Financial Impact to Flood Control Projects using 1-D and 2-D Modelling Methods in South San Francisco Bay

Flood Plain Management Association

September 6, 2018

Presented by:

Matt Powers, PE – GEI Consultants

Rohin Saleh, PE - Alameda County Flood Control District

Alameda County Flood Control and Water Conservation District

Mission: Support public safety, health, and welfare of residents and businesses in Alameda County

Flood Control District established in 1949

10 zones based loosely on watersheds

Western Alameda County:  EB Hills to Bay

Project Purpose

• Evaluate ability to maintain flood protection for the 1% Annual Exceedance Probability (1% AEP) coastal event– Impact of 1D and 2D approaches– What is cost of system improvements?

Study Overview• Evaluate coastal flooding scenarios and extents (1‐D and 2‐D)

• Identify existing flood protection alignments in study area

• Assess the current conditions and suitability for flood protection 

• Develop planning level design and construction cost estimates– Protection for 1% AEP coastal event

• Results inform comprehensive flood protection strategy– Consider planned SBSPRP restoration

Eden Landing Site

Alameda Creek FCC

Old Alameda Creek

Eden Landing North

Eden Landing South

Site History• Pre‐European ‐ extensive tidal marsh

• 1850’s on: solar salt works

• Early 2000’s: Acquired for wetlands restoration 

Eden Landing RestorationEden Landing North

Eden Landing Ecological Reserve (~2008)• North Creek and Mt. Eden Creek 

breaches• Tidal and muted tidal connection

SBSPRP Phase 1 Improvements (2013)• Numerous breaches, levee construction• Tidal and managed ponds

Eden Landing South

Following Acquisition (2000’s)• Improvements to water control 

structures

SBSPRP Phase 2 Improvements• Restoration planning and permitting 

in progress

Updated Topographic Model• Composite DEM for Eden Landing from best available sources

– SFEI LIDAR, 2004– Sanborn LIDAR, 2006– USGS LIDAR, 2010– USACE LIDAR, 2012– DHI Composite DEM, 2016– QSI LIDAR and bathymetric transects, 2016– Wood Rodgers, Inc. field transects, 2016

Hydraulic Evaluations• Evaluate coastal flood impacts from 1% EAP tidal event

– Maximum tide: El. 10.5’ NAVD88

• Compare inundation extents using 1‐D and 2‐D methodologies– Current site conditions

• EL North: includes completed restoration• EL South: no significant restoration

– 1‐D analysis: proposed FEMA FIRM mapping– 2‐D analysis: completed during this study

Existing Flood Control Features• Existing condition assessment

– Site reconnaissance and mapping– Evaluation of as‐built records

• Identify Potential Flood Protection Levee Alignments– Consider completed and planned restoration– North complex – one identified alignment– South Complex – three identified alignments

Existing Flood Control Features

• Identified Flood Protection Levee Alignments– North complex alignment (1)

Existing Flood Control Features

• Identified Flood Protection Levee Alignments– South complex alignments (3)

Project Determination• Comparison of flood levels to existing flood protection features

– 1‐D and 2‐D flood extents

Project Determination• Comparison of flood levels to existing flood protection features

– Determine need for system improvements

Project Determination• Comparison of flood levels to existing flood protection features

– Determine need for system improvements

Project Determination• Comparison of flood levels to existing flood protection features

– Determine need for system improvements

High Ground

High Ground

Project Determination• Comparison of flood levels to existing flood protection features

– Determine need for system improvements

Project Determination• Comparison of flood levels to existing flood protection features

– Determine need for system improvements– Significant improvements? (Project / No Project)

Project Determination Criteria Project / No Project

Levee Contains Flood and Meets Required Freeboard (Coastal levees - 2 feet) No Project

Landside Ground Surface Elevation Greater Than Flood Elevation No Project

Existing Levee Not Certifiable Project

Levee Contains Flood but Does Not Meet Required Freeboard Project

Flood Elevation Greater Than Crest and Landside Elevation (Levee Overtopped) Project

Project Determination• Comparison of flood levels to existing flood protection features

– North Complex Alignment 1 (4.4 miles)

Project Determination Criteria

North Complex Alignment 1

2-D Analysis 1% AEP Coastal Flood Level

1-D Analysis 1% AEP Coastal Flood Level

Levee Meets Required Freeboard 4.4 mi(Entire Alignment)

0.5 mi

Landside Elevation Greater Than Flood Elevation None 0.2 mi

Existing Levee Not Certifiable None None

Levee Does Not Meet Required Freeboard None None

Flood Elevation Greater Than Crest and Landside Elevation None 3.7 mi

Project Determination• Comparison of flood levels to existing flood protection features

– South Complex Alignment 1 (3.3 miles)

Project Determination Criteria

South Complex Alignment 1

2-D Analysis 1% AEP Coastal Flood Level

1-D Analysis 1% AEP Coastal Flood Level

Levee Meets Required Freeboard None None

Landside Elevation Greater Than Flood Elevation None None

Existing Levee Not Certifiable 1.6 mi 0.1 mi

Levee Does Not Meet Required Freeboard 0.7 mi 0.2 mi

Flood Elevation Greater Than Crest and Landside Elevation 1.0 mi 3.0 mi

Project Determination• Comparison of flood levels to existing flood protection features

– South Complex Alignment 2 (1.2 miles)

Project Determination Criteria

South Complex Alignment 2

2-D Analysis 1% AEP Coastal Flood Level

1-D Analysis 1% AEP Coastal Flood Level

Levee Meets Required Freeboard None None

Landside Elevation Greater Than Flood Elevation None None

Existing Levee Not Certifiable 0.5 mi None

Levee Does Not Meet Required Freeboard 0.4 mi None

Flood Elevation Greater Than Crest and Landside Elevation 0.3 mi 1.2 mi(Entire Alignment)

Project Determination• Comparison of flood levels to existing flood protection features

– South Complex Alignment 3 (3.6 miles)

Project Determination Criteria

South Complex Alignment 3

2-D Analysis 1% AEP Coastal Flood Level

1-D Analysis 1% AEP Coastal Flood Level

Levee Meets Required Freeboard None None

Landside Elevation Greater Than Flood Elevation None None

Existing Levee Not Certifiable 0.8 mi None

Levee Does Not Meet Required Freeboard 2.8 mi None

Flood Elevation Greater Than Crest and Landside Elevation None 3.6 mi(Entire Alignment)

Conceptual Levee Improvements

• Levee Design Criteria– Freeboard: 2 feet for coastal levee– Cross Section: 

• WS slope 5 to 1• LS slope 3 to 1• Crest width 18’ (allow future raise)

– Erosion Protection – vegetated slopes– Stability and under seepage 

• USACE levee stability FS criteria

– Settlement: Bay Mud foundation– Consider suitable fill material and  

construction approach

Construction Approach

Strip and excavate existing levee(north alignment ‐ partial degrade only)

Place geogrid and construct equipment corridor

Build levee embankment

Cost of Improvements• Conceptual cost estimates for construction

– 2017 cost basis– Base construction, non‐construction project costs

Non‐Construction Costs• Design engineering• CM and engineering during 

construction• Environmental compliance / 

permitting• Environmental mitigation• Legal / owner administration• Project contingency

Base Construction Costs• Mobilization / demobilization• Levee degrade• New Levee fill• Geotextile / geofabric• Foundation treatment• Hydroseeding• Misc. unlisted items

Estimated Project CostsEden Landing North (Phase 1)

1D Approach 2‐D Approach

Base Construction Costs $13.8MNo Significant 

Improvements RequiredNon‐Construction Costs $7.2M

Total Estimated Cost $21M

Estimated Project CostsEden Landing South (Phase 2)

1D Approach 2‐D Approach

Align 1 Align 2 Align 3 Align 1 Align 2 Align 3Base Construction Costs $22.7M $15.4M $20.8M $13.0M $8.4M $9.6MNon‐Construction Costs $12.5M $8.5M $10.6M $7.2M $4.6M $5.3MTotal Estimated Cost $35.2M $23.9M $31.4M $20.2M $13.0M $14.9M(% Increase) 74% 84% 101% ‐‐‐ ‐‐‐ ‐‐‐

Conclusions• Modelling methodology has significant impact to flood control project costs– 1‐D analysis approach results in higher coastal flood levels within the Eden Landing site.

– Higher level of protection required• Significant improvements needed

– Higher project costs ‐ Real tax payer costs

Questions?

Conceptual Construction Cost Estimate

DescriptionNorth Flood Protection Alignment Alternative 1

South Flood Protection Alignment

Alternative 1

South Flood Protection Alignment

Alternative 2

South Flood Protection Alignment

Alternative 3

Construction Item

Mob/Demob $834,000 $1,404,000 $953,000 $1,253,000

Existing Levee Degrade

46,000 CY (see note 1)

146,000 CY 68,000 CY 121,000 CY

$506,000 $1,606,000 $748,000 $1,331,000

New Levee Fill238,000 CY 419,000 CY 298,000 CY 361,000 CY

$5,474,000 $9,637,000 $6,854,000 $8,303,000

Geotextile/Geofabric

159,000 SY 303,000 SY 204,000 SY 300,000 SY

$636,000 $1,212,000 $816,000 $1,200,000

Foundation Treatment19,300 LF 17,600 LF 12,400 LF 19,000 LF

$1,602,000 $1,461,000 $1,029,000 $1,577,000

Hydroseeding38 Acres 36 Acres 25 Acres 36 Acres

$125,000 $119,000 $83,000 $119,000

Unlisted Items $2,517,000 $4,254,000 $2,879,000 $3,795,000

Base Construction Subtotal

$11,694,000 $19,693,000 $13,362,000 $17,578,000

Non‐Construction Items

Engineering for Detailed Design

$1,169,000 $1,969,000 $1,336,000 $1,758,000

CM & Engineering Services

$1,754,000 $2,954,000 $2,004,000 $2,637,000

Environmental Compliance/Permitting

$585,000 $985,000 $668,000 $879,000

Environmental Mitigation

$1,754,000 $2,954,000 $2,004,000 $2,637,000

Right‐of‐Way Acquisition Not Applicable

Legal/Owner Administration

$468,000 $788,000 $534,000 $703,000

Financing Not Included

Escalation Not Included

Order‐of‐Magnitude Subtotal

Subtotal $17,424,000 $29,343,000 $19,908,000 $26,192,00

Program Order‐of‐Magnitude Total

Contingency $3,485,000 $5,869,000 $3,982,000 $5,238,000

Total Estimated Cost $20,909,000 $35,212,000 $23,890,000 $31,430,000

1-D Hydraulic Analysis, 1% AEP Event

Conceptual Construction Cost Estimate

Description

North Flood Protection Alignment 

Alternative 1

South Flood Protection Alignment

Alternative 1

South Flood Protection Alignment

Alternative 2

South Flood Protection Alignment

Alternative 3

Construction Item

Mob/Demob

Not Applicable – No Significant 

Improvements Required

$809,000 $520,000 $595,000

Existing Levee Degrade

146,000 CY 68,000 CY 121,000 CY

$1,606,000 $748,000 $1,331,000

New Levee Fill185,000 CY 127,000 CY 108,000 CY

$4,255,000 $2,921,000 $2,484,000

Geotextile/Geofabric

170,000 SY 111,000 SY 122,000 SY

$680,000 $444,000 $366,000

Foundation Treatment

17,600 LF 12,400 LF 19,000 LF

$1,461,000 $1,029,000 $1,557,000

Hydroseeding25 Acres 16 Acres 20 Acres

$83,000 $53,000 $66,000

Unlisted Items $2,426,000 $1,559,000 $1,784,000

Base Construction Subtotal $11,320,000 $7,274,000 $8,325,000

Non‐Construction Items

Engineering for Detailed Design

Not Applicable – No Significant 

Improvements Required

$1,132,000 $727,000 $833,000

CM & Engineering Services

$1,698,000 $1,091,000 $1,249,000

Environmental Compliance/Permitting

$566,000 $364,000 $416,000

Environmental Mitigation

$1,698,000 $1,091,000 $1,249,000

Right‐of‐Way Acquisition

Not Applicable

Legal/Owner Administration

$453,000 $291,000 $333,000

Financing Not Included

Escalation Not Included

Order‐of‐Magnitude Subtotal

Subtotal Not Applicable $16,867,000 $10,838,000 $12,405,000

Program Order‐of‐Magnitude Total

ContingencyNot Applicable – No 

Significant Improvements 

Required

$3,373,000 $2,168,000 $2,481,000

Total Estimated Cost $20,240,000 $13,006,000 $14,886,000

2-D Hydraulic Analysis, 1% AEP Event