Transcript Department of Ecology

HYDROLOGIC COMPUTER
MODELING
Washington Hydrology Society
March 2006
Joe Brascher, President
Clear Creek Solutions, Inc.
Clear Creek Solutions’
Hydrologic Modeling Expertise
Clear Creek Solutions, Inc., provides complete range of
hydrologic and stormwater modeling services.
• Clear Creek specializes in continuous simulation hydrologic
modeling.
• We have 30+ years of experience modeling complex
hydrologic and stormwater problems.
• We created the Western Washington Hydrology Model
Version 3 (WWHM3) for Washington State Department of
Ecology.
• We teach WWHM and HSPF workshops.
Presentation
Introduction
History of Hydrologic Modeling
Single Event Models
Continuous Simulation Models
Western Washington Hydrology Model 3
Questions & Answers
History of Hydrologic Modeling
In the beginning: Single event
History of Hydrologic Modeling
Today: Continuous simulation
Single-event Hydrologic Models
Based on flood frequency.
When slide rules roamed the earth modeling
had to be simple.
Rational Method (Q = CIA)
SCS Method (Curve Numbers)
TR-20, TR-55, SBUH, HEC-1, Waterworks
Typical Synthetic Precipitation
Event
Precipitation (inches)
25-Year 24-Hour Precipitation Event
1.2
1
0.8
0.6
Precipitation (inches)
0.4
0.2
0
0
5
10
15
Time (hours)
20
25
30
Historical Precipitation Event
Precipitation (inches)
April 1991 Precipitation Event - Seatac Airport
0.35
0.3
0.25
0.2
0.15
Precipitation (inches)
0.1
0.05
0
0
5
10
15
Time (hours)
20
25
30
Single-event problems:
Single-event problems:
 Single-event frequency standards are
based on inappropriate assumptions.

Single-event methods cannot compute
flow durations (percent of time a flow is
exceeded).
Single-event inappropriate
assumptions:
 Assume stormwater detention facilities
are empty at start of a rain event.
 Assume too large predevelopment runoff
when using SCS Curve Numbers.
 Assume matching flow frequencies will
result in no increase in erosive flows.
 Assume 100-yr storm causes 100-yr
flood.
Single-event designed stormwater
facilities fail because:
 The facilities are too small to store the
additional runoff.
 The number of hours of erosive flows
increases even if the flow frequency does
not.
 The downstream riparian corridor is
damaged by the increase of erosive flows.
Continuous Simulation Models
Continuous simulation hydrology models the
entire hydrologic cycle for multiple years.
Continuous Simulation Models

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Stanford Watershed Model (original)
HSPF (EPA)
KCRTS (King Co)
MGS Flood (WSDOT)
LIFE (CH2M Hill)
WWHM (Ecology)
WWHM3 PRO (Clear Creek Solutions)
Continuous Simulation Models
HSPF: DOS-based, steep learning curve,
recommended only for experienced users
KCRTS: Limited to King County, pregenerated runoff from HSPF, limited LID
capabilities
MGS Flood (WSDOT): HSPF-based,
extended precip time series, proprietary
pond sizing option
Continuous Simulation Models
LIFE (CH2M Hill): soil measurementbased, proprietary
WWHM (Ecology): HSPF-based, NOAA
precip records, LID elements included in
WWHM3
WWHM3 PRO (Clear Creek Solutions):
WWHM3 with extra features
Western Washington
Hydrology Model (WWHM)
Developed for the State of Washington
Department of Ecology.
Project Manager: Dr. Foroozan Labib
Department of Ecology
PO Box 47600
Olympia, WA 98504-7600
(360) 407-6439
email: [email protected]
Where Are We Going?
Where Are We Going?
Models that do more
 Better user interfaces
 Combining the best models
WWHM
Ecology’s Stormwater Management Manual
 Specifies a flow duration standard
 Requires the use of Western Washington
Hydrology Model (WWHM)
WWHM
Developed for the 19 counties of western
Washington.
Part of
Ecology’s
Stormwater
Management
Manual
WWHM
Available free from the Washington State Department of
Ecology web site:
http://www.ecy.wa.gov/programs/wq/stormwater/
WWHM
Flow Duration Analysis: Percent of time the
flow exceeds a specific value.
Requires continuous simulation hydrology to
compute flow duration.
WWHM
Flow duration standard: based on erosive flows.
Erosive flow range: ½ of the 2-year to the 50-year
WWHM
 Guidance/help is provided by
 User Manual
 Training Workshops
 CCS Project Book
Evapotranspiration
Interflow
Surface
Runoff
La
de
wn
nt
ial
(fo
re
nt
st
ial
)
(p
as
tu
an
re
Re
)
sid
en
tia
M
l
ult
i- fa
mi
ly
Co
mm
er
cia
l
Im
pe
rv
iou
s
Impervious
Groundwater/Base Flow
Fo
re
st
PaForest
stu
re
100%
100%
80%
60%
40%
20%
0%0%
Where the rain goes:
Land use development
WWHM
WWHM uses continuous simulation hydrology to
compute stormwater runoff for both predevelopment
and post-development conditions.
Predevelopment
Post-development
WWHM
 WWHM continuous simulation computations
from HSPF (included in WWHM software).

HSPF runs in the background with
calibrated parameter values and local
meteorological data.
 HSPF sponsored and funded by EPA and
USGS.
WWHM
 Drainage areas are divided into pervious
land segments based on soil, vegetation, and
land slope and impervious land segments.
 Pervious and impervious segments are
linked to conveyance pathways (pipes, ditches,
ponds, streams, rivers, lakes, etc.)
 Historic rainfall and evaporation are used as
input.
WWHM
 The entire water cycle is modeled on an
hourly or shorter time step for multiple years.
 The model computes changes in soil
moisture, evapotranspiration, and runoff every
time step.
 Three types of runoff:
 surface runoff
 interflow
 groundwater/base flow
WWHM
 Calibrated parameter values are built into
WWHM (different calibrated parameter values
are used for different climatic regions).
 Local precipitation and evaporation data are
included in WWHM.
WWHM
 User locates project on county map, inputs
pre- and post-development land use, and
proposed mitigation measure(s).
 Predevelopment and mitigated flows are
compared at Point of Compliance (POC).
 Mitigated flows are not allowed to exceed
flow duration standards.
WWHM
 User outputs report file and project file.
 Output files can be submitted to the
permitting agency for approval.
 Permitting agency can load project file and
rerun analysis, if needed.
 Report file summarizes input data and
output results.
WWHM
WWHM-designed ponds meet Washington State
Department of Ecology’s standards:
WWHM: LID Options
WWHM includes the following LID options:
 Dispersion of impervious surface runoff on adjacent
pervious surface (example: roof runoff to lawn)
 Infiltration of impervious surface runoff on adjacent
pervious surface (soil dependent)
 Pervious pavement
 PSAT (Puget Sound Action Team) recommends how
to represent other LIDs in WWHM
Changes from WWHM2 to 3:
Goal: give the user greater flexibility
and options.
Ecology wanted:
 High groundwater element
 Lateral flow between basins
 More elements
 More output options
 New LID options
Changes from WWHM2 to 3:
Version 2 projects were limited to drainages
of less than 320 acres because of lack of
conveyance options (channels and pipes).
Version 3 projects have no limitations:
entire watersheds can be modeled.
Version 3 can be customized to local
jurisdictions (e.g., City of Bellingham)
Changes from WWHM2 to 3:
14 elements:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
basin
trapezoidal pond
tank
lateral pervious basin (NEW)
high groundwater/wetland (NEW)
vault
open channel (NEW)
time series (NEW)
lateral impervious basin (NEW)
gravel trench bed (NEW)
sand filter
flow splitter (IMPROVED)
irregular-shaped pond
stage-storage-discharge table
Changes from WWHM2 to 3:
 Complex stormwater systems can be modeled
WWHM3 LID Analysis Tool:
WWHM compares different development options
selected by the user and shows the runoff distribution:
POC 1: Conventional
POC 2: Dispersion
(20% reduction in
pond volume)
POC 3: Dispersion
and Infiltration
(84% reduction in
pond volume)
WWHM3 PRO:
WWHM3 with additional enhancements:
 user selected time step
(5 minutes to one hour)
 tagged flow routing
 additional elements
 culverts
 green roofs
 landscape swales/bioretention/
rain gardens
 SWMM routing connection
 GIS land use connection
City of Bellingham
 Comprehensive Stormwater Plan (streams
and pipe systems): Includes SWMM and GIS
connections
Seattle Public Utilities
Natural Drainage System Program:
Green/vegetated/eco-roof modeling
Examples of Green Roofs
Green Roof Model Results
Hamilton Bldg, Portland, OR
Green Roof Flow Duration
Blue: Conventional Roof
Red: Green Roof
Green Roof Hydrograph Change
Seattle Public Utilities
Rain garden/bioretention/landscape swale
modeling
Seattle Public Utilities
110th Street Cascades: 12 swales in 3 blocks
WWHM3 PRO
SWMM routing connection
WWHM3 PRO
GIS connection
WWHM3 PRO
WWHM3 PRO will be available
Spring 2006
See
www.clearcreeksolutions.com
for details.
Turning Hydrologic Modeling
Upside Down
WWHM3 PRO Future Enhancements
 additional low impact development/
source BMPs
 HSPF water quality
 3-D graphical interface
 your ideas?
Questions?