Halona_Final_Hydraulics_Report.pdf

I

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 Kapalama Canal ...................................................................................................................... 2-1

2.4 Culverts .................................................................................................................................. 2-1

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

2.6 Floodplain .............................................................................................................................. 2-2

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 ............................................................................. 3-4

3.6 Other Criteria and Methodology ........................................................................................... 3-4

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 USGS StreamStats ..................................................................................................... 4-1

4.1.3 Precipitation Data ..................................................................................................... 4-1

4.1.4 Hydrology for Surface Drainage Collection System .................................................. 4-2

4.1.4.1 Existing Conditions ................................................................................... 4-2

4.1.4.2 Proposed Conditions ................................................................................ 4-6

4.2 Hydraulic Analysis ................................................................................................................ 4-11

4.2.1 Existing Bridge ......................................................................................................... 4-11

4.2.2 Proposed Bridge ...................................................................................................... 4-11

4.2.3 Surface Drainage Collection System ....................................................................... 4-13

4.2.4 Bridge Scour ............................................................................................................ 4-13

4.2.4.1 Site Geology ............................................................................................ 4-13

4.2.4.2 Scour Design Flows .................................................................................. 4-13

4.2.4.3 Scour Parameters .................................................................................... 4-13

4.2.4.4 Scour Results ........................................................................................... 4-18

5 Summary .................................................................................................................................. 5-1

6 References ............................................................................................................................... 6-1

CONTENTS

II

Appendices

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

Figures

1-1 Vicinity Map (Google earth) ................................................................................................................. 1-1 2-1 Waters of the United States Map…..………………………………………………………………………………………… ...... 2-3 4-1 Drainage Map, 10-yr. 1-hr., Existing Conditions .................................................................................. 4-3 4-2 Drainage Map, 25-yr. 1-hr., Existing Conditions .................................................................................. 4-5 4-3 Drainage Map, 10-yr. 1-hr., Proposed Conditions ............................................................................... 4-7 4-4 Drainage Map, 25-yr. 1-hr., Proposed Conditions ............................................................................. 4-10 4-5 Halona Street Bridge 50-year Water Surface Profiles ........................................................................ 4-12 4-6 Scour Diagram, 100-Year Flood Event ............................................................................................... 4-20 4-7 Scour Diagram, 200-Year Flood Event ............................................................................................... 4-21

Tables

3-1 Recurrence Intervals for Hydrologic Design ........................................................................................ 3-1 4-1 Summary of Peak Flows for Kapalama Canal at Halona Street Bridge ................................................ 4-1 4-2 Summary of 10-Year 1-Hour Peak Flows, Existing Conditions ............................................................. 4-2 4-3 Summary of 25-Year 1-Hour Peak Flows, Existing Conditions ............................................................. 4-4 4-4 Summary of 10-Year 1-Hour Peak Flows, Proposed Conditions .......................................................... 4-6 4-5 Summary of 25-year 1-Hour Peak Flows, Proposed Conditions .......................................................... 4-8 4-6 Sediment Regime Parameters – 100-Year Event ............................................................................... 4-14 4-7 Sediment Regime Parameters – 200-Year Event ............................................................................... 4-15 4-8 Summary of Contraction Scour Parameters and Results – 100-Year Event ...................................... 4-15 4-9 Summary of Contraction Scour Parameters and Results – 200-Year Event ...................................... 4-16 4-10 Summary of Pressure Flow Scour Parameters and Results – 100-Year Event ................................... 4-16 4-11 Summary of Pressure Flow Scour Parameters and Results – 200-Year Event ................................... 4-17 4-12 Summary of Pier Scour Parameters and Results – 100-Year Event ................................................... 4-17 4-13 Summary of Pier Scour Parameters and Results – 200-Year Event ................................................... 4-18 4-14 Summary of Halona Street Bridge Scour Depth and Elevation Results – 100-Year Event ................. 4-18 4-15 Summary of Halona Street Bridge Scour Depth and Elevation Results – 200-Year Event ................. 4-19

1-1

SECTION 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 for the Halona Street Bridge site located on the southern side of the island of Oahu in the state of Hawai’i. This report includes final hydraulic analyses and design for the replacement of the existing deficient bridge.

1.2 Project Location and Identification

The Halona Street Bridge spans Kapalama Canal at MP 20.21, adjacent to Interstate Route H-1 on-ramp from Vineyard Boulevard. Halona Street Bridge is located between Kohou Street and Kokea Street and is located within a residential neighborhood. The bridge is surrounded by an urban setting. Based on the North American Datum of 1983 (NAD 83), Halona Street Bridge is located at 21°19’37”N latitude and 157°52’2”W longitude. See Figure 1-1 for Vicinity Map (Reference 1).

FIGURE 1-1

Vicinity Map (Google earth)

2-1

SECTION 2

Existing Site Conditions

2.1 General

A site investigation of the Halona Street Bridge was conducted on January 7th and 10th, 2014 by CFLHD, HDOT, CH2M HILL, ParEn (Hydraulics), Hirata (Geotechnical), and KSF (Structural). The bridge is located on a two-lane asphalt paved road with a 12.5’ lane, a 14’ lane, and 2’-4’ shoulders. The roadway is maintained by the HDOT and is located in the HDOT right-of-way (ROW). The roadway generally slopes in one direction from southwest to northeast and runoff collects in catch basins or discharges directly into Kapalama Canal via curb inlets and openings in the concrete rubble masonry canal walls.

2.2 Bridge

The existing Halona Street Bridge was built in 1938 and modified in later years. It consists of 5 spans supported by concrete piers on a concrete foundation. The as-built plans show that the bridge is supported on spread footings. The bridge is supported at each end by vertical-walled concrete abutments. The bridge has a total length of about 100 feet and a total width of approximately 55 feet. The bridge is not located in a Federal Emergency Management Agency (FEMA) regulated floodplain. There have been no reports of overtopping at the bridge site. The width of the Halona Street Bridge opening (waterway), from the north abutment wall to the south abutment wall, is approximately 82 ft., which is equivalent to the width of Kapalama Canal immediately upstream of the bridge. However, the Halona Street Bridge is narrower than the opening (waterway) through the adjacent, downstream H-1 Bridge. The flow will expand after passing through the Halona Street Bridge. See Appendix D for existing bridge photographs.

2.3 Kapalama Canal

Kapalama Canal runs through a residential development in the vicinity of the Halona Street Bridge. The canal has vertical concrete rubble masonry (CRM) walls and is concrete lined approximately 200 feet upstream of the bridge. The canal has a natural bottom from the limits of the concrete lining to the mouth at Honolulu Harbor, including the area beneath Halona Street Bridge. Kapalama Canal is also tidally influenced.

2.4 Culverts

There are no culverts within the project limits. However, there are several drain lines near the bridge including a 48-inch drain pipe that discharges stormwater runoff between the south abutments of the Halona Street Bridge and the H-1 Bridge. There is one 24-inch abandoned drain pipe at the north abutment.

There is also one 30-inch drain pipe 18-feet upstream of the abandoned drain pipe that discharges into Kapalama Canal.

2.5 Surface Drainage Collection System

For existing conditions, stormwater runoff from a portion of the bridge deck is conveyed to curb inlets located on the mauka and makai side of the bridge. These curb inlets discharge runoff directly into Kapalama Canal. Other portions of the bridge deck and approaches drain into existing catch basins located on Halona Street, Kokea Street and Kohou Street, and openings (scuppers) in the CRM wall located along Kokea Street.

There are no roadside ditches located within the project area.

2 EXISTING SITE CONDITIONS

2-2

2.6 Floodplain

Halona Street Bridge is not located within a FEMA-regulated floodplain according to the FEMA Flood Insurance Rate Map Community Panel No. 15003C0354G dated January 19, 2011. The project site is located in Zone X, areas determined to be outside the 0.2% annual chance floodplain.

2.7 Wetlands/Waters of the United States

A perennial, non-wetland Waters of the United States were identified within the project area. See Figure 2- 1 Waters of the United States Map in the vicinity of Halona Street Bridge. (Reference 2)

Kapalama Canal at the project site is tidally influenced. Therefore, the Mean Higher High Water (MHHW) elevation should be used to establish the U.S. Army Corps of Engineers jurisdictional limits for permitting purposes. According to the National Oceanic and Atmospheric Administration (NOAA), the MHHW elevation for the project site is approximately 1.1 feet above mean sea level. (Reference 3)

A Section 10 permit will likely be required because the project involves non-fill discharging activities. The proposed project could be subject to either a Section 10 or Section 404 Nationwide Permit if the project intends to place dredged or fill material (such as a bridge pier) within the MHHW. (Reference 2)

2.8 Water Quality

The project will not add more than 1.0 acre of new impervious surfaces. Therefore, no permanent storm water quality facilities and improvements are required based on the proposed bridge replacement and roadway improvements. Appropriate temporary erosion and sediment control measures and BMPs will be required during construction.

2-3

FIGURE 2- 1

Waters of the United States Map

3-1

SECTION 3

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 (Reference 4). 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 5) will be followed. The following sections are excerpts from the HDOT Manual, using only information that is applicable to the Halona Street 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

Halona Street Bridge is located on Halona Street at Kapalama Canal and adjacent to Interstate Route H-1 on-ramp from Vineyard Boulevard at Mile Post 20.21. Halona Street is functionally classified as a principal arterial. The roadway is on the National Highway System. As such, the design recurrence interval selected in the analyses of existing and proposed drainage facilities shall be in accordance with the following:

TABLE 3-1

Recurrence Intervals for Hydrologic Design

Recurrence Intervals (yrs)

Functional Classification

Bridge/Culvert Crossing

Roadway (at grade)

Roadway (sump)

Principal Arterial 50 or Match Existing Capacity, whichever is greater (See Other Criteria)

25 25

The project site is not located within a mapped FEMA floodplain. Therefore, the design of the replacement bridge is not required to comply with the National Flood Insurance Program’s regulations and requirements.

The bridge shall be analyzed for the 50-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”.

3 DESIGN CRITERIA AND METHODOLOGY

3-2

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 .

The following hydrologic methods were selected to determine peak discharge for this project. Refer to the Halona Street Bridge Hydraulic Recommendations Report (Reference 6) 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.

U.S. Geological Service (USGS) Regression Equations – This method is used to estimate peak discharge for medium and large watersheds. Statewide Regression Equations are applicable for culvert crossings and bridges and can be accessed from the following website: http://pubs.usgs.gov/sir/2010/5035/ (Reference 7). The USGS in cooperation with the HDOT has developed a web-based interactive Geographic Information Systems (GIS) application that uses the Statewide Regression Equations for estimating peak discharge rates.

This web-based application, StreamStats, (Reference 8) will be used to facilitate the estimation of peak discharge rates.

The 5-year peak discharge estimate shall be included in this hydraulic report for consideration by the Contractor during their design of temporary drainage facilities.

3.4 Hydraulic Analysis

Bridge Crossings

Bridges shall be designed with a minimum freeboard of two feet. 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 shall be designed for scour for the 100-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 Standard 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.

http://hdsc.nws.noaa.gov/hdsc/pfds/pfds_map_hi.html http://pubs.usgs.gov/sir/2010/5035/

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 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.

Storm Drain Manholes

Storm drain manholes shall be installed at horizontal pipe deflection, change in pipe slope or change in pipe size.

Storm drain manholes shall be located on the roadway shoulder or sidewalk and away from the travel lanes. If a storm drain manhole must be installed in the travel lane, then the manhole cover shall be situated away from the normal vehicle wheel line.

Drainage Pipes

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

The HGL shall be a minimum of one foot below the finish grade. The starting HGL for culverts shall apply to drainage pipes. Where a new drainage pipe system is to be connected to an existing system, the starting HGL shall be that of the receiving system. If the HGL of the existing system cannot be determined, the starting HGL shall be the soffit elevation of the new pipe.

Maximum pipe lengths between inlets and manholes for 36 inches or less in diameter shall be 250 feet.

For larger pipe diameters, the maximum spacing shall be 500 feet.

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 DESIGN CRITERIA AND METHODOLOGY

3-4

3.5 Criteria for Temporary Drainage Facilities

The Contractor shall provide the drainage design for 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 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 event.

3.6 Other Criteria and Methodology

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

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.

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

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

3.7 Fish Passage

There are no requirements for fish passage design for this project. Any encroachment into the Kapalama Canal for pier removal and the construction of new piers will be on a temporary basis and the channel geometry below the normal flow of the canal will be restored to its original configuration.

4-1

SECTION 4

Hydrologic and Hydraulic Analyses

4.1 Hydrologic Analysis

4.1.1 General

Multiple methods were employed to analyze the hydrology for the Halona Street Bridge drainage basin including Natural Resources Conservations Services (TR-55) (Reference 9), USGS StreamStats (Reference 7 and 8), and the City and County of Honolulu, Rules Relating to Storm Drainage Standards, Plate 6, dated January 2000 (Reference 10). Because the drainage area does not exceed 25 square miles, the NRCS TR-55 method was used for comparison. Details of each method are described in the Hydraulics Recommendation Report for the Halona Street Bridge Replacement (Reference 6). A description of the selected hydrologic method is included below.

4.1.2 USGS StreamStats

The USGS StreamStats for Hawaii web-based GIS application provided peak flow results for various recurrence intervals for the analysis and design of the Halona Street Bridge replacement. The application uses the USGS regression equations that were developed for the various islands in the state of Hawaii. The results of the peak flow estimates appeared the most reasonable based on the following reasons:

The results show good correlation with the results from the TR-55 method.

USGS StreamStats is an acceptable methodology to HDOT and CFLHD.

This methodology provides for consistent peak flow estimates for all bridge projects on Oahu.

Below is a table summarizing the design peak flows for the proposed Halona Street Bridge replacement project.

Table 4-1 Summary of Peak Flows for Kapalama Canal at Halona Street Bridge

Summary of Peak Flows (cfs) at Halona Street Bridge

Storm Frequencies (based upon drainage area of approximately 1.55 mi2)

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

1,170

2,350

3,000

3,700*

4,860

*The Q(200) value was estimated through graphical interpolation. See Reference 6.

A copy of the USGS StreamStats analysis is included in Appendix A.

4.1.3 Precipitation Data

The precipitation value for the analysis of roadway runoff was obtained from the NOAA Atlas 14 website for Hawaii (Reference 11). The 10-year 1-hour and 25-year 1-hour precipitation depths were determined to be

2.40 inches and 2.98 inches, respectively. See Appendix A for rainfall data.

4-2

4.1.4 Hydrology for Surface Drainage Collection System

A hydrologic analysis was conducted for the existing surface drainage collection system, which include catch basins and curb inlets along Halona Street, Kokea Street and Kohou Street, and openings (scuppers) in the CRM walls of Kapalama Canal along Kokea Street. The study focused on the existing surface drainage features and surrounding areas which may be impacted by the project.

The hydrologic analysis estimated the 10-year 1-hour and 25-year 1-hour peak flows using the Rational Method for both the existing and proposed conditions. According to the City and County of Honolulu Rules Relating to Storm Drainage Standards (Reference 10), drainage areas of 100 acres or less shall be designed for the 10-year recurrence interval. According to the HDOT Drainage Design Criteria (Reference 4), principal arterial roads should be designed for the 25-year recurrence interval. Therefore, the hydrologic results from the 10-year 1-hour peak flows will be used for the surface drainage analysis on Kohou and Kokea Street, and the hydrologic results from the 25-year 1-hour peak flows will be used for the surface drainage analysis on Halona Street. The peak flow estimates will be used to evaluate the impact the project may have on the existing surface drainage features and surrounding areas. The following sections summarize the results of the hydrologic analysis.

4.1.4.1 Existing Conditions

The results of the hydrologic analysis for the 10-year 1-hour peak flows are shown below in Table 4-2. See Appendix A for hydrologic calculations. See Figure 4-1 for the Existing Drainage Map for 10-Year 1-Hour Peak Flows.

Table 4-2 Summary of 10-Year 1-Hour Peak Flows, Existing Conditions

Drain Area No.

Surface Drainage Feature

Location C i10, in./hr. Area, acre Q10, cfs

1 Catch Basin Halona Street (mauka side)

0.72 5.76 0.45 1.87

2 Catch Basin Kohou Street (north side)

0.76 5.76 0.65 2.85

3 Catch Basin Kohou Street (south side)

0.74 5.76 0.47 2.02

4 Curb Inlet Halona Street Bridge (mauka side)

0.75 5.76 0.06 0.27

5 Curb Inlet Halona Street Bridge (makai side)

0.51 5.76 0.06 0.18

6 Openings in CRM Wall Kapalama Canal along Kokea Street

0.69 5.76 0.93 3.69

7 Catch Basin Kokea Street (south side)

0.80 5.76 1.35 6.20

8 Catch Basin Halona Street (mauka side)

0.75 5.04 1.01 3.79

TOTAL 4.98 20.87

HI HI STP SR 5_ _ (1)

HALONA STREET BRIDGE

HALONA STREET

DISTRICT OF HONOLULU, ISLAND OF OAHU, HAWAII

4-1

FIGURE 4-1

DRAINAGE MAP, 10-YR 1-HR,

LINEAR SCALE (FEET)

100 50 0 50 100 200

EXISTING CONDITIONS

4-4

The results of the hydrologic analysis for the 25-year 1-hour peak flows are shown below in Table 4-3. See Appendix A for hydrologic calculations. See Figure 4-2 for the Existing Drainage Map for 25-Year 1-Hour Peak Flows.

Table 4-3 Summary of 25-Year 1-Hour Peak Flows, Existing Conditions

Drain Area No.

Surface Drainage Feature

Location C i25, in./hr. Area, acre Q25, cfs

1 Catch Basin Halona Street (mauka side)

0.72 7.15 0.45 2.32

2 Catch Basin Kohou Street (north side)

0.76 7.15 0.65 3.53

3 Catch Basin Kohou Street (south side)

0.74 7.15 0.47 2.51

4 Curb Inlet Halona Street Bridge (mauka side)

0.75 7.15 0.06 0.33

5 Curb Inlet Halona Street Bridge (makai side)

0.51 7.15 0.06 0.22

6 Openings in CRM Wall Kapalama Canal along Kokea Street

0.69 7.15 0.93 4.58

7 Catch Basin Kokea Street (south side)

0.80 7.15 1.35 7.69

8 Catch Basin Halona Street (mauka side)

0.75 6.26 1.01 4.71

TOTAL 4.98 25.89

Drainage Area Nos. 2, 3, 6, 7 and 8 contribute stormwater runoff to existing catch basins and openings in the CRM wall in sump conditions. Stormwater runoff will approach these surface drainage features from two (2) directions. See Figures 4-1 and 4-2 for the location of the existing surface drainage features, drainage areas, and peak discharge rates for the 10-year 1-hour and 25-year 1-hour storm events.

The existing catch basins and curb inlets along Halona Street are located within the HDOT right-of-way.

These catch basins and curb inlets are maintained by HDOT. The catch basins and openings in the CRM wall along Kohou and Kokea Street are located within the City and County of Honolulu right-of-way. These surface drainage features are owned and maintained by the City and County of Honolulu.

HALONA STREET

DISTRICT OF HONOLULU, ISLAND OF OAHU, HAWAII

4-2

FIGURE 4-2

DRAINAGE MAP, 25-YR 1-HR,

LINEAR SCALE (FEET)

100 50 0 50 100 200

EXISTING CONDITIONS

4-6

4.1.4.2 Proposed Conditions

The results of the hydrologic analysis for the proposed conditions during a 10-year 1-hour storm are shown below in Table 4-4. The hydrologic calculations for proposed conditions are shown in Appendix A. See Figure 4-3 for the Proposed Drainage Map for 10-Year 1-Hour Peak Flows.

Table 4-4 Summary of 10-Year 1-Hour Peak Flows, Proposed Conditions

Drain

Surface Drainage Feature

Location C i10, in./hr. Area, acre Q10, cfs

1 Catch Basin Halona Street (mauka side)

0.72 5.76 0.45 1.87

2 Catch Basin Kohou Street (north side)

0.76 5.76 0.65 2.85

3 Catch Basin Kohou Street (south side)

0.78 5.76 0.54 2.43

4 Catch Basin Halona Street Bridge (mauka side)

Drainage Area No. 4 will contribute runoff to the existing catch basin on Kohou Street (south side).

5 Opening Between Halona Street and H-1 Bridges

0.83 5.76 0.05 0.24

6 Openings in CRM Wall Kapalama Canal along Kokea Street

0.69 5.76 0.93 3.67

7 Catch Basin Kokea Street (south side)

0.80 5.76 1.35 6.19

8 Catch Basin Halona Street (mauka side)

0.75 5.04 1.01 3.83

TOTAL 4.98 21.08

HALONA STREET

DISTRICT OF HONOLULU, ISLAND OF OAHU, HAWAII

4-3

LINEAR SCALE (FEET)

100 50 0 50 100 200

FIGURE 4-3

DRAINAGE MAP, 10-YR 1-HR,

PROPOSED CONDITIONS

4-8

The results of the hydrologic analysis for the proposed conditions during a 25-year 1-hour storm are shown below in Table 4-5. See Appendix A for hydrologic calculations. See Figure 4-4 for the Proposed Drainage Map for 25-Year 1-Hour Peak Flows.

Table 4-5 Summary of 25-Year 1-Hour Peak Flows, Proposed Conditions

Drain Area No.

Surface Drainage Feature

Location C i25, in./hr. Area, acre Q25, cfs

1 Catch Basin Halona Street (mauka side)

0.72 7.15 0.45 2.32

2 Catch Basin Kohou Street (north side)

0.76 7.15 0.65 3.53

3 Catch Basin Kohou Street (south side)

0.78 7.15 0.54 3.02

4 Catch Basin Halona Street Bridge (mauka side)

Drainage Area No. 4 will contribute runoff to the existing catch basin on Kohou Street (south side).

5 Opening Between Halona Street and H-1 Bridges

0.83 7.15 0.05 0.30

6 Openings in CRM Wall Kapalama Canal along Kokea Street

0.69 7.15 0.93 4.56

7 Catch Basin Kokea Street (south side)

0.80 7.15 1.35 7.69

8 Catch Basin Halona Street (mauka side)

0.75 6.26 1.01 4.75

TOTAL 4.98 26.16

The proposed bridge replacement and roadway improvements will alter the drainage pattern and 10-year and 25-year peak stormwater runoff rate for Drainage Area Nos. 3 through 8. The following paragraphs provide a brief discussion of the affected drainage areas.

Finished grades of the replacement bridge will be raised by a maximum height of 9 inches to allow the low chord of the proposed bridge to match or be higher than the low chord of the existing bridge. See Section

4.2.2 for a discussion regarding freeboard. The high point along Halona Street will shift from the vicinity of the north abutment near Sta. 12+15 to the vicinity mid-span of the bridge at Sta. 11+76. As a result of the grade changes, Drainage Area No. 4 will combine with Drainage Area No. 3 and contribute stormwater runoff to the existing catch basin located along Kohou Street (south side). The 10-year peak flow for Drainage Area No. 3 will increase from 2.02 cfs to 2.43 cfs.

The existing curb inlets (Drainage Area Nos. 4 and 5, Existing Conditions) located on Halona Street Bridge will be removed to prevent the direct discharge of stormwater runoff from the bridge deck into Kapalama Canal.

Drainage Area No. 5 for the proposed conditions will drain into the opening/separation that will be created between the Halona Street Bridge and the H-1 Bridge.

Adjustments to the roadway grades will reduce the area contributing to the openings in the CRM wall of Kapalama Canal along Kokea Street. Drainage Area No. 6 will be reduced by 0.003 acre. The 10-year peak flow will be reduced from 3.69 cfs to 3.67 cfs.

Adjustments to the roadway grades will reduce the area contributing to the existing catch basin on Kokea Street (south side). Drainage Area No. 7 will be reduced by 0.0002 acre. The 10-year peak flow will be reduced from 6.20 cfs to 6.19 cfs.

4-9

Adjustments to the roadway grades will increase the area contributing to the catch basin on Halona Street (mauka side) located south of the bridge. Drainage Area No. 8 will increase by 0.007 acre. The 25-year peak flow will increase from 4.71 cfs to 4.75 cfs.

The project is not anticipated to have any drainage related impacts to the existing catch basins on Halona Street located north of the bridge (Drainage Area No. 1), Kohou Street (Drainage Area No. 2), Kokea Street (Drainage Area No. 7), and openings in the CRM wall of Kapalama Canal along Kokea Street (Drainage Area No. 6). The drainage area and resulting peak flow for these drainage features will remain the same or decrease as compared to the existing conditions. Stormwater runoff from Drainage Area No. 5 will discharge into Kapalama Canal and will not have any impact to the existing surface drainage collection features.

A hydraulic analysis was performed for the existing catch basins on Kohou Street (Drainage Area No. 3) and Halona Street (Drainage Area No. 8) to determine the impact of the additional flows. See Section 4.2.3 for the results of the hydraulic analysis.

HALONA STREET

DISTRICT OF HONOLULU, ISLAND OF OAHU, HAWAII

4-4

LINEAR SCALE (FEET)

100 50 0 50 100 200

FIGURE 4-4

DRAINAGE MAP, 25-YR 1-HR,

PROPOSED CONDITIONS

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4.2 Hydraulic Analysis

4.2.1 Existing Bridge

The existing bridge is constructed of a reinforced concrete slab supported on four (4) piers. The bridge has a total of five (5) spans, and a length and width of approximately 100 feet and 55 feet, respectively. The low chord to invert clearance ranges from approximately 8.0 to 9.0 feet. Each of the four (4) piers consist of a group of square piles having a width of approximately 1.5 feet. The slope of the channel is estimated to be

0.0014 ft./ft.

Survey data was obtained for Kapalama Stream and Halona Street Bridge. The survey data was used to develop cross sections for hydraulic modeling in HEC-RAS (Reference 12). Based on the HEC-RAS model of the existing Halona Street Bridge, the results indicate that the bridge has the capacity to convey the 50-year flow. However, the results indicate that the existing bridge will provide 0.2 feet and 0.0 feet of freeboard at the north and south abutments, respectively. The results also indicate that overtopping of the roadway and bridge will not occur. The 50-year peak flow will be contained within the Kapalama Canal walls. See Appendix B for a printout of the HEC-RAS model output for the existing conditions.

4.2.2 Proposed Bridge

The proposed bridge will be constructed of a 2 feet thick reinforced concrete slab supported on two (2) piers. Each pier will be constructed of seven (7) each 24 inch octagonal precast prestressed concrete piles and a concrete pile cap. The proposed bridge piers will be aligned with existing H-1 Bridge piers. The existing Halona Street Bridge piers will be removed to a depth of 3 feet minimum below the stream invert.

The proposed bridge will have three (3) spans, a total length and width of 130.92 feet and 39.33 feet, respectively, and 3’-6” high concrete bridge rails at the upstream and downstream ends. Note, an opening or separation will be created between the proposed bridge and the existing H-1 Bridge due to a reduction of the bridge width. A reduced bridge width will be achieved by eliminating the concrete slab extension from the Halona Street Bridge.

The abutments for the new bridge will be set back from the existing bridge abutments to remain. Therefore, the proposed bridge opening will remain the same as the existing opening of approximately 82 feet. The existing bridge abutments will continue to serve as the Kapalama Canal walls. The proposed bridge abutments will be constructed of six (6) each 24 inch octagonal precast prestressed concrete piles and a concrete pile cap.

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As discussed in Section 4.1.4.2, the finish grades for the proposed bridge will be raised a maximum height of 9 inches as compared to the existing bridge elevations. A higher bridge will be necessary because of the increased span lengths and resulting increased superstructure thickness of the proposed bridge. A higher bridge will minimize the impacts the proposed bridge will have on the 50-year water surface elevations by allowing the low chord to match or be higher than the low chord of the existing bridge.

Results of the hydraulic analysis indicate that proposed bridge will not cause a rise in the 50-year water surface elevations. The proposed bridge will provide 0.3 feet minimum freeboard. The results also indicate that overtopping of the roadway and bridge will not occur. The 50-year peak flow will be contained within the Kapalama Canal walls. See Appendix B for a printout of the HEC-RAS model output for the proposed conditions. See Figure 4-5 for the 50-year water surface profile of the existing and proposed bridges.

The proposed bridge would need to be raised by at least 1.7 feet to meet the HDOT criteria of 2 feet minimum freeboard. Raising the bridge by 1.7 feet would impact Halona Street, the intersections at Kokea Street and Kohou Street, and the adjacent residential development. Two (2) feet of freeboard may not be required because the bridge and Kapalama Canal is situated within an urban development. There are a limited number of large trees along the canal compared to the upstream undeveloped reaches. Also, closed conduit drainage systems, which are located approximately 1,700 feet upstream of the bridge, will limit the size and amount of debris transported to the bridge. A design exception will be required for freeboard.

FIGURE 4-5

Halona Street Bridge 50-Year Water Surface Profiles

-4

-2

0 200 400 600 800 1000 1200 1400 1600

El ev at io n ft

M

SL

Channel Station [ft.]

Halona Street Bridge Water Surface Profiles

Prop. 50-yr. Water Surface

Exist. 50-yr Water Surface

Exist. Ground Surface

Prop. Halona Street Bridge

Exist. Halona Street Bridge

H-1 Bridge

Olomea St. Bridge

N. King St. Bridge

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4.2.3 Surface Drainage Collection System

Hydraulic calculations were performed for the existing catch basins on Kohou Street (Drainage Area No. 3) and Halona Street (Drainage Area No. 8). Calculations for gutter flow and inlet capacity were performed to determine the impact of the increased flows to these surface drainage features.

Results of the hydraulic calculations indicate that the additional flows to the existing catch basin on Kohou Street will not have a negative impact. The spread will be 6.37 ft., which is less than the 8 feet maximum spread allowed by the City and County of Honolulu Storm Drainage Standards (Reference 10).

Results of the hydraulic calculations indicate that the additional flows to the existing catch basin on Halona Street will not have a negative impact. The spread will be 6.42 ft., which is within the allowed on-street parking width of 8.25 ft. (Reference 17). The spread does not enter the travel lane, which meets the HDOT criteria (Reference 4) of gutter flow not exceeding 1/3 the width of the travel lane measured from edge of pavement to the gutter.

No ditches are proposed and analyzed for this project.

4.2.4 Bridge Scour

4.2.4.1 Site Geology

Borings were performed by Hirata & Associates, Inc. (Reference 13) within Kapalama Canal immediately upstream of Halona Street Bridge and near the north and south abutments. The borings indicate that subsurface materials primarily consist of silty clay, clayey silt and some silty gravel to depths ranging from 80 to 87 feet in two (2) of the borings and to 120 feet at the bottom of the third boring. This material consists of recent to older alluvium deposits located on the Kapalama Stream alluvial fan. Hirata & Associates mentions that variable amounts of sand, some pockets of gravel and occasional cobbles may be encountered. Silty coralline gravel may be found below the alluvial soils.

Groundwater was encountered at elevations of 0.7 feet and 1.7 feet above mean sea level near the abutments. It appears that the boring in Kapalama Canal was performed with at least a foot of water. The various observed groundwater elevations appears to be influenced by tidal fluctuations.

Soil samples were taken immediately upstream of the Halona Street Bridge at a depth of approximately 5.5 feet below the invert of Kapalama Canal. The material consists of gray clayey sand. Results of a sieve analysis indicate that the D50 and D90 particle sizes are approximately 0.19 millimeters and 7.0 millimeters, respectively.

Due to the relatively soft and compressible subsurface soils encountered at the project site, deep foundations are proposed for the replacement bridge.

4.2.4.2 Scour Design Flows

The Q100 of 3,000 cfs was used as the maximum scour flood.

4.2.4.3 Scour Parameters

As recommended by HEC-18 (Reference 14), long-term stream degradation, contraction scour, and local scour were considered for the proposed bridge. The following sections discuss the development of the parameters used in the equations to calculate each type of scour.

Long-term Stream Degradation Review of the as-built plans for Halona Street Bridge and the topographic survey of Kapalama Canal indicate that deposition has occurred over a period of about 75 years. The 1937 Halona Street Bridge plans show Kapalama Canal to have an invert or thalweg elevation of (-) 4.0 feet mean sea level at the bridge. The 2014 topographic survey map indicates a thalweg elevation of generally 1.0 foot below mean sea level at the bridge. See Appendix C for a copy of the Halona Street Bridge as-built plans.

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Site observations of Kapalama Canal conducted in September 2015 by ParEn staff revealed additional sediment deposition from recent storm events. It is anticipated that sediment deposition at Halona Street Bridge, the H-1 Bridge and Kapalama Canal will continue to occur for the following reasons:

There is an adequate supply of sediment at the upstream reaches of Kapalama Stream watershed.

Sediment will be transported through the upstream drainage systems which include unlined stream channels, concrete-lined or partially-lined drainage channels and closed conduit drainage systems.

The longitudinal slope of the upstream drainage systems appear to be adequate to generate flow velocities that flush sediment towards Halona Street Bridge.

The concrete-lined section of Kapalama Canal terminates approximately 200 feet upstream of Halona Street Bridge.

The longitudinal slope of Kapalama Canal in the vicinity of the bridge is relatively mild at 0.0014 ft./ft.

Halona Street Bridge is located at the upper limits of the tidally-influenced Kapalama Canal.

Sediment within Kapalama Stream will likely be displaced during the passage of larger storm events, as indicated by the sediment regime for the 100-year flood. However, the general long-term trend appears to be an aggrading channel condition. Periodic and routine inspection, maintenance and removal of the accumulated sediment is recommended to maintain the hydraulic capacity of Kapalama Canal.

For the purpose of bridge scour design, the analysis will assume that no long-term stream degradation will occur.

Contraction Scour The parameters used in the contraction scour equations were determined from the HEC-RAS model for proposed conditions based on the 100-year flood event. River Station 1385.59, which is located approximately 125 feet upstream of Halona Street Bridge, was selected as the approach cross section. This river station was deemed appropriate and representative of the upstream channel due to the prismatic nature of Kapalama Canal geometry. Parameters from River Station 1385.59 were compared to the parameters at the contracted bridge section (River Station 1274.64) to determine the magnitude of contraction scour.

Based on the average approach velocity (V) and critical velocity (Vc) of the median particle size, the live-bed contraction scour equation was used for the main channel. All flows will be contained within Kapalama Canal for the 100-year flood. There will be no overbank flows. Table 4-6 and Table 4-7 show the parameters used to calculate sediment regime in the main channel for the 100-year and 200-year event, respectively.

TABLE 4-6

Sediment Regime Parameters – 100-Year Event

Parameter Left Overbank Main Channel Right Overbank Unit

Ku 11.17 11.17 11.17 y NA 9.60 NA ft.

D50 NA 0.000623 NA ft.

V NA 3.82 NA ft./s

Vc NA 1.39 NA ft./s

Sediment Regime NA Live-bed NA

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TABLE 4-7

Sediment Regime Parameters – 200-Year Event

Parameter Left Overbank Main Channel Right Overbank Unit

Ku 11.17 11.17 11.17 y NA 10.25 NA ft.

D50 NA 0.000623 NA ft.

V NA 4.41 NA ft./s

Vc NA 1.41 NA ft./s

Sediment Regime NA Live-bed NA

The width at the approach section, W1, is defined as the bottom width of the channel that is transporting bed material. Based on the project topographic survey map, the width of Kapalama Canal at the approach section was determined to be approximately 82 feet.

The width at the contracted bridge section, W2, is the bottom width of the channel at Halona Street Bridge less the total width of the proposed piers. Since the existing Halona Street Bridge abutments will remain and continue to serve as the canal walls, the width at the contracted bridge section will be the width of Kapalama Canal minus the 24 inch octagonal piles at each pier/bent. The bottom width of the contracted section was determined to be approximately 78 feet.

Flow depths (y1 and yo) and flow rates (Q1 and Q2) for the approach and contraction sections were obtained from the HEC-RAS model for River Stations 1385.59 and 1274.64, respectively.

Table 4-8 and Table 4-9 summarize the parameters that were used to calculate contraction scour for the 100-year and 200-year events, respectively. The results are present at the bottom of the tables. The contraction scour calculations are included in Appendix C.

TABLE 4-8

Summary of Contraction Scour Parameters and Results – 100-Year Event

Parameter Left Overbank

Main Channel Right Overbank

Unit y1 NA 9.60 NA ft.

Yo NA 8.54 NA ft.

Q2 NA 3,000 NA ft.3/s

Q1 NA 3,000 NA ft.3/s

W1 NA 81.86 NA ft.

W2 NA 77.86 NA ft.

K1 NA 0.69 NA

y2 NA 9.94 NA ft.

ys (contraction scour depth)

NA 1.40 NA ft.

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TABLE 4-9

Summary of Contraction Scour Parameters and Results – 200-Year Event

Parameter Left Overbank

Main Channel Right Overbank

Unit y1 NA 10.25 NA ft.

Yo NA 8.54 NA ft.

Q2 NA 3,700 NA ft.3/s

Q1 NA 3,700 NA ft.3/s

W1 NA 81.86 NA ft.

W2 NA 77.86 NA ft.

K1 NA 0.69 NA

y2 NA 10.61 NA ft.

ys (contraction scour depth)

NA 2.07 NA ft.

The hydraulic analysis for the proposed conditions indicate that pressure flow conditions will occur at Halona Street Bridge.