p w w o r k \d

\w a a je f f e r A

O P

D e ta il S h e e ts

.d g n

TREATMENT

STREAM CULVERT

SIMULATED

PROJECT

NUMBER

SHEET

WA FLAP JEFFER 134309(2) H.13

WA FLAP JEFFER 134309(2)

DETAIL

PLATE AND CONNECTOR

NOTE:

LC

H

B

NO SCALE

24" typ.

FlowLC

H B

CROSS-SECTION

ROUND PIPE

SEDIMENT RETENTION SILLS

24" typ.

CROSS-SECTION

STRUCTURAL-PLATE PIPE ARCH

SEDIMENT RETENTION SILLS

X

B

H

CROSS-SECTION

PRECAST BOX CULVERT

SEDIMENT RETENTION SILLS

LC

DETAIL

CONCRETE SILL

X

Flow

H

0.25" retention sill

Top of sediment retention sill

Top of sediment

(0.25" A36 steel plate)

Gusset steel plate)

(0.25" A36

Gusset steel plate)

(0.25" A36

Gusset retention sill

Top of sediment

2 - #5

12"

1 row alternate sides

2 - #5

1" threaded inserts (typ.)

#5 @ 1'-6" with inserts (typ.)

1" threaded

1" threaded inserts (typ.)

Round pipe c l.

2" cl.

D

V a r ie s

D pipe arch culvert

Structural-plate wall Culvert

LOCATION (IN)

B

(IN)

H

(NO.)

Min.

SRS

(FT)

Max.

X

MITIGATION

SEDIMENT RETENTION SILLS (SRS)

locating SRS in corrugation valleys or away from plate seems.

X dimension may be varied +/- 6-inches as needed for

Apply two coats zinc paint to all welds.

Hot dip galvanized baffles and gussets.

3.

2.

1.

(A36 steel plate)

Sediment retention sill (SRS)

UNNAMED CREEK 3 12 36 15.5

Minor Concrete

:0

J u ly

D e s ig n S u r v p w w o r k

\d

\w a a je f f e r

A O

P

D e ta il

S h e e ts

.d g n

DETAILS

SEDIMENT RETENTION SILL

CULVERT

PROJECT

H.14

Flow lo wA

A

(in)

DIAMETER

FOOTER ROCK

TOP ROCK AND

(no.)

QUANTITY

ROCK WEIR

MITIGATION

ROCK WEIR

(ft)

B

(ft)

[5] Z

(ft)

W

LOCATION

ELEVATION

PLAN

SECTION A-A

NO SCALE

FOOTNOTE:

parameter Z.

Outside of culvert, weirs should be u-shaped as specified by

Align footer rocks flush against bed retention sills inside culvert. [5] and stable foundation for the top rocks.

Place footer rocks close together to create a tightly packed[4] streambed material.

Fill voids in top rock and footer rock with specified[3]

Space top rocks in center 1/3 only.[2]

Orient top rocks to deflect water towards center of stream.[1]

[4] [3]Footer rock

Z

D o w n s tr e a m f r o m c o n tr o l)

Top rock

Bottom of channel

Bottom of channel

[4] [3]Footer rock high water level

Ordinary normal low flow

Edge of water

Control point

[2] [1] [2] [1]

[2]

[3] [2]Top rock

[2]

[2] [2] [2]

[2] streambed material elevation or top of

Original streambed

[4] [3]Footer rock

[3]Top rock water level

Ordinary high

BWB

B W3

W 3

W3

B

W3

TWO TROUT CREEK 12 2.5 6 5

:5 u g u s t

D e s ig n S u r v p w w o r k

\d

\w a a je f f e r

A O

P

D e ta il

S h e e ts

.d g n

DETAIL

ROCK WEIR

PROJECT

H.15

Memorandum

Western Federal Lands Highway Division 610 E. Fifth Street

Vancouver, WA 98661-3801

TWO TROUT CREEK TS&L CONCEPTUAL OPTIONS MEMO

Date: October 2, 2023

To: John Davis, WFLHD Project Manager

From: Vernon Bevan, WFLHD Hydraulics Engineer Stephen Henry, WFLHD Civil Design Engineer Todd Hansen, WFLHD Geologic Engineer Steve Morrow, WFLHD Environmental Specialist

Project: Two Trout Creek Crossing

Jefferson County, Washington

INTRODUCTION

Oil City Road is a rural, two-lane road located south of Forks, Washington in Jefferson County. The road branches off US Highway 101 and travels west to Oil City, an unincorporated community at the mouth of the Hoh River. The road is primarily used to access the Oil City Trailhead in Olympic National Park, industrial timberland and a few private residences. The ADT is less than 250 and the posted speed limit is 30 miles per hour.

The roadway is part asphalt-paved and part gravel-surfaced. At Milepost (MP) 0.51 it narrows to a single-lane, gravel-surfaced road. In this vicinity, the road is approximately 15-feet wide with limited grass shoulders. The road crosses over Two Trout Creek and the surface is approximately nine feet above the thalweg of the stream. Two Trout Creek is conveyed through the roadway embankment by two parallel 48-inch diameter culverts. The crossing is located approximately 1,500 feet upstream of the creek’s confluence with the Hoh River. Figure 1 depicts the location of the site on Oil City Road relative to US Highway 101 and the Hoh River.

The gravel-surfaced road is free of extensive cracking, subsidence and other indications of active distress at the location of the creek crossing. However, the road surface is situated at a lower elevation than the pre-washout road profile.

Two Trout Creek Crossing - WA FLAP JEFFER 134309(2)

Figure 1. General location of Oil City Road crossing of Two Trout Creek.

The existing crossing was constructed in 1999 as an emergency repair after a head cut which was progressing upstream washed out the road. Jefferson County built the present road as an emergency project to act as a temporary roadway until permanent repairs could be made. The roadway was diverted north/upstream of its original alignment and twin 48-inch diameter CMP culverts were installed to convey Two Trout Creek beneath the roadway. Figure 2 illustrates the location of the present crossing as well as the location of the original crossing and road alignment.

This project aims to construct a permanent crossing of Two Trout Creek on the original roadway alignment which will facilitate anadromous fish passage. However, there are geotechnical and stream channel degradation issues as well as design and constructability considerations that should be taken into account when selecting a crossing structure. These topics will be discussed in the sections below.

N

Project site

US Hwy 101

Oil City Road

Hoh River

Figure 2. Existing and original locations of Oil City Road crossing of Two Trout Creek.

Geologic Setting

The project site is located within the Olympic Structural Complex geologic terrane, a known source for active landslides including very large prehistorical landslides on forest roads and US Highway

101. The mapped geologic formations have not been metamorphically altered but are folded and faulted with local exposures of mélange on the coast. Mélange is a weak sedimentary rock made up of fragmented rock debris embedded in a matrix of finer-grained material, making it more susceptible to landslide movement. As mapped by W.W. Rau (1979) the site is Quaternary aged (up to 1.8 million years old) Alpine glacial drift (Qg), consisting of glacial outwash, silt, sand, gravel and possible overridden till. Nearby bedrock outcrops contain the Miocene aged (up to 20 million

Two Trout Creek

Hoh River

Oil City Road original crossing

Existing culverts years old) Hoh Formation rock assemblage (Ths, Thss) which consists of steep to vertically bedded siltstone, sandstone and graywacke sandstone. The regional Hoh River Fault and two other inferred faults are close to the site. Figure 3 shows the geologic map of the area.

Figure 3. Geologic map of lower Bogachiel and Hoh River Valleys GM-24 (1979).

The most recent LiDAR available from the Washington State Department of Natural Resources is the “Hoh 2012” digital terrain model hillshade (Figure 4). The figure below shows there is an active landslide mass within a larger prehistoric landslide, extending upslope of Oil City Road. The Two Trout Creek drainage flows along the western lateral scarp of the prehistoric landslide boundary.

The open tension cracks and road deformation immediately up-road-grade and adjacent to Two Trout Creek in Figure 4 are indicative of continued, active landslide movement. During a recent site visit, newer tension cracks above the existing roadway on the forest road were observed. This is an indication that the active landslide limits are broadening within, and now expanding beyond the prehistoric landslide feature in some areas. Erosion at the toe of the active landslide by the Hoh River continues to debuttress the landslide feature, causing additional movement of the active portion of the landslide that has been reportedly confined to the area of the County Road as shown below. There is a concern that the Hoh River will continue to erode the active landslide toe and the landslide will continue to move and retrogress to the prehistoric landslide limits over time.

Approximate site location

Figure 4. Hoh 2012 LiDAR hillshade surface showing limits of larger prehistoric landslide (yellow dots) and currently active landslide scarps and limits within the larger prehistoric landslide feature (red dashed lines) and direction of movement (red arrow).

The segment of Oil City Road between the site and US Highway 101 is underlain by a prehistoric landslide with active landsliding expanding to potentially include the east bank of Two Trout Creek.

This segment of road will continue to experience landslide related deformation in the future as the Hoh River continues to erode and undermine the toe of the landslide. Regardless of the repair option selected, there are long term implications that should be considered during design.

Hydraulic Considerations

The watershed above the Oil City Road crossing is relatively small with an area of 0.26 mi2. It is heavily forested but a review of aerial imagery indicates that prior to 1994 approximately half of the basin was logged. Two Trout Creek generally flows in a southeasterly direction from its headwaters to the confluence with the Hoh River which is about 1,500 feet downstream of the crossing (refer to Figure 2).

A field study conducted by Watershed Science and Engineering (WSE) measured bankfull widths at several locations along the channel. Bankfull channel widths within 500 feet upstream and downstream of the crossing ranged from 10 feet to 14 feet with an average of 11.3 feet. The gradient of the stream is fairly steep with an average slope of 3.48% upstream of the crossing and an average slope of 7.98% downstream of the crossing.

Upstream of the crossing, the channel is relatively undisturbed and does not exhibit excessive bank erosion or incision. Downstream of the crossing, the channel is highly unstable. The stream is severely incised with a vertical drop of approximately 4 feet immediately below the crossing.

N Observed Summer

Site

Further downstream, incision is even more pronounced and the channel is flanked by steep side slopes that exceed 30 feet in height. The severity of the channel incision is depicted in Figure 5.

The channel is also experiencing widespread lateral bank erosion below the crossing which has resulted in large deposits of sediment in the stream. Due to this continuing lateral erosion, many mature trees have either been deposited in the channel or span the banks.

Figure 5. Severity of channel incision in Two Trout Creek below Oil City Road crossing.

The confluence of Two Trout Creek is located on the outside of a large meander bend in the Hoh River. The meander bend has been migrating outwards, gradually shortening the length of Two Trout Creek and lowering the elevation of the stream at its confluence. As a result, Two Trout Creek is adjusting by downcutting and steepening its grade. The stream will continue to undergo transition for the foreseeable future.

Hydrology

There are no active or historical streamflow gages on Two Trout Creek or similar streams in the vicinity. As a result, WSE employed the U.S. Geological Survey (USGS) StreamStats program to estimate flow frequency values. StreamStats uses regional regression equations (Mastin et al 2016) to determine peak streamflow statistics. The regression equations require values for basin area (0.26 mi2) and average annual precipitation (118 inches based on PRISM rainfall data). Peak flows derived from StreamStats and used by WSE in their hydraulic models are given in the table below.

Table 1. Peak annual flows estimated by USGS StreamStats.

Peak Annual Flow Discharge (ft3/2)

2-Year 32.7 25-Year 65.0 100-Year 78.4

Hydraulics

WSE developed a 1-dimensional steady-state hydraulic model for Two Trout Creek using the U.S.

Army Corps of Engineers HEC-RAS v 5.0.7. Two scenarios were evaluated: 1) an existing conditions model which includes the two existing 48-inch culverts, and 2) a proposed conditions model of a roughened channel design. The proposed conditions model simulates a reconstructed channel which would run under the proposed bridge crossing. It does not include a crossing structure.

The reconstructed channel has a gradient of 9.5% which was developed to connect the upstream and downstream reaches and smooth out the 4-foot vertical drop below the culverts.

The tables below present some of the modeling results for proposed and existing conditions. The first table includes the simulated top widths for the 2-Year and 100-Year peak flows. Note that the existing average top width of 11.9 feet estimated by HEC-RAS is close to the average bankfull width of 11.3 feet measured in the field. The second table shows the maximum, minimum and average channel depths of the 100-year peak annual flow for existing and proposed conditions.

Table 2. Two Trout Creek top widths estimated by HEC-RAS.

Peak Annual

Flow Existing Average

Top Width (ft) Proposed Average Top

Width (ft) 2-Year 11.9 15.1

100-Year 15.5 18.7

Table 3. Two Trout Creek 100-year peak flow maximum, minimum and average channel depths estimated by HEC-RAS.

Statistic Existing 100-Year Channel Depth (ft)

Proposed 100-Year Channel Depth (ft)

Maximum 3.41 2.97 Minimum 1.11 1.66 Average 1.65 2.03

Results of the hydraulic model informed development of two preliminary road crossing options: a bridge and an Aquatic Organism Passage (AOP) concrete box culvert.

Design Criteria and Constraints

The emergency repair in 1999, moved the roadway alignment upstream of its original tangent. One benefit of replacing the crossing will be to restore the original tangent alignment and reduce the vertical roadway grade at the crossing. This will improve safety and the overall driving experience at the crossing location. While the new crossing is under construction, it will be necessary to provide temporary traffic control measures to keep the road open and limit public delays to no more than 30 minutes at a time.

Different repair options will have different temporary traffic control needs. Traffic control needs are based on the overall size of the potential replacement structure, construction staging opportunities, differences in required work zones and availability of material staging areas.

Depending on the repair option selected, it may be possible to utilize the existing emergency repair roadway for public traffic during the first stage of construction, before shifting traffic to a partially completed structure. This scenario is more likely possible for a box culvert than a bridge, due to a combination of smaller footprint and additional construction staging opportunities which allow easier use of a half-width structure. However, due to the close proximity of the emergency repair roadway to the repair crossing site, supplemental measures – such as temporary shoring - may be required to allow construction without impacting the ability to pass traffic on the existing roadway.

When considering a bridge replacement, it is very likely that a temporary on-site diversion road will need to be constructed, as the larger structural footprint and associated work zones would not allow the existing roadway to be safely used by the public. Prior to construction of the bridge girders and decking, riprap will be installed for protection of the approach embankments, abutments and as part of stream channel scour counter measures. The excavation required for installation of the riprap will extend into the footprint of the existing roadway preventing its use as a diversion road (Figure 6).

Additionally, the width of the proposed bridge will not allow for staged construction such that public traffic could safely pass on a half-width structure, as would be possible with a box culvert.

Figure 6. Excavation needed for the installation of the riprap extends into the footprint of the existing roadway.

In the case that a temporary diversion road must be constructed, the most likely location would be immediately north/north-west of the existing roadway, paralleling it as closely as possible. This temporary diversion could be one-lane, with alternating traffic flow controlled by flaggers or automated signals. As the area adjacent to the existing roadway is wooded, the construction of this

New bridge

Edge of existing roadway

Required excavation for riprap prior…