TECHNICAL_MEMORANDUM_Roadway_Drainage_07_20_15_signed.pdf

TECHNICAL MEMORANDUM ROADWAY DRAINAGE 07_20_15.DOCX 1

T E C H N I C A L M E M O R A N D U M

Don Edwards Bridge Replacement Roadway Hydrologic and Hydraulic Design

Anthony Galardi/CFLHD

Bill Lang, PE/CH2M HILL

PREPARED BY: Douglas P. Stewart, PE/CH2M HILL Robert M. Henderson, PE, QSD/CH2M HILL

DATE: Updated July 20, 2015

PROJECT NUMBER: 485698

This memorandum summarizes the roadway hydrologic and hydraulic design for the Don Edwards Bridge Replacement project, with discussions of updates to the 2003 hydraulics report for the Don Edwards Bridge by PBS&J.

Project Description In 2003, the “Reconnaissance Report and Final Hydraulics Report” (Report) was completed for the replacement of the LaRiviere Marsh Bridge over the Marshlands Road in the Don Edwards National Wildlife Refuge. The Report was prepared for the Central Federal Lands Highway Division (CFLHD) in cooperation with the California Department of Transportation (Caltrans). The Report addressed the bridge replacement design, but did not include adjacent roadway drainage. This memorandum will discuss the hydrology and hydraulics of the adjacent roadway drainage and summarize information that has changed for the bridge design since the 2003 Report was written.

There is an existing paved Harrier Spur Trail that intersects with Marshlands Road just west of the bridge location. Runoff from Marshlands Road currently flows along the edge of the roadway, crosses over the top of the side road, and discharges in the slough. The new design has a V-ditch south of the Marshlands Road that ends in a flat area just before Harrier Spur Trail. Excess runoff from the flat area will overtop the trail road. A culvert was recommended under the trail road to avoid overtopping but this option was eliminated due to environmental concerns and encroachment into the slough.

Hydrology Existing Conditions For existing conditions, runoff begins at a high elevation above Marshlands Road and travels northwest along an unpaved road section until it reaches Marshlands Road. From this point the runoff continues along the south side of Marshlands Road to the south east where it currently overtops the paved side road. The total length of the existing flow path is 660 meters. At the upper elevations, the ground slopes are at approximately 35% and is covered with short grasses. The runoff continues along 3% to 8% sloped flat areas adjacent to the Marshlands Road, which are also covered with short grasses. The existing ditches along the south side of Marshlands Road are a combination of grass and rock with a slope ranging from 1% to 2.5%.

Proposed Conditions The land use for the project area was determined from the existing aerial images for the project area.

PREPARED FOR:

COPY TO:

ROADWAY HYDROLOGIC AND HYDRAULIC DESIGN

2 TECHNICAL MEMORANDUM ROADWAY DRAINAGE 07_20_15.DOCX

Existing hydrology was used to compute the proposed culvert size under the trail road but the option was eliminated. A V-ditch is proposed along the south side of Marshlands Road and upstream of the Harrier Spur Trail that overtops the trail road.

Hydrologic Analysis The design storm for the bridge is the 50-year storm event, based on the 2003 bridge plans and hydraulic analysis. No updates to the hydrology were made.

Hydrology was analyzed for a proposed culvert under the Harrier Spur Trail. The design storm for the trail crossing is the 10-year storm event, based on Caltrans Highway design manual for local roads. Because the watersheds for the project site are small (less than 320 acres), drainage systems are designed using the Rational Method.

The rational formula is: Q = (0.28) * C * i * A

Where: Q = maximum rate of runoff in cubic meters per second (cms)

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

A = basin area in square kilometers

The culvert watershed area is approximately 0.058 square kilometers. Based on the land uses within the watershed and from the aerial map information, the runoff coefficient used is 0.6.

The rainfall is based on the calculated time of concentration of 30 minutes. Based on point precipitation data obtained from the NOAA Atlas 14 website for Volume 6, Version 2 for Freemont, California, the rainfall intensity is 24mm/hr. The resulting 10-year runoff is determined to be 0.23 cms. See Attachments for hydrologic data and calculations.

Hydraulic Analysis Culverts A simplified analysis was used to ensure the culvert provides adequate conveyance for the design storm.

Manning’s Equation was used to determine the full flow capacity of the proposed culvert that was originally recommended under the side roadway. The culvert was assumed to be corrugated steel with a Manning’s n value (roughness coefficient) of 0.024. A 0.6 m diameter culvert was chosen to convey the 10-year runoff with additional capacity to allow for sedimentation. Based on the culvert design and slope, the full flow capacity of the culvert is 0.35 cms. See Attachments for hydraulic data and calculations.

Ditches Ditch grading will start at the beginning of the project at approximate station 10+600.0, 6.98m Lt. and continue south-east to the trail road. The cut backslope between Sta 10+600.0, 6.98m Lt. to Sta 10+503.67, 6.38m Lt. is steeper than 1:3, so, rolled erosion control blanket, Type 4 is recommended along the cut slope.

The longitudinal slope of the proposed V-ditch ranges from 0.36% to 0.76% and the depth is approximately 0.4m. Seeding will be performed within the construction limit including the ditch. Fiber rolls will be added across the ditch as per CFL standard sheet WM157-21.

TECHNICAL MEMORANDUM ROADWAY DRAINAGE 07_20_15.DOCX 3

Updates to 2003 Hydraulics Report Tides Data collected in 2014 from the National Oceanic and Atmospheric Administration (NOAA) Tide Station 9414750, Alameda, San Francisco Bay, California, indicated that there was a 100-year high tide datum increase of approximately 0.02 meters between 2001 data (national tidal datum epoch 1983-2001 = 1.82m) and 2014 data (projected exceedance tidal datum = 1.84m). Based on 2015 data, the 100-year high tide elevation has risen 0.04m since 2001. The 2003 Final Hydraulics Report stated a 100-year high tide of 3.26m, which is above the proposed lowest low chord elevation of the bridge (3.212m). The updated 100-year high tide elevation of 3.30m (3.26m plus 0.04m) would also be above the lowest low chord elevation of the bridge. See data in the Attachments.

Sea Level Rise

Caltrans requested a supplemental sea level rise evaluation to assess the impacts to the bridge due to an anticipated future sea level rise. Using Caltrans guidelines and the National Research Council (NRC, 2012) projections, the seal level rise for the High (A1FI) scenario is 166.4 cm by the year 2100. The projected 100-year water surface elevation of 4.54 m would flood the bridge superstructure, but the roadway would not be overtopped. See the Sea Level Rise Technical Memorandum in the Attachments.

Freeboard In the 2003 report, it stated that the freeboard for the proposed bridge is 0.52 meters, which is less than the minimum 50-year freeboard of 0.60 meters. After the model was updated with the correct size and type of pier, the actual freeboard would have been 0.54 meters. The Plans show a lowest low chord elevation of

3.212 meters. Subtracting the updated 50-year water surface elevation of 2.76 meters from the lowest low chord value reveals a freeboard of 0.45 meters. Based on the prospect of minimal debris, no buoyancy, and no overtopping, the 0.45m freeboard would be acceptable. Caltrans has agreed to this variance from the minimum freeboard requirement.

Geotechnical The “Final Geotechnical Design Report” was completed in April 2014 by the Geotechnical Services Branch of the CFLHD. The 2014 report identified the D50 grain size for the soils at the bridge to be 0.005mm. The 2003 Report used a D50 of 1mm for their scour calculations.

Scour The Don Edwards Bridge Replacement – Scour Analysis updated July 20, 2015 under separate cover, was prepared by CH2M HILL to reevaluate the scour due to cohesive soil conditions, as outlined in the updated Fifth Edition of HEC-18. It was noted that the original HEC-RAS hydraulics model, prepared by PBS&J in 2003, did not accurately reflect the proposed pier width and type, nor did it accurately reflect the proposed low chord elevations. Caltrans requested that the HEC-RAS model be updated to show accurate bridge information for the piers and low chord. CH2M HILL agreed to run the model with the updated information and present the resulting scour impacts. This information is included in the Don Edwards Bridge Replacement Scour Analysis updated July 20, 2015 under separate cover.

4 TECHNICAL MEMORANDUM ROADWAY DRAINAGE 07_20_15.DOCX

Temporary Drainage Systems A temporary culvert will be required to handle the runoff and tidal flows underneath the temporary detour road. The temporary detour is expected to be in operation during the construction of the bridge, which is anticipated to last from September 2016 to April 2017. This culvert will be removed in the ultimate condition. The culvert is designed to convey the 10-year peak flows, in accordance with the “High Standard Road” criteria specified by the PDDM. From the Final Hydraulics Report prepared by PBS&J in 2003, the following hydrologic information was obtained for the slough at the Don Edwards Bridge. English units were used in the 2003 report and will continue to be used for this temporary detour drainage analysis.

Return Period (years) Q (cfs)

2 152 10 381 50 654 100 800 500 1,360

Based on this data, the design flows for the culvert will be 381 cfs, or 10.79 cms.

For this culvert, a downstream hydraulic control is assumed to be the 100-year high tide, elevation 10.70 feet (NAVD 1988) according to the 2003 report.

The following are culvert options that could be used for the crossing assuming full flow and 0.5% slope (n=0.024 for CMP, n=0.013 for RCP):

HIGH STANDARD ROADS

Culvert Quantity Culvert size (in) Culvert type Total Conveyance* (cfs)

4 48 RCP 423

4 48 CMP 323

7 48 CMP 582

3 60 RCP 393

4 60 CMP 418

*Conveyance was estimated using CulvertMaster.

The four barrel 60-inch CMP design is selected to meet the design criteria. A LaRiviere Marsh Tidal Exchange Analysis was performed separately from this capacity analysis to further analyze the effects of temporary culverts on the tidal flow. The results are that the proposed culverts will cause minor damping of the tide, but still allow the higher high tides to inundate the marsh plain north of the bridge and would not adversely impact the water levels on the downstream side of the bridge. Refer to the LaRiviere Tidal Marsh and Don Edwards Bridge Tidal Exchange Analysis technical memorandum dated August 21, 2014 under separate cover for more details on the tidal analysis.

TECHNICAL MEMORANDUM ROADWAY DRAINAGE 07_20_15.DOCX 5

References

1. Don Edwards National Wildlife Refuge Bridge Hydrology and Hydraulics CA RRP DOED 10(1) Reconnaissance Report and Final Hydraulics Report for U.S. Department of Transportation, Federal Highway Administration, Central Federal Lands Highway Division, Denver, Colorado; by PBS&J; Dated January 2003.

Appendix G includes Scour Calculations.

2. NOAA Atlas 14, Volume 6, Version 2 http://hdsc.nws.noaa.gov/hdsc/pfds/pfds_map_cont.html?bkmrk=ca

3. Federal Highway Administration, 2014 “Federal Lands Highway Project Development and Design Manual “, U.S Department of Transportation, Washington, DC

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

5. Bentley Systems, Inc. CulvertMaster, version 3.3

6. Caltrans Highway Design Manual

WW

WW

WW

STOP

STOP

STOP

GUY POLE

W

CULVERTS

CULVERT

OBSCURE

AREA

OBSCURE

AREA

OBSCURE

AREA

OBSCURE

AREA

OBSCURE

AREA

OBSCURE

AREA

OBSCURE

AREA

OBSCURE

AREA

OBSCURE

AREA

OBSCURE

AREA

WATER

WATER

U T

IL

IT

Y

CL

10 10

CENTRAL FEDERAL LANDS HIGHWAY DIVISION

FEDERAL HIGHWAY ADMINISTRATION

U.S. DEPARTMENT OF TRANSPORTATION

METRIC DETAIL

STATE PROJECT

NO.

SHEET

SHEETS

TOTAL

REG

DETAIL

REVISED:

CENTRAL FEDERAL LANDS HIGHWAY DIVISION

FEDERAL HIGHWAY ADMINISTRATION

U.S. DEPARTMENT OF TRANSPORTATION

CA1 FTFW/FLAP DOED 10(3)

S

L m

80400

Scale in Meters

LEGEND

S .6

L = m

S

L = m

Area:14.3724 ac

Area:58163.0260 sq m

SEEDING

FIBER ROLLS

LIMITS OF DISTURBANCE

FLOW ARROW

DRAINAGE AREA

DRAINAGE BASIN MAP

DON EDWARDS

skarmach Rectangle

810-10 HIGHWAY DESIGN MANUAL

June 26, 2006 drainage facilities, it is occasionally used in the hydrologic analysis for other design parameters.

Information on flood hydrographs and methods to estimate the hydrograph may be found in Chapters

6, 7 and 8 of HDS No. 2, Hydrology.

Figure 816.5

Typical Flood Hydrograph

816.6 Time of Concentration (Tc) and

Travel Time (Tt)

Time of concentration is defined as the time required for storm runoff to travel from the hydraulically most remote point of the drainage basin to the point of interest.

An assumption made in some of the hydrologic methods for estimating peak discharge, such as the

Rational and NRCS Methods (Index 819.2), is that maximum flow results when rainfall of uniform intensity falls over the entire watershed area and the duration of that rainfall is equal to the time of concentration. Time of concentration (TC) is typically the cumulative sum of three travel times, including:

Sheet flow

Shallow concentrated flow

Channel flow

For all-paved watersheds (e.g., parking lots, roadway travel lanes and shoulders, etc.) it is not necessary to calculate a separate shallow concentrated flow travel time segment. Such flows will typically transition directly from sheet flow to channel flow or be intercepted at inlets with either no, or inconsequential lengths of, shallow concentrated flow.

In many cases a minimum time of concentration will have to be assumed as extremely short travel times will lead to calculated rainfall intensities that are overly conservative for design purposes. For all-paved areas it is recommended that a minimum time of concentration of 5 minutes be used. For rural or undeveloped areas, it is recommended that a minimum TC of 10 minutes be used for most situations. However, for slopes steeper than

1V:10H, or where there is limited opportunity for surface storage, a TC of 5 minutes should be assumed.

Designers should be aware that maximum runoff estimates are not always obtained using rainfall intensities determined by the time of concentration for the total area. Peak runoff estimates may be obtained by applying higher rainfall intensities from storms of short duration over a portion of the watershed.

(1) Sheet flow travel time. Sheet flow is flow of uniform depth over plane surfaces and usually occurs for some distance after rain falls on the ground. The maximum flow depth is usually less than 20 - 30 mm. For unpaved areas, sheet flow normally exists for a distance less than

25 – 30 m. An upper limit of 91 m is recommended for paved areas.

A common method to estimate the travel time of sheet flow is based on kinematic wave theory and uses the Kinematic Wave Equation:

6.92 L n

Tt = i S

3/5 3/5

2/5 3/10 where

Tt = travel time in minutes.

L = Length of flow path in meters.

S = Slope of flow in m/m.

HIGHWAY DESIGN MANUAL 810-11

July 1, 2008 n = Manning's roughness coefficient for sheet flow (see Table 816.6A).

i = Design storm rainfall intensity in mm/h.

If Tt is used (as part of TC) to determine the intensity of the design storm from the IDF curves, application of the Kinematic Wave

Equation becomes an iterative process: an assumed value of Tt is used to determine i from the IDF curve; then the equation is used to calculate a new value of Tt which in turn yields an updated i. The process is repeated until the calculated Tt is the same in two successive iterations.

To eliminate the iterations, use the following simplified form of the Manning’s kinematic solution:

5.476 L4/5 n4/5

Tt = _________________

P2 1/2

S 2/5 where P2 is the 2-year, 24-hour rainfall depth in mm (ref. NOAA Atlas 2, Volume XI or use either of the following web site addresses;

http://www.wrcc.dri.edu/pcpnfreq.html or, http://www.nws.noaa.gov/oh/hdsc/noaaatlas2.htm).

The use of flow length alone as a limiting factor for the Kinematic wave equation can lead to circumstances where the underlying assumptions are no longer valid. Over prediction of travel time can occur for conditions with significant amounts of depression storage, where there is high

Manning’s n-values or for flat slopes. One study suggests that the upper limit of applicability of the Kinematic wave equation is a function of flow length, slope and Manning’s roughness coefficient. This study used both field and laboratory data to propose an upper limit of 100 for the composite parameter of nL/s1/2. It is recommended that this criteria be used as a check where the designer has uncertainty on the maximum flow length to which the Kinematic wave equation can be applied to project conditions.

Where sheet flow travel distance cannot be determined, a conservative alternative is to assume shallow concentrated flow conditions without an independent sheet flow travel time conditions. See Index 816.6(2).

Table 816.6A

Roughness Coefficients For Sheet

Flow

Surface Description n

Hot Mix Asphalt 0.011-

0.016

Concrete 0.012-

0.014

Brick with cement mortar 0.014

Cement rubble 0.024

Fallow (no residue) 0.05 Grass

Short grass prairie

Dense grass

Bermuda Grass

0.15

0.24

0.41 Woods(1)

Light underbrush

Dense underbrush 0.40

0.80

(1) Woods cover is considered up to a height of 30 mm, which is the maximum depth obstructing sheet flow.

(2) Shallow concentrated flow travel time. After short distances, sheet flow tends to concentrate in rills and gullies, or the depth exceeds the range where use of the Kinematic wave equation applies. At that point the flow becomes defined as shallow concentrated flow.

The Upland Method is commonly used when calculating flow velocity for shallow concentrated flow. This method may also be used to calculate the total travel time for both the sheet flow and the shallow concentrated flow segments under certain conditions (e.g., where use of the Kinematic wave equation to predict sheet flow travel time is questionable, or where the designer cannot reasonably identify the point where sheet flow transitions to shallow concentrated flow).

810-12 HIGHWAY DESIGN MANUAL

Average velocities for the Upland Method can be taken directly from Figure 816.6 or may be calculated from the following equation:

V = kS1/2

Where S is the slope in percent and k (m/s) is an intercept coefficient depending on land cover as shown in Table 816.6B.

Table 816.6B

Intercept Coefficients for Shallow

Concentrated Flow

Land cover/Flow regime K

(m/s)

Forest with heavy ground litter; hay meadow

0.076

Trash fallow or minimum tillage cultivation; contour or strip cropped;

woodland

0.152

Short grass pasture 0.213

Cultivated straight row 0.274

Nearly bare and untilled alluvial fans 0.305

Grassed waterway 0.457

The travel time can be calculated from:

V 60

L T !t where Tt is the travel time in minutes, L the length in m, and V the flow velocity in m/s.

(3) Channel flow travel time. When the channel characteristics and geometry are known the preferred method of estimating channel flow time is to divide the channel length by the channel velocity obtained by using the

Manning equation, assuming bankfull conditions. See Index 864.3, Open Channel

Flow Equations for further discussion of

Manning's equation.

Appropriate values for "n", the coefficient of roughness in the Manning equation, may be found in most hydrology or hydraulics text and reference books. Table 864.3A gives some "n" values for lined and unlined channels, gutters, and medians. Procedures for selecting an appropriate hydraulic roughness coefficient may be found in the FHWA report, "Guide for

Selecting Manning's Roughness Coefficient for

Natural Channels and Flood Plains".

Generally, the channel roughness factor will be much lower than the values for overland flow with similar surface appearance.

Culvert or Storm Drain Flow. Flow velocities in a short culvert are generally higher than they would be in the same length of natural channel and comparable to those in a lined channel. In most cases, including short runs of culvert in the channel, flow time calculation will not materially affect the overall time of concentration (Tc). When it is appropriate to separate flow time calculations, such as for urban storm drains, Manning's equation may be used to obtain flow velocities within pipes.

The TR-55 library of equations for sheet flow, shallow concentrated flow and open channel flow is incorporated into the Watershed

Modeling System (WMS) for Time of

Concentration Calculations using Triangulated

Irregular Networks (TINs) and Digital

Elevation Maps (DEMs).

skarmach Rectangle

HIGHWAY DESIGN MANUAL 810-13

Figure 816.6

Velocities for Upland Method of

Estimating Travel Time for Shallow Concentrated Flow

Don Edwards

Side Road Culvert Analysis

By: Doug Stewart, PE

Date: 9/12/14

Hydrology ‐ Rational Method Hydraulics ‐ Manning's Equation

Q = 0.28*C*i*A Q = (1.0/n)*A*R2/3*S1/2

Q = Runoff in (cms) Q = Runoff in (cms)

C = Runoff coefficient n = Roughness coefficient i = Intensity in mm/hr A = Area in (m2)

A = Area in (km2) R = Hydraulic Radius in (m) R = A/Pw

Pw = Wetted Perimeter in (m)

S = Slope in (m/m)

Tc = Time of Concentration in min.

Metric Units Metric Units

Evaluate Hydrology for 10‐year event Evaluate culvert hydraulics based on full flow

Q = 0.234513 cms Q = 0.34697 cms

C = 0.6 from GoogleEarth n = 0.024 i = 24 mm/hr from NOAA Atlas 14 A = 0.291863 m2 d = 0.6096 m

A = 0.058163 km2 from microstation R = 0.1524 m

Pw = 1.915113 m

S = 0.01 m/m tc = 30 min (see below)

Time of Concentration

Overland

Tt = 5.476 * L4/5 * n4/5

P21/2 * S2/5

Tt = Travel time in (min.) Tt = 13.80174 min.

L = Length of flow path in (m) L = 100 m

S = Slope of flow in m/m S = 0.35 m/m n = Manning's roughness coefficient for sheet flow n = 0.2

P2 = 2‐year, 24‐hour rainfall depth in (mm) P2 = 44 mm NOAA Atlas 14

Shallow Concentrated

Tt = L

60 * V

Tt = Travel time in (min.) Tt = 18.07043096 min.

L = Length in (m) L = 400 m

V = Velocity in (m/s) V = 0.368926822 m/s

V = k * S 1/2 V = 0.368926822 m/s k = intercept coefficient depending on land cover in (m/s) k = 0.213 Table 816.6B Caltrans

S = slope in % S = 3 %

Open Channel Flow

V = R2/3*S1/2 n

Side Slope (z:1) = 4

Depth (d) = 0.33 m

Area (A) = 0.4356 sm

Pw = 1.360625 m

R = 0.320147 m

S = 0.0167 m/m n = 0.1

V = 0.604771 m/s

L = 160 m t = 4.40938 min

Total Time of Concentration = 36.28155 min.

use 30 min.

Culvert Calculator Report 60-inch RCP

Title: Don Edwards Temporary Crossing ...\4 design\culvertmaster\project1_10-03-2014.cvm

10/03/14 02:37:57 PM

CH2M Hill - United States © Bentley Systems, Inc. Haestad Methods Solution Center Watertown, CT 06795 USA +1-203-755-1666

Project Engineer: dstewar1 CulvertMaster v3.3 [03.03.00.04]

Solve For: Headwater Elevation

Culvert Summary

Allowable HW Elevation 6.00 ft Headwater Depth/Height 0.98

Computed Headwater Eleva 5.90 ft Discharge 381.00 cfs

Inlet Control HW Elev. 5.80 ft Tailwater Elevation 3.00 ft

Outlet Control HW Elev. 5.90 ft Control Type Entrance Control

Grades

Upstream Invert 1.00 ft Downstream Invert 0.80 ft

Length 40.00 ft Constructed Slope 0.005000 ft/ft

Hydraulic Profile

Profile S2 Depth, Downstream 3.08 ft

Slope Type Steep Normal Depth 3.05 ft

Flow Regime Supercritical Critical Depth 3.22 ft

Velocity Downstream 9.99 ft/s Critical Slope 0.004253 ft/ft

Section

Section Shape Circular Mannings Coefficient 0.013

Section Material Concrete Span 5.00 ft

Section Size 60 inch Rise 5.00 ft

Number Sections 3

Outlet Control Properties

Outlet Control HW Elev. 5.90 ft Upstream Velocity Head 1.40 ft

Ke 0.20 Entrance Loss 0.28 ft

Inlet Control Properties

Inlet Control HW Elev. 5.80 ft Flow Control Unsubmerged

Inlet Type Groove end projecting Area Full 58.9 ft²

K 0.00450 HDS 5 Chart 1

M 2.00000 HDS 5 Scale 3

C 0.03170 Equation Form 1

Y 0.69000

60-inch RCP

Title: Don Edwards Temporary Crossing ...\4 design\culvertmaster\project1_10-03-2014.cvm

10/03/14 02:39:16 PM

CH2M Hill - United States © Bentley Systems, Inc. Haestad Methods Solution Center Watertown, CT 06795 USA +1-203-755-1666

Project Engineer: dstewar1 CulvertMaster v3.3 [03.03.00.04]

Solve For: Discharge

Culvert Summary

Allowable HW Elevation 6.00 ft Headwater Depth/Height 1.00

Computed Headwater Eleva 6.00 ft Discharge 393.31 cfs

Inlet Control HW Elev. 5.90 ft Tailwater Elevation 3.00 ft

Outlet Control HW Elev. 6.00 ft Control Type Entrance Control

Grades

Upstream Invert 1.00 ft Downstream Invert 0.80 ft

Length 40.00 ft Constructed Slope 0.005000 ft/ft

Hydraulic Profile

Profile S2 Depth, Downstream 3.15 ft

Slope Type Steep Normal Depth 3.12 ft

Flow Regime Supercritical Critical Depth 3.28 ft

Velocity Downstream 10.08 ft/s Critical Slope 0.004324 ft/ft

Section

Section Shape Circular Mannings Coefficient 0.013

Section Material Concrete Span 5.00 ft

Section Size 60 inch Rise 5.00 ft

Number Sections 3

Outlet Control Properties

Outlet Control HW Elev. 6.00 ft Upstream Velocity Head 1.44 ft

Ke 0.20 Entrance Loss 0.29 ft

Inlet Control Properties

Inlet Control HW Elev. 5.90 ft Flow Control Unsubmerged

Inlet Type Groove end projecting Area Full 58.9 ft²

K 0.00450 HDS 5 Chart 1

M 2.00000 HDS 5 Scale 3

C 0.03170 Equation Form 1

Y 0.69000

60-inch CMP

Title: Don Edwards Temporary Crossing ...\4 design\culvertmaster\project1_10-03-2014.cvm

10/03/14 02:34:53 PM

CH2M Hill - United States © Bentley Systems, Inc. Haestad Methods Solution Center Watertown, CT 06795 USA +1-203-755-1666

Project Engineer: dstewar1 CulvertMaster v3.3 [03.03.00.04]

Solve For: Headwater Elevation

Culvert Summary

Allowable HW Elevation 6.00 ft Headwater Depth/Height 0.94

Computed Headwater Eleva 5.72 ft Discharge 381.00 cfs

Inlet Control HW Elev. 5.43 ft Tailwater Elevation 3.00 ft

Outlet Control HW Elev. 5.72 ft Control Type Outlet Control

Grades

Upstream Invert 1.00 ft Downstream Invert 0.80 ft

Length 40.00 ft Constructed Slope 0.005000 ft/ft

Hydraulic Profile

Profile M2 Depth, Downstream 2.78 ft

Slope Type Mild Normal Depth 3.91 ft

Flow Regime Subcritical Critical Depth 2.78 ft

Velocity Downstream 8.51 ft/s Critical Slope 0.012905 ft/ft

Section

Section Shape Circular Mannings Coefficient 0.024

Section Material CMP Span 5.00 ft

Section Size 60 inch Rise 5.00 ft

Number Sections 4

Outlet Control Properties

Outlet Control HW Elev. 5.72 ft Upstream Velocity Head 0.74 ft

Ke 0.90 Entrance Loss 0.66 ft

Inlet Control Properties

Inlet Control HW Elev. 5.43 ft Flow Control Unsubmerged

Inlet Type Projecting Area Full 78.5 ft²

K 0.03400 HDS 5 Chart 2

M 1.50000 HDS 5 Scale 3

C 0.05530 Equation Form 1

Y 0.54000

60-inch CMP

Title: Don Edwards Temporary Crossing ...\4 design\culvertmaster\project1_10-03-2014.cvm

10/03/14 02:35:53 PM

CH2M Hill - United States © Bentley Systems, Inc. Haestad Methods Solution Center Watertown, CT 06795 USA +1-203-755-1666

Project Engineer: dstewar1 CulvertMaster v3.3 [03.03.00.04]

Solve For: Discharge

Culvert Summary

Allowable HW Elevation 6.00 ft Headwater Depth/Height 1.00

Computed Headwater Eleva 6.00 ft Discharge 418.46 cfs

Inlet Control HW Elev. 5.73 ft Tailwater Elevation 3.00 ft

Outlet Control HW Elev. 6.00 ft Control Type Outlet Control

Grades

Upstream Invert 1.00 ft Downstream Invert 0.80 ft

Length 40.00 ft Constructed Slope 0.005000 ft/ft

Hydraulic Profile

Profile M2 Depth, Downstream 2.91 ft

Slope Type Mild Normal Depth 4.36 ft

Flow Regime Subcritical Critical Depth 2.91 ft

Velocity Downstream 8.80 ft/s Critical Slope 0.013321 ft/ft

Section

Section Shape Circular Mannings Coefficient 0.024

Section Material CMP Span 5.00 ft

Section Size 60 inch Rise 5.00 ft

Number Sections 4

Outlet Control Properties

Outlet Control HW Elev. 6.00 ft Upstream Velocity Head 0.78 ft

Ke 0.90 Entrance Loss 0.71 ft

Inlet Control Properties

Inlet Control HW Elev. 5.73 ft Flow Control Unsubmerged

Inlet Type Projecting Area Full 78.5 ft²

K 0.03400 HDS 5 Chart 2

M 1.50000 HDS 5 Scale 3

C 0.05530 Equation Form 1

Y 0.54000

T E C H N I C A L M E M O R A N D U M

Don Edwards - Sea Level Rise

James Herlyck/CFLHD

Ed Henderson, PE/CH2M HILL

PREPARED BY: Douglas P. Stewart, PE/CH2M HILL Robert Henderson, PE/CH2M HILL Martin Merklinger, PE/Rocksol

DATE: July 20, 2015

PROJECT NUMBER: 485698

Sea Level Rise Evaluation The California Department of Transportation (Caltrans) requested an evaluation of the projected Sea Level Rise (SLR) in the vicinity of the proposed Don Edwards Bridge replacement project in accordance with its Guidance on Incorporating Sea Level Rise (Caltrans, 2011). Because the structure is a bridge, a 75-year life time shall be considered.

Proposed Bridge The soffit elevations of the proposed bridge vary due to longitudinal roadway slope and super elevated cross slope. The lowest soffit elevation is 3.21 meters NAVD88. The lowest overtopping elevation at the bridge is

4.85 meters NAVD88. Additional details of the bridge design can be found in CH2M HILL (2015).

100-year Water Surface Elevation A HEC-RAS model was used to compute a 100-year water surface elevation of 2.88 meters NAVD88 at the bridge location for the current sea level (PBS&J, 2003). This elevation is in the range of those computed by earlier studies for San Francisco Bay, including: Moffatt & Nichol (2008) (2.96 meters MLLW); PWA (2006) (2.84 meters MLLW); and USACE (1984) (2.97 meters MLLW). This value is considered adequate for this assessment. In San Francisco Bay, NAVD88 is 0.07 meters above MLLW (according to the NOAA Alameda tide gage 9752695), so to reference the MLLW elevations to NAVD88, 0.07 meters needs to be subtracted from the MLLW elevations.

Sea Level Rise Per the Caltrans (2011) guidelines, the National Research Council (NRC, 2012) SLR projections should be used to assess the impact of SLR on State projects. The SLR projection value is added to the design water level (i.e. the 100-year water surface elevation for the current sea level) to estimate the water surface elevation for the proposed structure in SLR scenarios due to climate change. Table 1 shows the SLR projections produced by the NRC (2012) for San Francisco referenced to the year 2000 for low (B1), Medium (A1B) and high (A1FI) scenarios and years 2030, 2050, and 2100. The projections are based on ice loss rates for glaciers, and ice caps except Alaska, Greenland, and Antarctica. For new Bridge design with a 75-year design life, the high (A1F1) is appropriate to evaluate flooding impacts at the Bridge (NRC, 2012). The NRC projection for SLR is 1.66 meters.

PREPARED FOR:

COPY TO:

DON EDWARDS - SEA LEVEL RISE

Table 1 – SLR Projection by the NRC (2012) for San Francisco Bay.

SLR Comparison While Caltrans’ guidelines require SLR evaluation using the NRC projections, at Caltrans’ request, an alternative methodology is also used to provide background information and comparison. The USACE Sea- Level Change Curve Calculator (version 2014.88) located at http://www.corpsclimate.us/ccaceslcurves.cfm was used to estimate the SLR at the Don Edwards Bridge. The resulting USACE SLR estimate is 154 cm, or approximately 12 cm less than the NRC projection.

Summary of Sea Level Rise A bridge is a large monolithic structure with limited or no capacity to adapt to SLR. If the bridge is constructed in 2015, its design life (75 years) would extend to 2090, making the Year 2100 SLR estimates the most relevant. For both NRC (2012) and the USACE Curve Calculator, the HIGH scenario is recommended for bridges.

The SLR projection of 166.4 cm (1.664 meters) was added to the 100-year design water surface elevation of

2.88 meters NAVD88 to obtain a 100-year water surface elevation of 4.54 meters NAVD88 in a high A1FI NRC (2012) SLR scenario in the year 2100. The overtopping elevation of the proposed bridge is 4.85m NAVD88 and the low chord elevation is 3.21m NAVD88. During large storm events, the bridge superstructure would be flooded but the roadway would not be overtopped.

Bridge Impacts due to Sea Level Rise The bridge configuration at the beginning of its design life, will have the bridge components and low chord elevation above the normal water surface and above the 50-year design water surface elevation. During the 75-year design life of the bridge, the potential Sea Level Rise could result in water against the side of the bridge. The magnitude of the water depth against the side of the bridge is from the Sea Level Rise, and from the 50-year design water surface elevation. If a 50-year flow event occurs near the end of the bridge design life, both the Sea Level Rise and the 50-year design water would combine for the maximum water elevation against the side of the bridge; the maximum height of water against the side of the bridge is about 0.9 meters of the 1.2 meter superstructure depth. For the majority of time when a 50-year flow event is not occurring, the height of water against the side of the bridge would be due to the Sea Level Rise only; the height of water against the side of the bridge would be zero meters, since the potential Sea Level Rise would be at approximately the bridge low chord elevation.

The bridge was evaluated for various considerations due to Sea Level Rise:

a. Stability of the superstructure from lateral loads. Lateral loads from water against the side of the superstructure are smaller magnitude than lateral loads from seismic events. The bridge superstructure is designed to remain on the substructure elements during seismic events. By comparison, lateral loads from water against the side of the superstructure during the 50-year design event and after Sea Level Rise, would be a less controlling lateral loading, and will result in continued stability of the superstructure.

b. Stability of the superstructure from buoyancy. Air between girders would generate a small buoyant force for the condition of maximum water depth against the side of the superstructure. The magnitude of the buoyant force is significantly less than the dead load of the superstructure. The buoyant force will not overcome the dead load of the superstructure at the abutments, resulting in continued stability of the superstructure on the abutments. The buoyant force will not overcome the vertical connection capacity of the superstructure-to-pier connection, or the dead load of the superstructure at the piers, resulting in continued stability of the superstructure on the piers.

c. Stability of piers and abutments from lateral loads. Lateral loads from water against the side of the piers and abutments are smaller magnitude than lateral loads from seismic events. The bridge piers and abutments are designed for adequate seismic behavior (strength and ductility displacement), and will continue to support the superstructure on the substructure elements during seismic events.

By comparison, lateral loads from water against the piers and abutments during the 50-year design event and after Sea Level Rise, would be a less controlling lateral loading, and will result in continued stability of the bridge.

d. Stability of piers and abutments due to scour. Calculated scour depths at piers and abutments are less than the depth of liquefaction during a major seismic event. The bridge piers and abutments have been designed for adequate seismic behavior (strength and ductility displacement), and will continue to support the superstructure on the substructure elements during seismic events. By comparison, depth of scour, and corresponding loss of lateral support due to scour, is a less controlling condition than depth of liquefaction, and corresponding loss of lateral support due to liquefaction. In addition, riprap scour protection will reduce the magnitude of the scour depth.

e. Strength and behavior of girders due to lateral loads. Lateral loads from water against the side of the superstructure girders will apply lateral loads to girders. Girder webs have adequate flexural and shear capacity to resist lateral loads due to water on girder bottom flanges and webs. Girder bottom flanges are stiffer components than webs, and have adequate strength and stiffness to resist the lateral water loads between points of lateral support (piers, abutments, intermediate diaphragms).

The deck provides significant lateral stiffness at the top of the girders, and pier, abutment and intermediate diaphragms provide lateral support to along the depth of the girders. The girder length between points of lateral support is small, and stiffness and strength are larger than the applied lateral water loads.

f. Resiliency of bridge concrete and steel components. Water against the side of the bridge superstructure, which could occur during a 50-year flow event toward the end of the bridge 75-year design life, could cause deterioration of reinforced concrete and prestressed concrete components.

Water against the piers and abutments, which could occur toward the end of the bridge 75-year design life, could cause deterioration of reinforced concrete and prestressed concrete components.

Prestressed concrete piles have corrosion resistance in the form of epoxy coated prestress strand and Type V cement. Piers, abutments, and superstructure diaphragms have corrosion resistance in the form of epoxy coated reinforcement and design that conforms to service limit states (reinforcement well distributed to minimize crack width). Prestressed concrete girders have significant prestress strand that provides strength and limits applied stresses. Each of these corrosion resistances will help the bridge components last until the end of the 75-year design life, when the water against the side of the bridge could cause deterioration of components.

Summary Bridge Impacts due to Sea Level Rise The SLR in Year 2100 is 166.4 cm based on the NRC projections. This value is slightly greater than the USACE Curve Calculator. For new Bridge design, the High (A1F1) scenario is appropriate to evaluate flooding impacts at the Bridge (NRC, 2012). The resulting 100-year water surface elevation at the Bridge would be

4.54 meters, which would be above the minimum bridge soffit but would not overtop the structure.

While the timeframe for this bridge is long, the adaptive capacity of a bridge to SLR is low. However, the costs of raising the bridge and connecting roads to accommodate SLR are prohibitively high. The consequences of impacts due to flooding are low because elevated waters would impact the bridge with very low probability. Furthermore, the facility is a low-volume bridge that provides non-critical access to the refuge, the Cargill property and the US Fish and Wildlife visitor’s center. Most of the refuge and the Cargill property would be submerged, while the visitor’s center would be above the projected 100-year water surface elevation. A raised bridge and infrastructure is not considered feasible for the risk level involved.

References

CH2M HILL (2015). La Riviere Marsh Bridge and Marshlands Road Plan.

PBS&J (2003). Don Edwards National Wildlife Refuge Bridge Hydrology and Hydraulics Reconnaissance Report and Final Hydraulics Report. January 2003.

Caltrans (2011). Guidance on Incorporating Sea Level Rise For Use in the Planning and Development of Project Initiation Documents. May 16, 2011.

Moffatt & Nichol (2008). Report on Maintenance Dredging Needs, San Leandro Marina. January 2008.

National Research Council (2012). Sea-Level Rise for the Coasts of California, Oregon, and Washington: Past, Present, and Future. Committee on Sea Level Rise in California, Oregon, and Washington;

Board on Earth Sciences and Resources; Ocean Studies Board; Division on Earth and Life Studies.

Phil Williams & Associates, Ltd. (2006). South Bay Salt Pond Restoration Project. Flood Analyses Report. July 2006 – Revised.

U.S. Army Corps of Engineers (1984). San Francisco Bay: Tidal Stage vs. Frequency Study. San Francisco District.

USACE Sea Level Change Curve Calculator, http://www.corpsclimate.us/ccaceslcurves.cfm/