HYDROLOGIC COMPUTER MODELING Washington Hydrology Society March 2006

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HYDROLOGIC COMPUTER MODELINGWashington
Hydrology SocietyMarch 2006

• Joe Brascher, President
• Clear Creek Solutions, Inc.

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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.

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Presentation

• Introduction
• History of Hydrologic Modeling
• Single Event Models
• Continuous Simulation Models
• Western Washington Hydrology Model 3
• Questions Answers

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History of Hydrologic Modeling

• In the beginning Single event

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History of Hydrologic Modeling

• Today Continuous simulation

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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

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Typical Synthetic Precipitation Event
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Historical Precipitation Event
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Single-event problems

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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).

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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.

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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.

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Continuous Simulation Models

• Continuous simulation hydrology models the entire
  hydrologic cycle for multiple years.

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Continuous Simulation Models

• Stanford Watershed Model (original)
• HSPF (EPA)
• KCRTS (King Co)
• MGS Flood (WSDOT)
• LIFE (CH2M Hill)
• WWHM (Ecology)
• WWHM3 PRO (Clear Creek Solutions)

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Continuous Simulation Models

• HSPF DOS-based, steep learning curve,
  recommended only for experienced users
• KCRTS Limited to King County, pre-generated
  runoff from HSPF, limited LID capabilities
• MGS Flood (WSDOT) HSPF-based, extended precip
  time series, proprietary pond sizing option

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Continuous Simulation Models

• LIFE (CH2M Hill) soil measurement-based,
  proprietary
• WWHM (Ecology) HSPF-based, NOAA precip records,
  LID elements included in WWHM3
• WWHM3 PRO (Clear Creek Solutions)
• WWHM3 with extra features

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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
• [phone]
• email flab461_at_ecy.wa.gov

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Where Are We Going?
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Where Are We Going?

• Models that do more
• Better user interfaces
• Combining the best models

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WWHM

• Ecologys Stormwater Management Manual
• Specifies a flow duration standard
• Requires the use of Western Washington
  Hydrology Model (WWHM)

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WWHM
Developed for the 19 counties of western
Washington. Part of Ecologys Stormwater
Management Manual

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WWHM
Available free from the Washington State
Department of Ecology web site
http//www.ecy.wa.gov/programs/wq/stormwater/

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WWHM Flow Duration Analysis Percent of time
the flow exceeds a specific value.

• Requires continuous simulation hydrology to
  compute flow duration.

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WWHM

• Flow duration standard based on erosive flows.
• Erosive flow range ½ of the 2-year to the
  50-year

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WWHM

• Guidance/help is provided by
• User Manual
• Training Workshops
• CCS Project Book

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Where the rain goes
100
Evapotranspiration
Surface Runoff
Interflow

Groundwater/Base Flow
0
Land use development
Forest
Impervious
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WWHM

• WWHM uses continuous simulation hydrology to
  compute stormwater runoff for both predevelopment
  and post-development conditions.
• Predevelopment Post-development

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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.

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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.

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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

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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.

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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.

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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.

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WWHM

• WWHM-designed ponds meet Washington State
  Department of Ecologys standards

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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

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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

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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)

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Changes from WWHM2 to 3

• 14 elements
• 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

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Changes from WWHM2 to 3

• Complex stormwater systems can be modeled

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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)
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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

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City of Bellingham

• Comprehensive Stormwater Plan (streams and pipe
  systems) Includes SWMM and GIS connections

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Seattle Public Utilities
Natural Drainage System Program
Green/vegetated/eco-roof modeling

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Examples of Green Roofs

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Green Roof Model Results

Hamilton Bldg, Portland, OR
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Green Roof Flow Duration

Blue Conventional Roof Red Green Roof

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Green Roof Hydrograph Change

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Seattle Public Utilities
Rain garden/bioretention/landscape swale
modeling

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Seattle Public Utilities
110th Street Cascades 12 swales in 3 blocks

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WWHM3 PRO

• SWMM routing connection

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WWHM3 PRO

• GIS connection

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WWHM3 PRO

• WWHM3 PRO will be available
• Spring 2006
• See
• www.clearcreeksolutions.com
• for details.

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Turning Hydrologic Modeling Upside Down
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WWHM3 PRO Future Enhancements

• additional low impact development/
• source BMPs
• HSPF water quality
• 3-D graphical interface
• your ideas?

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Questions?