lincol57860(1)_Drainage TM_FINAL.pdf

Date: September 6, 2024

To: Brandon Stokes, FHWA Project Manager

From: David Baker; Jacobs

CC: Brandon Stokes, FHWA Project Manager

Sara Folk, Jacobs Project Manager

Subject: Hawk Creek Road Improvements Project; FINAL Hydraulic Report Memorandum Supplement

PURPOSE

The purpose of this memorandum is to supplement and update the 2021 memorandum named above, which is a summary of roadside drainage and crossdrain design for the Hawk Creek Road Improvement Project (Project).

LOCATION

The Project is located along Hawk Creek Road in Section 30, Township 27 North, Range 36 East Willamette Meridian in Lincoln County, Washington. The Project is approximately 15 miles northwest of the town of Davenport (Attachment 1, Map 1). The project crosses from Lincoln County jurisdiction to the east to National Park Service land to the west. The study area includes the delineation of the basin area (Attachment 1, Map 2) contributing to the existing drainage features (2 Ea. 36-inch diameter CMP culverts) located on the east end of the project, within the Lincoln County Right-of-Way, as defined by FHWA (Attachment 1, Map 3).

EXISTING CONDITIONS

The project is within the Lake Roosevelt floodplain, as identified on FEMA maps for the area.

However, modifications to the existing ground will not affect flood elevations, as the water surface elevation of Lake Roosevelt and the surrounding floodplain is controlled by the Grand Coulee Dam. Hawk Creek is not a fish passage concern, as the Hawk Creek Falls is a natural fish barrier. Hawk Creek originally ran along the toe of the fill sections of the roadway, however when Lincoln County constructed the new concrete prestressed girder bridge on Miles-Creston Road in 2016, the adjacent landowner redirected Hawk Creek to the south. When this was accomplished, Hawk Creek become a non-hydraulic issue for this project.

Hawk Creek Road is currently a 20-foot to 21-foot-wide gravel roadway with no graded ditches on either side. Roadway profile grades exceed 11% in some segments within project limits.

Surface runoff along the north side of Hawk Creek Road is collected between the base of the adjacent hillside and the toe of the roadway fill slope. Surface runoff flowing toward the south side of the roadway is generally not captured by roadside ditches and becomes overland flow.

Hawk Creek Road Improvements September 2024

Jacobs Engineering Group Inc. Page 2

The primary existing drainage crossing under Hawk Creek Road within the project limits is a pair of twin 36” diameter CMP culverts at the east end of the project. During early field reviews, these culverts displayed no signs of overtopping the roadway at the crossing inlet, and the culverts appeared to be in fair condition. Both culverts showed signs of rust throughout each pipe but were still functional. The inlet end has a riprap headwall, and the outlet end has a concrete headwall. Photographs of the existing culverts can be seen in Attachment 2. The outlet drains into a wide, flat channel headed to the south and west toward Hawk Creek. It is anticipated that majority of the flow will spread to become overland flow and ultimately infiltrate into the ground prior to reaching Hawk Creek.

Throughout the project limits west of the primary crossdrain, localized low points trap stormwater runoff between the roadway and adjacent hillside. Runoff volume in the ponding areas appears to be small enough to not result in overtopping of Hawk Creek Road before infiltrating. However, installation of 24” CMP culverts at these locations eliminates any ponding concerns and protects the roadway from being undermined.

METHODS

The largest drainage subbasin within the project limits contributing to roadside ditches and/or small (24”) crossing culverts is 18.30 acres. The Rational Method was selected to evaluate peak flows for capacity calculations, due to the small size of the watersheds. The rational formula (Q = C*i*A) estimates peak flow, Q (cubic feet/second), based on a dimensionless runoff coefficient, C, the average rainfall intensity, i (inches/hour), and the surface area, A (acres).

The project area is characterized by some trees and underbrush within areas of minimal foliage coverage. Runoff coefficients were taken from the WSDOT Hydraulics Manual, based on prevailing ground cover conditions, soil type, and the average ground slope.

An average rainfall intensity was calculated using WSDOT Hydraulics Manual Equation 2-7 (i, in inches/hour = m / (Tc)n), assuming a 10-year storm frequency, the minimum 10-minute time of concentration/storm duration, and dimensionless rainfall coefficients (m and n) from the nearest metropolitan area in Spokane.

Drainage Basins were delineated using USGS Topographical Maps, WA_Olsen_Canyon_20200225_TM_geo.pdf (Attachment 1, Map 4).

The peak flow rate for the 25-year and 100-year storm events passing through the existing 36” diameter twin culverts was provided in the 11/15/2021 Hydraulic Report Memorandum to be 88 CFS and 163 CFS, respectively. During field visits, there was no evidence of overtopping or reason to believe these peak flow rates are insufficient. The replacement facility should perform hydraulically as well as, or better than, the existing facility.

Ditch capacities and pipe sizes for minor culvert crossings were checked using Bentley Flowmaster, which utilizes Manning’s equation to perform calculations. The capacity of the large

Jacobs Engineering Group Inc. Page 3 culvert crossing replacing the pair of 36-inch-diameter culverts was checked using FHWA’s HY-8 program, also utilizing Manning’s equation.

Riprap sizes in lined ditches and outlet pads were evaluated using WSDOT Hydraulics Manual Equation 6-1 (Vc = Ku * y1/6 * D1/3) to determine the critical velocity, Vc, above which bed material of size, D, will be transported; where Ku is a dimensionless coefficient, and y is the upstream flow depth. After calculating the flow velocities earlier, we ensured the critical velocity was not exceeded for the selected bedding material.

PROPOSED DRAINAGE FEATURES:

A pair of twin-36-inch Dia. CMP culverts, located near the east end of the Project is the only existing culvert crossing in the project area under Hawk Creek Rd. Calculating the end area of each pipe as A = (pi)r2 = 3.1416 x (1.5ft)2, yields 7.07 square feet of hydraulic opening per pipe, for a total of 14.14 square feet for the crossing.

Lincoln County initially requested a CMP arch pipe to replace the aging 36” CMP culverts, to minimize the excavation cost associated with the replacement. Per information provided by manufacturers, an equivalent standard arch pipe at full-flow conditions would measure 64” (W) by 43” (H). Since initial discussions with Lincoln County, the profile of the roadway has been raised and a circular CMP culvert of equivalent hydraulic opening end area, measuring 54” in diameter, can be accommodated with the same or less excavation than an arch pipe installation.

Based on this, the 54-inch-diameter circular CMP culvert with concrete head walls and Class IV Riprap at the inlet and outlet ends of the culvert is recommended.

Shallow ditches are recommended on the north side of Hawk Creek Road, at the base of the adjacent hillside, throughout most of the project limits to route roadway and hillside stormwater to crossdrains. In areas of steep slopes where flow velocities exceed critical velocities for soil erosion, ditches will be lined with Class I riprap to protect the roadway. Crossdrains are typically the minimum 24” diameter CMP culverts with flared end sections and Class I riprap pads at the outlets. An additional crossing culvert will be installed immediately upstream from the soil nail wall ending near roadway station 26+10 to minimize storm flows at the base of the wall.

Near roadway station 14+00, a low point in the proposed roadway profile and an existing rock outcrop will create two areas of ponding due to contributing roadside and hillside storm drainage. Additionally, a mapped wetland is located on the fill side of the roadway. At this location, a French Drain, supplemented with 6 inch perforated underdrains is proposed to drain the low area and provide stormwater treatment prior to discharge into the wetland.

DESIGN SERVICE LIFE:

Corrosion testing was performed on soil samples from boreholes near the proposed culvert locations. Soils were tested for resistivity, sulfate content, and chloride content, then classified as “aggressive” or “non-aggressive” based on the results. Steel gage thicknesses were selected using the Federal Lands Hydrology and Hydraulics December 2012 Manual Exhibit 7.3-B, Jacobs Engineering Group Inc. Page 4 assuming a minimum service life of 50 years, and based on soil resistivity test results.

Anticipated service life and recommended minimum steel gage for CMP walls are shown in Attachment 4.

RESULTS

The results of the 100-year storm event analysis for the 54” diameter CMP culvert are summarized below; the results show that replacing the twin 36” Dia. CMP Culverts with a single 54” diameter CMP culvert will meet applicable design standards. Calculations for smaller culvert crossings are provided in Attachment 3.

CULVERT

CULVERT

DESCRIPTION Culvert Data

HEADWATER CALCULATIONS Control Headwater Elevation

Outlet Velocity

INLET CONTROL OUTLET CONTROL

MATERIAL - SHAPE -

SIZE - ENTRANCE

Di am et er

, D (in

M an ni ng

's n

TO

TA

L

FL

O W

, Q (c fs

FL

O

W P

ER

B

AR

RE

L, Q

/N (c fs

HW

/D

H W

I

(in

T (in

El i

(ft

El hi

(ft

TW (in d c (in d r

D 2 h o (in k e H (ft

El o

(ft

EL

1 54” Dia. Circular Corrugated Steel 54

0.

1.

.4

.4

.5

.4

.8

.4

.4

0.

3.

.9

.5

.9

.2

RECOMMENDATIONS

The Hawk Creek Road Improvement Project will pave an existing gravel roadway with minimal existing drainage facilities. Based on hydraulic analysis, findings from field reviews and the Project geotechnical report, as well as proposed changes to the roadway geometry, there are multiple recommendations for drainage improvements on the Project:

While the existing roadside drainage needs are minimal, the additional impervious surface area will increase runoff volumes, requiring improved conveyance facilities. Establishing graded ditches, including riprap-lined ditches on steep slopes, will also serve to protect the roadway in severe storm events.

It is recommended to replace the twin-36” Dia. CMP Culverts with a 54” diameter CMP culvert.

Provide concrete headwalls and a Class IV Riprap pad at the inlet and outlet ends of the culvert to prevent erosion beneath the roadway. The analysis suggests that this culvert will accommodate the 100-year storm event and will prevent the flooding or washing out of the roadway, Hawk Creek Road. A 64” x 43” arch pipe was considered, but ultimately not recommended over the 54” circular CMP due to increased cost.

Finally, it is recommended to install 24” diameter CMP culvert crossings at localized low points, as well as a crossing immediately upstream from the soil nail wall to minimize the amount of runoff in the gutter in front of the wall. Fit all minor culvert crossings with pipe aprons or ditch inlets, as appropriate, at the inlet side of the pipe. Provide aprons and Class I riprap pads at all culvert outlets.

Attachments:

Attachment 1: Maps Attachment 2: Photographs Attachment 3: Calculation Summary Attachment 4: Culvert Service Life Analysis

Jacobs Engineering Group Inc.

ATTACHMENT 1

MAPS

Jacobs Engineering Group Inc.

Map 1. Vicinity Map

Map 2. Drainage Basin – Twin 36” CMP Culvert Pipes

Map 3. Hawk Creek Road Project – Project Limits

Map 4. USGS Topographical Map WA Olsen Canyon 20200225 TM geo.

Jacobs Engineering Group Inc.

ATTACHMENT 2

PHOTOGRAPHS

Downstream drainage channel for the twin – 36” Dia. CMP culvert pipes. Minimal water scour in the soils along with the vegetation depicts minimal water reaches this area. (Looking South).

Jacobs Engineering Group Inc.

Concrete headwall of the twin -36” Dia. CMP Culvert pipes which cross Hawk Creek Road on the East end of the project. (Looking North)

Jacobs Engineering Group Inc.

Concrete headwall of the twin -36” Dia. CMP Culvert pipes which cross Hawk Creek Road on the East end of the project. (Looking westerly)

Jacobs Engineering Group Inc.

Inlet condition of the twin -36” Dia. CMP Culvert pipes which cross Hawk Creek Road on the East end of the project. (Looking South)

Wooden weir structure at the inlet end of the twin-36” Dia. CMP Culverts.

Jacobs Engineering Group Inc.

Inlet condition of the channel entering into the twin-36” Dia. CMP Culverts. This appears to be a settling basin but doesn’t appear to have received water for a period. (Looking North)

Jacobs Engineering Group Inc.

ATTACHMENT 3

CALCULATION SUMMARY

Flow Calculations using Rational Method per Highway Hydrology Manual Using Intensity from WSDOT Hydraulics Manual (April 2024)

NHI-02-001

C Intensity, I Flow, Q in/h SF ACRE CFS

French Drains SF per ACRE 43560 Offsite 0.22 1.72 308250.56 7.08 2.67 Roadway 0.93 1.72 6060.61 0.14 0.22 Total 314311.17 7.22 2.9

Culvert, STA 19+40.00 Offsite 0.22 1.72 492577.75 11.31 4.27 Roadway 0.93 1.72 7224.72 0.17 0.26 Total 499802.47 11.47 4.5

Culvert, STA 25+96.18 Offsite 0.22 1.72 4788.90 0.11 0.04 Roadway 0.93 1.72 3063.61 0.07 0.11 Total 7852.51 0.18 0.2

Culvert, STA 33+90.92 Offsite 0.22 1.72 785871.67 18.04 6.82 Roadway 0.93 1.72 11347.61 0.26 0.42 Total 797219.28 18.30 7.2 From WSDOT Hydraulics Manual

Culvert, STA 41+69.96 25-year 88 100-year 163

Soil Nail Wall Offsite 0.22 1.72 90162.63 2.07 0.78 Roadway 0.93 1.72 0.00 0.00 0.00 Total 90162.63 2.07 0.8

Soil Nail Wall Gutter Offsite 0.22 1.72 90162.63 2.07 0.78 Roadway 0.93 1.72 7224.72 0.17 0.26

97387.35 2.24 1.0

*Assuming minimum time of concentration = 10 minutes *Rainfall intensity for 10 year recurrence

Drainage Area, A Conversions

Culvert Type Roughness Slope (%) Slope (ft/ft)

Flow Required

(CFS)

Min Diameter to Meet Capacity (in)

Maximum Discharge (CFS)

Pipe Length (ft)

Selected Pipe Size (in)

Notes

STA 19+40.00 Circular 0.028 5.92 0.0592 4.54 18 12.76 32 24 Checked in FlowMaster STA 26+10.00 Circular 0.028 2 0.0200 0.15 6 0.40 41 24 Checked in FlowMaster STA 33+90.92 Circular 0.028 2 0.0200 7.23 24 15.98 35 24 Checked in FlowMaster

STA 41+69.96 Elliptical or Arch 88 Checked in HY-8

*Minimum Pipe Size for culverts crossing roadways = 24" **Profiles for pipes with diameters < 48" are not included in plan set but are in a separate document

Slope (ft/ft)

Discharge (cfs)

Left Side Slope (H:1V)

Right Side Slope (H:1V)

Normal Depth (in)

Velocity (ft/s)

Critical Velocity, Check (ft/s)

Normal Depth (in)

Velocity (ft/s)

Critical Velocity, Check (ft/s)

Selected Riprap Class

Riprap Ditch w/Max Slope 0.1100 2.90 3.00 3.00 5.2 2.95 7.71 8.2 3.18 9.52 I Gutter Outfall 0.0220 1.05 - - 5.6 1.19 7.81 5.6 1.19 8.94 I

Culvert, STA 19+40.00 0.059 4.54 - - 7.70 6.27 8.23 7.70 6.27 9.43 I Culvert, STA 26+10.00 0.02 0.15 - - 2.70 1.78 6.91 2.70 1.78 7.91 I Culvert, STA 33+90.92 0.02 7.23 - - 11.80 4.70 8.84 11.80 4.70 10.12 I

25-yr 100-yr 25-yr 100-yr

CIRCULAR

US Channel 2.75 3.73 8.64 11.57 3.73 5.00 12.64 3.73 11.57 13.91 3.73 11.57 14.98 IV DS Channel (Tailwater Data) 2.02 2.70 6.27 7.35 2.70 7.35 11.98 2.70 7.35 13.18 2.70 7.35 14.20 IV DS Channel (Outlet Data) 1.88 2.68 13.96 16.01 2.68 16.01 11.96 2.68 16.01 13.16 2.68 16.01 14.18 -

4" Depth 0.81 1.53

Critical Velocity for Sand (D50=0.2mm) = Critical Velocity for Sand (D50=1.35mm) =

Selected Riprap Class

Depth (ft) Velocity

(ft/s)

Critical Velocity, Check (ft/s) Depth (ft)

Velocity (ft/s)

Critical Velocity, Check (ft/s)

Class II (9-inch Riprap)

Depth (ft) Velocity (ft/s) from HY-8 Class III (12-inch Riprap)

Depth (ft) Velocity

(ft/s)

Critical Velocity, Check (ft/s)

Class I (6-inch Riprap)

100-year Class II (9-inch Riprap) Class IV (15-inch Riprap)

Jacobs Engineering Group Inc.

ATTACHMENT 4

CULVERT SERVICE LIFE ANALYSIS

H ydrology and H ydraulics D ecem ber 2012

R oadw ay H ydraulics

7-53

Exhibit 7.3-B

ESTIM

A

TIN

G

STEEL PIPE SER

VIC

ES LIFE

FEDERAL LANDS HIGHWAY MODIFIED CALIFORNIA METHOD CHART FOR

ESTIMATING SERVICE LIFE OF PLAIN GALVANIZED STEEL CULVERTS

Service Life Estimation Chart for Average Service Life of Plain Galvanized Culverts

NOTES:

1. The curves in this Chart are based on the data in FHWA-FLP-91-006 which uses the factors in California Test 643, “Method for Estimating the Service Life of Steel Culverts”. These factors increased the estimated service life by 25% after first perforation.

2. The Chart has also been modified to reflect a minimum metal thickness of 0.064 inch or 16 gage [1.63 mm]

3. Under conditions with pH between 5 and 9, and above R ≥ 1500, the average service life determined for plain galvanized culverts should be multiplied by 2.0 for Aluminum coated steel, (Type 2).

THICKNESS FACTORS

0.168

4.27

2.6

Note: Multiply the average Service Life by the Thickness Factor

0.138

3.51

2.2

0.109

2.77

1.7

0.079

2.01

1.2

0.064

1.63

1.0

0.052

1.32

0.8

THICKNESS, inch

GAGE

THICKNESS, mm

FACTOR

dbaker3 Change Reccomended

STA 41+74

dbaker3 Change Reccomended Calculations Service Life = 2.39R0.41 Service Life = 2.39*64500.41 = 87 YR Min. steel gage = 16 dbaker3 Line dbaker3

Service Life based on observed resistivity of 6450 ohm-cm at boring SW-10

WA LINCOL 57860(1), Hawk Creek Road Improvements Geotechnical Report, GR 04-24

111954 April 30, 2024

Exhibit 5-1: Estimated Liquefaction-Induced Settlement

Exploration Exploration

Type Total Depth

(feet)1

Design As (g)

Liquefiable Layer Depths (ft) Settlement (in)

SW-12 Boring 26.5 0.14 12 - 16 1 – 1½

SW-108 Boring 26.5 0.14 13 - 15 < ½

SW-109 Boring 14.0 0.14 7 – 10 ¼ – ¾

NOTES:

These borings are less than 80 feet deep and therefore additional settlement my occur.

5.2 Corrosive Soil

To assist in estimating the corrosion potential at the site, samples of soil were tested for pH, resistivity, water soluble sulfates, and chlorides. The results are presented below in Exhibit 5-2.

Exhibit 5-2: Corrosion Testing Results

Boring Depth (feet) pH

Resistivity (ohm-cm)

Sulfate Content (ppm)

Chloride Content (ppm)

SW-01 8 -- 2,670 -- --

SW-10 6 -- 6,450 -- --

SW-103 60 8.7 2,220 < 10 < 10

SW-105 65 8.3 1,720 93 < 13

NOTES:

Water-soluble sulfate and chloride content values are shown as percent weight in dry soil.

ppm = parts per million, ohm-cm = ohm-centimeter

The Geotechnical Engineering Circular (GEC) No. 7, Soil Nail Walls – Reference Manual (USDOT, 2015) provides recommendations on classifying a soil as “aggressive” and “non-aggressive” when assessing ground corrosion potential. Exhibit 5-3 provides a summary of the recommended tests and the threshold limit for those tests. The ground is classified as aggressive if just one test meets the criteria.

Exhibit 5-3: Summary of Corrosion Tests and Associated Limits

Test Units Non-Aggressive Aggressive pH -- 5.5 < pH < 10 5.5 > pH > 10

Resistivity ohm-cm > 3,000 ≤ 3,000

Sulfates ppm < 200 ≥ 200

Chlorides ppm < 100 ≥ 200

NOTES:

ppm = parts per million, ohm-cm = ohm-centimeter

0 200 400

Approximate Scale In Feet

Hawk Creek Road Improvements Lincoln County, Washington

SITE AND EXPLORATION PLAN

FIG. 2

April 2024 111954-001

SHANNON & WILSON, INC.

Geotechnical and Environmental Consultants

00 13

+0

0 15

+00

20+00

21+00

22+00

23+00

24+00

25+00

27+00

28+00

29+

+00

00 37

00 38

SW-103

SW-105

SW-108

SW-109

SW-01 SW-02

SW-03

SW-04

SW-05

SW-06

SW-07

SW-08

SW-09

SW-10

SW-11

SW-12

SW-13

SW-14

Maxar, Microsoft, Google

N

LEGEND

&< 2024 Shannon & Wilson, Inc. Boring Designation and Approximate Location

2022 Shannon & Wilson, Inc. Boring Designation and Approximate Location

"*" 2021 Lincoln County Test Pit

Observed Bedrock Outcrop

Proposed Road Alignment

Lincoln County Test Pit, 2021 dbaker3 Change Reccomended dbaker3 Change Reccomended dbaker3 Change Reccomended

BORING LOCATION WITH CORROSION TESTING

dbaker3 Change Reccomended dbaker3 Change Reccomended dbaker3