Non-point Source Control in a Changing
Climate
More than just extreme events
Presented by
Theresa McGovern
Sarah Widing
April 21, 2016
“The past century is no longer a reasonable guide to the future
for water management.”
Expanding on our Common Language
 We often use the following terms interchangeably:
– 100-year Storm,
– the 100-year Flood,
– the 100-year Design Event
 These are imprecise, but easy-to-understand ways of referring
to the precipitation event or the resultant flood that has
occurred, based on past observations:
– Once, on average, every 100 years
– With a recurrence interval of 100 years
– With an annual exceedance probability (AEP) of 1%
 Sometimes we call it the 1% annual chance event
Intense, short-duration events can overwhelm stormwater
infrastructure
Estimating Design Flow Rates
 Rational Method (for stormwater conveyance)
 TR-55 Runoff Curve Number Method
 USGS Gage Data
 USGS Regression Equations
 NETC Regression Equations for Steep Watersheds
Defining a Precipitation Design Event




Recurrence Interval
Depth
Duration
Distribution
Extreme Precipitation in New York and
New England
 Northeast Regional Climate
Center (NRCC)
 http://precip.eas.cornell.edu/
 Depths: Extreme
Precipitation Tables
 Distributions: Distribution
Curves
 IDF Curves: Intensity,
Frequency, Distribution
– 5-minute
– 1-hour
– 1-day
NOAA Atlas 14 Volume 10, Version 2
 NOAA
 http://hdsc.nws.noaa.gov/hd
sc/pfds/index.html
 Depths:
 Distributions:
 IDF Curves: Intensity,
Frequency, Distribution
 No new PMP resources
 HMR 51, 52, and 53 (1980,
1982) are still current
(Eastern US)
Cumulative Distribution
SCS Type III
NRCC 100-year
1
0.75
0.5
0.25
0
0
6
12
18
24
Intensity
SCS Type III
NRCC 100-year
0.25
0.2
0.15
0.1
0.05
0
0
6
12
18
Precipitation Distributions
Comparing the SCS Type III, NRCC Distribution, and Atlas 14 (100-year, 24-hour event)|
24
First-Quartile Cases
1
1
Second-Quartile Cases
0.75
0.75
SCS Type III
NRCC 100-year
NOAA Atlas 14
80%
70%
60%
50%
40%
30%
20%
10%
0.5
0.25
0
0
6
12
18
0.5
0.25
0
24
0
6
12
18
24
1
1
Fourth Quartile Cases
Third Quartile Cases
0.75
0.75
0.5
0.5
0.25
0.25
0
0
0
6
12
18
24
0
6
12
18
Precipitation Distributions
Comparing the SCS Type III, NRCC Distribution, and Atlas 14 (100-year, 24-hour event)|
24
12.0
11.7
TP-40
11.0
NOAA Atlas 14, Volume 10, Version 2
10.2
10.0
NRCC (Cornell)
2030
(Projected)
2070
(Projected)
8.9
Depth (inches)
9.0
8.2
7.9
8.0
7.3
7.0
6.8
6.4
6.1
6.2
6.0
5.6
5.0
5.0
4.8
5.5
4.9
4.0
10-year Event
25-year Event
100-year Event
Progression of Precipitation Depths for the 24-hour duration event
From TP-40 to Today to Tomorrow |
7.0
TP-40
6.0
NOAA Atlas 14
5.8
NRCC (Cornell)
5.2
5.0
4.8
Depth (inches)
4.1
4.0
4.0
3.8
3.3
3.3
3.1
3.0
2.0
1.0
0.0
10-year Event
25-year Event
100-year Event
Progression of Precipitation Depths for the 6-hour duration event
From TP-40 to Today |
In the Northeast, the intensity of large, infrequent storms is
predicted to increase by 7% by the end of the century
NECIA 2006
Resources for Following Climate Change
Research

 U.S. Global Change Research
Program:
http://nca2009.globalchange.gov/
 FHWA: Regional Climate Change
Effects: Useful Information for
Transportation Agencies
 Intergovernmental Panel on
Climate Change (IPCC)
Resources for Following Climate Change
Research

 U.S. Global Change Research
Program:
http://nca2009.globalchange.gov/
 FHWA: Regional Climate Change
Effects: Useful Information for
Transportation Agencies
Design Considerations
 Risk
– Safety / Level of Service
– Property damage
– Environmental Impacts
 Project Life
 Regulatory
–
–
–
–
Water quality
Stream crossing
Flood plain
Environmental
Modeling Exercise
 BMPs – varying sizes
– Infiltration
– Filtering
 Flood Control
– 1-year
– 100-year
 Water Quality
–
–
–
–
Annual average patterns
Impervious watershed
Phosphorus as build-up / wash – off
Treatment as infiltration and settling
 Current → Future
Flood Control - Infiltration
1 Year Event (Atlas 14)
1.0
0.8
Atlas 14 Runoff
Flow / ac (cfs)
0.4 in, 19% reduction
0.6
1 in, 49% reduction
2 in, 97% reduction
0.4
0.2
0.0
0:00
6:00
12:00
18:00
0:00
6:00
Flood Control - Infiltration
1 Year Event (2070)
1.0
Atlas 14 Runoff
0.8
Flow / ac (cfs)
0.4 in, 17% reduction
1 in, 43% reduction
0.6
2 in, 85% reduction
0.4
0.2
0.0
0:00
6:00
12:00
18:00
0:00
6:00
Flood Control - Infiltration
100 Year Event (Atlas 14)
3.0
Atlas 14 Runoff
0.4 in, 6% reduction
2.5
1 in, 15% reduction
Flow / ac (cfs)
2.0
2 in, 29% reduction
1.5
1.0
0.5
0.0
0:00
6:00
12:00
18:00
0:00
6:00
Flood Control - Infiltration
100 Year Event (2070)
3.0
2070 Runoff
0.4 in, 4% reduction
2.5
1 in, 10% reduction
2 in, 21% reduction
Flow / ac (cfs)
2.0
1.5
1.0
0.5
0.0
0:00
6:00
12:00
18:00
0:00
6:00
Flood Control - Bioretention
1 Year Event (Atlas 14)
1.0
Atlas 14 Runoff
0.4 in, 6% reduction
0.8
1 in, 16% reduction
Flow / ac (cfs)
2 in, 23% reduction
0.6
0.4
0.2
0.0
0:00
6:00
12:00
18:00
0:00
6:00
Flood Control - Bioretention
1 Year Event (2070)
1.0
Atlas 14 Runoff
0.4 in, 5% reduction
0.8
1 in, 13% reduction
Flow / ac (cfs)
2 in, 21% reduction
0.6
0.4
0.2
0.0
0:00
6:00
12:00
18:00
0:00
6:00
Flood Control - Bioretention
100 Year Event (Atlas 14)
3.0
Atlas 14 Runoff
0.4 in, 2% reduction
2.5
1 in, 5% reduction
Flow / ac (cfs)
2.0
2 in, 11% reduction
1.5
1.0
0.5
0.0
0:00
6:00
12:00
18:00
0:00
6:00
Flood Control - Bioretention
100 Year Event (2070)
3.0
2070 Runoff
0.4 in, 1% reduction
2.5
1 in, 3% reduction
Flow / ac (cfs)
2.0
2 in, 8% reduction
1.5
1.0
0.5
0.0
0:00
6:00
12:00
18:00
0:00
6:00
Modeling Exercise
 BMPs – varying sizes
– Infiltration
– Filtering
 Flood Control
– 1-year
– 10-year
– 100-year
 Water Quality
–
–
–
–
Annual average patterns
Impervious watershed
Phosphorus as build-up / wash – off
Treatment as infiltration and settling
 Current → Future
Conclusions:
- Infiltration BMPs can
provide some
significant flood control
- Back-to-back storms
will reduce benefit
Predicted Changes in Seasonal Precipitation
Spring
16
14
12
10
8
6
4
2
0
% Change
% Change
Winter
Near-term
Mid-century
16
14
12
10
8
6
4
2
0
Near-term
End-of-Century
16
14
12
10
8
6
4
2
0
Near-term
Mid-century
End-of-Century
Fall
% Change
% Change
Summer
Mid-century
End-of-Century
16
14
12
10
8
6
4
2
0
Near-term
Mid-century
End-of-Century
Excerpted from Table 3-5 of the FHWA report Regional Climate Change Effects:
Useful Information for Transportation Agencies
Table 3-5: Seasonal precipitation percent changes for the Northeast region over the
near-term (2010-2029),
mid-century (2040-2059) and
end-of-century (2080-2098) relative to 1961-1979.
Data are from the USGCRP (2009).
Water Quality
Recent
Projected End
of Century
Percent
Change
Annual Average Rainfall (inches)
42.9
45.9
6.9%
Watershed Annual P Load (lbs)
2.7
2.8
3.2%
(0.4 in)
92%
92%
-0.4%
(1.0 in)
98%
98%
-0.2%
(2.0 in)
99.6%
99.5%
-0.1%
(0.4 in)
69%
69%
-0.8%
(1.0 in)
91%
90%
-0.5%
(2.0 in)
93%
93%
-0.3%
Infiltration Basin % Removal
Bioretention % Removal
Modeling Exercise
 BMPs – varying sizes
– Infiltration
– Filtering
 Flood Control
– 1-year
– 10-year
– 100-year
 Water Quality
–
–
–
–
Annual average patterns
Impervious watershed
Phosphorus as build-up / wash – off
Treatment as infiltration and settling
 Current → Future
Conclusions:
-Increased rainfall does
not significantly effect
BMP performance
Conclusions
 Choose design criteria based on specific project/site
 Use the latest data
 Water Quality BMPs can provide flood control
 Increased rainfall volumes will not significantly decrease water
quality treatment ability
 Future conditions may effect water quality loads and BMP
treatment performance
 Need more data and analysis (always!)
Sarah Widing| swiding@vhb.com | 508.513.2720
www.vhb.com
Theresa McGovern| tmcgovern@vhb.com | 617.607.6158
Offices located throughout the east coast