ak pfh 58(1)_FinalHydraulicReport.pdf

Prepared for:

WESTERN FEDERAL LANDS HIGHWAY DIVISION

610 East Fifth Street, Vancouver, WA 98661

FINAL HYDRAULIC DESIGN MEMORANDUM

SEGMENT 1

NECK LAKE ROAD, AK PFH 58(1)

IDIQ Contract DTFH7015D00007

Task Order 69056718F000007

March 2018

Prepared by:

ROBERT PECCIA &

ASSOCIATES

Helena, Montana

Final Hydraulic Design Memorandum March 2018 i

TABLE OF CONTENTS

1.0 Project Overview

2.0 Purpose

3.0 Agency Coordination and Guidance / GENERAL DESIGN METHODOLOGY

4.0 Hydrology

4.1 Lake Effects

4.2 Rainfall and Runoff

5.0 Culverts

5.1 General

5.1.1 Corrosion

5.1.2 Service Life

5.2 Primary Basin and Relief Culverts

5.3 Major Culverts

5.4 AOP Culverts

5.4.1 Site Specific AOP Culvert and Design Information

5.4.2 Stream Simulation Culvert Interior and Channel Design

5.4.3 AOP Culvert #1, STA. 32+18

5.4.4 AOP Culvert #2, STA. 56+21

5.4.5 AOP Culvert #3, STA. 64+34

5.4.6 AOP Culvert #4, STA. 78+82

5.4.7 AOP Culvert #5, STA 116+39

5.4.8 AOP Culvert #6, STA 131+22

5.4.9 AOP Culvert #7, STA 152+11

5.5 Causeway Culverts

6.0 Bridges

6.1 Drainage Basin Delineation

6.2 Bridge Drainage Basin Hydrologic Estimates

6.3 Bridge Hydraulics

6.4 Bridge BR-1Hydraulic Analysis

6.4.1 Existing Conditions and Characteristics

6.4.2 Existing Condition HEC-RAS Model and Calibration

6.4.3 Existing Bridge Hydraulics and Freeboard

6.4.4 Proposed Bridge HEC-RAS Model

6.4.5 Proposed Bridge Scour Analysis

6.4.6 Proposed Bridge Abutment Riprap Recommendations

7.0 Ditch Stabilization

8.0 Curb and Gutter

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Figures

Figure 1.1: Neck Lake Road Corridor Figure 1.2: LTF Intersection – Segment 1 & 2 Transition Figure 5.1: Existing AOP#1 outlet Figure 5.2: Existing AOP #1 inlet Figure 5.3: AOP#2 Bed Sample Figure 5.4: AOP#2. Existing Cascade and Channel Jog at Inlet Figure 5.5: AOP#3: Perched Outlet Figure 5.6: Existing culvert outlet to Neck Lake Figure 5.7: AOP#5 Bed Material Sample Figure 5.8: AOP#5, Channel Bend at Existing Road Figure 5.9: Existing Culvert Outlet to Lake Figure 5.10: Upstream Waterfall and Glaciomarine Figure 5.11: Existing Culvert Outlet to Neck Lake Figure 5.12: Existing Culvert Inlet and Upstream reach Figure 6.1: Downstream Face of Existing Bridge BR-1

Tables

Table 4.1: Neck Lake Water Surface Elevations Table 5.1: Basin Culvert Summary Table 5.2: Major Culvert Summary Table 5.3: AOP Culvert and Design Standard Summary Table 5.4: Causeway Culvert Summary Table 6.1: Existing Bridge Characteristics Table 6.2: Bridge Drainage Basin Hydrology Table 6.3: Existing and Proposed Bridge Hydraulic Analysis Summary Table 6.4: Proposed Bridge Scour Analysis Summary Table 8.1: Curb Flow Widths

Appendices

Appendix A: Drainage Basin Hydrology Appendix B: Corrosion Tests Appendix C: Basin Culvert Capacities Appendix D: AOP and Causeway Culvert Details Appendix E: Stream Simulation Details Appendix F: Stream Channel Details Appendix G: Low Flow Channel Design Appendix H: AOP Culvert Capacity Calculations Appendix I: AOP Bed Stability Calculations Appendix J: AOP #3 Modeling Calibration Appendix K: AOP #3 Manning's Sensitivity Appendix L: AOP #4 Culvert Design Appendix M: Bridge 1 Design Calculations Appendix N: Bridge 1 Scour Calculations Appendix O: Bridge 1 Riprap Calculations Appendix P: Ditch Riprap Stability Calculations

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ABBREVIATIONS/ACRONYMS

840 Uncataloged anandromous or resident fish streams

870 Cataloged anadromous fish stream

AASHTO American Association of State Highway and Transportation Officials

ADF&G Alaska Department of Fish and Game

ADOT&PF Alaska Department of Transportation and Public Facilities

ADT Average Daily Traffic

AOP Aquatic Organism Passage

ARD Acid Rock Drainage

BST Bituminous Surface Treatment cfs Cubic Feet per Second

EA Neck Lake and El Capitan Cave Road Environmental Assessment

FH Forest Highway

FHWA Federal Highway Administration

FLHD Federal Lands Highway Division

Golder Golder Associates

HEC Hydraulic Engineering Circulars

HEC-RAS Hydrologic Engineering Center's River Analysis System

HW/D Headwater to Diameter ratio

LiDAR Light Detection and Ranging

LTF Log Transfer Facility

MOA Memorandum of Agreement between ADF&G and ADOT&PF

MPH Miles Per Hour

NCHRP National Cooperative Highway Research Program

NEPA National Environmental Policy Act

NFSR National Forest Service Road

PDDM Project Development and Design Manual

PS&E Plans, Specifications, and Estimate

Q25 25-year design event

Q50 50-year design event

Q100 100-year design event

RPA Robert Peccia and Associates

SATP Southeast Alaska Transportation Plan

SCRs Special Contract Requirements

SH State Highway

SSD USFS Stream Simulation Design

SSRAA Southern Southeast Regional Aquaculture Association

TS&L Type, Size, and Location

USFS United States Forest Service

USGS United States Geological Survey

VLVLR Guidelines for Geometric Design of Very Low-Volume Local Roads (ADT ≤ 400), 2001

VPD Vehicles per Day

WFLHD Western Federal Lands Highway Division

WSE Water Surface Elevation

Final Hydraulic Design Memorandum – Segment 1 March 2018 1

1.0 PROJECT OVERVIEW

The Western Federal Lands Highway Division (WFLHD) of the Federal Highway Administration (FHWA), in cooperation with the U.S. Forest Service (USFS), is proposing to reconstruct and rehabilitate approximately 8.1 miles of Neck Lake Road on Prince of Wales Island Alaska. Robert Peccia and Associates (RPA) was selected in 2013, by FHWA, to assist in the development of this project. The existing Neck Lake Road system connects Forest Highway (FH) 43, also known as North Prince of Wales Island Road, to the community of Whale Pass. The route is a combination of existing United States Forest Service (USFS) gravel roads (National Forest Service Road (NFSR) 25, NFSR 30, and NFSR 3065) along the shorelines of Neck Lake and Whale Passage, as shown in Figure 1.1.

Figure 1.1: Neck Lake Road Corridor

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The Improvements for Neck Lake and El Capitan Cave Road Environmental Assessment (EA) was completed for a potential road corridor between Whale Pass and El Capitan Cave, including Neck Lake Road, by the USFS in September of 2016. The design and construction effort on Neck Lake Road will be completed in two segments, as described below:

Segment 1: The project route along NFSR 25 from FH 43 to the intersection of NFSR 25 and NFSR 30, otherwise known as the Log Transfer Facility (LTF) intersection.

Segment 2: The project route along NFSR 30 and NFSR 3065 from the LTF intersection to Whale Pass.

Figure 1.2: LTF Intersection – Segment 1 & 2 Transition

Only Segment 1 is discussed in this memorandum. Figure 1.2 shows an example section of roadway.

The existing roadway along Segment 1 is generally constrained by the shoreline of Neck Lake and adjacent rock outcrops. The existing gravel road width generally ranges between 18 and 22 feet. Isolated sections of single-lane roadway exist, notably at the existing 16-foot-wide bridge, described as bridge site BR-1 in this memorandum. A potential detour route via NFSR 27 is available for Segment 1 and is partially shown in Figure 1.2.

The first 3.6 miles of Segment 1 pass through USFS Tongass National Forest lands. The remaining portion passes through primarily Alaska State lands with a few private parcels intermixed. The existing right-of-way width is generally 100 feet on State lands within the Segment 1 corridor. A 300-foot wide corridor is proposed on USFS lands.

The Segment 1 project route contains two existing bridge structures and six causeway culvert locations.

The water surface elevation (WSE) of Neck Lake and the associated wave effects impact road features throughout. Archeologically sensitive areas have been identified within the project corridor. Seven fish-bearing streams require aquatic organism passage (AOP) considerations.

Field surveys completed jointly by the Alaska Department of Fish & Game (ADF&G) and US Forest Service (USFS) determined that there were seven streams with enough quality fish habitat upstream of proposed crossings to require AOP/ fish passage designs to current Forest Service stream simulation standards.

Two of these seven crossings are also included in the seven designated causeway connections. These two will be analyzed as AOP culverts, leaving five culverts to be designed as causeways.

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The geotechnical investigation for Segments 1 was completed in September 2016 and many geotechnical challenges have been identified, including the presence of acid rock drainage (ARD), deep lacustrine deposits, potential karst, and elevated marine beach deposits.

A project agreement between the partner agencies (WFLHD, Alaska Department of Transportation and Public Facilities [ADOT&PF], and USFS) was developed to capture the scope of work, delivery schedule, and respective roles and responsibilities. All three agencies, as well as the ADF&G, have contributed input to the design direction documented under this memorandum. ADOT&PF will assume operation and maintenance responsibility of Neck Lake Road once construction is completed.

2.0 PURPOSE

The intent of the project is to upgrade the existing Neck Lake Road system to a two-lane paved road consistent with the American Association of State Highway and Transportation Officials (AASHTO), FHWA, and ADOT&PF standards.

The purpose of this memorandum is to document hydrologic and hydraulic calculations and decisions in support of roadway and stream channel improvements on Segment 1 of Neck Lake Road. Included are general calculations for standard drainage culverts, as well as detailed site-specific design for seven AOP culverts, four causeway culverts, and two bridges, noted as bridge sites BR-1 and BR-2 in this memorandum.

3.0 AGENCY COORDINATION AND GUIDANCE / GENERAL

DESIGN METHODOLOGY

The four partner agencies supporting this project each have standards and guidance for hydraulic analysis and design, that while similar in most respects, differ in detail. Agency coordination completed to-date has chosen from among these standards to provide design direction.

WFLHD is the primary funding agency with overall responsibility for the project. In general, they use the FHWA Project Development and Design Manual (PDDM), Hydraulic Engineering Circulars (HEC), computer modeling, guidance and directives.

The USFS owns most of the land that Segment 1 passes through. They prepared the EA for the improvements to the Neck Lake and El Capitan Cave Roads. The USFS is the author of “Stream Simulation: An Ecological Approach to Providing Passage for Aquatic Organisms at Road Crossings”, a design guide for constructing road-stream crossings. They are also responsible for cataloging streams (anadromous or resident), identifying species (types and key development stages), and critical use times (development, travel, spawning).

Once the project is completed, ownership of the roadway will be transferred to the ADOT&PF for maintenance and upkeep. The State DOT has road design standards and the Alaska Highway Drainage Manual that set policy and procedures for roadway construction.

The ADF&G holds permitting authority over construction affecting fish-bearing waters in Alaska. They are the authority that identifies fish-bearing waters in Alaska, species of concern, “design fish” size, seasonal use, stream type (870 or 840), spawning sites, and high-value rearing sites.

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ADF&G and ADOT&PF have signed onto a Memorandum of Agreement (MOA) for the “Design, Permitting, and Construction of Culverts for Fish Passage” that agrees on standard procedures, design criteria, and guidelines to be followed when planning, designing, permitting, and constructing roadway crossings of fish-bearing waters in the State of Alaska. This MOA is the agreed upon, primary AOP design criteria for the Neck Lake Road reconstruction. It provides for 3 tiers of design effort and permit justification, from a simple Tier 1, to a computationally-founded complex Tier 3 design.

WFLHD has requested that the road profile be set relative to a 25-year Neck Lake water surface elevation with 2 feet of freeboard to protect the roadway from wave erosion. The USFS requested that the FHWA design for the road be upgraded from low to high standard. This increased the design storm for bridges from a 50-year to a 100-year event, and from a 25-year to a 50-year storm for culverts.

There was a request from WFLHD to document both standards, so that there is a record of how much or how little the design storm change impacted the ultimate hydraulic design of the culverts along Segment 1.

At AOP culvert sites, the stream bank full width geometry was the primary driver of the AOP culvert size selection. There was no size increase or associated additional cost for the upgrade in design storm at these locations.

The four existing causeway culverts along the project serve to equalize lake elevations as the roadway bisects portions of Neck Lake. These culverts were documented during a 2014 field review as functioning property and will be replaced “in kind” with minor variation due to site conditions. Again, there was no additional cost for the upgrade in design storm at causeway culvert locations.

While there could be project cost savings at many primary drainage and relief culvert locations by using the 25-year design event, these size variations are minor and the associated cost differences are nearly incidental to the project. The upgrade to Q50 flows did not result in adjustments to the road alignment, nor to an increase in material costs in the road prism at all primary and relief culvert locations.

4.0 HYDROLOGY

About 40% of the Neck Lake Road will be constructed adjacent to the shoreline of Neck Lake. When designing culverts, causeways, and bridges along this route, it is necessary to plan for both runoff into the lake and lake backwater effects on the drainage.

4.1 LAKE EFFECTS

A significant portion of the Segment 1 alignment follows the south shore of Neck Lake. The existing road grade is perched only slightly above the average water surface elevation and has been prone to flooding during large runoff events. Portions of both the existing and proposed roadway are exposed the erosive force of wave action.

A professional geomorphologist used survey data of various “high water markings”, correlation of a January 2014 flood event with surrounding rain gages, and an estimate of the storm’s exceedance probability to estimate the lake elevations corresponding to specific return intervals. His results are summarized in Table 4.1.

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Table 4.1: Neck Lake Water Surface Elevations

Design Storm Recurrence (yr)

Lake Elevation (feet MSL)

2 95.0 25 99.0 50 100.0 100 101.0

Additionally, he concluded that the January 2014 storm, which caused significant overtopping of the existing roadway, produced runoff corresponding to the 20-year storm.

There was general agreement by those attending the August 2015 field review that the lake level was at or near the seasonal low water elevation at that time. Calculations from on-site measurements and surveyed data place the ordinary low water surface elevation at 92.4’. This elevation was used as a starting point for low-water fish passage at causeway culverts discussed later in this memorandum.

When designing culverts with lake backwater effects, it was assumed the peak runoff through the culvert occurred more quickly than lake levels peaked. Calculations for a 50-year culvert capacity assumed a 25-year lake level as a constant tailwater.

4.2 RAINFALL AND RUNOFF

USGS Regional Regression Equations detailed in Scientific Investigations Report 2016-5024 were used to develop design flows for the project’s drainage basins. The required variables for the regression equations are drainage basin area and average annual precipitation.

Drainage basin areas were delineated using USGS Petersburg Quadrangle (A-4) 1:63360 series topographic map, and project survey data. Project drainage basins of all proposed major drainage structures (bridges and culverts with a diameter ≥ 48”) are shown in the drainage basin map included in Appendix A. Average annual rainfall was calculated as the area-weighted mean annual precipitation from the 1971-2000 Prism Precipitation Dataset over the project’s drainage basins and was determined to be 100 inches.

RPA’s surveyors collected numerous “high water marks” that were likely remnants of the January 2014 runoff. These near-Q25 marks in the stream channel geometry were used to calibrate the drainage basin’s hydrology model.

Table 4.2 contains a summary of the hydrologic analysis. Detailed hydrologic calculations for each drainage basin can be found in Appendix A.

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Table 4.2: Hydrology Summary

Basin Name Station of Crossing

Area (acre)

Area

(sq. mile)

Q2 (cfs)

Q5 (cfs)

Q10 (cfs)

Q25 (cfs)

Q50 (cfs)

Q100 (cfs)

Basin 2 10+68 12.26 0.019 3.8 7.2 10.0 14.1 17.4 21.3

AOP-1 32+14 22.70 0.035 6.4 11.8 16.2 22.5 27.6 33.4

Basin 4 39+80 6.45 0.010 2.2 4.3 6.1 8.7 10.8 13.3

Basin 5 46+82 7.92 0.012 2.7 5.1 7.2 10.2 12.6 15.4

AOP-2 56+14 78.40 0.123 18.1 31.6 42.3 57.3 69.3 82.7

AOP-3 64+33 37.86 0.059 9.9 17.7 24.1 33.1 40.3 48.5

Basin 8 66+75 8.91 0.014 2.9 5.6 7.8 11.1 13.8 16.8

AOP-4 78+82 60.25 0.094 14.6 25.6 34.5 47.0 56.9 68.2

Basin 10 84+32 6.38 0.010 2.2 4.3 6.1 8.6 10.7 13.2

Basin 11 91+18 6.57 0.010 2.3 4.4 6.2 8.8 11.0 13.5

Basin 12 95+31 2.90 0.005 1.2 2.3 3.3 4.8 6.0 7.4

Basin 13 100+36 3.94 0.006 1.5 2.9 4.2 6.0 7.5 9.3

Basin 14 105+06 15.49 0.024 4.7 8.7 12.0 16.9 20.8 25.2

Basin 15 107+58 1.52 0.002 0.7 1.4 2.0 2.9 3.7 4.6

Basin 16 111+01 1.04 0.002 0.5 1.0 1.5 2.2 2.8 3.5

Basin 17 112+20 19.11 0.030 5.6 10.3 14.2 19.8 24.3 29.4

AOP-5 115+95 87.27 0.136 19.8 34.4 46.0 62.2 75.0 89.4

Basin 19 120+55 16.47 0.026 4.9 9.1 12.6 17.7 21.7 26.4

AOP-6 130+83 34.97 0.055 9.2 16.6 22.6 31.2 38.0 45.8

Basin 21 140+38 9.91 0.015 3.2 6.1 8.5 12.0 14.9 18.2

Basin 22 150+01 43.47 0.068 11.1 19.8 26.8 36.7 44.7 53.7

AOP-7 151+51 75.85 0.119 17.6 30.8 41.2 55.9 67.6 80.7

Basin 24 162+67 1.13 0.002 0.5 1.1 1.6 2.3 3.0 3.7

Basin 27 192+02 5.68 0.009 2.0 3.9 5.5 7.9 9.8 12.1

Basin 28.1 204+54 29.41 0.046 8.0 14.5 19.8 27.3 33.4 40.3

Basin 28 207+62 47.42 0.074 11.9 21.2 28.7 39.2 47.7 57.2

Basin 29 211+13 11.36 0.018 3.6 6.8 9.5 13.3 16.5 20.1

Q ( ) = Estimated discharge based on ( ) flow event cfs = Cubic feet per second

5.0 CULVERTS

The collection of culverts proposed for Segment 1 of the Neck Lake Road reconstruction are grouped into four general classes for ease of discussion: Relief and primary basin culverts, major drainage culverts, AOP culverts, and causeway culverts. Relief culverts are 24-inch diameter roadway cross drains. Primary basin culverts are mainline crossings less than 48” in diameter. Major drainage culverts are crossings requiring a 48” or larger pipe. AOP pipes are larger culverts designed to provide adequate hydraulic conveyance and aquatic habitat connectivity. Causeway culvert connect bodies of water on each side of the road, and can have flow in either direction.

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All primary basin, major drainage and AOP culverts are hydraulically designed to convey the 50-year design flow with no roadway overtopping, provide opportunities for cost savings during competitive bidding, resist environmental hazards, and provide a reasonable service life. Relief culverts are placed at a regular spacing (less than 500 feet) between a drainage basin divide and the primary basin culvert. Major drainage culverts or AOP culverts are located at the bottom of applicable drainage basins. While relief culverts convey a portion of the applicable drainage basin flow across the roadway, the hydraulic capacity of the relief culverts is not included in the analysis of the primary basin, major drainage and AOP culverts.

5.1 GENERAL

Federal Lands Highway Division’s (FLHD) Project Development and Design Manual (PDDM) Section 7.3.6 directs the specification of alternate pipe materials. However, Southeast Alaska has environmental, practical, and economic issues that work against some pipe materials. Transportation of pipe materials can significantly increase concrete pipe costs. Abrasive bed loads tend to discourage metallic coatings on steel pipes. There are identified ARD locations on this project that could easily drop water pH values and rapidly corrode steel pipes. Existing galvanized steel pipes all show moderate rusting at common water levels. The combination of these factors has led ADOT&PF to request aluminum pipe for culvert diameters over 48-inch, and aluminum or plastic for smaller piping.

Some AOP culvert designs on this project require pipe baffles for sediment retention. These baffles can be made from either steel or aluminum. Construction of baffles and gussets from aluminum is the preferred method, allowing either welded or bolted installation into the aluminum pipe. Steel baffles and gusset assemblies will be required to be shop-constructed and hot-dipped galvanized prior to bolted assembly.

This uniform zinc coating should provide a reasonable resistance to corrosion for steel baffles. Additionally, steel baffle assemblies have been slightly over-sized to extend longevity via sacrificial materials.

The PDDM requires incorporating pipe anchors for corrugated metal pipes on a slope of 25% or greater (7.3.1.4.5). There are no culverts designed along the Segment 1 portion of this project that meet this grade criteria and require pipe anchors.

All project culverts are designed to convey the 50-year design storm congruent with the high-standard roadway classification. The capacity analysis for all primary basin culverts, major drainage culverts, and aquatic organism passage (AOP) culverts, was completed with the HY-8 Federal Highway culvert analysis program.

5.1.1 Corrosion

Aluminum alloy pipe materials are allowed when the soil pH is between 4 & 9 and the resistivity is greater than 500 Ω-cm. Tested soil samples have pH’s ranging from 5.9 to 7.8. Resistivity testing shows a single sample location at 2500 Ω-cm, a cluster in the 6600-9400 Ω-cm range, and another grouping over 12,000 Ω-cm. Both pH and resistivity testing are well within the acceptable range for aluminum pipe materials.

Complete test results from the Geotechnical Report are included in Appendix B.

Plastic pipe materials are well suited to a much wider range of pH and resistivity, but only have the necessary structural strength and common availability in 48-inch and smaller sizes.

5.1.2 Service Life

The project scope of work defines pipe service life to be 50 years (revised SOW, 4/22/15). Aluminum pipe is assumed to have a service life of 50 years in favorable applications. When exposed to moderate abrasion, the PDDM recommends increasing the standard thickness by one step.

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To bear the additional stresses of bolted baffle connections, the wall thickness of noted AOP culverts that are designed with baffles and infill material are increased at a second step beyond the standard thickness.

The assumed service life of plastic pipe designed in accordance with AASHTO Section 18 is 50 years.

5.2 PRIMARY BASIN AND RELIEF CULVERTS

Basin culverts are generally defined as the culvert with lowest invert elevation in the delineated drainage basin. Failure of a basin culvert could lead to localized basin or roadway overtopping. Relief culverts are additional culverts within a drainage basin intended to delay road over-topping when a basin culvert fails as well as alleviate accumulating flow along the roadside ditch. Failure of a relief pipe will not result in roadway overtopping.

The PDDM specifies a minimum mainline crossing size of 24-inch diameter and recommends that relief culverts be spaced at approximate 500-foot intervals between basin high and low points. Given the uncritical nature of relief pipes, these pipes were sized at 24-inch and no hydraulic analysis was performed.

The hydraulic analysis of each primary basin culvert was completed to ensure adequate conveyance of the Q50 flow under specified headwater criteria. As a factor of safety, the hydraulic conveyance of all applicable relief culverts was not included in this analysis. Per the PDDM design criteria, the headwater water surface elevation cannot rise into the roadway aggregate, overtop into an adjacent drainage basin, or surpass the allowable headwater depth to diameter ratio established for the pipe shape. Exceeding any of these headwater criteria resulted in upsizing the primary basin culvert.

At station 80+56 a relief culvert is designed as a 36-inch pipe culvert. While this culvert is not the primary basin culvert for Basin 9, it is sized to match the existing culvert at this location and maintain adequate hydraulic conveyance across the roadway within an extensive wetland area.

Culverts at the following locations were upsized to 30” for the stated reasons:

Sta. 10+68: meet headwater to diameter ration of 1.5 Sta. 66+75: avoid overtopping into adjacent drainage basin Sta. 105+06: meet headwater to diameter ratio of 1.5 and not overtop into adjacent drainage basin Sta. 120+55: meet headwater to diameter ratio of 1.5 and not overtop into adjacent drainage basin

Culverts at these locations were upsized to 36” (or equivalent 42” x 29”) for the stated reasons:

Sta. 80+56: match existing culvert at this location (relief pipe) Sta. 112+20: avoid overtopping into adjacent drainage basin Sta. 204+54: avoid overtopping into adjacent drainage basin Sta. 211+13: avoid overtopping into adjacent drainage basin

Basin culverts are summarized in Table 5.1. HY-8 capacity calculations are included in Appendix C.

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Table 5.1: Basin Culvert Summary

Basin Name Crossing Station

Existing Proposed Size (in)

Type Size (in)

Type

Basin 2 10+68 n/a n/a 30 CAP Basin 4 39+80 n/a n/a 24 CAP Basin 5 46+82 n/a n/a 24 CAP Basin 8 66+75 18 CMP 30 CAP Basin 9 80+56 36 CMP 36 CAP Basin 10 84+32 24 CMP 24 CAP Basin 11 91+18 n/a n/a 24 CAP Basin 12 95+31 18 CMP 24 CAP Basin 13 100+36 n/a n/a 24 CAP Basin 14 105+06 18 CMP 30 CAP Basin 15 107+58 18 CMP 24 CAP Basin 16 111+01 n/a n/a 24 CAP Basin 17 112+20 24 CMP 42 x 29 CAPA Basin 19 120+55 18 CMP 30 CAP Basin 21 140+38 18 CMP 24 CAP Basin 24 162+67 n/a n/a 24 CAP Basin 27 192+02 18 CMP 24 CAP

Basin 28.1 204+54 24 CMP 42 x 29 CAPA Basin 29 211+13 n/a n/a 42 x 29 CAPA

CAP = Corrugated Aluminum Pipe CAPA = Corrugated Aluminum Pipe Arch

5.3 MAJOR CULVERTS

Major culverts are mainline culverts that have been upsized to a 48” diameter or greater.

Culverts at the following locations were upsized to 54” for the stated reasons:

Sta. 207+62: meet a headwater to depth ratio of 0.8 to avoid debris clogging concerns at the crossing

Culverts at the following locations were upsized to 72” for the stated reasons:

Sta. 150+01: meet a headwater to depth ratio of 1.2, the minimum allowable for a pipe larger than 48”

Major culverts are summarized in Table 5.2. HY-8 capacity calculations can be found in Appendix C.

Table 5.2: Major Culvert Summary

Basin Name Crossing Station

Existing Proposed Size (in)

Type Size (in)

Type

Basin 22 150+01 24 CMP 72 CAP Basin 28 207+62 36 CMP 54 CAP

CAP = Corrugated Aluminum Pipe CAPA = Corrugated Aluminum Pipe Arch

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5.4 AOP CULVERTS

The design intentions for designated AOP culverts was to generally improve aquatic organism passage across the proposed roadway at seven identified sites. The USFS and ADF&G identified fish-bearing waters by species and the extent of the potential habitat along the Segment 1 corridor. Of primary concern were cut throat trout in Neck Lake and its contributing streams, and coho salmon in reaches below the Neck Lake cannery bulkhead. WFLHD agreed to use the ADF&G - ADOT&PF MOA design procedure for AOP culverts on this project.

Of the seven identified AOP culvert sites along Segment 1 of the project corridor, road alignment relocation removed one as an AOP designated culvert, two are designed under the Tier 1 flat channel exception (“No Slope”) design criteria, three are designed under the standard Tier 1 Stream Simulation criterial listed in the MOA and one is designed under Tier 3 due to steep slopes. A summary of the AOP culvert location and the applicable design standards is listed in Table 5.3.

Table 5.3: AOP Culvert and Design Standard Summary

AOP

Crossing

Crossing Station

Proposed Size (in)

Proposed Type

AOP Design Procedure

AOP #1 32+18 48 CAP n/a AOP #2 56+21 108 CAP Tier 1 AOP #3 64+34 60 CAP Tier 3 AOP #4 78+82 60 CAP Tier 1 - No Slope AOP #5 116+39 9’-3” x 6’-5” SAPPA Tier 1 AOP #6 131+22 72 CAP Tier 1 AOP #7 152+11 96 CAP Tier 1 - No Slope

The MOA’s AOP culvert design guidance and permitting process is presented in a tiered manner based on the proposed culvert slope and design complexity. The USFS Stream Simulation Design method is used to satisfy the standard Tier 1 criteria at three locations identified in Table 5.3 and applicable for AOP culvert design in narrow drainages with entrenched flood flows. This method attempts to replicate the natural stream channel conditions within the proposed culvert. Sediment transport, flood and debris conveyance, and fish passage are designed to function as they would in a natural channel. Tier 1 design is applicable for stream gradients up to 6%. The AOP culvert design guidelines for a Tier 1 Stream Simulation Design are listed below. If these guidelines are followed, it is assumed that fish passage is met.

1. Culverts are sized with a span or diameter equal to 90% of the OHW width at a minimum. The OHW width is identified as the bank full width in this memorandum.

2. The proposed culvert grade should approximate the natural channel slope and not deviate from that slope by more than 1%

3. Culvert burial depths should be at least 40% of the culvert diameter for round pipes and at least 20% of the rise for arch pipes.

4. Culvert infill material should remain dynamically stable at all flood discharges up to and including the 50-year flood. This may require the placement of oversized material that can resist critical shear forces or substrate retention baffles that allow bed load to continuously recruit.

5. Culvert baffles are generally necessary to retain culvert infill material in culverts designed with a slope greater than 3%.

6. If culvert baffles are used, they should have a minimum weir height equal to 0.5 times the culvert burial depth and a spacing equal to 60% of the culvert rise.

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7. Culvert outlet aprons should be investigated and designed to extend three culvert widths downstream if needed.

8. Culvert boundary roughness is a necessity for successful fish passage. Proposed metal culverts should be designed with large wall corrugations to ease fish passage along the boundary layer.

Tier 1 design also includes a “flat channel exception” that relaxes some of the requirements and refers the designer to the “No Slope” design criteria in Appendix B of the 2008 USFS Stream Simulation: An Ecological Approach to Providing Passage for Aquatic Organisms at Road-Stream Crossings report.

The “No Slope” design guidelines are:

1. The bed within the proposed culvert must be at least as wide as the natural channel bank full width.

2. The culvert is level and the downstream invert is countersunk below the channel bed by a minimum of 20% of the culvert rise.

3. The upstream invert is countersunk a maximum of 40% of the culvert rise.

For culverts with slopes greater than 10%, the MOA requires a Tier 3 “professionally-recognized hydraulic engineering method”. These steep culverts are required to have internal baffles to aid in embedment material retention and a stability analysis of the embedding aggregate.

Details of all proposed AOP culvert designs are included in Appendix D.

5.4.1 SITE SPECIFIC AOP CULVERT AND DESIGN INFORMATION

The following is a listing of site specific AOP culvert and design information relative to the seven identified AOP crossing listed in Table 5.3.

1) AOP #1: As originally proposed, this stream included approximately 92 feet of fish habitat upstream of the existing culvert. However, the proposed roadway is realigned south of the existing alignment and all 92 feet of identified fish habitat is now downstream of the proposed culvert location. Therefore, the AOP designation is removed from this culvert crossing and the culvert is designed as standard drainage culvert meeting the culvert size recommendations provided.

Additional channel realignment and channel stabilization provision downstream of the proposed culvert where the existing culvert is removed from the abandoned road alignment are also included.

Channel realignment is discussed in the following sections of this memorandum.

2) AOPs #4 and #7 are fish passage culvert that also function as causeway culverts. These culverts connect lacustrine water bodies and palustrine ponds. USFS Stream Simulation, Appendix B “No-slope” design criteria were used to complete a “Tier 1” permitting design. The “flat channel exception” was utilized for these two culverts to be set at 0.0% grade. While these two culverts are designed to be placed at an embedment depth of 20-40%, no infill is required per the following 9/15/15 e-mail from Mark Minnillo, the ADF&G Area Habitat Biologist.

“The channels are more [or] less palustrine channels with muck bottoms. The culverts will be installed more or less flat and will be submerged (completely backwatered). I see no need to put rock infill in these culverts.”

Additionally, as these culverts are designed with less than 3% slopes, they do not require internal baffles to retain naturally recruited sediments. Near the proposed location of AOP #7 there are currently two culverts, one set at a low-flow elevation, the other a perched relief structure. The lower pipe is nearly filled with mucky sediment, indicating that natural infill is occurring up to a certain elevation without baffles.

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3) AOP #’s 2, 5, and 6 are shallow-sloped culverts meeting the MOA Tier 1 Stream Simulation Design criteria. These culverts must meet the width, grade, substrate, and embedment criteria outlined in Tier 1 (MOA, Exhibit A, Section 4) and noted above. Additional channel realignment and channel stabilization provisions near two of these sites are also included and discussed in the following sections of this memorandum.

4) AOP #3 is a steep-sloped culvert requiring MOA Tier 3 professionally-recognized design criteria.

Tier 1 information is provided, as well as substrate sizing and HY-8 AOP analysis supporting fish passage.

5.4.2 STREAM SIMULATION CULVERT INTERIOR AND CHANNEL DESIGN

All seven of the identified AOP crossing sites are located along a 2.3 mile stretch of the Segment 1 alignment. Each of these streams traverse similar topography and landforms ultimately discharging to Neck Lake. While the individual stream sizes range from a 3-foot to 5-foot bottom width and stream gradients vary dramatically between sites, the general composition of the existing bed and bank materials is similar between each stream.

Existing streambed materials are generally composed of silts, gravels and small cobbles in a well graded mix with the largest stones approaching 4-inches in diameter. Channel bank materials include larger angular stones ranging from 8-inch to 2-feet in diameter. Mid-stream fish passage boulders existing randomly along each of the identified streams are similar to the bank stones and range from 8-inch to 2-feet in diameter.

The biggest challenges in Tier 1 Stream Simulation design include both matching the existing channel material composition and geometry within new culvert or reconstructed channel reaches and then ensuring that material is dynamically stable up to the 50-year flood event flows.

Each of the four proposed AOP culverts governed by the Tier 1 and Tier 3 design guidelines, as noted in Table 5.3, are embedded 40% of the proposed culvert rise. Within each of these culverts, bank stone cobbles are placed along the culvert sides and streambed material is placed along the culvert centerline.

The stream bed material extends to the embedment depth and creates a channel bottom width matching the associated stream channel bottom width identified in a reference reach. Bank stone cobbles are designed along the culvert sides and extend slightly above the embedment depth to create simulated and characteristic channel banks within each culvert. Additionally, fish passage boulders are evenly spaced on opposing sides along the culvert length. A detail of the proposed Simulated Stream Culvert Interior Treatment is included in Appendix E.

As the majority of the existing stream channels affected by new AOP culvert installation along this project have similar bed and bank material characteristics, one new streambed material gradation was selected for all applications. This gradation includes material characterized at 100% passing 3”, 75-55% passing 1.5”, 40-30% passing 0.5”, 15-5% through No.16, and 10-2% finer than No. 200 (approximately: D5 = 0.0165”, D16 = 0.1”, D50 = 3/4”, D84 = 2”, D95 = 3”). This gradation was provided by ADOT&PF (Bob Trousil e-mail of 8/17/15). Mr. Trousil indicated that this streambed gradation is similar to the existing streambed material at many fish bearing streams on Prince of Wales Island and the gradation has worked well on other AOP culvert installations associated with nearby projects.

The proposed bank stone cobbles, both within AOP culverts and along reconstructed channel reaches are sized to generally match the existing bank material along each stream. Similar to streambed material, one gradation of proposed bank stone cobbles was chosen to mimic the existing condition. This gradation is similar to Class 1 riprap and provides interlocking angular stones that add to both streambank stability and channel roughness.

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Fish passage boulders are sized to generally match the random stones existing within each of the identified streams. These stones are called out in the plans by size and number. (see Appendix E)

The stability analysis of the proposed culvert interior materials was initially completed with HY-8 AOP module. This module identifies the fish passage stones and bank stone cobbles as the “lower bed” and the stream bed material as the “upper bed.” Through the material analysis process, fish passage boulders are sized from the D95 gradation or erratics noted in the stream reach. The stream bed material and bank stone cobble mixture is based on the gradation from D85 and finer. However, the proposed gradations of streambed material, bank stone cobbles and fish passage boulders used on this project are composed of slightly smaller materials better matching the existing conditions. Therefore, the stability of the proposed material gradations within AOP culverts is primarily based on the additional stability provided by the full-depth baffles designed within each applicable culvert.

Three of the identified AOP sites require the realignment or reconstruction of the existing stream channel to recover fish habitat from the existing culvert site, facilitate the new road alignment or transition to a new AOP culvert. At these locations a new trapezoidal stream channel is deigned to mimic the existing stream geometry, grade and sinuosity. The alignment and grade of these channels was designed to match a reference reach along the respective existing stream. The typical section of these channels is designed to match the respective existing stream bottom width and bank slopes. At each location, 1-foot of stream bed material is designed along the channel bottom over the proposed width and 1:2 channel banks are designed with bank stone cobbles. Additional rock weirs, log weirs and stream mitigation root wads are also included at various locations to promote stream stability and fish habitat. Details of each proposed stream channel realignment or reconstruction are included in Appendix F.

For design and analysis purposes, a fish passage flow is calculated for each AOP culvert site. The MOA, Exhibit A, Section 3, defines the interim fish passage design flow for Southeast Alaska as 40% of the instantaneous 2-year flow in the associated drainage basin. Unfortunately, the drainage basins associated with the identified AOP stream crossings on this project are relatively small. The typical basin size is smaller than the smallest basin contributing to the USGS Regional Regression Equations (SIR 2016-5024) and the calculated 2-year flows are somewhat over-estimated. However, Exhibit A also states a need for a minimum water depth of 2.5 times the depth of the design fish’s caudal fin, while noting that shallower depth may be passable “if resting areas are available within the culvert barrel.” The general consensus of the people attending project field reviews was a need for 6-8 inches of water depth in each AOP culvert during low flow events to provide adequate fish passage.

To ensure a minimum 6-8-inch low flow depth in each proposed AOP culvert, an extreme low flow of 1 cfs was analyzed. Flow depths measured in culverts during the field reviews combined with culvert geometry and Manning’s equation allowed calculation of the typical low flow rates witnessed in August to be in the range of 1 cfs at various AOP stream locations. A 1 cfs flow at typical culvert slopes provides 8” of flow depth in a V channel approximately 8” wide (see Appendix G). With large culverts installed to contain simulated stream beds, the only viable method of forcing a low flow channel this small is to install culvert baffles to the full depth of embedment with a narrow channel cut for low flow. The taller baffle will eliminate interstitial flows, concentrate the flows into a periodically controlled weir, and force re-establishment of a low-flow channel after flood events. All AOP culverts designed with a slope greater than a 3% slope therefore include baffles to the full depth of embedment with an 8” x 8” V-shaped weir cut from the top line of the baffle. The V-shaped weir cut is designed at an alternating offset from culvert centerline between successive weirs to promote sinuosity in the low flow channel.

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Figure 5.2: Existing AOP #1 inlet.

Culvert baffles extending to the full embedment depth are evenly spaced longitudinally within each culvert at a distance equal to 60% of the culvert rise. These baffles are to stabilize bank stone cobbles and streambed material at flows up to the 50-year event. While fish will experience a more “man-made” environment inside the culvert than in the natural bed, the sharp-edged weir with fish passage boulders will produce a cascade-pool bed form with scour pools and resting eddies at regular intervals through the pipe.

The taller baffles will produce deeper pools and either retain both the streambed material and the bank stone cobbles from washing out during high flow events, or allow for their rapid re-establishment as storm waters reside. The Tongass National Forest’s target streambed drop between successive baffles is 3”.

Designs below verify drops under or near 3”. A detail of the proposed culvert baffles is included in Appendix E.

5.4.3 AOP CULVERT #1, STA. 32+18

AOP culvert #1 is located at Station 32+18 along the proposed project alignment. There is an existing 42’ x 24” CMP with some general rusting and impact damage at both ends under the existing roadway downstream. The stream banks are well vegetated. The stream slope is about 2% for 60’ upstream of the existing culvert, then has an 80’ reach at 5%, before steepening to a 20’ section at 17%. The channel is mildly incised and has a well-graded bed with 4”-minus sub-angular gravels. The bank full width is approximately seven feet.

During a 2013 field review no fish were trapped, but Forest Service records show 92’ of Dolly Varden habitat upstream of the existing culvert. A field visit by ADF&G and USFS personnel in September of 2015 confirmed potential upstream fish habitat prior to a steep mossy hillslope. This crossing was a late addition to fish passage design.

The proposed road centerline was relocated slightly over 110’ upstream from the existing road centerline.

While the proposed road uses a deeper fill section with a wider footprint, the alignment results in recovery of over 60’ of the potential fish habitat. Additionally, the project proposes to obliterate the existing road and replace the existing culvert with approximately 50’ of realigned channel.

Figure 5.1: Existing AOP#1 outlet

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The proposed channel includes a 4-foot bottom width and 1:2 side slopes with a longitudinal slope of 1.2%.

The streambed of the proposed channel includes 1-foot of streambed material and the banks are protected with bank stone cobbles. The geometry and sinuosity is based on a reference reach of similar slope 300’ downstream. The realigned channel includes two log weirs intended to provide sediment retention and force a low flow channel meander along the length. Strategically-placed root wads also protect the channel banks and develop quality habitat.

By relocating the road alignment, 108’ of habitat will be recovered or created. However, since none of the 92’ of identified fish habitat extends upstream of the proposed roadway, the new roadway culvert at this location is designed hydraulically with provisions for debris passage, but not for fish passage.

The proposed culvert is a 48-inch CAP, 76’ in length, set at 5.3% slope. It will not be embedded, nor provide other AOP design elements, since there is no fish habitat upstream of the relocated culvert. The hydraulic capacity of the proposed culvert is approximately four times the Q50 design flow before overtopping the roadway or local basin divide occurs. The headwater to diameter ratio (HW/D) is 0.6 and well below the

0.8 heavy debris threshold. Calculations are included in Appendix H.

Rather than attenuate the exit velocity of the proposed culvert with a riprap outlet apron, the culvert installation includes a downstream rock weir intended to stabilize a permanent scour pool. The pool will provide settling, aeration, and potential habitat.

5.4.4 AOP CULVERT #2, STA. 56+21

AOP culvert #2 is located at project Station 56+21. The existing stream crossing is located at Station 56+31 and includes a 39’-long 48” CMP. The existing culvert is on a level grade with some general rusting and impact damage at both ends. The existing stream banks are well vegetated and the channel bed is well-graded with 3”-minus angular gravels.

Upstream of the existing culvert, the existing stream bottom is approximately 4-feet wide and cascades over 2’-diameter boulders. The bank full width is approximately seven feet.

During a 2013 field review Dolly Varden and cut-throat trout were trapped and an upstream beaver dam was noted. There is no recorded extent of upstream fish habitat.

The proposed culvert at Station 56+21 is a 74-foot long, 108” CAP. The size of the proposed culvert was determined through coordination with WFLHD, RPA and the USFS prior to final culvert design. The proposed culvert is oriented generally in line with the upstream channel to allow debris passage. At this location, the proposed roadway fill slopes require that the new culvert inlet catch the existing stream thalweg approximately 24 feet upstream and at a higher elevation than the existing culvert inlet. From this location to the downstream channel, the proposed culvert is sloped at 4.3%. This slope is within 1% of the average 4.5% stream grade upstream of the proposed culvert.

Figure 5.3: AOP#2 Bed Sample.

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Per the Tier 1 Stream Simulation guidelines, the proposed culvert is embedded 40% (3.6 feet). At this embedment depth, the section width of the proposed culvert is approximate 8.8 feet and slightly wider than the identified 7’ OHW or bank full width of the stream. Culvert interior treatment in the form of streambed material, bank stone cobbles and fish passage boulders are designed within the culvert to generally match the geometry and composition of the existing stream channel bed and banks. This material is held in place by interior culvert baffles spaced at 60% of the culvert rise and extending to the full depth of the culvert embedment. These baffles include an 8-inch V notch, as previously noted, to provide a low flow channel and enhance fish passage.

The HY-8 analysis of the proposed culvert indicates that roadway or local basin divide overtopping occurs at a flow over 6 times the Q50 design flow. HW/D = 0.16 and well below the 0.8 heavy debris threshold.

A stability analysis of the simulated stream culvert interior material indicates that the proposed stream bed sediment will be stable as an “upper bed” and the lower bed will be stable if similar to Class 2 riprap.

However, this analysis does not include the proposed culvert baffles designed to retain and stabilize placed material inside the culvert. With the addition of full depth baffles, it is estimated that the proposed culvert interior treatment is stable at flows up to the 50-year design flow and the proposed AOP culvert is in compliance with all guidelines detailed under Tier 1 Stream Simulation. HY-8 culvert capacity calculations are included in Appendix H, and HY-8 streambed stability calculations are included in Appendix I.

To avoid the potential for debris blockage, the new culvert is generally aligned with the main channel upstream of the crossing. However, this alignment introduces a sharp bend (~39 degrees) in the stream channel at the proposed culvert outlet. Therefore, stream mitigation root wads are incorporated along the existing channel banks to stabilize the outside bank of the existing channel at the bend.

Figure 5.4: AOP#2. Existing Cascade and Channel Jog at Inlet.

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5.4.5 AOP CULVERT #3, STA. 64+34

AOP crossing #3 is located at project Station 64+34. The existing stream channel at this location has a bottom width of approximately 3 feet and a bank full width of approximately 5 feet. The alignment of the stream is nearly perpendicular to the roadway and the existing culvert is a 34.8’-long, 36” CMP sloped at

4.3 %. The existing culvert has a 2.6’ drop from the outlet to the existing streambed and upstream grades are in the 20% - 25% range, after the first 20’ at 30%. Downstream grades are 11 +/- 4%. The pipe has no signs of corrosion, but has minor damage at the outlet.

The existing…