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Hydrologic and Hydraulic Models

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Hydrologic and Hydraulic Models – PowerPoint PPT presentation

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Title: Hydrologic and Hydraulic Models


1
Hydrologic and Hydraulic Models
  • Hydrologic Modeling
  • Demonstration of HEC-HMS
  • Uses / Limitations of Hydrologic Models
  • Hydraulic Modeling
  • Step-Backwater Method
  • Demonstration of HEC-RAS
  • Uses / Limitations of Hydraulic Models

2
Hydrologic Modeling
  • Simulate the precipitation-runoff processes of
    dendritic watershed systems
  • Q f (cover, rainfall intensity, area)
  • Models simplify organization and management of
    complex basins

3
Hydrologic Model Uses
  • Water availability
  • Urban drainage
  • Flow forecasting
  • Impacts of urbanization
  • Reservoir spillway design
  • Flood damage reduction
  • Floodplain regulation

4
Hydrologic Model Uses
  • Landuse change hydrologic impacts
  • Water resources systems operation
  • Restoration studies

5
HEC-HMS
  • HEC-HMS USACE Hydrologic Engineering Center -
    Hydrologic Modeling System
  • Automates precipitation - runoff calculations
  • Organizes calculations for complex basins

6
HEC-HMS DEMO
  • Rancho Seco Powerplant Project
  • Objectives
  • Determine 100-year discharge with impervious area
    of new plant
  • Site Conditions

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HEC-HMS DEMO
  • Create basin model
  • Run basin model
  • Discuss model output

13
Hydrologic Model Limitations
  • Backwater effects
  • Floodplain storage
  • Interaction of channel slope and hydrograph
  • Configuration of flow networks
  • Subcritical and supercritical flow
  • Availability of data for calibration

14
Hydraulic Modeling
  • Simulate characteristics of flow through channels
    (or over floodplains)
  • Water Surface Elevation
  • Velocity
  • Sediment Transport
  • Most commonly applied models based on the step
    backwater method

15
Step Backwater Method
  • Balance energy between cross sections
  • EXS1 EXS2
  • Requires geometry and other attributes of both
    cross sections

16
Step Backwater Method
17
Step Backwater Method
  • HP1 HV1 HP2 HV2 Losses
  • or p rgh 1/2rV2 constant
  • HP2 (depth at initial XS) must be known
  • Using geometry and flow rate, calculate velocity
    at downstream XS and resulting velocity head
    (HV2) V2/2g
  • Guess water surface elevation of upstream XS (HP1)

18
Step Backwater Method
  • Compute velocity and velocity head (HV1) for
    upstream XS
  • Compute losses (friction and eddy)
  • Substitute into energy equation
  • Iterate until error is acceptable
  • Repeat for next upstream cross section

19
Step Backwater Method
  • Select cross sections to capture
  • Changes in flow rate
  • Changes in roughness
  • Changes in conveyance (geometry, slope)
  • Large distances

20
HEC-RAS
  • HEC-RAS USACE Hydrologic Engineering Center -
    River Analysis System
  • Automates step backwater method
  • Organizes complex channel calculations

21
HEC-RAS DEMO
  • Rancho Seco Powerplant Project
  • Objectives
  • Determine water surface elevations during
    100-year discharge
  • Determine velocity in channel and near proposed
    powerplant
  • Assess capacity of existing flood control
    infrastructure
  • Site Conditions

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HEC-RAS DEMO
  • Show network
  • Show cross sections
  • Run model
  • Discuss profile
  • Discuss 3D profile

31
HEC-RAS Uses
  • Flood studies
  • Channel alteration design
  • Encroachment studies
  • Stream restoration design
  • Bridge pier design
  • Culvert design
  • Scour investigations

32
HEC-RAS Limitations
  • 1-dimension only
  • Data required for calibration
  • Gauge data vs Normal depth
  • The depth at which flow is steady and hydraulic
    characteristics are uniform.
  • Tweakability
  • Calculations invisible

33
Other Hydraulic Models
  • 1-D
  • Mike-11 (Danish Hydraulic Institute)
  • WS-PRO, BRI-STARS (FHWA)
  • UNET (USACE)
  • 2-D
  • AquaDyn (Softkit Technologies)
  • Mike-21 (Danish Hydraulic Institute)
  • RMA-2 (USACE-WES)

34
Other Hydraulic Models
  • 3-D
  • UnTRIM
  • 2-D and 3-D costly, mostly used in research

35
Two Dimensional Hydraulic and Sediment Transport
Modeling
  • RMA-2 and SED2D
  • Calibrated using available information
  • Focused on in-channel flows (i.e. 45,000 cfs and
    below)
  • Velocities and shear stresses

36
Watershed Hydrology
  • Watershed includes LMR and East Fork LMR
  • Area 1,758 mi2
  • Reservoir regulation since 1975
  • Caesar Creek Lake and William H. Harsha Lake
    control 33 of watershed area
  • Reduced peak flows
  • Backwater vs downvalley floods

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Useful urls
  • http//www.hec.usace.army.mil/
  • http//www.dhi.dk/
  • http//water.usgs.gov/software/wspro.html
  • http//www.fhwa.dot.gov/bridge/bristars.htm
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