Download AC15_Session30_CJewell

BWSC Climate Change Risk Assessment,
Findings and Mitigation/Adaptation Strategies
for Wastewater and Storm Drainage
Presented By:
Charlie Jewell, BWSC
John Sullivan, BWSC
Bill McMillin, CH2M HILL
NEWEA
Annual Conference & Exhibit
January 28, 2015
Copyright © 2014 Boston Water and Sewer Commission 980 Harrison Ave. Boston, MA 02119 617-989-7000
BWSC Infrastructure:
Wastewater and Storm Drainage Systems
• 1,455 linear miles of sewers:
•
•
•
•
•
•
•
•
•
•
•
622 miles of sanitary sewers
595 miles of storm drains
235 miles of combined sewers
3 miles of combined sewer overflow outfalls
8 pumping stations
35,934 catch basins
47,413 manholes
174 combined sewer regulators
430 CSO and stormwater outfalls
202 tide gates
8 rainfall gauges
Tide gates on CSO outfalls in Fort
Point Channel prevent high tides
from entering combined sewers
Copyright © 2014 Boston Water and Sewer Commission 980 Harrison Ave. Boston, MA 02119 617-989-7000
Wastewater and Storm Drainage Facilities Plan
• Capital improvement planning and construction to:
• Continue to provide drainage and sewer services to
protect public health and safety with climate change and
during and after storm events
• Protect critical BWSC infrastructure vulnerable to
flooding now and in the future.
• Develop planning and design guidelines for climate
change:
• Drainage design
• Sewer design
• Pump Station and other facilities
Copyright © 2014 Boston Water and Sewer Commission 980 Harrison Ave. Boston, MA 02119 617-989-7000
Climate Change Risks
• Increased Rainfall
• Average annual rainfall will increase
• Storms will become more intense
• Storm drains and combined sewer systems will have to convey
more runoff
• Increased river flows and flooding
• Charles River, Neponset River and Mystic River may flood areas of
the City during storms
• Sea Level Rise and Storm Surge
• Storm surge with hurricanes and nor’easters will flood city streets
now.
• Sea level rise will increase the elevation of the storm surge and the
areas that will flood.
• Sewer systems may be inundated in flooded areas.
• Pump stations may be flooded and disabled.
• More streets may be flooded if the water has nowhere to go.
Copyright © 2014 Boston Water and Sewer Commission 980 Harrison Ave. Boston, MA 02119 617-989-7000
Climate Change Goals and Objectives
1. Identify what others are doing.
2. Evaluate precipitation, river flooding and sea level trends.
3. Define climate change scenarios for the Boston area
based on globally projected greenhouse gas (GHG)
emission scenarios through the year 2100.
4. Evaluate SLR, storm surge, and river flooding on the
Commission’s infrastructure and operations.
5. Evaluate changes in rainfall coupled with SLR, storm
surge, and river flooding on the Commission’s sewer and
storm drain system conveyance.
6. Recommend strategies, design standards, and climate
change data collection and analyses for sewer and storm
drain systems, facilities and structures for flooding
resilience, and climate change.
Copyright © 2014 Boston Water and Sewer Commission 980 Harrison Ave. Boston, MA 02119 617-989-7000
Monitoring Rainfall
Regional Rainfall Data
Collection
8 BWSC Rainfall Gauges
BWSC Data: www.bwsc.org
Click on Public Outreach, Rainfall Data
Copyright © 2014 Boston Water and Sewer Commission 980 Harrison Ave. Boston, MA 02119 617-989-7000
Regional Average Annual Rainfall Depth and Linear
Trend (1948-2012)
Copyright © 2014 Boston Water and Sewer Commission 980 Harrison Ave. Boston, MA 02119 617-989-7000
Summary of 24-hour Rainfall Calculations on
Historical Record for 2- to 500-year Return Periods
12-Station Regional Average Precipitation
Volumes (in)
Return Period
(Year)
L-Moments
SimCLIM
NRCC AMS
6-Station BWSC Average
Precipitation Volumes (in)
NRCC
L-Moments
AMS
2
3.16
3.16
3.00
3.17
2.90
5
4.34
4.30
4.02
4.35
3.89
10
5.23
5.18
4.85
5.24
4.70
25
6.51
6.45
6.17
6.53
5.98
50
7.58
7.52
7.38
7.60
7.15
100
8.75
8.71
8.82
8.78
8.56
500
11.98
12.07
13.39
12.01
12.99
Derived from L-Moments, SimCLIM and NRCC Annual Maximum Series.
Copyright © 2014 Boston Water and Sewer Commission 980 Harrison Ave. Boston, MA 02119 617-989-7000
Calculated Boston Area Rainfall Volumes,
Durations and Frequencies (1948-2011)
Rainfall Volume (inches)
Duration
3-Month
6-Month
1-Year
2-Year
5-Year
10-Year
25-Year
50-Year
100-Year
5 min
0.17
0.22
0.27
0.34
0.45
0.51
0.60
0.68
0.74
10 min
0.27
0.34
0.42
0.53
0.70
0.81
0.96
1.07
1.21
15 min
0.33
0.42
0.52
0.66
0.88
1.02
1.22
1.38
1.57
30 min
0.43
0.55
0.68
0.87
1.17
1.39
1.68
1.94
2.22
1 hour
0.55
0.69
0.85
1.10
1.50
1.80
2.25
2.61
3.02
2 hour
0.69
0.87
1.08
1.38
1.91
2.32
2.90
3.41
3.96
3 hour
0.80
1.01
1.25
1.59
2.22
2.70
3.39
3.98
4.65
6 hour
1.02
1.29
1.60
2.00
2.79
3.38
4.27
5.00
5.82
12 hour
1.31
1.65
2.05
2.52
3.48
4.23
5.30
6.19
7.19
24 hour
1.68
2.12
2.63
3.17
4.35
5.24
6.53
7.60
8.78
48 hour
1.85
2.34
2.92
3.52
4.87
5.88
7.36
8.60
10.00
Based on data from 12 regional stations (1948-2011) and 6 BWSC stations (2002-2011).
Copyright © 2014 Boston Water and Sewer Commission 980 Harrison Ave. Boston, MA 02119 617-989-7000
Boston Harbor Sea Level Rise Trend
Historical sea level rise is 0.1 inch/year
Copyright © 2014 Boston Water and Sewer Commission 980 Harrison Ave. Boston, MA 02119 617-989-7000
The Number of Higher High Water Tides Are
Increasing
Water Levels in Boston
Harbor
Number of Days in Which Water
Levels in Boston Harbor Exceed
MHHW
Source: NOAA
Copyright © 2014 Boston Water and Sewer Commission 980 Harrison Ave. Boston, MA 02119 617-989-7000
Emissions Scenarios Selected for Climate Change
Risk Analysis
In 2000, the Intergovernmental Panel
on Climate Change (IPCC) published a
special report on emissions scenarios
(SRES) that described a family of six
GHG emission scenarios to condition
general circulation models.
The six scenarios are derived from four
GHG emissions scenario storylines: A1,
A2, B1, and B2.
BWSC GHG Scenarios
Description
B2
Medium
Assumes slower population growth and trend
toward emphasis on sustainability
A1FI
Precautionary
High-emission, fossil-fuel intensive; assumes
rapid population growth
Copyright © 2014 Boston Water and Sewer Commission 980 Harrison Ave. Boston, MA 02119 617-989-7000
Forecasted 10-year, 24-hour Design Storm Volumes
and Peak Hourly Intensities
Total Storm Volume
(inches)
Peak Hourly Intensity
(inches per hour)
Scenario
2035
2060
2100
2035
2060
2100
Medium (B2)
5.55
5.76
6.08
1.76
1.83
1.93
Precautionary
(A1FI)
5.60
6.03
6.65
1.78
1.91
2.11
BWSC’s current design standard is 4.8 inches
Climate change is increasing the size and intensity of this
statistical storm and it could be 6.65 inches by 2100.
Copyright © 2014 Boston Water and Sewer Commission 980 Harrison Ave. Boston, MA 02119 617-989-7000
Observed and Forecasted Sub-daily Rainfall for the
Medium Scenario (B2) at the Year 2035
Copyright © 2014 Boston Water and Sewer Commission 980 Harrison Ave. Boston, MA 02119 617-989-7000
Sea Level Rise Projections
Source: Vermeer & Rahmstorf, 2009
Medium SLR Projections
through 2100
Precautionary SLR
Projections through 2100
Component
2035
2060
2100
Component
2035
2060
2100
Global (feet)
0.79
1.54
3.51
Global (feet)
1.21
2.20
6.20
Subsidence (feet)
0.08
0.16
0.30
Subsidence (feet)
0.08
0.16
0.30
0
0
0
Regional (feet)
0.23
0.39
0.66
0.87
1.70
3.81
Total (feet)
1.52
2.75
7.16
Regional (feet)
Total (feet)
Copyright © 2014 Boston Water and Sewer Commission 980 Harrison Ave. Boston, MA 02119 617-989-7000
Storm Surge Heights and Recurrence Intervals
Return Period
(years)
Boston (mm)
Boston (m)
Boston (ft)
2
868
0.87
2.85
5
1,067
1.07
3.50
10
1,194
1.19
3.92
20
1,311
1.31
4.30
50
1,457
1.46
4.78
100
1,562
1.56
5.12
200
1,664
1.66
5.46
500
1,793
1.79
5.88
1,000
1,887
1.89
6.19
Copyright © 2014 Boston Water and Sewer Commission 980 Harrison Ave. Boston, MA 02119 617-989-7000
Evaluate Flooding Vulnerabilities to SLR, Storm
Surge and Rivers
Copyright © 2014 Boston Water and Sewer Commission 980 Harrison Ave. Boston, MA 02119 617-989-7000
Evaluated Flooding Risks to Sewer Systems
• Ran Computer Models
of the Storm Drain and
Sewer Systems (SWMM)
to Calculate Flows Now
and in The Future
• Ran 2-dimensional
computer models
(CH2M HILL’s ISIS-FAST)
to map surface flooding
due to drainage and
storm surge
Copyright © 2014 Boston Water and Sewer Commission 980 Harrison Ave. Boston, MA 02119 617-989-7000
Calculated Inundation Depths for the Precautionary
2035 Climate Change Scenario with Storm Surge
Copyright © 2014 Boston Water and Sewer Commission 980 Harrison Ave. Boston, MA 02119 617-989-7000
Risks Of Flooding With Sea Level Rise And Storm
Surge – Year 2060
Year 2060 Rain
Sea Level Rise, No Storm Surge
Year 2060 Rain
Sea Level Rise, With Storm Surge
Copyright © 2014 Boston Water and Sewer Commission 980 Harrison Ave. Boston, MA 02119 617-989-7000
Adaptation Strategies
• Applying Green Infrastructure
• Applying Low Impact Development Techniques
• Adding Hydraulic Capacity to the Drainage Network
• Moving Flow Between Parts of the System
• Increasing Storage Capacity
• Constructing Wet Weather Pumping Stations
• Tide Gates on All Outfalls
• Elevating or Waterproofing Existing Facilities
• Changing Design Standards
Copyright © 2014 Boston Water and Sewer Commission 980 Harrison Ave. Boston, MA 02119 617-989-7000
Future Drainage and Conveyance Controls
Evaluation
• Alternatives to Mitigate
Impacts of Climate
Change:
• Adding conveyance
capacity
• Increasing pump station
capacity
• Adding storage capacity
• Sewer separation
• Calculated potential
surcharge reductions
Copyright © 2014 Boston Water and Sewer Commission 980 Harrison Ave. Boston, MA 02119 617-989-7000
BWSC
Port Norfolk
(11LPS316)
Austin Street
(27JPS1)
Symphony Hall
(21IPS1)
MWRA DeLauri
(MWRA002)
Union Park (21KPS2)
Summer Street
(22MPS5)
Public Alley 701
(21JPS526)
Trilling Way
(22MPS2)
Caruso
(29NPS4)
MWRA Prison Point
(MWRA003)
Commonwealth Ave
(22IPS1)
Sullivan Square
(29JPS1)
MWRA Cottage Farm
(MWRA001)
TOTAL RISK (0-100)
Pump Station Risk Scoring for Medium 2100
Scenario without Storm Surge
Pump Station Total Risk Score for M2100 without Storm Surge (15.04 feet)
100
90
80
70
60
50
40
30
20
10
0
PUMP STATION (FACILITY ID)
MWRA
Copyright © 2014 Boston Water and Sewer Commission 980 Harrison Ave. Boston, MA 02119 617-989-7000
Design Flood Elevations (DFEs) to Protect Facilities
and Operations
Recommended DFEs for Pump Stations and other Structures
Project Life cycles up to the Year
(feet – Boston City Base)
Design Condition
2035
2060
2100
Minimum
18.22
19.06
21.16
Higher Risk Mitigation
18.88
20.11
24.50
Recommended DFEs are based on:
• The current MHHW elevation of 11.23 feet
• Sea Level Rise
• 100-year storm surge of 5.12 feet
• 1-foot freeboard
Apply to:
• Construction of new infrastructure
• Capital improvements to existing infrastructure
• Tide gates
Copyright © 2014 Boston Water and Sewer Commission 980 Harrison Ave. Boston, MA 02119 617-989-7000
Future Condition Without and With Flood Walls
Precautionary 2060
Precautionary 2060 With
Flood Walls
Flooding due to SLR and storm surge only, no rainfall in these calculations
Copyright © 2014 Boston Water and Sewer Commission 980 Harrison Ave. Boston, MA 02119 617-989-7000
Drainage Would Still Have to be Addressed
Precautionary 2060 With Flood Walls and 10-year/24-hour rainfall
Additional mitigations beyond flood walls along shorelines would be needed to prevent
street flooding should a significant rainfall occur during a storm surge event in the future
Copyright © 2014 Boston Water and Sewer Commission 980 Harrison Ave. Boston, MA 02119 617-989-7000
Sewer and River Monitoring Systems
• Sewer Metering:
• Six permanent metering stations located near the
downstream end of BWSC’s sanitary sewer system prior
to discharge to the MWRA system.
• More than 20 other metering stations moving around
the City to identify problems and plan solutions.
• Characterize flow throughout the system and determine
how it reacts to climate change conditions.
• Identify and eliminate extraneous flow to increase
capacity to convey increased storm flows.
Copyright © 2014 Boston Water and Sewer Commission 980 Harrison Ave. Boston, MA 02119 617-989-7000
Update Annual Rainfall for Planning
• Annual rainfall used to identify the frequency,
overall magnitude and operational costs of wet
weather discharges
• Should range from 50.0 to
55.4 inches by the year 2100
• Apply to CSO control and TMDL
planning
• Apply to operations and
maintenance planning
New Gauge Being Installed at BWSC HQ
Copyright © 2014 Boston Water and Sewer Commission 980 Harrison Ave. Boston, MA 02119 617-989-7000
Update Design Storm for Drainage and Conveyance
Engineering, Planning and Design
• Current 10-year/24-hour design storm
• 5.20 inches (instead of 4.80 inches)
• Peak hourly intensity of 1.65 inches per hour (Type III
hyetograph found in TR-55)
• For life cycles through the year 2100:
• Consider range from 5.55 inches to 6.65 inches
• Depending on the life cycle starting and end date.
Copyright © 2014 Boston Water and Sewer Commission 980 Harrison Ave. Boston, MA 02119 617-989-7000
Modify CSO and Storm Drain Outfall Operations
• All CSO outfalls should have tide gates to protect
facilities and operations from flooding due to a
combination of storm surge and SLR.
• The DFEs should also be used to determine if and
when backflow prevention is required on storm
drain system outfalls.
• The frequency and procedures for tide gate and
outfall maintenance and replacement will have to
be reevaluated periodically in the future to assure
proper operations under more submergence due to
higher sea levels.
Copyright © 2014 Boston Water and Sewer Commission 980 Harrison Ave. Boston, MA 02119 617-989-7000
Pursue Regional Solutions
• A regional concept of erecting barriers along shorelines
at strategic locations would protect the Commission’s
service area and facilities from inundation.
• Additional mitigations would be needed to prevent
street flooding due to surcharging should a significant
rainfall occur during a storm surge event in the future.
• Hydraulic capacity limitations in the storm drain and
combined sewer systems would have to be addressed
to prevent surcharging
• Other solutions such as additional pump stations would
be required to pump stormwater from low lying areas
into the harbor.
Copyright © 2014 Boston Water and Sewer Commission 980 Harrison Ave. Boston, MA 02119 617-989-7000
Questions?
Copyright © 2014 Boston Water and Sewer Commission 980 Harrison Ave. Boston, MA 02119 617-989-7000