Hanapepe_Final_Hydraulics_Report_(1).pdf

Final Hydraulics Report

Hanapepe Bridge Replacement, Kaumualii Highway, Route 50, District of Waimea, Island of Kauai, State of Hawaii

Prepared for Federal Highway Administration

Central Federal Lands Highway Division 12300 West Dakota Avenue

Lakewood, CO 80228

October 2016

9191 South Jamaica Street Englewood, CO 80112 5946

III

Contents Section Page

1 Introduction ................................................................................................................................ 1‐1

1.1 General ................................................................................................................................... 1‐1

1.2 Project Location and Identification ........................................................................................ 1‐1

2 Existing Site Conditions ............................................................................................................... 2‐1

2.1 General ................................................................................................................................... 2‐1

2.2 Bridge ..................................................................................................................................... 2‐1

2.3 Hanapepe River ...................................................................................................................... 2‐1

2.4 Culverts .................................................................................................................................. 2‐1

2.5 Surface Drainage Collection System ...................................................................................... 2‐1

2.6 Floodplain .............................................................................................................................. 2‐1

2.7 Wetlands/Waters of the United States ................................................................................. 2‐2

2.8 Water Quality ......................................................................................................................... 2‐2

3 Design Criteria and Methodology ................................................................................................ 3‐1

3.1 Applicable Drainage Criteria .................................................................................................. 3‐1

3.2 General Design Criteria .......................................................................................................... 3‐1

3.3 Hydrologic Design .................................................................................................................. 3‐1

3.4 Hydraulic Analysis .................................................................................................................. 3‐2

3.5 Criteria for Temporary Drainage Facilities ............................................................................. 3‐3

3.6 Other Criteria and Methodology ........................................................................................... 3‐3

3.7 Fish Passage ........................................................................................................................... 3‐4

4 Hydrologic and Hydraulic Analyses .............................................................................................. 4‐1

4.1 Hydrologic Analysis ................................................................................................................ 4‐1

4.1.1 General...................................................................................................................... 4‐1

4.1.2 FEMA Hydrology ....................................................................................................... 4‐1

4.1.3 USACE 2010 Study .................................................................................................... 4‐1

4.1.4 Rational Method for surface drainage ...................................................................... 4‐1

4.1.5 Precipitation Data ..................................................................................................... 4‐2

4.2 Hydraulic Analysis .................................................................................................................. 4‐2

4.2.1 Existing Bridge ........................................................................................................... 4‐2

4.2.2 Proposed Bridge ........................................................................................................ 4‐2

4.2.3 Surface Drainage Collection System ......................................................................... 4‐4

4.2.4 Bridge Scour .............................................................................................................. 4‐4

5 Summary .................................................................................................................................... 5‐1

6 References .................................................................................................................................. 6‐1

Appendices

A Hydrology B Hydraulics C Scour Analysis D Photographs E HDS Addendum F Certification Forms

CONTENTS

IV

Tables

4‐1 Hydrologic Flows .................................................................................................................................. 4‐1 4‐2 Surface Drainage Flows ........................................................................................................................ 4‐2 4‐3 Sediment Regime Parameters – 200 Year Event ................................................................................. 4‐5 4‐4 Sediment Regime Parameters – 500 Year Event ................................................................................. 4‐5 4‐5 Sediment Regime Parameters – Incipient Overtopping and Pressure Flood ...................................... 4‐6 4‐6 Vertical Contraction Scour Parameters – 200 Year Event ................................................................... 4‐6 4‐7 Vertical Contraction Scour Parameters – 500 Year Event ................................................................... 4‐6 4‐8 Vertical Contraction Scour Parameters – Incipient Overtopping and Pressure Flood ........................ 4‐6 4‐9 Pier Scour Parameters – 200 Year Event ............................................................................................. 4‐7 4‐10 Pier Scour Parameters – 500 Year Event ............................................................................................. 4‐7 4‐11 Pier Scour Parameters – Incipient Overtopping and Pressure Flood................................................... 4‐7 4‐12 Summary of Hanapepe Stream Scour Depth and Elevation Results – 200 Year Event ........................ 4‐8 4‐13 Summary of Hanapepe Stream Scour Depth and Elevation Results – 500 Year Event ........................ 4‐8 4‐14 Summary of Hanapepe Stream Scour Depth and Elevation Results – Incipient Overtopping and Pressure Flood ..................................................................................................................................... 4‐9

Figures

1‐1 Vicinity Map (Google earth) ................................................................................................................. 1‐1 2‐1 Waters of the United States Map ........................................................................................................ 2‐3 4‐1 Hanapepe River Bridge 100‐year Water Surface Profiles .................................................................... 4‐4 4‐2 Scour Depth Profile from Vertical Contraction Scour Method – 200 Year Event ................................ 4‐9 4‐3 Scour Depth Profile from Vertical Contraction Scour Method – 500 Year Event ................................ 4‐9 4‐4 Scour Depth Profile from Vertical Contraction Scour Method – Incipient Overtopping and Pressure Flood ............................................................................................................................................... ...4‐10

SECTION 1

1-1

Introduction

1.1 General

Central Federal Lands Highway Division (CFLHD) is working with the Hawaii Department of Transportation (HDOT) to provide bridge replacements for multiple bridges throughout the Hawaiian Islands. This report presents the results of a site reconnaissance and final drainage analyses performed at the Hanapepe Bridge site on the southern side of the Kauai Island in the state of Hawaii. The report includes a recommendation for the replacement of the existing deficient bridge.

1.2 Project Location and Identification

The Hanapepe Bridge spans the Hanapepe River along the Kaumualii Highway/ Route 50 on the Island of Kauai in the state of Hawaii. The bridge is approximately 0.4 mile north from Hanapepe Bay. There is also an existing County Bridge on Hana Road north of the project area. Based on the North American Datum of 1983 (NAD83), Hanapepe Bridge is located at 21°54'31.77"N latitude and 159°35'27.95"W longitude. See Figure 1‐1 for Vicinity Map (Reference 1).

FIGURE 1-1

Vicinity Map (Google earth)

SECTION 2

2-1

Existing Site Conditions

2.1 General

A site investigation of the Hanapepe Bridge was conducted in January and June, 2014 by CH2M, CFLHD, and ParEn Inc. The bridge is located on a two‐lane asphalt paved road with 12‐foot lanes, 8‐foot shoulders, and two 5‐foot sidewalks. The roadway is maintained by HDOT and is located in the HDOT right‐of‐way (ROW).

The roadway is generally crowned and runoff sheet flows off of the pavement. The project site area is mostly residential with some commercial.

2.2 Bridge

The existing bridge was built in 1938. It is approximately 275 feet long and consists of three arched spans supported by concrete piers. It is supported at each end by vertical‐walled concrete abutments. The bridge crosses the river at a skew angle of approximately 45 degrees. The existing bridge is inadequate to convey the 100‐year design flow and the roadway is frequently overtopped. The capacity of the existing bridge is controlled by the downstream channel geometry.

See Appendix D for existing bridge photos.

2.3 Hanapepe River

The Hanapepe River is perennial and drains an area of approximately 26.5 square miles into Hanapepe Bay.

It is lined with levees on both banks upstream of the county‐owned bridge on Hana Road. A levee exists on the east bank between the county‐owned Hana Road Bridge and the Kaumualii Highway Bridge, but there are no levees along the west bank of the river in this area or downstream of the bridge. This levee is made up of an earthern and riprap berm and is 12 feet high with a 3‐foot high concrete wall. The levee and wall were built as part of the Hanapepe River Flood Control Project which was authorized by the 1944 Flood Act.

A 2010 USACE study determined that the levees could not be certified through FEMA due to not meeting the freeboard requirement for the 100‐year flood. Riprap lines the channel upstream and and partially downstream of the bridge. The channel is fairly uniform in cross section, with the abutments of the existing bridges encroaching into the channel.

2.4 Culverts

There are no culverts within the project limits.

2.5 Surface Drainage Collection System

For existing conditions, runoff on the bridge deck is conveyed along curbs on the edge of the bridge to scuppers, where the flow drops to the channel and the ground below the bridge. Runoff from the approach road drains overland to roadside ditches that drain to the channel.

2.6 Floodplain

The Hanapepe Bridge is located within a Zone AE FEMA‐regulated floodway of the Special Flood Hazard Area. Refer to Community Panel No. 1500020287F, dated November 26, 2010. A FEMA “No Rise” analysis and certification will be required in accordance with the County of Kauai flood hazard regulations. Hanapepe River Bridge is not located within a special flood hazard area Zone VE. Therefore, the bridge is not required to be designed for a coastal flood event, including storm surge, storm waves, tsunami and hurricane generated waves.

2 EXISTING SITE CONDITIONS

2-2

2.7 Wetlands/Waters of the United States

According to the determination and delineation of wetlands and other waters for the Hanapepe River bridge project report (Reference 2), “The stream was noted to be tidal during the survey, connecting to the Pacific Ocean”. The report states that because the project involves non‐fill discharging activities over Waters of the United States, a Section 10 permit will likely be required. The report further states that if the proposed project intends to place dredged or fill material within the delineated feature (e.g., bridge foundations or pillars), it could be subject to either a Section 10 or Section 404 Nationwide Permit (NWP). These conclusions are subject to confirmation by the USACE Honolulu District.

See Figure 2‐1 for the Waters of the Unites States Map in the project area.

2.8 Water Quality

No permanent storm water quality facilities are required for this site. Appropriate temporary erosion and sediment control BMPs will be required during construction.

2 EXISTING SITE CONDITIONS

TBG091114133012DEN 2-3

COPYRIGHT 2014 BY CH2M HILL ENTITY COMPANY CONFIDENTIAL

FIGURE 2-1

Waters of the United States Map

SECTION 3

3-1

Design Criteria and Methodology

3.1 Applicable Drainage Criteria

Criteria and methods will be consistent with the HDOT Highways Division “Design Criteria for Highway Drainage”, dated October 2010, as amended. For criteria and guidance not included in the HDOT manual, the guidance in the Federal Lands’ Project Development and Design Manual (PDDM) Chapter 7 (Reference 3) will be followed. The following sections are excerpts from the HDOT Manual, using only information that is applicable to the Hanapepe Bridge replacement project. The last section, Other Criteria and Methodology, outlines applicable guidelines and criteria not found in the HDOT manual.

3.2 General Design Criteria

The following are general guidelines and policies for highway design projects.

Capacity of proposed facilities shall not be less than the capacity of the existing facilities.

The proposed design shall take into consideration the accessibility of maintenance personnel to inspect and clean the facilities.

Utilities and conduits shall not be installed inside of the proposed drainage facilities.

3.3 Hydrologic Design

Hanapepe Bridge is located along Kaumualii Highway (Route 50). Kaumualii Highway is categorized as an Urban Minor Arterial. As such, the design recurrence interval selected in the analysis of existing and proposed drainage facilities shall be in accordance with the following:

RECURRENCE INTERVALS (yrs)

Functional Classification

Bridge/Culvert Crossing

Roadway (at grade)

Roadway (sump)

Arterial 100** 25 25

** 100‐year interval for sites covered under the Flood Insurance Rate Map (FIRM). The Design Engineer shall comply with the National Flood Insurance Program’s regulations and requirements.

The project site is located within a Federal Emergency Management Agency Zone AE floodway. Therefore, the design of the replacement bridge is required to comply with the National Flood Insurance Program’s regulations and requirements for Zone AE improvements.

The bridge shall be analyzed for the 100‐year storm event.

Ditches and channels designed to intercept and divert runoff from off‐site shall be based on a recurrence interval used for roadway crossings.

For recurrence intervals used to determine scour potential at bridges, refer to applicable FHWA Hydraulic Engineering Circulars and HDOT Highway Division manual, “Design Criteria for Highway Drainage” (Reference 4) and the HDS addendum dated March 20, 2014.

Point rainfall values shall be interpolated from the National Oceanic and Atmospheric Administration’s (NOAA) Precipitation Frequency Data Server website:

http://hdsc.nws.noaa.gov/hdsc/pfds/pfds_map_hi.html .

3 DESIGN CRITERIA AND METHODOLOGY

3-2

The following hydrologic methods and sources were selected to determine peak discharge for this project.

Refer to the Hanapepe Hydraulics Recommendations Report (Reference 5) for a description of other hydrologic methods analyzed.

Rational Method (as needed for roadway runoff analysis) – The Rational Method shall be used to estimate peak flow rates for drainage areas up to 200 acres. This method is applicable at small culvert crossings, and can be exclusively used for on‐site roadway drainage. The minimum time of concentration shall be 10 minutes.

FEMA Hydrology ‐ Published FEMA hydrology for “No‐Rise” scenario (Reference 6).

USACE 2010 Study ‐ Hydrology used in “Hydrologic and Hydraulic Evaluation for levee certification, Hanapepe River, Island of Kauai, Hawaii” by the Department of the Army, U.S. Army Corps of Engineers, Honolulu District, Fort Shafter, Hawaii, 17 March 2010, for scour analysis (Reference 7).

The 5‐year peak discharge found in the USACE study will be included in this hydraulics report for consideration by the Contractor during their design of temporary drainage facilities. The published 100‐, 200‐ and 500‐year peak discharge rates will also be included in this hydraulics report for the hydraulic and scour analyses and designs.

3.4 Hydraulic Analysis

Bridge Crossings

Bridges shall be designed with a minimum freeboard of two feet for the design storm. Freeboard shall be defined as the vertical distance between the approach design water surface elevation and the low chord of the bridge. (A variance or design exception may be required due to the vertical profile of the roadway and the surrounding topography).

Bridge abutment face shall be set back from the main stream channel section to minimize potential abutment scour. Design smooth transition from the abutment to the upstream channel embankment.

Bridges scour shall be designed for the 200‐year recurrence interval.

The minimum cross‐slope of the bridge deck shall be 1.5%.

The minimum longitudinal slope along the bridge deck shall be 0.5%. Longitudinal slopes less than the minimum may be accepted in areas restricted by physical parameters.

Runoff discharge directly into the stream channel shall be minimized.

Attention is directed to Appendix C on memorandum HWY‐DH 2.2443, “Invert Lining at Highway Bridges,” dated 6/26/09. The memorandum describes lining of bridge invert as a possible scour protection measure.

Water surface elevations and peak flow rates for the 50‐ and 100‐year storm events shall be shown in the Contract Plans.

Roadway Drainage

Inlet Types

Inlet types may include catch basins, grated drop inlet, or a combination of both. Inlet details shown in the HDOT Standard Plans shall be used in the design. If necessary, modifications can be made to the inlets in the HDOTStandard Plans to accommodate additional runoff capacity or to avoid conflicts with other utilities and obstructions.

Slotted drains are not allowed unless approved by the State Hydraulic Design Engineer.

3-3

Grated inlets are the preferred inlet type for roadways with curb and gutter sections. Catch basins or combination‐type inlets shall be considered along flat continuous slopes, sag points, and areas that may accumulate debris.

Pedestrian‐safe grates shall be installed where applicable. The grate details (Type A‐9P, 61614P, etc) shown in the HDOT Standard Plans are designed to address both bicycle and pedestrian safety.

Inlet Locations

Inlets located on continuous slope shall be designed for a minimum of 70% catch and 30% by‐pass. The width of flow on the pavement surface shall not exceed 1/3 the width of the travel lane measured from the edge of pavement adjacent to the gutter or shoulder. For the purposes of this document, the associated ramps and auxiliary lanes are considered travel lanes.

Inlets located immediately upstream of bridge approaches and roadway intersections shall be designed for 100% interception with no by‐pass flow.

Inlets located at the low or sag points shall be designed for no encroachment on the travel way. Flanker inlets shall be designed on each side of the low point inlet structure.

Regardless of hydrologic requirements, inlets shall be installed at the following locations:

o Curb returns at the upstream side of intersections o Immediately upstream of bridge approaches, median breaks, entrance and exit off‐ramps, bus turnouts.

o Upstream of cross slope reversals

Spacing of inlet structures shall be based on hydraulic requirements, economics, and engineering judgment.

Drainage Pipes

Minimum pipe size, slope, cover, and clearances from other utilities and obstructions for culverts shall apply to drainage pipes.

Pipe material shall be consistent throughout a drainage system. A drainage system is considered to be all pipe segments leading from inlet structures to the outlet structure.

Roadside Gutters and Ditches

Maximum cross‐slope within the highway clear zone shall be 6:1. Preferred cross‐slope within the clear zone is 12:1.

The backslope of V‐shaped gutters in cut sections shall be no greater than the slope of the cut‐section.

3.5 Criteria for Temporary Drainage Facilities

The Contractor shall provide the drainage design of temporary construction‐related drainage facilities, including roadway detours. Design, layout and construction of the detour road, including erosion and sediment control BMPs, shall be performed by the Contractor. HDOT criteria states, “The recurrence interval for detour road crossings shall be equivalent to a five year storm event.” See Appendix B section of HDOT’s Design Criteria for Highway Drainage Manual for further guidelines for the design of temporary drainage facilities. Temporary channel diversions not associated with the roadway diversion shall be designed to convey, at a minimum, the five‐year storm.

3.6 Other Criteria and Methodology

Bridge deck drainage design shall follow the guidance of HEC‐21 Design of Bridge Deck Drainage

(Reference 8).

Section 7.3.3.5 Bridge Deck Design Guidance of the PDDM shall be considered in the bridge design.

Section 7.4.2.4.4 Bridge Scour of the PDDM shall be considered when designing for debris at piers.

3-4

Section 7.4.3.4.1 Capacity Design of the PDDM shall be considered for freeboard when the potential for woody debris is significant.

The maximum recommended drainage basin area for use with TR‐55 is 25 square miles.

A FEMA “No Rise” Certification will be required to comply with the County of Kauai flood hazard requirements.

In addition to the above criteria, applicable sections of the HDS Addendum to Design Flood Criteria updated April 16, 2015 shall apply to this project. See HDS Addendum on Appendix E.

3.7 Fish Passage

There are no requirements for fish passage design for this project. Any encroachment into the Hanapepe River for the construction of proposed Hanapepe Bridge, temporary roadway diversion bridge and bank stabilization improvements will be on a temporary basis and the channel profile below the normal flow of the river will be restored to its original geometry.

SECTION 4

4-1

Hydrologic and Hydraulic Analyses

4.1 Hydrologic Analysis

4.1.1 General

Multiple methods were employed to analyze the hydrology for the Hanapepe Bridge drainage basin including USGS StreamStats, USGS Regional Regression Equations, published FEMA data, and published USACE data. The drainage area of 26.5 square miles exceeded the recommended 25 square‐mile limit used by TR‐55 (Reference 9), therefore, TR‐55 was not used for comparison. Details of each method are described in the Hydraulics Recommendation Report for the Hanapepe Bridge Replacement by CH2M dated March 2015. Descriptions of the selected hydrologic methods are included below.

4.1.2 FEMA Hydrology

The FEMA Flood Insurance Study (FIS) documented the 100‐year runoff for the Hanapepe River near the bridge to be 38,000 cfs. This value will be used in the hydraulic analysis to confirm that there is no rise in the 100‐year water surface elevation in the proposed condition.

4.1.3 USACE 2010 Study

The selection of a “best” estimate was done by USACE by comparing the various derived discharge‐ frequency curves graphically and by the accuracy or uncertainty of each method. The methods compared were Frequency analysis of gage data, HEC‐HMS model, FEMA Regional Regression Equations, and Kauai Drainage Standards (Plate 6). Refer to the 2010 report “Hydrologic and Hydraulic Evaluation for levee certification, Hanapepe River, Island of Kauai, Hawaii” for detailed information on each method analyzed. As this study compares favorably with the hydrology in the FEMA FIS, the hydrologic results of the USACE study will be used for the proposed bridge scour analysis.

Below is a summary table comparing the results of each method described above.

TABLE 4-1

Hydrologic Flows

Flow Results (cfs) at Hanapepe Bridge

Hydrologic Method

Storm Frequencies (based upon the drainage area of approximately 26.5 mi²)

Comments Q(2) Q(5) Q(10) Q(25) Q(50) Q(100) Q(200) Q(500)

FEMA FIS 21,000 32,000 38,000 52,000

Selected results for no‐rise design

USACE 2010

Study

9,830 16,800 21,900 33,700 38,900 44,200 51,300 Selected results for scour design.

See Appendix A for excerpts from FEMA FIS and USACE 2010 study report.

4.1.4 Rational Method for Surface Drainage

The Rational Method was used to calculate the stormwater runoff tributary to the proposed bridge inlets.

The rational formula is: Q = CIA

Where:

Q = maximum rate of runoff in cubic feet per second

4 HYDROLOGIC AND HYDRAULIC ANALYSES

4-2

C = runoff coefficient I =the average intensity of rainfall in inches per hour for a duration equal to the time of concentration.

A = basin area in acres

The 25‐year frequency was used for the design of the bridge deck drainage system for major collector and arterials roadways per HDOT criteria. Table 4‐2 shows the 25‐year peak discharges at the four proposed inlet locations, using a 10 minute time of concentration.

TABLE 4-2

Surface Drainage Flows

Bridge inlets Q25 (cfs)

Northeast Bridge inlet 0.64

Southeast Bridge inlet 0.53

Northwest Bridge inlet 0.55

Southwest Bridge inlet 0.64

See Appendix A for the runoff and Appendix B for the spread calculation at the proposed inlets. The calculated spread at each of the four proposed inlets satisfies the HDOT criteria for the 25‐year event and falls within the proposed 8 feet shoulder.

4.1.5 Precipitation Data

Precipitation values for the 2‐year through 500‐year storms, for durations for 5‐minutes through 24 hours, were obtained from the NOAA Atlas 14 website for Hawaii (Reference 10). See Appendix A for rainfall data.

4.2 Hydraulic Analysis

4.2.1 Existing Bridge

The existing bridge is approximately 275 feet long with three arched spans and top‐of‐arch‐to‐invert clearance ranging from approximately 11’‐13’. Two of the piers are located in the active waterway. The 100‐ year flow overtops the roadway at the structure. The existing bridge experiences pressure flow during the 100‐year flood. See Appendix B for the HEC‐RAS model output for existing bridge conditions.

4.2.2 Proposed Bridge

The existing bridge will be replaced with a new bridge with a length of 307.5 feet and a width of 52.33 feet.

The bridge width includes a 5‐foot sidewalk and a 3’‐6” high bridge railing on both sides. The new bridge will be a three arched span bridge with varying girder depths along its length. The existing left and right abutment walls will be removed and their foundations and piles will be remained in place. The existing piers will be removed and replaced with the new piers. The proposed wingwalls are parallel to the road, which is 45 degrees with the proposed abutments at both ends of the bridge. Construction work will be allowed to take place within the ordinary high water mark (OHWM) of the stream. The OHWM of the Hanapepe stream is at an elevation of 1 foot. Class 8 riprap will be provided along the proposed left and right abutments at 1(V):2(H) slope to the contraction scour depth. The riprap will be extended 25 feet upstream and 50 feet downstream at southwest side of the bridge. On the northeast side, riprap will not be extended at the upstream side due to the presence of existing riprap and on downstream side, it will be extended to 50 feet.

Class 8 riprap will also be provided along the embankments at the proposed wingwalls as per the HEC‐23 guidelines for the 100‐year storm event (Reference 11). Class 1 riprap will be used as a filter material and a “cushion” for placing the Class 8 riprap. Geotextile will be used between the Class 1 riprap and the base soil.

See plan sheets for the riprap and filter limits. See Appendix B for the riprap and filter size calculations.

The hydraulic analysis software used for the bridge opening is the Hydrologic Engineering Center (HEC) – River Analysis System (HEC‐RAS) version 4.1.0 (Reference 12). HEC‐RAS is used to evaluate alternative

4-3 waterway opening sizes, predict water surface elevations and backwater depths, and determine outlet velocities and roadway overtopping depths.

The 2010 USACE HEC‐RAS model was obtained from Kauai County and was used as the base model for analysis of the Hanapepe Bridge. It is the most recent model that has been approved by both the County and FEMA. The 100‐year design flow in the model is 38,900 cfs versus the 38,000 cfs in the FEMA FIS. The higher flow was used to analyze scour and the regulatory flow was used to determine no‐rise.It was found that the original 2010 model did not use the skew option, but rather made manual bridge open area adjustments to compensate for the skew. CH2M could not recreate their open area based on the current survey, so a corrected effective model was created by using the model’s skew option with a 45‐degree angle. In addition, the regulatory 100‐year flow of 38,000 cfs wasn’t included in the flow data in the model. CH2M added this flow data in the model to compare the no‐rise scenario. The left levee station in the 2010 USACE HEC‐RAS model was also updated from sta 1893.66 to sta 1339.02 to account for a skew in the existing corrected effective model. The proposed conditions model was then created using the corrected effective model. The left levee station in the proposed condition geometery was updated to sta 1332.564 to account for a skew and the proposed bridge opening.

The roadway on either side of the bridge overtops at the 100‐year peak flow of 38,900 cfs in the existing as well as the proposed condition. The 100‐year water surface elevation for the proposed condition is less than the existing water surface elevation for the existing condition, therefore there is a no‐rise scenario.

See Appendix B for the HEC RAS model output for the recommended bridge conditions.

See below the HEC‐RAS output for 100‐, 200‐ and 500‐year recurrence intervals.

Hanapepe Bridge 100‐year 200‐year 500‐year Incipient Overtopping and Pressure Flood

Q (cfs) 38,900 44,200 51,300 24,000

WSEL (ft) 11.01 9.93 13.35 10.64

V (fps) 11.49 14.15 10.78 7.29

See Figure 4‐1 for 100‐year (FEMA) water‐surface profile comparison between the existing and proposed conditions.

4-4

FIGURE 4-1

Hanapepe River Bridge 100-year Water Surface Profiles

4.2.3 Surface Drainage Collection System

Runoff from the bridge was analyzed using the methods from HEC‐21, Design of Bridge Deck Drainage, with the exception of using the 25‐year frequency instead of the 10‐year frequency, per HDOT criteria. Two‐foot deep concrete box inlets with HDOT Double Type A‐9P grates will be constructed at each corner of the bridge just upslope of the approach expansion joints. Two grates are required at each inlet location to exend out from the curb at an appropriate distance to intercept 100% of the gutter flows prior to crossing the expansion joint. The runoff collected in these four inlets will be discharged to an 8‐inch PVC pipe exiting from the bottom of each inlet. The PVC pipe will be routed through the abutment cap. The pipe should pass perpendicularly through the abutment cap to avoid reinforcement conflicts. Vertical and horizontal bends and field‐adjusted lengths may be required to field fit the pipe. The end of all four pipes will be flush with the face of the abutment cap and discharge at elevation 5.0 feet, 6 inches above the riprap grade elevation.

4.2.4 Bridge Scour

4.2.4.1 Site Geology

Borings were performed by Hirata & Associates, Inc. behind each existing bridge abutment, bridge approaches, and within the Hanapepe River. The borings indicate that subsurface materials primarily consist of silty sand, sand, silty gravel, clayey silt. Groundwater was encountered at elevations of ‐0.5 to ‐2 feet near the abutments. The median bed material size (D50) for the subsurface material was determined to range between 0.4 mm and 4.0 mm.

4.2.4.2 Scour Design Flows

The Q200 discharge is used as the design scour flood and the Q500 discharge is used as the check scour flood.

4-5

4.2.4.3 Scour Parameters

As recommended by HEC‐18, long‐term stream degradation, contraction scour, pier scour, and abutment scour were assessed for the bridge. The following sections describe the development of the equation parameters for each type of scour.

Long Term Stream Degradation

The Hanapepe River does not appear to experience degradation in the vicinity of the Hanapepe Bridge.

Because of the tidal action at the crossing location, it is assumed that the current main channel thalweg elevation is in equilibrium and that this elevation will be re‐establish after any significant flow event.

Consequently, the potential for any long‐term degradation at the Hanapepe Bridge is expected to be zero.

Pressure Flow Scour (Vertical Contraction Scour)

Since the water surface elevation for 200‐year event at the upstream face of the bridge is greater than the low chord of the bridge superstructure, the low chord becomes inundated and the flow through the bridge opening changes from free surface flow to pressure flow confirming the existence of pressure flow (vertical contraction). Such pressure flow could result in different magnitudes of contraction scour than at bridges with water flowing under free surface conditions.

The parameters used in the contraction scour equations were determined from proposed Hanapepe HEC‐ RAS model. Section 1935.112, which is located approximately 135 feet upstream from the Hanapepe Bridge, was chosen as the approach cross‐section. This section accurately represents the general channel geometry upstream from the bridge, and it was compared to the contracted bridge cross‐section to determine the magnitude of the contraction scour.

Based on average velocity (V) and critical velocity (Vc) calculations in the approach cross‐section, the live‐ bed contraction scour equation was used for the main channel and clear‐water for left and right abutments.

Table 4‐3,Table 4‐4, and Table 4‐5 show the parameters used to calculate the sediment regime in the channel and the left and right abutments for the 200‐year, 500‐year, and incipient overtopping and pressure flood events.

TABLE 4-3

Sediment Regime Parameters – 200 Year Event

Parameters Left Overbank Channel Right Overbank Unit

Ku 11.17 11.17 11.17 y 4.66 14.10 4.63 ft

D50 0.0013 0.0013 0.0013 ft

V 1.13 10.06 1.21 ft/s

Vc 1.58 1.89 1.57 ft/s

Sediment Regime Clear‐water Live‐bed Clear‐water

TABLE 4-4

Sediment Regime Parameters – 500 Year Event

Parameters Left Overbank Channel Right Overbank Unit

Ku 11.17 11.17 11.17 y 5.67 15.78 5.90 ft

D50 0.0013 0.0013 0.0013 ft

V 1.12 9.94 1.30 ft/s

Vc 1.63 1.93 1.64 ft/s

4-6

TABLE 4-5

Sediment Regime Parameters – Incipient Overtopping and Pressure Flood

Parameters Left Overbank Channel Right Overbank Unit

Ku 11.17 11.17 11.17 y 4.19 13.17 4.20 ft

D50 0.0013 0.0013 0.0013 ft

V 0.66 5.96 0.72 ft/s

Vc 1.55 1.87 1.55 ft/s

Table 4‐6 , 4‐7 and 4‐8 summarize the parameters used to calculate the vertical contraction scour for the Hanapepe Bridge for 200‐year, 500‐year, and incipient overtopping and pressure flood events. Y2 represents the average equilibrium depth in the contracted section after contraction scour (live‐bed at channel and clear‐water at left and right overbanks), t represents the separation zone thickness and hb represents the vertical size of the bridge opening prior to scour. Since the left and right abutments are next to the top of bank of the channel, the vertical contraction scour depth of the channel will be used as the scour depth at left and right abutments.

TABLE 4-6

Vertical Contraction Scour Parameters – 200 Year Event

Parameters Channel Unit

Y2 8.73 ft t 3.65 ft hb 10 ft ys (scour depth) 2.37 ft

TABLE 4-7

Vertical Contraction Scour Parameters – 500 Year Event

Parameters Channel Unit

Y2 13.63 ft t 3.73 ft ys (scour depth) 7.37 ft

TABLE 4-8

Vertical Contraction Scour Parameters – Incipient Overtopping and Pressure Flood

Parameters Channel Unit

Y2 15.27 ft t 3.56 ft ys (scour depth) 8.83 ft

4-7

Pier Scour

Table 4‐9, 4‐10 and 4‐11 summarize the parameters used to calculate the pier scour for the Hanapepe Bridge for the 200‐year, 500‐year, and incipient overtopping and pressure flood events. Y1 represents the flow depth upstream of the pier at face cross section 1860.69* at the channel.

TABLE 4-9

Pier Scour Parameters – 200 Year Event

Parameters Channel Unit

Y1 14.76 ft

K1 1

K2 1

K3 1.1

Fr 0.65 a 8 * ft

L 52 ft ys (scour depth) 18.12 ft

* Assumes 2 times the pier width to account for debris

TABLE 4-10

Pier Scour Parameters – 500 Year Event

Parameters Channel Unit

Y1 18.18 ft

K1 1

K2 1

K3 1.1

Fr 0.45 a 8 * ft

L 52 ft ys (scour depth) 16.64 ft

* Assumes 2 times the pier width to account for debris

TABLE 4-11

Pier Scour Parameters – Incipient Overtopping and Pressure Flood

Parameters Channel Unit

Y1 15.47 ft

K1 1

K2 1

K3 1.1

Fr 0.33 a 8 * ft

L 52 ft ys (scour depth) 13.76 ft

* Assumes 2 times the pier width to account for debris

Complete scour calculations are presented in Appendix C.

4-8

Abutment Scour

Pressure flow (vertical contraction) scour depth will be used as an abutment scour depth for the pressurized Hanapepe Bridge. Riprap will be placed at the left and right abutments at 1V:2H from elevation 4.5 feet as a horizontal countermeasure to the scour depth on both abutments as recommended by HEC‐23. Riprap will be extended to 25 feet upstream and 50 feet downstream from the proposed bridge. For embankment slopes steeper than 1V:2H at the upstream and downstream of the bridge where they tie into existing steep embankments, partially grouted ripraps are recommended. At the northeast corner of the bridge, riprap will not be extended to the full 25 feet, but will tie in with the existing riprap embankment.

Incipient Overtopping and Pressure Flood

The magnitude of the flood discharges were iterated in the RAS model to calculate the incipient overtopping and pressure flood as per the HEC‐18 guidelines to determine the maximum scour depth at the proposed bridge. The iteration resulted in the same incipient overtopping and pressure flood i.e.24,000 cfs that falls between the 10‐year and 20‐year recurrence intervals. The scour depth relative to the incipient flood was found to be higher than the design scour flood of 200 year event. See Appendix C for the vertical contraction (pressure flow) scour depth calculation as well as the cross section at the upstream face section of the Hanapepe Bridge for incipient overtopping flood.

4.2.4.4 Scour Results

The results of the scour analysis are summarized in Table 4‐12, 4‐13 and 4‐14 for the 200‐year, 500‐year, and incipient overtopping and pressure flood events. Figures 4‐2, 4‐3, and 4‐4 present the theoretical scour depths from a profile view of the bridge. Detailed scour calculations are located in Appendix C. The scour elevations at left and right abutments are calculated using main channel thalweg as a reference elevation since both abutments are very close to the main channel i.e. scour condition (a) as described in the HEC‐18 manual (Reference 13).

TABLE 4-12

Summary of Hanapepe Stream Scour Depth and Elevation Results – 200 Year Event

Methods Left (west) abutment Channel Right (east) abutment Unit

Long‐Term Degradation 0 0 0 ft

Vertical Contraction Scour Depth 2.37 2.37 2.37 ft

Pier Scour Depth 18.12 ft

Total scour depth 2.37 20.49 2.37 ft

Ground Elevation ‐2 ‐5 ‐4 ft

Scour depth elevation ‐4.37 ‐25.49 ‐6.37 ft

TABLE 4-13

Summary of Hanapepe Stream Scour Depth and Elevation Results – 500 Year Event

Methods Left abutment Channel Right abutment Unit

Long‐Term Degradation 0 0 0 ft

Vertical Contraction Scour Depth 7.37 7.37 7.37 ft

Pier Scour Depth 16.64 ft

Total local scour depth 7.37 24.01 7.37 ft

Scour depth elevation ‐9.37 ‐29.01 ‐11.37 ft

4-9

TABLE 4-14

Summary of Hanapepe Stream Scour Depth and Elevation Results – Incipient Overtopping and Pressure Flood

Methods Left abutment Channel Right abutment Unit

Long‐Term Degradation 0 0 0 ft

Vertical Contraction Scour Depth 8.83 8.83 8.83 ft

Pier Scour Depth 13.76 ft

Total local scour depth 8.83 22.59 8.83 ft

Scour depth elevation ‐10.83 ‐27.59 ‐12.83 ft

FIGURE 4-2

Scour Depth Profile from Vertical Contraction Scour Method – 200 Year Event

FIGURE 4-3

Scour Depth Profile from Vertical Contraction Scour Method – 500 Year Event

4-10

FIGURE 4-4

Scour Depth Profile from Vertical Contraction Scour Method – Incipient Overtopping and Pressure Flood

SECTION 5

5-1

Summary The hydrologic results of the USACE 2010 study at the Hanapepe Bridge were selected for use in design of the proposed bridge.

The design 100‐year flow is not fully contained in the channel upstream and downstream of the bridge.

The design 100‐year flow is not fully conveyed under the existing or proposed bridge. Roadway overtopping occurs.

The water surface elevation at 100‐year event in the proposed condition is less than the existing condition using corrected effective model, therefore there is no‐rise scenario.

It is not feasible to raise the roadway to meet freeboard requirements; therefore, the replacement bridge will continue to be overtopped.

The conveyance capacity of the proposed bridge exceeds the conveyance capacity of the existing bridge.

The historic significance of the “look” of the existing bridge is an important issue in the replacement of the bridge. Therefore, the proposed replacement structure is a 3‐span arched bridge to replace the existing 3‐ span arched bridge.

Temporary erosion and sediment control BMPS shall be used in accordance with CFLHD standards and FP‐14 specifications (Reference 14).

SECTION 6

6-1

References

1. “Hanapepe River Bridge.” 21°54'31.77"N and 159°35'27.95"W. Google Earth. April 9, 2013. November 1,

2. SWCA Environmental Consultants, March 2015, “Determination and Delineation of Wetlands and Other Waters of the U.S. for the Hanapepe Bridge Project, Hanapepe, Kauai Island, Hawaii, prepared for CH2M

HILL.”

3. Federal Highway Administration, 2011. “Federal Lands Highway Project Development and Design Manual”, U.S. Department of Transportation, Washington, DC

4. State of Hawaii Department of Transportation Highways Division Design Criteria for Highway Drainage 10/1/10

5. “Final Hydraulics Recommendations Report for Hanapepe Bridge Replacement, Kaumualii Highway, Route 50, District of Waimea, Island of Kauai, State of Hawaii”, prepared for Federal Highway Administration, Central Federal Lands Highway Division by CH2M HILL, March 2015.

6. Federal Emergency Management Agency. Flood Insurance Study: Kauai County, Hawaii, November 26,

7. Department of the Army, U.S. Army Corps of Engineers, Honolulu District, Fort Shafter, Hawaii, 17 March 2010, “Hydrologic and Hydraulic Evaluation for levee certification, Hanapepe River, Island of Kauai, Hawaii”.

8. HEC‐21, “Design of Bridge Deck Drainage”, Hydraulic Engineering Circular No. 21, FHWA‐SA‐92‐010, 1993.

9. Technical Release 55 (TR‐55), 1986, “Urban Hydrology for Small Watersheds”

10. NOAA ATLAS 14 Volume 4 Precipitation Frequency Data Server (PFDS) http://www.nws.noaa.gov/oh/hdsc/index.html/

11. HEC‐23, “Bridge Scour and Stream Instability Countermeasures: Experience, Selection, and Design Guidance”, FHWA‐NHI‐09‐111, 2009, Volume 1 and 2, Third Edition

12. U.S. Army Corps of Engineers, 2010, "HEC‐RAS, Hydrologic Engineering Centers River Analysis System,” Version 4.1

13. HEC‐18, “Evaluating Scour at Bridges”, FHWA‐HIF‐12‐003, April 2012, Fifth Edition

14. Standard Specifications for Construction of Roads and Bridges on Federal Highway Projects, FP‐14

15. Federal Highway Administration (FHWA‐NHI‐02‐001), 2002. “Highway Hydrology”, Hydraulic Design Series No. 2, U.S. Department of Transportation, Washington, DC, Second Edition

16. StreamStats (USGS) http://water.usgs.gov/osw/streamstats/ssonline.html/

17. Soil Survey Staff, Natural Resources Conservation Service, United States Department of Agriculture.

Web Soil Survey. Available online at http://websoilsurvey.nrcs.usda.gov/. Accessed [10/20/2014].

18. Oki, D.S., Rosa, S.N., and Yeung, C.W., 2010, Flood‐frequency estimates for streams on Kaua’i, O’ahu, Moloka’i, Maui, and Hawai’i, State of Hawai’i: U.S. Geological Survey Scientific Investigations Report 2010‐5035, 121 p.

19. FlowMaster V8i (SELECT series 1) © 2009 Bentley Systems, Inc.

Appendix A Hydrology

Soil Report

Soil Map—Island of Kauai, Hawaii (Hanapepe Bridge)

Natural Resources Conservation Service

Web Soil Survey National Cooperative Soil Survey

12/11/2014

438850 438870 438890 438910 438930 438950 438970 438990 439010 439030 439050 439070 439090 439110

438850 438870 438890 438910 438930 438950 438970 438990 439010 439030 439050 439070 439090 439110

21° 54' 35'' N

9°

5'

1' ' W

21° 54' 35'' N

9°

5'

1'

' W

21° 54' 29'' N

9°

5'

1'

' W

21° 54' 29'' N

9°

5'

1'

' W

N

Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 4N WGS84 0 50 100 200 300

Feet 0 15 30 60 90

Meters Map Scale: 1:1,260 if printed on A landscape (11" x 8.5") sheet.

MAP LEGEND MAP INFORMATION

Area of Interest (AOI) Area of Interest (AOI)

Soils Soil Map Unit Polygons

Soil Map Unit Lines

Soil Map Unit Points

Special Point Features Blowout

Borrow Pit

Clay Spot

Closed Depression

Gravel Pit

Gravelly Spot

Landfill

Lava Flow

Marsh or swamp

Mine or Quarry

Miscellaneous Water

Perennial Water

Rock Outcrop

Saline Spot

Sandy Spot

Severely Eroded Spot

Sinkhole

Slide or Slip

Sodic Spot

Spoil Area

Stony Spot

Very Stony Spot

Wet Spot

Other

Special Line Features

Water Features Streams and Canals

Transportation Rails

Interstate Highways

US Routes

Major Roads

Local Roads

Background Aerial Photography

The soil surveys that comprise your AOI were mapped at 1:24,000.

Warning: Soil Map may not be valid at this scale.

Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale.

Please rely on the bar scale on each map sheet for map measurements.

Source of Map: Natural Resources Conservation Service Web Soil Survey URL: http://websoilsurvey.nrcs.usda.gov Coordinate System: Web Mercator (EPSG:3857)

Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required.

This product is generated from the USDA-NRCS certified data as of the version date(s) listed below.

Soil Survey Area: Island of Kauai, Hawaii Survey Area Data: Version 9, Sep 25, 2014

Soil map units are labeled (as space allows) for map scales 1:50,000 or larger.

Date(s) aerial images were photographed: Aug 26, 2011—Oct 3, The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident.

Soil Map—Island of Kauai, Hawaii (Hanapepe Bridge)

Natural Resources Conservation Service

Web Soil Survey National Cooperative Soil Survey

12/11/2014

Map Unit Legend

Island of Kauai, Hawaii (HI960)

Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI

HmA Hanalei silty clay loam, 0 to 2 percent slopes

2.2 44.8%

JkB Jaucas loamy fine sand, dark variant, 0 to 8 percent slopes

0.8 15.3%

PdA Pakala clay loam, 0 to 2 percent slopes

0.8 15.8%

W Water > 40 acres 1.2 24.1%

Totals for Area of Interest 5.0 100.0%

Soil Map—Island of Kauai, Hawaii Hanapepe Bridge

Natural Resources Conservation Service

Web Soil Survey National Cooperative Soil Survey

Hydrologic Soil Group—Island of Kauai, Hawaii

Natural Resources Conservation Service

Web Soil Survey National Cooperative Soil Survey

12/11/2014

438850 438870 438890 438910 438930 438950 438970 438990 439010 439030 439050 439070 439090 439110

438850 438870 438890 438910 438930 438950 438970 438990 439010 439030 439050 439070 439090 439110

21° 54' 35'' N

9°

5'

1' ' W

21° 54' 35'' N

9°

5'

1'

' W

21° 54' 29'' N

9°

5'

1'

' W

21° 54' 29'' N

9°

5'

1'

' W

N

Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 4N WGS84 0 50 100 200 300

Feet 0 15 30 60 90

Area of Interest (AOI)

Soils Soil Rating Polygons

A

A/D

B

B/D

C

C/D

D

Not rated or not available

Soil Rating Lines A

A/D

B

B/D

C

C/D

D

Not rated or not available

Soil Rating Points A

A/D

B

B/D

C

C/D

D

Not rated or not available

Water Features Streams and Canals

Transportation Rails

Interstate Highways

US Routes

Major Roads

Local Roads

Background Aerial Photography

The soil surveys that comprise your AOI were mapped at 1:24,000.

Warning: Soil Map may not be valid at this scale.

Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale.

Please rely on the bar scale on each map sheet for map measurements.

Source of Map: Natural Resources Conservation Service Web Soil Survey URL: http://websoilsurvey.nrcs.usda.gov Coordinate System: Web Mercator (EPSG:3857)

Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required.

This product is generated from the USDA-NRCS certified data as of the version date(s) listed below.

Soil Survey Area: Island of Kauai, Hawaii Survey Area Data: Version 9, Sep 25, 2014

Soil map units are labeled (as space allows) for map scales 1:50,000 or larger.

Date(…