State Board Modeling Needs and Interests

1
State Board Modeling Needs and Interests

• Eric Berntsen, PH, CPESC, CPSWQ
• State Water Resources Control Board
• CWEMF Hydrology and Watershed Modeling Workshop
• June 22, 2007

2
State Board Modeling Needs and Interests

• Quick Overview of Event-Based and Continuous
  Simulation Modeling
• Program Modeling Needs/Interests
• Water Rights
• TMDL
• Storm Water

3
Hydrologic Cycle
From Lake (2004)
4
From King County Department of Natural Resources
5
From King County Department of Natural Resources
6
Event-Based vs. Continuous Simulation Modeling

• Event-based models
• e.g., NRCS Runoff Curve Number Method
• Rational Method (QCIA)
• Input rainfall, desired simulation period, and
  watershed characteristics

7
Event-Based Models

• Rainfall
• Usually based on statistical analysis
• Sometimes, historical storm information used
• Example 10-year, 24-hour storm

8
(No Transcript)
9
(No Transcript)
10
(No Transcript)
11
Event-Based Models

• Simulation period
• Period typically ranges from 5 minutes to 24
  hours
• Shorter durations for peak flow calculations
  (e.g., 10-year, 30-minute storm)

12
Event-Based Models

• Watershed Characteristics
• Relationship between rainfall and runoff
  identified (e.g. Rational Method C factor,
  Runoff Curve Number).
• These coefficients/factors depend on soil
  infiltration rate, vegetation, land use,
  imperviousness, etc.

13
Type of Drainage Area Runoff Coefficient (C)
Lawns
Sandy soils, flat, 2 0.05 0.10
Sandy soils, average, 2 -7 0.10 0.15
Sandy soils, steep, 7 0.15 0.20
Heavy soil, flat, 2 0.13 0.17
Heavy soil, average, 2 -7 0.18 0.22
Heavy soil, steep, 7 0.25 0.35
Business
Downtown areas 0.70 0.95
Neighborhood areas 0.50 0.70
Residential
Single family 0.30 0.50
Multi units, detached 0.40 0.60
Multi units, attached 0.60 0.75
Suburban 0.25 0.40
Apartment dwelling areas 0.50 0.70
From V.T. Chow (1964)
14
(No Transcript)
15
(No Transcript)
16
Continuous Simulation Models

• Use long term rainfall record (20-30 years) and
  can simulate flows for entire period of record
• Incorporate evapotranspiration and infiltration
  estimates simulate the water balance
• Well talk about the major ones being used these
  days (HSPF, SWMM, etc.)

17
Continuous Simulation Models

• Continuous simulation models are better at
  predicting variability in flow and pollutant
  loads because they are based on long term
  observed hydrologic data
• Output from these models can help assess expected
  variability and inform water resource decisions

18
Program Needs Water Rights

• Two fundamental questions for each application to
  appropriate water
• Is there enough water available to supply
  applicant with the requested water amount?
• Will diverting the requested amount affect
  existing users and beneficial uses?
• Currently, no approved procedure to estimate
  flows

19
Program Needs Water Rights

• Flow estimation procedures currently used
• Extrapolate gage data to gaged and ungaged
  watersheds
• Modified Rational Method used in North Coast
  Streams
• Desire to develop a suite of methods to estimate
  flow on daily time step (i.e., continuous
  simulation methods)

20
Program Needs Water Rights

• Continuous simulation procedures would allow
  applicants and water rights staff to
• Estimate unimpaired runoff
• Simulate various diversion scenarios
• Estimate the range of geomorphically-significant
  flows

21
Program Needs TMDL

• Accurate estimates of flow and pollutant loads
  are necessary to determine assimilative capacity
  of waterbodies and load allocations for land uses
  in watershed
• Calculating flow and load on a daily timestep
  desireable

22
Program Needs Storm Water

• Compliance with post-construction treatment
  requirements usually verified through modeling
• Example-requirement to capture/treat 80 annual
  runoff volume
• Projects may have specific load reduction targets
• Event-based and continuous simulation models can
  be used

23
Program Needs Storm Water
Sources of Impairment (USEPA 2006)
24
Program Needs Storm Water
Hydromodification-historic approach (still done
in many places)
25
Program Needs Storm Water

• Need modeling tools that will allow us to assess
  and mitigate impacts from hydromodification
• Event-based models are good at predicting large,
  infrequent flood flows, may not be as good at
  simulating the range of geomorphically-significant
  flows
• Continuous simulation modeling is a promising
  approach