100915-H&H_Tech_Memo.pdf

Haleakala Summit Road Rehabilitation - Hydrologic and Hydraulic Criteria and Computational Methods

May 19, 2010

N:\HI\hale10(2)\ProjectManagers\Hydraulics\100915-H&H Tech Memo.docx

TECHNICAL MEMORANDUM

TO: Matt Ambroziak, P.E.

FROM: Geoffrey L. Casburn, P.E. –

DATE: September 15, 2010

SUBJECT: Hydrologic and Hydraulic Criteria and Computational Methods Report Project Name: NPS PMIS #120655 FHWA Project: HI PRA Hale 10(2) per TO# DTFH68-06-D-00011/T-10- 003 Mod #1

1.0 INTRODUCTION

The Haleakala Summit Road is located on the island of Maui, Hawaii. The present road alignment traverses the northwesterly slope of Haleakala Volcano from the Haleakala National Park entrance to the summit of the volcano. The roadway within the park is a two-lane highway approximately 22-foot wide with steep grades (5%-7%) and nine (9) switchbacks. The road was originally constructed circa 1933. See Figure 1 for the road location.

September 15, 2010

The Haleakala Summit Road Rehabilitation Project ("Summit Road Project") is approximately 3.8 miles in length and is a 3R project. The rehabilitation work would be performed for the Federal Highway Administration ("FHWA"); the Central Federal Lands Highway Division ("CFLHD"); and, the National Park Service ("NPS"). The project bidding method would be design-bid-build. See Figure 2 for the limits of Summit Road Project.

Figure 2 – Limits of Project

The purpose of this Technical Memorandum is to provide a brief summary of the applicable hydrologic and hydraulic design criteria that would be applied in the preparation of the bid documents and plans. Also this document provides a description of calculation methods that would be applied to the design of drainage facilities.

Specific hydrologic and hydraulic components within the scope of design would include:

developing the applicable hydraulic and hydrologic memoranda; identifying and evaluating the existing pavement drainage facilities; identifying areas having deficient road-shoulder drainage facilities; supporting the environmental review process with water quality recommendations; and, developing recommendations for proposed improvements as the design progresses.

2.0 PROJECT BACKGROUND AND DESCRIPTION

The Summit Road Project area has undergone numerous reconstruction phases since its initial construction. These construction activities have included roadway widening, installation of metal and concrete box culvert extensions, plus new overlays of new bituminous surfacing. The maintenance history of the roadway is described in in Table 1- Chronologic History of Roadway Construction.

Table 1 - Chronologic History of Roadway Construction*

YEAR DESCRIPTION

STATION

TO

STATION

Length (mi.)

MP

TO

MP

Overlay Thickness

(in)

Total Pavement Section**

1933-

Began October 13, 1933, completed

•Grading, surfacing •Concrete

Boxes

• Culverts

0+00(Park.

Bdry) 10.643

10.3 to

20.93

4-inches Loose measured bituminous surface treatment

Sub-base to first overlay

1934 Bridge constructed

Completed August 1934.

85+15 to 85+50 35 feet 11.9 -----

1952 ----- Seal Coat ----- ----- ----- -----

1979- 1980 ------ 1 ½”-

Overlay 0+00 – 490+83 9.296

10.3 to

19.60

2 ¾” Asphalt Stabilized Base(AS) overlay

2.75

1979- 1980 ----- 1 ½”-

Overlay 49+50 – 490+83 8.359

11.2 to

19.60

1 ½ “ Hot AC

(HACP)

overlay

4.25

1993- 1994 ----- Overlay 0+00 -

49+50 0.938 10.3 to 11.24

3.0” AC

(HACP)

overlay

1993- 1994 ----- Overlay 49+50 –

465+00 7.869 11.24 to 19.10

1 ½” Hot AC

(HACP)

overlay

5.75

1999- 2000 ----- Overlay

Park Brdy to Red Hill

9.296 10.3 to 20.9

1 ½” Hot AC

(HACP)

overlay

7.25

1999- 2000 ----- Chip Seal ----- -----

10.3 to

18.5

Application of chips

2007 ----- Lava Tube Bridge work 235+00 0.055 14.8 -----

2009 ----- Chip Seal

(PLANNED) ----- -----

18.5 to

20.9

Application of chips

*Table 1 from Pavement Report (2009), as amended (pavement overlay activities in bold) ** Column added to Table 1

The information shown in Table 1 is illustrated in Figure 3-Typical Existing Road Pavement Cross-Section.

Figure 3- Typical Existing Road Pavement Cross-section

3.0 DRAINAGE CRITERIA

Drainage analysis and design work associated with the proposed improvements will be in accordance with the methods, guidelines, and criteria set forth by both the CFLHD, and the American Association of State Highway and Transportation Officials (AASHTO).

CFLHD has developed both drainage criteria manuals and standard drainage details in order to provide guidance or references to aid in the design process and/or to establish specific design standards: These documents are:

• Federal Lands Highway Project Development and Design Manual (PDDM), 2008

• CFLHD Standard Drainage Details, 2010

FLOOD HISTORY

The project improvements do not lie within a Federal Emergency Management Agency (FEMA) Flood Hazard Area.

HYDROLOGY

Hydrologic analysis for the Summit Road Project would be determined using the Rational Method. Rational Method calculations would be carried out using the InteliSOLVE HydraFlow Hydrographs 2007 software.

Rainfall intensities and times of concentration would be based on the County of Maui Storm Drain Standards ("COM Standards"). COM Standards provide a source for short-term rainfall intensity values. Intensity-Duration-Frequency (IDF) curves have been developed for the project site using materials contained in the COM Standards. The calculated IDF rainfall intensities for the project area are shown in Table 2 - Design Point Rainfall Intensities for Rational Method Calculations.

Table 2 - Design Point Rainfall Intensities for Rational Method Calculations

IDF Curve Values* from COM Standards, Plate 2 Time of Concentration

Return- Period (Years)

1-hr Depth**

(in) 5 Min. 15 Min. 30 Min. 60 Min.

2 1.3 3.5 2.4 1.8 1.3

5 1.5 4.1 2.8 2.1 1.5

10 1.8 4.9 3.4 2.5 1.8

25 2.0 5.4 3.7 2.7 2.0

50 2.3 6.2 4.3 3.1 2.3

* Tabulated values in inches per hour for stated time of concentration.

** Source: TP-43

Watershed boundary delineations will be prepared using both U.S. Geological Survey Quad maps and the project topographic survey.

Both soil data and maps were obtained from the National Resources Conservation Service (NRCS). Based on the NRCS soil survey website, the soils in the Map Unit Area (within and around the project area) are as shown in Table 3-Hydrologic Soil Groups.

See also Figure 4 Hydrologic Soil Groups.

Table 3- Hydrologic Soil Groups

Map Unit Map Unit Name HSG* Acres (Ac)

% of Area of Interest**

KDIE Kaipoioi loam, 7 to 40 percent slopes B 13.5 1.3%

LMF Laumaia loam, 40 to 70 percent slopes B 27.6 2.6% rRK Rock land D 3.2 0.3% rRO Rock outcrop D 0.0 0.0% rVS Very stony land C 1,031 95.9%

Totals for Area of Interest 1,076 100.0%

* Hydrologic Soil Group ** Area of Interest is the total area encompassed by the Map Unit Analysis.

The project area watershed is located within the Haleakala National Park and the existing watershed is expected to remain in open space.

Site-specific soil information was obtained from the Pavement Report (2009). Soil samples were obtained for the preparation of the pavement report by auguring through existing pavement sections at three locations. Results from previous soils investigations conducted along the Summit Road were also included in the Pavement Report. A summary of the reported results are shown in Table 4-On-Site Soils Data.

Table 4-On-Site Soils Data

MP Elevation Lane AC Thickness Classifications (feet) Up Down (In) AASHTO USCS

11.26 7035 U SM

11.3 D 7

11.4 U 5.5

11.47 7078 SP

11.77 7159 SM

11.8(S3) U 5.5 11.9(S4) D 6.5

11.95 7199 A-1-a(0) SP

12.1 U 5.5

12.19 7264 SM

12.2 D 6.5

12.4(S5) U 5.5

12.46 7338 SM

12.5 D 6.5

12.7 U 5.5

12.8 D 6

13.0 U 5.5

13.15 7488 SP-SM

13.4 D 6.5

13.5 U 6.5

14.0(S6) D 6 14.0(S6) U 6

14.13 7801 A-2-5(0) GM

14.27 7846 GP

14.5 D 8

14.5 U 7.5

14.77 7963 SM

Table notations:

• Location, (MP = mile point),

• Elevation,

• Lane, (U = uphill lane, D = downhill lane),

• Asphalt Cement Thickness (AC Thickness),

• S# = indicates that a soil sample for lab analysis was taken at this location.

Table 5 - Hydrologic Design Standards summarizes the hydrologic design requirements per Federal Lands Highway’s PDDM.

Table 5 - Hydrologic Design Standards

Facility Category Description Recommended Design Storm (Years)

Culverts Cross culverts 50

Culverts for roadside ditches 10

Inlets for Pavement Drainage On-grade 10

Sump 50

Storm Drains On-grade 10

Sump 50

Ditches Ditch 10

Rundowns Chute 10 Pipe 10

Culvert Design Note: The existing culverts within the project limits may not currently meet the minimum capacity requirements given in Table 5 Hydrologic Design Standards.

However, because this is a 3R project, only culverts that are identified by Park staff as hydraulically inadequate and/or damaged will be recommended for modification.

4.0 HYDRAULIC ANALYSIS

4.1 EXISTING CONDITIONS

Existing Pavement

The existing pavement within the Summit Road Project has experienced substantial failure.

The CFLHD has determined that the pavement within the Summit Road Project has reached the end of its useful life. The pavement is to be reconditioned as part of this project.

Existing Curbs

Asphalt curbs have been installed along the roadway. These curbs prevent pavement runoff from crossing the shoulder and flowing down the face of the roadway embankment.

Existing Roadside Ditches

Roadside ditches do not exist along a good part of the Summit Road Project. Shoulder areas generally have bare native soil located between the edge of pavement and the edge of shoulder. Some areas however do have paved (grouted rock or asphalt) ditches and rundowns. Typically, the roadside shoulders convey surface runoff along the right-of-way on both sides of the roadway.

Storm water is being discharged from some shoulder areas onto the pavement as a result of adverse pavement cross-slope and the configuration of the shoulder area. In other sections of the roadway the shoulder areas convey the storm water to culverts and/or rundowns.

There is very little erosion in the unpaved shoulder areas. In spite of the steep roadway grades, the flow velocities in the road shoulder areas do not appear to be sufficient to cause erosion of the sandy loam soil. The presence of lined ditches at some locations indicates that erosion has occurred and that this erosion was at some point repaired by "hard lining" those portions of the shoulder area.

Existing Culverts

There are a total of 39 existing cross-drains plus one bridge within the Summit Road Project area. The location by road station and the corresponding cross-culvert configurations are shown in Table 6-Existing Culverts.

Table 6- Existing Culverts (have asked surveyor to provide missing values)

Road Station Length (Ft) Size Type EOP

Elev.

Invert Elev.

Cover Calc'd

102+04.75 38 24" C 7032.1 7023.3 6.8 104+22.51 35 24" C 7041.7 7038.8 0.9 107+91.40 62 24" C-P 7054.3 7050.9 1.4 111+99.84 30 24" C 7079.7 7076.3 1.4 119+27.23 30 24" C 7115.1 7111.5 1.7 122+63.87 28 24" C 7134.5 7130.8 1.8 125+43.93 28 24" C 7149.7 7145.2 2.5 136+31.06 -- Clr Span Bridge 7196.9 7193.5 3.4 137+94.24 30 24" C 7206.0 7203.2 0.8 140+87.62 27 24" C 7223.2 7219.1 2.1 144+39.44 33 24" C 7243.0 7234.7 6.3 148+41.85 29 24" C 7263.0 7256.2 4.8

156+01.92 29 7.5’ x

7.5’ RCB 7304.1 7294.4 2.2

159+48.60 31 24" C 7323.5 7321.3 0.2 162+36.72 26 24" C 7334.8 7330.6 2.2 166+70.01 28 24" C 7349.0 7345.7 1.3 173+65.99 29 24" C 7375.5 7371.4 2.1 178+75.76 26 24" C 7396.4 7393.4 1.0 182+61.56 26 24" C 7419.0 7415.6 1.4

186+92.10 50 6X8 RCB 7442.2 7428.8 7.4

Table 6- (Con’t.)

Road Station Length (Ft) Size Type EOP

Elev.

Invert Elev.

Cover Calc'd

189+18.53 27 36" C 7457.9 7453.0 1.9 197+89.89 27 24" C 7509.3 7506.1 1.3 201+90.86 29 24" C 7528.0 7520.9 5.1 204+30.56 29 24" C 7540.0 7535.6 2.5 205+96.28 41 24" C 7549.0 7534.7 12.4 208+96.82 42 10’ x 10’ RCB 7568.7 7554.4 4.3 220+01.20 27 24" C 7627.0 7623.0 2.0 227+27.86 38 24" C 7667.0 7652.1 12.9 230+71.36 49 24" C-P 7679.9 7669.9 8.0 235+81.63 27 30" C 7708.0 7700.7 4.8 239+65.12 30 24" C 7731.0 7728.1 1.0 245+67.28 31 24" C 7767.3 7763.5 1.8 250+37.66 48 10’ x 9’ RCB 7792.7 7781.4 1.3 254+32.37 31 24" C 7814.7 7811.5 1.2 259+84.39 28 6’ x 6’ RCB 7848.3 7839.2 3.1 266+78.92 37 32" C 7880.3 7876.4 1.2 272+57.21 22 42" C 7902.3 7889.8 9.0 277+39.11 26 24" C 7926.8 7922.4 2.5 283+77.78 29 24" C 7961.0 7957.7 1.3 294+52.28 29 24" C 8019.9 8015.0 2.9

* C denotes Pipe culvert; RCB denotes Box Culvert; C-P Pipe Culvert projecting

Existing Subsurface Flows

As evidenced by the maintenance history illustrated in Table 1, the Summit Road Project area has experienced repeated pavement failures. The pavement report considers that future control of groundwater is a critical step in controlling premature pavement failures.

There are a number of components contributing to subsurface flow within the project area. There include:

1. Rainfall entering through the pavement in cracks

2. Runoff from the pavement infiltrating into the unpaved road shoulders

3. Surface runoff from the upper watershed infiltrating into the unpaved road shoulders

4. Subsurface runoff from the upper watershed entering the road prism

These components are illustrated in Figure 4 -- Sources of Moisture and Pavement Systems.

Figure 4 - Sources of Moisture in Pavement Systems

The use of paved shoulders and/or roadside ditches would reduce both the infiltration of pavement runoff and also the uphill surface runoff into the shoulder area soils. Control of subsurface flow would require a "sub-drain" system.

Shoulder area soils have been sampled, tested and classified in the Pavement Report. The shoulder area soils are classified as SP, SM and GP (FHWA, 2009, Appendix D.). These soils are classified as "coarse-grained soils". The laboratory tests conducted as part of the pavement report preparation showed that the project area soils are primarily cinder, gravel, silt and sand; with limited clay content. The shoulder area soils are very permeable.

The Summit Road Project area is underlain by basalt, as illustrated in Figure 3. The permeability of basalt varies considerably depending on the extent, width and the interconnection of existing cracks within the formation. No specific information is available for the basalt located under the Summit Road Project area. However, exposed bedrock in tributary streams indicates that the permeability of the basalt layer is not excessive (basalt permeability can exceed 100 feet per day in areas with extensive and interconnected cracking).

For the purposes of subsurface flow control, it will be assumed that the basalt permeability is less than the road shoulder area soil permeability. Should information come to light which changes this assumption, then the use of an edge drain would not be required.

Control of Subsurface Flow

Control of subsurface flow involves first the collection of subsurface flow and then the conveyance of that flow to a sufficient depth below the ground surface in order to lower the groundwater table under the road. One method to accomplish this is through the installation of edge drains (more fully described later in this report) in the road shoulder area. Extensive research has been carried out by FHWA on the types and the required design parameters for edge drains. A major concern to FHWA is the long-term maintainability of this type of structure.

4.2 FUTURE CONDITIONS

General

The location and limits of new drainage facilities will be determined during plan-in-hand field inspections at the project site. The NPS has required that the rehabilitated road section be installed with limited earth work and that existing cut and fill slopes be maintained. The new drainage facilities first must conform to the existing site and then to design considerations such as flow capacity and/or freeboard.

Culverts

There are currently no plans to replace the existing culverts nor any plan to install new culverts. New or replacement culverts, if required during final design, would be designed to meet CFLHD hydraulic design criteria. New culverts would be designed using Bentley CulvertMaster software.

New Pavement, Curbs and Shoulders

New pavement drainage facilities would be designed to meet CFLHD hydraulic design standards where practicable. The steep road slope and back-to-back "S" curves along road may result in drainage flows crossing the road centerline. Pavement spread will be determined using Bentley FlowMaster software.

Existing curbs will, for most of the road, be replaced in kind. To limit spread of runoff into the traveled way additional rundowns and cross culverts will be considered during the design. There are areas however were curbs have been extended beyond a useful point (the curbs are not needed to contain runoff within the pavement area). The existing curbs will be reviewed in the field and adjustments made to the location of new curbs to remove un-needed curb.

Roadside ditches

New roadside ditches will be designed in accordance with CFLHD criteria. The pavement report identifies both inadequate roadside drainage and control of surface infiltration and subsurface flows as the primary causes for the premature deterioration of the roadway pavement. Flexible linings such as riprap are not suitable for roadside ditches on this project. Flexible linings would permit the continued infiltration of surface water into the shoulder area soils.

The use of asphalt lined ditches will be investigated in order to provide erosion protection and also to limit infiltration of roadside water into the shoulder area soils. New cross drains to limit the volume of flow in roadside ditches will be considered during the design of the project.

Three alternative roadside ditch cross-sections would be considered:

• a paved transverse extension of the road pavement (with or without a curb)

• a paved circular ditch

• a paved V ditch

The determination of the ditch cross section will be based upon what ditch cross-section will physically fit within the limited shoulder area. Ditches will be sized to carry the design flows without freeboard. Each of the ditch sections and possible lining materials will be considered as roadway design continues.

In order to minimize the depth, and/or width of the ditches, it is recommended that addition of cross-culverts and rundowns be considered as part of the roadway drainage design.

Subsurface flow control

Design of subsurface control facilities will include the consideration of the traditional french drain, a non-piped fin-drain, and a piped fin-drain. Each of these options will be covered separately below. See Figure 5 - Typical Cross-Sections for Edge Drain. This project will pulverize the existing pavement in place and it will not possible to place open-graded base under the pavement. Lack of open-graded base will limit the effectiveness of the roadside sub-drains.

Figure 5 - Typical Cross-Sections for Edge Drain

French Drain

FHWA recommends the use of geotextile wrapped french drains for use as longitudinal edge drains. The primary consideration in this case is maintainability. This system permits the installation of a piping system with clean outs, multiple outlets and pipe with sufficient strength to permit power cleaning. See Figure 6 Geotextile Wrapped French Drain.

Figure 6- Geotextile Wrapped French Drain

Non-piped fin-drain

The water conduit is essentially an open grid system with water passages stacked vertically. This grid system is completely enclosed in a geotextile fabric. The individual lengths are connected and laid vertically in an excavated trench located along the shoulder. See Figures 7 & 8.

Figure 7 –Non-piped Fin-drain Drain Placement

Figure 8- Water Flowing in bottom of Fin-Drain

A fin-drain should be located in an excavated trench as shown in Figure 9 - Recommended Drain Placement in Trenches. Installation of the fin-drain on the shoulder-side of the ditch will allow the sand backfill to completely fill voids in the pavement subgrade resulting from the excavation of the ditch.

Figure 9 - Recommended Drain Placement in Trench Piped fin-drain

Piped fin-drains are manufactured by a number of companies. They consist of a vertical waffle element completely encased in geotextile fabric. The waffle element keeps the geotextile away from the central element thereby providing a flow path for water passing through the geotextile. A drain pipe is attached to the lower end of the fin-drain. This pipe is connected to outlets for disposal of flow. See Figure 10 - Piped Fin-drain Installation.

Figure 10-Piped Fin-drain Installation

The collection pipe used in the piped fin-drain is flexible and corrugated. The fin drain is generally supplied in rolls and the pipe is normally installed in the drain during manufacture. The flexible corrugated pipe used in this design does not have the same structural strength as the solid wall pipe used in the french drain. This corrugated pipe has been a source of installation and maintenance problems (crushing during installation, damage during cleaning, etc.).

Further investigation is required during design to select a product that is both constructible and maintainable (See Figure 11 & 12).

End Treatment for Sub-drain Outlets

All new sub-drain outlets will be designed for scour protection. The proposed treatments include flared end sections and rundowns for the outlets. Typical outlet protection will use CFLHD standard details.

Figure 11- Damaged Ribbed Pipe

Figure 12- Rodent Problem (nesting and plugging)

5.0 PERMANENT BMP DESIGN

Permanent BMP measures are mandated by section 401 of the Clean Water Act, as described in the following quotation:

“The purpose of section 401 of the Clean Water Act is to ensure that federally permitted activities comply with the Act and appropriate state laws. Any applicant for a Federal permit for an activity that could result in a discharge of a pollutant to a state's waters is required to obtain certification from the state where the activity will occur. The state certifies that the materials or pollutants discharged comply with the effluent limitation, water quality standards, and other applicable state laws” (emphasis added) (FHWA, 1999).

Permanent BMP requirements for road projects are regulated in the state of Hawai’i by the Hawai’i Department of Transportation (HDOT). The HDOT Storm Water Permanent Best Management Practices Manual has established categories for exemptions and variances to the requirement for construction of permanent BMP facilities. The following are the applicable sections from that manual:

"2.2.1 Unified Criteria Any project (new or redevelopment) is required to install a permanent BMP(s) for storm water management if it generates equal to or greater than one (1) acre of new permanent impervious surface."

"3.2 Variances The following projects may receive special variances to the permanent BMP requirements:

• Projects which are located within an area with an approved special watershed management plan as approved by HDOT and HDOH; and

• The impervious area created by the project does not exceed six (6) feet in width, is linear in nature such as bike paths, walkways, highway noise barriers etc. and retains the predevelopment drainage patterns."

The need for permanent BMP facilities will be determined as the design proceeds. This item should also be discussed with the National Park staff as the Summit Road traverses sensitive environmental areas.

6.0 CONSTRUCTION SITE BEST MANAGEMENT PRACTICES

Erosion control measures will be used to protect the existing project site from sediment transport during construction. An erosion control plan will be prepared during project development and refined during construction phases. The erosion control plan would be based on FHWA Best Management Practices for Erosion and Sediment Control as well as NPDES requirements.

The erosion control practices would include, but not be limited to:

• Storm drain and culvert inlet protection

• Silt fence

• Erosion control logs

• Vehicle tracking control

7.0 SUMMARY

The information contained in this memorandum is a summary of the applicable criteria from the CFLHD PDDM. Further development of criteria should include confirmation of the design criteria for each category of drainage improvement.

During the design process all criteria will be adhered to by the design consultant. The review process will check adherence to this criteria during the quality assurance/quality control process. Any changes to the design criteria during the design process shall be noted in future memorandums. Both drainage analysis and design work associated with the proposed improvements will be in accordance with the methods, guidelines, and criteria set forth in the Federal Lands Highway PDDM, FHWA HEC and Hydraulic Design Series publications, and FHWA Best Management Practices for Erosion and Sediment Control.

8.0 DRAINAGE REFERENCES

American Society of Civil Engineers, Hydrology Handbook, Second Edition, 1996

County of Maui, Department Of Public Works And Waste Management - County Of Maui - Chapter 4 - Rules For The Design Of Storm Drainage Facilities In The County Of Maui" , 1995.

Federal Lands Highway, Project Development and Design Manual, March 2008

FEMA, Flood Insurance Rate Map, Maui County, Hawaii, 1995

FHWA, Hydraulic Design Series, No. 2, October 2002.

FHWA, HEC No. 14, Hydraulic Design of Energy Dissipators for Culverts and Channels, July 2006

FHWA, Design of Roadside Channels with Flexible Linings Hydraulic Engineering Circular Number 15, Third Edition, September 2005

FHWA, Urban Drainage Design Manual, Third Edition-HEC-22, 2009

FHWA, HDS No. 5, Hydraulic Design of Highway Culverts, September 2005

FHWA, Construction of Pavement Subsurface Drainage Systems (Reference Manual), Office of Pavement Technology. January 3, 2002

U.S. Department of Agriculture, NRCS, Web Soil Survey, Maui County, Hawaii, April

U.S. Weather Bureau, Rainfall-Frequency Atlas of the Hawaiian Islands, Technical Paper No. 43, 1962.

USDOT FHWA, HEC No. 15, Design of Roadside Channels with Flexible Linings, 1988.

USDOT FHWA, HEC No. 5, Hydraulic Design of Highway Culverts, 1985.

FLH, Project Development and Design Manual, 2008.

FHWA, Tetra-Tech, Inc., Stormwater Best Management Practices in an Ultra-Urban Setting: Selection and Monitoring, 1999

HDOT, Highways Division, Storm Water Permanent Best Management Practices Manual - State of Hawaii, 2007

FHWA, Design of Roadside Channels with Flexible Linings Hydraulic Engineering Circular Number 15, Third Edition, September 2005